Scanning the Issue

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Scanning the Issue

Special Issue on Flat-Panel Display Technology

I. INTRODUCTION

Since the publication of the last special issue of the PROCEEDINGS OF THEIEEE on flat-panel displays in 1973, display technology has progressed in ways beyond recogni- tion from those early days. This progress has been especially rapid during the last ten years. As Kawamoto describes in his historical review of liquid-crystal displays (LCDs), the recent history of flat panel displays (FPDs) is dominated by the emergence of LCDs. Fuelled by the phenomenal growth in the mobile computing and communications markets, LCDs have emerged as the dominant visual interfaces for computing and communication devices. Most industry ana- lysts believe that this will continue for the foreseeable future.

Recently, LCDs have also started to challenge seriously cathode-ray tubes (CRTs) in the desktop-monitor market and in high-end digital television applications. Coincidently, this occurs at the time of the 100-year anniversary of the invention of the Braun, or cathode-ray, tube.

While the last ten years has seen unparalleled growth in the size of the display market, increased price pressure and continued erosion of profit margins has led to a rapid consolida- tion in the FPD industry. A number of major companies have either exited the display business or consolidated their operation into joint ventures with others. This extremely com- petitive environment has also inhibited the introduction of new technologies. Besides major Japanese technology companies, the last decade also saw the emergence of Korean companies and, more recently, a number of Taiwanese companies as major competitors in the FPD market. More recently, several Chinese operations have also emerged as significant LCD competitors. In this short span of a dozen years, display fabs have moved across four generations of glass substrate technologies while significantly increasing display resolution, pixel content, and size. However, with increased panel size and higher resolution, the cost to build a single FPD fab has gone beyond a billion dollars.

As a technology, FPDs are as diverse as the applications.

Plasma display panels (PDPs) and LCDs and even flat-screen CRTs are now mature technologies. After three decades of research and development, plasma displays are finally available in quantity at reasonable prices. A number of more

Publisher Item Identifier S 0018-9219(02)03949-X.

recent technologies such as organic electroluminescent displays, field-emission displays (FEDs), microdisplays, and various projection display technologies are undergoing rapid growth, receiving significant attention from the technical and investment communities. Organic light-emitting diode (OLED) displays show great promise, but need further research to improve the reliability and display lifetime. After a decade of intense research and development, FEDs are far from commercial success, as major issues in reliability and manufacturing are yet to be fully resolved. Electrophoretic displays are in early commercialization as are a number of microdisplay technologies.

II. FPD TECHNOLOGIES

Current display technology has been an outgrowth of developments in a number of areas including advanced materials, microelectronics manufacturing and packaging, glass science and driver circuit engineering.

With active-matrix LCDs (AMLCDs) providing performance comparable to CRTs, within the last two years, flat panels have penetrated onto the desktop, a market segment that was traditionally dominated by CRTs. No longer are LCDs found only in portable devices. With the start of fourth generation fabs, AMLCDs reaching a meter in diagonal are already being demonstrated and are expected to enter the market in significant volume over the coming years. Because of continued refinements and cost reductions, we are also now seeing wall-hanging PDPs as a factor in the marketplace.

In addition, emerging technologies such as organic electroluminescent displays are rapidly moving from research into various new applications.

Besides LCD and direct-view emissive display, there is another emerging display field based on microdisplays. The emergence of microdisplay technology has started to have a great impact on electronic projection display industry. Mi- crodisplays based on digital micromirror devices (DMDs) or liquid-crystal on silicon (LCoS) are single-chip solutions, which effectively integrate the imaging and projection capabilities in a small package. Microdisplays also find wide- spread use in digital cameras and may lead to many head- mounted display applications.

In addition to light valve projection displays, there are other technologies that can be used to create ultralarge displays. AMLCDs and PDPs are both being pursued not only

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as flat-panel display competitors to the bulky CRT for color video and monitor applications, but also for ultralarge display modules. Tiling has been shown to provide ultralarge FPDs in sizes not possible with a single panel.

Apart from portable computers, hand-held consumer electronics such as personal digital assistants and cellular phones are very much display centric. With the rapid advances in high-speed wireless networks, hand-held wireless devices are becoming integrated multimedia terminals with small high-resolution color displays providing the user interface. Displays utilizing low-temperature polysilicon AMLCDs provide opportunities to realize functions that have been considered impractical with LCDs implemented with amorphous-silicon thin-film transistors (TFTs).

However, we should not forget the obvious. Right now, FPDs are synonymous with AMLCDs using amorphous silicon TFTs. In the beginning of the last decade, passively ad- dressed LCDs were confined to niche applications such as pocket calculators and watches. Notebook computers were the killer application that propelled the rapid development of FPD technology into a market larger than 25 billion dollars.

With all these developments, one can only think that the future of FPDs will be much brighter than it has ever been.

III. OVERVIEW OF THESPECIALISSUE

In this issue, we are fortunate to have leading figures in the FPD industry review the state of the technology and to provide insights into the emergence of new display concepts, devices, and applications. We are pleased with the excellent mix of industry and academic representation among the authors contributing to this issue. We believe that there are a number of exciting papers covering the whole gamut of display technology. The issue is led by Mentley of Stanford Re- sources, who specializes in consulting and market research for the worldwide FPD industry. He brings in a global per- spective on the status of various FPDs and presents his views on the future.

This is followed by a review summarizing the status of the Korean display industry by Jang et al. Over the last five or six years, the Korean display industry emerged very strong and a number of Korean companies have clearly become technology leaders in their respective areas. They review the Ko- rean display industry and its state-of-the-art research.

As noted earlier, the modern history of FPDs is predomi- nantly the history of the development of LCDs. Kawamoto documents the history of the development of LCDs over the last 40 years. He presents the story in vivid detail along with personal recollections of the events. He provides much needed insights and balance into the early developments in the 1970s and 1980s along with a comprehensive summary of the recent past.

AMLCDs are on the way to becoming the dominant technology for enabling high-resolution high-content monitors.

There have been continuous advances toward bigger panels, greater viewing angles, and higher screen resolutions. As an example of the increased performance that can be expected from state-of-the-art monitors, IBM has recently introduced

a product with a wide aspect ratio of 16:10, panel size of 22-in diagonal with a resolution of 204 pixels per inch with a pixel content of 9.2 million pixels (3840 2400). This, combined with high contrast ratio of 400:1 at 235 nits of brightness and a viewing angle of greater than 170 , demonstrates the capabilities of upcoming LCD monitors. Just as important has been the additional performance enhancements that have been accomplished in the display system electronics, including addressing schemes, AMLCD driver chips, digital interfaces, and integrated display controllers.

Over the last five decades, there have been many efforts at developing emissive displays identical to CRTs, but in a thin profile. One of the more recent manifestations of such an effort is the FED. Based on electron emission from mi- crofabricated electron sources, FEDs are expected to provide all the visual attributes of a CRT, but in a package similar to LCDs. Itoh and Tanaka review their experience in this area and present a comprehensive summary on the status of FED technology. Though FEDs have been reported by a number of companies, most are still limited to low-voltage monochrome devices. High-voltage full-color FEDs are still under development and have a number of reliability problems to solve.

Though most commercial FEDs are based on the Spindt-type Mo emitter arrays, electron sources using carbon nanotubes is an activity being pursued in a number of industrial and academic research laboratories. If fully commercialized, FEDs are expected to provide low-power emissive displays with capabilities for high-speed high-brightness applications. How- ever, to fully realize the potential of this technology, further research is needed in phosphor technology, improved device and spacer reliability, and many aspects of vacuum packaging.

The emergence of microdisplay technology is starting to revolutionize the projection display industry. McLaughlin presents the state of the art of projection displays based on various microdisplay technologies including DMDs, LCoS light valves, and grating light-valve technologies.

The emergence of microdisplay technology over the past decade has revolutionized the electronic projection display industry. Microdisplays integrate the imaging capabilities and capacity of a desktop monitor onto a chip. Small integrated-circuit (IC) backplanes are combined with light modulating front planes to produce a microdisplay device.

One to three of these microdisplays are combined with projection lamps and optical devices into a projection system with a broad range of performance and price. In addition to projection and large area displays, microdisplays are also starting to find wide use in personal displays such as digital cameras and body-worn productivity tools.

Uchiike, in his paper on plasma displays, correctly notes that monochrome PDPs were the first FPDs to be used in early notebook computers. They were later replaced by color TFT LCDs in the early 1990s. With the advent of high-definition and big-screen televisions, plasma displays have finally started to penetrate the consumer market. Though plasma displays have been known for over 30 years, only recently have manufacturing costs been reduced to allow them to enter the consumer market. However, manufacturing cost is still

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a big limiting issue for further market penetration. The two problems of panel and driver circuit cost are closely coupled since there are many things that can be done to the panel that will make the circuit costs smaller and vice versa, as Uchiike describes.

From the very early stages of color picture tubes, vacuum- based display technologies have been intimately linked with vacuum quality or contamination issues and getters were the natural solution to these problems. Even today, with the advent of new FPD technologies, getters still play a crucial role to enhance the reliability and lifetime of display devices.

Tominetti and Amiotti review the importance of getters and maintenance of residual gas ambient in the case of flat CRTs, PDPs, OLED, and flat lamps. In this paper, they focus on the dominant FPD technologies, showing how proper getter solutions can increase their lifetime and improve the manufacturing process conditions.

With the ever-increasing cost of large flat-panel fabs, there have been efforts directed toward alternative methods to create ultralarge FPDs. One such approach is based on tiling of a number of small displays to create ultralarge FPDs in sizes that are not accessible with monolithic construction. Krusius et al. review the design and devel- opment of ultralarge FPDs based on tiling methods. They present a detailed review of the requirements for ultralarge displays and show how the design and manufacturing of tiled AMLCDs can meet the demanding requirements of a large-area high-performance FPDs.

One of the most important drivers of display technology is in portable electronics. In fact, displays for portable communication devices are one of the most rapidly evolving market segments with enormous technological and business impli- cations. Kimmel et al. present details on the displaycentric nature of new mobile communication devices and discuss how these developments are opening opportunities for display manufacturers to provide functions on the host devices that previously have been considered impractical. They show how advances in new display technologies such as reflective color LCDs, bistable displays, organic emissive displays, and microdisplays might provide additional functionality to the communication devices.

For a number of years, FPD technologies have provided the tools for medical-imaging technology. One of the most interesting applications for FPDs is as an X-ray image sensor for digital radiography. Kasap and Rowlands review the development of flat panel detectors for X-ray imaging.

Advances in active-matrix array technology over the last decade have led to the development of AMLCD X-ray image detectors. These advancements have resulted in X-ray imagers with image quality on par with film. In addition to providing high-resolution images, digital X-ray imagers are ideally suited for the transition to digital radiography.

Human factors are a critical consideration for all display technologies. Thus, how FPDs compare with CRTs in color rendition and color-gamut considerations is very important. In his paper, Sharma presents a comparative analysis of LCDs versus CRTs from color-calibration and gamut considerations. Similar analysis for other commercially

important FPDs will be useful and this paper provides the reference framework for further work when appropriate.

IV. FURTHERDETAILS

While the papers presented in this special issue cover a significant number of important topics, it is by no means a complete review of the FPD field. Display technology is much too diverse for a single issue to address. We would like to briefly mention other significant topics of great interest. These include display manufacturing and packaging technology, glass and substrate technology, driver ICs, addressing schemes, system electronics and display controllers for displays, advanced materials (liquid crystal materials, polymers for OLEDs), and backlights and color filters for LCDs. Other topics, which could not be covered in this issue, include recent advances in flat CRTs, electrophoretic displays, inorganic electroluminescent displays, and display phosphors.

An emerging display technology is based on electroluminescence in organic thin films. Unlike FEDs, OLEDs do not require sealed vacuum packages. However, they do require hermetically sealed packages because many of the organic materials are sensitive to water and oxygen, especially when there is electric current passing through the material. OLEDs are similar to inorganic electroluminescent display devices in that when electrical current is passed through the active film, light is emitted due to electroluminescence. In its simplest form, an OLED device consists of a thin film of luminescent material sandwiched between two electrodes, one of which is transparent. Full-color displays based on this technology have recently started to appear in cell phones and automo- tive dashboard applications. OLEDs have some potential ad- vantages as they do not require backlights and have a greater viewing angle and faster response time than LCDs. OLEDs will reach their full potential when cost effective means for integration with active matrix back planes becomes available.

Packaging is a key aspect of all FPD technologies. A number of issues go into package design, including elec- tromechanics and human factors. Along with expected long-term reliability and ruggedness, package technologies are expected to provide low cost solutions compatible with large volume manufacturing processes. Most FPDs still use glass as the packing material. Requirements range from high vacuum operation for CRTs and FEDs to moderate pressure operation for PDPs to liquid-filled operation for LCDs. There is a growing interest in producing flexible displays using plastic substrates. Plastic substrates are expected to provide improved ruggedness, lighter weight, and potentially lower cost if displays can be produced using roll-to-roll manufacturing technology. OLEDs and LCDs appear to be the best candidates for plastic substrates in the near term. There are many issues related to sealing, surface roughness, and permeability that must be resolved before flexible substrates become useful.

The push to introduce low-temperature polysilicon (LTPS) in AMLCDs is driven by improved device char- acteristics. LTPS is already in production application for

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small AMLCDs and could migrate into more mainstream applications and other developing areas such as OLED displays. One advantage is higher transmissivity because the pixel control transistor is smaller. A second advantage is the saving in driver cost and package integration complexity.

For a number of years, carrier mobility in TFTs made of amorphous silicon has limited the application of LCDs in real-time video applications. The carrier mobility of amorphous silicon is 0.5–1 cm V s, over two orders lower than LTPS. Because of their high carrier mobilities, LTPS circuits are much faster and can handle high-definition images such as those required to render real-time video. LTPS now enables the integration of row and column drivers on the glass substrate, eliminating the need for separate device drivers. With additional improvements in carrier mobility, it is not inconceivable to have memory for limited storage and buffering on the glass substrate itself. Putting functionality like microprocessors is not in the works right now, but it could happen in the not too distant future. LTPS will be the enabler for this to occur in displays. Two emerging areas in the development of LPTS are as-deposited nanocrystalline silicon and laser-crystallized polysilicon. Both technologies offer the potential for very low-temperature processing.

Increasing activity in the development of low-termperature dielectrics will further enable TLPS device technology. The growth of LTPS technology can be expected to follow trends that occurred with bulk semiconductors with an ultimate goal of a “system-on-a-panel” capability.

In the case of glass substrate technology, there are two major trends: larger size and reduced thickness. The need for large substrate size, approaching 1 m 1 m, is largely driven by manufacturing economics. Large substrates allow for multiple displays per substrate, thus, increasing the number of displays that can be produced per factory.

Thinner substrates are primarily driven by the requirement to reduce the weight of the display. FPDs are moving toward substrates with 0.5-mm thickness from 1.1 mm. However, increased size and reduced thickness of the glass substrates makes for increasing complex process equipment. In fact, the cost of building a new FPD fab is approaching a billion dollar range. Flexible substrates and web processing might offer opportunities for low cost manufacturing. However, for this to happen, a number of technical issues related to flexible substrates need to be resolved.

Improved understanding of fundamental materials prop- erties are required for every display technology, even for the mature CRT technology. While there have been significant improvements in organic light emitting materials, there is still a need for improved efficiency and reliability. At the same time, a better understanding of the fundamental degra- dation mechanisms in OLEDs is needed. There is also a need to improve the efficiency and reliability of cathodolumines- cent and electroluminescent phosphors. Further advances in liquid-crystal materials that provide longer hold times and improved refresh times will improve the video performance of AMLCDs. There continues to be a need for ongoing research in the area of display materials.

So far, the development of head-mounted displays has been primarily driven by military applications. The principal technologies that have been used for head-mounted displays are active matrix inorganic electroluminescence and AMLCDs. There is also research on using OLEDs and MEMs scanners as image sources for headmounted displays.

One of the more unique head mounted displays is a retinal display, where a low-power laser beam is directly scanned onto the retina to generate the image. While applications of head-mounted displays are expanding, they are still limited.

There has been a lot of activity in electrophoretic displays for applications in electronic books and small portable displays where power consumption is a primary concern. Re- cent advances in electrophoretic display technology based on encapsulating charged media in small spheres has significantly improved the performance and the reliability of electrophoretic displays.

Another interesting display technology that is in the early stages of development is volumetric three-dimensional (3-D) displays. While there has been significant interest in 3-D volumetric displays for a long time, the fundamental problem has been and continues to be the tremendous number of voxels (volume elements) required to provide a display with useful resolution. The terabit-per-second data rates needed are well beyond current capabilities. Until new concepts are introduced to reduce the data rate, volumetric 3-D displays will remain a novelty.

Display drivers provide the intelligence for the display to operate and without appropriate driver technology, FPDs are incomplete and nonfunctional. Modern driver technology is highly sophisticated; display drivers are complex systems on a chip with integrated-data and image-processing circuitry along with onchip memory. Display drivers are very spe- cialized devices and are designed for each particular display system. Display drivers are generally directly attached to the display using technologies such as chip-on-glass and tab-au- tomated bonding. Using bare die reduces the driver cost, which in many cases can be as low as one cent line.

V. FUTURETRENDS

Today, the convergence of television and computer applications is creating new development opportunities for products that integrate the ability to display full motion video and support interactive capabilities such as browsing the Web while watching television. This convergence makes the inter- pretation and display of information more complex. At the same time, there is the desire to provide this capability on hand-held portable devices, where screen size and resolution may be at a premium. While significant growth is forecasted for display devices, the increasing need to rapidly process and display large amounts of information delivered in a mul- titude of broadcast and Web transmission formats could con- strain this growth. This bottleneck limits access to the full visual potential of content. This mixed data format also provides a need for all-digital displays, where data manipulation at the display level will reduce the requirements on graphic processors.

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With increasing functionality of consumer electronic products, more and more products are becoming displaycentric. In a majority of these applications displays provide the primary user interface. In most cases, the user interface can be a dominant factor in distinguishing one’s product from the competition. This trend will become more intense as display technologies continue to improve and offer more functionality. Coincident with this growth in the importance of the display to the products “look and feel,” new types of display products should become pervasive. Thus, flexible/foldable displays based on LCDs and OLEDs are forecast. Sales of personal information and productivity en- hancement tools with integrated microdisplays are expected to grow. Finally, megasized wall displays, which have been the FPDs “holy grail,” will be available to many users with a choice of technology options.

ACKNOWLEDGMENT

The guest editors would like to thank J. Calder, Managing Editor of the PROCEEDINGS, for his support throughout the planning and preparation of the issue. They would also like to thank M. Scanlon for her constant support and assistance and

all the authors for kindly accepting our invitation to create this special issue. Finally, they would like to thank all the referees for their service.

BABUR. CHALAMALA

Guest Editor

Semiconductor Products Sector Motorola, Inc.

Tempe, AZ 85284 USA FRANKE. LIBSCH

Guest Editor

IBM T.J. Watson Research Center Yorktown Heights, NY 10598 USA ROBERTH. REUSS

Guest Editor

Defense Advanced Research Projects Agency Arlington, VA 22203-1714 USA

BRUCEE. GNADE

Guest Editor

University of North Texas Denton, TX 76203 USA

Babu R. Chalamala (Senior Member, IEEE) received the B.Tech. degree in electronics and communications engineering from Sri Venkateswara University, Tirupati, India, in 1987 and the Ph.D. degree in physics from the University of North Texas, Denton, in 1996.

He is currently a Principal Staff Scientist with the Semiconductor Products Sector, Mo- torola Inc., Tempe, AZ. From 1996 to 2000, he was a Researcher with the Flat-Panel Display Division of Motorola, where he was involved in the development of field-emission displays, vacuum microelectronic devices, and advanced materials and process technologies. Previously, he was with in the Flat Display Products Department of Texas Instruments for one year, was an International Fellow with SRI International, and a Visiting Scientist at the FOM Institute for Atomic and Molecular Physics, Amsterdam, The Netherlands. He has authored or coauthored over 70 referred papers and five U.S. patents. His current research interests include in flat-panel displays, macroelectronics, electronic materials, organic electronics, and advanced memory technologies.

Dr. Chalamala is a Member of the American Physical Society, the American Vacuum Society, the Materials Research Society, and the Society for Information Display. He was Co-Chair of the Flat Panel Displays and Sensors Symposium at the 1999 MRS Spring Meeting and is the Chair of the IEEE Lasers and Electro-Optics Society Technical Committee on Displays.

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Frank E. Libsch (Member, IEEE) received the B.S., M.S., and Ph.D. degrees in electrical engineering from Lehigh University, Bethlehem, PA, in 1982, 1984, and 1989, respectively.

He is currently a Manager of Advanced Display Array Design, Processes, and Tests Group at the IBM T.J. Watson Research Center, Yorktown Heights, NY. In 1989, he joined IBM at the Thomas J. Watson Research Center as a Research Staff Member, where he focused on various aspects of drive schemes and electronics, pixel and array designs, CMOS FETs and TFTs, and their application in various direct-view and projection, transmissive, emissive, and reflective flat-panel displays. He has authored or coauthored more than 60 papers, most recently a book chapter “SONOS Nonvolatile Semiconductor Memories” in Nonvolatile Semiconductor Memory Technology (New York: Wiley, 2000), and several U.S. and foreign patents. His cur- rent research interests include solid-state devices and circuits applied to emerging technologies, including the areas of flat-panel displays, nonvolatile memories, and organic electronics.

Dr. Libsch is a Member of the Society for Information Display, the New York Academy of Sciences, and Sigma Xi. He has served in various capacities for various organizations, including as Organizer and Co-Chair of the IS&T/SPIE AMLCD ’97 Technologies and Applications Electronic Imaging Symposium, as a Member of the IEEE ISSCC’97 Sensors, Imagers, and Display Committee, and as Co-Chair and Co-Editor of the 1999 MRS Spring Meeting’s Flat Panel Displays and Sensors Symposium and Proceedings. He is currently the Chairperson of the AMLCD Subcommittee of the Society for Information Display, a Member of the Executive Committee of the Society for Information Display, and the Technical Program Chair and General Chair for the Society of Information Display 2001 and 2003 Conferences, respectively.

Robert H. Reuss (Senior Member, IEEE) received the Ph.D. degree in chemistry from Drexel University, Philadelphia, PA, in 1971.

He joined the Defense Advanced Research Projects Agency (DARPA) as a Program Man- ager in the Microsystems Technology Office in August 2001, where he is responsible for several research programs including the MARCO Focus Center Research Program, Technology for Efficient, Agile Mixed Signal Microsystems, and Mission Specific Processing programs.

Prior to joining DARPA, he spent 20 years in technology and research management positions with Motorola. Previously, he worked for the U.S. government as a Research and Develop- ment Manager for seven years and was a Research Faculty Member with the University of Colorado for three years. In 1994, he began work with the Flat Panel Display Division of Motorola, where his interests included technology assessment and benchmarking as well as managing advanced emitter and display materials development and was an Elected Member of Motorola’s Science Advisory Board. He has authored or coauthored over 50 papers and has been awarded 13 U.S. patents. His current research interests include application of materials and electrochemistry technologies for advanced microelectronic applications and microsystems integration as well as large area electronics and displays.

Dr. Reuss is a Member of the Electrochemical Society and Society for Information Display. He was Chairman of the Phoenix Chapter of IEEE Waves and Device Societies.

Bruce E. Gnade received the Ph.D. degree in nuclear chemistry from the Georgia Institute of Technology, Atlanta, in 1982.

He is currently a Professor of Materials Science and Chairman of Materials Science Depart- ment at the University of North Texas, Denton. Previously, he was on a three year assignment as a Program Manager at the Defense Advanced Research Projects Agency, where he managed or comanaged the High Definition Systems Program, the Molecular Electronics Program, and the Heterogeneous Integration of Materials on Silicon Program. He was actively engaged in research and managed several research and technology groups during his 15 years at Texas Instruments, including the Si Materials and Processing Research Group, the Field Emission Display Technology Development Group, and the Advanced DRAM Materials Group. He currently serves on the Emissive Display Subcommittee for the Society of Information Display and is a Member of the Board of Directors of PixTech, Inc., a field-emission display development company. He has authored or coauthored approximately 80 refereed papers, 60 U.S.

patents, and 28 foreign patents. His current research interests include electronic materials deposition and evaluation, high-K dielectric materials for transistor and capacitor applications, molecular electronics, and display-related materials.