A Bright Future for Displays

Every year, thousands of tourists flock to the California coastal city of Long Beach, the last resting place of the ocean liner Queen Mary-a notable showcase of what was once state-of-the-art technology. But for a select group of visitors last May, the city’s main attraction was not a memento of the past but a technology of the future: a dime-thin sheet of glass 14 centimeters along the diagonal whose unparalleled ability to exhibit ultrabright colors and process high-clarity video images holds the potential to have far greater impact on the world than any single ship, no matter how splendid.

These advantages, especially the ability to handle video, give the upstart technology the inside track to become the screen of choice for the coming third generation of mobile phones. About to debut in Japan, the third-generation standard seeks to spur the production of phones that are aimed at eyes as well as ears, by giving them the ability to handle high-speed video over the Internet. These wireless Web phones are expected to quickly become a multibillion-dollar global business. But that may be only the start for organic light-emitting diodes, which are threatening to challenge the 30-year hegemony of liquid crystal displays in a broad range of portable electronics.

This promise has fired the imaginations of scientists and engineers and spurred a worldwide race to develop the technology that pits startups against heavyweights such as Kodak and Sanyo. Difficult problems remain to be solved before the promise can be realized. But the potential is too great for some savvy technology companies to ignore. Notes Dalen Keys, chief technology officer of DuPont Displays, the chemical giant’s spinoff that is out to win a big share of this emerging market, “We are trying to achieve a complete change of the paradigm of what is a display, and the cost of the display.”

If ever a technology has begged to be disrupted, it is liquid crystal displays. Invented in 1963 and originally envisioned as a slimmed-down replacement for bulky cathode-ray tubes or as screens for wall-mounted televisions-a use never realized due to problems scaling up to large surfaces-liquid crystal displays have instead become the standard for everything from watches to laptop computers.

Perhaps the remarkable thing about liquid crystal displays is not that they are so expensive but that, given their technological complexity, they are affordable at all. The core of the screen is a sandwich of two flat sheets of glass a few microns apart, with the liquid crystals that form the display medium poured in between. Since the crystals themselves cannot produce light, it’s necessary to provide a source-a backlight. A diffuser is then needed to distribute the light evenly across the crystals, as well as front-and-back polarizers to orient the light. And that’s just for monochromatic screens. Full-color displays also require expensive red/green/blue filters made of dichromated gelatin-fish glue. To make things fast and bright for, say, a laptop requires another pricey addition: an active-matrix backplane that puts a thin-film transistor behind every pixel. Finally, to manufacture this Byzantine monster takes a superclean factory that won’t leave much change out of a billion-dollar bill.

The result is that for the dozen or so firms, mostly Japanese, that have overcome these obstacles to produce active-matrix liquid crystal displays-only to see them become a commodity item, with wafer-thin margins to match-victory has often been Pyrrhic.

Into this chasm of opportunity, with the potential for cheaper but higher-margin and more versatile displays made of common materials like the dyes used in photocopying and photographic paper, come organic light-emitting diodes. Their story begins in 1979, with a scene straight out of a low-budget sci-fi movie. That’s when Ching Tang, a Hong Kong-born chemist at Kodak’s research laboratories in Rochester, NY, noticed that one of the organic solar cells he was working on was giving off…well, a strange, blue glow. Curiosity aroused, the Kodak scientist launched a long investigation into this phenomenon, known as “organic electroluminescence.” His seminal work, reported in Applied Physics Letters in 1987, showed that organic materials were efficient converters of electricity into light that could be switched on and off quickly-especially crucial for showing video, where images are updated 50 or 60 times a second and get blurred if the screen can’t keep up. Furthermore, Tang noted, these effects could be obtained with low voltage. In short, organic light-emitting diodes had all the makings of a sensational display technology.

Another breakthrough occurred a year later, when Jeremy Burroughes, a doctoral student at the University of Cambridge’s famous Cavendish Laboratory, showed that electroluminescence was characteristic not just of the small molecules studied by Tang but also of far larger polymer molecules (see “Displaying a Winning Glow,” TR January/February 1999). This was important because it’s much easier in principle to make displays out of polymers than out of small molecules. The smaller materials must be vaporized in a vacuum, then patterned through a perforated metal foil or shadow mask-a costly and delicate process. At least for monochrome displays, however, polymers can be deposited by inexpensive “spin-coating,” in which they are simply squirted at a rotating target to achieve a uniform surface.

Such simplicity should translate into a manufacturing process between 20 and 50 percent cheaper than liquid crystal display processes. It also means a thinner and lighter screen with far lower power consumption: backlights in conventional screens are a major drain on laptop batteries. In addition, organic light-emitting diodes shine much brighter than their conventional rivals and are visible even in daylight. In short, enthuses analyst Mentley, “They have all the ideal features you look for in a display.”

These impressive qualities have sparked a flood of gushy predictions about potential applications for organic light-emitting diodes that range from a new generation of affordable wall-hung TVs to highly flexible displays that can be rolled up and carried around like newspapers. It’s still too early to evaluate most of these uses, which hinge on clearing formidable engineering hurdles. But there is one arena where the technology is ready to have immediate impact: cell phones.

All this activity represents the first wave of what many insiders believe will be a revolution in displays for devices ranging from small-screen applications such as digital camera viewfinders to handheld computers and laptops. Here, the stakes are far bigger than with cell phones, which DisplaySearch estimates will represent only about a tenth of the total $75 billion liquid crystal display market in 2005.

Indeed, if the industry buzz is to be believed, organic light-emitting diodes hold the potential to blow away the entire economics of display making. One approach is to dramatically lower manufacturing costs by printing displays directly from an inkjet printer onto a substrate. Last July, Seiko Epson demonstrated a full-color 6.3-centimeter screen made using this method. A next step might be to replace glass with plastic as the screen’s substrate. That will produce a display cheaper, lighter and more rugged than today’s organic offerings. But the critical point is that once the substrate is plastic, it is easy to imagine a transition from the current, hands-on batch production to an automated rolling process where displays are churned out more like newspapers than chips.

Beyond new forms of manufacturing comes a potentially even bigger step, in which polymers replace silicon in the thin-film transistors that form the active matrix backbone. Philips Electronics, Lucent Technologies, and Plastic Logic, formed last year by Richard Friend, are among those exhibiting prototype polymer transistors. Combined with a plastic substrate, this advance could enable a further milestone: electronic paper (see “Electronic Paper Turns the Page,” TR March 2001).

Of course, talk about e-paper and other advanced applications is getting ahead of the story, since organic light-emitting diodes face obstacles in nearly every application. One serious current problem is color. Leave the Kodak screens on for a month or so, and the color becomes very nonuniform. Reds and blues die first, leaving a very green display. Cambridge Display Technology has done better with its polymer displays, achieving a working life of 100,000 hours for red and 30,000 hours for green-but just 1,000 hours for blue.

Both technologies are probably good enough for cell phones, which are typically used 200 hours a year and would likely be replaced before the colors start to fade. But such performance is not adequate for handheld or laptop displays, for which several thousand hours of life are required. “Whether the material technology can make it to that level has yet to be proven,” admits Kodak’s Tang. And the list of technical obstacles grows longer the farther out one looks.

Ultimately, however, the biggest challenge that organic light-emitting diodes face may not be so much technological as commercial. That is, while liquid crystal displays will probably fail to match the attractiveness or performance of organic light-emitting diodes, they will continue to be reliable and affordable-and their manufacturers will no doubt find ingenious ways of further lowering costs and improving capabilities. As analyst Mentley warns, “I haven’t heard of any of these LCD guys saying they’re just going to fold up and go away. It’s going to be a battle.”

Still, the battle is joined. And, as Richard Friend notes, few technologies last forever. “I mean, really new things will happen,” he asserts. It looks as though organic displays could be one of those really startling new things that come barreling over the technology horizon.