Revealing the Unknown

When the winners of the Society for Information Display's major 2005 awards did not obtain the results they expected from their investigations, they appreciated the greater value in what they saw before them – and their insights changed the display industry.

by Alfred Poor

HENRY DAVID THOREAU once wrote that "the process of discovery is very simple. An unwearied and systematic application of known laws to nature causes the unknown to reveal themselves." Last May, within the mirror-and-brocade walls of a Boston hotel banquet room and far removed from the crowded confines of a typical research lab, the Society for Information Display honored men who had taken on the unwearied and systematic task of discovery, though in both cases the end result was not what they set out to find. Thanks to their genius in recognizing the opportunities presented by the unknowns that were revealed by their efforts, the display industry has been changed forever.

A New Light Valve

The Karl Ferdinand Braun prize was awarded to Dr. William P. Bleha, Vice President of Engineering with the JVC ILA (Image Light Amplifier) Technology Group, for his invention of the liquid-crystal light valve, for fostering its refinement, and for leadership in its application to large-screen projection displays (Fig. 1). Yet, were it not for a fortuitous moment and a mind prepared to recognize it, the technology might never have come to light.

In 1972, Dr. Bleha was working at Hughes Research Labs in Malibu, California, trying to develop a way to create holographic movies. He developed a thin-film technology using reflective liquid-crystal material to create a liquid-crystal light valve (LCLV). This was an optical-to-optical image transducer, which was addressed by the image on a CRT and produced a much brighter image by reflecting the light generated by a scanning laser. It wascapable of handling large amounts of information, but not enough for real-time holographic movies.

 Ken Werner

Fig. 1: Dr. William Bleha receiving the Karl Ferdinand Braun prize from SID Awards Chair Dr. Larry Weber at SID '05 in Boston.

The moment of discovery occurred at a quarterly project review, when Bleha presented his team's progress on their project to other groups at Hughes. One member of another team was charged with developing on-board displays for naval ships. At the time, the U.S. Navy still relied on crew members writing backwards with grease pencils on the back of clear plastic panels, and there was a strong need for reliable and rugged displays capable of showing real-time information to many viewers at a time. The Hughes colleague from the other group approached Bleha to inquire whether or not the technology could be adapted to this purpose.

This chance exchange transformed the project. While the laser research continued as a data-processing application, it never developed into a practical product. Bleha realized that replacing the laser with a bright lamp for the light source created a graphics projector, and the application of this novel technology to the needs of the Navy – and later to Air Force as well – opened the pipeline of development funding and eventual production. One of the earliest demonstrations was a projector that could display black-and-white television images (Fig. 2).

ILA Technology

The technology became known as an Image Light Amplifier (ILA). It relied on a photoconductor film, a dielectric mirror, and a liquid-crystal layer (Fig. 3). This imaging layer responded rapidly to the content of a CRT that was used to address the device optically and had the benefit of no physical pixel structure – similar to a monochrome CRT – so there was no pixelation of the resulting image. A xenon arc lamp provided the illumination. This use of liquid-crystal material for an analog-driven imaging device created the foundation for what would become liquid-crystal–on–silicon (LCOS) imaging panels.

It turned out that JVC in Japan was working on a similar technology, and in 1992 the Hughes–JVC Technology Corp. was created as a joint venture between the two companies. This enterprise developed and produced ILA projectors and sold over 3000 of them in the 1990s.

In June 1999, ILA technology helped usher in the digital-cinema era when two theaters on both the East and West Coasts were set up with digital projectors to screen Star Wars, Episode I: The Phantom Menace. Two theaters used projectors based on the Texas Instruments DLP^™ imaging chips, and the other two – in Paramus, New Jersey, and Los Angeles, California – used ILA equipment. The ILA projectors were rated at more than 12,000 lm and better than 1000:1 contrast ratio and had a wide-format resolution of 2000 x 1280 pixels. Bleha was the project manager for the Los Angeles installation of this historic event.

 JVC

Fig. 2: Changing the readout light source from a laser to a bright lamp transformed the Image Light Amplifier (ILA) to a practical graphics projector. This early demonstrator was a projector that could display black-and-white television images.

JVC researchers then came up with a way to eliminate the CRT and replace it with an active-matrix backplane that delivered the digital information directly to the imaging layer. The result was a digital ILA, known as D-ILA. The technology development was transferred to Japan, while the American group focused on application development. Bleha continued to consult on the development of the technology as well as promote its application for digital cinema and simulation projects.

JVC now ships the QX-1, which is the highest-resolution projector available at 2048 x 1536 pixels. Sony and Kodak are among the companies that have chosen D-ILA technology for their projector projects, and Nippon Telegraph and Telephone has demonstrated a projector with 4000 x 2000-pixel resolution using the D-ILA technology.

Although Bill Bleha has spent much of his life in labs, he also finds time for outdoor activities. Like many others in technological fields, he balances his high-tech working world with simpler pursuits closer to nature. He is an avid jogger – he has run a marathon – and enjoys backpacking. He finds that the time away from the office and lab distractions gives him a good opportunity for thinking. "It's a good time to open your mind to possibilities, to solve problems, and be creative," he says.

As digital cinema starts to take hold worldwide and as D-ILA technology is poised to play an increasing role in this new wave, the international display community can be glad that Bleha had an open and creative mind and was able to see that a laser-based analog system for holography could be converted into a practical approach to digital projection.

Cool Light

The other major-award presentation of the evening was the Jan Rajchman prize, presented to Prof. Donal Bradley, Dr. Jeremy Henley Burroughes, and Prof. Sir Richard Friend for their discovery of light-emitting polymers (LEPs) and their contributions to the understanding and development of LEPs for display applications (Fig. 4). Their work was curiously foreshadowed decades earlier by a fictional invention.

The famous and prolific science-fiction (and science) writer, Isaac Asimov, once wrote a story about a scientist who stumbled onto a new light-emitting technology that was highly efficient and did not waste energy producing heat. Asimov called it "cool light." And as the story continued, the scientist turned off his new invention and discovered that it also "ran back-wards." When light was shone on the panel, it produced electricity. About half a century later, life imitated fiction when polymer-based organic light-emitting diodes (OLEDs) were discovered.

The discovery occurred in 1989 when Jeremy Burroughes and Donal Bradley were post-doctoral students working with Prof. Friend at Cavendish Laboratory of Cambridge University. Friend had already done pioneering research into the use of organic polymers to create semiconductors.

Burroughes and Bradley were working on experiments to see how well certain organic polymers worked as electrical insulators. Burroughes was running a series of tests in the lab one day and as current was applied to one sample, it emitted light that could be seen right through the thin aluminum layer that coated the sample, even from a distance of several feet away.

At first, Burroughes thought it might be a reflection from some other light source, but he quickly discovered that the light was indeed coming from the experimental sample. He turned off the electricity to the sample – thus ruining the test run that was in progress – and the light went out. He applied the current again and the light came back. He then replicated the result using a second sample and realized that he had chanced upon something important. Soon Bradley arrived, sharing in the excitement of the discovery. Prof. Friend appeared a little later, and the three started drafting a patent application that afternoon.

In addition to the filing of a patent by Friend, Bradley, and Burroughes, their unanticipated discovery led to the publishing of an article in Nature magazine in 1990, "Light-emitting diodes based on conjugated polymers." Ultimately, the discovery led to the founding in 1992 of Cambridge Display Technology (CDT) – Cambridge University's first commercial spin-off – to develop and market the new technology.

Fig. 3: The basic elements of the ILA were a photoconductor film, a dielectric mirror, and a liquid-crystal layer which responded rapidly to the content of a CRT that addressed the device optically. The device had the benefit of no physical pixel structure – similar to a monochrome CRT – so there was no pixelation of the resulting image. A xenon arc lamp provided illumination.

OLEDs rely on a fundamentally simple structure in which layers of materials are applied to a substrate. Typically, this involves an electron-injection layer and a hole-injection layer, with an emissive polymer in between. The electrons and holes combine in the polymer layer and light is emitted. It has since been found that – like Asimov's "cool light" – OLEDs can "run backwards" and be used as photovoltaic devices to convert light back into electricity.

There have been two major camps in the development of OLED materials. One group, based on technology developed by Kodak, relies on small-molecule materials. These must be deposited on substrates using vapor deposition and similar processes. The advantage of the large-molecule polymer materials developed by CDT is that they are much larger molecules, which, as a result, can be dissolved in a carrier fluid. This makes it easier to deposit small quantities of the material in precise locations; this can be accomplished using standard ink-jet-printing technology.

The fact that the materials are polymers means that they are more flexible than other display technologies. This makes OLEDs ideally suited to applications using flexible substrates, and researchers seek to create bright, emissive color displays that can be rolled up like a sheet of paper. Such displays could be produced in roll-to-roll processing, much the way newspapers are printed on large rolls of paper, which could greatly reduce costs compared with the current batch processing of individual substrates used in LCD and plasma-panel production.

Today, CDT has licensed its large-molecule polymer OLED technology to nine companies around the world, including DuPont, Epson, Philips, OSRAM (part of Siemens), Dai Nippon Printing, Delta, and Innoled. Philips was the first to bring the technology into small-scale production in a retail product – an electric razor that used OLEDs as the display. Last year, Philips started selling a mobile telephone with an OLED display. CDT continues to expand the technology through research on its own and with other partners. This work covers the full range of inquiry, from basic materials to processing procedures to small-scale production equipment. CDT has also joined ULVAC in a joint venture named Litrex, which is developing ink-jet equipment for production-scale fabrication of OLED displays.

Prof. Friend also founded Plastic Logic, a company created to develop his discoveries in the field of plastic semiconductors. The company now has strong ties to Siemens and Mitsubishi and is involved in developing flexible displays. It has demonstrated printed electronics in a flexible display using E Ink Corp.'s bistable display technology.

Dr. Bradley is currently part of the Experimental Solid State Physics Group at Imperial College in London, working on polymer optoelectronics. And Dr. Burroughes is now Chief Technology Officer with CDT, guiding the company along its technology roadmap as it takes on new research partners and commercial customers. •

 (a)  (b)  (c)

Fig. 4: SID's Jan Rajchman prize was presented to (a) Prof. Donal Bradley, (b) Dr. Jeremy Henley Burroughes, and (c) Prof. Sir Richard Friend for their discovery of light-emitting polymers (LEPs) and their contributions to the understanding and development of LEPs for display applications.