CHEAH Kok Wai (謝國偉 )
Department of Physics
Hong Kong Baptist University
1. Displays of the Future
2. Basic Principles of Flat Panel Display
3. Liquid Crystal Display
4. Organic LED Display
5. Science & Science Fiction
Flat Panel Display (FPD) refers to display units that do
not have a bulky project unit at the back of the
display unit.
Bulky display unit is the old television (TV) that was
being used from the 1950s to turn of 21st century.
FPD is thin and light in comparison to the old TV.
This new form factor means can be large (more than
100 inch now).
It is now used not only for TV, but used in information
display, PC monitor and most critical in mobile
communicators/platforms e.g. notebook, mobile
phone and tablet.
1950 Television
1990 Television
Thin FPD
Dynamic display from 1950s to end of 20th century is represented by
television, and there is only one television technology - cathode ray tube.
In cathode ray tube, electron beam is generated which sweeps a phosphor
screen rapidly (faster than your eyes refreshing rate) to give an image.
However, the electron beam requires a large travelling distance, so as the
size of the screen increases, the TV gets bigger and heavier.
Displaying information is an important way to let other
people to know what you are doing
An example is advertising what you are selling in your
shop; what types of goods, their prices etc.
However, at the moment most displays for this purpose
are static.
Dynamic display and interactive display allows a person
greater access on selective information.
Dynamic display is also more attractive.
With transparent display and flexible display or both, the future
display form factors can be in many forms.
There are several Software and Hardware companies put forward
their ideas of future communication.
We will show two examples:
Microsoft shows how information can be shared and notice the
smart table, electronic newspaper (Harry Potter style) and NFC file
transfer.
Corning (they make glasses e.g. gorilla glass) shows display mirror,
augmented reality, lighting control and giant outdoor transparent
display.
In Microsoft’s view on communication, mobile and desktop
systems share files with seamless data transfer.
Large transparent displays are everywhere and linked to cloud
system making some tasks very smooth and fast e.g. instant
translation and animation.
Smart working desk/table, with Near Field Contact (NFC) for easy
file sharing and transfer.
Near Field Contact (NFC) is already being used.
Will it emerge as something similar that Microsoft envision?
Newspaper that looks similar to that of today is in fact electronic
newspaper (where is the battery?)
Corning being glass manufacturer focuses on how new
types of glass can fit into the future communication.
Architectural display glass can be installed everywhere
(bedroom, sitting, kitchen, offices…)
Theme transfer and not just data transfer and is not just
NFC.
Most impressive is remote medical consultation coupled
with 3-D imaging system.
Augmented reality display is major theme.
Mood lighting is also featured albeit just slightly.
Using shape memory alloy material, a phone can
change its shape as and when desired.
So the display can curve, or fold as you wish it.
Then you can have a large screen that can be
folded into your pocket when not in use.
Cathode Ray Tube (CRT) started life as glass tube
with low pressure gas.
This glass tube was used for studying the properties
of gas molecules/atoms.
That was in 1890s; 19th century!
It was soon discovered that it was electron beam
that was being emitted from cathode.
In fact it is possible to scan out waveforms and
graphics by controlling the electron beams.
J. J. Thompson who used CRT to discover
electrons in1897. He got the Nobel Prize in 1906.
Oscilloscope
Television
Since CRT based TV has great difficulty in making TV beyond 30
inches, so alternate technologies were being looked into.
By 1960s, liquid crystal (LC) was beginning to be used in
commercial display products.
This started the flat panel display technology when typical display
is less than 100mm thick.
This new class of material was first noticed in in mid-19th century
One of the earliest synthetic chemist
to make more 2700 LC.
Prof. Daniel Vorlander and he kept
working in the field of LC for 30 years
since 1905.
• The Twisted Nematic (TN) was
patented by Fergason (USA) and
Helfrich and Schadt (Europe).
• TN was used in calculators and
watches by RCA and Ilixco.
• Then Japanese companies
acquired the technology through
licensing agreement.
• Now TN is still being used by
many Asia companies.
The LC molecules of TN turn by 90o when a voltage is applied.
For STN, the LC molecules turn by 270o.
This gives a sharper transition, giving better contrast.
TN
STN
Backlight Unit (BLU)
To have images, light is needed to pass through
the LC layer - backlight.
In fact LC is acting as shutters – it was referred to
as light valves.
Two ways to generate backlight: reflector to
reflect light and an active backlight unit (BLU).
Most monochrome LCD displays used reflective
backlight.
Most colour LCD displays use active backlight
unit.
Most commonly used BLU is CCFL
(Compact Cathode Florescent Light).
Its working principle is low pressure gas
discharge just like florescent lamp.
The next commonly used BLU is LED.
This type of BLU uses LED matrix or light
guide.
LCD consists primarily of two glass plates with some
liquid crystal material between them. There is no
bulky picture tube.
LCDs use much less power than their cathode-ray
tube (CRT) counterparts.
Many LCDs are reflective, meaning that they use only
ambient light to illuminate the display.
Even displays that do require an external light source
(i.e. computer displays) consume much less power
than CRT devices.
Liquid crystal displays do have drawbacks; viewing
angle, contrast ratio, and response time.
To display dynamic graphic or text information, in
colour or monochrome, the display needs to have
a sophisticated electronics to deliver the signals
to the pixels.
Display electronics require to decode, multiplex,
and drive the display pixels.
Hence, they are also known as display address
electronics, driving electronics, and matrix
electronics.
Broadly speaking there are two methods to
address the display pixels.
Addressing is the process by which pixels are turned on
and off in order to create an image.
There are two main types of addressing, direct and
multiplexing.
Direct addressing is convenient for displays where there
are only a few elements that have to be activated.
In multiplex addressing, a larger number of pixels are
involved.
When the elements are in a regular order, they can be
addressed by their row and column instead of each
element being driven separately.
The passive matrix display is addressed by a set of
multiplexed transparent electrodes, perpendicular
to one another, above and below the liquid crystal
layer in a row and column formation.
Cathodes
Display layers
Substrate
Anodes
Active matrix displays are currently available in
high end laptop computers.
In this type of display, the addressing takes
place completely behind the liquid crystal film.
The front surface of the display is coated with a
continuous electrode while the rear surface
electrode is patterned into individual pixels.
A thin film transistor (TFT) acts as a switch for
each pixel.
Glass (polarizer)
Colour filter
Liquid crystal
Pixel(color cells):
TFT
electrode
Glass (polarizer)
Light
Samsung 82 inch LCD-TV 2006
Sharp 108 inch LCD-TV 2007
85 inch 4K TV by Samsung
55-65 inch 4K TV by LG
Plastic (polymers) do not conduct electricity
normally.
In 1970s, Hedeki Shirakawa, Jack G MacDiarmid
and Alan Heeger (Chemistry Nobel, 2000)
discovered conducting polymer.
the polymers conduct is because electrons from
this type of polymers are allowed to move freely
(delocalised) along the main bonds (backbone) of
the polymer.
This type of polymer is called π-conjugated
polymer.
OLED History
Dr. Fred CH Chen
HKBU/NJTU
Rochester University
OLED
LCD
View Angle
>1600
Limited
Contrast
Response Time
high
µs
Low
ms
Light Emission
Active
Passive ( Backlighting)
Temperature Range
Mfg. Processes
~ -500C to ~800C
~ -00C to ~1000C
~6 steps
~9 steps
Traditional Semiconductor Diode
Organic LED
Polymers have bigger molecules and therefore
cannot be thermally deposited.
Instead, thin films are spin coated onto the
substrate.
Although it has advantage of fabricating device in
ambient atmosphere, it has solvent problem when
depositing multi-layer thin films.
An alternate approach is being considered instead
of spin coating.
PixDro, a subsidiary of OTB-Group, has
released a new desktop inkjet printer for the
development of printed electronics
applications.
Small molecule based full colour display is mature
enough for commercial production.
While Korea and Japan (e.g. Samsung and Sony)
concentrate on larger display unit like TV, Taiwan
and others are working hard on smaller display for
handheld device application.
2007 was the lowest point for OLED and this year we
see some up-turn this year.
Some of the reasons are listed here:
Korea display companies lead in AMOLED display
with usage
Samsung SDI continues to boost her AMOLED
panels monthly production from 1.5 million in 2007
second half to 4.5 million in 2008 third quarter.
Both Mitsubishi Heavy Industries, Toshiba and
Sumitomo have declared their intention to expand
their OLED activities.
Nokia decided that they will use OLED display in
their mobile phones (N85).
Sony sells the first world OLED TV; 11” XEL-1.
There are several possible device configuration for
full colour display in OLED.
Standard RGB, RGBW, colour by blue and colour by
white.
In all the configurations above one of the key
colour needed is deep blue.
The reason is as follow:
CIE Color Coordinate vs Power Consumption
in Full Color OLEDs
0.55
Power (W)
0.50
0.45
0.40
Power ratio
0.35
Blue-y
0.30
0.00
0.05
0.10
Blue-y
0.15
0.20
All Angle
Ultra-thin
Power Efficient
High Contrast
Motion
OLED display has began to make appreciable inroad into the commercial market.
Initially OLED display is being used in handheld
devices; mobile phone, tablet and now OLED TV.
Now 4G is being realised, then OLED display will
have an edge because of the faster time response,
contrast and better colour saturation.
Larger display for TV, notebook (?) and picture
frame are being actively investigated.
Double sided AMOLED by AUO (10.12.04)
• 143 ppi
• 200 nits
• Independent image
• 1.8 mm
• Single module design
• New desiccant
• Perfect for mobile phone with 2” main and 1.5” subdisplay
Samsung Note 3 and Gear
Bluetooth watches for iPhone and
Android
Samsung S series
SONY XEL-1, 11” TV with luminance of
600 cd/m2 and contrast 1,000,000:1.
Resolution: 960x540
Lifetime: 30,000 hours.
Cost: US$2,295.00 - US$2,499.99
Samsung develops 21-in a-Si TFT AM-OLED (1.4.2005)
• 1000 nits brightness
• 6.22 million pixels resolution
• 5000:1 contrast ratio capability
• 1000 x response time over LCD
• Reduced production cost using
LCD G4 line
• Market $830 US in 2005
• 2.2 Billion in 2008
LG 84 inch OLED TV
85 inch 4K OLED TV by Samsung
SONY
Panasonic 65 inch OLED TV
The Future
OLED is very likely to become part of the
commercial display products.
For example, LG, Samsung, Sony, Toshiba,
Matsushita, Idemitsu Kosan and Sumitomo
Chemicals have joint together to develop OLED HD
TV.
Other types of OLED based display are likely to
emerge, e.g. transparent display, conformable
display.
The Return of OLED has just began
Alternative 3-D Display
German Effort
Effort by Universal Display
The transparent cathode
material developed can
be adapted into any
existing OLED device
structure with minor or
no modification.
0V
3.0 V
3.4 V
3.2 V
The emergent of FPD has broadened the way we use display.
Large size display; thin, touch screen and even transparent and
gesture responsive can be part of our office and home.
For mobile communicators (phones, tablets, ultra-book etc),
thin, flexible, touch screen, gesture responsive allow
communication everywhere.
Once other emerging technologies such as NFC, cloud
computing are mature.
Then the dividing line between science and science fiction
becomes blurr.
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