Organic Light Emitting Diode (OLED) displays on show at
the Tokyo Electronic Display Expo this week have failed to live up
to the promise of requiring less power than liquid crystal displays
(LCDs).
For the past couple of years electronics companies researching
OLED displays have been making technology promises that are almost
as bright as the displays themselves, but commercial products have
been lacking.
The first commercial OLED began shipping in March. However, both
it and the latest batch of prototypes suggest that the
power-reduction assurances about the technology may have been
optimistic, at least for the first generation of products.
OLEDs are a fundamentally different technology to LCDs. They are
made by sandwiching a layer of organic material between two
electric connectors. When a charge is applied to one connector it
flows through the organic material, causing it to glow.
This means that no backlight is needed and so the entire display
panel can be made thinner, lighter and will require less power than
an equivalent LCD. However, current prototypes consume about the
same power as an LCD and in some cases more.
A prototype 2.1in panel from Seiko Epson consumes about 150mW
when displaying a moving image. A thin film transistor LCD of a
similar size consumes just over 150mW with its backlight switched
on, making the OLED power saving negligible.
"The technology is still young," said Tsutomu Takenouchi of
Seiko Epson's OLED technology division. "We hope to improve the
power saving with future generations."
Toshiba Matsushita also displayed prototype versions of 2.2in
and 3.5in panels. Commercial production is scheduled to begin
sometime in 2004, said Jun Hanari of the company's research and
development centre. On power consumption, he said that in some
cases, such as a still screen of black text on a white background,
it could be as much as double that of a modern LCD.
However, to write off OLED technology because it does not live
up to promises about power consumption would be to ignore its other
features, and to dismiss a market that DisplaySearch estimates will
reach $8bn (£5.1bn) in 2007.
In addition to being physically smaller, the prototype displays
on show in Tokyo were brighter, showed more vibrant colours and
were much better at displaying moving images than similar LCDs.
One of the biggest hurdles to be overcome is the length of time
the display can be used before its organic structure breaks down,
said David Hsieh, an analyst at DisplaySearch. The problem is that
the organic layer slowly succumbs to a chemical reaction that
eventually renders it useless.
For applications such as cellular telephones and camcorders, the
industry is aiming for a lifetime of more than 10,000 hours. Most
of the prototypes developed so far, Hsieh estimates, have a
lifetime of between 6,000 and 8,000 hours.
Eastman Kodak and Sanyo Electric were showing a new 2.16in OLED
developed by their SK Display joint venture. Sanyo said the display
has a lifetime of 5,000 hours measured at full white light, which
consumes the most power, and will last in average use for between
two and five years when used in a digital still camera.
The display is the first commercial, full-colour, active-matrix
OLED to be produced and is used in Kodak's just-launched EasyShare
LS633 digital still camera.
The display has a resolution of 521 pixels by 218 pixels,
luminance of 120 candela per square metre and is less than 2mm
thick. Alongside it Sanyo was showing a prototype 2.2in OLED. It is
targeted at cell phones and so has a lower resolution of 176 pixels
by 220 pixels but is also full colour.