The light brigade

Companies specialising in LED technologies are stepping up their research and development operations to meet demand for the next generation of light, flexible display screens and light sources.

Cambridge Display Technology, a UK pioneer in organic LEDs (OLEDs), has won funding from the DTI to collaborate on a metal deposition project that could aid the manufacture of flexible display screens.

‘This project could have important implications for the development of next-generation displays,’ said CDT chief executive Dr David Fyfe.

OLEDs, while not as bright as standard LEDs, are self-luminous, so do not require backlighting, reducing their size, weight and power consumption. This gives them obvious applications in the field of portable, mobile devices.

Also, they can be manufactured using inkjet printing technology.

As well as OLEDs, the process being developed by CDT will be applicable to the manufacture of thin-film transistor backplates for flat screens, plasma and LCD displays. The results of the research will be known by mid-2007.

Meanwhile, German company Osram Optical Semiconductor is working on the use of OLEDs for general illumination.

‘In future, OLEDs will be used not only in mobile terminals such as MP3 players and mobile phones, but also as extremely thin light sources with large surface areas,’ said a spokeswoman.

Osram said initial findings indicate a luminous efficacy for white OLED elements of up to 25 lm/W — already better than conventional light bulbs (12 lm/W) and almost on a par with halogen lamps.

In the field of standard LEDs, manufacturer Cree of Durham, North Carolina, recently unveiled a prototype white LED with a luminous efficacy of a dazzling 131 lm/W, putting OLEDs in the shade.

‘This is the highest level of efficacy that has been publicly reported for a white LED and raises the bar for the LED industry,’ claimed Scott Schwab, Cree general manager, LED chips.

According to Fritz Morgan, chief technology officer for Color Kinetics, a US LED lighting systems and technologies company based in Boston: ‘Technical advancements at the component level are critical to expanding the emerging white LED lighting field.

‘Cree’s results show the exciting developments under way that will enable new white light applications and their subsequent adoption by the market.’

It is barely 15 years since Shuji Nakamura invented blue, green and white LEDs, yet they have proved so affordable, versatile, robust, reliable and durable that their adoption and development has become fast and furious.

The market for LEDs, laser diodes and OLEDs is booming, and at least one major product launch in Europe, Sony’s Playstation 3, has been postponed because of a shortage of blue laser diodes.

Nakamura is keeping faith in the future potential of LEDs as light sources for general illumination.

‘The biggest issue with OLEDs is how to remove the heat ‘ he told The Engineer. ‘Gallium nitride [GaN] LEDs can operate at 500°C, while OLEDs can operate at only up to 50-60°C, so I think that for illumination [OLEDs] have no future. It’s a different matter for displays, of course.’

Last month, Nakamura received the €1m 2006 Millennium Technology Prize — the world’s most lucrative award of its type — for his LED breakthroughs and inventing the blue laser diode, the technology behind high capacity Blu-ray DVDs.

The Helsinki-based Millennium Prize Foundation recognised that the solid state light technology will have a profound impact.

LEDs use so little energy compared with the incandescent bulb, that they are expected to reduce the world’s electricity bill by £60bn within another two decades — enough to make 133 power stations redundant and prevent the release of 258 million tonnes of carbon dioxide.

Nakamura told The Engineer how, as a company scientist, he had simply wanted to boost his income by getting a PhD and chose to study GaN because few people were looking at that area, so there would be a better chance of his work being published.

‘I never expected I could invent [white LEDs], just that I could publish a paper,’ he said.

Nakamura, now a professor at University of California, Santa Barbara, with an $8m income boost from a patent settlement, is researching how to improve the manufacture of GaN crystals so that they can yield better materials for blue laser diodes.

If Nakamura can solve the next challenges in LED research, he’ll light up the eyes of manufacturers and games players worldwide.