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Organic displays near critical mass

Posted: 03 Jan 2003 ?? ?Print Version ?Bookmark and Share

Keywords:organic polymers? color displays? OLED? flat-panel display? tft-lcd?

Organic polymers are expected to play a larger role soon in enabling flexible color displays for computers, comms devices and consumer electronics.

Hopes run high that big-time players, buoyed by a major infusion of research cash, will cooperate to help push organic light-emitting diodes out the door in volume in the next few years. Indeed, by 2007 analysts expect OLEDs ? now a minuscule sliver of the fast-growing flat-panel display market ? to be doing well over $2 billion a year in business.

Among the heavyweights in the OLED race, by last count, were DuPont Displays, Samsung, Sony, Hewlett-Packard, IBM, Kodak, Lucent and Philips. Many smaller companies are also dabbling in niche polymer technologies for displays, including Cambridge Display Technology, Optronics, Opsys and Universal Display.

Overall, the flat-panel display market has been hot despite the economic downturn. In 2001 and 2002, FPDs posted average annual growth rates between 12 and 13 percent. By 2006, the market is expected to grow to $44.8 billion, on 17.6 percent annual growth.

Today, OLEDs account for a scant $100 million piece of the $31 billion flat-panel display market. But DisplaySearch projects OLEDs to grow to $2.8 billion by 2007. More cautious, Stanford Resources Inc. projects a $2.3 billion market by 2008. Nevertheless, either expectation makes OLEDs a viable rival for TFT LCDs.

Unlike the liquid crystals in many of today's flat-panel displays, OLEDs are electroluminescent, and are made by applying a thin film of polymer onto a glass or plastic substrate that has been coated with transparent electrodes. Light is emitted from the polymer when an electric field is applied across the electrodes.

Most OLED displays can still only be found on the exhibit floor of a display conference or hidden away in labs. Still, they are making their way into an array of applications available commercially, including cell phones, Gameboys, microdisplays and surprising applications like razors. In the latest James Bond movie thriller, Die Another Day, the hero shaves with a Philips-Norelco Sensotec, introduced in July. The razor has a polymer-based organic LED display showing battery life and shave-sensitivity adjustments.

Successive firsts

Notable milestones are falling fast. After Samsung only recently produced the largest OLED at 15 inches, bypassing Sony's 13-inch entry, Toshiba trumped them both with a 17-inch display, currently the largest full-color active-matrix OLED, which costs approximately $2 million.

With better colors and brightness than LCDs ? albeit in small form factors, for now ? OLEDs show endless potential. Unlike traditional LCDs, OLEDs are self-luminous and do not require backlighting, diffusers, polarizers or any of the other matter that goes with LCDs. But technical problems keep them from becoming cost-effective replacements for LCDs. For larger displays in cost-effective volume, OLEDs remain susceptible to water damage, inadequate display uniformity and crosstalk and are limited in longevity, luminosity, stability and color rendition.

Manufacturing is also proving difficult. Techniques like roll-to-roll processing, fluidic self-assembly or ink-jet deposition are being sporadically applied to increase yields and cut costs. Major manufacturers including Pioneer, Samsung, RiTdisplay and Alien Technologies are working to develop large manufacturing plants.

One recently announced program might speed wider acceptance of OLEDs in all kinds of devices. As part of federally funded research and development, DuPont and Sarnoff Corp. will develop new organic thin-film transistor (organic TFT) technology on plastic substrates. Organic TFTs offer major advances in commercializing future-generation flexible display devices such as full-color polymer-based active-matrix OLEDs.

In contrast to passive-matrix OLEDs, an active-matrix OLED has an integrated electronic backplane as its substrate and lends itself to high-resolution, high-information-content applications, including the display of video and graphics. Polysilicon technology makes this kind of display possible. With its high carrier mobility, polysilicon technology gives thin-film-transistors high current-carrying capability and high switching speed.

"With high-caliber collaborators like DuPont, Sarnoff and Bell Labs working together, we are accelerating efforts toward commercializing moldable display devices with full color video capability," said DuPont Displays R&D leader Dalen Keys. "With the combined skills, knowledge and capabilities of all three organizations, this partnership has the potential to revolutionize the display industry."

Federal support

The federal program is a three-year initiative sponsored by the National Institute of Standards and Technology's Advanced Technology Program. Lucent Technologies' Bell Labs also has been subcontracted to develop a new class of organic-TFT materials and design processes. The technical collaboration combines DuPont's expertise in OLED panels, flexible substrates, cost-effective printing and organic-TFT technologies and Sarnoff's expertise in active-matrix TFT designs and video display systems.

"Organic-TFTs are an exciting development that promises a new era in displays," said Ray Camisa, Sarnoff's vice president for technology operations. "They have the potential to transform the industry from a capital-intensive batch process on glass to a much lower-cost, higher-throughput process compatible with plastic substrates. We envision solutions for applications from portable devices to large area displays, and ultimately very low-cost displays and bar coding for package labels."

The venture plans to create flexible organic-TFT technology, which could dramatically lower the cost of display backplanes and the fabrication of flexible display devices. Flexible displays, representing DuPont Displays' third-generation OLED products, would potentially address market applications ranging from small and medium to very large displays. DuPont Displays expects the technology to be available by 2007. A mass production line in Hsinchu, Taiwan, is producing passive-matrix, polymer-based OLED displays on glass for handheld devices like cell phones and PDAs. DuPont Displays also plans to upgrade its pilot line in Santa Barbara, Calif. to accommodate flexible polymer-based OLED displays by the end of 2004.

Sarnoff, a subsidiary of SRI International, developed color television and liquid-crystal displays and led in creating the new U.S. digital television and HDTV standard. DuPont Displays focuses on flat-panel displays while Bell Labs leads in organic TFT.

Elsa Reichmanis, director of polymer and organic materials research at Bell Labs, called the three-way collaboration very open. "What we are trying to achieve is a seamless collaboration with a free exchange of information," she said. "We will transmit our results of material structures and how structure deposition is executed on device structures for Sarnoff to pick up to produce the TFT devices and then for DuPont to actually manufacture the active-matrix OLEDs. We should know the major results of our progress within the second year of our three-year collaboration."

Precursor circuits

Bell Labs researchers recently detailed a way to use "soft," conformable electrical contacts and lamination procedures to fabricate printed plastic circuits ? a precursor to flexible TFT-based OLED displays. In their approach, parts of a circuit are fabricated on different substrates, at least one of which incorporates high-resolution, conformable electrical contacts. Bonding the substrates creates embedded, high-performance circuits. Among other practical advantages of this approach, researchers say, patterning and deposition steps can be separated. It also enables transistors with geometries that are conducive to high performance. It allows embedded circuits that resist fracture during bending and also forms completely encapsulated devices.

The encapsulation that automatically follows from the lamination process yields devices that are insensitive to prolonged exposure to demanding operating conditions, including complete immersion. These soft, conformable electrical contacts provide efficient, non-invasive probes for the transport properties of chemically and mechanically fragile, ultrathin organic semiconducting films. When combined with high-resolution printing and lamination techniques, these soft contacts also form the basis of a powerful technique for fabricating flexible plastic circuits. The scheme allows the transistors and circuit elements to be naturally and efficiently encapsulated, and the active organic semiconductor layer be placed near the neutral mechanical plane.

Researchers said the same method may also be suitable for organic light-emitting devices, memory cells and other systems. It is also compatible with a variety of conventional and unconventional patterning techniques and it should scale well into the nanometer regime. Straightforward techniques for introducing via connections will enable complex, multilevel circuits. In addition, the compatibility of the approach with a range of organic semiconductors suggests that it may provide a general method for non-invasively establishing efficient electrical contacts to many different types of fragile or ultrathin organic and bio-organic materials.

Soluble solution

Meanwhile, DuPont Displays and Universal Display Corp. are jointly developing a new generation of soluble OLED materials and technology. Based on groundbreaking work in phosphorescent OLED (PHOLED) technology by Universal and expertise in solution-based processing by DuPont, it is expected that the new OLED materials developed by the parties will have significant performance and cost advantages.

The joint development involves intellectual property collaboration aimed at combining the best elements of both developing small molecule OLEDs and OLED processing research, the companies said. This technical approach builds on the performance advantages of phosphorescent small molecule materials and marries it to solution-based application methods, such as ink jet printing, to produce a phosphorescent, printable PHOLED. DuPont will use the results to expand OLED manufacturing. Universal, in turn, will have exclusive right to license the results of the collaboration to third parties.

Under a cross-licensing deal, DuPont will make an initial payment to Universal as well as a running royalty for products sold that use Universal's background phosphorescent emitter, transparent cathode and ink jet printing.

Universal Display calls its patented PHOLED technology up to four times more efficient than other OLED platforms. The company, which has more than 400 patents issued or pending worldwide in OLEDs, is collaborating with organizations to penetrate the electronic flat-panel display market, including a longstanding relationship for OLED research with Princeton University and the University of Southern California. Universal Display also has a joint development agreement with Sony Corp. for OLED television monitors and with Samsung SDI that is focused on portable OLED devices.

One of the first companies to make a splash with OLEDs, Cambridge Display Technology of Cambridge, England, along with Seiko Epson of Japan demonstrated a 2.8-inch polymer LED display that was less than a tenth of an inch thick. The display, with resolution of 100 pixels per inch, was made using ink-jet printing techniques. Drops of red, blue and green LEP material were sprayed on to the substrate to allow the various colors in the image that was being displayed to be flipped on and off as required. Cambridge Display hopes to be producing small, full-color displays in volume next year.

- Nicolas Mokhoff

EE Times

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