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Transcript of amoled
Amoled Display
CHAPTER 1
INTRODUCTION
AMOLED (active-matrix organic light-emitting diode) is a display technology for use in
mobile devices and televisions. OLED describes a specific type of thin-film display technology in
which organic compounds form the electroluminescent material, and active matrix refers to the
technology behind the addressing of pixels.
As of 2012, AMOLED technology is used in mobile phones, media players and digital
cameras and continues to make progress toward low-power, low-cost and large-size (for example,
40-inch) applications
An AMOLED display consists of an active matrix of OLED pixels that generate light
upon electrical activation that have been deposited or integrated onto a thin film transistor
(TFT) array, which functions as a series of switches to control the current flowing to each
individual pixel.
Typically, this continuous current flow is controlled by at least two TFTs at each pixel, one to start
and stop the charging of a storage capacitor and the second to provide a voltage source at the level
needed to create a constant current to the pixel and eliminating the need for the very high currents
required for passive matrix OLED operation.
TFT backplane technology is crucial in the fabrication of AMOLED displays. Two primary TFT
backplane technologies, namely polycrystalline silicon (poly-Si) and amorphous silicon (a-Si), are
used today in AMOLEDs. These technologies offer the potential for fabricating the active matrix
backplanes at low temperatures (below 150°C) directly onto flexible plastic substrates for
producing flexible AMOLED displays
Currently, OLEDs are used in small-screen devices such as cell phones, PDAs and digital cameras.
In September 2004, Sony Corporation announced that it was beginning mass production of OLED
screens for its CLIE PEG-VZ90 model of personal-entertainment handhelds.
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Fig. 1.1. OLED display for Sony Clie
Kodak was the first to release a digital camera with an OLED display in March 2003, the EasyShare LS633
Fig.1.2.Kodak LS633 EasyShare with OLED display
In May 2005, Samsung Electronics announced that it had developed a prototype40inch, OLED-
based, ultra-slim TV, the first of its size. And in October 2007, Sony announced that it would be the
first to market with an OLED television. The XEL-1 was available in December 2007 for customers
in Japan.
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Fig.1.3. The Sony 11-inch XEL-1 OLED TV.
As of 2012, AMOLED technology is used in mobile phones, media players and
digital cameras, and continues to make progress toward low-power, low-cost and large-size (for
example, 40-inch) applications
Research and development in the field of OLEDs is proceeding rapidly and may lead to future
applications in heads-up displays, automotive dashboards, billboard-type displays, home and office
lighting and flexible displays. Because OLEDs refresh faster than LCDs almost 1,000 times faster - a
device with an OLED display could change information almost in real time. Video
Images could be much more realistic and constantly updated. The newspaper of the future might be
an OLED display that refreshes with breaking news and like a regular newspaper, you could fold it
up when you're done reading it and stick it in your backpack or briefcase.
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CHAPTER 2
OLED
2.1. OLED COMPONENTS
Like an LED, an OLED is a solid-state semiconductor device that is 100 to 500 nanometers
thick or about 200 times smaller than a human hair. OLEDs can have either two layers or three layers
of organic material; in the latter design, the third layer helps transport electrons from the cathode to
the emissive layer. In this article, we'll be focusing on the two-layer design.
Fig.2.1. OLED structure
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An OLED consists of the following parts:
Substrate (clear plastic, glass, foil) - The substrate supports the OLED.
Anode (transparent) - The anode removes electrons (adds electron "holes") when a current flows
through the device.
Organic layers - These layers are made of organic molecules or polymers. Molecules commonly
used in OLEDs include organometallic chelates.
Conducting layer - This layer is made of organic plastic molecules that transport "holes" from the
anode. One conducting polymer used in OLEDs is polyaniline.
Emissive layer - This layer is made of organic plastic molecules (different ones from the conducting
layer) that transport electrons from the cathode; this is where light is made. One polymer used in the
emissive layer is polyfluorene.
Cathode (may or may not be transparent depending on the type of OLED) - The cathode injects
electrons when a current flows through the device.
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2.2. OLED WORKING
OLEDs emit light in a similar manner to LEDs, through a process called
electrophosphorescence.
Fig.2.2. Working of Oled
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The process is as follows:
1. The battery or power supply of the device containing the OLED applies a
voltage across the OLED.
2. An electrical current flows from the cathode to the anode through the organic layers
(an electrical current is a flow of electrons). The cathode gives electrons to the
emissive layer of organic molecules. The anode removes electrons from the
conductive layer of organic molecules. (This is the equivalent to giving electron holes
to the conductive layer.)
3. At the boundary between the emissive and the conductive layers, electrons find
electron holes. When an electron finds an electron hole, the electron fills the hole (it
falls into an energy level of the atom that's missing an electron). When this happens,
the electron gives up energy in the form of a photon of light.
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2.3. TYPES OF OLEDS
There are mainly two types of OLEDs , they are
2.3.1. PASSIVE MATRIX
2.3.2 ACTIVE MATRIX
2.3.1 PASSIVE MATRIX OLED
PMOLEDs have strips of cathode, organic layers and strips of anode. The
anode strips are arranged perpendicular to the cathode strips. The intersections of the cathode and
anode make up the pixels where light is emitted. External circuitry applies current to selected strips
of anode and cathode, determining which pixels get turned on and which pixels remain off. Again,
the brightness of each pixel is proportional to the amount of applied current.
Fig.2.3. Structure of PMOLED
PMOLEDs are easy to make, but they consume more power than other types of OLED, mainly due
to the power needed for the external circuitry. PMOLEDs are most efficient for text and icons and
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are best suited for small screens (2- to 3-inch diagonal) such as those you find in cell phones, PDAs
and MP3 players. Even with the external circuitry, passive-matrix OLEDs consume less battery
power than the LCDs that currently power these devices.
So while PMOLEDs are easy (and cheap) to fabricate, they are not efficient and the OLED
materials suffer from lower lifetime (due to the high voltage needed). PMOLED displays are also
restricted in resolution and size (the more lines you have, the more voltage you have to use).
Fig.2.4. MP3 player
PMOLED displays are usually small (up to 3" typically) and are used to display character data or
small icons: they are being used in MP3 players, mobile phone sub displays, etc.
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CHAPTER 3
ACTIVE MATRIX OLED
AMOLEDs have full layers of cathode, organic molecules and anode, but the anode layer
overlays a thin film transistor (TFT) array that forms a matrix. The TFT array itself is the circuitry
that determines which pixels get turned on to form an image.
Fig.3.1. Structure of AMOLED
AMOLEDs consume less power than PMOLEDs because the TFT array requires less power than
external circuitry, so they are efficient for large displays. AMOLEDs also have faster refresh rates
suitable for video. The best uses for AMOLEDs are computer monitors, large-screen TVs and
electronic signs or billboards.
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Fig.3.2.Active Matrix Addressing
Fig.3.3. AMOLED crossection
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CHAPTER 4
AMOLED MANUFACTURING PROCESS
The biggest part of manufacturing AMOLEDs is applying the organic layers to the substrate. This
can be done in three ways:
Vacuum deposition or vacuum thermal evaporation (VTE) - In a vacuum chamber,
the organic molecules are gently heated (evaporated) and allowed to condense as thin films
onto cooled substrates. This process is expensive and inefficient.
Organic vapor phase deposition (OVPD) - In a low-pressure, hot-walled reactor
chamber, a carrier gas transports evaporated organic molecules onto cooled substrates, where
they condense into thin films. Using a carrier gas increases the efficiency and reduces the
cost of making OLEDs.
Inkjet printing - With inkjet technology, OLEDs are sprayed onto substrates just like inks
are sprayed onto paper during printing. Inkjet technology greatly reduces the cost of OLED
manufacturing and allows OLEDs to be printed onto very large films for large displays like
80-inch TV screens or electronic billboards.
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4.1 COMPARISON TO OTHER TECHNOLOGIES
AMOLED displays provide higher refresh rates than their passive-matrix OLED
counterparts, improving response time often to under a millisecond, and they consume significantly
less power. This advantage makes active-matrix OLEDs well suited for portable electronics, where
power consumption is critical to battery life.
The amount of power the display consumes varies significantly depending on the color and
brightness shown. As an example, one commercial QVGA OLED display consumes 3 watts while
showing black text on a white background, but only 0.7 watts showing white text on a black
background. Because the black pixels actually turn off, AMOLED also has contrast ratios that are
significantly better than LCD. AMOLED mobile phone users can save battery power by avoiding
white backgrounds and many methods exist to achieve this, such as using Black Google Mobile to
search with a black background. The Windows Phone 7 platform takes advantage of this
characteristic, as it instructs the user to maintain the "white text on black background" theme to have
a better battery autonomy.
AMOLED displays may be difficult to view in direct sunlight compared to LCDs because of
their reduced maximum brightness. Samsung's Super AMOLED technology addresses this issue by
reducing the size of gaps between layers of the screen. Additionally, PenTile technology is
sometimes used, rearranging the subpixels for each color and in the case of PenTile RGBW, adding a
white subpixel, which emits more light due to a lack of a R/G/B filter, thereby increasing brightness,
albeit while introducing graininess.
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4.2 COMPARISON OF SCREEN TECHNOLOGIES
There are a number of contenders for screen technology within the television, computer monitor
and other related areas. Although cathode ray tubes are now well out of the picture, developers of
equipment have a choice of technologies of which the AMOLED is one.
AMOLED LCD PLASMA
Potentially the lowest cost. Medium cost. Highest cost
Consumes lowest power Lower Power consumption than plasma
Highest power consumption
Self emissive. Requires backlight. Requires backlight.
Displays wider colour range. Colour range not good. Displays a very deep black.
No screen burn potential No screen burn potential Screen burn potential
Shorter overall lifetime Backlight bulb typically requires replace at around 30 k hours
Half life ~60k hours
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CHAPTER 5
APPLICATIONS OF AMOLED
The AMOLED has a number of advantages over its passive relation. This means that AMOLED
displays can be used in many more areas.
AMOLED display are manufactured by the companies like – Samsung Mobile Display , LG
display, Kodak etc for Smartphones, TV, Digital Cameras, Mp3 Players and Tablets. Currently the
AMOLED is used in the Android smartphones like Samsung Galaxy S II, Nexus S, HTC, Nokia.
Since then AMOLED displays have been used in a number of televisions. Currently sizes are not
as large as those available with LCD or Plasma displays, but in view of the anticipated cost
advantages that are likely to be gained from the use of AMOLED displays, much investment is
being directed towards the development of AMOLEDs.
As such the major application for AMOLEDs is likely to be within televisions and computers,
although the life of the display is currently an issue.
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CHAPTER 6
ADVANTAGES AND DISADVANTAGES
6.1. ADVANTAGES
The different manufacturing process of OLEDs lends itself to several advantages over flat
panel displays made with LCD technology.
Lower cost: OLEDs can be printed onto any suitable substrate by an inkjet printer or
even by screen printing, theoretically making them cheaper to produce than LCD or
plasma displays. However, fabrication of the OLED substrate is more costly than that of
a TFT LCD, until mass production methods lower cost through scalability. Roll-roll
vapor-deposition methods for organic devices do allow mass production of thousands of
devices per minute for minimal cost, although this technique also induces problems in
that multi-layer devices can be challenging to make due to registration issues, lining up the
different printed layers to the required degree of accuracy.
They resist instant pressure, brakeless when fall from certain height.
It uses plastic layer instead of Glass layers.
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High contrast ratio: Higher contrast ratio gives impression for higher
brightness.AMOLED is much transmissive than TFT for sunlight readability.
Fig.6.1. High Contrast Ratio
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AM
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Wider viewing angles & improved brightness :OLEDs can enable a greater
artificial contrast ratio (both dynamic range and static, measured in purely dark
conditions) and viewing angle compared to LCDs because OLED pixels directly emit
light. OLED pixel colours appear correct and unshifted, even as the viewing angle
approaches 90° from normal.
Fig.6.2. Wide Viewing Angle of Amoled
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AM
AM
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Fast Response Time: AMOLEDs can also have a faster response time than standard LCD
screens. Whereas LCD displays are capable of between 2 and 16 ms response time offering
a refresh rate of 60 to 480 Hz, an AMOLED can theoretically have less than 0.01 ms
response time, enabling up to 100,000 Hz refresh rate.
Fig.6.3 Fast Response of Ampled
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AM
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Better power efficiency: LCDs filter the light emitted from a backlight, allowing a
small fraction of light through so they cannot show true black, while an inactive
OLED element does not produce light or consume power.
Fig.6.4.Power efficiency Comparison
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Light weight & flexible: plastic substrates: OLED displays can be fabricated on
flexible plastic substrates leading to the possibility of flexible organic light-emitting
diodes being fabricated or other new applications such as roll-up displays embedded in
fabrics or clothing. As the substrate used can be flexible such as PET, the displays may
be produced inexpensively.
Fig.6.5 Amoled Flexible
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Ultra Thin: It is very slim compared to other display technology.
Fig.6.6. Amoled Slimness
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6.2. DISADVANTAGES
Current costs: OLED manufacture currently requires process steps that make it
extremely expensive. Specifically, it requires the use of Low-Temperature Polysilicon
backplanes; LTPS backplanes in turn require laser annealing from an amorphous silicon start,
so this part of the manufacturing process for AMOLEDs starts with the process costs of
standard LCD, and then adds an expensive, time-consuming process that cannot currently be
used on large-area glass substrates.
Lifespan: The biggest technical problem for OLEDs was the limited lifetime of the
organic materials. In particular, blue OLEDs historically have had a lifetime of around
14,000 hours to half original brightness (five years at 8 hours a day) when used for flat-
panel displays. This is lower than the typical lifetime of LCD, LED or PDP technology—
each currently rated for about 25,000-40,000 hours to half brightness, depending on
manufacturer and model. However, some manufacturers' displays aim to increase the lifespan
of OLED displays, pushing their expected life past that of LCD displays by improving light
out coupling, thus achieving the same brightness at a lower drive current. In 2007,
experimental OLEDs were created which can sustain 400 cd/m2 of luminance for over
198,000 hours for green OLEDs and 62,000 hours for blue OLEDs.
Color balance issues: Additionally, as the OLED material used to produce blue light
degrades significantly more rapidly than the materials that produce other colors; blue light
output will decrease relative to the other colors of light. This variation in the differential color
output will change the color balance of the display and is much more noticeable than a
decrease in overall luminance. This can be partially avoided by adjusting color balance but
this may require advanced control circuits and interaction with the user, which is
unacceptable for some users. In order to delay the problem, manufacturer’s bias the color
balance towards blue so that the display initially has an artificially blue tint, leading to
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complaints of artificial-looking, over-saturated colors. More commonly, though,
manufacturers optimize the size of the R, G and B subpixels to reduce the current density
through the subpixel in order to equalize lifetime at full luminance. For example, a blue
subpixel may be 100% larger than the green subpixel. The red subpixel may be 10% smaller
than the green.
Efficiency of blue OLEDs: Improvements to the efficiency and lifetime of blue OLEDs is
vital to the success of OLEDs as replacements for LCD technology. Considerable research
has been invested in developing blue OLEDs with high external quantum efficiency as well
as a deeper blue color. External quantum efficiency values of 20% and 19% have been
reported for red (625 nm) and green (530 nm) diodes, respectively. However, blue diodes
(430 nm) have only been able to achieve maximum external quantum efficiencies in the
range of 4% to 6%.
Water damage: Water can damage the organic materials of the displays. Therefore,
improved sealing processes are important for practical manufacturing.Water damage may
especially limit the longevity of more flexible displays.
Outdoor performance: As an emissive display technology, OLEDs rely completely upon
converting electricity to light, unlike most LCDs which are to some extent reflective; e-ink
leads the way in efficiency with ~ 33% ambient light reflectivity, enabling the display to be
used without any internal light source. The metallic cathode in OLED acts as a mirror, with
reflectance approaching 80%, leading to poor readability in bright ambient light such as
outdoors. However, with the proper application of a circular polarizer and anti-reflective
coatings, the diffuse reflectance can be reduced to less than 0.1%. With 10,000 fc incident
illumination (typical test condition for simulating outdoor illumination), that yields an
approximate photopic contrast of 5:1.
Power consumption: While an OLED will consume around 40% of the power of an LCD
displaying an image which is primarily black, for the majority of images it will consume 60-
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80% of the power of an LCD: however it can use over three times as much power to display
an image with a white background such as a document or website. This can lead to reduced
real-world battery life in mobile devices when white backgrounds are used.This
disadvantage has led to alternative mobile platform solutions, such as Black Google Mobile,
that provide black background alternatives when otherwise unavailable.
UV sensitivity: OLED displays can be damaged by prolonged exposure to UV light. The
most pronounced example of this can be seen with a near UV laser (such as a Bluray
pointer) and can damage the display almost instantly with more than 20 mW leading to dim
or dead spots where the beam is focused. This is usually avoided by installing a UV
blocking filter over the panel and this can easily be seen as a clear plastic layer on the glass.
Removal of this filter can lead to severe damage and an unusable display after only a few
months of room light exposure.
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CHAPTER 7
FUTURE PERSPECTIVE
Super AMOLED
Super AMOLED is Samsung's term for an AMOLED display with an integrated digitizer,
meaning, the layer that detects touch is integrated into the screen, rather than being overlaid on top
of it. According to Samsung, Super AMOLED reflects 5 times less sunlight compared to the first
generation AMOLED. The display technology itself is not changed.
Super AMOLED Advanced
Super AMOLED Advanced is a term marketed by Motorola to describe a brighter display than
Super AMOLED screens, but also a higher resolution – qHD or 960 × 540 for Super AMOLED
Advanced compared to WVGA or 800 × 480 for Super AMOLED. This display equips
the Motorola Droid RAZR
Super AMOLED Plus
Super AMOLED Plus, first introduced with the Samsung Galaxy S II and Samsung Droid Charge
smartphones, is a branding from Samsung where the PenTile RGBG pixel matrix (2 subpixels)
used in Super AMOLED displays has been replaced with a traditional RGB RGB (3 subpixels)
arrangement typically used in LCD displays. This variant of AMOLED is brighter and therefore
more energy efficient than Super AMOLED displays and produces a sharper, less grainy image
because of the increased number of subpixels. In comparison to AMOLED and Super AMOLED
displays, the Super AMOLED Plus displays are even more energy efficient and brighter.
HD Super AMOLED
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HD Super AMOLED is a branding from Samsung for an HD-resolution (>1280×720) Super
AMOLED display. The first device to use it was the Samsung Galaxy Note. The Galaxy
Nexus and the Galaxy S III both implement the HD Super AMOLED with a PenTile RGBG-
matrix (2 subpixels/pixel) , while the Galaxy Note II uses an RBG matrix (3 subpixels/pixel) but
not in the standard 3 stripe arrangement.
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CHAPTER 8
CONCLUSION
Performance of AMOLEDs depend upon many parameters such as electron and hole
mobility, magnitude of applied field, nature of hole and electron transport layers and excited life-
times. Organic materials are poised as never before to transform the world IF circuit and display
technology. Major electronics firms are betting that the future holds tremendous opportunity for
the low cost and sometimes surprisingly high performance offered by organic electronic and
optoelectronic devices. Organic Light Emitting Diodes are evolving as the next generation of
light sources. Researches are going on, on this subject and it is sure that OLED will emerge as
future solid state light source.
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[2] Kim, Yang Wan; Kwak, Won Kyu; Lee, Jae Yong; Choi, Wong Sik; Lee, Ki Yong; Kim, Sung
Chul; Yoo, Eui Jin (2009). "40 Inch FHD AM-OLED Display with IR Drop Compensation Pixel
Circuit". SID Symposium Digest of Technical Papers 40: 85.
[3] Lin, Chih-Lung; Chen, Yung-Chih. "A Novel LTPS-TFT Pixel Circuit Compensating for TFT
Threshold-Voltage Shift and OLED Degradation for AMOLED". IEEE Electron Device Letters28:
129.
[4] Suyko, Alan. "Oleds Ready For The Mainstream." Electronics News (2009): 20. Associates
Programs Source Plus. Web. 9 Dec. 2011.
[5] Mian Dong; Choi, Y.-S.K; Lin Zhong (July 2009). "Power modeling of graphical user
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