Recent developments in large‐area photomasks for display applications

One of the most critical areas in the manufacturing process for FPD panels or shadow masks for CRTs is lithography. Most existing lithography technologies require high‐quality large‐area photomasks. The requirements on these photomasks include positioning accuracy (registration) and repeatability (overlay), systematic image quality errors (“mura” or display quality), and resolution (minimum feature size). The general trend toward higher resolution and improved performance, e.g., for TFT desktop monitors, has put a strong focus on the specifications for large‐area‐display photomasks. This article intends to give an overview of the dominant issues for large‐area‐display photomasks, and illustrates differences compared with other applications. The article will also present state‐of‐the‐art methods and trends. In particular, the aspects of positioning accuracy over large areas and systematic image‐quality errors will be described. New qualitative and objective methods have been developed as means to capture systematic image‐quality errors. Results indicating that errors below 25 nm can be found early in the manufacturing process is presented, thus allowing inspection for visual effects before the actual display is completed. Positioning accuracy below 400 nm (3 sigma) over 720 × 560 mm have been achieved. These results will in the future be extended up toward 1 × 1 m for generation 4 in TFT‐LCD production.     

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.     

Masking model for accurate colorimetric characterization of LCD

Abstract— A color management system (CMS) such as ICC profile or sRGB space have been proposed for color transformation and reproduction of cross media. In such a CMS, accurate colorimetric characterization of a display device plays a critical role in achieving device‐independent color reproduction. In the case of a CRT, colorimetric characterization based on a GOG model is accurate enough for this purpose. However, there is no effective counterpart in liquid‐crystal displays (LCDs) since the characterization of an LCD has many difficulties, such as channel interaction and non‐constancy of channel chromaticity. In this paper, a new method of display characterization is proposed which is applicable to the assessment of color reproduction of LCDs. The proposed method characterizes an electro‐optical transfer function considering both channel interaction and non‐constancy of channel chromaticity. Experimental results show that the proposed method is very effective in the colorimetry of LCDs.     

Organic‐polymer thin‐film transistors for active‐matrix flat‐panel displays?

Abstract— Organic‐polymer‐based thin‐film transistors (OP‐TFTs) look very promising for flexible, large‐area, and low‐cost organic electronics. In this paper, we describe devices based on spin‐coated organic polymer that reproducibly exhibit field‐effect mobility values around 5 × 10^?3 cm²/V‐sec. We also address fabrication, performance, and stability issues that are critical for the use of such devices in active‐matrix flat‐panel displays.     

Redox behavior of indium in molten chlorides

An electrochemical study on the redox behavior of indium in the eutectic LiCl-KCl system at 450 °C was carried out with the transient techniques of cyclic voltammetry and chronopotentiometry on an inert molybdenum electrode. The reduction of In(III) was found to be a two-step process involving In(III)/In(I) and In(I)/In couples at the potentials of about ?0.4 and ?0.8 V versus Ag/AgCl, respectively. The redox mechanism was further confirmed by the theoretical evaluation of the number of transferred electrons based on cyclic voltammetry and characterizations of the precipitates generated by the potentiostatic electrolysis. The diffusion coefficients of indium ions in the eutectic LiCl-KCl melt at 450 °C were estimated by cyclic voltammetry and chronopotentiometry. The results obtained through the two methods are in fair agreement, delivering an average diffusion coefficient of approximately 1.8×10^?5 cm²/s for In(III), and 1.4×10^?4 cm²/s for In(I).     

Technologies towards patterned optical foils applied to transflective LCDs

Abstract— For better front‐of‐screen performance for transflective LCDs, a technology with extra free optimization parameters for the optical stack is needed. Thin wet coatable retarders which enable adjustment of the optical activity on the (sub)pixel level have been developed. Isotropic domains have been created in nematic retardation films by thermal patterning or photopatterning. Employing such a patterned retarder in a transflective LCD leads to an LCD that is lighter and thinner with good reflectivity, high transmission, and low chromaticity at all gray levels and wide viewing angles. The patterned thin‐film technology has been proven to be versatile and applicable in various LCD designs.     

Low‐power‐consumption TFT‐LCD with dynamic memory embedded in the pixels

A low‐power‐consumption thin‐film‐transistor liquid‐crystal display (TFT‐LCD) with dynamic memory cells embedded in each pixel using low‐temperature poly‐Si technology has been developed. By holding data in the memory, the operating rate of the data driver can be dramatically reduced to 4 Hz. Eight levels of gray scale with low power consumption can be achieved by using the area‐ratio gray‐scale method. This TFT‐LCD can be used for displaying fine still images, with low power consumption.     

Medical displays in the healthcare system

Abstract— As the healthcare system changes and progresses, the need for different types of high‐performing displays is also evolving. There are three categories of displays: (a) embedded (as part of life saving devices), (b) informative (for patient data and history, and managing workflow), and (c) imaging (high performing for diagnosis). The challenges of AMLCDs, which are the display of choice at the moment mainly in digital imaging, will be discussed. These challenges include very high resolution, high brightness, and wide viewing angle. The current performance of AMLCDs and the areas which they need to improve will be reviewed. A brief summary of the standards used to specify medical (diagnostic) displays will follow. A look into the future will predict the role of displays in hospitals.     

Displays for hand-held portable electronic products

Abstract— The hand-held electronic-product field includes most telecommunication, palm computing, and navigation products, making this a large market for smaller displays (typically from 1 to 4 in. on the diagonal). Historically, this market has demanded displays with low power and cost, rather than high image quality, as evidenced by the historical dominance of monochrome TN and STN displays. However, within these constraints there is a strong trend toward larger displays capable of higher information content, including a migration toward low-power color solutions.     

Reflective direct-view LCDs using polymer-dispersed liquid crystal (PDLC) and dielectric reflectors

Abstract— Novel color and monochrome reflective direct-view display configurations have been developed by combining light-scattering PDLC layers with dielectric reflectors. Diffuse reflectances comparable to white paper were achieved.