Low Level Measurements and Sourcing

Low Level Measurements and Sourcing

Low Level Measurements and Sourcing

Low Voltage/Low Resistance Measurements

Technical Information . . . . . . . . . . . . . . . . . . . . . . . 224

Selector Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

2182A

Nanovoltmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

6220

DC Current Source . . . . . . . . . . . . . . . . . . . . . . . . . 235

6221

AC and DC Current Source . . . . . . . . . . . . . . . . . . . 235

Series 3700

System Switch/Multimeter and Plug-In Cards . . . . 240

Low Current/High Resistance Measurements

Technical Information . . . . . . . . . . . . . . . . . . . . . . . 241

Selector Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

6485

Picoammeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

6487

Picoammeter/Voltage Source . . . . . . . . . . . . . . . . . 248

2502

Dual-Channel Picoammeter . . . . . . . . . . . . . . . . . . 252

428-PROG

Programmable Current Amplifier . . . . . . . . . . . . . . 255

6514

Programmable Electrometer . . . . . . . . . . . . . . . . . 257

6517B

Electrometer/High Resistance Meter . . . . . . . . . . . 261

65

High Resistivity Measurement Package . . . . . . . . . 265

6521

Low Current, 10-channel Scanner Card

(for Model 6517x Electrometer) . . . . . . . . . . . . . . . 268

6522

Low Current, High Impedance Voltage,

High Resistance, 10-channel Scanner

Card (for Model 6517x Electrometer) . . . . . . . . . . 268

6220/6514

High Impedance Semiconductor Resistivity and Hall Effect Test System . . . . . . . . . . . . . . . . . . . 269

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Technical

Information

Low Voltage/Low Resistance

Measurements

224

How to Select a Voltmeter

Many kinds of instruments can measure voltage, including digital multimeters (DMMs), electrometers, and nanovoltmeters. Making voltage measurements successfully requires a voltmeter with significantly higher input impedance than the internal impedance

(source impedance) of the device under test (DUT).

Without it, the voltmeter will measure less potential difference than existed before the voltmeter was connected. Electrometers have very high input impedance (typically in the order of 100TΩ [10

14

Ω]), so they’re the instrument of choice for high impedance voltage measurements. DMMs and nanovoltmeters can typically be used for measuring voltages from

10MΩ sources or lower. Nanovoltmeters are appropriate for measuring low voltages (microvolts or less) from low impedance sources.

Low Voltage Measurements

Significant errors may be introduced into low voltage measurements by offset voltage and noise sources that can normally be ignored when measuring higher signal levels. Steady offsets can generally be nulled out by shorting the ends of the test leads together, then enabling the instrument’s zero (relative) feature. The following paragraphs discuss non-steady types of error sources that can affect low voltage measurement accuracy and how to minimize their impact on the measurements.

Thermoelectric EMFs

The most common sources of error in low voltage measurements are thermoelectric voltages (thermoelectric EMFs) generated by temperature differences between junctions of conductors (Figure 1).

Experiment

(source)

V

S

R

V

IN

HI

Nanovoltmeter

LO

Ground 1

I

Ground bus

V

G

Input voltage to the nanovoltmeter is:

V

IN

= V

S

+ I R

Resistance of input LO connection

(typically around 100m

Ω)

Current passing through input LO connection due to ground voltages (V

G

) in the ground bus

(magnitude may be amperes).

Source voltage (desired signal)

IR may exceed V

S

by orders of magnitude.

Ground 2

Figure 2a: Multiple grounds (ground loops)

Experiment

(source)

V

S

R

V

IN

HI

Nanovoltmeter

LO

I

Z

CM

Ground bus

V

G

Input voltage to the nanovoltmeter is:

V

IN

= V

S

+ I R

Current passing through Z

CM

G Ω) due to V

G

(M Ω or

and currents in the source (magnitude is typically nA’s).

V

IN

≈ V

S

, since IR is now insignificant compared to V

S

.

Single

System

Ground

A

T

1

B

T

2

A

V

AB

HI

LO

Nanovoltmeter

The thermoelectric voltage developed by dissimilar metals A and B in a circuit is:

V

AB

= Q

AB

( T

1

– T

2

)

Temperatures of the two junctions in

°C

Seebeck coefficient of material A with respect to B,

µV/°C

Figure 1. Thermoelectric EMFs

Constructing circuits using the same material for all conductors minimizes thermoelectric EMF generation. For example, connections made by crimping copper sleeves or lugs on copper wires results in cold-welded copper-to-copper junctions, which generate minimal thermoelectric EMFs. Also, connections must be kept clean and free of oxides.

Figure 2b: Single system ground

Minimizing temperature gradients within the circuit also reduces thermoelectric EMFs. A way to minimize such gradients is to place all junctions in close proximity and provide good thermal coupling to a common, massive heat sink. If this is impractical, thermally couple each pair of corresponding junctions of dissimilar materials to minimize their temperature differentials which will also help minimize the thermoelectric EMFs.

Johnson Noise

The ultimate limit to how well the voltmeter can resolve a voltage is defined by Johnson (thermal) noise. This noise is the voltage associated with the motion of electrons due to their thermal energy.

All sources of voltage will have internal resistance and thus produce Johnson noise. The noise voltage developed by any resistance can be calculated from t he following equation:

V = 4kTBR k = Boltzmann’s constant (1.38 × 10

–23

J/K)

T = absolute temperature of the source in Kelvin

B = noise bandwidth in Hz

R = resistance of the source in ohms

From this equation, it can be observed that

Johnson noise may be reduced by lowering the temperature and by decreasing the bandwidth of the measurement. Decreasing the bandwidth of the measurement is equivalent to increasing the response time of the instrument; thus, in addition to increasing filtering

, the bandwidth can be reduced by increasing instrument integration (typic ally in multiples of power line cycles).

Ground Loops

When both the signal source and the measurement instrument are connected to a common ground bus, a ground loop is created (Figure 2a). This is the case when, for instance, a number of instruments are plugged into power strips on different instrument racks. Frequently, there is a difference in potential between the ground points. This potential difference—even though it may be small—can cause large currents to circulate and create unexpected voltage drops. The cure for ground loops is to ground the entire measurement circuit at only one point. The

easiest way to accomplish this is to isolate the DUT

(source) and find a single, good earth-ground point for the measuring system, as shown in Figure 2b.

Avoid grounding sensitive measurement circuits to the same ground system used by other instruments, machinery, or other high power equipment.

Magnetic Fields

Magnetic fields generate spurious voltages in two circumstances: 1) if the field is changing with time, and 2) if there is relative motion between the circuit and the field (Figure 3a). Changing magnetic fields can be generated from the motion of a conductor in a magnetic field, from local AC currents caused by components in the test system, or from the deliberate ramping of the magnetic field, such as for magnetoresistance measurements.

a.

Area A (enclosed)

DUT

B

Voltmeter

The voltage developed due to a field passing through a circuit enclosing a prescribed area is:

V

B

= d

φ dt

= d (BA) dt

= B dA dt

+ A dB dt b.

DUT

Voltmeter

Figure 3: Minimizing interference from

magnetic fields with twisted leads

To minimize induced magnetic voltages, leads must be run close together and should be tied down to minimize movement. Twisted pair cabling reduces the effects of magnetic fields in two ways: first, it reduces the loop area through which the magnetic

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Low Voltage/Low Resistance

Measurements field is interfering; second, a magnetic field will create voltages of opposite polarities for neighboring loops of the twisted pair that will cancel each other.

(Figure 3b)

Low Resistance Measurements

Low resistances (<10Ω) are typically best measured by sourcing current and measuring voltage. For very low resistances (micro-ohms or less) or where there are power limitations involved, this method will require measuring very low voltages, often using a nanovoltmeter. Therefore, all the low voltage techniques and error sources described previously also apply here. Low resistance measurements are subject to additional error sources. The next sections describe methods to minimize some of these.

Lead Resistance and Four-Wire Method

Resistance measurements in the normal range

(>10Ω) are generally made using the two-wire method shown in Figure 4a. The main problem with the two-wire method for low resistance measurements

(<10Ω) is the error caused by lead resistance. The voltage measured by the meter will be the sum of the voltage directly across the test resistance

DMM

Test Current (I)

HI

R

LEAD

I

V

M

LO

V

M

Lead

Resistances

V

R

R

S

Resistance

Under Test

R

LEAD

V

M

V

R

= Voltage measured by meter

= Voltage across resistor

Measured

Resistance

=

V

M

I

= R

S

+ (2

× R

LEAD

)

= R

S

Figure 4a: Two-wire resistance measurement:

Lead resistance error

DMM or Micro-ohmmeter

Source HI

Sense HI

I

V

M

R

LEAD

Test Current (I)

R

LEAD

Sense Current

(pA)

Sense LO

V

M

Lead

Resistances

V

R

R

LEAD

Source LO

R

LEAD

R

S

Resistance

Under Test

Because sense current is negligible, V

M

= V

R and measured resistance =

V

M

I

=

V

I

R

= R

S

Figure 4b: Four-wire resistance measurement

and the voltage drop across the leads. Typical lead resistances lie in the range of 1mΩ to 100mΩ.

Therefore, the four-wire (Kelvin) connection method shown in Figure 4b is preferred for low resistance measurements. In this configuration, the test current is forced through the DUT through one set of test leads while the voltage is measured using a second set of leads called the sense leads. There is very little current running through the sense leads, so the sense lead resistance has effectively been eliminated.

Thermoelectric EMFs

Thermoelectric voltages can seriously affect low resistance measurement accuracy. Given that resistance measurements involve controlling the current through the DUT, there are ways to overcome these unwanted offsets in addition to those mentioned in the low voltage measurement section, namely, the offset- compensated ohms method and the currentreversal method.

Offset Compensation Technique (Figure 5a) applies a source current to the resistance being measured only for part of the measurement cycle.

When the source current is on, the total voltage measured by the instrument is the sum of the voltage due to the test current and any thermoelectric EMFs present in the circuit. During the second half of the measurement cycle, the source current is turned off and the only voltage measured is that due to the thermoelectric EMF. This unwanted offset voltage can now be subtracted from the voltage measurement made during the first half of the delta mode cycle.

With the Offset Compensation technique, the source current is decided by the instrument.

To characterize at a specific current or a variety of currents, the Current Reversal technique/

Two-step Delta technique (described below) will provide more flexibility.

Current Reversal Technique/Two-Step Delta

Technique (Figure 5b)

Thermoelectric EMFs can also be cancelled by taking two voltages with test currents of opposite polarity. The voltage due to the test current can now be calculated using the formula shown in Figure 5b. This method provides 2× better signal-to-noise ratio and, therefore, better accuracy than the offset compensation technique.

(This is the method employed by the Model

2182A Nanovoltmeter/Model 622x Current Source

combination.

)

For these methods to be effective, the consecutive measurements need to be made rapidly when compared with the thermal time constant of the circuit under test. If the instruments’ response speed is too low, changes in the circuit temperature during the measurement cycle will cause changes in the thermoelectric EMFs, with the result that the thermoelectric EMFs are no longer fully cancelled.

b. Voltage measurement with source current on

V

M1

Source

Current

On

Off a. Offset compensation measurement cycle

One measurement cycle

Thermal offset measurement

R

S

I

S

V

EMF

I

S

V

M2

R

S c. Voltage measurement with source current off

V

M1

= V

EMF

+ I

S

R

S

V

M2

= V

EMF

V

M

= (V

M1

– V

M2

) = I

S

R

S

I

S

R

S

V

EMF

V

M+

= V

EMF

+ I

S

R

S

V

EMF

V

M+

V

M–

V

M–

= V

EMF

– I

S

R

S

V

M

=

V

M+

– V

M–

2

= I

S

R

S

R

S

V

EMF

Figure 5a: Subtracting thermoelectric EMFs with Offset Compensation

a. Measurement with Positive Polarity b. Measurement with Negative Polarity

Figure 5b: Canceling thermoelectric EMFs with Current Reversal

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Technical

Information

Resistance Measurements on the Nanoscale

Three-Step Delta Technique

The Three-step Delta technique eliminates errors due to changing thermo electric voltages

(offsets and drifts) and significantly reduces white noise. This results in more accurate low resistance measurements (or more accurate resistance measurements of any type when it is necessary to apply very low power to DUTs that have limited power handling capability).

This technique offers three advantages over the Two-step Delta technique.

A Delta reading is a pair of voltage measurements made at a positive test current and a negative test current. Both the Two-step and Three-step Delta techniques can cancel constant thermoelectric voltage by alternating the test current. The

Three-step technique can also cancel changing thermoelectric voltages by alternating the current source three times to make two Delta measurements: one at a negative-going step and one at a positive going step. This eliminates errors caused by changing thermoelectric EMFs 10× better than the Two-step technique (Figure 6).

The Three-step technique provides accurate voltage readings of the intended signal unimpeded by thermoelectric offsets and drifts only if the current source alternates quickly and the voltmeter makes accurate voltage measurements within a short time interval. The Model 622x Current

Source paired with the Model 2182A Nano voltmeter is optimized for this application. These products implement the Three-step technique in a way that offers better white noise immunity than the Two-step technique by spending over

90% of its time performing measurements. In addition, the Three-step technique is faster, providing 47 readings/second to support a wider variety of applications. Interestingly, the formula used for the Three-step technique is identical to that used for differential conductance

(Figure 10).

Pulsed, Low Voltage Measurements

Short test pulses are becoming increasingly important as modern electronics continue to shrink in size. Short pulses mean less power put into the DUT. In very small devices, sometimes even a small amount of power is enough to destroy them. In other devices, a small amount of power could raise the temperature significantly, causing the measurements to be invalid.

With superconducting devices, a small amount of heat introduced while making measurements can raise the device temperature and alter the results. When sourcing current and measuring voltage, the sourced current dissipates heat (I

2 R) into the device and leads. With the lowest resistance devices (<10µΩ), the power dissipated during the measurement may be primarily at contact points, etc., rather than in the device itself. It is important to complete the measurement before this heat can be conducted to the device itself, so fast pulsed measurements are critical even at these lowest resistances.

With higher resistance devices, significant power is dissipated within the device. Therefore, with these devices, it is even more important to reduce the measurement power by reducing the source current or the source pulse width. Many tests measure device properties across a range of currents, so reducing the current is not usually an option. Shorter pulses are the only solution.

The Model 6221 Current Source was designed with microsecond rise times on all ranges to enable short pulses. The Model 2182A

Nanovoltmeter offers a low latency trigger, so that a measurement can begin as little as 10µs after the Model 6221 pulse has been applied.

The entire pulse, including a complete nanovolt measurement, can be as short as 50µs. In addition, all pulsed measurements of the 6221/2182A are line synchronized. This line synchronization, combined with the Three-Step Delta technique, causes all 50/60Hz noise to be rejected

(Figure 7).

Dry Circuit Testing

Applications that involve measuring contact resistance may require that existing oxide layers remain unbroken during the measurement. This can be done by limiting the test current to less than 100mA and the voltage drop across the sample to no more than 20mV. Most low resistance meters have this “dry circuit” measurement technique built in.

160.00

140.00

120.00

100.00

80.00

60.00

40.00

20.00

0.00

2pt Delta Resistance 3pt Delta Resistance

Sourced

I

Measured

V

1ms

0.6

µA

60Hz (50Hz) line frequency noise

(e.g. 0.4mV rms)

Time

DCV offset level

(e.g. 0.5mV)

Time

226

Figure 6. 1000 delta resistance readings using 100 resistor and 10nA

source current.

Figure 7. Operating at low voltage levels, measurements are susceptible to line frequency interference. Using line synchronization eliminates line frequency noise.

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Resistance Measurements on the Nanoscale

Nanovolt Level

Resistance Measurements

In the macroscopic world, conductors may have obeyed Ohm’s “Law” (Figure 8a), but in the nanoscale, Ohm’s definition of resistance is no longer relevant (Figure 8b). Because the slope of the I-V curve is no longer a fundamental constant of the material, a detailed measurement of the slope of that I-V curve at every point is needed to study nanodevices. This plot of differential conductance (dG = dI/dV) is the most important measurement made on small scale devices, but presents a unique set of challenges.

2

1

I (

µA)

0

–1

–2

–0.01

–0.005

0

V

0.005

0.01

300

200 dI/dV

( µs)

100

0

–100

–0.01

–0.005

0

V

0.005

0.01

I I

V

Figure 8a.

Macroscopic scale

(Classical)

V

Figure 8b. Nanoscale

(Quantum)

Differential conductance measurements are performed in many areas of research, though sometimes under different names, such as: electron energy spectroscopy, tunneling spectroscopy, and density of states. The fundamental reason that differential conductance is interesting is that the conductance reaches a maximum at voltages (or more precisely, at electron energies in eV) at which the electrons are most active. This explains why dI/dV is directly proportional to the density of states and is the most direct way to measure it.

Existing Methods of Performing

Differential Conductance

The I-V Technique:

The I-V technique performs a current-voltage sweep (I-V curve) and takes the mathematical derivative. This technique is simple, but noisy.

It only requires one source and one measurement instrument, which makes it relatively easy to coordinate and control. The fundamental problem is that even a small amount of noise becomes a large noise when the measurements are differentiated (Figure 9). To reduce this noise, the I-V curve and its derivative must be measured repeatedly. Noise will be reduced by

√N, where N is the number of times the curve is measured.

Figure 9a. I-V curve

The AC Technique:

The AC technique superimposes a low amplitude AC sine wave on a stepped DC bias to the sample. It then uses lock-in amplifiers to obtain the AC voltage across and AC current through the DUT. The problem with this method is that while it provides a small improvement in noise over the I-V curve technique, it imposes a large penalty in system complexity, which includes precise coordination and computer control of six to eight instruments. Other reasons for the complexity of the system include the challenges of mixing the AC signal and DC bias, of ground loops, and of common mode current noise.

Keithley has developed a new technique that is both simple and low noise: the Four-Wire,

Source Current–Measure Voltage technique.

2182A

V-Meas

622X

I-Source

Figure 9b. Differentiated I-V curve. True dI/dV curve obscured by noise.

Four-Wire, Source Current –

Measure Voltage Technique

Now there is another approach to differential con ductance. This technique is performed by adding an alternating current to a linear staircase sweep. The amplitude of the alternating portion of the current is the differential current, dI (Figure 10). The differential current is constant throughout the test. After the voltage is measured at each current step, the delta voltage between consecutive steps is calculated. Each delta voltage is averaged with the previous delta voltage to calculate the differential voltage, dV.

The differential conductance, dG, can now be derived using dI/dV. This technique requires only one measurement sweep when using the

Model 2182A Nano volt meter and a Model 622x

Current Source, so it is faster, quieter, and

simpler than any previous method.

Meas

V1

Meas

V2

Meas

V3

Meas

V4

Meas

V5

Meas

V6

Each A/D conversion integrates (averages) voltage over a fixed time.

Delay dI dI

4th Cycle

3rd Cycle

2nd Cycle

1st Cycle

1st Reading ∆V = [(V1–V2) + (V3–V2)]/4

Figure 10. Detail of applied current and measured device voltage

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227

Selector Guide

Low Voltage/Low Resistance Meters

Model

Page

2182A

229

VOLTAGE RANGE (Full Scale)

From

10 mV

To

100 V

Input Voltage Noise

1.2 nV rms

CURRENT RANGE

6220/6221

235

N/A

N/A

N/A

3706

240

100 mV

300 V

100 nV rms

2750

40

100 mV

1000 V

<1.5 µV rms

2010

29

100 mV

1000 V

100 nV rms

2002

23

200 mV

1000 V

150 nV rms

From

To

N/A

N/A

100 fA DC

(also 2 pA peak

AC, 6221 only)

±105 mA DC

(also 100 mA peak AC, 6221 only)

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

RESISTANCE RANGE

From

To

2

1

10 nΩ

100 MΩ

3

3

10 nΩ (when used with 2182A)

100 MΩ (when used with 2182A)

0.9 mΩ

100 MΩ

0.4 mΩ

100 MΩ

0.9 mΩ

100 MΩ

1.2 mΩ

1 GΩ

THERMOCOUPLE TEMPERATURE

From

–200°C

To

1820°C

FEATURES

IEEE-488

RS-232

CE •

Input Connection

Special low thermoelectric w/copper pins. Optional

2187-4 Modular Probe Kit adds banana plugs, spring

Special Features

clips, needle probes, and alligator clips.

Delta mode and differential conductance with Model

6220 or 6221. Pulsed I-V with

Model 6221. Analog output.

IEEE-488. RS-232.

N/A

N/A

–150°C

1820°C

–200°C

1820°C

–200°C

1372°C

–200°C

1820°C

Trigger Link,

Digital I/O,

Ethernet

Controls

Model 2182A for low-power resistance and I-V measurements.

Rear panel 15 pin

D-SUB. Optional accessories:

3706-BAN,

3706-BKPL,

3706-TLK

Dry circuit. Offset compensation.

Plug-in switch/relay modules. USB. LXI

Class B/Ethernet.

Digital I/O.

Banana jacks (4)

Dry circuit.

Offset compensation.

DMM. IEEE-488.

RS-232. Digital I/O.

Plug-in modules.

Banana jacks (4)

Dry circuit.

Offset compensation.

DMM. IEEE-488.

RS-232. Plug-in scanner cards.

Banana jacks (4)

8½ digits. DMM.

Plug-in scanner cards.

NOTES

1. Lowest resistance measurable with better than 10% accuracy.

2. Highest resistance measurable with better than 1% accuracy.

3. Delta mode, offset voltage compensation with external current source. 10nΩ if used with 5A test current with Model 2440.

228

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2182A

Nanovoltmeter

The two-channel Model 2182A Nanovoltmeter is optimized for making stable, low noise voltage measurements and for characterizing low resistance materials and devices reliably and repeatably. It provides higher measurement speed and significantly better noise performance than alternative low voltage measurement solutions.

The Model 2182A represents the next step forward in Keithley nanovoltmeter technology, replacing the original Model 2182 and offering enhanced capabilities including pulse capability, lower measurement noise, faster current reversals, and a simplified delta mode for making resistance measurements in combination with a reversing current source, such as the Model 6220 or 6221.

• Make low noise measurements at high speeds, typically just 15nV p-p noise at 1s response time,

40–50nV p-p noise at 60ms

• Delta mode coordinates measurements with a reversing current source at up to 24Hz with 30nV p-p noise (typical) for one reading. Averages multiple readings for greater noise reduction

• Synchronization to line provides

110dB NMRR and minimizes the effect of AC common-mode currents

• Dual channels support measuring voltage, temperature, or the ratio of an unknown resistance to a reference resistor

• Built-in thermocouple linearization and cold junction compensation

Flexible, Effective Speed/Noise Trade-offs

The Model 2182A makes it easy to choose the best speed/filter combination for a particular application’s response time and noise level requirements. The ability to select from a wide range of response times allows optimizing speed/noise trade-offs. Low noise levels are assured over a wide range of useful response times, e.g., 15nV p-p noise at 1s and 40-50nV p-p noise at 60ms are typical. Figure 1 illustrates the Model 2182A’s noise performance.

150

100 nV

50

0

-50

Keithley 2182A nV/

µΩ Meter

-100

0

Number of Readings

100

Figure 1. Compare the Model 2182A’s DC noise performance with a nanovolt/micro-ohmmeter’s. All the data shown was taken at 10 readings per second with a low thermal short applied to the input.

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2182A

Nanovoltmeter

Ordering Information

2182A Nanovoltmeter

Accessories Supplied

2107-4 Low Thermal Input Cable with spade lugs, 1.2m (4 ft).

User manual, service manual, contact cleaner, line cord, alligator clips.

ACCESSORIES AVAILABLE

2107-30

2182-KIT

2187-4

2188

4288-1

4288-2

7007-1

7007-2

7009-5

8501-1

8501-2

8502

8503

Low Thermal Input Cable with spade lugs,

9.1m (30 ft)

Low Thermal Connector with strain relief

Input Cable with safety banana plugs

Low Thermal Calibration Shorting Plug

Single Fixed Rack Mount Kit

Dual Fixed Rack Mount Kit

Shielded GPIB Cable, 1m (3.2 ft)

Shielded GPIB Cable, 2m (6.5 ft)

Shielded RS-232 Cable, 1.5m (5 ft)

Trigger Link Cable, 1m (3.2 ft)

Trigger Link Cable, 2m (6.5 ft)

Trigger Link Adapter to 6 female BNC connectors

Trigger Link Cable to 2 male BNC connectors

KPCI-488LPA IEEE-488 Interface/Controller for the PCI Bus

KUSB-488A IEEE-488 USB-to-GPIB Interface Adapter

SERVICES AVAILABLE

2182A-3Y-EW 1-year factory warranty extended to 3 years from date of shipment

C/2182A-3Y-ISO 3 (ISO-17025 accredited) calibrations within 3 years of purchase*

TRN-LLM-1-C Course: Making Accurate Low-Level

Measurements

* Not available in all countries

Reliable Results

Power line noise can compromise measurement accuracy significantly at the nanovolt level. The

Model 2182A reduces this interference by synchronizing its measurement cycle to line, which minimizes variations due to readings that begin at different phases of the line cycle. The result is exceptionally high immunity to line interference with little or no shielding and filtering required.

Optimized for Use with Model 6220/6221 Current Sources

Device test and characterization for today’s very small and power-efficient electronics requires sourcing low current levels, which demands the use of a precision, low current source. Lower stimulus currents produce lower—and harder to measure—voltages across the devices. Linking the Model

2182A Nanovoltmeter with a Model 6220 or 6221 Current Source makes it possible to address both of these challenges in one easy-to-use configuration.

When connected, the Model 2182A and Model 6220 or 6221 can be operated like a single instrument.

Their simple connections eliminate the isolation and noise current problems that plague other solutions. The Model 2182A/622X combination allows making delta mode and differential conductance measurements faster and with less noise than the original Model 2182 design allowed. The Model

2182A will also work together with the Model 6221 to make pulse-mode measurements.

The 2182A/622X combination is ideal for a variety of applications, including resistance measurements, pulsed I-V measurements, and differential conductance measurements, providing significant advantages over earlier solutions like lock-in amplifiers or AC resistance bridges. The 2182A/622X combination is also well suited for many nanotechnology applications because it can measure resistance without dissipating much power into the device under test (DUT), which would otherwise invalidate results or even destroy the DUT.

An Easy-to-Use Delta Mode

Keithley originally created the delta mode method for measuring voltage and resistance for the Model

2182 and a triggerable external current source, such as the Model 2400 SourceMeter instrument.

Basically, the delta mode automatically triggers the current source to alternate the signal polarity, and then triggers a nanovoltmeter reading at each polarity. This current reversal technique cancels out

5nV

230

APPLICATIONS

Research

• Determining the transition temperature of superconductive materials

• I-V characterization of a material at a specific temperature

• Calorimetry

Metrology

• Intercomparisons of standard cells

• Null meter for resistance bridge measurements

4 µV

DC

Measurement

Delta Mode

Measurement

Figure 2. Results from a Model 2182A/6220 using the delta mode to measure a 10m resistor

with a 20µA test current. The free Model 6220/6221 instrument control example start-up software used here can be downloaded from www.keithley.com.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

2182A

Nanovoltmeter any constant thermoelectric offsets, so the results reflect the true value of the voltage being measured. The improved delta mode for the Model 2182A and the Model 622X current sources uses the same basic technique, but the way in which it’s implemented has been simplified dramatically. The new technique can cancel thermoelectric offsets that drift over time (not just static offsets), produces results in half the time of the original technique, and allows the current source to control and configure the Model 2182A.

Two key presses are all that’s required to set up the measurement. The improved cancellation and higher reading rates reduce measurement noise to as little as 1nV.

Differential Conductance Measurements

Characterizing non-linear tunneling devices and low temperature devices often requires measuring differential conductance (the derivative of a device’s I-V curve). When used with a Model 622X current source, the

Model 2182A is the industry’s fastest, most complete solution for differential conductance measurements, providing 10X the speed and significantly lower noise than other instrumentation options. There’s no need to average the results of multiple sweeps, because data can be obtained in a single measurement pass, reducing test time and minimizing the potential for measurement error.

Pulsed Testing with the Model 6221

When measuring small devices, introducing even tiny amounts of heat to the DUT can raise its temperature, skewing test results or even destroying the device. When used with the

Model 2182A, the Model 6221’s pulse capability minimizes the amount of power dissipated into a DUT. The Model 2182A/6221 combination synchronizes the pulse and measurement. A measurement can begin as soon as 16µs after the Model 6221 applies the pulse. The entire pulse, including a complete nanovolt measurement, can be as short as 50µs.

Competition

100 µs

0.5

µA

Model 2182A

RS-232

Trigger Link

Figure 3. It’s simple to connect the Model 2182A to the Model

6220 or 6221 to make a variety of measurements. The instrument control example start-up software available for the Model 622X current sources includes a step-by-step guide to setting up the instrumentation and making proper connections.

2182A

2182A NANOVOLTMETER

DUT

Model 622X

6220 DC AND AC CURRENT SOURCE

2182A in delta mode

GPIB or

Ethernet

Figure 4. The Model 2182A produces the lowest transient currents of any nanovoltmeter available.

In the delta, differential conductance, and pulse modes, The Model 2182A produces virtually no transient currents, so it’s ideal for characterizing devices that can be easily disrupted by current spikes

(see Figure 4).

Metrology Applications

The Model 2182A combines the accuracy of a digital multimeter with low noise at high speeds for high-precision metrology applications. Its low noise, high signal observation time, fast measurement rates, and

2ppm accuracy provide the most cost-effective meter available today for applications such as intercomparison of voltage standards and direct measurements of resistance standards.

Nanotechnology Applications

The Model 2182A combined with the Model 622X current source or Series

2400 SourceMeter ® instrument is a highly accurate and repeatable solution for measuring resistances on carbon nanotube based materials and silicon nanowires.

Research Applications

The Model 2182A’s 1nV sensitivity, thermoelectric EMF cancellation, direct display of “true” voltage, ability to perform calculations, and high measurement speed makes it ideal for determining the characteristics of materials such as metals, low resistance filled plastics, and high and low temperature superconductors.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

231

2182A

Nanovoltmeter

Three Ways to Measure Nanovolts

DC nanovoltmeters. DC nanovoltmeters and sensitive DMMs both provide low noise

DC voltage measurements by using long integration times and highly filtered readings to minimize the bandwidth near DC.

Unfortunately, this approach has limitations, particularly the fact that thermal voltages develop in the sample and connections vary, so long integration times don’t improve measurement precision. With a noise specification of just 6nV p-p, the Model 2182A is the lowest noise digital nanovolt meter available.

AC technique. The limitations of the long integration and filtered readings technique have led many people to use an AC technique for measuring low resistances and voltages.

In this method, an AC excitation is applied to the sample and the voltage is detected syn chronously at the same frequency and an optimum phase. While this technique removes the varying DC component, in many experiments at high frequencies, users can experience problems related to phase shifts caused by spurious capacitance or the L/R time constant. At low frequencies, as the

AC frequency is reduced to minimize phase shifts, amplifier noise increases.

The current reversal method. The Model

2182A is optimized for the current reversal method, which combines the advantages of both earlier approaches. In this technique, the DC test current is reversed, then the difference in voltage due to the difference in current is determined. Typically, this measure ment is performed at a few hertz (a frequency just high enough for the current to be reversed before the thermal voltages can change). The Model 2182A’s low noise performance at measurement times of a few hundred milliseconds to a few seconds means that the reversal period can be set quite small in comparison with the thermal time constant of the sample and the connections, effectively reducing the impact of thermal voltages.

220

215

210

205

Temperature

( °C)

200

195

Voltage

(nV)

10

5

190

185

0

–5

180 –10

0 8 17 25 33 42 50 58 67 75 83 92 100 108 117 125

Minutes

30

25

20

15

Figure 5. The Model 2182A’s delta mode provides extremely stable results, even in the presence of large ambient temperature changes. In this challenging example, the 200nV signal

results from a 20µA current sourced by a Model 6221 through a 10m test resistor.

Optional Accessory: Model 2187-4 Test Lead Kit

The standard cabling provided with the Model

2182A Nano volt meter and Model 622X Current

Sources provides everything normally needed to connect the instruments to each other and to the DUT. The Model 2187-4 Test Lead Kit is required when the cabling provided may not be sufficient for specific applications, such as when the DUT has special connection requirements.

The kit includes an input cable with banana terminations, banana extensions, sprung-hook clips, alligator clips, needle probes, and spade lugs to accommodate virtually any DUT. The

Model 2187-4 is also helpful when the DUT has roughly 1GW impedance or higher. In these cases, measuring with the Model 2182A directly across the DUT will lead to loading errors. The

Model 2187-4 Test Lead Kit provides a banana

Figure 6. Model 2187-4 Test Lead Kit

cable and banana jack extender to allow the Model 2182A to connect easily to the Model 622X’s low impedance guard output, so the Model 2182A can measure the DUT voltage indirectly. This same configuration also removes the Model 2182A’s input capacitance from the DUT, so it improves device response time, which may be critical for pulsed measurements.

232

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Figure 7. Model 2182A rear panel

A G R E A T E R M E A S U R E O F C O N F I D E N C E

2182A

Nanovoltmeter

Volts Specifications

(20% over range)

CONDITIONS: 1PLC with 10 reading digital filter or 5PLC with 2 reading digital filter.

Channel 1

Range Resolution

Input

Resistance

10.000000 mV

2, 3, 4

100.00000 mV

1.0000000 V

10.000000 V

100.00000 V

4

1 nV

10 nV

100 nV

1 µV

10 µV

>10 GΩ

>10 GΩ

>10 GΩ

>10 GΩ

10 MΩ ±1%

Channel 2

6, 10

100.00000 mV

1.0000000 V

10.000000 V

10 nV

100 nV

1 µV

>10 GΩ

>10 GΩ

>10 GΩ

T

Accuracy: ±(ppm of reading + ppm of range)

(ppm = parts per million) (e.g., 10ppm = 0.001%)

24 Hour

1

CAL

±1°C

20 + 4

T

90 Day

CAL

±5°C

40 + 4

T

1 Year

CAL

±5°C

50 + 4

T

2 Year

CAL

±5°C

60 + 4

10 + 3

7 + 2

2 + 1 5

10 + 3

25 + 3

18 + 2

18 + 2

25 + 3

30 + 4

25 + 2

25 + 2

35 + 4

40 + 5

32 + 3

32 + 3

52 + 5

10 + 6

7 + 2

2 + 1

5

25 + 6

18 + 2

18 + 2

30 + 7

25 + 2

25 + 2

40 + 7

32 + 3

32 + 3

Temperature

Coefficient

0°–18°C & 28°–50°C

(1 + 0.5)/°C

(1 + 0.2)/°C

(1 + 0.1)/°C

(1 + 0.1)/°C

(1 + 0.5)/°C

(1 + 1 )/°C

(1 + 0.5)/°C

(1 + 0.5)/°C

CHANNEL 1/CHANNEL 2 RATIO: For input signals ≥1% of the range, Ratio Accuracy =

±{[Channel 1 ppm of Reading + Channel 1 ppm of Range * (Channel 1 Range/Channel 1 Input)] + [Channel 2 ppm of Reading + Channel 2 ppm of Range * (Channel 2 Range/Channel 2 Input)]}.

DELTA (hardware-triggered coordination with Series 24XX, Series 26XXA, or Series 622X current sources for low noise R measurement):

Accuracy = accuracy of selected Channel 1 range plus accuracy of I source range.

DELTA MEASuREMENT NOISE WITH 6220 or 6221: Typical 3nVrms / Hz (10mV range)

21

. 1Hz achieved with 1PLC, delay = 1ms, RPT filter = 23 (20 if 50Hz).

PuLSE-MODE (WITH 6221): Line synchronized voltage measurements within current pulses from 50µs to 12ms, pulse repetition rate up to 12Hz.

PuLSE MEASuREMENT NOISE (typical rms noise, R

DuT

<10): ±(0.009ppm of range*) / meas_time / pulse_avg_count + 3nV** / (2 · meas_time · pulse_avg_count) for 10mV range.

* 0.0028ppm for the 100mV range, 0.0016ppm for ranges 1V and above.

** 8nV/ Hz for ranges above 10mV. meas_time (seconds) = pulsewidth – pulse_meas_delay in 33µs incr.

DC Noise Performance

7

(DC noise expressed in volts peak-to-peak)

Response time = time required for reading to be settled within noise levels from a stepped input, 60Hz operation.

Channel 1

Response

Time

25.0

4.0

1.0 s s s

667 ms

60 ms

Channel 2

6, 10

25.0 s

4.0 s

1.0 s

85 ms

NPLC, Filter

5, 75

5, 10

1, 18

1, 10 or 5, 2

1, Off

5, 75

5, 10

1, 10 or 5, 2

1, Off

10 mV

6 nV

15 nV

25 nV

35 nV

70 nV

100 mV

20 nV

50 nV

175 nV

250 nV

300 nV

150 nV

150 nV

175 nV

425 nV

Range

1 V

75 nV

150 nV

600 nV

650 nV

700 nV

200 nV

200 nV

400 nV

1 µV

10 V

750 nV

1.5 µV

2.5 µV

3.3 µV

6.6 µV

750 nV

1.5 µV

2.5 µV

9.5 µV

100 V

75 µV

75 µV

100 µV

150 µV

300 µV

Operating Characteristics

13, 14

60Hz (50Hz) Operation

VOLTAGE NOISE VS. SOURCE RESISTANCE

11

(DC noise expressed in volts peak-to-peak)

Source

Resistance

0 Ω

100 Ω

1 kΩ

10 kΩ

100 kΩ

1 MΩ

Noise

6 nV

8 nV

15 nV

35 nV

100 nV

350 nV

Analog

Filter

Off

Off

Off

Off

On

On

TEMPERATURE (Thermocouples)

12

(Displayed in °C, °F, or K. Accuracy based on

ITS-90, exclusive of thermocouple errors.)

TYPE RANGE RESOLUTION

N

T

E

R

J

K

S

B

–200 to +760°C

–200 to +1372°C

–200 to +1300°C

–200 to +400°C

–200 to +1000°C

0 to +1768°C

0 to +1768°C

+350 to +1820°C

0.001 °C

0.001 °C

0.001 °C

0.001 °C

0.001 °C

0.1 °C

0.1 °C

0.1 °C

Digital

Filter

100

100

100

100

100

100

ACCURACY

90 Day/1 Year

23° ±5°C

Relative to Simulated

Reference Junction

±0.2 °C

±0.2 °C

±0.2 °C

±0.2 °C

±0.2 °C

±0.2 °C

±0.2 °C

±0.2 °C

Function

DCV Channel 1,

Channel 2,

Thermocouple

Channel 1/Channel 2 (Ratio),

Delta with 24XX, Scan

Delta with 622X

System Speeds

13, 15

Digits

7.5

7.5

17, 19

6.5

18, 19

6.5

18, 19, 20

5.5

17, 19

4.5

16, 17, 19

7.5

7.5

17, 19

6.5

18

6.5

18, 20

5.5

17

4.5

17

6.5

NMRR

8

110 dB

100 dB

95 dB

90 dB

60 dB

110 dB

100 dB

90 dB

60 dB

RANGE CHANGE TIME: 14

FuNCTION CHANGE TIME: 14

AuTORANGE TIME:

14

<40 ms (<50 ms).

<45 ms (<55 ms).

<60 ms (<70 ms).

ASCII READING TO RS-232 (19.2K Baud): 40/s

MAX. INTERNAL TRIGGER RATE: 16

120/s

(40/s).

(120/s).

MAX. EXTERNAL TRIGGER RATE: 16

120/s (120/s).

Readings/s

3

6

(2)

(4)

18 (15)

45 (36)

80 (72)

115 (105)

1.5 (1.3)

2.3 (2.1)

8.5 (7.5)

20 (16)

30 (29)

41 (40)

47 (40.0)

22

CMRR

9

140 dB

140 dB

140 dB

140 dB

140 dB

140 dB

140 dB

140 dB

140 dB

PLCs

1

1

5

5

0.1

0.01

5

5

1

1

0.1

0.01

1

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

233

2182A

Nanovoltmeter

Measurement Characteristics

A/D LINEARITy: ±(0.8ppm of reading + 0.5ppm of range).

FRONT AuTOzERO OFF ERROR

10mV–10V: Add ±(8ppm of range + 500µV) for <10 minutes and ±1°C.

NOTE: Offset voltage error does not apply for Delta Mode.

AuTOzERO OFF ERROR

10mV: Add ±(8ppm of range + 100nV) for <10 minutes and ±1°C.

100mV–100V: Add ±(8ppm of range + 10µV) for <10 minutes and ±1°C.

NOTE: Offset voltage error does not apply for Delta Mode.

INPuT IMPEDANCE

10mV–10V:

10mV–10V:

100V:

>10GΩ, in parallel with <1.5nF (Front Filter ON).

>10GΩ, in parallel with <0.5nF (Front Filter OFF).

10MΩ ±1%.

DC INPuT BIAS CuRRENT: <60pA DC at 23°C, –10V to 5V. <120pA @ 23°C, 5V to 10V.

COMMON MODE CuRRENT: <50nA p-p at 50Hz or 60Hz.

INPuT PROTECTION: 150V peak to any terminal. 70V peak Channel 1 LO to Channel 2 LO.

CHANNEL ISOLATION: >10GΩ.

EARTH ISOLATION: 350V peak, >10GΩ and <150pF any terminal to earth. Add 35pF/ft with

Model 2107 Low Thermal Input Cable.

Analog Output

MAXIMuM OuTPuT: ±1.2V.

ACCuRACy: ±(0.1% of output + 1mV).

OuTPuT RESISTANCE: 1kΩ ±5%.

GAIN: Adjustable from 10 –9 to 10 6 . With gain set to 1, a full range input will produce a 1V output.

OuTPuT REL: Selects the value of input that represents 0V at output. The reference value can be either programmed value or the value of the previous input.

Triggering and Memory

WINDOW FILTER SENSITIVITy: 0.01%, 0.1%, 1%, 10%, or full scale of range (none).

READING HOLD SENSITIVITy: 0.01%, 0.1%, 1%, or 10% of reading.

TRIGGER DELAy: 0 to 99 hours (1ms step size).

EXTERNAL TRIGGER DELAy: 2ms + <1ms jitter with auto zero off, trigger delay = 0.

MEMORy SIzE: 1024 readings.

Math Functions

Rel, Min/Max/Average/Std Dev/Peak-to-Peak (of stored reading), Limit Test, %, and mX+b with userdefined units displayed.

Remote Interface

Keithley 182 emulation.

GPIB (IEEE-488.2) and RS-232C.

SCPI (Standard Commands for Programmable Instruments).

GENERAL

POWER SuPPLy: 100V/120V/220V/240V.

LINE FREquENCy: 50Hz, 60Hz, and 400Hz, automatically sensed at power-up.

POWER CONSuMPTION: 22VA.

MAGNETIC FIELD DENSITy: 10mV range 4.0s response noise tested to 500 gauss.

OPERATING ENVIRONMENT: Specified for 0° to 50°C. Specified to 80% RH at 35°C.

STORAGE ENVIRONMENT: –40° to 70°C.

EMC: Complies with European Union Directive 89/336/EEC (CE marking requirement), FCC part 15 class B, CISPR 11, IEC 801-2, IEC-801-3, IEC 801-4.

SAFETy: Complies with European Union Directive 73/23/EEC (low voltage directive); meets

EN61010-1 safety standard. Installation category I.

VIBRATION: MIL-T-28800E Type III, Class 5.

WARM-uP: 2.5 hours to rated accuracy.

DIMENSIONS: Rack Mounting: 89mm high × 213mm wide × 370mm deep (3.5 in × 8.375 in × 14.563 in). Bench Configuration (with handles and feet): 104mm high × 238mm wide × 370mm deep (4.125 in × 9.375 in ×14.563 in).

SHIPPING WEIGHT: 5kg (11 lbs).

NOTES

1. Relative to calibration accuracy.

2. With Analog Filter on, add 20ppm of reading to listed specification.

3. When properly zeroed using REL function. If REL is not used, add 100nV to the range accuracy.

4. Specifications include the use of ACAL function. If ACAL is not used, add 9ppm of reading/°C from T

CAL

to the listed specification. T

CAL

is the internal temperature stored during ACAL.

5. For 5PLC with 2-reading Digital Filter. Use ±(4ppm of reading + 2ppm of range) for 1PLC with

10-reading Digital Filter.

6. Channel 2 must be referenced to Channel 1. Channel 2 HI must not exceed 125% (referenced to Channel 1 LO) of Channel 2 range selected.

7. Noise behavior using 2188 Low Thermal Short after 2.5 hour warm-up. ±1°C. Analog Filter off.

Observation time = 10× response time or 2 minutes, whichever is less.

8. For L

SYNC

On, line frequency ±0.1%. If L

SYNC

Off, use 60dB.

9. For 1kΩ unbalance in LO lead. AC CMRR is 70dB.

10. For Low Q mode On, add the following to DC noise and range accuracy at stated response time: 200nV p-p @ 25s, 500nV p-p @ 4.0s, 1.2µV p-p @ 1s, and 5µV p-p @ 85ms.

11. After 2.5 hour warm-up, ±1°C, 5PLC, 2 minute observation time, Channel 1 10mV range only.

12. For Channel 1 or Channel 2, add 0.3°C for external reference junction. Add 2°C for internal reference junction.

13. Speeds are for 60Hz (50Hz) operation using factory defaults operating conditions (*RST).

Autorange Off, Display Off, Trigger Delay = 0, Analog Output off.

14. Speeds include measurements and binary data transfer out the GPIB. Analog Filter On, 4 readings/s max.

15. Auto Zero Off, NPLC = 0.01.

16. 10mV range, 80 readings/s max.

17. Sample count = 1024, Auto Zero Off.

18. For L

SYNC

On, reduce reading rate by 15%.

19. For Channel 2 Low Q mode Off, reduce reading rate by 30%.

20. Front Auto Zero off, Auto Zero off.

21. Applies to measurements of room temperature resistances <10Ω, Isource range ≤20µA.

22. Display off, delay 1ms.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6220

6221

DC Current Source

AC and DC Current Source

6220 and 6221

• Source and sink (programmable load) 100fA to 100mA

• 10

14

output impedance

ensures stable current sourcing into variable loads

• 65000-point source memory allows executing comprehensive test current sweeps directly from the current source

• Built-in RS-232, GPIB, Trigger

Link, and digital I/O interfaces

• Reconfigurable triax output simplifies matching the application’s guarding requirements

• Model 220 emulation mode eliminates need to reprogram existing applications

6221 Only

• Source AC currents from 4pA to 210mA peak to peak for AC charac ter iza tion of components and materials. The 6221’s

10MHz output update rate generates smooth sine waves up to 100kHz

• Built-in standard and arbitrary waveform generators with

1mHz to 100kHz frequency range. Applications include use as a complex programmable load or sensor signal and for noise emulation

• Programmable pulse widths as short as 5µs, limiting power dissipation in delicate components. Supports pulsed I-V measurements down to 50µs when used with Model 2182A

Nanovoltmeter

• Built-in Ethernet interface for easy remote control without a

GPIB controller card

The Model 6220 DC Current Source and Model 6221 AC and DC Current Source combine ease of use with exceptionally low current noise. Low current sourcing is critical to applications in test environments ranging from R&D to production, especially in the semiconductor, nanotechnology, and superconductor industries. High sourcing accuracy and built-in control functions make the Models 6220 and 6221 ideal for applications like Hall measurements, resistance measurements using delta mode, pulsed measurements, and differential conductance measurements.

The need for precision, low current sourcing. Device testing and characterization for today’s very small and power-efficient electronics requires sourcing low current levels, which demands the use of a precision, low current source. Lower stimulus currents produce lower—and harder to measure— voltages across the device. Combining the Model 6220 or 6221 with a Model 2182A Nanovoltmeter makes it possible to address both of these challenges.

AC current source and current source waveform generator. The Model 6221 is the only low current AC source on the market. Before its introduction, researchers and engineers were forced to build their own AC current sources. This cost-effective source provides better accuracy, consistency, reliability, and robustness than “home-made” solutions. The Model 6221 is also the only commercially available current source waveform generator, which greatly simplifies creating and outputting complex waveforms.

Simple programming. Both current sources are fully programmable via the front panel controls or from an external controller via RS-232 or GPIB interfaces; the Model 6221 also features an Ethernet interface for remote control from anywhere there’s an Ethernet connection. Both instruments can source DC currents from 100fA to 105mA; the Model 6221 can also source AC currents from 4pA to

210mA peak to peak. The output voltage compliance of either source can be set from 0.1V to 105V in

10mV steps. Voltage compliance (which limits

TYPICAL APPLICATIONS

the amount of voltage applied when sourcing a current) is critical for applications in which overvoltages could damage the device under test (DUT).

• Nanotechnology

- Differential conductance

- Pulsed sourcing and resistance

Drop-in replacement for the Model 220

current source. These instruments build upon

Keithley’s popular Model 220 Programmable

Current Source; a Model 220 emulation mode makes it easy to replace a Model 220 with a

Model 6220/6221 in an existing application without rewriting the control code.

• Optoelectronics

- Pulsed I-V

• Replacement for AC resistance bridges (when used with Model

2182A)

- Measuring resistance with low power

Define and execute current ramps easily.

Both the Models 6220 and 6221 offer tools for defining current ramps and stepping through predefined sequences of up to 65,536 output values using a trigger or a timer. Both sources support linear, logarithmic, and custom sweeps.

• Replacement for lock-in amplifi ers (when used with Model

2182A)

- Measuring resistance with low noise

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235

6220

6221

DC Current Source

AC and DC Current Source

Ordering Information

6220 DC Precision Current Source

6221 AC and DC Current Source

6220/2182A

Complete Delta Mode

System, w/DC Current

Source, Nanovoltmeter, and all necessary cables

(GPIB cables not included)

6221/2182A

Complete Delta Mode

System, w/AC and DC

Current Source, Nano voltmeter, and all necessary cables (GPIB cables not included)

Accessories Supplied

237-ALG-2 6.6 ft (2m), Low Noise,

Input Cable with Triaxto-Alligator Clips

8501-2 6.6 ft (2m) Trigger Link

Cable to connect 622x to 2182A

CA-180-3A Ethernet Crossover

Cable (6221 only)

CA-351 Communication Cable between 2182A and 622x

CS-1195-2 Safety Interlock

Connector

Instruction manual on CD

Getting Started manual (hardcopy)

Software (downloadable)

The Model 6221’s combination of high source resolution and megahertz update rates makes it capable of emulating high fidelity current signals that are indistinguishable from analog current ramps.

Free Instrument Control Example Start-up Software

The instrument control example software available for the sources simplifies both performing basic sourcing tasks and coordinating complex measurement functions with the Keithley Model 2182A. The software, developed in the LabVIEW ® programming environment, includes a step-by-step measurement guide that helps users set up their instruments and make proper connections, as well as program basic sourcing functions. The advanced tools in the package support delta mode, differential conductance, and pulse mode measurements. From this package, users can print out the instrument commands for any of the pre-programmed functions, which provides a starting point for incorporating these functions into customized applications.

Differential Conductance

Differential conductance measurements are among the most important and critical measurements made on non-linear tunneling devices and on low temperature devices. Mathematically, differential conductance is the derivative of a device’s I-V curve. The Model 6220 or 6221, combined with the

Model 2182A Nano voltmeter, is the industry’s most complete solution for differential conductance measurements. Together, these instruments are also the fastest solution available, providing 10× the speed and significantly lower noise than other options. Data can be obtained in a single measurement pass, rather than by averaging the result of multiple sweeps, which is both time-consuming and prone to error. The Model 622X and Model 2182A are also easy to use because the combination can be treated as a single instrument. Their simple connections eliminate the isolation and noise current problems that plague other solutions.

236

ACCESSORIES AVAILABLE

7006-*

7007-1

GPIB Cable with Straight-On Connector

Shielded IEEE-488 Cable, 1m (3.3 ft)

7007-2 Shielded IEEE-488 Cable, 2m (6.6 ft)

7078-TRX-5 5ft (1.5m), Low Noise, Triax-to-Triax Cable

(Male on Both Ends)

KPCI-488LPA IEEE-488 Interface/Controller for the PCI Bus

KUSB-488A IEEE-488 USB-to-GPIB Interface Adapter

SERVICES AVAILABLE

6220-3Y-EW 1-year factory warranty extended to 3 years from date of shipment

6221-3Y-EW 1-year factory warranty extended to 3 years from date of shipment

C/6220-3Y-ISO 3 (ISO-17025 accredited) calibrations within 3 years of purchase*

C/6221-3Y-ISO 3 (ISO-17025 accredited) calibrations within 3 years of purchase*

*Not available in all countries

Figure 1. Perform, analyze, and display differential conductance measurements.

Delta Mode

Keithley originally developed the delta mode method for making low noise measurements of voltages and resistances for use with the Model 2182 Nanovoltmeter and a triggerable external current source.

Essentially, the delta mode automatically triggers the current source to alternate the signal polarity, then triggers a nanovoltmeter reading at each polarity. This current reversal technique cancels out any constant thermoelectric offsets, ensuring the results reflect the true value of the voltage.

This same basic technique has been incorporated into the Model 622X and Model 2182A delta mode, but its implementation has been dramatically enhanced and simplified. The technique can now cancel thermoelectric offsets that drift over time, produce results in half the time of the previous technique, and allow the source to control and configure the nanovoltmeter, so setting up the

measurement takes just two key presses. The improved cancellation and higher reading rate reduces measurement noise to as little as 1nV.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6220

6221

DC Current Source

AC and DC Current Source

4

µV

DC

Measurement

Delta Mode

Measurement

Figure 2. Delta mode offers 1000-to-1 noise reduction.

5nV

The delta mode enables measuring low voltages and resistances accurately. Once the Model 622X and the Model 2182A are connected properly, the user simply presses the current source’s Delta button, followed by the Trigger button, which starts the test. The Model 622X and the Model 2182A work together seamlessly and can be controlled via the GPIB interface (GPIB or Ethernet with the Model

6221). The free example control software available for the Model 622X includes a tutorial that “walks” users through the delta mode setup process.

Pulsed Tests

Even small amounts of heat introduced by the measurement process itself can raise the DUT’s temperature, skewing test results or even destroying the device. The Model 6221’s pulse measurement capability minimizes the amount of power dissipated into a DUT by offering maximum flexibility when making pulsed measurements, allowing users to program the optimal pulse current amplitude, pulse interval, pulse width, and other pulse parameters.

The Model 6221 makes short pulses (and reductions in heat dissipation) possible with microsecond rise times on all ranges. The Model 6221/2182A combination synchronizes the pulse and measurement—a measurement can begin as soon as 16µs after the Model 6221 applies the pulse. The entire pulse, including a complete nanovolt measurement, can be as short as 50µs. Line synchronization between the Model 6221 and Model 2182A eliminates power line related noise.

Standard and Arbitrary Waveform Generator

The Model 6221 is the only low current AC source on the market. It can be programmed to generate both basic waveforms (sine, square, triangle, and ramp) and customizable waveforms with an arbitrary waveform generator (ARB) that supports defining waveforms point by point. It can generate waveforms at frequencies ranging from 1mHz to 100kHz at an output update rate of

10 megasamples/ second.

Performance Superior to AC Resistance Bridges and Lock-In Amplifiers

The Model 622X/2182A combination provides many advantages over AC resistance bridges and lock-in amplifiers, including lower noise, lower current sourcing, lower voltage measurements, less power dissipation into DUTs, and lower cost. It also eliminates the need for a current pre-amplifier.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

Models 6220 and 6221 vs.

Homemade Current Sources

Many researchers and engineers who need a current source attempt to get by with a voltage source and series resistor instead. This is often the case when an AC current is needed.

This is because, until the introduction of the

Model 6220/6221, no AC current sources were available on the market. However, homemade current sources have several disadvantages vs. true current sources:

Homemade Current Sources Don’t Have

Voltage Compliance. You may want to be sure the voltage at the terminals of your homemade “current source” never exceeds a certain limit (for example, 1–2V in the case of many optoelectronic devices). The most straightforward way to accomplish this is to reduce the voltage source to that level. This requires the series resistor to be reduced to attain the desired current. If you want to program a different current, you must change the resistor while the voltage is held constant! Another possibility is to place a protection circuit in parallel with the DUT. These do not have precise voltage control and always act as a parallel device, stealing some of the programmed current intended for the DUT.

Homemade Current Sources Can’t Have

Predictable Output. With a homemade

“current source” made of a voltage source and series resistor, the impedance of the

DUT forms a voltage divider. If the DUT resistance is entirely predictable, the current can be known, but if the DUT resistance is unknown or changes, as most devices do, then the current isn’t a simple function of the voltage applied. The best way to make the source predictable is to use a very high value series resistor (and accordingly high voltage source), which is in direct contradiction with the need for compliance.

While it’s possible to know (if not control) the actual current coming from such an unpredictable source, this also comes at a cost. This can be done with a supplemental measurement of the current, such as using a voltmeter to measure the voltage drop across the series resistor. This measurement can be used as feedback to alter the voltage source or simply recorded. Either way, it requires additional equipment, which adds complexity or error. To make matters worse, if the homemade current source is made to be moderately predictable by using a large series resistor, this readback would require using an electrometer to ensure accuracy.

237

6220

6221

DC Current Source

AC and DC Current Source

The Model 6221 can also expand the capabilities of lock-in amplifiers in applications that already employ them. For example, its clean signals and its output synchronization signal make it an ideal output source for lock-in applications such as measuring second and third harmonic device response.

Model 2182A Nanovoltmeter

The Model 2182A expands upon the capabilities of Keithley’s original Model 2182 Nano voltmeter. Although the Model 6220 and 6221 are compatible with the Model 2182, delta mode and differential conductance measurements require approximately twice as long to complete with the Model 2182 as with the Model 2182A. Unlike the Model 2182A, the Model 2182 does not support pulse mode measurements.

Figure 4. The Model 6221 and the free example start-up control software make it easy to create complex waveforms by adding, multiplying, stringing together, or applying filters to standard wave shapes.

Source Current

Voltage measurement noise at line frequency

Measured response voltage

Programmable: 50 µs to 12ms

Measurement integration period

Measuring difference voltage eliminates line frequency noise, DC offsets

1/60 second (1/50 when operating off 50Hz power)

Pulsed measurement without line sync Line synchronized pulse measurements

Figure 3. Measurements are line synchronized to minimize 50/60Hz interference.

APPLICATIONS OF 622X/2182A

COMBINATION:

• Easy instrument coordination and intuitive example software simplifies setup and operation in many applications.

• Measure resistances from 10nΩ to

100MΩ. One measurement system for wide ranging devices.

• Low noise alternative to AC resistance bridges and lock-in amplifiers for measuring resistances.

• Coordinates pulsing and measurement with pulse widths as short as 50µs (6221 only).

• Measures differential conductance up to 10× faster and with lower noise than earlier solutions allow. Differential conductance is an important parameter in semicon ductor research for describing density of states in bulk material.

• Delta mode reduces noise in low resistance measurements by a factor of 1000.

• For low impedance Hall measurements, the delta mode operation of the Model 622X/2182A combination provides industry-leading noise performance and rejection of contact potentials. For higher impedance

Hall measurements (greater than

100MΩ), the Model 4200-SCS can replace the current source, switching, and multiple high impedance voltage measurement channels. This provides a complete solution with pre-programmed test projects.

238

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6220

6221

DC Current Source

AC and DC Current Source

Source Specifications

Range

(+5% over range)

Accuracy

(1 Year)

23°C ±5°C

±(% rdg. + amps)

2 nA 0.4 % + 2 pA

20 nA 0.3 % + 10 pA

200 nA 0.3 % + 100 pA

2 µA 0.1 % + 1 nA

20 µA 0.05% + 10 nA

200 µA 0.05% + 100 nA

2 mA 0.05% + 1 µA

20 mA 0.05% + 10 µA

100 mA 0.1 % + 50 µA

Programming

Resolution

100 fA

1

10 pA pA

100

1

10

100

1

10 pA nA nA nA

µA

µA

Temperature

Coefficient/°C

0°–18°C &

28°–50°C

0.02 % + 200 fA

Typical Noise

(peak-peak)/RMS

3

0.1Hz–10Hz

400 / 80 fA

0.02 % + 200 fA

0.02 % + 2 pA

4 / 0.8 pA

20 / 4 pA

0.01 % + 20 pA

0.005% + 200 pA

0.005% + 2 nA

0.005% + 20 nA

0.005% + 200 nA

0.01 % + 2 µA

200 / 40

2 / 0.4

20 / 4

200 / 40

2 / 0.4

10 / 2 pA nA nA nA

µA

µA

6221 Only

Typical Noise

(peak-peak)/RMS

3

10Hz–(Bw)

250 / 50

250 / 50

2.5 / 0.5 pA pA nA

Output

Response

Bandwidth

(BW) Into

Short

10 kHz

10 kHz

100 kHz

25 / 5.0

500 / 100

1.0 / 0.2

5.0 / 1

20 / 4.0

100 / 20 nA nA

µA

µA

µA

µA

1 MHz

1 MHz

1 MHz

1 MHz

1 MHz

1 MHz

Settling Time

1, 2

(1% of Final Value)

Output

Response

Fast (Typical

3

)

(6221 Only)

90 µs

90 µs

30 µs

4 µs

2 µs

2 µs

2 µs

2 µs

3 µs

6220, 6221 with Output

Response

Slow (Max.)

100 µs

100 µs

100 µs

100 µs

100 µs

100 µs

100 µs

100 µs

100 µs

ADDITIONAL SOURCE SPECIFICATIONS

OuTPuT RESISTANCE: >10

14 Ω (2nA/20nA range).

OuTPuT CAPACITANCE: <10pF, <100pF Filter ON (2nA/20nA range).

LOAD IMPEDANCE: Stable into 10µH typical, 100µH for 6220, or for 6221 with Output Response SLOW.

VOLTAGE LIMIT (Compliance): Bipolar voltage limit set with single value. 0.1V to 105V in 0.01V programmable steps.

MAX. OuTPuT POWER: 11W, four quadrant source or sink operation.

GuARD OuTPuT ACCuRACy: ±1mV for output currents <2mA

(excluding output lead voltage drop).

PROGRAM MEMORy: Number of Locations: 64K. Offers point-by-point control and triggering, e.g. sweeps.

MAX. TRIGGER RATE: 1000/s.

RMS NOISE 10Hz–20MHz (2nA–20mA Range): Less than

1mVrms, 5mVp-p (into 50Ω load).

SOURCE NOTES

1. Settling times are specified into a resistive load, with a maximum resistance equal to 2V/ I full scale

of range. See manual for other load conditions.

2. Settling times to 0.1% of final value are typically <2× of 1% settling times.

3. Typical values are non warranted, apply at 23°C, represent the 50th percentile, and are provided solely as useful information.

2182A MEASUREMENT FUNCTIONS

DuT RESISTANCE: Up to 1GΩ (1ns) (100MΩ limit for pulse mode).

DELTA MODE RESISTANCE MEASuREMENTS AND

DIFFERENTIAL CONDuCTANCE: Controls Keithley Model

2182A Nanovoltmeter at up to 24Hz reversal rate (2182 at up to 12Hz).

PuLSE MEASuREMENTS (6221 ONLy):

Pulse Widths: 50µs to 12ms, 1pA to 100mA.

Repetition Interval: 83.3ms to 5s.

ARBITRARY FUNCTION GENERATOR

(6221 only)

WAVEFORMS: Sine, Square, Ramp, and 4 user defined arbitrary waveforms.

FREquENCy RANGE: 1mHz to 100kHz.

5

FREquENCy ACCuRACy

4

: ±100ppm (1 year).

SAMPLE RATE: 10 MSPS.

AMPLITuDE: 4pA to 210mA peak-peak into loads up to 10

12 Ω.

AMPLITuDE RESOLuTION: 16 bits (including sign).

AMPLITuDE ACCuRACy (<10kHz):

5

Magnitude: ±(1% rdg + 0.2% range).

Offset: ±(0.2% rdg + 0.2% range).

SINE WAVE CHARACTERISTICS:

Amplitude Flatness: Less than 1dB up to 100kHz.

6

SquARE WAVE CHARACTERISTICS:

Overshoot: 2.5% max.

6

Variable Duty Cycle:

4

Settable to 1µs min. pulse duration,

0.01% programming resolution.

Jitter (RMS): 100ns + 0.1% of period.

6

RAMP WAVE CHARACTERISTICS:

Linearity: <0.1% of peak output up to 10kHz.

6

ARBITRARy WAVE CHARACTERISTICS:

Waveform Length: 2 to 64K points.

Jitter (RMS): 100ns + 0.1% of period.

6

WAVEFORM NOTES

4. Minimum realizable duty cycle is limited by current range response and load impedance.

5. Amplitude accuracy is applicable into a maximum resistive load of 2V/ I full scale

of range. Amplitude attenuation will occur at higher frequencies dependent upon current range and load impedance.

6. These specifications are only valid for the 20mA range and a

50Ω load.

GENERAL

COMMON MODE VOLTAGE: 250V rms, DC.

COMMON MODE ISOLATION: >10

9 Ω, <2nF.

REMOTE INTERFACE: SCPI (Standard Commands for

Programmable Instruments).

DIGITAL I/O: 1 trigger input, 4 TTL/relay drive outputs.

OuTPuT CONNECTIONS:

Teflon insulated 3-lug triax connector for output.

Banana safety jack for GUARD, OUTPUT LO.

Screw Terminal for CHASSIS.

DB-9 connector for EXTERNAL TRIGGER INPUT,

OUTPUT, and DIGITAL I/O.

Two position screw terminal for INTERLOCK.

ENVIRONMENT: Operating: 0°–50°C, 70%R.H. up to

35°C. Derate 3% R.H./°C, 35°–50°C. Storage: –25°C to

65°C, guaranteed by design.

EMC: Conforms to European Union Directive 89/336/EEC,

EN 61326-1.

SAFETy: Conforms to European Union Directive 73/23/

EEC, EN61010-1.

VIBRATION: MIL-PRF-28800F Class 3, Random.

WARMuP: 1 hour to rated accuracies.

PASSIVE COOLING: No fan.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

239

Series 3700

System Switch/Multimeter and Plug-In Cards

240

• Combines the functions of a system switch and a high performance multimeter

• LXI Class B compliance with

IEEE 1588 time synchronization

• 3½- to 7½-digit measurement resolution

• Embedded Test Script Processor

(TSP

®

) offers unparalleled system automation, throughput, and flexibility

Extended low ohms (1) range

with 100n resolution

• Extended low current (10µA) range with 1pA resolution

• >14,000 readings/second

• Low noise, <0.1ppm rms noise on 10VDC range

• Expanded dry circuit range

(2k)

• Four-wire open lead detection

(source and sense lines)

For more information about Series 3700 systems, see page 74.

A Series 3700 system combines the functionality of an instrument grade relay switching system with a high performance multimeter. Integrating the multimeter within the mainframe ensures you of a high quality signal path from each channel to the multimeter. This tightly integrated switch and measurement system can meet the demanding application requirements of a functional test system or provide the flexibility needed in stand-alone data acquisition and measurement applications. It is ideal for multiple pin count applications where relay switching can be used to connect multiple devices to source and measurement instruments.

The high performance multimeter in the Series 3700 offers low noise, high stability 3½- to 7½-digit readings for leading-edge measurement performance. This flexible resolution sup plies a DC reading rate from >14,000 readings/second at 3½ digits to 60 readings/second at 7½ digits, offering customers maximum reading throughput and accuracy. The multimeter also provides an expanded low ohms (1Ω) range, low current (10µA) range, and dry circuit (1Ω to 1kΩ) range, extending utility beyond typical

DMM applications.

The multimeter supports 13 built-in measure ment functions, including: DCV, ACV, DCI, ACI, frequency, period, two-wire ohms, four-wire ohms, three-wire RTD temperature, four-wire RTD temperature, thermocouple temperature, thermistor temperature, and continuity. In-rack calibration is sup ported, which reduces both maintenance and calibration time. Onboard memory can store up to 650,000 readings, and the USB device port provides easy transfer of data to memory sticks.

Single-Channel Reading Rates

Resolution

7½ Digits (1 NPLC)

6½ Digits (0.2 NPLC)

5½ Digits (0.06 NPLC)

4½ Digits (0.006 NPLC)

3½ Digits (0.0005 NPLC)

DCV/

2-Wire Ohms 4-Wire Ohms

60

295

29

120

935

6,300

14,000

285

580

650

4.0

3.0

2.0

1.0

0.0

–1.0

–2.0

–3.0

Low Noise Performance

Model 3706 vs. Leading Competitor

Leading Competitor

Keithley 3706

APPLICATIONS

• System- and rack-level signal referencing

• Power supply burn-in testing

(PC, network, telecom)

• Low ohms testing (contacts, connectors, relays)

• Temperature profiling

• Plant/environment monitoring and control

• Automotive and aerospace systems

• Consumer product certification/ testing laboratories

–4.0

0.0 5.0 10.0 15.0 20.0

1000 Readings at 1PLC

25.0 30.0 35.0

Compare the Model 3706's 10V DC noise and speed performance with that of the leading competitor. All the data was taken at 1PLC with a low thermal short applied to the input, which resulted in 10× lower noise and 7× faster measurements for the Model 3706.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

Technical

Information

Low Current/High Resistance

Measurements

An ammeter is an instrument for measuring electric current flow, calibrated in amperes. There are two main types of ammeter architectures: shunt ammeters and feedback ammeters.

Shunt vs. Feedback Ammeters

Shunt ammeters are the most common type and work in many applications; feedback ammeters are more appropriate when measuring small currents; their use is growing because the typical magnitude of the test currents used today is decreasing. However, choosing the proper ammeter depends not only on the magnitude of the current, but also on characteristics (most typically, the impedance) of the device under test (DUT).

Shunt Ammeters: DMMs

Shunt ammeters are the most common ammeter type and are found in almost all digital multimeters

(DMMs). These meters measure current by developing a voltage at the input terminal that is proportional to the current being measured (Figure 1).

I

V

BURDEN

= 200mV at full scale

DMM (shunt) ammeter

+

R

SHUNT

A/D

Figure 1

The main drawback associated with shunt ammeters is their fundamentally high input impedance design. This drawback becomes more significant with decreasing current, because a larger shunt resistor must be used in order to develop a measurable voltage. However, as long as the shunt resistor is significantly smaller than the resistance of the DUT and the currents to be measured are not very small (not much lower than microamp level [10

–6

A]), shunt ammeters work fine.

Voltage Burden

The terminal voltage of an ammeter is called the voltage burden. This voltage burden developed across the meter could result in significantly lower current through the load than before the meter was inserted, therefore, the ammeter can’t read the current it was intended to measure.

An ideal ammeter would not alter the current flowing in the circuit path, so it would have zero resistance and zero voltage burden. A real ammeter will always introduce a non-zero voltage burden. In general, the error term caused by an ammeter is stated as the ammeter’s voltage burden divided by the resistance of the DUT. A shunt ammeter’s voltage burden is typically on the order of hundreds of millivolts.

I

1V

Figure 3

Picoammeter/Electrometer

300mV – V

BURDEN

0.7V

+

I

A/D

V

OFFSET

CAL V

OFFSET

Total voltage burden<0.2mV

Figure 2

Feedback Ammeter

Feedback ammeters are closer to “ideal” than shunt ammeters, and should be used for current measurements of microamps or less (10

–6

A) or where it is especially critical to have an ammeter with low input impedance. Instead of developing a voltage across the terminals of the ammeter, a feedback ammeter develops a voltage across the feedback path of a high gain operational amplifier (Figure 2). This voltage is also proportional to the current to be measured; however, it is no longer observed at the input of the instrument, but only through the output voltage of the opamp. The input voltage is equal to the output voltage divided by the op-amp gain (typically 100,000), so the voltage burden has now typically been reduced to microvolts. The feedback ammeter architecture results in low voltage burden, so it produces less error when measuring small currents and when measuring currents generated by low impedance devices. Keithley electrometers and picoammeters employ feedback ammeter technology.

V

BURDEN

Figure 3 illustrates the problems caused by high voltage burden when measuring the emitter current of a transistor. Even though the basic current measurement could be well within the measuring capability of the DMM, the DMM’s voltage burden significantly reduces the voltage applied to the DUT, resulting in lower measured emitter current than intended. If a picoammeter or electrometer were used instead, the voltage burden would cause a negligible change in emitter current.

Sources of Generated Current Error

Low current measurements are subject to a number of error sources that can have a serious impact on measurement accuracy. All ammeters will generate some small current that flows even when the input is open. These offset currents can be partially nulled by enabling the instrument current suppress. External leakage currents are additional sources of error; therefore, making properly guarded and/or shielded connections is important. The source impedance of the DUT will also affect the noise performance of the ammeter. In addition, there are other extraneous generated currents in the test system that could add to the desired current, causing errors. The following paragraphs discuss various types of generated currents and how to minimize their impact on the measuremen ts.

Coaxial

Cable

+

Frictional motion at boundary due to cable motion

Insulation

+

Outer

Jacket

Inner

Conductor

Outer

Shield

I

I

Conductive lubricant in low noise cable

Figure 4

Triboelectric effects are created by charge imbalance due to frictional effects between a conductor and an insulator, as shown in Figure 4. Keithley’s low noise cables greatly reduce this effect by introducing an inner insulator of polyethylene coated with graphite underneath the outer shield. The graphite provides lubrication and a conducting equipotential cylinder to equalize charges and minimize the charge generated.

Piezoelectric currents are generated when mechanical stress is applied to certain crystalline materials when used for insulated terminals and interconnecting hardware. In some plastics, pockets of stored charge cause the material to behave in a manner similar to piezoelectric materials. An example of a terminal with a piezoelectric insulator is shown in

Figure 5. To minimize the current due to this effect, remove mechanical stresses from the insulator and use insulating materials with minimal piezoelectric and stored charge effects.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

241

Technical

Information

Low Current/High Resistance

Measurements

242

Applied

Force

Figure 5

I

I

Piezoelectric

Insulator

+

Printed

Wiring

+

+

Metal

Terminal

Flux or other chemical

“track” and moisture

I

I

Conductive

Plate

Epoxy Printed

Circuit Board

Figure 6

Contamination and humidity can produce error currents, which arise from electrochemical effects that occur when contaminants (in the form of ionic chemicals) create weak “batteries” between two conductors on a circuit board. For example, commonly used epoxy printed circuit boards, if not thoroughly cleaned of etching solution, flux, oils, salts (e.g., fingerprints) or other contaminants, can generate currents of a few nanoamps between conductors (see

Figure 6). To avoid the effects of contamination and humidity, select insulators that resist water absorption and keep humidity to moderate levels. Also, keep all insulators clean and free of contamination.

Figure 7 summarizes approximate magnitudes of the various currents.

High Resistance Measurements

For high resistance measurements (>1GΩ), a constant voltage is most often applied across the unknown resistance. The resulting current is measured from an ammeter placed in series, and the resistance can be found using Ohm’s law (R= V/I).

This method of applying a voltage and measuring the current (as opposed to applying a current and measuring the voltage), is preferred for high resistance measurements, because high resistances often change as a function of applied voltage. Therefore, it’s important to measure the resistance at a relevant and controllable voltage. This method most often requires measuring low currents using an electrometer or picoammeter. All the low current techniques and error sources described in previous paragraphs also apply here.

Leakage currents are typical sources of error in high resistance measurements. They are generated by unwanted high resistance paths (leakage resistance) between the measurement circuit and nearby voltage sources; they can be reduced by employing proper guarding techniques, using clean, quality insulators, and minimizing humidity.

Typical resistance values of various insulating materials are shown in Figure 8. Absorbed moisture may also change the

Volume

Resistivity

(Ohm-cm)

10 16 – 10 18

10 17 – 10 18 Ω

10 14 – 10 18 Ω

10

12 – 10 18 Ω

10 17 – 10 18 Ω

10

12

– 10

14 Ω

10 12 – 10 14 Ω

10 10 – 10 17

10 10 – 10 15 Ω

10 5 – 10 12

Table 1

resistance of certain insulators by orders of magnitude. Table 1 shows a qualitative description of water absorption and other effects.

Alternating Polarity Method

When measuring materials with very high resistivity, background currents may cause significant measurement errors. They may be due to charge stored in the material (dielectric absorption), static or triboelectric charge, or piezoelectric effects.

The Alternating Polarity Method can virtually eliminate the effects of background currents in the sample. In this method, a bias voltage of positive polarity is applied, then the current is measured after a predetermined delay. Next, the polarity is reversed and the current is measured again, using the same delay. The polarity reversal process can be repeated any number of times. The resistance is calculated based on a weighted average of the most recent current measurements.

Material

Sapphire

Teflon

®

Polyethylene

Polystyrene

Kel-F ®

Ceramic

Nylon

Glass Epoxy

PVC

Phenolic

Resistance to Water

Absorption

+

+

0

0

+

+

PROPERTY

Minimal

Piezoelectric

Effects

0

0

0

0

0

+

+

0

+

Minimal

Triboelectric

Effects

+

0

+

0

0

KEY: + Material very good in regard to the property.

0 Material moderately good in regard to the property.

– Material weak in regard to the property.

Typical

Current

Generated

10 –7 A

10

–8

10

–9

10 –10

10 –11

10 –12

10 –13

10 –14

10 –15

Standard

Cable

Dirty surface

Epoxy board

Low

Noise

Cable

Clean surface

Teflon 10 9 Ω

Ceramics

Triboelectric

Effects

10 12

Piezoelectric

Effects

Electrochemical

Effects

Resistor

Noise in 1Hz

Bandwidth

Current-Generating Phenomena

Figure 7

Resistance

10 18 Ω

10 17 Ω

10 16 Ω

10 15 Ω

10 14 Ω

10 13

10 12

10 11

10 10

10 9

10

8 Ω

G-10

Figure 8

PVC

Insulating Material

Polyethylene P

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

Selector Guide

Low Current/High Resistance

Measurements

Selector Guide: Picoammeters, Electrometers, Source-Measure Units

(Measurement)

Current

Amplifier

MODEL

Page

CURRENT MEASURE

428-PROG

255

From

To

1

VOLTAGE MEASURE

From

2

1.2 fA

10 mA

To

RESISTANCE MEASURE

4

From

5

To

6

CHARGE MEASURE

From

2

To

FEATURES

Input Connection

IEEE-488

RS-232

Guard

CE

Other

BNC

2 µs rise time.

10 11 V/A gain.

6485

245

20 fA

20 mA

BNC

5

1

2

digits.

Autoranging.

1000 rdg/s.

Picoammeters

6487

248

20 fA

20 mA

10 Ω

1 PΩ

2502

252

15 fA

20 mA

Electrometers

6514

257

6517B

261

<1 fA

20 mA

10 µV

200 V

10 Ω

200 GΩ

10 fC

20 µC

<1 fA

20 mA

10 µV

200 V

100 Ω

10 PΩ

3

10 fC

2 µC

Source-

Measure Unit

6430

216

400 aA

100 mA

10 µV

200 V

100 µΩ

10 PΩ

3

3 Slot

Triax

3 Slot

Triax

5

1

2

digits. Builtin 500V source.

Alternating voltage method for

HI-R sweeps.

5

1

2

digits.

Dual channel. Builtin 100V source per channel.

3 Slot

Triax

5

1

2

digits. Replaces

Models 6512,

617-HIQ.

3 Slot

Triax

5

1

2

digits. Builtin ±1kV source.

Temperature,

RH measurements.

Alternating polarity method for HI-R.

Plug-in switch cards available.

Replaces 6517A.

3 Slot

Triax

SourceMeter with

Remote PreAmp to minimize cable noise.

NOTES

1. Includes noise.

2. Digital resolution limit. Noise may have to be added.

3. PΩ (Petaohms) = 10 15 Ω.

4. Resistance is measured with the Model 237 using Source V/Measure I or Source I/Measure V, but not directly displayed.

5. Lowest resistance measurable with better than 1% accuracy.

6. Highest resistance measurable with better than 10% accuracy.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

243

Selector Guide

Low Current/High Resistance

Measurements

Selector Guide: Sources and Source-Measure Units

(Sourcing)

MODEL

Page

Current Source

Voltage Source

Sink

CURRENT OUTPUT

Accuracy

1

6220

Current Sources

6221

235

235

2 pA

Voltage Source

248

182

Resolution 2

Maximum

VOLTAGE OUTPUT

From

To

POWER OUTPUT

100 fA

±105 mA

11 W

2 pA DC

4 pA AC

100 fA

(DC & AC)

±105 mA

11 W

±1.5 V

±5000 V

25 W

CURRENT LIMIT

VOLTAGE LIMIT

105 V 105 V

ACCURACY (±Setting)

I

V

FEATURES

Output Connector

Ethernet

RS-232

IEEE-488

Memory

Remote Sense

Current Source Guard

CE

Other

0.05%

3 Slot Triax

65,000 pt.

0.05%

3 Slot Triax

65,000 pt.

Controls 2182A for low-power resistance and I-V measurements.

AC and DC current source. ARB waveforms up to 100kHz. Controls

2182A like 6220, adds pulsed I-V.

1. Best absolute accuracy of source.

2. Resolution for lowest range, smallest change in current that source can provide.

5.25 mA

0 to 5000 V

0.01%

SHV High

Voltage Coax

Voltage monitor

output.

Programmable

voltage limit.

Source-Measure Units

237 6430

221

216

450 fA

100 fA

±100 mA

10 fA

50 aA

±105 mA

±100 µV

±1100 V

11 W

±5 µV

±210 V

2.2 W

1 pA to 100 mA 1 fA to 105 mA

1 mV to 1100 V 0.2 mV to 210 V

0.05%

0.03%

0.03%

0.02%

Two 3 Slot Triax

1000 pt.

Source/measure capability. Pulse mode. High speed. Built-in waveforms.

3 Slot Triax

2500 pt.

244

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6485

Picoammeter

• Cost-effective low current measurement solution

• 10fA resolution

• 5

1

2

-digit resolution

• <200µV burden voltage

• Up to 1000 readings/second

• Built-in Model 485 emulation mode

• IEEE-488 and RS-232 interfaces

• Analog output

The 5

1

2

-digit Model 6485 Picoammeter combines

Keithley’s expertise in sensitive current measurement instrumentation with enhanced speed and a robust design. With eight current measurement ranges and high speed autoranging, this costeffective instrument can measure currents from 20fA to 20mA, taking measurements at speeds up to 1000 readings per second.

The Model 6485’s 10fA resolution and superior sensitivity make it well suited for characterizing low current phenomena, while its 20mA range lets it measure currents high enough for applications such as measuring 4-20mA sensor loops.

Although it employs the latest current measurement technology, it is significantly less expensive than other instruments that perform similar functions, such as optical power meters, competitive picoammeters, or user-designed solutions. With a price that’s comparable to a general purpose DMM, the Model 6485 makes picoamp-level measurements affordable for virtually any laboratory or

production floor.

Low Voltage Burden and Higher Accuracy

While DMMs typically employ shunt ammeter circuitry to measure current, the Model 6485 is a feedback picoammeter. This design reduces voltage burden by several orders of magnitude, resulting in a voltage burden of less than 200µV on the lower measurement ranges. The low voltage burden makes the Model 6485 function much more like an ideal ammeter than a DMM, so it can make current measurements with high accuracy, even in circuits with very low source voltages.

Current Ranges

Model 485 Model 6485

2nA–2mA

Successor to the Model 485

Voltage Burden 200µV

2nA–20mA

200µV (1mV on

20mA range)

1000/s

The Model 6485 builds on the strengths of one of

Keithley’s most popular picoammeters, the Model 485, offering an additional 20mA measurement range, as well as much higher measurement speeds. With a top speed

Reading Rate

Digits

Analog Output

Battery Option

Storage Buffer

3/s

4 1 ⁄

2

Yes

Yes

100 points

5 1 ⁄

2

Yes

No

2500 points of up to 1000 readings per second, the Model 6485 is the fastest picoammeter Keithley has ever made. It offers ten times greater resolution than the Model

485 on every range. A time-stamped 2500-reading data buffer provides minimum, maximum, and standard deviation statistics. A built-in emulation mode simplifies upgrading existing applications originally configured with a Model 485. This emulation mode makes it possible to control the Model

6485 with any custom code written to control the Model 485. Refer to the comparison table for additional information.

When do you need a picoammeter?

Measuring low DC currents often demands a lot more than a digital multimeter (DMM) can deliver. Generally, DMMs lack the sensitivity required to measure currents less than 100nA. Even at higher currents, a DMM’s input voltage drop (voltage burden) of hundreds of millivolts can make accurate current measurements impossible. Electrometers can measure low currents very accurately, but the circuitry needed to measure extremely low currents, combined with functions like voltage, resistance, and charge measurement, can increase an electrometer’s cost signifi cantly. The Model

6485 Picoammeter combines the economy and ease of use of a DMM with low current sensitivity near that of an electrometer.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

245

6485

Picoammeter

246

Ordering Information

6485 Picoammeter

Accessories Supplied

CAP-18 Protective Shield/

Cap (2-lug)

4801 Low Noise BNC Input

Cable, 1.2m (4 ft)

APPLICATIONS

• Beam monitoring and radiation monitoring

• Leakage current testing in insulators, switches, relays, and other components

• SEM beam current measurements

• Optoelectronic device testing and characterization

• Optical fiber alignment

• Circuit test and analysis in DCLF circuits

• Sensor characterization

• I-V measurements of semiconductors and other devices

• Nanoelectronic device characterization

• Teaching labs

Features that Expand Test and Measurement Flexibility

Scaled voltage analog output. This output allows the Model 6485 to transmit measurement results to devices like DMMs, data acquisition boards, oscilloscopes, or strip chart recorders.

220V overload protection. This high overload protection and a robust design let the Model 6485 withstand abusive overflows.

One-touch front panel design. Functions can be configured easily with the push of a button, without complicated function menus.

Built-in Trigger Link interface. The Trigger Link interface simplifies synchronizing the Model

6485 with other instruments and voltage sources. This interface combines six independent selectable trigger lines on a single connector for simple, direct control over all instruments in a system.

• RS-232 and IEEE-488 interfaces. These interfaces make it easy to integrate the Model 6485 into automated test and measurement systems.

• Display on/off switch. For research on light-sensitive components, such as measuring the dark currents of photodiodes, the front panel display can be switched off to avoid introducing light that could significantly reduce the accuracy of the results.

• REL and LOG functions. The Model 6485 can make relative readings with respect to a baseline value or display the logarithm of the absolute value of the measured current.

• Resistance calculations. The Model 6485 can calculate resistance by dividing an externally sourced voltage value by the measured current.

• Rear panel BNC inputs. Inexpensive, easy-to-use BNC cables can be employed, rather than more expensive triax cables.

ACCESSORIES AVAILABLE

CABLES

4802-10 Low Noise BNC Input Cable, 3m (10 ft)

4803 Low Noise Cable Kit

7007-1 Shielded IEEE-488 Cable, 1m (3.3 ft)

7007-2 Shielded IEEE-488 Cable, 2m (6.6 ft)

7007-4 Shielded IEEE-488 Cable, 4m (13.1 ft)

7009-5 RS-232 Cable

7754-3 BNC to Alligator Cable, 0.9m (3 ft)

8607 Banana Cable set for Analog Output

8501-1 Trigger Link Cable with Male Micro-DIN Connectors at each End, 1m (3.3 ft)

8501-2 Trigger Link Cable with Male Micro-DIN Connectors at each End, 2m (6.6 ft)

8502

8503

Micro-DIN to 6 BNCs Adapter Box. Includes one 8501-1

DIN-to-BNC Trigger Cable

ADAPTERS

CS-565 BNC Barrel

7078-TRX-BNC Female BNC to 3-Slot Male Triax for connecting

BNC cable into triax fixture

RACK MOUNT KITS

4288-1 Single Fixed Rack Mounting Kit

4288-2 Dual Fixed Rack Mounting Kit

GPIB INTERFACES

KPCI-488LPA IEEE-488 Interface/Controller for the PCI Bus

KUSB-488A IEEE-488 USB-to-GPIB Interface Adapter

SERVICES AVAILABLE

6485-3Y-EW 1-year factory warranty extended to 3 years from date of shipment

C/6485-3Y-ISO 3 (ISO-17025 accredited) calibrations within 3 years of purchase*

TRN-LLM-1-C Course: Making Accurate Low-Level Measurements

*Not available in all countries

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6485

Picoammeter

5

1

2

Digit

Default

Accuracy (1 Year)

1

±(% rdg. + offset) Typical

Analog

Rise Time

3

Range Resolution 18°–28°C, 0–70% RH RMS Noise

2

(10% to 90%)

2 nA

20 nA 100 fA

200 nA

2 µA

20 µA

200 µA

2 mA

20 mA

10 fA

1 pA

10 pA

100 pA

1 nA

10 nA

100 nA

0.4 % + 400 fA

0.4 % + 1 pA

0.2 % + 10 pA

0.15% + 100 pA

0.1 % + 1 nA

0.1 % + 10 nA

0.1 % + 100 nA

0.1 % + 1 µA

20 fA

100 fA

1 pA

10 pA

100 pA

1 nA

10 nA

100 nA

8 ms

8 ms

500 µs

500 µs

500 µs

500 µs

500 µs

500 µs

TEMPERATuRE COEFFICIENT: 0°–18°C & 28°–50°C. For each °C, add 0.1 ×

(% rdg + offset) to accuracy spec.

INPuT VOLTAGE BuRDEN: <200µV on all ranges except <1mV on 20mA range.

MAXIMuM INPuT CAPACITANCE: Stable to 10nF on all nA ranges and 2µA range; 1µF on 20µA and 200µA ranges, and on mA ranges.

MAXIMuM COMMON MODE VOLTAGE: 42V.

MAXIMuM CONTINuOuS INPuT VOLTAGE: 220 VDC.

ISOLATION (Meter COMMON to chassis): Typically >5×10

11 Ω in parallel with <1nF.

NMRR

1

(50 or 60Hz): 60dB.

ANALOG OuTPuT: Scaled voltage output (inverting 2V full scale on all ranges) 3% ±2mV, 1kΩ impedance.

NOTES

1. At 1 PLC – limited to 60 rdgs/second under this condition.

2. At 6 PLC, 1 standard deviation, 100 readings, filter off, capped input – limited to 10 rdgs/sec under this condition.

3. Measured at analog output with resistive load >100kΩ.

IEEE-488 BUS IMPLEMENTATION

MuLTILINE COMMANDS: DCL, LLO, SDC, GET, GTL, UNT, UNL, SPE, SPD.

IMPLEMENTATION: SCPI (IEEE-488.2, SCPI-1996.0); DDC (IEEE-488.1).

uNILINE COMMANDS: IFC, REN, EOI, SRQ, ATN.

INTERFACE FuNCTIONS: SH1, AH1, T5, TE0, L4, LE0, SR1, RL1, PP0, DC1, DT1, C0, E1.

PROGRAMMABLE PARAMETERS: Range, Zero Check, Zero Correct, EOI (DDC mode only),

Trigger, Terminator (DDC mode only), Calibration (SCPI mode only), Display Format, SRQ,

REL, Output Format, V-offset Cal.

ADDRESS MODES: TALK ONLY and ADDRESSABLE.

LANGuAGE EMuLATION: Keithley Model 485 emulation via DDC mode.

RS-232 IMPLEMENTATION:

Supports: SCPI 1996.0.

Baud Rates: 300, 600, 1200, 2400, 4800, 9600, 19.2k, 38.4k, 57.6k.

Protocols: Xon/Xoff, 7 or 8 bit ASCII, parity-odd/even/none.

Connector: DB-9 TXD/RXD/GND.

GENERAL

INPuT CONNECTOR: BNC on rear panel.

DISPLAy: 12 character vacuum fluorescent.

RANGING: Automatic or manual.

OVERRANGE INDICATION: Display reads “OVRFLOW.”

CONVERSION TIME: Selectable 0.01 PLC to 60 PLC (50 PLC under 50Hz operation).

(Adjustable from 200µs to 1s)

READING RATE:

To internal buffer: 1000 readings/second 1

To IEEE-488 bus: 900 readings/second

1, 2

Notes:

1. 0.01 PLC, digital filters off, front panel off, auto zero off.

2. Binary transfer mode. IEEE-488.1.

BuFFER: Stores up to 2500 readings.

PROGRAMS: Provide front panel access to IEEE address, choice of engineering units or scientific notation, and digital calibration.

EMC: Conforms with European Union Directive 89/336/EEC, EN61326-1.

SAFETy: Conforms with European Union Directive 73/23/EEC, EN61010-1.

TRIGGER LINE: Available, see manual for usage.

DIGITAL FILTER: Median and averaging (selectable from 2 to 100 readings).

ENVIRONMENT:

Operating: 0°–50°C; relative humidity 70% non-condensing, up to 35°C. Above 35°C, derate humidity by 3% for each °C.

Storage: –25° to +65°C.

WARM-uP: 1 hour to rated accuracy (see manual for recommended procedure).

POWER: 100–120V or 220–240V, 50–60Hz, 30VA.

PHySICAL:

Case Dimensions: 90mm high × 214mm wide × 369mm deep (3

1

2

in. × 8

3

8

in. × 14

9

16

in.).

Working Dimensions: From front of case to rear including power cord and IEEE-488 connector: 394mm (15.5 in).

Net Weight: <2.8 kg (<6.1 lbs).

Shipping Weight: <5 kg (<11 lbs).

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247

6487

Picoammeter/ Voltage Source

248

• 10fA resolution

• 5

1

2

-digit resolution

• <200µV burden voltage

• Alternating Voltage method ohms measurements

• Automated voltage sweeps for

I-V characterization

• Floating measurements up to

500V

• Up to 1000 readings/second

• Built-in Model 486 and 487 emulation mode

• IEEE-488 and RS-232 interfaces

• Analog output

• Digital I/O

The 5

1

2

-digit Model 6487 Picoammeter/Voltage

Source improves on the measurement capability of the award-winning Model 6485, and adds a high resolution 500V source. It provides higher accuracy and faster rise times than the 6485, as well as a damping function for use with capacitive devices. With eight current measurement ranges and high speed autoranging, this costeffective instrument can measure currents from

20fA to 20mA, take measure ments at speeds up to 1000 readings per second, and source voltage from 200µV to 505V.

The Model 6487’s 10fA resolution, superior sensitivity, voltage sweeping, and Alternating Voltage resistance measurements make it well suited for characterizing low current devices. Using the latest current measurement technology, it is significantly less expensive than other instruments that perform similar functions, such as optical power meters, tera-ohmmeters, competitive picoammeters, or user-designed solutions. With a price that’s comparable to a high-end DMM, the Model 6487 makes picoamp-level measurements affordable for virtually any laboratory or production floor.

Low Voltage Burden and Higher Accuracy

While DMMs typically employ shunt ammeter circuitry to measure current, the Model 6487 is a feedback picoammeter. This design reduces voltage burden by several orders of magnitude, resulting in a voltage burden of less than 200µV on the lower measurement ranges. The low voltage burden makes the Model 6487 function much more like an ideal ammeter than a DMM, so it can make current measurements with high accuracy, even in circuits with very low source voltages.

Successor to the Model 487

The Model 6487 builds on the strengths of one of Keithley’s most popular picoammeters, the Model 487, offering an additional 20mA measurement range, as well as much higher measurement speeds, up to 1000 readings per second. It simplifies device characterization with built-in voltage sweeping capability and the

Alternating Voltage method for high resistances.

A time-stamped 3000-reading data buffer provides minimum, maximum, and standard deviation statistics. A built-in emulation mode makes it possible to control the Model 6487 with any custom code written to control the Model 487.

Current Ranges

Voltage Burden

Reading Rate

Voltage Sweeps

Alternating Voltage

Ohms

Analog Output

Storage Buffer

Best V Source

Resolution

Model 487

2 nA–2 mA

200 µV

Up to 180/s

No

No

Yes

(non-inverting)

512 points

1 mV

Model 6487

2 nA–20 mA

200 µV (1 mV on

20 mA range)

Up to 1000/s

Yes

Yes

Yes

(inverting)

3000 points

0.2 mV

Features that Expand Test and Measurement Flexibility

• Direct resistance measurements. Optimized for resistances from 50Ω to 5×10 14

Source Voltage/Measure Current method.

Ω using the

• Alternating Voltage method resistance measurements. This method improves resistance measurements on devices with high background current or high noise. It extends the measurable resistance range up to 10 16 Ω.

500V overload protection. This high overload protection and a robust design let the Model 6487

tolerate abusive overflows, including accidentally shorting the voltage source directly into the ammeter.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6487

Picoammeter/ Voltage Source

Ordering Information

6487 Picoammeter/

Voltage Source

Accessories Supplied

CA-186-1B

Ground Connection

Cable, Banana to Screw-Lug

CAP-31 Protective Shield/

Cap (3-lug)

CS-459 Safety Interlock Plug

7078-TRX-3

Low Noise Triax Input

Cable, 1m (3 ft)

8607 High Voltage Banana

Cable Set for Voltage

Source Output

APPLICATIONS

• Resistance/resistivity measurements

• Beam monitoring and radiation monitoring

• Leakage current testing in insulators, switches, relays, and other components

• I-V characterization on semiconductor and optoelectronic devices

• Fiber alignment

• Circuit test and analysis in DCLF circuits

• Sensor characterization

• Rear panel triax input. This allows the picoammeter to be used in floating operation, up to

500V. When not floating, the addition of a triax to BNC adapter allows inexpensive, easy-to-use

BNC cables to be employed, rather than more expensive triaxial cables.

• RS-232 and IEEE-488 interfaces. These interfaces make it easy to integrate the Model 6487 into automated test and measurement systems.

Scaled voltage analog output. This output allows the Model 6487 to transmit measurement results to devices like DMMs, data acquisition cards, oscilloscopes, or strip chart recorders.

Built-in Trigger Link interface. The Trigger Link interface simplifies synchronizing the Model

6487 with other instruments and voltage sources. This interface combines six independent selectable trigger lines on a single connector for simple, direct control over all instruments in a system.

• Display on/off switch. For research on light-sensitive components, such as measuring the dark currents of photodiodes or I-V measurements on unpackaged semiconductors, the front panel display can be switched off to avoid introducing light that could significantly reduce the accuracy of the results.

One-touch front panel design. Functions can be configured easily with the push of a button, without complicated function menus.

A Broad Range of Low Current Applications

Wafer-Level Photodiode Testing

The Model 6487 Picoammeter/Voltage Source can be paired with a calibrated light source and a probing fixture to create a cost-effective photodiode test system. Multiple Model 6487s can be connected to the DUT’s probe pads to provide photocurrent readings or, with the addition of a switch matrix, one pico ammeter can take current measurements from multiple pads. In the first step of the measurement process, performed in total darkness, the Model 6487 produces a voltage sweep and then measures the resulting dark current. In the second step, a voltage bias is applied and the resulting photocurrent is meas ured while the light level is increased in calibrated steps. The same basic test configuration can be used for testing positive intrinsic negative (PIN) and avalanche photodiodes

(APDs). The 6487’s high resolution on the 10V source range provides superior sweeping and biasing when small biases are required. The 500V source capability is necessary to bias APDs.

Calibrated Light Source

Probe

Needles

Photo Diode

Pads

Probe Needles

Wafer

V source

Ammeter

6487 Picoammeter/Voltage Source

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249

6487

Picoammeter/ Voltage Source

Monitoring and Control of Focused Ion Beam Currents

In semiconductor fabrication, focused ion beam systems are often used for nanometer-scale imaging, micromachining, and mapping. Careful monitoring of the magnitude of the beam current with an ion detector is critical. The ion detector generates a secondary current that’s proportional to the current of the primary ion beam. When this secondary current is measured, it can be used to control the intensity of the primary beam. However, this secondary current is very low, often just a few picoamps, so the instrumentation measuring it must provide high measurement accuracy and repeatability, as well as sub-picoamp resolution. The Model 6487’s wide measurement range and 5

1

2

-digit resolution make it ideal for this application. Signal connections to the Model 6487 are made through the instrument’s triax connector. Often, a detector may require high voltage to attract ions, making the 6487’s 500V source a necessity.

6487

Picoammeter/Voltage Source

Ion

Detector

Ion Beam

I

M

When do you need a picoammeter?

Measuring low DC currents often demands a lot more than a digital multimeter can deliver. Generally,

DMMs lack the sensitivity required to measure currents less than

100nA. Even at higher currents, a DMM’s input voltage drop

(voltage burden) of hun dreds of millivolts can make accurate current measurements impossible.

Electrometers can measure low currents very accu rately, but the circuitry needed to measure extremely low currents, combined with functions like voltage, resistance, and charge measurement, can increase an electrometer’s cost significantly. The Model

6487 Picoammeter/Voltage

Source combines the economy and ease of use of a DMM with low current sensitivity near that of an electrometer.

High Resistance Measurements

The Model 6487 Picoammeter can be used to measure high resistances (>1GΩ) in applications such as insulation resistance testing. A constant voltage is placed in series with the unknown resistance and the picoammeter. The voltage drop across the picoammeter is negligible, so all the voltage appears across the unknown resistance. The resulting current is measured by the picoammeter and the resistance is calculated using Ohm’s Law (R = V/I). To prevent generated current due to electrostatic interference, the unknown resistance is housed in a shielded test fixture. A small series resistor may be added to reduce noise if the un known resistor has high stray capacitance across it.

Metal Shield

R

6487 Picoammeter/

Voltage Source

HI

Ammeter

LO

HI

V source

LO

ACCESSORIES AVAILABLE

CABLES

6517-ILC-3 Interlock Cable for 8009 Resistivity Test Fixture

7007-1

7007-2

Shielded IEEE-488 Cable, 1m (3.3 ft)

Shielded IEEE-488 Cable, 2m (6.6 ft)

7007-4 Shielded IEEE-488 Cable, 4m (13.1 ft)

7078-TRX-10 Low Noise Triax Cable, 3.0m (10 ft)

7078-TRX-20 Low Noise Triax Cable, 6.0m (20 ft)

8501-* Trigger Link Cable with male Micro-DIN connectors at each end, 1m or 2m (3.3 ft or 6.6 ft)

ADAPTERS

237-TRX-BAR Triax Barrel

7078-TRX-BNC Triax-to-BNC Adapter

TEST FIXTURES

8009 Resistivity Test Fixture

RACK MOUNT KITS

4288-* Single or Dual Fixed Rack Mounting Kit

GPIB INTERFACES

KPCI-488LPA IEEE-488 Interface/Controller for the PCI Bus

KUSB-488A IEEE-488 USB-to-GPIB Interface Adapter

SERVICES AVAILABLE

6487-3Y-EW 1-year factory warranty extended to 3 years from date of shipment

C/6487-3Y-ISO 3 (ISO-17025 accredited) calibrations within 3 years of purchase*

TRN-LLM-1-C Course: Making Accurate Low-Level

Measurements

*Not available in all countries

250

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6487

Picoammeter/ Voltage Source

Range

2 nA

20 nA

200 nA

2 µA

20 µA

200 µA

2 mA

20 mA

5

1

2

Digit

Default

Resolution

10 fA

100 fA

1 pA

10 pA

100 pA

1 nA

10 nA

100 nA

Accuracy (1 Year)

1

±(% rdg. + offset)

18°–28°C, 0–70% RH

0.3 % + 400 fA

0.2 % + 1 pA

0.15% + 10 pA

0.15% + 100 pA

0.1 % + 1 nA

0.1 % + 10 nA

0.1 % + 100 nA

0.1 % + 1 µA

Typical

RMS Noise

2

20 fA

20 fA

1 pA

1 pA

100 pA

100 pA

10 nA

10 nA

Typical Analog

Rise Time (10% to 90%)

3

Damping

4

Off On

4 ms

4 ms

300 µs

300 µs

110 µs

110 µs

110 µs

110 µs

80 ms

80 ms

1 ms

1 ms

110 µs

110 µs

110 µs

110 µs

TEMPERATuRE COEFFICIENT: 0°–18°C & 28°–50°C. For each °C, add 0.1 × (% rdg + offset) to accuracy spec.

INPuT VOLTAGE BuRDEN: <200µV on all ranges except <1mV on 20mA range.

MAXIMuM INPuT CAPACITANCE: Stable to 10nF on all nA ranges and 2µA range; 1µF on 20µA and 200µA ranges, and on mA ranges.

MAXIMuM CONTINuOuS INPuT VOLTAGE: 505 VDC.

NMRR 1

: (50 or 60Hz): 60dB.

ISOLATION (Ammeter Common or Voltage Source to chassis): Typically >1×10 11 Ω in parallel with <1nF.

MAXIMuM COMMON MODE VOLTAGE (between chassis and voltage source or ammeter): 505 VDC.

ANALOG OuTPuT: Scaled voltage output (inverting 2V full scale on all ranges): 2.5% ±2mV.

ANALOG OuTPuT IMPEDANCE 3

: <100Ω, DC–2kHz.

VOLTAGE SOuRCE:

Accuracy

5

Range Step Size ±(% prog. + offset)

±10.100

±50.500

±505.00

200 µV

1 mV

10 mV

0.1 % + 1 mV

0.1 % + 4 mV

0.15% + 40 mV

Noise

(p-p)

(Max.) (typical) 18°–28°C, 0–70% R.H. 0.1–10 Hz

Temperature

Coefficient

<50 µV (0.005% + 20 µV)/°C

<150 µV (0.005% + 200 µV)/°C

<1.5 mV (0.008% + 2 mV)/°C

Typical Typical

Rise Time

6, 8

Fall Time

7, 8

(10%–90%) (90%–10%)

250 µs

250 µs

4.5 ms

150 µs

300 µs

1 ms

SELECTABLE CuRRENT LIMIT: 2.5mA, 250µA, 25µA for 50V and 500V ranges, 25mA additional limit for 10V range. All current limits are –20%/+35% of nominal.

WIDEBAND NOISE

9

: <30mVp-p 0.1Hz–20MHz.

TyPICAL TIME STABILITy: ±(0.003% + 1mV) over 24 hours at constant temperature (within 1°C, between 18°–28°C, after 5 minute

settling).

OuTPuT RESISTANCE: <2.5Ω.

VOLTAGE SWEEPS: Supports linear voltage sweeps on fixed source range, one current or resistance measurement per step.

Maximum sweep rate: 200 steps per second. Maximum step count 3000. Optional delay between step and measure.

RESISTANCE MEASuREMENT (V/I): Used with voltage source; resistance calculated from voltage setting and measured current.

Accuracy is based on voltage source accuracy plus ammeter accuracy. Typical accuracy better than 0.6% for readings between 1kΩ and 1TΩ.

ALTERNATING VOLTAGE RESISTANCE MEASuREMENT: Offers alternating voltage resistance measurements for resistances from

10

9 Ω to 10 15 Ω. Alternates between 0V and user-selectable voltage up to ±505V.

NOTES

1. At 1 PLC – limited to 60 rdgs/s under this condition.

2. At 6 PLC, 1 standard deviation, 100 readings, filter off, capped input – limited to 10 rdgs/sec under this condition.

3. Measured at analog output with resistive load >2kΩ.

4. Maximum rise time can be up to 25% greater.

5. Accuracy does not include output resistance/load regulation.

6. Rise Time is from 0V to ± full-scale voltage (increasing magnitude).

7. Fall Time is from ± full-scale voltage to 0V (decreasing magnitude).

8. For capacitive loads, add C·∆V/ILimit to rise time, and C·∆V/1mA to fall time.

9. Measured with LO connected to chassis ground.

REMOTE OPERATION

IEEE-488 BuS IMPLEMENTATION: SCPI (IEEE-488.2,

SCPI-1996.0); DDC (IEEE-488.1).

LANGuAGE EMuLATION: Keithley Model 486/487

emulation via DDC mode.

RS-232 IMPLEMENTATION:

Supports: SCPI 1996.0.

Baud Rates: 300, 600, 1200, 2400, 4800, 9600, 19.2k,

38.4k, 57.6k.

Protocols: Xon/Xoff, 7 or 8 bit ASCII, parity-odd/even/ none.

Connector: DB-9 TXD/RXD/GND.

GENERAL

AMMETER INPuT CONNECTOR: Three lug triaxial on rear panel.

ANALOG OuTPuT CONNECTOR: Two banana jacks on rear panel.

VOLTAGE SOuRCE OuTPuT CONNECTOR: Two banana jacks on rear panel.

INTERLOCK CONNECTOR: 4 pin DIN.

TRIGGER LINE: Available, see manual for usage.

DISPLAy: 12 character vacuum fluorescent.

DIGITAL FILTER: Median and averaging (selectable from

2 to 100 readings).

RANGING: Automatic or manual.

AuTORANGING TIME

3

: <250ms (analog filter off, 1PLC).

OVERRANGE INDICATION: Display reads “OVRFLOW.”

CONVERSION TIME: Selectable 0.01PLC to 60PLC (50PLC under 50Hz operation). (Adjustable from 200µs to 1s)

READING RATE:

To internal buffer 1000 readings/second

1

To IEEE-488 bus 900 readings/second

1, 2

BuFFER: Stores up to 3000 readings.

PROGRAMS: Provide front panel access to IEEE address, choice of engineering units or scientific notation, and digital calibration.

EMC: Conforms with European Union Directive 89/336/

EEC, EN61326-1.

SAFETy: Conforms with European Union Directive 73/23/

EEC, EN61010-1, CAT I.

ENVIRONMENT:

Operating: 0°–50°C; relative humidity 70% noncondensing, up to 35°C. Above 35°C, derate humidity by 3% for each °C.

Storage: –10°C to +65°C.

WARM-uP: 1 hour to rated accuracy (see manual for recommended procedure).

POWER: 100–120V or 220–240V, 50–60Hz, (50VA).

PHySICAL:

Case Dimensions: 90mm high × 214mm wide ×

369mm deep (3

1

2

in. × 8 ⁄

3

8

in. × 14 ⁄

9

16

in.).

Working Dimensions: From front of case to rear including power cord and IEEE-488 connector:

394mm (15.5 inches).

NET WEIGHT: <4.7 kg (<10.3 lbs).

NOTES

1. 0.01PLC, digital filters off, front panel off, auto zero off.

2. Binary transfer mode. IEEE-488.1.

3. Measured from trigger in to meter complete.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

251

2502

Dual-Channel Picoammeter

252

• Dual-channel instrument for optical power measurements

• ±100V photodetector bias capability

• Measure photodetector current from

1fA to 20mA

• 1fA dark current measurement resolution

• Measure optical power directly when used with Model 2500INT Integrating

Sphere

• 0–10V analog output for high resolution optical power feedback

• Provides a high accuracy, high speed fiber alignment solution

• Supports assembly process, final testing, parts binning, and specification

• Allows faster alignment of the fiber with the laser diode’s optimum light emitting region

• Combines fiber alignment and device characterization processes

• User-programmable photodetector calibration coefficients

• 3000-point buffer memory on each channel allows data transfer after test completion

• Digital I/O and Trigger Link for binning and sweep test operations

• IEEE-488 and RS-232 interfaces

The Model 2502 Photodiode Meter is designed to increase the throughput of Keithley’s LIV (lightcurrent-voltage) test system for production testing of laser diode modules (LDMs). Developed in close cooperation with leading manufacturers of LDMs for fiberoptic telecommunication networks, this dual-channel instrument has features that make it easy to synchronize with other system elements for tight control over optical power measurements. The Model 2502 features a high speed analog output that allows using the LIV test system at the fiber alignment stage of the LDM manufacturing process. Through the use of buffer memory and a Trigger Link interface that’s unique to Keithley instruments, the Model 2502 can offer the fastest throughput available today for LIV testing of laser diode modules. These instruments are ruggedly engineered to meet the reliability and repeatability demands of continuous operation in round-the-clock production environments.

Low-Level, High Speed Measurements

The Model 2502 combines Keithley’s expertise in low-level current measurements with high speed current measurement capabilities. Each channel of this instrument consists of a voltage source paired with a high speed picoammeter. Each of the two channels has an independent picoammeter and voltage source with measurements made simultaneously across both channels.

Part of a High Speed LIV Test System

In a laser diode module DC/CW test stand, the Model 2502 provides the voltage bias to both the back facet monitor diode and a Model 2500INT Integrating Sphere or to a fiber-coupled photodetector. At the same time it applies the voltage biases, it measures the current outputs of the two photodetectors and converts these outputs to measurements of optical power. The conversion is performed with the user-programmed calibration coefficient for the wavelength of the laser diode module. Fast, accurate measurements of optical power are critical for analyzing the coupling efficiency and optical power characteristics of the laser diode being tested. When testing modules with multiple detectors, the

Model 2502 packs more testing capabilities into less test rack space.

Fiber Alignment

The Model 2502’s built-in high speed analog output makes it suitable for precision fiber alignment tasks. This instrument combines the ability to align the optical fiber quickly and accurately with a laser diode’s optimum light emitting region and the capability to make precision LIV measurements, all in the same test fixture. The Model 2502’s wide dynamic range allows early beam skirt detection, reducing the time required for fiber alignment. An LIV sweep can be performed during the alignment process to optimize fiber location for an entire operating range. High speed feedback minimizes delays in the alignment process, so it’s unnecessary to sacrifice alignment speed to ensure accurate device characterization.

Wide Dynamic Measurement Range

The Model 2502 offers current measurement ranges from 2nA to 20mA in decade steps. This provides for all photodetector current measurement ranges for testing laser diodes and LEDs in applications such as LIV testing, LED total radiance measurements, measurements of cross-talk and insertion loss on optical switches, and many

others. The Model 2502 meets industry testing requirements for the transmitter as well as pump laser modules.

Model 2502 rear panel

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

2502

Dual-Channel Picoammeter

Ordering Information

2502 Dual-Channel

Picoammeter

Accessories Supplied

User’s Manual

ACCESSORIES AVAILABLE

7007-1

7007-2

KPCI-488LPA

KUSB-488A

Shielded IEEE-488 Cable, 1m (3.3 ft)

Shielded IEEE-488 Cable, 2m (6.6 ft)

IEEE-488 Interface/Controller for the PCI Bus

IEEE-488 USB-to-GPIB Interface Adapter

SERVICES AVAILABLE

2502-3Y-EW 1-year factory warranty extended to 3 years from date of shipment

C/2502-3Y-DATA 3 (Z540-1 compliant) calibrations within 3 years of purchase*

*Not available in all countries

2400/

2420

Thermistor

2510

Peltier

High Accuracy Dark Current

Measurements

APPLICATIONS

The Model 2502’s 2nA current measurement range is ideal for measuring dark currents with 1fA resolution. Once the level of dark current has been determined, the instrument’s REL function automatically subtracts the dark current as an offset so the measured values are more accurate for optical power measurements.

Production testing of:

• Laser diode modules

• Chip on submount laser diodes

• LEDs

• Passive optical components

• Laser diode bars

Voltage Bias Capability

• Fiber alignment

The Model 2502 provides a choice of voltage bias ranges: ±10V or ±100V. This choice gives the system integrator the ability to match the bias range more closely to the type of photodetector being tested, typically ±10V for large area photodetectors and ±100V for avalanche-type photodetectors. This ability to match the bias to the photodetector ensures improved measurement linearity and accuracy.

High Testing Throughput

The Model 2502 is capable of taking 900 readings/second per channel at 4½-digit resolution. This speed is comparable with the measurement speed of the Model 2400 SourceMeter instrument, which is often used in conjunction with the Model 2502 to perform opto electronic device test and characterization. Both instruments support Trigger Link (a proprietary “hardware handshaking”

Trigger Link

triggering system that’s unique to Keithley products) and buffer memory.

When programmed to execute a sweep, Trigger Link ensures measurement integrity by keeping the source and measurement functions working in lock step while the buffer memories record the measurements. Together, source memory, buffer memory, and Trigger Link eliminate GPIB traffic during a test sweep, improving test throughput dramatically.

2502

Ratio and Delta Measurements

The Model 2502 can provide ratio or delta measurements between the two completely isolated channels, such as the ratio of the back facet monitor detector to the fiber-coupled photodetector at varying levels of input current.

These functions can be accessed via the front panel or the GPIB interface. For test setups with multiple detectors, this capability allows for targeted control capabilities for the laser diode module.

Computer

GPIB

Fiber

2500INT Integrating Sphere

The Model 2502 is designed for tight integration with other

Keithley instruments that are often used in LIV test systems for laser diode modules. These other instruments include the Model

2400 SourceMeter

®

and Model 2510 TEC SourceMeter instruments.

Programmable Limits and Filters

As with most Keithley instruments, the Model 2502’s current and voltage limits can be programmed to ensure device protection during critical points such as start of test, etc. These instruments also provide Average and Median filters, which can be applied to the data stored in the buffer memory.

Adaptable to Evolving DUT Requirements

Unlike optical power meters with integrated detectors, the Model 2502 allows the user to choose from a wide range of measurement capabilities simply by selecting an appropriate photodetector and programming the calibration

coefficient of this detector at the wavelength of choice.

Interface Options

To speed and simplify system integration and control, the Model 2502 includes the Trigger Link feature and digital I/O lines, as well as standard IEEE-488 and RS-232 interfaces. The Trigger Link feature combines six independent software selectable trigger lines on a single connector for simple, direct control over all instruments in a system. This feature is especially useful for reducing total test time if the test involves a sweep. The Model 2502 can sweep through a series of measurements based on triggers received from the SourceMeter Instrument. The digital I/O lines simplify external handler control and binning operations.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

253

2502

Dual-Channel Picoammeter

The Model 2502 Dual Photodiode Meter can measure and display either photo diode current or optical power for two photodiodes with appropriate user- supplied optical power gain/wavelength calibration factors.

The Model 2502 includes an analog output jack on the rear panel for each channel.

Measurement Specifications

Range

2.000000 nA

20.00000 nA

200.0000 nA

2.000000 µA

20.00000 µA

200.0000 µA

2.000000 mA

20.00000 mA

MAXIMuM INPuT: ±20.0mA.

Maximum

Accuracy

1, 2

23°C ±5°C

Temperature

Coefficient Dc Input

0°–18°C & 28°–50°C Impedance

3

Resolution ±(% rdg. + offset) ±(%rdg. + offset)/°C (Maximum)

1 fA

10 fA

100 fA

1 pA

10 pA

100 pA

1 nA

10 nA

1.00% + 2 pA

0.40% + 2 pA

0.30% + 200 pA

0.20% + 200 pA

0.10% + 20 nA

0.10% + 20 nA

0.10% + 2 µA

0.10% + 2 µA

0.01 + 200 fA

0.01 + 200 fA

0.02 + 20 pA

0.02 + 20 pA

0.01 +

0.01 +

2 nA

2 nA

0.02 + 200 nA

0.02 + 200 nA

20 kΩ

20 kΩ

200 Ω

200 Ω

2.0 Ω

2.0 Ω

0.2 Ω

0.2 Ω

TYPICAL SPEED AND NOISE REJECTION

4

Digits

Readings/s

GPIB (SCPI) GPIB (488.1)

4

1

2

5 1 ⁄

2

6

1

2

700

460

58

900

475

58

NPLC

0.01

0.1

1

NMRR

60 dB

PHOTODIODE VOLTAGE BIAS SPECIFICATIONS

2

Range Resolution

Accuracy

23°C ±5°C

Maximum Load Temperature

Current Regulation

5

Coefficient

0 to ±10 V

0 to ±100 V

<400 µV

<4 mV

±(0.15% of setting

+ 5 mV)

±(0.3% of setting

+ 50 mV)

20 mA

20 mA

< 0.30%,

0 to 20 mA

< 0.30%,

0 to 20 mA

150 ppm/°C

300 ppm/°C

NOTES

1. Speed = Normal (1.0 NPLC), Filter On.

2. 1 year.

3. Measured as ∆Vin/∆Iin at full scale (and zero) input currents.

4. Dual channel, internal trigger, measure only, display off, Autorange off, Auto Zero off, source delay = 0, filters off, limits off,

CALC5 and CALC6 off, 60Hz.

5. Measured as ∆Vin/∆Iin at full scale (20mA) and zero load currents.

6. Noise floor measured as rms (1 standard deviation), 100 samples, Filter off, open (capped) input.

7. Specification by design.

8. Measured (at input triax) as ∆Vin at full scale (20mA) vs. zero input currents.

GENERAL

Typical Noise Floor Measurement Specification

6

Range

2.000000 nA

20.00000 nA

200.0000 nA

2.000000 µA

20.00000 µA

200.0000 µA

2.000000 mA

20.00000 mA

Typical Noise Floor

RMS (1 STDEV), 100 Samples

0.01 NPLC 0.1 NPLC 1.0 NPLC 10 NPLC

2 pA

2 pA

200 pA

200 pA

1 pA

1 pA

100 pA

100 pA

40 fA

40 fA

2 pA

2 pA

15 fA

15 fA

500 fA

500 fA

20 nA

20 nA

2 µA

2 µA

10 nA

10 nA

1 µA

1 µA

200 pA

200 pA

25 nA

25 nA

50 pA

50 pA

5 nA

5 nA

SOuRCE CAPACITANCE: Stable to 10.0nF typical.

INPuT BIAS CuRRENT

7

: 50fA max. @ 23°C.

INPuT VOLTAGE BuRDEN 8

: 4.0mV max.

VOLTAGE SOuRCE SLEW RATE: 3.0ms/V typical.

COMMON MODE VOLTAGE: 200VDC.

COMMON MODE ISOLATION: Typically 10

9 Ω in parallel with 150nF.

OVERRANGE: 105% of measurement range.

MEMORy BuFFER: 6000 readings (two 3000 point buffers). Includes selected measured value(s) and time stamp.

PROGRAMMABILITy: IEEE-488 (SCPI-1995.0), RS-232, five user- definable power-up states plus factory default and *RST.

DIGITAL INTERFACE:

Enable: Active low input.

Handler Interface: Start of test, end of test, 3 category bits. +5V @ 300mA supply.

Digital I/O: 1 trigger input, 4 TTL/Relay Drive outputs (33V @ 500mA, diode clamped).

POWER SuPPLy: 100V/120V/220V/240V ±10%.

LINE FREquENCy: 50, 60Hz.

POWER DISSIPATION: 60VA.

EMC: Complies with European Union Directive 89/336/EEC.

VIBRATION: MIL-T-28800F Random Class 3.

SAFETy: Complies with European Directive 73/23/EEC.

WARM-uP: 1 hour to rated accuracy.

DIMENSIONS: 89mm high × 213mm wide × 370mm deep (3

1

2

in × 8

3

8

in ×

14

9

16

in). Bench configuration (with handle and feet): 104mm high ×

238mm wide × 370mm deep (4

1

8

in × 9

3

8

in × 14

9

16

in).

WEIGHT: 23.1kg (10.5 lbs).

ENVIRONMENT:

Operating: 0°–50°C, 70% R.H. up to 35°C non-condensing. Derate 3%

R.H./°C, 35°–50°C.

Storage: –25° to 65°C, non-condensing.

254

ANALOG OUTPUT SPECIFICATIONS

OuTPuT VOLTAGE RANGE

1

: Output is inverting: –10V out for positive full scale input.

+10V out for negative full scale input.

OuPuT IMPEDANCE: 1kΩ typical.

Range

2.000000 nA

20.00000 nA

200.0000 nA

2.000000 µA

20.00000 µA

200.0000 µA

2.000000 mA

20.00000 mA

Accuracy

6.0% + 90 mV

3.0% + 9 mV

6.0% + 90 mV

3.0% + 9 mV

6.0% + 90 mV

2.5% + 9 mV

6.0% + 90 mV

2.5% + 9 mV

Temperature

Coefficient

23°C ±5°C 0°–18°C & 28°–50°C Typical

±(%output + offset) ±(%output + offset)/°c (10% to 90%)

0.30% + 7 mV

0.11% + 700 µV

0.30% + 4 mV

0.11% + 400 µV

0.30% + 4 mV

0.11% + 400 µV

0.30% + 4 mV

0.11% + 400 µV

Rise Time

6.1 ms

6.1 ms

395 µs

395 µs

135 µs

135 µs

21 µs

21 µs

1. The analog output voltage for each channel is referenced to that channel’s floating ground.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

428-PROG

Programmable Current Amplifier

• 2µs rise time

• 1.2fA rms noise

• Up to 10

11

V/A gain

• IEEE-488 interface

Ordering Information

428-PROG

Programmable

Current Amplifier with

IEEE-488 Interface

ACCESSORIES AVAILABLE

CABLES

4801

7007-1

7007-2

Low Noise BNC Input Cable, 1.2m (4 ft)

Shielded IEEE-488 Cable, 1m (3.3 ft)

Shielded IEEE-488 Cable, 2m (6.6 ft)

ADAPTERS

7078-TRX-BNC 3-Slot Male Triax to Female BNC Adapter

KPCI-488LPA IEEE-488 Interface/Controller for the PCI Bus

KUSB-488A IEEE-488 USB-to-GPIB Interface Adapter

(requires 7010 Adapter)

RACK MOUNTS

4288-1 Single Fixed Rack Mount Kit

4288-2 Dual Fixed Rack Mount Kit

SERVICES AVAILABLE

428-PROG-3Y-EW 1-year factory warranty extended to 3 years from date of shipment

APPLICATIONS

The Model 428-PROG satisfies a broad range of applications in research and device labs due to its cost-effective ability to amplify fast, low currents. A few of these applications include:

Biochemistry Measurements:

• Ion channel currents through cell walls and membranes

Beam Position Monitoring:

• Used on electron storage rings and

synchrotrons

Surface Science Studies:

• Scanning Tunneling Electron

Microscope system amplifier

• Observation of secondary electron emission, as in X-ray and beam line currents

Laser and Light Measurements:

• Fast, sensitive amplifier for use with PMTs and photodiodes

• Analysis of fast photoconductive materials

• IR detector amplifier

Transient Phenomena:

• Current DLTS studies

• Breakdown in devices and dielectric materials

The Model 428-PROG Programmable Current

Amplifier converts fast, small currents to a voltage, which can be easily digitized or displayed by an oscilloscope, waveform analyzer, or data acquisition system. It uses a sophisticated “feedback current” circuit to achieve both fast rise times and sub-picoamp noise. The gain of the

Model 428-PROG is adjustable in decade increments from 10 3 V/A to 10 11 times from 2µs to 300ms.

V/A, with selectable rise

The Model 428-PROG offers fast response at low current levels, which is unmatched by either electrometers or picoammeters. The nine current amplification ranges allow the greatest flexibility in making speed/noise tradeoffs.

The Model 428-PROG can be used with any of

Keithley’s data acquisition boards to implement a very cost-effective, low curreent measurement system with wide bandwidth and fast response.

The Model 428-PROG incorporates a secondorder Bessel-function filter that mini mizes noise without increasing rise time on high-gain ranges.

This can be de feated in situations where 6dB/ oc tave roll-off is de sired, as in control loops of scan ning tunneling electron microscopes.

Input and output connections to the Model

428-PROG are made with BNC connectors.

INPUT HI is connected to a program mable ±5V supply, which permits suitable bias voltages to be applied to devices-under-test or current collectors. This eliminates the need for a separate bias supply.

For applications where voltage offset errors exist, the ZERO CHECK and OFFSET functions can be used, thereby maintaining maximum instrument accuracy. Current suppression is also available up to 5mA, useful for suppressing background currents, such as dark currents.

The Model 428-PROG also incorporates an exterior design with simple front panel operation, improved display, and convenient system integration. Pushbutton controls have an LED to indicate if that function is activated. The display features three selectable intensities (bright, dim, and off) for use in light-sensitive environments.

All setup values can be displayed from the front panel. An IEEE-488 interface is included.

The Model 428-PROG as

Preamplifier to an Oscilloscope

The Model 428-PROG can be connected to an oscilloscope or waveform digitizer to display very low currents in real time.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

255

428-PROG

Programmable Current Amplifier

Accuracy

1

Gain Setting

V/A

18°–28°C

±(% input + offset)

Temperature

Coefficient

Low Noise

±(% input + offset)/°C

Rise Time

(10%–90%)

ms

3

2

Maximum Speed

Noise rms

Rise Time

4

3

(10%–90%)

µs

Noise

rms

4

10

3

10

4

10

5

10

6

10

7

10

8

10

9

10

10

10

11 5

0.45 + 1.2 µA

0.31 + 120 nA

0.31 + 12 nA

0.34 + 1.2 nA

0.5 + 122 pA

1.4 + 14 pA

2.5 + 3 pA

2.5 + 1.6 pA

2.7 + 1.6 pA

0.01 + 40 nA

0.01 + 4 nA

0.01 + 400 pA

0.01 + 40 pA

0.015 + 4.3 pA

0.015 + 700 fA

0.025 + 300 fA

0.025 + 250 fA

0.028 + 250 fA

0.1

1

10

100

300

0.1

0.1

0.1

0.1

90 nA

9 nA

900 pA

90 pA

9 pA

0.5 pA

50 fA

4 fA

1.2 fA

15

40

100

250

250

2

2

5

10

100 nA

15 nA

2 nA

500 pA

200 pA

30 pA

10 pA

2 pA

2 pA

NOTES

1. When properly zeroed using zero correct.

2. Selectable filtering will improve noise specifications; see operator’s manual for details (typical value shown).

3. Bandwidth = 0.35/rise time.

4. With up to 100pF shunt capacitance; autofilter on; low pass filter off.

5. 10 11 setting is 10 10 setting with GAIN ×10 enabled; other entries are for GAIN ×10 disabled.

SPECIFICATIONS

INPuT:

Voltage Burden: <200µV (18°–28°C) for inputs <100µA; <10mV for inputs ≥

100µA; 20µV/°C temperature coefficient.

Maximum Overload: 100V on 10 4 to 10 11 V/A ranges; 10V on 10 voltage sources must be current limited at 10mA.

3 V/A range. Higher

OuTPuT:

Range: ±10V, 1mA; bias voltage off.

Impedance: <100Ω DC–175kHz.

LOW PASS FILTER:

Ranges: 10µs to 300ms (±25%) in 1, 3, 10 sequence or OFF.

Attenuation: 12dB/octave.

GAIN ×10: Rise time, noise, and input resistance are unchanged when selecting

GAIN ×10; gain accuracy and temperature coefficient are degraded by 0.2% and

0.003%/°C respectively.

CURRENT SUPPRESSION

Range Resolution

±5 nA

±50 nA

±500 nA

±5 µA

±50 µA

±500 µA

±5 mA

1 pA

10 pA

100 pA

1 nA

10 nA

100 nA

1 µA

Accuracy

±(%setting + offset)

3.0 + 10 pA

1.6 + 100 pA

0.8 + 1 nA

0.7 + 10 nA

0.6 + 100 nA

0.6 + 1 µA

0.6 + 10 µA

BIAS VOLTAGE:

Range: ±5V.

Resolution: 2.5mV.

Accuracy: ±(1.1%rdg + 25mV).

DC Input

Resistance

< 0.6 Ω

< 0.7 Ω

< 1.6 Ω

< 10 Ω

< 100 Ω

< 1 kΩ

< 10 kΩ

< 100 kΩ

< 100 kΩ

GENERAL

DISPLAy: Ten character alphanumeric LED display with normal/dim/off intensity control.

REAR PANEL CONNECTORS:

Input BNC: Common connected to chassis through 1kΩ.

Output BNC: Common connected to chassis.

IEEE-488 Connector

5-Way Binding Post: Connected to chassis.

EMI/RFI: Complies with the RF interference limits of FCC Part 15 Class B and VDE 0871 Class B.

EMC: Conforms to European Union Directive 89/336/EEC.

SAFETy: Conforms to European Union Directive 73/23/EEC (meets EN61010-1/IEC 1010).

WARM-uP: 1 hour to rated accuracy.

ENVIRONMENT: Operating: 0°–50°C, <70% R.H. up to 35°C; linearly derate R.H. 3%/°C up to 50°C.

Storage: –25°C to 65°C.

POWER: 105–125VAC or 210–250VAC, switch selected. (90–110/180–220VAC available.) 50Hz or 60Hz. 45VA maximum.

DIMENSIONS: 90mm high × 213mm wide × 397mm deep (3

1

2

in × 8

3

8

in × 15

5

8

in).

IEEE-488 BUS IMPLEMENTATION

PROGRAMMABLE PARAMETERS: All parameters and controls programmable except for IEEE-488 bus address.

EXECuTION SPEED: (measured from DAV true to RFD true on bus).

zero Correct & Auto Suppression commands: <3s.

Save/Recall Configuration commands: <500ms.

All other commands: <40ms.

256

Model 428-PROG rear panel

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6514

Programmable Electrometer

• <1fA noise

>200T input impedance on

voltage measurements

• Charge measurements from 10fC to 20µC

• High speed—up to 1200 readings/second

• Interfaces readily with switches, computers, and component handlers

• Cancels voltage and current offsets easily

Ordering Information

6514 Programmable

Electrometer

Accessories Supplied

237-ALG-2 Low Noise

Triax Cable, 3-Slot Triax to

Alligator Clips, 2m (6.6 ft)

SERVICES AVAILABLE

6514-3Y-EW 1-year factory warranty extended to 3 years from date of shipment

C/6514-3Y-ISO 3 (ISO-17025 accredited) calibrations within 3 years of purchase*

TRN-LLM-1-C Course: Making Accurate Low-Level

Measurements

*Not available in all countries

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The Model 6514 Electrometer combines flexible interfacing capabilities with current sensitivity, charge measure ment capabilities, resolution, and speed that are equal or superior to our earlier electrometers. The Model 6514’s built-in IEEE-488,

RS-232, and digital I/O interfaces make it simple to

configure fully automated, high speed systems for low-level testing.

The 5 1 ⁄

2

-digit Model 6514 is designed for applications that demand fast, yet precise measurements of low currents, voltages from high resistance sources, charges, or high resistances.

The Model 6514’s exceptional measurement performance comes at an affordable price. While its cost is comparable with that of many high end DMMs, the

Model 6514 offers far greater current sensitivity and sig nificantly lower voltage burden (as low as 20µV) than other instruments can provide.

R&D on a Budget

The Model 6514 offers the flexibility and sensitivity needed for a wide array of experiments, providing better data far faster than older electrometer designs. Applications include measuring currents from light detectors and other sensors, beam experiments, and measuring resistances using a current source. In addition to use by researchers in areas such as physics, optics, and materials science, the

Model 6514’s affordable price makes it an attractive alternative to high end DMMs for low current measurement applications, such as testing resistance and leakage current in switches, relays, and other components. For more information on how the Model 6514 does this, refer to the section titled

“Low Voltage Burden.”

The Model 6514 builds on the features and capabilities of the Keithley electrometers that preceded it. For example, like those instruments, a built-in constant current source simplifies measuring

resistance.

Two analog outputs—a 2V output and a preamp output—are available for recording data with stripchart recorders.

ACCESSORIES AVAILABLE

CABLES

237-ALG-2

7007-1

7007-2

Low Noise Triax Cable, 3-Slot Triax to Alligator

Clips

Shielded IEEE-488 Cable, 1m (3.3 ft)

Shielded IEEE-488 Cable, 2m (6.6 ft)

7009-5

7078-TRX-10

RS-232 Cable

7078-TRX-3 Low Noise Triax Cable, 3-Slot Triax Connectors,

0.9m (3 ft)

Low Noise Triax Cable, 3-Slot Triax Connectors,

3m (10 ft)

7078-TRX-20

8501-1

8501-2

Low Noise Triax Cable, 3-Slot Triax Connectors,

6m (20 ft)

Trigger-Link Cable, 1m (3.3 ft)

Trigger-Link Cable, 2m (6.6 ft)

RACK MOUNT KITS

4288-1 Single Fixed Rack Mounting Kit

4288-2 Dual Fixed Rack Mounting Kit

ADAPTERS

7078-TRX-BNC 3-Lug Triax to BNC Adapter

237-TRX-NG Triax Male-Female Adapter with Guard

Disconnected

237-TRX-T 3-Slot Male Triax to Dual 3-Lug Female Triax Tee

Adapter

237-TRX-TBC 3-Lug Female Triax Bulkhead Connector

(1.1kV rated)

7078-TRX-TBC 3-Lug Female Triax Bulkhead Connector with Cap

GPIB INTERFACES

KPCI-488LPA IEEE-488 Interface/Controller for the PCI Bus

KUSB-488A IEEE-488 USB-to-GPIB Interface Adapter

A G R E A T E R M E A S U R E O F C O N F I D E N C E

257

6514

Programmable Electrometer

Economical Component Testing

Once, electrometers were simply considered too slow to keep up with the high throughput that production test applications demand. The Model 6514 is designed for fast, sensitive measurements, providing speeds up to 1200 readings per second with fast integration or 17 measurements per second with 60Hz line-cycle integration. It offers 10fA resolution on 2nA signals, settling to within 10% of the final value in just 15ms. A normal-mode rejection ratio (NMRR) of 60dB allows making accurate low current measurements, even in the presence of line frequency induced currents, which is a common concern in production floor environments. The instrument’s sensitivity makes it easy to determine the leakage resistance on capacitances up to 10nF or even on higher capacitances when a series resistor is used.

While the Model 6514 can be easily operated manually using the front panel controls, it can also be externally controlled for automated test applications. Built-in IEEE-488 and RS-232 interfaces make it possible

Leakage

Resistance

R

L

I

L

(error current due to

V

BURDEN

)

R

L

I

L

= 0

Photodiode

(no incident light)

I

D

Photodiode

(no incident light)

I

D

Electrometer

+

V

BURDEN

+

V

BURDEN

CAL V

OFFSET

A/D

Figure 1. Dark Current Measurement with Burden Voltage Uncorrected

6514 Electrometer

A/D

Total offset voltage = 0

Figure 2. Dark Current Measurement with Burden Voltage Corrected

to program all instrument functions over the bus through a computer controller. The instrument’s interfaces also simplify integrating external hardware, such as sources, switching systems, or other instruments, into the test system. A digital I/O interface can be used to link the Model 6514 to many popular component handlers for tight systems integration in binning, sorting, and similar applications.

These features make the Model 6514 a powerful, low cost tool for systems designed to test optical devices and leakage resistance on low-value capacitors, switches, and other devices, particularly when the test system already includes a voltage source or when the source current/measure voltage technique is used to determine resistance.

Low Voltage Burden

The Model 6514’s feedback ammeter design minimizes voltage offsets in the input circuitry, which can affect current measurement accuracy. The instrument also allows active cancellation of its input voltage and current offsets, either manually via the front panel controls or over the bus with

IEEE-488 commands.

Dark Current Measurements

When measuring dark currents (Figure 1) from a device such as a photodiode, the ammeter reads the sum of two different currents. The first current is the dark current (I

D

) generated by the detector with no light falling upon the device (in other words, the signal of interest); the second one is

L

) generated by the voltage burden (V the leakage current (I

BURDEN

) appearing at the terminals of the ammeter. In a feedback ammeter, the primary

“voltage burden” is the amplifier offset voltage. This leakage current represents an error current. Without the use of cancellation techniques, I

V

BURDEN

/R

L

. Figure 2 illustrates how the Model 6514’s CAL V ed to cancel V

BURDEN the measured current is only the true dark current (I

OFFSET

L

=

is adjust-

to within the voltage noise level of a few microvolts, so

D

) of the photodiode.

In a similar manner, offset currents can also be cancelled. Earlier electrometers used an internal numerical correction technique in which the voltage burden was still present, so the measured dark current included the error term I

L

= V

BURDEN

/R

L

.

Voltage Burden and Measurement Error

Electrometers provide current measurement with lower terminal voltage than is possible when making DMM meas urements. As shown in Figure

3, DMMs measure current using a shunt resistance that develops a voltage

(typically 200mV full-range) in the input circuit. This creates a terminal voltage (V

BURDEN

) of about 200mV, thereby lowering the measured current.

Electrometers reduce this terminal voltage by using the feedback ammeter configuration illustrated in Figure 1. The Model 6514 lowers this terminal voltage still further—to the level of the voltage noise—by canceling out the small offset voltage that remains, as shown in Figure 2. Any error signals that remain are negligible in comparison to those that can occur when measuring current with a DMM.

258

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6514

Programmable Electrometer

I

V

SOURCE

R

V

BURDEN

= 200mV at full range

Desired Current Reading: I =

DMM’s Actual Current Reading: I =

V

SOURCE

R

V

SOURCE

– V

R

BURDEN

DMM Offset Currents

DMM

Typically, offset currents in DMMs are tens or hundreds of picoamps, which severely limits their low current measuring capabilities compared to the Model 6514 with 3fA input bias current.

+

A/D

Figure 3. Errors Due to Burden Voltage when Measuring with a DMM

The example below compares a DMM’s voltage burden errors with the 6514’s.

If: V

SOURCE

= 1V, R = 50k

The desired current reading is: I = 1V

= 20

µA

Actual Reading

(20

µA range

on DMM):

Refer to Figure 3.

V

BURDEN

= 200mV

I = 1V – 200mV

50k

= 800mV

50k

= 16

µA = 20% Burden error with a DMM

6514 Actual Reading: V

BURDEN

= 10

µV

Refer to Figure 2.

I = 0.999990V

50k

= 19.9998

µA = 0.001% Burden error

with the 6514

VOLTS

Range

2 V

20 V

200 V

5

1

2

-Digit

Resolution

10 µV

100 µV

1 mV

Accuracy

(1 Year)

1

18°–28°C

±(%rdg+counts)

0.025 + 4

0.025 + 3

0.06 + 3

Temperature

Coefficient

0°–18°C & 28°–50°C

±(%rdg+counts)/°C

0.003 + 2

0.002 + 1

0.002 + 1

NOTES

1. When properly zeroed, 5 1 ⁄

2

-digit. Rate: Slow (100ms integration time).

NMRR: 60dB on 2V, 20V, >55dB on 200V, at 50Hz or 60Hz ±0.1%.

CMRR: >120dB at DC, 50Hz or 60Hz.

INPuT IMPEDANCE: >200TΩ in parallel with 20pF, <2pF guarded (10MΩ with zero check on).

SMALL SIGNAL BANDWIDTH AT PREAMP OuTPuT: Typically 100kHz (–3dB).

AMPS

Range

20 pA

200 pA

2 nA

20 nA

200 nA

2 µA

20 µA

200 µA

2 mA

20 mA

5

1

2

-Digit

Resolution

100 aA

2

1 fA

2

10 fA

100 fA

1 pA

10 pA

100 pA

1 nA

10 nA

100 nA

Accuracy

(1 Year)

1

18°–28°C

±(%rdg+counts)

1 + 30

1 + 5

0.2 + 30

0.2 + 5

0.2 + 5

0.1 + 10

0.1 + 5

0.1 + 5

0.1 + 10

0.1 + 5

Temperature

Coefficient

0°–18°C & 28°–50°C

±(%rdg+counts)/°C

0.1 + 5

0.1 + 1

0.1 + 2

0.03 + 1

0.03 + 1

0.005 + 2

0.005 + 1

0.005 + 1

0.008 + 2

0.008 + 1

NOTES

1. When properly zeroed, 5½-digit. Rate: Slow (100ms integration time).

2. aA =10

–18

A, fA=10

–15

A.

INPuT BIAS CuRRENT: <3fA at T

CAL

(user adjustable). Temperature coefficient = 0.5fA/°C.

INPuT BIAS CuRRENT NOISE: <750aA p-p (capped input), 0.1Hz to 10Hz bandwidth, damping on. Digital filter = 40 readings.

INPuT VOLTAGE BuRDEN at T

CAL

±1°C (user adjustable):

<20µV on 20pA, 2nA, 20nA, 2µA, 20µA ranges.

<100µV on 200pA, 200nA, 200µA ranges.

<2mV on 2mA range.

<4mV on 20mA range.

TEMPERATuRE COEFFICIENT OF INPuT VOLTAGE BuRDEN: <10µV/°C on pA, nA, µA ranges.

PREAMP SETTLING TIME (to 10% of final value): 2.5s typical on pA ranges, damping off, 3s typical on pA ranges damping on, 15ms on nA ranges, 5ms on µA and mA ranges.

NMRR: >95dB on pA, 60dB on nA, µA, and mA ranges at 50Hz or 60Hz ±0.1%. Digital Filter = 40.

OHMS

Range

2 kΩ

20 kΩ

200 kΩ

2 MΩ

20 MΩ

200 MΩ

2 GΩ

20 GΩ

200 GΩ

5

1

2

-Digit

Ac cu ra cy

(1 Year)

1

18°–28°C

Temperature

Coefficient Test

0°–18°C & 28°–50°C Current

Resolution ±(% rdg+counts) ±(% rdg+counts)/°C (nominal)

10 mΩ

100 mΩ

1 Ω

10 Ω

100 Ω

1 kΩ

10 kΩ

100 kΩ

1 MΩ

0.20 + 10

0.15 + 3

0.25 + 3

0.25 + 4

0.25 + 3

0.30 + 3

1.5 + 4

1.5 + 3

1.5 + 3

0.01 + 2

0.01 + 1

0.01 + 1

0.02 + 2

0.02 + 1

0.02 + 1

0.04 + 2

0.04 + 1

0.04 + 1

0.9 mA

0.9 mA

0.9 mA

0.9 µA

0.9 µA

0.9 µA

0.9 nA

0.9 nA

0.9 nA

NOTES

1. When properly zeroed, 5 1 ⁄

2

-digit. Rate: Slow (100ms integration time).

MAXIMuM OPEN CIRCuIT VOLTAGE: 250V DC.

PREAMP SETTLING TIME (To 10% of final reading with <100pF input capacitance): 2kΩ through 200kΩ: 2ms; 20MΩ through 200MΩ: 90ms. 2GΩ through 200GΩ: 1s.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

259

6514

Programmable Electrometer

COULOMBS

Range

20 nC

200 nC

2 µC

20 µC

6

1

2

-Digit

Resolution

10 fC

100 fC

1 pC

10 pC

Accuracy

(1 Year)

1, 2

18°–28°C

±(%rdg+counts)

0.4 + 50

0.4 + 50

1 + 50

1 + 50

Temperature

Coefficient

0°–18°C & 28°–50°C

±(%rdg+counts)/°C

0.04 + 10

0.04 + 10

0.05 + 10

0.05 + 10

Notes:

1. Charge acquisition time must be <1000s, derate 2% for each additional 10,000s.

2. When properly zeroed, 6½-digit. Rate: Slow (100ms integration time).

INPuT BIAS CuRRENT: <4fA at T

CAL

. Temperature coefficient = 0.5fA/°C.

IEEE-488 BUS IMPLEMENTATION

MuLTILINE COMMANDS: DCL, LLO, SDC, GET, GTL, UNT, UNL, SPE, SPD.

IMPLEMENTATION: SCPI (IEEE-488.2, SCPI-1996.0); DDC (IEEE-488.1).

uNILINE COMMANDS: IFC, REN, EOI, SRQ, ATN.

INTERFACE FuNCTIONS: SH1, AH1, T5, TE0, L4, LE0, SR1, RL1, PP0, DC1, DT1, C0, E1.

PROGRAMMABLE PARAMETERS: Function, Range, Zero Check, Zero Correct, EOI (DDC mode only), Trigger, Terminator (DDC mode only), Data Storage 2500 Storage, Calibration (SCPI mode only), Display Format, SRQ, REL, Output Format, Guard, V-offset Cal, I-offset Cal.

ADDRESS MODES: TALK ONLY and ADDRESSABLE.

LANGuAGE EMuLATION: 6512, 617, 617-HIQ emulation via DDC mode.

TRIGGER TO READING DONE: 150ms typical, with external trigger.

RS-232 IMPLEMENTATION:

Supports: SCPI 1996.0.

Baud Rates: 300, 600, 1200, 2400, 4800, 9600, 19.2k, 38.4k, 57.6k.

Protocols: Xon/Xoff, 7 or 8 bit ASCII, parity-odd/even/none.

Connector: DB-9 TXD/RXD/GND.

GENERAL

OVERRANGE INDICATION: Display reads “OVRFLOW.”

RANGING: Automatic or manual.

CONVERSION TIME: Selectable 0.01PLC to 10PLC.

PROGRAMS: Provide front panel access to IEEE address, choice of engineering units or

scientific notation, and digital calibration.

MAXIMuM INPuT: 250V peak, DC to 60Hz sine wave; 10s per minute maximum on mA ranges.

MAXIMuM COMMON MODE VOLTAGE (DC to 60Hz sine wave): Electrometer, 500V peak.

ISOLATION (Meter COMMON to chassis): Typically 10

10 Ω in parallel with 500pF.

INPuT CONNECTOR: Three lug triaxial on rear panel.

2V ANALOG OuTPuT: 2V for full range input. Inverting in Amps and Coulombs mode.

Output impedance 10kΩ.

PREAMP OuTPuT: Provides a guard output for Volts mea sure ments. Can be used as an inverting output or with external feedback in Amps and Coulombs modes.

DIGITAL INTERFACE:

Handler Interface: Start of test, end of test, 3 category bits.

Digital I/O: 1 Trigger input, 4 outputs with 500mA sink capability.

Connector: 9 pin D subminiature, male pins.

EMC: Conforms with European Union Directive 89/336/EEC EN55011, EN50082-1,

EN61000-3-2, EN61000-3-3, FCC part 15 class B.

SAFETy: Conforms with European Union Directive 73/23/EEC EN61010-1.

GuARD: Switchable voltage and ohm guard available.

TRIGGER LINE: Available, see manual for usage.

READING STORAGE: 2500 readings.

READING RATE:

To internal buffer 1200 readings/second 1

To IEEE-488 bus

To front panel

500 readings/second

1, 3

17 readings/second at 60Hz;

15 readings/second at 50Hz.

2

2

Notes:

1

0.01PLC, digital filters off, front panel off, auto zero off.

2

1.00PLC, digital filters off.

3

Binary transfer mode.

DIGITAL FILTER: Median and averaging (selectable from 2 to 100 readings).

DAMPING: User selectable on Amps function.

ENVIRONMENT:

Operating: 0°–50°C; relative humidity 70% non-condensing, up to 35°C.

Storage: –25° to +65°C.

WARM-uP: 1 hour to rated accuracy (see manual for recommended procedure).

POWER: 90–125V or 210–250V, 50–60Hz, 60VA.

PHySICAL:

Case Dimensions: 90mm high × 214mm wide × 369mm deep (3

1

2

in. × 8

3

8

in. × 14

9

16

in.).

Working Dimensions: From front of case to rear including power cord and IEEE-488 connector: 15.5 inches.

Net Weight: <4.6kg (<10.1 lbs).

Shipping Weight: <9.5kg (<21 lbs).

Model 6514 rear panel

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

6517B

Electrometer/High Resistance Meter

• Measures resistances up to

10

16

• 1fA–20mA current measurement range

• <20µV burden voltage on lowest current ranges

200T input impedance

• <3fA bias current

• Up to 425 rdgs/s

• 0.75fA p-p noise

• Built-in ±1kV voltage source

• Unique voltage reversal method for high resistance measurements

• Optional plug-in scanner cards

Ordering Information

6517B Electrometer/High

Resistance Meter

Accessories Supplied

237-ALG-2 Low Noise

Triax Cable, 3-slot Triax to

Alligator Clips, 2m (6.6 ft)

8607 Safety High Voltage

Dual Test Leads

6517-TP Thermocouple Bead Probe

CS-1305 Interlock Connector

Exceptional Performance Specifications

The half-rack-sized Model 6517B has a special low current input amplifier with an input bias current of <3fA with just 0.75fA p-p (peak-to-peak) noise and <20µV burden voltage on the lowest range. The input impedance for voltage and resistance measurements is 200TΩ for nearideal circuit loading. These speci fi ca tions ensure the accuracy and sensitivity needed for accurate low current and high imped ance volt age, resistance, and charge measure ments in areas of re search such as physics, optics, nanotechnology, and materials science. A built-in ±1kV voltage source with sweep capability simplifies performing leak age, break down, and resis tance testing, as well as volume (Ω-cm) and surface resistivity (Ω/square) mea sure ments on insulating materials.

Wide Measurement Ranges

The Model 6517B offers full autoranging over the full span of ranges on current, resistance, voltage, and charge mea sure ments:

• Current measurements from 1fA to 20mA

• Voltage measurements from 10µV to 200V

• Resistance measurements from 50Ω to 10 16

• Charge measurements from 10fC to 2µC

Keithley’s 5

1

2

-digit Model 6517B Electrometer/High

Resistance Meter offers accuracy and sensitivity specifications unmatched by any other meter of this type. It also offers a variety of features that simplify measur ing high resistances and the resistivity of insulating materials. With reading rates of up to 425 read ings/second, the

Model 6517B is also significantly faster than competitive electrometers, so it offers a quick, easy way to measure low-level currents.

ACCESSORIES AVAILABLE

CABLES

6517B-ILC-3

7007-1

7007-2

7009-5

7078-TRX-3

7078-TRX-10

7078-TRX-20

8501-1

8501-2

8503

8607

PROBES

6517-RH

6517-TP

TEST FIXTURE

8009

OTHER

CS-1305

Interlock Cable

Shielded IEEE-488 Cable, 1m (3.2 ft)

Shielded IEEE-488 Cable, 2m (6.5 ft)

RS-232 Cable

Low Noise Triax Cable, 3-Slot Triax Connectors,

0.9m (3 ft)

Low Noise Triax Cable, 3-Slot Triax Connectors,

3m (10 ft)

Low Noise Triax Cable, 3-Slot Triax Connectors,

6m (20 ft)

Trigger Link Cable, 1m (3.3 ft)

Trigger Link Cable, 2m (6.6 ft)

Trigger Link Cable to 2 male BNCs, 1m (3.3 ft)

1kV Source Banana Cables

Humidity Probe with Extension Cable

Temperature Bead Probe (included with 6517B)

Resistivity Test Fixture

Interlock Connector

ADAPTERS

237-BNC-TRX Male BNC to 3-Lug Female Triax Adapter

237-TRX-NG

237-TRX-T

Triax Male-Female Adapter with Guard

Disconnected

3-Slot Male Triax to Dual 3-Lug Female Triax

Tee Adapter

237-TRX-TBC 3-Lug Female Triax Bulkhead Connector

(1.1kV rated)

7078-TRX-BNC 3-Slot Male Triax to BNC Adapter

7078-TRX-GND 3-Slot Male Triax to BNC Adapter with guard removed

7078-TRX-TBC 3-Lug Female Triax Bulkhead Connector with

Cap

SOFTWARE

6524 High Resistance Measurement Software

RACK MOUNT KITS

4288-1 Single Fixed Rack Mounting Kit

4288-2 Dual Fixed Rack Mounting Kit

SCANNER CARDS

6521

6522

Low Current Scanner Card

Voltage/Low Current Scanner Card

GPIB INTERFACES

KPCI-488LPA IEEE-488 Interface/Controller for the PCI Bus

KUSB-488A IEEE-488 USB-to-GPIB Interface Adapter

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261

6517B

Electrometer/High Resistance Meter

Simple DMM-like Operation

The Model 6517B is designed for easy, DMM-like operation via the front panel, with single-button control of im por tant functions such as resistance measurement. It can also be controlled via a built-in IEEE-488 inter face, which makes it possible to program all func tions over the bus through a computer controller.

High Accuracy High Resistance Measurements

The Model 6517B offers a number of features and capabili ties that help ensure the accuracy of high resistance mea sure ment applications. For example, the built-in volt age source simplifies determining the relation ship between an insulator’s resistivity and the level of source voltage used. It is well suit ed for capacitor leakage and insulation resistance mea sure ments, tests of the surface insula tion resis tance of printed circuit boards, voltage coefficient test ing of resistors, and diode leakage characteriza tion.

A test sequence in the Model 6517B incorporates a volt age reversal method for measuring very high resis t anc es, especially in materials and devices where the inherent background currents in the sample previous ly made accurate measurements impos sible. The op tion al Model 6524 software package simplifies operat ing the Model 6517B via a compu ter controller and makes it easy to optimize the test parameters (delay time, volt age, etc.) for the specific material or device under test. The Model 6517B meter, the software, and a resistivity fixture are avail able as a combination for specific material or device testing applications. Re fer to the Model 65 for more informa tion.

Temperature and Humidity Stamping

Humidity and temperature can influence the resist ivity values of materials significantly. To help you make ac curate comparisons of readings acquired un der varying conditions, the Model 6517B offers a built-in type K thermocouple and an optional Model 6517-RH Relative Humidity Probe. A built-in

SERVICES AVAILABLE

6517B-3Y-EW 1-year factory warranty extended to 3 years from date of shipment

C/6517B-3Y-ISO 3 (ISO-17025 accredited) calibrations within 3 years of purchase*

TRN-LLM-1-C Course: Making Accurate Low-Level Measurements

*Not available in all countries data storage bu f fer allows recording and recalling read ings stamped with the time, tempera ture, and relative humidity at which they were acquired.

Accessories Extend Measurement Capabilities

A variety of optional accessories can be used to extend the Model 6517B’s applications and enhance its performance.

Scanner Cards. Two scan ner cards are available to simplify scan ning multiple signals. Either card can be easily inserted in the option slot of the instru ment’s back panel. The Model 6521 Scan ner Card offers ten channels of low-level cur rent scanning. The Model 6522 Scanner Card provides ten channels of high impedance vol t age switching or low current switching.

Test Fixture. The Model 8009 Resistivity Chamber is a guard ed test fixture for measuring vol ume and sur face resistivities of sam ple mat er ials. It has stain less-steel elec trodes built to ASTM stan dards. The fixture’s elec trode dimensions are pre- programmed into the Model 6517B, so there’s no need to calculate those values then enter them man ually. This accessory is designed to protect you from contact with potentially hazardous voltages

—opening the lid of the cham ber automatically turns off the Model 6517B’s volt age source.

Applications

The Model 6517B is well suited for low current and high impedance voltage, resistance, and charge meas ure ments in areas of re search such as physics, optics, and mater ials science. Its extremely low voltage bur den makes it particularly appropriate for use in solar cell applica tions, and its built-in voltage source and low current sensitivity make it an excellent solution for high resistance measurements of nanomaterials such as polymer based nanowires. Its high speed and ease of use also make it an ex cellent choice for quality control, product engineering, and production test appli ca tions involving leakage, breakdown, and resistance testing. Volume and sur face resistivity measurements on non-conduc tive mater ials are particularly enhanced by the Model 6517B’s voltage reversal method.

Model 6517B Enhancements

The Model 6517B is an updated version, replacing the earlier Model 6517A, which was introduced in 1996. Software applications created for the Model

6517A using SCPI commands can run without modifications on the Model

6517B. However, the Model 6517B does offer some useful enhancements to the earlier design. Its internal battery-backed memory buffer can now store up to 50,000 readings, allowing users to log test results for longer periods and to store more data associated with those readings. The new model also provides faster reading rates to the internal buffer (up to 425 readings/ second) and to external memory via the IEEE bus (up to 400 readings/ second). Several connector modifications have been incorporated to address modern connectivity and safety requirements.

262

Model 6517B rear panel

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6517B

Electrometer/High Resistance Meter

VOLTS

5½-DIGIT

RANGE

2 V

20 V

200 V

ACCURACY

(1 Year)

1

TEMPERATURE

COEFFICIENT

18°–28°C 0°–18°C & 28°–50°C

RESOLUTION ±(%rdg+counts) ±(%rdg+counts)/°C

10 µV

100 µV

1 mV

0.025 + 4

0.025 + 3

0.06 + 3

0.003 + 2

0.002 + 1

0.002 + 1

NMRR: 2V and 20V ranges >60dB, 200V range >55dB. 50Hz or 60Hz 2 .

CMRR: >120dB at DC, 50Hz or 60Hz.

INPuT IMPEDANCE: >200TΩ in parallel with 20pF, <2pF guarded (1MΩ with zero check on).

SMALL SIGNAL BANDWIDTH AT PREAMP OuTPuT: Typically 100kHz (–3dB).

NOTES

1. When properly zeroed, 5½-digit, 1 PLC (power line cycle), median filter on, digital filter

= 10 readings.

2. Line sync on.

AMPS

5½-DIGIT

RANGE

20 pA

200 pA

2 nA

20 nA

200 nA

2 µA

20 µA

200 µA

2 mA

20 mA

ACCURACY

(1 Year)

1

TEMPERATURE

COEFFICIENT

18°–28°C 0°–18°C & 28°–50°C

RESOLUTION ±(%rdg+counts) ±(%rdg+counts)/°C

100 aA

10 fA

100 fA

1 pA

10 pA

100 pA

1 nA

10 nA

100 nA

2

1 fA 2

1 + 30

1 + 5

0.2 + 30

0.2 + 5

0.2 + 5

0.1 + 10

0.1 + 5

0.1 + 5

0.1 + 10

0.1 + 5

0.1 + 5

0.1 + 1

0.1 + 2

0.03 + 1

0.03 + 1

0.005 + 2

0.005 + 1

0.005 + 1

0.008 + 2

0.008 + 1

INPuT BIAS CuRRENT: <3fA at T

CAL

20pA range.

. Temperature coefficient = 0.5fA/°C,

INPuT BIAS CuRRENT NOISE: <750aA p-p (capped input), 0.1Hz to 10Hz bandwidth, damping on. Digital filter = 40 readings, 20pA range.

INPuT VOLTAGE BuRDEN at T

CAL

±1°C:

<20µV on 20pA, 2nA, 20nA, 2µA, and 20µA ranges.

<100µV on 200pA, 200nA, and 200µA ranges.

<2mV on 2mA range. <5mV on 20mA range.

TEMPERATuRE COEFFICIENT OF INPuT VOLTAGE BuRDEN: <10µV/°C on pA, nA, and µA ranges.

PREAMP SETTLING TIME (to 10% of final value) Typical: 0.5sec (damping off)

2.0 sec (damping on) on pA ranges. 15msec on nA ranges damping off, 1msec on

µA ranges damping off. 500µsec on mA ranges damping off.

NMRR: >60dB on all ranges at 50Hz or 60Hz 3 .

NOTES

1. When properly zeroed, 5½-digit, 1PLC (power line cycle), median filter on, digital filter = 10 readings.

2. aA = 10

–18

A, fA = 10

–15

A.

3. Line sync on.

OHMS (Normal Method)

ACCURACY

1

TEMPERATURE

COEFFICIENT

(10–100% Range) (10–100% Range)

5½-DIGIT 18°–28°C (1 Year) 0°–18°C & 28°–50°C AUTO

RANGE RESOLUTION ±(% rdg+counts) ±(% rdg+counts) V SOURCE

2 MΩ

20 MΩ

200 MΩ

2 GΩ

20 GΩ

200 GΩ

2 TΩ

20 TΩ

200 TΩ

10 Ω

100 Ω

1 kΩ

10 kΩ

100 kΩ

1 MΩ

10 MΩ

100 MΩ

1 GΩ

0.125 + 1

0.125 + 1

0.15 + 1

0.225 + 1

0.225 + 1

0.35 + 1

0.35 + 1

1.025 + 1

1.15 + 1

0.01 + 1

0.01 + 1

0.015 + 1

0.035 + 1

0.035 + 1

0.110 + 1

0.110 + 1

0.105 + 1

0.125 + 1

40 V

40 V

40 V

40 V

40 V

40 V

400 V

400 V

400 V

AMPS

RANGE

200 µA

20 µA

2 µA

200 nA

20 nA

2 nA

2 nA

200 pA

20 pA

NOTES

1. Specifications are for auto V-source ohms, when properly zeroed, 5½-digit, 1PLC, median filter on, digital filter = 10 readings. If user selectable voltage is required, use manual mode. Manual mode displays resistance (up to 10

18 Ω) calculated from measured current. Accuracy is equal to accuracy of V-source plus accuracy of selected Amps range.

PREAMP SETTLING TIME: Add voltage source settling time to preamp settling time in Amps specification.

Ranges over 20GΩ require additional settling based on the characteristics of the load.

OHMS (ALTERNATING POLARITY METHOD)

The alternating polarity sequence compensates for the background (offset) currents of the material or device under test. Maximum tolerable offset up to full scale of the current range used.

using Keithley 8009 fixture

REPEATABILITy: ∆I

BG

× R/V

ALT

+ 0.1% (1σ) (instrument temperature constant ±1°C).

ACCuRACy: (V

SRC

Err + I

MEAS

Err × R)/V

ALT where: ∆I

BG

is a measured, typical background current noise from the sample and fixture.

V

ALT

is the alternating polarity voltage used.

V

SRC

Err is the accuracy (in volts) of the voltage source using V

ALT

as the setting.

I

MEAS

Err is the accuracy (in amps) of the ammeter using V

ALT

/R as the reading.

VOLTAGE SOURCE

RANGE

100 V

1000 V

5½-DIGIT

RESOLUTION

5 mV

50 mV

ACCURACY (1 Year)

18°–28°C

±(% setting + offset)

0.15 + 10 mV

0.15 + 100 mV

MAXIMuM OuTPuT CuRRENT:

100V Range: ±10mA, hardware short circuit protection at <14mA.

1000V Range: ±1mA, hardware short circuit protection at <1.4mA.

SETTLING TIME:

100V Range: <8ms to rated accuracy.

1000V Range: <50ms to rated accuracy.

NOISE (typical):

100V Range: <2.6mV rms.

1000V Range: <2.9mV rms.

TEMPERATURE

COEFFICIENT

±(% setting+offset)/°C

0°–18°C & 28°–50°C

0.005 + 1 mV

0.005 + 10 mV

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263

6517B

Electrometer/High Resistance Meter

COULOMBS

RANGE

ACCURACY

(1 Year)

1, 2

TEMPERATURE

COEFFICIENT

5½-DIGIT 18°–28°C 0°–18°C & 28°–50°C

RESOLUTION ±(%rdg+counts) ±(%rdg+counts)/°C

2 nC

20 nC

200 nC

2 µC

10 fC

100 fC

1 pC

10 pC

0.4 + 5

0.4 + 5

0.4 + 5

0.4 + 5

0.04 + 3

0.04 + 1

0.04 + 1

0.04 + 1

NOTES

1. Specifications apply immediately after charge acquisition. Add

|Q

AV

RC

|

(4fA + _____ ) T

A

where T

Q

AV

A

= period of time in seconds between the coulombs zero and meas urement and

= average charge measured over T

A

, and RC = 300,000 typical.

2. When properly zeroed, 5½-digit, 1PLC (power line cycle), median filter on, digital filter = 10 readings.

INPuT BIAS CuRRENT: <4fA at T

CAL

. Temperature coefficient = 0.5fA/°C, 2nC range.

TEMPERATURE (Thermocouple)

THERMOCOUPLE

TYPE

K

RANGE

–25°C to 150°C

ACCURACY (1 Year)

1

18°–28°C

±(% rdg + °C)

±(0.3% + 1.5°C)

NOTES

1. Excluding probe errors, T cal

± 5°C, 1 PLC integration time.

HUMIDITY

RANGE

0–100%

ACCURACY (1 Year)

1

18°–28°C, ±(% rdg + % RH)

±(0.3% +0.5)

NOTES

1. Humidity probe accuracy must be added. This is ±3% RH for Model 6517-RH, up to 65°C probe environment, not to exceed 85°C.

IEEE-488 BUS IMPLEMENTATION

IMPLEMENTATION: SCPI (IEEE-488.2, SCPI-1999.0).

TRIGGER TO READING DONE: 150ms typical, with external trigger.

RS-232 IMPLEMENTATION: Supports: SCPI 1991.0. Baud Rates: 300, 600, 1200, 2400,

4800, 9600, 19.2k, 38.4k, 57.6k, and 115.2k.

FLOW CONTROL: None, Xon/Xoff.

CONNECTOR: DB-9 TXD/RXD/GND.

GENERAL

OVERRANGE INDICATION: Display reads “OVERFLOW” for readings >105% of range. The display reads “OUT OF LIMIT” for excesive overrange conditions.

RANGING: Automatic or manual.

CONVERSION TIME: Selectable 0.01PLC to 10PLC.

MAXIMuM INPuT: 250V peak, DC to 60Hz sine wave; 10sec per minute maximum on mA ranges.

MAXIMuM COMMON MODE VOLTAGE (DC to 60Hz sine wave): Electrometer, 500V peak;

V Source, 750V peak.

ISOLATION (Meter COMMON to chassis): >10 10 Ω, <500pF.

INPuT CONNECTOR: Three lug triaxial on rear panel.

2V ANALOG OuTPuT: 2V for full range input. Non-inverting in Volts mode, inverting when measuring Amps, Ohms, or Coulombs. Output impedance 10kΩ.

PREAMP OuTPuT: Provides a guard output for Volts measurements. Can be used as an inverting output or with external feedback in Amps and Coulombs modes.

EXTERNAL TRIGGER: TTL compatible External Trigger and Electro meter Complete.

GuARD: Switchable voltage guard available.

DIGITAL I/O AND TRIGGER LINE: Available, see manual for usage.

EMC: Conforms to European Union Directive 89/336/EEC, EN 61326-1.

SAFETy: Conforms to European Union Directive 73/23/EEC, EN 61010-1.

READING STORAGE: 50,000.

READING RATES:

To Internal Buffer: 425 readings/second

To IEEE-488 Bus: 400 readings/second

Bus Transfer: 3300 readings/second 2 .

1, 2

1 .

.

1. 0.01PLC, digital filters off, front panel off, temperature + RH off, Line Sync off.

2. Binary transfer mode.

DIGITAL FILTER: Median and averaging.

ENVIRONMENT: Operating: 0°–50°C; relative humidity 70% non-condensing, up to 35°C.

Storage: –25° to +65°C.

ALTITuDE: Maximum 2000 meters above sea level per EN 61010-1.

WARM-uP: 1 hour to rated accuracy (see manual for recommended procedure).

POWER: User selectable 100, 120, 220, 240VAC ±10%; 50/60Hz, 100VA max.

PHySICAL: Case Dimensions: 90mm high × 214mm wide × 369mm deep (3

1

2

in. × 8

1

2

in.

× 14 1

2

in.).

Working Dimensions: From front of case to rear including power cord and IEEE-488 connector: 15.5 inches.

Net Weight: 5.4kg (11.8 lbs.).

Shipping Weight: 6.9kg (15.11 lbs.).

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Model 65

High Resistivity Measurement Package

• Complete high resistance measurement solution

• Package includes measuring instrument, software, and fixturing

• Model 65 designed for high resistivity materials testing

• 0.3% repeatability on

10

14

-cm material

• Compatible with Keithley’s

6517A and 6517B Electrometers

Ordering Information

Model 65 High Resistivity

Measurement Package

Model 6517B Electrometer/High

Resistance Meter, Model 6524 High

Resistance Software, and Model

8009 Resistivity Test Fixture

Accessories Supplied

Instruction manual

3.5˝ installation disk set

On-line help

The Model 65 includes the Model 6517B Electrometer/High

Resistance Meter, Model 6524 software, all meter and fixture cables, and the Model 8009 Resistivity Test Fixture. The Model

8009 includes a high resistance material sample to verify system operation.

Improved High Resistivity Measurements

Many test applications require measuring high levels of resistivity (surface or volume) of materials. The conventional method of making these measurements is to apply a sufficiently large voltage to a sample, measure the current that flows through the sample, then calculate the resistance using Ohm’s Law (R=V/I).

While high resistance materials and devices produce very small currents that are difficult to measure accurately, Keithley’s electrometers and picoammeters have been used successfully in the past for such measurements. However, even with high quality instrumentation, inherent background currents in the material have made these measurements difficult to perform accurately. Insulating materials, polymers, and plastics typically exhibit background currents due to piezoelectric effects, capacitive elements charged by static electricity, and polarization effects. These background currents are often equal to or greater than the current stimulated by the applied voltage. In these cases, the result is often unstable, inaccurate resistance or resistivity readings or even erroneous negative values.

Keithley’s Model 6517B is designed to solve these problems and provides consistent, repeatable, and accurate measurements for a wide variety of materials and components, especially when used in combination with the Model 6524 software and the appropriate fixturing in the Model 65 system.

Alternating Polarity Method

The Model 6517B uses the Alternating Polarity method, which virtually eliminates the effect of any background currents in the sample. First and second order drifts of the background currents are also canceled out. The Alternating Polarity method applies a voltage of positive polarity, then the current is measured after a specified delay (Measure Time). Next, the polarity is reversed and the current measured again, using the same delay. This process is repeated continuously, and the resistance is calculated based on a weighted average of the four most recent current measurements. This method typically produces a highly repeatable, accurate measurement of resistance (or resistivity) by the seventh reversal on most materials (i.e., by discarding the first three readings). For example, a 1mm-thick sample of 10 14 Ω-cm material can be measured with 0.3% repeatability in the Model 8009 test fixture in the Model 65, provided the background current changes less than 200fA over a 15-second period.

Easy to Use

The factory default settings of the Model 6517B (Measure Time, Offset Voltage, Alternating Voltage, and

Readings to Discard) provide good results on many materials. Different materials and conditions may require different settings—the Model 6524 software simplifies determining the appropriate settings for these cases.

Stand Alone Operation

Once the appropriate settings for the Model 6517B have been determined via the 6524 software, they can be programmed into the 6517B, stored in internal memory, and used just like the original default settings. Up to ten different settings can be stored in the Model 6517B. Subsequent measurements can then be made using the 6517B and fixtures

ACCESSORIES AVAILABLE

alone, without the use of the PC or software.

All the operations observed via the software are then done internally to the 6517B and only the final resistance/resistivity measurement result is displayed. This is ideal for production testing or repetitive testing of materials or devices.

4288-1

6517-RH

7007-1

7007-2

Single Fixed Rack Mount Kit

Humidity Probe

Shielded IEEE-488 Cable, 1m (3.3 ft)

Shielded IEEE-488 Cable, 2m (6.6 ft)

KPCI-488A IEEE-488 Interface/Controller for the PCI Bus

KUSB-488A IEEE-488 USB-to-GPIB Interface Adapter

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265

Model 65

High Resistivity Measurement Package

This graph, using Model 6524 software, shows the actual current waveform that results from the applied Alternating

Polarity DC voltage. The square wave represents the alternating applied voltage. From this window, the researcher or test engineer can determine whether the parameters used are appropriate for the material or device under test. This picture also demonstrates the Alternating Polarity method.

It shows the material’s response to a change in applied voltage, as well as the background currents that are rejected when using this method.

Model 6524 High Resistance Measurement Software

When used with a PC with an IEEE-488 interface (requires the KPCI-488A or KUSB-

488A), the Model 6524 software provides a visual overview of the Alternating Polarity resistance measurement method and makes it easy to select the most appropriate parameters (Measure Time, Offset Voltage, Alternating Voltage, and number of

Readings to Discard) for the Model 6517B’s enhanced resistivity mode. It also simplifies analyzing time constants and correlating results with environmental factors.

The Model 6517B’s built-in firmware ensures much tighter timing control and more repeatable results when making Alternating Polarity resistance and resistivity measurements than are possible when using the original Model 6517 electrometer with external software control. The 6517B/6524 combination can be used to determine the impact of voltage and timing parameters on the measurement by sweeping these variables and plotting the result. It can also be used to plot results vs. time, along with temperature or relative humidity, in order to determine the correlation between resistance or resistivity and these environmental factors. The Model 6524 software may also be used with the Model 6517B electrometer to make Alternating Polarity resistivity or resistance measurements and to determine time constants and/or the best exponential fit. In each of these programs, the user may specify the axes as either logarithmic or linear. All tests can be configured to measure volume resistivity, surface resistivity, or resistance.

Model 8009 Resistivity Test Fixture

The Model 8009 Resistivity Test Fix ture is designed for measuring the vol ume and surface resistivity of insulating materials such as dielectric or insulating films. It can also be used to assess the quality of sheets of materials and/or products such as printing paper, photographic film, glass, etc. by measuring the resist ance of these items under vari ous conditions. The Model 6517B already con tains the geometric parameters of the 8009 for surface and volume resistivity, which are automatically selected when the user switches the fixture for volume or surface mode. The fixture’s stainless steel electrodes are built to the ASTM D-257 standard. The Model 8009 is designed to ensure complete electrostatic shielding and can accommodate sheet samples from 64mm to

102mm (2

1

2

to 4 in.) in diameter and up to 3.2mm (

1

8

in.) thick. A safety interlock feature automatic ally turns off the instrument’s voltage source unless the fixture’s lid is firmly closed. The fixture is specified to operate at voltages of up to 1000V.

Model 8009

The Model 65 package can eliminate drift and noise in difficult materials, so it is possible to determine characteristics of the material that were previously obscured, such as temperature coefficient. The Model 6524 software allows graph ing resistance/resistivity plus temperature or humidity vs. time on the same screen. This makes it easy to observe and calculate the dependence of a sample’s resistance/resistivity vs. temperature and humidity.

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A G R E A T E R M E A S U R E O F C O N F I D E N C E

Model 65

High Resistivity Measurement Package

MINIMUM SYSTEM REQUIREMENTS

Pentium Class processor running Windows

®

2000/XP.

Keithley KPCI-488A or KUSB-488A GPIB interfaces.

(The Model 6524 software is not compatible with GPIB interfaces from

National Instruments, IOtech, or Measurement Computing.)

OPTIONS

The Model 6524 High Resistance Measurement Software can be purchased separately in order to employ the Alternating Polarity method with a

Model 6517 (the predeces sor to the Model 6517A) in software only, using a PC to control the Model 6517 via the IEEE-488 bus. When used with a

Model 6517, the Model 6524 software does not allow graph ing Resistance/

Resistivity vs. Temperature and Humidity or vs. a series of volt age or time parameters.

The 6524 Package Includes Four Programs:

The 6517 Hi-R Test performs the Al ter nating Polarity Method by a series of commands from the PC to the 6517A and displays cur rent transients resulting from the alternating stimulus voltage, as well as volume resistivity, surface resistivity, or resistance results. It allows the user to change settings easily and observe the results via the PC. This is useful for research and experimentation and for determin ing the optimum settings for a given material. Since this program does not use the

6517A’s internal Al ter nating Polarity firmware, it can be used with the

6517 to mimic the 6517A’s capabilities.

The 6517 Hi-R Step Response Pro gram plots and analyzes the current transients that result from a single voltage step. It performs a fit to ex po nential decays to permit analysis of samples with multiple time con stants. It allows easy viewing of the step response current in log or lin e ar scale vs. log or linear time and is par tic ularly useful in determining the appropriate measure time set ting. It also can be used with the

Mo del 6517.

The 6517A/B Hi-R Sweep Test per forms a sequence of Alternating

Po l ar i ty tests, sweeping one of the following parameters—Alternating

Voltage, Offset Voltage, or Measure Time—while measuring current or resistance/resistivity.

The 6517A/B Hi-R, T, and RH Program allows plotting resistivity/ resistance plus temperature, relative humidity over time.

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267

6521

6522

Low Current, 10-channel

Scanner Cards for 6517B

• 10 channels of multiplex switching

• Install directly in 6517B’s option slot

• Choose from low current scanning or high impedance voltage switching with low current switching

• <200µV contact potential

• <1pA offset current

• Compatible with Keithley’s

Model 6517 and 6517A

Electrometers

Ordering Information

6521

6522

Low Current,

10-channel Scanner

Card (for Model 6517B)

Low Current, High

Impedance Voltage,

High Resistance,

10-channel Scanner

Card (for Model 6517B)

Two optional 10-channel plug-in scanner cards are available to extend the measurement performance of the Model 6517B Electrometer/High Resistance Meter. The cards install directly into the option slot in the back panel of the Model 6517B. The cards are also compatible with the Models 6517A and 6517.

The Model 6521 Low Current Scanner Card is a 10-channel multiplexer, designed for switching low currents in multipoint testing applications or when the test configuration must be changed. Offset current on each channel is <1pA and high isolation is maintained between each channel (>10

15 Ω).

The Model 6521 main tains the current path even when the channel is deselected, making it a true current switch. BNC input con nectors help provide shielding for sensitive measurements and make the card compatible with low noise co axial cables. The Model 6521 is well suited for automating reverse leakage tests on semiconductor junc tions or gate leakage tests on FETs.

The Model 6522 Voltage/Low Current Scanner Card can provide up to ten channels of low-level

current, high impedance voltage, high resistance, or charge switching. Although it is similar to the

Model 6521 in many ways, the Model 6522’s input connectors are 3-lug triax. The card can be software configured for high im pe dance voltage switching of up to 200V. Triaxial connectors make it possible to float the card 500V above ground and drive guard to 200V.

MODEL 6521 SPECIFICATIONS

CHANNELS PER CARD: 10.

FuNCTIONS: Amps.

CONTACT CONFIGuRATION: Single pole, “break-beforemake” for signal HI input. Signal LO is common for all 10 channels and output. When a channel is off, sig nal HI is connected to signal LO.

CONNECTOR TyPE: Inputs BNC, Outputs Triaxial.

SIGNAL LEVEL: 30V, 500mA, 10VA (resistive load).

CONTACT LIFE: >10

6

closures at maximum signal level;

>10

7

closures at low signal levels.

CONTACT RESISTANCE: <1Ω.

CONTACT POTENTIAL: <200µV.

OFFSET CuRRENT: <1pA (<30fA typical at 23°C, <60%

RH).

ACTuATION TIME: 2ms.

COMMON MODE VOLTAGE: <30V peak.

ENVIRONMENT: Operating: 0° to 50°C up to 35°C at 70%

R.H. Storage: –25° to 65°C.

MODEL 6522 SPECIFICATIONS

CHANNELS PER CARD: 10.

FuNCTIONS: Volts, Amps.

CONTACT CONFIGuRATION: Single pole, “break-beforemake” for signal HI input. Signal LO is common for all 10 channels and output. When a channel is off, signal HI is connected to signal LO. 6517B can also configure channels as voltage switches.

CONNECTOR TyPE: Inputs: Triaxial. Outputs: Triaxial.

SIGNAL LEVEL: 200V, 500mA, 10VA (resistive load).

CONTACT LIFE: >10

6

closures at maximum signal level;

>10

7

closures at low signal levels.

CONTACT RESISTANCE: <1Ω.

CONTACT POTENTIAL: <200µV.

OFFSET CuRRENT: <1pA (<30fA typical at 23°C, <60% RH).

CHANNEL ISOLATION: >10

13 Ω, <0.3pF.

INPuT ISOLATION: >10

10 Ω, <125pF (Input HI to Input LO).

ACTuATION TIME: 2ms.

COMMON MODE VOLTAGE: <300V peak.

ENVIRONMENT: Operating: 0° to 50°C up to 35°C at 70%

R.H. Storage: –25° to 65°C.

6521-3Y-EW

6522-3Y-EW

SERVICES AVAILABLE

1-year factory warranty extended to 3 years from date of shipment

1-year factory warranty extended to 3 years from date of shipment

H

OUT L

G

H

L

IN 1

H

L

IN 10

H

OUT L

G

H

L

G

IN 1

H

L

G

IN 10

268

1.888.KEITHLEY

(U.S. only) www.keithley.com

A G R E A T E R M E A S U R E O F C O N F I D E N C E

6220/6514

High Impedance Semiconductor

Resistivity and Hall Effect Test System

The Model 6220 Current Source offers material researchers ±0.1pA/step to

±105mA DC output, combined with

10

14

output resistance.

The Model 6514 Electrometer provides

>200T input impedance and <3fA

input bias current.

Ordering Information

6220

6514

2000

7001

7152

DC Current Source

Programmable

Electrometer

Digital Multimeter

Switch System

4×5 Low Current

Matrix Card

Alternative eco nom i cal ap proach es to Hall coefficient and resistivity measurements

Occasionally, when working with samples with very high resistivity, semiinsulating GaAs, and similar materials with resistivities above 10

8 Ω, alternative system configurations may be able to produce more reliable data than standard, pre-configured Hall Effect systems.

Such systems demand careful shielding and guard ing, and typically include a current source, two electrometer buffers, and an isolated voltmeter. The schematics show two suggested con fig u ra tions for these high resistivity applications: one that requires manual switching and one with automated switching.

The range of the systems shown here is very wide. The high resistance end is limited by the minimum output of the current source. A current of 100pA can be supplied with an accuracy of about 2%. If the resistance of each leg of the sample is no more than 1TΩ, the maximum voltage developed will be 100V, within the range of the Model

6220 current source and the Model 6514 electrometer. This system will provide good results with samples as low as 1Ω per leg, if a test current level of 100mA is acceptable. Even at 100mΩ per leg, accuracy is approximately 2%.

Leakage currents are the most important sources of error, especially at very high resistances. One important advantage of this circuit is that a guard voltage is avail able for three of the sample terminals, which virtually eliminates both leakage currents and line capacitance.

The fourth terminal is at circuit LO or ground potential and does not need guarding.

Call Keithley for additional guidance in selecting equipment for specific high resistivity applications.

HI

6220

LO

Preamp

Out

HI

2000

LO

Preamp

Out

R

R = 1 T Ω

R

R

6514

LO

HI

HI

6514

LO

6220

HI

LO

R

HI

6514

LO

HI

6514

LO

1

1

1

2

4

3

Preamp Out

V1

HI

V

LO

Preamp Out

V2

4

7152 Low Current Matrix Card in 7001 Mainframe

2000

DMM

The equipment configuration with manual switching (above) was developed for very high resistance van der Pauw or Hall Effect measurements. This measurement system includes a Model 6220 current source, two Model 6514 electrometers (used as unity-gain buffers), and a Model 2000 digital multimeter (DMM). The current source has a builtin guard, which minimizes the time constant of the current source and cable. The insulation resistance of the leads and supporting fixtures for the sample should be at least 100 times the leg resistance (R).

The entire sample holder must be shielded to avoid electrostatic pickup. If the sample is in a dewar, this should be part of the shield.

2

3

2 3 4 5

One Model 7152 Matrix Card, housed in a Model

7001 mainframe, is used to connect the electrometers and the current source to the sample. Two Model

6514 electrometers are used as unity gain buffers, and their output difference is measured with a Model

2000 DMM. To ensure faster measurement time, guarded measurements are made by turning the

Guard switch ON for both of the Model 6514s, and by guarding the Model 6220 output. Call Keithley’s

Applications Department for cabling information.

ACCESSORIES AVAILABLE

7078-TRX-10 Triax Cable, 3m (10 ft)

1.888.KEITHLEY

(U.S. only) www.keithley.com

A G R E A T E R M E A S U R E O F C O N F I D E N C E

269

270

1.888.KEITHLEY

(U.S. only) www.keithley.com

A G R E A T E R M E A S U R E O F C O N F I D E N C E

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