Super‐large‐sized TFT‐LCD (55 in.) for HDTV application

Abstract— We have developed the world's largest TFT‐LCD, which has a 55‐in.‐diagonal size. This LCD features a 1920 × 1080 (16:9) resolution for full‐HDTV images, 500‐nit luminance, 72% color gamut, and 12‐msec response time at all gray levels. The size of the panel (55 in.) was determined by the maximum efficiency of our fifth‐generation line (glass size: 1100 × 1250 mm). To overcome the limitation of size in photolithography equipment, a new stitcking‐free technology was applied in both the TFT and color‐filter side. And the super‐IPS mode was used as a wide‐viewing‐angle technology because it is suitable in the fabrication of large panels. In this paper, we present issues on both the fabrication and characteristics of the 55‐in. TFT‐LCD.     

New era for TFT‐LCD size and viewing‐angle performance

Abstract— Samsung has announced the development of a full‐high‐definition (1920 × 1080) 82‐in. TFT‐LCD panel using Super‐PVA (S‐PVA) technology, the world's largest TFT‐LCD. In addition to the size breakthrough, this product achieves 600 nits of brightness, a contrast ratio of over 1200:1, an angle of view of 180°, a color gamut of 92%, and an 8‐msec response time. Several key enabling technologies were developed to achieve these specifications, including two‐transistor direct‐driven independently controlled S‐PVA subpixels, non‐even‐area‐ratio subpixels for optimal off‐axis gamma, gate overlap driving for larger driving margin, new CCFL technology for higher color gamut, and advanced fabrication techniques including the use of Samsung's new Gen 7 line. Many of these technologies will be applied to other products within Samsung's LCD‐TV product line. Samsung's broader development efforts toward the overall LCD‐TV market, including production status of the Gen 7 facility, will be updated.     

Development of “Advanced TFT‐LCD” with good legibility under any ambient light intensity

A new LCD referred to as an “Advanced TFT‐LCD” has been developed. It consists of both transmissive and reflective electrodes in every pixel. Its subjective legibility and characteristics, such as contrast ratio, color gamut, and luminance, have been investigated at several ambient illumination intensities. As a result, it was confirmed that Advanced TFT‐LCDs offer better legibility than transmissive LCDs under any ambient illumination intensity.     

New approaches to process simplification for large‐area high‐resolution TFT‐LCDs

Abstract— Novel process architectures are proposed for fabricating large‐area high‐resolution TFT‐LCDs with a minimal number of process steps. A low contact resistance between Al bus lines and the transparent conductive oxide layer, necessary for large‐area panels, is obtained by inducing a self‐formed inter‐metallic compound layer at the interface without using any additional buffer or capping layers. For enhanced brightness and resolution, a new TFT array structure integrated on a color‐filter substrate, referred to as an Array on Color Filter (AOC) structure, has been developed. Good‐quality TFTs were successfully constructed on the newly developed color filter for AOC within a sufficiently wide process margin. By adopting these novel technologies, a 15.0‐in. XGA prototype panel was fabricated and shows good display performance. Thus, these novel technologies have improved cost efficiency and productivity for TFT‐LCD manufacturing, and can be applied to the development of TFT‐LCDs of extended display area and enhanced resolution, benefiting from the low resistance bus lines, the high aperture ratio, and reduction in total process steps.     

LED‐backlight feedback control system with integrated amorphous‐silicon color sensor on an LCD panel

Abstract— Thin‐film‐transistor liquid‐crystal displays (TFT‐LCDs) have the largest market share of all digital flat‐panel displays. An LCD backlighting system employing a three‐color red‐green‐blue light‐emitting diode (RGB‐LED) array is very attractive, considering its wide color gamut, tunable white point, high dimming ratio, long lifetime, and environmental compatibility. But the high‐intensity LED has problems with thermal stability and degradation of brightness over time. Color and white luminance levels are not stable over a wide range of temperature due to inherent long‐term aging characteristics. In order to minimize color point and brightness differences over time, optical feedback control is the key technology for any LED‐backlight system. In this paper, the feasibility of an optical color‐sensing feedback system for an LED backlight by integrating the amorphous‐silicon (a‐Si) color sensor onto the LCD panel will be presented. To minimize the photoconductivity degradation of a‐Si, a new laser exposure treatment has been applied. The integrated color‐sensor optical‐feedback‐controlled LED‐backlight system minimized the color variation to less than 0.008 Δu'v' (CIE1976) compared to 0.025 for an open‐loop system over the temperature range of 42–76°C.     

Energy‐efficient liquid‐crystal displays (e2‐LCDs) using a photonic‐crystal backlight system

Abstract— Cholesteric liquid crystals automatically form one‐dimensional photonic crystals. For a photonic crystal in which light‐emitting moieties are embedded, unique properties such as microcavity effects and simultaneous light emission and light reflection can be expected. Three primary‐color photonic‐crystal films were prepared based on cholesteric liquid crystal in which fluorescent dye is incorporated. Microcavity effects, i.e., emission enhancement and spectrum narrowing, were observed. Two types of demonstration liquid‐crystal displays (LCDs) were fabricated using the prepared photonic‐crystal films in a backlight system. One is an area‐color LCD in which a single photonic‐crystal layer is used for each color pixel and the other is a full‐color TFT‐LCD in which three stacked photonic‐crystal layers are used as light‐conversion layers. The area‐color LCD was excited by using 365‐nm UV light, and the full‐color TFT‐LCD was excited by using 470‐nm blue LED light. Because of the photonic crystal's unique features that allow it to work as light‐emitting and light‐reflecting layers simultaneously, both LCDs demonstrate clear readable images even under strong ambient light, such as direct‐sunlight conditions, under which conventional displays including LCDs and OLED displays cannot demonstrate clear images. In particular, an area‐color LCD, which eliminated color filters, gives clear images under bright ambient light conditions even without backlight illumination. This fact suggests that a backlight system using novel photonic‐crystal layers will be suitable for energy‐efficient LCDs (e²‐LCDs), especially for displays designed for outdoor usage.     

Wide gamut LCD using locally dimmable four‐primary‐color LED backlight

This paper proposes a wide gamut LCD using locally dimmable four‐primary‐color (4PC) LED backlight. Although the color gamut of LCDs has been improved in recent years, it is insufficient to reproduce all the colors in the real world. The objective of this paper is to propose a wide gamut LCD that reproduces all the colors in the real world while keeping the cost increases to a minimum. We evaluated the color gamut reproduced by LEDs of multiple primary colors and selected cyan as the optimal color to be added to the three primary colors to reproduce all the colors in the real world. Therefore, we designed an LED backlight consisting of an additional only‐cyan LED with three‐primary‐color LEDs and developed a prototype LCD with 4PC LED backlight. Furthermore, we developed a local dimming algorithm for the 4PC LED backlight. As a result, we confirmed that the prototype LCD with the 4PC LED backlight is able to cover almost all the colors in the real world and also able to display natural images with highly saturated colors by local dimming.     

Evaluation of single‐, pre‐emphasis,and dual‐driving methods in large‐sized TFT‐LCDs

Abstract— As the panel size and the frame frequency of TFT‐LCDs increases, driving issues become much more important for larger‐sized and higher‐resolution TFT‐LCDs. In our previous paper, the pre‐emphasis driving method was proposed to shorten the driving time of the data line with heavy loads of the large‐sized TFT‐LCDs. This paper proposes a simulation model based on the evaluation results of the developed pre‐emphasis source driver, and the issues of driving the data line with heavy loads are reviewed. The single‐, pre‐emphasis, and dual‐driving methods are compared in terms of their driving time and power consumption for large‐sized TFT‐LCDs with various resistances and capacitances of the data lines. At a panel load of 250‐pF capacitance and 15‐kΩ resistance in full‐HD resolution, the pre‐emphasis driving can reduce the pixel driving time to 66% with a 54% increase in the analog power consumption.     

A novel pixel memory using integrated voltage‐loss‐compensation (VLC) circuit for ultra‐low‐power TFT‐LCDs

Abstract— A novel pixel memory using an integrated voltage‐loss‐compensation (VLC) circuit has been proposed for ultra‐low‐power TFT‐LCDs, which can increase the number of gray‐scale levels for a single subpixel using an analog voltage gray‐scale technique. The new pixel with a VLC circuit is integrated under a small reflective electrode in a high‐transmissive aperture‐ratio (39%) 3.17‐in. HVGA transflective panel by using a standard low‐temperature‐polysilicon process based on 1.5‐μm rules. No additional process steps are required. The VLC circuit in each pixel enables simultaneous refresh with a very small change in voltage, resulting in a two‐orders‐of‐magnitude reduction in circuit power for a 64‐color image display. The advanced transflective TFT‐LCD using the newly proposed pixel can display high‐quality multi‐color images anytime and anywhere, due to its low power consumption and good outdoor readability.     

Preferred balance between luminance and color gamut in mobile displays

Abstract— To improve the image quality of a mobile display, the balance between color‐gamut size and luminance was studied in two subjective experiments. The first experiment was performed during the Asian Society for Information Display (ASID) conference in Nanjing, February 2004. Nearly 600 participants ranked the quality of images displayed for fixed combinations of color‐gamut size and display luminance on small color supertwisted nematic (CSTN) and thin‐film transistor (TFT) twistednematic (TN) displays. In the second experiment, a broader range of color‐gamut sizes and luminance levels were simulated on a cathode‐ray tube (CRT) display, and 20 participants were asked to score perceived image quality. The results of these experiments were used to model image quality as a function of color‐gamut size and display luminance for images differing in the level of chromaticity of their content. This model can be used to estimate the increase in luminance required to compensate for a reduction in color‐gamut size.     

Narrow‐gap field‐sequential TN‐LCD with and without nanoparticle doping

Abstract— The fabrication and demonstration of field‐sequential‐color (FSC) LCDs using modules of narrow‐gap twisted‐nematic (NTN) LCDs with and without doping of newly synthesized PγCyD‐ZrO² nanoparticles is reported. Two types of FSC‐LCDs are demonstrated: one is a direct multiplexed NTN‐LCD and the other is TFT driven. The advantages of FSC‐LCDs include their high legibility even under direct sunlight, and the mechanism for the doping of nanoparticles in LCDs is discussed.     

A dual‐gap RGBW transflective TFT‐LCD with adjustable color gamut

Abstract— An adjustable‐color‐gamut dual‐gap RGBW transflective liquid‐crystal display that uses a four‐color manufacturing process and a color‐processing algorithm to achieve the appropriate color performance in both the transmissive and reflective modes is presented. Based on superior‐color‐transformation units, the total brightness and color gamut can be modified under different ambience. The highest NTSC color gamut in the reflective mode (reflectance, 4.4%) that has been fabricated successfully for a RGBW 1.5‐in. dual‐gap panel is 23% with a 7%, 17%, and 40% NTSC color gamut in the transmissive mode by using different algorithms. Compared to a typical RGB panel, it not only provides flexibility for any environment but also satisfies a variety of personal requirements. Based on personal preference, users have more choices to adjust the LCD settings such as color saturation, brightness, etc. The smart RGBW TRLCD will definitely become the developing trend towards sunlight‐readable LCDs in the near future.     

Current manufacturing technologies for TFT‐LCDs

Abstract— TFT‐LCD panels for notebook‐PC applications requires a thin and light form factor, low power consumption, and good display quality, whereas the desktop monitor has different requirements such as large panel size, wide viewing angle, high resolution, brightness, etc. However, for the fifth‐generation of mass production, current panel technologies have to improve in order to cope with these requirements. In this article, various approaches to the manufacturing technologies of next‐generation TFT‐LCDs are discussed.     

Relationship between mode‐boundary from surface color to fluorescent appearance and preferred gamut on wide‐gamut displays

Abstract— Color‐gamut design is a major concern in wide‐gamut displays. To determine a preferred gamut for displaying object color in natural scenes on a wide‐gamut display, subjective evaluations were conducted to investigate the preferred color and acceptable limit. Then, simple synthesized images were used to determine the mode boundary between surface color and fluorescent color appearance. It was found that (1) observers perceived the colors with high saturation and high lightness as fluorescent colors and (2) the fluorescent appearance decreased preference. The color‐mode index (CMI) was defined as an evaluation index of the color‐appearance mode so that the boundary between surface color and fluorescent color appearance was defined as CMI 100. Additionally, it was found that the CMI 100 loci could be interpreted as an optimal color loci. Then, it was clarified that the mode boundary and the preferred gamut were closely related and that the acceptable limit for L* was 1.1 times L* for CMI 100.     

Active‐matrix organic light‐emitting displays employing two thin‐film‐transistor a‐Si:H pixels on flexible stainless‐steel foil

Abstract— An active‐matrix organic light‐emitting diode (AMOLED) display driven by hydrogenated amorphous‐silicon thin‐film transistors (a‐Si:H TFTs) on flexible, stainless‐steel foil was demonstrated. The 2‐TFT voltage‐programmed pixel circuits were fabricated using a standard a‐Si:H process at maximum temperature of 280°C in a bottom‐gate staggered source‐drain geometry. The 70‐ppi monochrome display consists of (48 × 4) × 48 subpixels of 92 ×369 μm each, with an aperture ratio of 48%. The a‐Si:H TFT pixel circuits drive top‐emitting green electrophosphorescent OLEDs to a peak luminance of 2000 cd/m².     

Novel super fast response vertical alignment‐liquid crystal display with extremely wide temperature range

We have developed a novel super fast response (SFR) thin‐film transistor liquid crystal display (TFT‐LCD) with an extremely wide temperature range. Nematic liquid crystal molecules with positive dielectric anisotropy are vertically aligned initially. Any gray‐to‐gray response is forcibly controlled by applying an electric field. Response times of the SFR TFT‐LCD are over several times shorter than those of conventional LCDs such as vertical alignment or in‐plane switching LCDs.     

Current status and future prospect of in‐cell‐polarizer technology

Abstract— A thin‐crystalline‐film (TCF) polarizer has been developed which can be used internally in liquid‐crystal‐display cells. Based on this material, a manufacturing process has been developed for the fabrication of monochrome LCDs with internal polarizers. A new TCF polarizer material and coating equipment, developed to realize a high‐performance color TFT‐LCD, are discussed.     

Multioutputs single‐stage gate driver on array with wide temperature operable thin‐film‐transistor liquid‐crystal display for high resolution application

A hydrogenated amorphous silicon (a‐Si:H) thin‐film transistor (TFT) gate driver with multioutputs (eight outputs per stage) for high reliability, 10.7‐inch automotive display has been proposed. The driver circuit is composed of one SR controller, eight driving TFTs (one stage to eight outputs) with bridging TFTs. The SR controller, which starts up the driving TFTs, could also prevent the noise of gate line for nonworking period. The bridging TFT, using width decreasing which connects between the SR controller and the driving TFT, could produce the floating state which is beneficial to couple the gate voltage, improves the driving ability of output, and reaches consistent rising time in high temperature and low temperature environment. Moreover, 8‐phase clocks with 75% overlapping and dual‐side driving scheme are also used in the circuit design to ensure enough charging time and reduce the loading of each gate line. According to lifetime test results, the proposed gate driver of 720 stages pass the extreme temperature range test (90°C and ?40°C) for simulation, and operates stably over 800 hours at 90°C for measurement. Besides, this design is successfully demonstrated in a 10.7‐inch full HD (1080 × RGB×1920) TFT‐liquid‐crystal display (LCD) panel.     

Sequential‐color LCD based on OCB with an LED backlight

We have fabricated a 13.3‐in. XGA (1024 × 768) TFT sequential‐color liquid‐crystal display using optically compensated birefringency (OCB), illuminated by an LED backlight. We fabricated the sequential‐color display feasible process technology, and examined the performance and potential of a field‐sequential‐color scheme. The display was connected to a laptop computer and examined for flicker.     

Low‐temperature amorphous‐silicon backplane technology development for flexible displays in a manufacturing pilot‐line environment

Abstract— A low‐temperature amorphous‐silicon (a‐Si:H) thin‐film‐transistor (TFT) backplane technology for high‐information‐content flexible displays has been developed. Backplanes were integrated with frontplane technologies to produce high‐performance active‐matrix reflective electrophoretic ink, reflective cholesteric liquid crystal and emissive OLED flexible‐display technology demonstrators (TDs). Backplanes up to 4 in. on the diagonal have been fabricated on a 6‐in. wafer‐scale pilot line. The critical steps in the evolution of backplane technology, from qualification of baseline low‐temperature (180°C) a‐Si:H process on the 6‐in. line with rigid substrates, to transferring the process to flexible plastic and flexible stainless‐steel substrates, to form factor scale‐up of the TFT arrays, and finally manufacturing scale‐up to a Gen 2 (370 × 470 mm) display‐scale pilot line, will be reviewed.