Journal of the

A preview of the papers appearing in the February 2007 issue of theJournal of the SID. To obtain access to these articles on-line, please go to

Edited by Aris Silzars

Flat-plate encapsulation solution for OLED displays using a printed getter

Janine Buseman-Williams
Kyle D. Frischknecht
Matt D. Hubert
Ameen K. Saafir
James D. Tremel

DuPont Displays, U.S.A.

Abstract — The encapsulation of organic light-emitting layers is a key development item on the roadmap to OLED commercialization and needs to be resolved in order to compete with the incumbent LCD technology. DuPont Drylox cover glass is a product developed by DuPont Displays to improve the features of the OLED encapsulation solution. Thin displays, low design cycle time, and substantial reduction in encapsulation cost are the driving forces for the product improvement. The permeation theory will be discussed, a manufacturing method will be described, and the performance characteristics achieved to date will be documented.

One major difference between the packaging and encapsulation of LCDs and OLEDs is the need to encapsulate OLEDs with a desiccant in order to prevent the degradation of the light-emitting stack from the ingression of moisture and oxygen. Because of the desiccant requirement, OLED cover glass must have its cavities machined (etched or sandblasted) to house the desiccant and prevent incidental contact with the active area of the display. The cavity along with the physical desiccant accounted for approximately 10–20% of the OLED-display cost on the pilot line using 1.1-mm soda-lime cavity glass and zeolite tablets. DuPont Displays, Inc. (DDI) developed Dry-lox cover glass to lower the cost of encapsulation without sacrificing display performance or cycle time.


FIGURE 7 — Typical encapsulation flow for Drylox cover glass.

PECVD-based nanocrystalline-silicon TFT backplanes for large-sized AMOLED displays

Kunal S Girotra
Yong-Mo Choi
Byoung-June Kim
Young-Rok Song
Beomrak Choi
Sung-Hoon Yang
Shiyul Kim
Soonkwon Lim

Samsung Electronics Co., Ltd.

Abstract — A 14.1-in. AMOLED display using nanocrystalline silicon (nc-Si) TFTs has been developed. Nanocrystalline silicon was deposited using conventional 13.56-MHz plasma-enhanced chemical vapor deposition (PECVD). Detailed thin-film characterization of nc-Si films was followed by development of nc-Si TFTs, which demonstrate a field-effect mobility of about 0.6–1.0 cm2/V-sec. The nc-Si TFTs show no significant shift in threshold voltage when over 700 hours of constant current stress is applied, indicating a stable TFT backplane. The nc-Si TFTs were successfully integrated into a 14.1-in. AMOLED display. The display shows no significant current decrease in the driving TFT of the 2T-1cap circuit because the TFTs are highly stable. In addition to the improved lifetime of AMOLED displays, the development of nc-Si TFTs using a conventional 13.56-MHz PECVD system offers considerable cost advantages over other laser and non-laser polysilicon-TFT technologies for large-sized AMOLEDs.

The fabricated nc-Si TFT had a conventional bottom-gate TFT structure with a three-layered structure of silicon nitride (SiNx)/nc-Si/n+Si. The gate and source/drain metal layers were Al/Mo and Mo/Al/Mo, respectively, with IZO as the pixel material. A standard TFT process with a five-mask-step photolithography process similar to that for TFTs in AMLCDs was used. Figure 4 describes a standard bottom-gate nc-Si TFT structure.


FIGURE 4 — Cross section of bottom-gate nc-Si TFTs. The structure is the same as that used for a-Si TFTs except for the active silicon layer being replaced by nanocrystalline silicon.

Pixel-isolated liquid-crystal mode by using a patterned anisotropic phase separation for flexible LCDs

Se-Jin Jang 
Jong-Wook Jung
Hak-Rin Kim
Min Young Jin
You-Jin Lee
Jae-Hoon Kim

Hanyang University

Abstract — A pixel-isolated liquid-crystal (PILC) mode for enhancing the mechanical stability of flexible-display applications is proposed. Because liquid-crystal (LC) molecules in this mode are isolated in each pixel by patterned or phase-separated microstructures, and the two substrates are tightly attached to each other by a solidified polymer layer, the LC alignment is stable against external pressure, and the cell gap of our structure is uniformly preserved against bending deformation of the plastic substrates. The mechanical stability of the PILC structure having plastic substrates was tested for its electro-optic properties.


FIGURE 11 — A 3-in. plastic LCD sample in the PILC mode.


FIGURE 1 — Schematic diagram of a PILC structure made by patterned microstructures.

Color displays and flexible displays using quick-response liquid-powder technology for electronic paper

Ryo Sakurai
Shingo Ohno
Shin-ichi Kita
Yoshitomo Masuda
Reiji Hattori

Bridgestone Corp.

Abstract — Color displays and flexible displays that use electronic liquid powder have been developed. Novel types of color displays using either a colored powder or a color filter are discussed. A flexible display with low-cost substrate films with a high-throughput roll-to-roll manufacturing method has also been developed. These technologies enable a QR-LPD to be widely used as an electronic-paper display.

The structure of a QR-LPD is very simple, and it does not require additional optical films (e.g., optical filters, polarizers, or backlight) and TFT arrays. In this work, low-cost PET-based film was applied to a QR-LCD, indium zinc oxide (IZO) and metal electrodes were patterned into stripes, and ribs were placed on the upper substrate. Metal-coated PET films are inexpensive and the flexibility of electrodes made with these films is outstanding, and ACF bonding reliability is good. Although it is only for one side of the electrode, it is fruitful for those reasons.


FIGURE 11 — PET-based flexible QR-LPD (576 x 384 pixels, 81 ppi).

Novel WV film for wide-viewing-angle TN-mode LCDs

Tokuju Oikawa
Shoji Yasuda
Kazuhiko Takeuchi
Eiichi Sakai
Hiroyuki Mori


Abstract — A new optical compensation film refered to as WV-EA film for TN-mode TFT-LCDs has been developed, resulting in higher contrast ratio, wider-viewing-angle characteristics, and improved color shift than their predecessors, especially in the horizontal direction. These features of the new WV film were achieved as a result of haze reduction and optimizing the optical characteristics of the polymerized discotic material layer and TAC film. These features are suitable for large-sized and wide-aspect-ratio LCD monitors and TVs.

A pair of WV film consists of TAC film and a hybrid alignment structure composed of a polymerized discotic material layer. The polymerized discotic material layer is refered to as a "PDM" layer in this paper. It is designed that TAC film and the PDM layer totally compensates the on-state TN-LC layer. The TN LC layer in the on-state has a complicated alignment structure because the direction of the director continuously changes in the thickness direction. This structure cannot be expressed by a single-index ellipsoid. The WV film corresponds to the alignment structure of the on-state TN-LC layer. And, thus, the WV film three dimensionally compensates for it. This compensation con-figuration minimizes light leakage at all incident angles.


FIGURE 10 — Comparison of image quality at an oblique angle. (a) Attached WV-SA. (b) Attached newly developed WV film WV-EA.

An IPS-LCD with a high contrast ratio of over 80:1 at all viewing angles

D. Kajita
I. Hiyama
Y. Utsumi
K. Miyazaki
M. Hasegawa
M. Ishii

Hitachi, Ltd.

Abstract — A 32-in. IPS-LCD with a significantly wide-viewing-angle performance has been developed using a new optical compensation method. It provides a contrast ratio of over 80:1 at all viewing angles, which enhances its color saturation at oblique angles. According to this study, it is important to shorten the path of the optical compensation in the Poincaré sphere. An effective method using two retardation films, one with an Nz value larger than 0.5 and one with a value smaller than 0.5, was found.

In-plane-switching (IPS) LCDs have good viewing-angle performance with bright images. For such images, they are suitable for standard uses. However, it has been pointed out that further improvement is needed for dark image quality at oblique angles. The issues are the light leakage and the color shift in the black state. To solve these issues, several good optical compensation methods have been proposed. However, it is hard to develop these methods because suitable retardation films are expensive or hard to be manufacture. Our studies have focused on the new optical compensation method that has a large selection of retardation films and a viewing-angle performance better than that of our previous optical compensation method


FIGURE 12 — Comparison of the actual dark image quality at oblique angles between (a) IPS-Pro with the conventional optical compensation technology and (b) IPS-Pro with the new optical compensation technology.

A new pixel design and a novel driving scheme for multi-domain vertically aligned LCDs

Po-Sheng Shih
Wei-Hsin Wang
Hsuan-Lin Pan
Kei-Hsiung Yang

HannStar Display Corp.

Abstract — By using a new pixel design and a novel driving scheme that adds a bias electrode and a bias TFT to the ordinary pixel structure, a high-contrast-ratio and wide-viewing-angle LCD mode, refered to as the biased vertical-alignment (BVA) mode, has been sucessfully developed. Compared to the published data on the PVA and MVA modes, the BVA mode has a distinct advantage of lower manufacturing cost due to the elimination of a lithographic process step that forms either ITO cuts or protrusions on the color-filter substrates. The BVA mode requires ITO cuts on the TFT substrate similar to that for the PVA and MVA modes. The 15-in. BVA-mode XGA prototype exhibits a high contrast ratio of 1200:1 and high cell transmittance of 4.3%.

A 15-in. XGA TFT-LCD panel using BVA-mode technology has been developed. A photograph of a pixel is shown in Fig. 9. It is clear that the disclination line due to an insufficient bias voltage is not observed, confirming the validity of BVA mode. The viewing angle (CR > 10) is over 160°. The ON/OFF response time is about 20 msec, on the same order as that for the MVA or PVA modes. The ON and OFF voltages are 6.2 and 1.3 V, respectively, during the measurement.


FIGURE 9 — The magnified image of BVA-mode pixels taken by an optical microscope.

Value-added integration of functions for silicon-on-glass (SOG) based on LTPS technologies

Tohru Nishibe
Hiroki Nakamura

Toshiba Matsushita DisplayTechnology Co., Ltd.

Abstract — Low-temperature polycrystalline-silicon (LTPS) TFT-LCDs are on their way to becoming advanced displays, which will lead to the use of system-on-glass (SOG) technology. Improvement in poly-Si TFT performance is essential in order for them to become value-added displays, where circuits for various functions are integrated onto the substrate. In this paper, the key processes of the applications for future displays will be described, including the recent development of SOG.

SOG technology has the potential of integrating the input function as well as the output function of a display, which will pave the way for advanced future displays. A key device for functional integration is a poly-Si photosensor system which can be applied to almost all possible applications, and it is desirable that the photosensor has a common manufacturing process with the conventional TFT array. The reason why we selected the photosensor system is that it has advantages over competitive systems such as a pressure sensor system or a capacitive sensor system.


FIGURE 14 — New concept of light-pen input. We can write freely and directly on the panel; for example, sending a message "Daddy, come back home early!!"

GaN-based high-output-power blue laser diodes for display applications

Takashi Miyoshi
Tokuya Kozaki
Tomoya Yanamoto
Yasushi Fujimura
Shin-ichi Nagahama
Takashi Mukai

Nichia Corp.

Abstract — High-output-power blue (445 nm) laser diodes (LDs) with an output power of 500 mW have been successfully fabricated. The operating current, voltage, and wall-plug efficiency of these LDs were 480 mA, 4.8 V, and 21.7%, respectively. The lifetime of these LDs was estimated to be 10,000 hours under continuous-wave operation at 25°C. From examination of the degradation mode, it was found that the operating current seriously affects the lifetime of LDs. In the next stage, the optimization and sophistication of the manufacturing processes to fabricate longer-lifetime (>30,000 hours) blue LDs will be focused on.

Full-color display systems using laser light sources are attracting attention for wide-color-gamut applications. In three-primary-color systems, red and green high-power laser light sources are realized by using AlInGaP LDs and second-harmonic-generation (SHG) lasers, respectively. On the other hand, in the blue region, we have proposed GaN-based blue LDs with an emission wavelength of 445 nm and output power of 200 mW. However, higher-output-power blue LDs are required because the display screen size is becoming larger and larger. Consequently, our next goal is to fabricate LDs with a higher output power of more than 200 mW.


FIGURE 1 — Schematic diagram of blue LDs.

Highly conductive SnO2 thin films for flat-panel displays

Takamitsu Isono
Takeshi Fukuda
Kouji Nakagawa
Reo Usui
Ryohei Satoh
Eiji Morinaga
Yu Mihara

Matsushita Electric Industrial Co., Ltd.

Abstract — SnO2 is considered to be a promising alternative material for indium tin oxide (ITO), which is used for thin-film transparent electrodes in flat-panel displays (FPDs) and is facing a serious indium-depletion problem. However, annealing processes in the manufacture of plasma-display panels (PDPs), which are major FPDs, cause high resistivity in SnO2 films. To obtain lower resistivity after the annealing processes, the relationship between deposition conditions and resistivity and the influences of annealing on resistivity, both theoretically and experimentally, were investigated. As a solution, a method involving the formation of a coating of SiO2 on SnO2 is proposed, and a SnO2 resistivity as low as 6.60 x 10–5 Ω-m was obtained after annealing.

SnO2 and ZnO are expected to be alternative materials to ITO. SnO2, in particular, is an abundant natural material and is low in cost. SnO2 is also more stable against thermal and chemical processes than either ITO or ZnO. However, practical application of SnO2 is facing problems such as difficulty in a wet-etching process and generally higher resistivity (1 x 10–4 Ω-m1) compared to ITO. Furthermore, high resistivity after annealing (at up to 873K) is a serious problem in the achievement of high-cost-performance FPDs


FIGURE 1 — Depletion times of indium. (Current scenario: for the case of only further zinc mining; Scenario I: for the case of both further zinc mining and recycling; Scenario II: for the case of reduction of contained amount and utilization of alternative materials, in addition to Scenario I).