Despite mobile operators clamouring for handsets that use full-colour Oled (organic light-emitting diode) displays, Oled display developer Sanyo does not think the technology is currently ready to serve duty as the main display on mobile phones.

"You read [in magazines] that mobile handsets are the applications for Oleds, but I can't agree with that yet," said Tadahiko Tanaka, president of Sanyo's semiconductor division.

Oled displays are generally expected to replace LCDs (liquid crystal displays) in mobile phones, especially for 3G (third-generation) handsets, because Oleds emit their own light, removing the need for a backlight and thus saving power and allowing display modules to be slimmed down. Oleds are also brighter, have better contrast with a wider viewing angle and have a faster response time, improving video quality.

Passive-matrix Oled displays offering up to five colours, which have been on the market since 1997, are already used as secondary displays on the back of some clam-shell style mobiles.

The next step is for full-colour, active-matrix Oled to replace LCDs as the main display for mobile phones. Prototypes of Oled-based handsets have been unveiled by makers such as Sanyo, Epson and Toshiba. But technical obstacles remain before active-matrix Oleds can be used as the main display.

One of the major bottlenecks continues to be the short lifespan of Oleds. The useful life of a handset's LCD depends on the longevity of its backlight, which typically runs for about 10,000 hours.

But Oled displays currently do not last that long. For the Oled-based mobile phone that Sanyo plans to launch next year, engineers at the company expect the Oled to last for 3,000 to 4,000 hours.

That may not be long enough to satisfy many users.

"Mobile handsets are the devices you always compare with what others are carrying," said Eiji Kotobuki, president of Sanyo's multimedia division. "Once the Oled quality starts degrading, users can immediately see an obvious quality difference between Oleds and LCDs."

Sanyo has been one of the most active companies to develop Oled-based phones, responding to pressure from Japanese operators. In Japan, mobile handsets are sold through mobile telco carriers' distribution channels and handset makers generally develop handsets in accordance with carriers' marketing strategies.

"Carriers have been overly persistent in their desire for Oled displays," Tanaka said.

Sanyo's first Oled-based handset is expected to be offered in Japan as early as the first quarter next year. But this plan may be set back if the handset's cost is significantly higher than that of other models.

"Carriers wanted to provide an Oled display handset soon, but the price is too expensive," said Toshiba's Tadashi Matsumoto.

While Oleds may not yet be ready for widespread use as main handset screens, display makers keep unveiling more advanced LCDs for mobile handsets and carriers can live with the current LCD technologies for a while, Toshiba's Matsumoto said.

"Omitting a need for a backlight considerably saves power and space, therefore I think the Oled display is ultimately the next-generation display not only for mobile handsets but for every device," Matsumoto said "But it will take at least another two to three years before it comes out."