Organic LEDs Get Brighter, Sharper
Rapid advances in the development of organic LEDs have set the stage for the next step in global commercialization.
David J. Williams
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 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.
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.
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