Source: http://www.indiana.edu/~hightech/fpd/papers/ELDs.html
Timestamp: 2019-04-25 22:00:44+00:00

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We are grateful for the comments provided by Christopher King, Sey Shing Sun, Richard Tuenge, T. Peter Brody, and Runar Tornqvist. Research assistance was provided by Craig Ortsey. This research was supported by a grant from the Alfred P. Sloan Foundation. Please do not cite or quote without the written permission of the authors.
Electroluminescent displays (ELDs) have their origins in scientific discoveries in the first decade of the twentieth century, but they did not become commercially viable products until the1980s. ELDs are particularly useful in applications where full color is not required but where ruggedness, speed, brightness, high contrast, and a wide angle of vision is needed. Color ELD technology has advanced significantly in recent years, especially for microdisplays. The two main firms that have developed and commercialized ELDs are Sharp in Japan and Planar Systems in the United States.
There are two main ways of producing light: incandescence and luminescence. In incandescence, electric current is passed through a conductor (filament) whose resistance to the passage of current produces heat. The greater the heat of the filament, the more light it produces. Luminescence, in contrast, is the name given to "all forms of visible radiant energy due to causes other than temperature."
There are a number of different types of luminescence, including (among others): electroluminescence, chemiluminescence, cathodoluminescence, triboluminescence, and photoluminescence. Most "glow in the dark" toys take advantage of photoluminescence: light that is produced after exposing a photoluminescent material to intense light. Chemiluminescence is the name given to light that is produced as a result of chemical reactions, such as those that occur in the body of a firefly. Cathodoluminescence is the light given off by a material being bombarded by electrons (as in the phosphors on the faceplate of a cathode ray tube). Electroluminescence is the production of visible light by a substance exposed to an electric field without thermal energy generation.
An electroluminescent (EL) device is similar to a laser in that photons are produced by the return of an excited substance to its ground state, but unlike lasers EL devices require much less energy to operate and do not produce coherent light. EL devices include light emitting diodes, which are discrete devices that produce light when a current is applied to a doped p-n junction of a semiconductor, as well as EL displays (ELDs) which are matrix-addressed devices that can be used to display text, graphics, and other computer images. EL is also used in lamps and backlights.
4. The luminescent center relaxes toward the ground state and emits a photon.
All ELDs have the same basic structure. There are at least six layers to the device. The first layer is a baseplate (usually a rigid insulator like glass), the second is a conductor, the third is an insulator, the fourth is a layer of phosphors, and the fifth is an insulator, and the sixth is another conductor.
ELDs are quite similar to capacitors except for the phosphor layer. You can think of an ELD as a "lossy capacitor" in that it becomes electrically charged and then loses its energy in the form of light. The insulator layers are necessary to prevent arcing between the two conductive layers.
An alternating current (AC) is generally used to drive an ELD because the light generated by the current decays when a constant voltage is applied. There are, however, EL devices that are DC driven (see below).
Electroluminescence was first observed in silicon carbide (SiC) by Captain Henry Joseph Round in 1907. Round reported that a yellow light was produced when a current was passed through a silicon carbide detector. Round was an employee of the Marconi Company and a personal assistant to Guglielmo Marconi. He was an inventor in his own right with 117 patents to his name by the end of his life.
The second reported observation of electroluminescence did not occur until 1923, when O.V. Lossev of the Nijni-Novgorod Radio Laboratory in Russia again reported electroluminescence in silicon carbide crystals.
B. Gudden and R.W. Pohl conducted experiments in Germany in the late 1920s with phosphors made from zinc sulfide doped with copper (ZnS:Cu). Gudden and Pohl were solid state physicists at the Physikalisches Institut at the University of G`ttingen. They reported that the application of an electrical field to the phosphors changed the rate of photoluminescent decay.
The next recorded observation of electroluminescence was by Georges Destriau in 1936, who published a report on the emission of light from zinc sulfide (ZnS) powders after applying an electrical current. Destriau worked in the laboratories of Madame Marie Curie in Paris. The Curies had been early pioneers in the field of luminescence because of their research on radium. According to Gooch, Destriau first coined the word "electroluminescence" to refer to the phenomenon he observed.
Gooch also argues that one should keep in mind the differences between the "Lossev effect" and the "Destriau effect:"
The Lossev effect should be distinguished from the Destriau effect. Destriau's work involved zinc sulphide phosphors, and he observed that those phosphors could emit light when excited by an electric field…[The Lossev effect, in contrast, involves electroluminescence] in p-n junctions.
During World War II, a considerable amount of research was done on phosphors in connection with work on radar displays (which was later to benefit the television industry in the form of better cathode ray tubes). Wartime research also included work on the deposition of transparent conductive films for deicing the windshields of airplanes. That work was later to make possible a whole generation of new electronic devices.
In the 1950s, GTE Sylvania fired various coatings, including EL phosphors onto heavy steel plates to create ceramic EL lamps. During this period, most research focused on powder EL phosphors to get bright lamps requiring minimal power and with a potentially long lifetime. Research funding was cut back when it was determined that product lifetimes were too short (approximately 500 hours).
The first thin-film EL structures were fabricated in the late 1950s by Vlasenko and Popkov. These two scientists observed that luminance increased markedly in EL devices when they used a thin film of Zinc Sulfide doped with Manganese (ZnS:Mn). Luminance was much higher in thin film EL (TFEL) devices than in those using powdered substances. Such devices however were still too unreliable for commercial use.
Russ and Kennedy introduced the idea of depositing insulating layers under and above the phosphor layer on a TFEL device. The implications for reliability of TFEL devices was not appreciated at the time, however.
Soxman and Ketchpel conducted research between1964 and 1970 that demonstrated the possibility of matrix addressing a TFEL display with high luminance, but again unreliability of the devices remained a problem.
In the mid-1960s, there was a revival of EL research in the United States focused on display applications. Sigmatron Corporation first demonstrated a thin-film EL (TFEL) dot-matrix display in 1965. Unfortunately, Sigmatron was unable to successfully commercialize these displays and it folded in 1973.
In 1968, Aron Vecht first demonstrated a direct current (DC) powered EL panel using powdered phosphors. Research on powdered phosphor DC-EL devices continued, especially for use in watch dials, nightlights and backlights, but most subsequent research on ELDs focused on thin-film AC driven devices. An early example was the work of Peter Brody and his associates at Westinghouse Research Laboratories on EL and AM-EL devices between 1968 and 1974.
In 1974, Toshio Inoguchi and his colleagues at Sharp Corporation introduced an alternating current (AC) TFEL approach to ELDs at the annual meeting of the Society for Information Display (SID). The Sharp device used zinc sulfide doped with manganese (ZnS:Mn) as the phosphor layer and yttrium oxide (Y2O3) for the sandwiching insulators. This was the first high-brightness long-lifetime ELD ever made. Sharp introduced a monochrome ELD television in 1978. The paper Inoguchi published on his group's research helped to reinvigorate EL research in the rest of the world, including at Tektronix, a U.S. electronics firm based in Portland, Oregon.
The most important problem that had to be solved before mass production of ELDs could begin was increasing the reliability of the EL thin film stack. Since the devices operated at very high field levels -- about 1.5 MV/cm -- there was a high probability that they would break down, especially if there was insufficient uniformity in the stack. Sharp, Tektronix, and Lohja Corporation in Finland were able to solve this problem between 1976 and 1983 using slightly different approaches.
The second major problem was to get access to high-voltage drivers for the displays. Sharp ended up developing their own; Tom Engibous developed drivers for EL displays at Texas Instruments by modifying the design his group had done for plasma displays. Planar used the TI drivers in its products until it could find additional suppliers.
The introduction to the market in 1985 of Grid and Data General laptops with EL displays from Sharp and Planar respectively helped to build the foundations for the nascent laptop computer industry at a time when LCDs did not have sufficient brightness or contrast to be used in commercial products. Both Planar and Sharp monochrome ELDs used a phosphor layer made from zinc sulfide doped with manganese (ZnS:Mn). These displays gave off an amber (orange-yellow) color that was bright but also pleasing to the eye.
One of the key disadvantages of ELDs relative to liquid crystal displays (LCDs) was that until 1981 ELDs were not capable of displaying more than one color. Even after 1981, color ELDs were limited to a limited range of colors (red, green, and yellow) until 1993 when a blue phosphor was discovered.
In 1981, Okamoto reported that a rare-earth doped ZnS could be used in the phosphor layer of a TFEL device.
In 1984, William Barrow of Planar and his colleagues announced that they were able to get blue-green emissions from strontium sulfide doped with cerium (SrS:Ce).
In 1985, Shosaku Tanaka at Tottori University and his colleagues reported that they had duplicated the work done at Planar on SrS:Ce phosphors but added that they had gotten calcium sulfide (CaS) to emit a deep red color. In 1988, Tanaka's group announced that they had gotten white light from a TFEL display using a combination of SrS:Ce and SrS doped with Europium (SrS:Eu). The idea here was to use the white light in connection with a color filter to produce a full color display analogously to the way that it is done in liquid crystal displays. The advantage of doing this with ELDs was that such a display would not require a backlight. The main disadvantage was the added cost and difficulty of introducing a color filter.
In 1994, Soininen and coworkers at Planar International in Finland announced that a SrS:Ce/ZnS:Mn white phosphor deposited by atomic layer epitaxy achieves sufficient luminance and stability for use in color EL display products.
Further work on blue phosphors was done by Reiner Mach and his colleagues at the Heinrich Hertz Institute in Berlin. Additional work on SrS:Ce blue phosphors was done at Westaim Corporation.
A SrS:Cu blue phosphor showing improved blue color and efficiency was reported by Sey-Shing Sun of Planar in 1997. Planar demonstrated true white color EL prototype displays using this blue phosphor in a SrS:Cu/ZnS:Mn multi-layer structure. The SrS:Cu phosphor will enable color EL displays to be produced with a wider color gamut.
Barrow and his team at Planar announced a prototype of a multi-color EL display using ZnS:Mn and ZnS:Tb phosphor layers in 1986. By 1988, they had a prototype full-color display using a patterned phosphor structure. Commercial production of multicolor ELDs did not occur until 1993 at Planar, however, and full color ELDs have been produced only in the form of microdisplays (see section below on AMEL microdisplays). These color AMEL microdisplays used the ALE SrS:Ce/ZnS:Mn white phosphor with either sequential or spatial color filtering.
Planar Systems, Inc., was formed in 1983 as a spinoff from Tektronix. It was founded by three senior managers from Tektronix' Solid State Research and Development Group: John Laney, James Hurd, and Christopher King. Hurd became the President and CEO, Laney worked on manufacturing issues, and King became the firm's chief technical officer. Tektronix gave Planar its rights to certain technologies in exchange for an equity stake (in 1994 its share was still 7.5 percent). Planar remained privately held until it went public in 1993.
In 1984, Planar opened its first manufacturing facility in Beaverton, Oregon. It shipped its first bulk order in 1985 to Nippon Data General for an early laptop computer with a CGA (640x200) EL panel.
3. Gray scale capability of ELDs had to be enhanced.
The initial ELD prototypes had brightness levels of only about 20 foot lamberts (fLs). Commercial products in the 1990s were to have brightness levels of 100 fLs.
The initial drive scheme for ELDs at Planar was to apply a single polarity voltage pulse to each line of the display and then an opposite polarity pulse to the entire panel. This was called "the refresh method." In 1984/85, it was determined that this drive method led to "burn in" -- some pixels would become unusable over time. A new drive scheme invented by Tim Flegal called symmetric drive replaced the refresh method. In symmetric drive, pulses of alternate polarities were applied to each line so that a net zero dc voltage was developed. This prevented "burn in."
Tim Flegal was also responsible for pioneering a variety of gray scale driving methods, including pulse width, analog voltage, and frame rate modulation. High performance analog drivers at reasonable prices were difficult to obtain, and Planar had difficulty getting Texas Instruments to supply them because of the relatively low volumes involved (from TI's perspective), but eventually Planar found a new supplier for these circuits: Supertex.
One of Planar's key markets after the decline in demand for monochrome displays for laptop computers was military displays. Planar provided EL displays to defense contractors like Norden Systems and Computing Devices Canada, Ltd. (CDC). These displays were monochrome with limited gray scaling. Planar diversified its sales out of military applications toward industrial and medical equipment. By the mid 1990s, over a third of Planar's sales were to medical equipment firms.
Figure 3. Sales of Planar Displays by Type of Application, c. 1998.
Source: Planar Systems at http://www.planar.com on July 28, 1999.
Because of Planar's willingness to work with customers to adapt products for specific applications, it was able to command a price premium over the products of its main competitor, Sharp. By the late 1980s, Planar controlled over 90 percent of the world market for ELDs.
Planar purchased the Finlux Display Electronics unit of Lohja Oy (Finland) in December 1990. Finlux was renamed Planar International, Ltd. Its headquarters remained in Espoo, Finland. The main reason for the purchase of Finlux was to obtain a marketing and production base in Europe but an important secondary reason was to get access to Finlux's atomic layer epitaxy (ALE) technology (see the section on Finlux below).
EL displays were not well suited to military applications by the early 1990s. By that time, the military wanted color displays that were bright enough to be seen in airplane cockpits and tanks under a variety of environmental lighting conditions. In August 1994, Planar purchased the avionics display operations of Tektronix and formed a wholly owned subsidiary called Planar Advance to manage this business. Planar Advance initially invested about $10 million in CRT-based displays for cockpits, but was blindsided by the DoD's policy of switching to ruggedized TFT LCDs. In response to this shift, Planar Advance purchased TFT LCD glass from dpiX and assembled them into "mil spec" units for the DoD. This move permitted Planar to diversify its display offerings out of ELDs but it also necessitated a redefinition of the core competence of the firm.
In 1992, Planar helped to organized a consortium to develop color ELDs called the American Display Consortium. This consortium was funded by the Department of Commerce under the Advanced Technology Program (ATP) created by the Clinton administration. The total funding for the consortium was to be $30 million; half funded by the government and half by the consortium's private firms. The National Institute for Standards and Technology (NIST) supervised the consortium on behalf of the Department of Commerce. Other members of this consortium were: Candescent Technologies, dpiX, Electro Plasma, FED Corporation, Kent Display Systems, Lucent Technologies, OIS, Photonics Imaging, SI Diamond, Standish Industries, Three-Five Systems, and Versatile Information Products.
In Spring 1995 Planar organized a consortium to develop the next generation of High Resolution and Color TFEL Displays. This consortium was funded by the Department of Defense under the DARPA managed Technology Reinvestment Program (TRP). The total funding for the consortium was to be $30 million; half funded by the government and half by the consortium’s private firms. Other members of the consortium were: AlliedSignal Aerospace, Computing Devices of Canada, Ltd., Advanced Technology Materials, Boeing, CVC Products, Georgia Tech Research Institute, Hewlett Packard, Honeywell, Lawrence Livermore National Laboratory, Los Alamos National Laboratory, Oregon State University, Positive Technologies and the University of Florida.
In 1989, the Defense Advanced Research Projects Agency (DARPA) began to fund work on advanced displays as part of its High Definition Systems program. DARPA issued a Broad Area Announcement in that year and in subsequent years asking for proposals.
Planar won one of the first grants from DARPA in 1990 and used the funds to set up a laboratory to develop color ELDs.
Planar participated in a variety of DARPA programs, but perhaps the most significant was its work with Kopin and the David Sarnoff Research Center on active matrix EL (AMEL) microdisplays beginning in 1993.
The AMEL device is processed on a silicon wafer substrate using the inverted EL structure with a transparent ITO top electrode. The lower EL electrode is the top metallization layer of the silicon IC.
ALE was used to make the device because of its excellent "conformal coating" characteristics. ALE resulted in very few pinhole defects, a key requirement for reliable EL devices with top electrodes.
The pixel size of the first generation of AMEL displays was 24 microns. The second generation of displays used pixels of 12 microns. Smaller pixels meant higher resolution, lower power consumption and lower cost of production for a given display format.
In October 1995, Planar announced an arrangement to supply AMEL displays to Virtual I-O, a Seattle-based manufacturer of consumer head mounted displays for virtual reality entertainment systems. Unfortunately, Virtual I-O went bankrupt in 1997 before any of these displays could be sold to the public.
In March 1996, Planar was a awarded a DoD contract to supply an AMEL-based head mounted display (HMD) for the military's Land Warrior Program. On May 16, 1996, Planar announced that it had developed an AMEL microdisplay that was one-inch square, 3mm thick, and weighed only 4 grams. In 1997 Planar announced that it had developed a 0.75 inch diagonal full-color VGA AMEL microdisplay using an LC sequential color shutter.(ref: R. Tuenge, et al., SID 97 Digest (1997), p.862 ). Planar now has a brighter full-color microdisplay capable of displaying 32k colors that does not require the LC shutter.
Planar has experienced a steady growth in revenues (see Figure 5 below).
Source: Annual Report (1998) accessed at http://www.planar.com on July 15, 1999.
Its profits also steadily increased in both absolute terms and per share but with a decline in 1998. Planar went public with an IPO in 1993.
The head of research at Sharp, Sanai Mita, was convinced that ELDs could be used eventually to make flat TVs. Mito was formerly a professor at Osaka Municipal University. He and his team mounted a major effort in the mid 1970s to develop TFELs.
The key research at Sharp was done by Toshio Inoguchi and his colleagues. The successful demonstration of a working TFEL display in September 1978 at the Consumer Electronics Show in Chicago was the "finest hour" of Inoguchi's group. This display was only a few inches in diagonal, but it was also only 3 cm thick.
Sharp began mass production of ELDs in 1983. One of its earliest displays was used in the U.S. Space Shuttle's obital navigation system in that same year. Another early application of a Sharp ELD was in a Grid laptop computer. This display provided resolution equivalent to a quarter VGA (320x240).
1983 was also the year that Shinji Morozumi at Seiko announced that his group was able to build a TFT LCD television. That announcement took Sharp by surprise and they redirected their efforts toward catching up with Seiko in LCDs. By 1987, Sharp was able to market their own TFT LCD television. They were able to capitalize on their lead in mass production of STN LCDs for calculators to quickly develop production technologies for high-volume TFT manufacturing. After 1987, TFT LCD production was far more important to Sharp's corporate strategy than EL production. Nevertheless, the firm remained active in both research and production of ELDs, providing strong competition to Planar and Lohja. Sharp continues to market EL displays for niche markets.
In 1975, a research group headed by Dr. Tuomo Suntola recognized that thin film electroluminescence would be an ideal flat panel display technology provided that luminance stability and reliability problems could be overcome. To solve these problems a new thin-film deposition method called atomic layer epitaxy (ALE) was developed (see Figure 6). The basic idea was to build thin films layer by layer using surface-controlled chemical exchange reactions. The result is a dense, pinhole film with very good step coverage properties. This research activity started in a small company called Intrumentarium that was acquired in 1977 by Lohja Oy, a Finnish conglomerate which was primarily a manufacturer of construction material. Lohja was the second largest Finnish electronics company after Nokia, and the new ELD technology was considered a good fit for its strategy of diversification into electronics.
A. First precursor reacts with the surface. Chemi­sorption occurs through ligand exchange between the precursor molecules and the bonding sites.
B. When all bonding sites are filled the surface reaction is saturated. Bonding sites for the second precursor have been created.
D. and the formation of bonding sites for the first precursor begins again. The cycle of sequences A to D are repeated the necessary number of times for the desired layer thickness.
Excellent ELD results based on its proprietary ALE technology were for the first time presented at the annual meeting of the Society for Information Display (SID) in 1980, where they received a lot of attention. In 1983, three large information boards were delivered to the Helsinki Vantaa airport. Each of these was comprised of more than 700 character modules. They proved that ALE technology could meet reliability requirements necessary for commercial use. That technology was licensed to Sintra Alcatel in France in 1983. However, the driver costs of the ELD character modules were too high to make them commercially viable, and as a result Finlux began development of a 9-inch 512x256 matrix display for computer and industrial applications. A large manufacturing plant was constructed in a new science park set up in Espoo close to Helsinki. Core manufacturing technologies, including ALE deposition equipment, were developed in-house, which delayed the start of mass production until 1986. Half-page ELD matrix displays with resolutions of 640x200, 650x350 and 640x400 were subsequently manufactured at this plant.
The investments and development costs for ELDs were essentially funded internally by Lohja Oy because little public or customer-paid funding was available. This situation changed when color ELD development was started in 1988 as part of an EU-supported international consortium. The first color EL display based on an innovative device structure was brought to market in 1993.
Lohja Corporation was never able to make the Finlux Display Division profitable because of a lack of experience in managing microelectronics businesses. The Finnish economy benefited from rapid economic growth from the late 1970s until the late 1980s. But when the Soviet Union broke apart in 1991, the Finnish economy suffered because of its dependence upon the Soviet Union as a customer for exports. In 1991, the Finlux Display Division was sold to Planar Systems and was renamed Planar International.
The two ELD operations were of approximately the same size at the time of the merger. The merger permitted savings in marketing costs and materials purchases. Planar Systems succeeded in making Planar International profitable in just a few years by using more experienced management, but without changing manufacturing technology and with only minor changes in staffing. The ALE manufacturing technology still forms the basis for the production of high volume ELDs at both Planar Systems and Planar International. Much of the color development results that were achieved in Finland were also of direct benefit to the work on color ELDs at Planar Systems in the United States, and in particular the AMEL microdisplays discussed above.
In addition, in 1996, Planar Systems began to market a new generation of monochrome ELDs called ICEBrite displays. The ICEBrites combined ALE grown phosphors and insulators with high contrast layers developed by Eric Dickey in the late 1980s.
In the late 1990s, several research laboratories announced that they had made breakthroughs in getting thin films of organic materials to emit light analogously to EL devices. Because organic materials offered a number of process advantages over inorganic phosphors, these announcements were taken very seriously by potential investors. This is not the place to go into the details of these developments. Suffice it to say that the emergence of OLEDs led to a relative decline in interest in further work on color ELDs. Planar Systems set up its own OLED program in collaboration with ___ as did several other display manufacturers. It is possible that inability to solve the technological problems that have to be solved in order to manufacture OLEDs in high volumes will result in a return to research on color ELDs and other alternatives to TFT LCDs. For the moment, however, the momentum is with the OLED research groups.
Electroluminescent displays (ELDs) have a venerable history starting with the experiments of Captain Henry J. Round in 1907, O.V. Lossev in the Soviet Union, and Georges Destriau in France. Electroluminescence was mostly a scientific curiosity until the invention of thin film deposition techniques and the discovery that a sandwich of conductors, insulators and phosphors could result in a very efficent and long-lasting form of emissive display. ELDs were very important in the early days of the laptop computer industry and remained important in niche markets for military, medical and industrial equipment where high brightness, speed, contrast, and ruggedness are necessary. The rise of the color TFT LCD display forced the ELD producers to engage in research on color ELDs with the result that there are now multicolor ELDs on the market and full-color AMELs in development for microdisplays. The ELD industry is currently limited to two major players: Planar and Sharp. Planar acquired its only European competitor, the Finlux Display Division of Lohja Oy, in 1990. Sharp remains committed to competing in ELDs but its main focus is on liquid crystal displays. Most of the important research on ELDs remains within the corporate laboratories of Planar and Sharp, but several publicly funded research laboratories and consortia have also made important contributions to ELD technology.
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Soininen, Erkki, M. Leppanen, and Arno Pakkala, Proc. 13th Int. Display Res. Conf. (EuroDisplay'93, 1993) p. 229.
Soxman, Edwin J. and Richard D. Ketchpel, "Electroluminescence Thin Film Research Reports" JANAIR Final Report 720903 (July 15, 1972). JANAIR is the Joint Army-Navy Aircraft Instrumentation Project. Soxman and Ketchpel were employed by Sigmatron, Inc.
Suntola, Tuomo, "Atomic Layer Epitaxy," Material Science Reports, (1989), 261- .
Tannas, Lawrence E., Jr., ed., Flat Panel Displays and CRT's (New York: Von Nostrand Reinhold Company, 1985).
Vecht, Aron, "High Efficiency D.C. Electroluminescence in ZnS (Mu, Cu)," British Journal of Applied Physics, vol. 1 (January, 1968), 134-136.
Velthaus, Karl Otto, Reiner H. Mach, H.W. Schock, Shosaku Tanaka, Kimihiko Yamada, Koutoku Ohmi, and Hiroshi Kobayashi, "Efficient Elecroluminescent Devices Based on ZnS/SrS:Ce Multilayered Phosphors," in Vijay P. Singh and John C. McClure (eds.), Electroluminescence: Proceedings of the Sixth International Workshop on Electroluminescence (El Paso, Texas: Cinco Puntos Press, 1992).
Vlasenko, N.A. and Iu.A. Popkov, "Study of the Electroluminescence of a Sublimed ZnS-Mn Phosphor," Optics & Spectroscopy, 8 (1960), 39-42.
 "Solid State Lamp Theory," Technical Information provided by Lumex Opto/Components, Inc. at http://lumex.com/tech_notes/thery_1.html, access on July 13, 1999.
 P.D. Rock, A. Naman, P.H. Holloway, Sey Shing Sun, and R.T. Tuenge, "Materials Used in Electroluminescent Displays," http://www.distec.com/Electro.htm, accessed on July 13, 1999.
 Ken Burrows, "Screen Printing EL Lamps for Membrane Switches," http://www.screenweb.com/main/newstand/99/el_lamps990128.html accessed on July 13, 1999.
 Http://nina.ecse.rpi.edu/shur/SiC/tsld011.htm accessed on July 13, 1999. The publication of his observations was in Henry J. Round, "A Note on Carborundum," Electrical World, v. 19 (February 9, 1907), p. 309.
 C.H. Gooch, Injection Electroluminescent Devices (New York: Wiley, 1973), p. 2.
 W.J. Baker, A History of the Marconi Company (New York: St. Martin's Press, 1972), pp. 281-285; http://members.xoom.com/_XOOM/jon_uk/biography.html accessed on July 13, 1999.
O.V. Lossev, "Wireless Telegraphy and Telephony," Telegrafia i Telefonia bez provodor, no. 18 (1923), p. 61 and no. 26 (1924), p. 403; and O.V. Lossev, "Luminous Carborundum Detector and Detection Effect and Oscillations with Crystals," Philosophical Magazine, v. 6, no. 39 (1928), 1024-1044. See also http://www.lumex.com/tech_notes/thery_1.html accessed on July 13, 1999; and Gooch, p. 2.
 http://gwdu19.gwdg.de/~ugmk/his_eng.html accessed on July 15, 1999.
 B. Gudden and R.W. Pohl, "gber Ausleuchteung der Phosphoreszenz durch elektrische Felder," Zeitschrift fhr Physik, vol. 2 (1929), 192-196; B. Gudden and R.W. Pohl, "Lichtelektrische Beobachtungen an Zinksulfiden," Zeitschrift fhr Physik, vol. 2 (1930), 181-191.
 Georges Destriau, "Recherches sur les scintillations des sulfures de zinc aux rayons "," Journal de Chemie Physique, v. 33 (1936), 587-625.
 Rack, et al., p. 2.
 N.A. Vlasenko and Iuri A. Popkov, "Study of the Electroluminescence of a Sublimed ZnS-Mn Phosphor," Optics & Spectroscopy, v. 8 (1960), 39-42.
 M.J. Russ and D.I. Kennedy, "The Effects of Double Insulating Layers on the Electroluminescence of Evaporated ZnS:Mn Films," Journal of the Electrochemical Society, v. 114 (1967), 1066- 1071.
 Edwin J. Soxman and Richard D. Ketchpel, "Electroluminescence Thin Film Research Reports" JANAIR Final Report 720903 (July 15, 1972). JANAIR is the Joint Army-Navy Aircraft Instrumentation Project. Soxman and Ketchpel were employed by Sigmatron, Inc. See also, Yoshimasa A. Ono, Electroluminescent Displays (Singapore: World Scientific, 1995), pp. 3-4.
 Bob Johnstone, We Were Burning: Japanese Entrepreneurs and the Forging of the Electronic Age (New York: Basic Books, 1999), p. 139.
 Aron Vecht, "High Efficiency D.C. Electroluminescence in ZnS (Mn,Cu)," British Journal of Applied Physics, vol. 1, Ser. 2 (January 1968), 134-136.
 Peter Brody, et al., "A 6x6 inch 20-lpi Electroluminescent Display Panel," IEEE Transactions, Electron Devices (September 1975), 22,739.
 Toshio Inoguchi, M. Takeda, Y. Kakihara, Y. Nakata, and M. Yoshida, Digest of the 1974 SID International Symposium (1974), 84- .
 Email correspondence from Chistopher King on July 15, 1999.
 K. Okamoto, Ph.D. Dissertation, Osaka University (1981).
 Email correspondence from Richard Tuenge, August 18, 1999.
 http://www.planar.com/profile.htm accessed on May 8, 1997; and email correspondence from Christopher King on July 15, 1999. Also coming to Planar from Tektronix were: Richard Coovert, Brian Dolinar, Donald Cramer, William Barrow, and Hal Merritt.
 Hoover's Online profile, accessed at http://www.hoovers.com on May 8, 1997.
 Email correspondence from Christopher King on July 15, 1999.
 Interview with James Hurd, CEO of Planar, on June 10, 1996.
 Annual Report (1994), p. 14.
 "Planar and ARPA Sign TRP Agreement," Business Wire, March 22, 1995.
 Christopher N. King, "Electroluminescent Displays…," accessed at http://planar.com/download/tech/mrsnf98.pdf, p. 6.
 "Planar Systems announces the world's first full-color active matrix electroluminescent (AMEL) miniature headmount display," Business Wire, May 15, 1996.
 Andrew MacLellan, "Smaller Displays Gain," Electronic News, May 20, 1996, p. 1.
 Richard T. Tuenge, et al., SID 97 Digest (1997), p.862.
 Electronic Industries Association of Japan (EIAJ), Research Report on the Visions of the Electronic Display Industry in the Year 2000, translated from Japanese by InterLingua (Tokyo: EIAJ, 1993), p. 58; and Johnstone, p. 140.
 Information for this section was provided by Runar Tornqvist of Planar International.
 Eric Dickey, U.S. Patent No. 5,404,389 (1996).

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