Organic LEDs Get Brighter, Sharper

David J. Williams

Organic light-emitting diodes are the hottest new display technology. Incredibly, it can often take 20 to 30 years to fully commercialize a display technology, but these devices are already ahead of the curve and poised to move into the next phase of commercialization. Scientists at Eastman Kodak Co. invented this technology in the late 1980s and stepped up development efforts in the mid-1990s.

Organic LED displays involve two variations of the technology. Kodak, along with more than a dozen companies worldwide, is commercializing the “small molecule” technology. Products have been on the market since 1999. The other variation, based on polymers, has a smaller following and is two to three years behind the small-molecule approach in terms of development and commercialization.

Eastman Kodak and Sanyo recently introduced a 15-in. organic LED monitor that is only 1.4 mm thick.

Passive-matrix organic LEDs based on our technology and materials were the first to market, with Pioneer offering high-end car radios that used them. Motorola followed with a cell phone display. Now, half a dozen factories are poised to pump out passive-matrix organic LED panels for a host of customers and applications. A flood of new products should begin arriving on the market early this year.

The initial manufacturers of the small-molecule organic LED displays worked on many of the mass-production problems you would expect when trying to commercialize a new technology: getting the transparent electrode material to be smooth and flat, removing contaminating particles from the manufacturing process and improving yields. These problems have been solved. Pioneer and RitDisplay are the first to make organic LED products. TDK, Nippon Seiki, Teco and others are expected to follow soon.

As evidence of the technology’s maturity, we point to the fact that the cost of some passive-matrix organic LED panels is now comparable with that of passive-matrix supertwisted nematic liquid crystal display (LCD) panels for many handheld appliances. Passive-matrix organic LEDs are typically limited to smaller-size displays with fewer than 120 rows of pixels. Colors are good, being slightly less saturated than NTSC TV values, and operational lifetimes have improved to at least 5000 hours, which is acceptable for many products.

Active-matrix production

Active-matrix organic LEDs are coming, too. With an active-matrix device, a transistor (or series of transistors) is dedicated to each pixel in the display. This improves performance and allows construction of much bigger and higher-resolution displays.

To commercialize this technology, we have formed a manufacturing joint venture with Sanyo, called SK Display. To date, no other companies have been licensed for the small-molecule active-matrix technology for direct-view organic LED displays, but we expect to have several in the next year or two. EMagin is the only Kodak licensee for active-matrix microdisplays.

An initial foundry was established about a year ago to process 300 x 400-mm glass sheets. The active matrix is formed using low-temperature polysilicon processing, and the organic LED layers are added on top of this. Each sheet is diced into several smaller displays. In October 2002, mass production was initiated. Engineering samples began shipping in early 2002, and production samples are shipping today. These displays are being targeted for applications with sizes of less than about 7 inches.

By the middle of 2003, a second line is scheduled to begin production. This line will have a capacity to process 550 x 670-mm sheets at a faster rate.

Refinements continue

Manufacturing active-matrix displays presents new challenges, such as ensuring the uniformity of the various layers in the display over the large substrate area. Efforts to improve process stability and reduce variability have been ongoing and are at the point where mass production has begun.

Some of the problems associated with passive-matrix manufacture are not as serious with active-matrix. A pixel short in a passive matrix will take out an entire row and column, for example, making the device unacceptable. This is not the case with an active matrix, where repair techniques may work, or in the worst case, a single pixel is lost.

As with any new technology, active-matrix devices will be premium-priced at first, but we expect them to become competitive with other mainstream display technologies within a relatively short time. The potential of the technology is apparent. Last October, for example, a 15-in. organic LED monitor was introduced that was extremely thin — only 1.4 mm thick — and that exhibited excellent color performance and high speed.

Compared with a similar LCD panel, the organic LED panel has higher contrast, is more vibrant and is richer in color. It is an impressive display — the wave of the future.

Meet the author

David J. Williams is chief technical officer of Eastman Kodak Co.’s display products business unit. He has been responsible for the development of organic LED technology there since the early ’90s.