43W, 52% PAE X-Band AlGaN/GaN HEMTs MMIC

43W, 52% PAE X-Band AlGaN/GaN HEMTs MMIC
43W, 52% PAE X-Band AlGaN/GaN HEMTs
MMIC Amplifiers
S. PiotrowiczI, Z. OuarchII, E. ChartierI, R. AubryI, G.CalletI,III, D. FloriotII, J.C.JacquetI,
O. JardelI, E. MorvanI, T. ReveyrandIII, N. SarazinI, and S.L. DelageI.
I
: ALCATEL-THALES III-V Lab, Route de Nozay, 91461 Marcoussis, France.
II
: United Monolithic Semiconductors, Rd. 128, 91401 Orsay, France.
III
: XLIM, Faculté des sciences de Limoges, 87060 Limoges, France
Abstract — This paper presents the results obtained on XBand GaN MMICs developed in the frame of the Korrigan
project launched by the European Defense Agency.
GaN has already demonstrated excellent output power levels,
nevertheless demonstration of excellent PAE associated to very
high power in MMIC technology is still challenging.
In this work, we present State-of-the-Art results on
AlGaN/GaN MMIC amplifiers. An output power of 43W with
52% of PAE was achieved at 10.5 GHz showing that high
power associated with high PAE can be obtained at X-band
using MMIC GaN technology.
temperature of 900°C. Mean contact resistance extracted
from TLM measurement is 0.2 Ω.mm. Mo-based T-gates
with 0.25µm length were defined by electron beam
lithography. The devices were then passivated using plasma
enhanced chemical vapor deposition (PECVD) of
SiO2/Si3N4. After front side processing, the SiC wafer was
thinned down to 100 µm. Plasma etching via-holes
technology was used to ground the devices. Fig.1 shows the
gain current cut-off frequency (Ft) and maximum available
gain cut-off frequency (Fmag) for various total gate width
devices.
Index Terms — GaN, HEMT, MMIC, power amplifier, Xband.
Fmag (GHz) & Ft (GHz)
60
I. INTRODUCTION
The presence of piezoelectric effects in the GaN material
leads to the presence of piezoelectric charges at interfaces,
giving a 2-dimensional electron gas with an electron density
larger than that created in GaAs HEMTs using intentional
doping. The large bandgap of 3.4eV results in a high
breakdown field of 3MV/cm, the thermal conductivity of
GaN at 300K is 190Wm-1K-1 and that of SiC is 400Wm-1K-1
allowing a good dissipation of the heat generated in the
channel. On the other hand the high breakdown field allows
an increase in bias voltage by a factor of at least 5. These
combined characteristics lead to power densities up to a
factor of 10 times larger than in GaAs HEMTs [1],
[2],[3],[4]. The higher power available in GaN devices
means that there is an opportunity to trade power for PAE. In
this work, we report on the performances obtained with
MMIC power amplifiers at X-band on AlGaN/GaN HEMT
technology on SiC substrate.
12x100µm
4x 75µm
16x100µm
40
16x140µm
30
20
10
0
0
0.5
1
1.5
2
2.5
Total gate width (mm)
Fig. 1. Fmag and Ft evolution versus total gate width (Vds=5V,
Ids=100mA/mm)
A typical power device of 1.6mm total gate width
presents a Ft value of 18 GHz and a Fmag value of 35 GHz.
A ratio of 2 between Ft and Fmag values is well conserved
from elementary to power devices.
III. DEVICE TOPOLOGY
II. DEVICE FABRICATION
Elementary devices are based on 16x100µm topology.
This power device, presented on Fig. 2, is used both in the
first and second stage. It has a maximum available gain of
11.8dB at 10 GHz and a maximum available gain cut-off
The AlGaN/GaN HEMT epitaxial layer was grown on a
silicon carbide substrate by low-pressure metal organic
chemical vapor deposition (MOCVD). Electrical isolation of
devices was performed by helium implantation. Ti/Al/Ni/Au
ohmic contacts were formed using rapid thermal annealing at
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µm² (18 mm²). Due to the high level of output power reached
and in order to reduce both DC and RF losses in the
transmission lines of matching and biasing networks,
electroplated gold layer of 6µm thickness was deposited on
the output combiner as well as on the first and on the interstage combiners. A parallel RC network in series at the input
of each transistor enhances the stability of HPAs and
prevents the occurrence of parametric oscillation phenomena
[5]. The simulation of the stability of these amplifiers was
first performed in linear operation mode at the quiescent
biasing point. Then, the non linear stability was analyzed at
high input power level [6].
frequency of 35 GHz at a Vds voltage of 20V and 320mA of
drain current in continuous mode.
Fig. 2. Photograph of the microstrip 16x100µm power device.
Fig. 4. Photograph of amplifier.
V. AMPLIFIER RESULTS – BATCH 1
60
PAE
40
30
Pout
20
Gp
10
0
0
5
10
15
20
25
30
35
Pin (dBm)
Fig. 3. Load-Pull measurement of 16x100µm device at optimum
load for PAE. (Vds0=25V, Ids0=430mA, F0=10 GHz, pulsed
10µs/10%).
0
40
-2
36
-4
32
S22
-6
28
S11
-8
24
-10
20
-12
16
-14
S21
-16
-18
dB (S21)
50
Different batches of amplifiers were realized. This part
presents results obtained in the frame of the first one.
Amplifiers were first measured on wafer with a pulsed SParameter bench. Fig. 5 shows S-Parameter measurements of
amplifier at reduced drain voltage of 20V and drain current
of 2A.
dB(S11) & dB(S22)
Pout (dBm), Gp (dB) & PAE (%)
Fig. 3 shows load-pull power measurements of this
1.6mm device at 10 GHz. Measurements are performed in
pulse mode with a pulse length of 10µs with 10% of duty
cycle and without any harmonic frequencies optimization.
The device is biased at a voltage of 25V and a quiescent
drain current of 430 mA. At the optimum load at the
fundamental frequency for maximum PAE (5+j.5 Ω), the
device shows a PAE of 55% with a typical output power of
38dBm (6.4W) corresponding to a power density of 4W/mm
and 9.5dB of associated gain. The linear gain is 11dB. At the
optimum load at the fundamental frequency for maximum
output power (10-j.2 Ω), the output power reached 40.6dBm
(11.4W – 7.1W/mm) with 51% of associated PAE and 10dB
gain. Appropriate harmonic tuning and re-tuned of the
fundamental frequency bring the optimal impedances for
maximum power and PAE together and thus contribute to
increase the output power and PAE of devices in MMIC
circuits.
12
8
4
-20
0
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
Frequency (GHz)
IV. AMPLIFIER DESIGN
Fig. 5. On wafer pulsed S-parameter measurements of amplifier
(Vds0=20V, Ids0=2A).
Amplifier is based on two stages architecture (Fig. 4).
Two devices are used in the first stage which drives four
transistors in the output stage. The chip size is 4500 x4000
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Pout(W), Gain (dB) and PAE (%)
S11 and S22 are better than -7dB in the [8.5-10.5] GHz
bandwidth. S21 is better than 14dB with a maximum of 20dB
at 9.8 GHz.
Amplifiers were then characterised at large signal input
power with drain pulse length of 20µs with 10% of duty
cycle. The drain voltage and quiescent current are
respectively 25V and 2.5A. Fig. 6 shows the output power,
associated gain and PAE of the amplifier over the frequency
range of 8.5 GHz to 10.5 GHz at an input power of 32dBm.
50
45
5us/10%
35
30
Pout
25
20
Gain
15
10
8,5
9
50
9,5
10
10,5
Frequency (GHz)
45
Fig. 8. Output power, Gain and PAE of amplifier in test Jig at input
power of 32dBm (Vds0=25V, Ids0=2.3A) for different pulse
conditions.
PAE
40
35
30
Between the two pulse conditions the output power decreases
by 3W in the bandwidth corresponding to around 8% of power
losses. The PAE decreases by around 2 pts. The high level of
output power and PAE are well retrieved. The differences of
behaviour in the bandwidth can be explained by the use of input
and output wire bondings for RF connections.
Pout
25
20
Gp
15
10
8,5
9
9,5
10
10,5
VI. AMPLIFIER RESULTS – BATCH 2
Frequency (GHz)
A second batch of amplifiers was processed without any
design modification. Fig. 9 shows on wafer performances at
10.5 GHz. The amplifier shows 2dB more gain than
amplifier from batch n°1 and power performances slightly
shifted towards high frequencies.
Fig. 6. On wafer measurements of amplifier (batch1) at 32dBm of
input power (Vds0=25V, Ids0=2.5A).
Pout(dBm), Gp (dB) & PAE (%)
The amplifier delivers a maximum output power of
45.5dBm (35.8W) with 39.5% of PAE and 13.5dB of
associated gain at 9.5 GHz. Over the 2 GHz bandwidth, the
output power is above 30W with a very flat PAE between
38% and 39.5%. The compression level of 4dB enables the
amplifier to deliver its best PAE. The small signal gain is
17.7 dB at 9.5 GHz.
Amplifiers were then mounted in typical test Jig
presented in Fig. 7. The chip is glued directly on the Jig
without additional heat spreader.
60
55
50
6
PAE
5
45
40
35
Pout
30
25
20
15
4
3
Id
2
Gp
10
5
0
Drain current (A)
Pout (W), Gain (dB) & PAE (%)
50us/20%
PAE
40
1
0
0
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32
Pin (dBm)
Fig. 9. Gain, Ouput power, PAE and drain current of amplifier
(batch2) at 10.5 GHz versus the input power (Vds0=25V,
Ids0=2.2A, pulsed 20µs/10%).
Fig. 7. Typical amplifier mounted in test Jig.
Fig. 8 shows the results for various pulse conditions:
short pulse of 5 µs length with 10% of duty cycle and for
long pulse condition of 50 µs length with 20% of duty cycle.
978-1-4244-6057-1/10/$26.00 ©2010 IEEE
The amplifier delivers a maximum output power of
46.3dBm (43W) corresponding to a power density of 6.7
W/mm with 52% of PAE and 16.3dB of associated gain. To
our knowledge, this result represents State-of-the-Art PAE
obtained with X-band GaN MMIC amplifier with over 10W
of output power. Fig. 10 shows the power performances
measured from 8.5 GHz to 11 GHz.
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Pout (W), Gain (dB) & PAE (%)
60
55
50
45
40
35
30
25
20
15
10
5
0
technology. An output power of above 35W with PAE higher
than 40% over 2GHz of bandwidth were measured. This
paper demonstrates once again the great interest of GaN
technology for X-band radar applications.
PAE
ACKNOWLEDGEMENT
Pout
The authors would like to thank the French MOD and
DGA component department under European Defense
Agency contract KORRIGAN for their support. They would
like also to acknowledge QinetiQ for providing epitaxial
structures and Prof. J.Obregon for his constant technical
advice.
Gp
8,5
9
9,5
10
10,5
11
Frequency (GHz)
Fig. 10. Gain, Ouput power and PAE of amplifier (batch2) at
pin=30dBm (Vds0=25V, Ids0=2.2A, pulsed 20µs/10%).
REFERENCES
[1]
The output power is above 35W with PAE higher than
40% on 2 GHz bandwidth. Fig. 11 represents, to our
knowledge, the state of the art results of GaN HPA MMIC in
X-Band. While many results have been already reported with
PAE up to 67% with lower output power, this paper reports a
PAE of 52% with 43W of output power showing that high
power and high PAE can be achieved at X-band using GaN
technology.
[2]
[3]
Output Power (W)
[4]
70
60
50
40
30
20
10
0
[7]
[5]
[this paper]
[7]
[11]
[8]
[6]
[9]
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[10]
[12]
[13]
[7]
[13]
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[8]
Fig. 11. State-of-the-Art GaN MMIC HPAs in X-Band
VII. CONCLUSIONS
[9]
In this paper we present results obtained on X-band
MMIC amplifiers using AlGaN/GaN HEMT 0.25µm gate
length technology developed in the frame of the European
KORRIGAN contract.
[10]
A first batch of 18mm² MMIC amplifiers exhibited a
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PAE and 13.5dB of associated gain at 9.5 GHz. Over the 2
GHz bandwidth, the output power is above 30W with a very
flat PAE between 38% and 39.5%. On wafer and in test Jig
measurements were performed under pulse conditions.
[11]
[12]
[13]
A second batch allows us to obtain State-of-the-Art
results: An output power of 43W with 52% of PAE was
achieved at a drain bias voltage of 25V showing that high
power and high PAE can be obtained in X-band using GaN
978-1-4244-6057-1/10/$26.00 ©2010 IEEE
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IMS 2010
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