Flat-panel displays (FPDs) will soon become ubiquitous products in our homes, workplaces, and a number of places in between. Familiar display applications pioneered by the venerable cathode-ray tube (CRT) will progressively utilize a number of different FPDs. Flat-panel displays will also initiate and pioneer new applications, as was the case with notebook computers and personal digital assistants.

The future proliferation of FPDs can no longer be doubted for two simple reasons. First, such devices help us cope with this already information-saturated society. Second, the technological momentum and financial commitment needed for FPDs to take hold are already irreversibly set in place. It is the insatiable current and near-future demand that are pulling the field, and that are fueling a flurry of research and development activities. The display market has grown in size from tens of millions of dollars only a decade ago to a nearly ten-billion-dollar industry. This market growth is expected to continue at a brisk pace during the next decade.

This of course is in no way bad news for materials scientists and engineers. We nearly always benefit from development of new and complex products. It is in regard to these rather incipient but advanced manufacturing technologies where we often encounter challenging, relevant, and interesting materials problems. The better we address these obstacles during these early and therefore critical times, the more successful the FPD technology will be in fulfilling the potential opportunities that lie ahead.

One material exists in most types of flat panel displays that are used in high information content applications, from liquid crystal displays to electroluminescent displays. This material is glass, something we all use daily. As a substrate, glass plays a significant role in the manufacture and function of flat panel displays (FPDs). In the case of active-matrix liquid crystal displays (AMLCDs), the semiconductor-based thin-film transistors (TFTs) or diodes are fabricated on the active glass substrate. In addition, AMLCDs require color-filter structures consisting of dyed or pigmented resins built upon the passive plate of an AMLCD cell. For plasma and electroluminescent display panels, the glass provides the surface upon which are deposited phosphors, conductive lines, and dielectrics.

The excellent properties of glass make it the substrate of choice in FPDs. It is the only material that can meet the demanding requirements of high-information-content FPD manufacturing processes and operation. Glass' transparency is an obvious requirement. For all types of displays, the rigidity of glass also plays a important role because it adds overall mechanical integrity and strength.

One of the most important attributes of glass in terms of the display manufacturing process is its thermal stability. Glass substrates, particularly those made of “hard” or high temperature glasses, can be processed at elevated temperatures with minimal deformation. In addition, the dimensional precision required in the alignment of various display components is maintained throughout the specific manufacturing processes.

In today's world of increasing office automation and computer-aided personal-communications systems, display devices play a very important role as person-machine interfaces. Above all, high-definition, full-color flat-panel displays will be key devices in the near future when processing huge amounts of information—including pictorial images via computer networks and telecommunication systems that transcend the present limitations of time and place—will be possible.

Passive-matrix liquid-crystal displays (LCDs) represent the most widely used choice for portable display devices. Figure 1 illustrates the essential components and operating principle of a typical LCD. Each pixel is addressed by the top- and bottom-line electrodes of the cell based on information signals, producing a light image. By installing a color filter of red, green, or blue for each pixel, full-color images can be displayed. However, the essential problems of crosstalk among pixels and low response speed become serious with an increase in the number of pixels, resulting in a low contrast ratio and failure of the display to keep up with the signals.

The fabrication of thin-film-transistor (TFT) devices on a transparent substrate lies at the heart of active-matrix-liquid-crystal-display (AMLCD) technology. This is both good and bad. On one hand it is a difficult task to manufacture millions of intricate semiconductor devices reliably over such large display substrates. On the positive side, AMLCD technology can aspire to become much more than a “display” technology. The idea is as follows: It is possible for one to readily fabricate additional transistors to execute various electronic functions—those that would otherwise be handled by separate large-scale-integration (LSI) and very large-scale-integration (VLSI) circuits—on the periphery of the display. Since this can be done, in principle, with no—or a minimal number of—additional processing steps, substantial cost reduction is possible and significant value can be added to the final product.

Doing so and doing it well can ultimately lead to “system-on-glass” products in which the entire electronic circuitry needed for a product is incorporated directly onto a glass substrate. This means that integrated active-matrix liquid-crystal displays (IAMLCDs) have the potential to bypass conventional Si-wafer-based products and may lead TFT technology to compete directly against Si-wafer-based monolithic integrated circuits.

The flat-panel-display (FPD) market is experiencing rapid growth due to increased demand for portable computers, communication equipment, and consumer electronic products. In all of these applications, the display is the primary human interface that conveys information. The size of the flat-panel-display market is presently estimated to be $10 billion/year and is projected to grow to over $18 billion/year by 1998. Although most current FPDs utilize either passive- or active-matrix liquid-crystal-display (LCD) technology, electroluminescent (EL) displays and light sources, because of their solid-state construction and self-emissive characteristics, can provide improved performance for many demanding display applications. Thin-film electroluminescent (TFEL) technology has been demonstrated over a broad range of display sizes from 1-in. to 18-in. diagonal with resolutions from 50 to 1,000 lines per inch. Also, because of its unique solid-state characteristic, TFEL technology is well-suited to provide a fully integrated display with the light-emitting element and electronics fabricated on the same substrate. An example of a full-color TFEL display is shown in Figure 1.

Thin-film electroluminescent display panels are finding increasing applications in the FPD marketplace due to several fundamental performance advantages over LCDs. These include wide viewing angle, high contrast, wide operating-temperature range, ruggedness, and long lifetime. Alternating-current (ac)-driven monochrome TFEL displays (ACTFEL displays) have become the most reliable, longest running devices on the market. Commercial ACTFEL display panels have operated for more than 50,000 hours with less than 10% luminance change, the equivalent of 25 working years.

Diamond has existed in the natural state for thousands of years. It was mainly used as a jewel for its optical brilliance and for its hardness. In the 1950s methods were developed to fabricate synthetic diamonds commercially. This greatly increased diamond's industrial use, mostly for grinding and lapping applications. Diamond is a crystalline form of carbon, a group-IV element in the periodic table. Silicon and germanium are also Group-IV elements and also have the same crystalline lattice structure as diamond. Hence there has been theoretical interest in diamond's electronic properties since the beginning of the semiconductor age. However the cost and poor crystalline quality of both natural and synthetic diamond have precluded any real industrial interest in diamond as an electronic material. Methods of low-temperature and low-pressure diamond-film deposition, developed initially by the Russians in the 1950s and 1960s (and thence by the Japanese, and eventually by others) has made it possible to use this exotic material as an electronic substrate.

Diamond, in single-crystalline, polycrystalline, and diamondlike carbon (DLC) forms, is a material with many unusual properties. It is the hardest naturally occurring material, the most thermally conductive, and the most transparent. It also has the slickness of Teflon. In regard to many physical properties, it is at the extreme end of the scale. One of the more unusual and important properties that it possesses is its presentation of a rather small barrier to the emission of electrons into a vacuum.

Recent demonstrations of color-plasma displays with exceptional image quality and performance that meet and in some cases exceed that of cathode-ray tubes (CRTs) have resulted in a renewed interest in this 25-year-old technology. The tremendous market potential for large-area plasma displays for both home-entertainment and computer applications now appears to be an attainable goal. This new generation of plasma displays features full color capability, high brightness and contrast ratio, wide viewing angles, and rapid refresh rate. The success of today's plasma displays is the result of the integration of advancements in driver electronics and the materials and processes used in the fabrication of the plasma-display structures.

Using color-plasma technology, two-inch-thick direct-view displays can be made that are up to 60 inches in diagonal. During the past several months, numerous articles have appeared in the media announcing major investments in facilities and technology for largescale manufacturing of these large-area plasma displays. Table I lists the companies committed to plasma-display research and development. Additional advancements in materials, processes, and electronics will be required to achieve high-volume, low-cost manufacturing.