Organic displays make slow progress

Feature

Organic displays make slow progress

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.


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This was first published in April 2003

 

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