New solid-state x-ray imagers known as digital flat-panel x-ray detectors are about to be launched in the field of medical diagnostics. The combination of active-matrix technologies developed for active-matrix liquid-crystal displays and x-ray detection materials constitutes the basis of the detectors. Recently, two kinds of direct-conversion detectors have been developed in order to improve their performance. One is a detector using a thick x-ray photoconductor (∼1 mm) made of amorphous selenium, and the other is a novel hybrid panel detector using an x-ray photoconductor made of polycrystalline Cd(Zn)Te. As a result, excellent resolution and good linear sensitivity have been achieved. These detectors have great promise as next-generation digital imaging systems for fluoroscopy and radiography.

This introductory article reviews the topics covered in this issue of MRS Bulletin on advanced flat-panel displays and materials. The common requirements of flat-panel displays are compact dimensions, low power consumption, light weight, and high performance. Flat-panel displays are incorporated in many consumer products as well as in a large range of industrial, medical, military, transportation-related, and scientific instruments. In recent years, there have been dramatic improvements in flat-panel display technology due to an enhanced understanding of various new or existing materials as well as fabrication processes. “Flat-panel display” is a general term that includes many different types of technologies. It includes panels that are in mass production, such as passive or active addressed liquid-crystal displays or plasma displays, and those in the early production or development stages, such as organic light-emitting devices or electrophoretic displays. It also includes novel products that are based on the principle of flat-panel display technology, such as solid-state x-ray imagers. The articles in this issue cover a range of these topics.

The elimination of conventional peripheral LSI (large-scale integration) drivers is considered essential to the development of future low-cost, energy-efficient, lightweight, and thin displays. System-on-glass (SOG) displays are a type of display with various functional circuits integrated on a glass substrate. Low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) make the integration of circuits possible because they can be assembled into complex, high-current driver circuits. Furthermore, LTPS TFTs are attracting attention for driving organic light-emitting devices (OLEDs). This article introduces present and future LTPS TFT technologies for SOG displays.

Color tracking describes the ability of a display to faithfully reproduce the color quality of the source image. In liquid-crystal displays (LCDs), color tracking is dependent on brightness. In order to achieve high-performance color reproduction in LCDs, the accuracy of color tracking needs to be improved. By analyzing the characteristics of twisted-nematic (TN) and in-plane switching (IPS) modes of display, the cause of poor color tracking in each mode and the differences in their causes can be clarified. In TN mode displays, both chromaticity and brightness relate to the director configuration, that is, the directional alignment of the rod-like molecules of the liquid crystals, which varies with applied voltage. The ideal IPS LCD, by virtue of its operating principle, theoretically achieves perfect color tracking; however, in actual use, the color tracking is less than optimal due to twist deformation caused by the fixed directors on the alignment layer. Based on our analysis of these phenomena, we propose strategies for improving color tracking in IPS LCDs.

Microencapsulated electrophoretic (MEP) materials exhibit high optical reflectance and contrast, wide viewing angle, high resolution, and excellent image stability. MEP materials can be easily printed on large plastic sheets and laminated to a variety of electronic backplanes to construct displays. The combination of a MEP material with flexible transistor technologies enables displays that offer both the look and form of the printed page. This article reviews the basic architecture and properties of MEP materials and describes the integration of MEP materials with transistor backplanes to produce high-resolution, low-power, paperlike displays. Recent developments in ultrathin flexible displays are also reported.

Reflective full-color liquid-crystal displays (LCDs) are attracting a great deal of interest as portable information systems because of their extremely low power consumption and light weight; also, the color does not wash out in outdoor use. In this article, reflective LCDs are classified into three types. Among them, the diffusing-reflector type and the front-diffusing film type are suitable for high-quality active-matrix displays. Diffusing-reflector LCDs have the advantage of uniform reflectance at the desired viewing angle due to the design of the surface microstructure of the reflector. Front-diffusing film LCDs using metallic mirrors and an optimally designed light-controlling film enable high contrast in a wide viewing-angle range and uniform reflectance with no blurring. Thus, both types have a high potential for achieving excellent color quality comparable to printed paper. In the near future, these reflective LCDs will likely be applied not only to portable systems, but also to high-performance wireless monitor displays and various other information systems.

Organic light-emitting devices (OLEDs) have attracted considerable interest in the last five years and are now viewed as an important competitor with liquid crystals for a wide variety of display applications. Current research focuses on the use of small-molecule and polymer materials to make organic electroluminescent displays with both passive-and active-matrix technologies. This article will discuss work on the device architecture for a polymer passive-matrix display application, the stability of polymer light-emitting displays, and the use of ink-jet printing for high-resolution patterning of red, green, and blue light-emitting polymers.

Recent trends in the development of plasma display panels (PDPs) are reviewed in this article with special emphasis on materials. New developments in the panel structure, discharge gases and phosphors used, and drive methods have improved many of the display characteristics over a wide range of operating conditions. As a result, much progress has been seen in large-scale panel development; for example, 50-in. and 61-in. PDPs have been commercialized. Improvements in phosphor longevity, discharge gas efficiency, and characteristics of the protective layers can be attributed in part to materials solutions. The longevity of the blue phosphor has been improved by the development of new materials and a greater understanding of the phosphor deterioration mechanism. The luminous efficiency has been greatly increased by the use of high-density Xe gas. The protective-layer characteristics have been improved as a result of advancements in processes, materials, and analytical methods.