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Wednesday 7 January 2009
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|NewsletterDisplays and Opto
OLED displays move into mobile mainstream
Wednesday 23 August 2006
The first mobile phone to have an OLED (organic light-emitting diode) as its main display appeared a few months ago. This was the BenQ-Siemens S88, with a 2in. active matrix colour OLED. Samsung is also making phones with full colour OLEDs, suggesting that the technology is moving into the mainstream, certainly for short-lived consumer items.
The OLED in its two basic formats – single molecule and polymer – has for some time been hailed as the perfect display, being thinner and more power efficient than LCDs, with better colour saturation and no need for a backlight. And with material costs typically 20 per cent less than LCDs, OLEDs should be cheaper than LCDs once production yields have improved.
“The killer benefits are viewing angle and contrast, which are better than any other display technology,” explains Mike Caddy, product manager for displays at Anders Electronics. “Viewing angle is nearly 180 degrees and there is a completely symmetrical cone. Also, brightness, contrast and colour balance doesn’t change with viewing angle. This is because the OLED is an inherently emissive display so there is no light being manipulated through the depths of the display.”
But OLED technology has failed to live up to its promise so far because of the short lifetime of the materials, in particular the blue emitter, which causes differential aging in colour OLEDs (based on red, blue and green emitters). In other words, a white screen would turn a sickly green over a relatively short time.
Although mobile phones are not designed to become heirlooms, their recent adoption of OLEDs indicates that full colour displays now have lifetimes good enough to satisfy the majority of users.
“Blue lifetimes have improved a lot over the last few years and now they have a half-life in excess of around 20k hours [at 100cd/m2,” says Myrddin Jones, CEO of OLED-T, which supplies materials to small molecule OLED makers. “That is still shorter than the red and green, which can be in excess of 100k hours, but works out at around 2.5 years of continuous use. Most mobiles spend a lot of time in standby, so the calculation that’s been made is that it’s good enough.”
Reflecting the market ramp-up, OLED-T raised $7m in venture funding in May this year and in June invested $900,000 in an R&D facility at Brunel University Science park. It is currently focusing on its two high efficiency, low-voltage transport layer materials, which potentially could be used in all single-molecule OLEDs. “Compared to the standard materials our voltage is between 0.5 and 1V lower. We hope to have business with around six display manufacturers over the next five years for at least these two materials,” says Jones.
In most respects, OLEDs are evolving in much the same way as LCDs. Active matrix displays are coming onto the market, bringing higher resolutions with good brightness, and displays are getting bigger. This is where CDT’s polymer technology is expected to come into its own. The current market is dominated by small-molecule OLEDs and 0.5 to 2.5in. displays, but the general view is that the ease of manufacture of polymer OLEDs will bring a new generation of much bigger OLEDs for computers and TVs.
The dream product is the battery-operated, roll-up TV screen of 8 or 9ft diagonal, costing less than £500. Today’s short lifetimes make P-OLEDs unsuitable for these applications, where a TV could be on ten hours a day and not replaced for ten years.
Terry Nicklin, marketing director of CDT, says the lifetimes of its current P-OLED materials (at 400cd/m2) are 50k hours for red and green and 12.5k for blue. But there are many factors that influence these figures. “As well as looking at the raw materials, we’re also looking at device construction and architecture, driver schemes and so on to increase the lifetimes,” Nicklin says. “A number of display firms have stated they will have P-OLED TVs in 2008/9 timeframe. We feel that the materials would be okay for that.”
Today’s P-OLEDs are inkjet printed but there is the potential to use cheaper methods. CDT has shown a roll-printed display, developed in conjunction with Japan’s largest printing company, Toppan, which was a 5.5in. full colour, active matrix display. “The display we showed was about 90 pixels per square inch, but Toppan is confident they can get to 200 pixels per square inch,” explains Nicklin. “It is a true step towards roll-to-roll printing where you’re taking a roll of plastic and rolling out displays.”
Another improvement has been in shelf-life. “A few years ago, the shelf-life on an OLED might have been only one or two times its natural operational life because of the sensitivity of OLED materials to moisture,” says Caddy from Anders. “Now it is many times the operational life, which has been achieved by better sealing processes.”
Trident represents a number of OLED makers but until recently has refused to sell OLEDs because, according to Martin Cobb the firm’s technology manager, the technology was not mature enough. “Now, some of Univision’s monochrome displays will reach 50k hours half-life and we are designing them in,” he says. However, he stresses that design-in is on a project basis and OLEDs are not a standard distribution product.
Yet despite his reservations, Cobb, like many others in the displays industry, sees OLEDs as the future, particularly for large screen displays. “OLED technology is the most dramatic thing that has ever happened to the displays industry. It hasn’t taken very long and TFT LCDs can’t get much cheaper because they have to be made on glass. If you can screenprint on sheets of plastic, it’s a big difference. It’s a no-brainer,” he says.
The OLED in its two basic formats – single molecule and polymer – has for some time been hailed as the perfect display, being thinner and more power efficient than LCDs, with better colour saturation and no need for a backlight. And with material costs typically 20 per cent less than LCDs, OLEDs should be cheaper than LCDs once production yields have improved.
“The killer benefits are viewing angle and contrast, which are better than any other display technology,” explains Mike Caddy, product manager for displays at Anders Electronics. “Viewing angle is nearly 180 degrees and there is a completely symmetrical cone. Also, brightness, contrast and colour balance doesn’t change with viewing angle. This is because the OLED is an inherently emissive display so there is no light being manipulated through the depths of the display.”
But OLED technology has failed to live up to its promise so far because of the short lifetime of the materials, in particular the blue emitter, which causes differential aging in colour OLEDs (based on red, blue and green emitters). In other words, a white screen would turn a sickly green over a relatively short time.
Although mobile phones are not designed to become heirlooms, their recent adoption of OLEDs indicates that full colour displays now have lifetimes good enough to satisfy the majority of users.
“Blue lifetimes have improved a lot over the last few years and now they have a half-life in excess of around 20k hours [at 100cd/m2,” says Myrddin Jones, CEO of OLED-T, which supplies materials to small molecule OLED makers. “That is still shorter than the red and green, which can be in excess of 100k hours, but works out at around 2.5 years of continuous use. Most mobiles spend a lot of time in standby, so the calculation that’s been made is that it’s good enough.”
Reflecting the market ramp-up, OLED-T raised $7m in venture funding in May this year and in June invested $900,000 in an R&D facility at Brunel University Science park. It is currently focusing on its two high efficiency, low-voltage transport layer materials, which potentially could be used in all single-molecule OLEDs. “Compared to the standard materials our voltage is between 0.5 and 1V lower. We hope to have business with around six display manufacturers over the next five years for at least these two materials,” says Jones.
In most respects, OLEDs are evolving in much the same way as LCDs. Active matrix displays are coming onto the market, bringing higher resolutions with good brightness, and displays are getting bigger. This is where CDT’s polymer technology is expected to come into its own. The current market is dominated by small-molecule OLEDs and 0.5 to 2.5in. displays, but the general view is that the ease of manufacture of polymer OLEDs will bring a new generation of much bigger OLEDs for computers and TVs.
The dream product is the battery-operated, roll-up TV screen of 8 or 9ft diagonal, costing less than £500. Today’s short lifetimes make P-OLEDs unsuitable for these applications, where a TV could be on ten hours a day and not replaced for ten years.
Terry Nicklin, marketing director of CDT, says the lifetimes of its current P-OLED materials (at 400cd/m2) are 50k hours for red and green and 12.5k for blue. But there are many factors that influence these figures. “As well as looking at the raw materials, we’re also looking at device construction and architecture, driver schemes and so on to increase the lifetimes,” Nicklin says. “A number of display firms have stated they will have P-OLED TVs in 2008/9 timeframe. We feel that the materials would be okay for that.”
Today’s P-OLEDs are inkjet printed but there is the potential to use cheaper methods. CDT has shown a roll-printed display, developed in conjunction with Japan’s largest printing company, Toppan, which was a 5.5in. full colour, active matrix display. “The display we showed was about 90 pixels per square inch, but Toppan is confident they can get to 200 pixels per square inch,” explains Nicklin. “It is a true step towards roll-to-roll printing where you’re taking a roll of plastic and rolling out displays.”
Another improvement has been in shelf-life. “A few years ago, the shelf-life on an OLED might have been only one or two times its natural operational life because of the sensitivity of OLED materials to moisture,” says Caddy from Anders. “Now it is many times the operational life, which has been achieved by better sealing processes.”
Trident represents a number of OLED makers but until recently has refused to sell OLEDs because, according to Martin Cobb the firm’s technology manager, the technology was not mature enough. “Now, some of Univision’s monochrome displays will reach 50k hours half-life and we are designing them in,” he says. However, he stresses that design-in is on a project basis and OLEDs are not a standard distribution product.
Yet despite his reservations, Cobb, like many others in the displays industry, sees OLEDs as the future, particularly for large screen displays. “OLED technology is the most dramatic thing that has ever happened to the displays industry. It hasn’t taken very long and TFT LCDs can’t get much cheaper because they have to be made on glass. If you can screenprint on sheets of plastic, it’s a big difference. It’s a no-brainer,” he says.
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