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The technological trends of future AMOLED

Authors:
  • Kangbuk Samsung Hospital, Sunkyunkwan University School of Medicine

Abstract and Figures

The authors review the technological trends for the future AMOLED, especially for unique applications to small- and medium-sized displays as well as large-sized AMOLED TV. The unique characteristics of AMOLED enable paper-thin, foldable, bendable and transparent displays which the other display technology can't easily realize. For large-sized AMOLED TV, TFT backplane, color patterning and encapsulation are the key technological issues and the new technologies should be developed for the mass production of AMOLED TV. The issues and some candidate technologies which can pave the way for mass production of AMOLED TV are also briefly reviewed.
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The Technological Trends of Future AMOLED
Jong hyuk Lee*, Hye Dong Kim, Chang Ho Lee, Hyun-Joong Chung,
Sung Chul Kim, and Sang Soo Kim
Technology Center, Samsung Mobile Display Co., LTD
San#24 Nongseo-Dong, Kiheung-Gu, Yongin-Si, Gyeonggi-Do 446-711, Korea
ABSTRACT
The authors review the technological trends for the future AMOLED, especially for unique applications to small- and
medium-sized displays as well as large-sized AMOLED TV. The unique characteristics of AMOLED enable paper-thin,
foldable, bendable and transparent displays which the other display technology can’t easily realize. For large-sized
AMOLED TV, TFT backplane, color patterning and encapsulation are the key technological issues and the new
technologies should be developed for the mass production of AMOLED TV. The issues and some candidate technologies
which can pave the way for mass production of AMOLED TV are also briefly reviewed.
Keywords: AMOLED, AMOLED TV, Back Plane, Color Patterning, Encapsulation, OLED
1. INTRODUCTION
Since the first commercial product of OLED for car audio display by Pioneer, the evolution of OLED technology has
been accelerated with the increasing demands for better image quality and novel applications. Indeed, AMOLED has
been rapidly expanding its market share for small-sized mobile applications since the launch of mass production in 2007.
The vivid color image, low power consumption and novel design pushed industries dive into the market of AMOLED for
mobile phones and the other potable displays.
In a mass production point of view, small-sized AMOLED almost attained a stage of technological maturity. However, it
still needs some more improvements in power consumption, life time, image sticking and so on. In order to meet those
stringent requirements, new materials with high efficiency and optimization of OLED device structure is necessary.
Apart from applications to mobile phones, AMOLED can open the new area of applications that the other display
devices can’t easily realize. The unique characteristics of AMOLED enable paper-thin, foldable, bendable and
transparent displays.
Since the AMOLED is self-emitting, light emission can be controlled for each pixel at extremely high speed. Therefore,
it is intrinsically possible for AMOLED to express high contrast, blur-less motion features, vivid colors, and wide
viewing angle. Samsung already exhibited 31” [1] and 40” [2] AMOLED TV prototypes in the conferences and
exhibitions and many people sympathize that AMOLED could be an ultimate solution for future TV.
In this article, the technological trends for the AMOLED are reviewed, especially for the unique applications for small-
and medium-sized displays, excluding normal applications to mobile phones or other portable displays. And the authors
also report the technological issues of large-area AMOLED TV, including TFT backplane, color patterning and
encapsulation technologies.
2. THE UNIQUE APPLICATIONS OF AMOLED
Invited Paper
Organic Light Emitting Materials and Devices XIII, edited by Franky So, Chihaya Adachi,
Proc. of SPIE Vol. 7415, 74150O · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.829021
Proc. of SPIE Vol. 7415 74150O-1
2.1 Paper-thin, foldable, flexible AMOLED
For future display technologies, there is significant interest in providing display devices with mechanical flexibility and
transparency. And also, there are continuous requirements for ultra-thin display and extendable or foldable display
without seam line between the two panels.
Different from LCD which, in principle, needs two glass panels, AMOLED needs not upper glass panel if the organic
materials and metal cathode layer in OLED device are protected from environmental water vapors or other gases. The
single glass device gives many unique characteristics to AMOLED. Owing to these characteristics, paper-thin and
bendable card display or foldable display can be realized, as is shown in figure 1.
(a) (b)
Fig. 1. (a) 6.5” flexible and (b) foldable AMOLED display by Samsung.
A number of technology developments are pointing towards flexible display surfaces that can be rolled, like paper.
AMOLED rather than the other displays is considered as optimum solution for that purpose. Many different types of
applications are envisaged such as roll-up displays incorporated into mobile phones, or handheld navigation systems that
provide larger information screens to be carried on the move, and there may also be a considerable market in smart cards
and ticketing.
Paper-thin, foldable, flexible even flapping AMOLEDs can’t easily made by normal way of encapsulation method which
seals two glass panels; instead, thin film encapsulation technology should be employed that protects the organic device
but leaves it thin and flexible. Thin film encapsulation is very powerful solution for obtaining unique characteristics of
AMOLED[3]. Instead of using upper encapsulation glass, TFE employs layer-by-layer deposition of thick films with
compensating diffusion barrier properties. The biggest merit of TFE is that it enables single glass display, which makes
extremely slim and flexible panels possible. The challenges for TFE include material optimization, minimization of
stacking layers, and applicability for large size mother glasses. Figure 2 shows a new and promising application of
electronic passport which AMOLED is included in the passport and credit card, Electronic passport, which
Bundesdruckerei and Samsung co-developed, has been displayed in the Cebit 09 and drew much attention by the public.
2.2 Transparent AMOLED
If you've seen the movie "Minority Report" and amazed with the transparent display controlled by Tom Cruise, you can
expect to see transparent OLED pixels sooner or later. Transparent OLED is divided into two types of both-direction
emitting type and see-though type. Both direction emitting type of transparent OLEDs have only transparent components
(substrate, cathode and anode) and, when turned off, are up to 85 percent as transparent as their substrate and electrode.
When a transparent OLED display is turned on, it allows light to pass in both directions. Most approach for this type of
transparent OLED is to use transparent TFTs (thin-film transistors) made of a 100-nanometer-thick layer of zinc-tin-
oxide, which transmits more than 90 percent of visible light.
Proc. of SPIE Vol. 7415 74150O-2
(a) (b)
Fig. 2. (a) Electronic passport and (b) credit card display
A see-through type of transparent OLED display can be either active or passive-matrix. See-through type of transparent
OLED composes of small area emitting part and see-through part like window. Top-emitting OLEDs region have a
substrate that is either opaque or reflective. They are best suited to active-matrix design. In this type, the TFTs and the
OLED pixels are positioned next to each other. The OLED pixel can be placed on top of the TFT driver circuit without
interference. Samsung showcased the "Window Display," an OLED panel with a transparent of 30%. Samsung used four
12.1-inch Window Displays to make a "window". The resolution of the panel is 840×504, and its luminance is 200cd/m
2
.
The color reproduction range is 100% of the NTSC standard. The response time is 0.01ms. Samsung 12.1 inch qFHD
transparent display is shown in figure 3.
Fig. 3. Samsung 12.1 inch qFHD transparent display at SID 2009.
In most transparent OLED, transparent ITO anode and semi-transparent metal cathode such as Mg:Ag are used with
good hole and electron injection properties. However, resistance and transparence of Mg:Ag semi-transparent metal
cathode is not enough to be applied to the Transparent OLEDs. Recently, many efforts have been made to use indium tin
oxide (ITO) and zinc oxide (ZnO) doped with impurities as transparent cathode by sputter deposition method [4-7].
However, it has already reported that the high sputtering power and their high work function led to failures of transparent
Proc. of SPIE Vol. 7415 74150O-3
OLEDs [8]. It is sure that novel transparent cathode material with low resistance, high transparency and no drawbacks on
the device stability should be developed for the better transparent display with enough transparency and image quality.
3. TECHNOLOGICAL ISSUES FOR LARGE-SIZED AMOLED
The basic and the most important feature of TV is the ability to reproduce real image. With the launch of high-definition
digital broadcasting, spectators can now feel the vivid presence from the large flat-panel TV screen. Therefore, the
perceptual image quality becomes more important than the simple measures such as contrast, luminance, and color
gamut. Since the AMOLED is self-emitting, light emission can be controlled for each pixel at extremely high speed.
Therefore, it is intrinsically possible for AMOLED to express high contrast, blur-less motion features, vivid colors, and
wide viewing angle. In that sense, many people sympathize that AMOLED could be an ultimate solution for future TV.
Figure 4 shows world largest 40” AMOLED TV by Samsung.
However, there should be some technological progresses for the mass production, although the prototypes of AMOLED
TVs have been displayed in many conferences and exhibitions. In the following sections, the key technological issues of
TFT back plane, color patterning, encapsulation and materials for the large-sized AMOLED will be discussed.
Fig. 4. World largest 40” AMOLED TV by Samsung.
3.1 Technological issue of backplane
Low temperature poly-Si (LTPS) TFTs fabricated by ELA is currently employed in the mass production of AMOLEDs
owing to their excellent TFT performance and device stability. For large area applications, however, uniformity and
scalability issues challenge its application. Moreover, ELA-based LTPS TFT requires large number of masks (8~11)
compared to that of LCD (4). Amorphous oxide TFTs can be an attractive solution to the scaling up issue. Basically,
oxide TFTs can combine the merits of a-Si and LTPS TFTs [9]; good uniformity, large carrier mobility (~10 cm
2
/V.sec),
excellent subthreshold gate swing (down to 0.20 V/dec) and simple sputtering process at low temperature. However,
device instability problem should be solved to use oxide TFTs for AMOLEDs. Therefore, proper passivation material
and production process are required to oxide TFT fabrication. Figure 5 shows oxide TFT-based AMOLED display for
note PC.
Proc. of SPIE Vol. 7415 74150O-4
Fig. 5. Samsung 12.1” WXGA oxide TFT-based AMOLED display for note PC.
3.2 Technological issue of OLED patterning
Shadow mask technology, also known as fine metal mask (FMM), is currently employed in the mass production of
AMOLEDs. However, the FMM are prone to confront sagging problems when applied to large-size mother glass
because the masks are made by too thin metal films (50μm thick) to sustain large area. In addition, FMM has other
issues such as pixel size variation by ±10μm, shadow effect by the metal thickness, and alignment accuracy between the
mask and substrate. Therefore, it is considered that direct printing methods, such as ink-jet and nozzle printing, are the
most effective for large-size AMOLED because they exploit the complete use of OLED materials. In comparison with
evaporation-based materials, however, soluble materials for AMOLED have a serious disadvantage – short lifetime.
Therefore, development of good soluble OLED materials with good stability and surface uniformity is the biggest
challenge for printing techniques.
3.3 Technological issue of encapsulation
For small-sized AMOLED devices, edge sealing encapsulation with inorganic frit material which is locally heated with
laser is enough to fabricate reliable panels. However, for large devices, edge sealing with the frit has serious problems
such as mechanical strength under external stress. In order to prevent those drawbacks, new techniques such as filling the
gap between two glasses are currently under development. The challenges for these techniques include the development
of liquid filler material and filler-injecting technology. And also thin film encapsulation (TFE) can also be another
interesting solution which enables single glass display.
4. CONCLUSION
In this article, the authors have shown the unique advantages of AMOLED and technological issues for large-sized
AMOLED. The unique characteristics of AMOLED can open the new area of applications for paper-thin, foldable,
bendable and transparent displays. For the large-sized AMOLED TV, new technologies and materials for TFT backplane,
color patterning and encapsulation should be developed for the mass production in the near future.
Proc. of SPIE Vol. 7415 74150O-5
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Proc. of SPIE Vol. 7415 74150O-6
... As a result, the smartphones, hybrid notebooks and tablets are selling leaders of technological devices. Some of such devices do not demonstrate the flexibility, nevertheless are defined as active matrix light emitting diode (AMOLED) confirming the presence of organic materials on industry [10] . As a result, the organic transistors will be able to manufacture the flexible components. ...
Thesis
Full-text available
The universal and simple approach for region-selective deposition of variable metal oxide core-shell nanomaterials (NMs) as a layer-by-layer assembly is demonstrated within this research work. The aluminium oxide (AlOx) nanoparticles (NPs), iron(III) oxide (Fe2O3) NPs, titanium dioxide (TiO2) NPs and nanorods (NRs) are functionalized by 6-phosphonohexanoic acid (PHA) and aminomethylphosphonic acid (AMPA) molecules resulting into metal oxide inorganic-organic core-shell NMs. Additionally, the substrate is pre-patterned with self-assembled monolayer (SAM) based on AMPA and semi-fluorinated phosphonic acid (PA) molecules representing the primary amine (R-NH2) and non-polar semi-fluorinated terminated groups respectively. As a result, the deposition of functional core-shell NMs is alternatively performed with controlled multilayer thickness, precise region-selectivity and full order control of each layer on pre-patterned substrate surface. The stacking of NMs layer-by-layer between themselves on pre-patterned AMPA SAM substrate surface is performed with resulted secondary amide binding (SAB) from covalently reacted -NH2 and -COOH terminated groups available on substrate (R-NH2) and functionalized NMs (R-COOH and R-NH2) respectively. In order to form SAB, the chemical reaction is supported by amide coupling agents. Afterwards, the semi-fluorinated PA is used to prevent the undesired adsorption of NMs on substrate after deposition on AMPA SAM. As a result, the defined pattern of NMs is created in μm scale. The controlled deposition of functional AlOx NPs as a 1st core-shell layer is successfully expanded into three-dimensional nanostructure. This nanostructure is composed of multiple-assembling of functional TiO2 NRs and alternatively Fe2O3 NPs as a 2nd core-shell layer. The functional TiO2 NPs as a 3rd core-shell layer are applied. The termination of nanostructural fabrication is achieved by functionalization of latter deposited core-shell TiO2 NPs by 1-aminopyrene molecules resulting into inorganic-organic hybrid formation. The UV-light excitation of manufactured nanostructure under 365 nm demonstrates region-selective fluorescence emission. The deposition is characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and total internal reflection fluorescence microscope (TIRFM). The significant versatility of stacked metal oxide core-shell NMs via amide coupling method represents the excellent and efficient applicability in manufacture of hybrid inorganic-organic nanostructure with favorable photo-thermal-electrical-mechanical properties for organic electronic fields.
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Fully encapsulated passive matrix, video rate, phosphorescent OLED displays on flexible plastic substrates using a multilayer barrier encapsulation technology are described. The flexible OLED (FOLED™) displays are based on highly efficient electrophosphorescent OLED (PHOLED™) technology deposited on barrier coated plastic film (Flexible Glass™ substrate) and are hermetically sealed with an optically transmissive multilayer barrier coating (Barix™ Encapsulation). Preliminary lifetime to half initial luminance (Lo∼100 cd/m2) of order 200 h is achieved on the encapsulated 80 dpi displays using a passive matrix drive at room temperature; 2500 h lifetime is achieved on a dc tested encapsulated 5 mm2 FOLED test pixel. The encapsulated displays are flexed 1000 times around a 1″ diameter cylinder and show minimal damage.
Article
We report the demonstration of transparent organic light emitting devices (OLEDs) which are ∼70% transparent throughout the visible spectrum when switched off, and emit light from both sides with a total external quantum efficiency of ∼0.1% when turned on. The devices are Alq3‐based single heterostructure OLEDs grown on an ITO‐coated glass substrate with a top electrode composed of a very thin layer of Mg–Ag and an overlaying ITO film. The top electrode is both electron injecting and transparent. The transparent OLEDs are expected to be useful in high‐resolution full‐color displays, as well as for helmet‐mounted, windshield‐mounted, or other ‘‘head‐up’’ display applications. © 1996 American Institute of Physics.
  • T C Gorjanc
  • D Leong
  • C Py
  • D Roth
T. C. Gorjanc, D. Leong, C. Py, D. Roth, Thin Solid Film 181, 413 (2002)
  • M Ohyama
  • H Kozuka
  • T Yoko
M. Ohyama, H. Kozuka, T. Yoko, Thin Solid Films 78, 306 (1997)
  • R Martins
  • P Barquinha
  • I Ferreira
  • L Pereira
  • G Goncalves
  • E Fortunato
R. Martins, P. Barquinha, I. Ferreira, L. Pereira, G. Goncalves, E. Fortunato, J. Appl. Phys. 044505, 101 (2007)
  • A B Chwang
  • M A Rothman
  • S Y Mao
  • R H Hewitt
  • M S Weaver
  • J A Silvernail
  • M Rajan
  • J J Hack
  • X Brown
  • L Chu
  • T Moro
  • N Krajewski
  • Rutherford
A.B. Chwang, M.A. Rothman, S.Y. Mao, R.H. Hewitt, M.S. Weaver, J.A. Silvernail, K Rajan, M. Hack, J.J. Brown, X. Chu, L. Moro, T. Krajewski, and N. Rutherford, Symposium Digest Tech Papers 34, 868-871 (2003).
  • M Chung
  • B S Kim
  • J.-S Gu
  • Y.-G Park
  • H D Mo
  • H K Kim
  • Chung
Chung, M. Kim, B. S. Gu, J.-S. Park, Y.-G. Mo, H. D. Kim, and H. K. Chung, SID Symposium Digest Tech Papers 39, 1-4 (2008).
  • T Yamada
  • A Miyake
  • S Kishimoto
  • H Makino
  • N Naoki
  • T Yamamoto
T. Yamada, A. Miyake, S. Kishimoto, H. Makino, N. Naoki, T. Yamamoto, Appl. Phys. Lett. 051915, 91 (2007)