Chip promises faster light-to-circuit link

By Kimberly Patch, Technology Research News

Although silicon is an excellent material for computer chips, it doesn't conduct light well, which has always meant that the interface between silicon computer chips and fiber optic communications lines requires a translator.

Researchers at the University of London, however, have come up with a way to directly connect an organic light emitting diode (LED) to silicon, which could eventually prove an inexpensive way to integrate fiber-optic lines with the silicon circuits that control networks.

The researchers layered two types of short-chain polymers and aluminum on top of silicon, and coaxed electricity running through the silicon to produce photons in the polymers.

The first layer of polymer serves as a sort of transport layer, while the second layer, which includes erbium, takes in electrons and emits photons at the key telecommunications wavelength of 1.5 microns. Also important, the device works at room temperature. "The aim... is to develop a means of producing an integrated optoelectronic technology based on silicon," said William Gillin, a lecturer in experimental physics at Queen Mary and Westfield College, University of London.

The idea for the work came from a previous, failed attempt to produce a type of silicon that would emit light, Gillen said. "I had done some work on trying to dope silicon directly with erbium to produce a silicon-based [light] source, which was not very successful," he said. "I had the idea of combining ... erbium-based systems with organic LED's to try and produce an erbium-containing molecule that would produce electroluminescence at 1.5 microns and which could potentially be deposited directly onto silicon substrates," said Gillin.

The work is impressive because the device is electrical, said Rajeev Ram, associate professor of electrical engineering at the Massachusetts Institute of Technology. "Most work that's been done with organic light emission has been where you excite the organic material with a laser .... This was nice because they actually electrically injected it and it was nice because they used silicon and aluminum, materials that are very common to integrated circuits, Ram said.

Although the research has proved it is possible to join silicon with an inexpensive organic LED, there's a lot of work to be done to make a practical, said Gillin. The next step is to improve the efficiency, he said.

The device currently draws 17 volts of current and produces .01 photons for each electron put into the system. A practical system would need to work at 1.5 volts and change 10 to 50 percent of the electrical energy to optical energy, according to Ram. This means it must be improved to use 1/10 the electricity and at the same time produce 1000 times more photons, said Ram, adding that it is a difficult but not insurmountable engineering problem.

It will take about five years of research to make the device ready for commercial use, said Gillin.

In the meantime, there are other technologies proposing to bridge the gap between silicon and fiber, said Ram. "There are a lot of other approaches, and some [others] are probably further ahead ... but I think this is interesting because it's potentially very cheap just because it uses organics. Organics in general are very cheap to make emit light," said Ram.

Gillin's research colleagues were Richard Curry from Queen Mary and Westfield College, University of London and Andrew Knights and Russell Gwilliam from the University of Surrey. The research was funded by the University of London, the Royal Society, and the Engineering and Physical Sciences Research Council (EPSRC). The researchers published their results in the October 9, 2000 issue of the journal Applied Physics Letters.

Timeline:   > 5 years
Funding:   Government, University
TRN Categories:  Optical Computing, Optoelectronics and Photonics
Story Type:   News
Related Elements:   Technical paper, "Silicon-based organic light emitting diode operating at a wavelength of 1.5 Microns," in Applied Physics Letters, October 9, 2000


November 8, 2000

Page One

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Chip promises faster light-to-circuit link

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Tiny silicon crystals loom large

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