Making light work of silicon chips

Materials World magazine
1 Nov 2009
silicon chip

Silicon chips that can emit light could be demonstrated within four years, thanks to a team of international researchers who claim to have overcome previous limitations.

They say such technology would enable a massive increase in data transfer rates in and out of the home, as computers and telephones could connect directly to a fibre-optic cable. At present, data, in the form of electrons, is carried out of the home by copper wire before being converted to photons and transferred over long distances by fibre optics.

Light-emitting chips could perform this electron to photon conversion themselves, by integrating the functions of several existing communications devices – including processors, waveguides and lasers – onto a single chip.

Researchers at The University of Manchester, UK, and partners, say they have created silicon chips that incorporate lasers or light emitting diodes.

It is well understood that adding small amounts (one per cent) of erbium to silicon oxide produces a light-emitting material. But at these levels, erbium tends to form clusters, which destroys the optical effect.

‘The [proprietary] process we’ve developed with McMaster [University, Canada] reduces the clustering to a level that we think is practical to make on-chip light sources,’ says Matthew Halsall, a senior lecturer in the Department of Electrical and Electronic Engineering at Manchester. The exact details of the technology are confidential.

They have combined it with the use of silicon nanocrystals, which, when embedded into the amorphous silicon matrix, help excite the laser more efficiently. Silicon nanocrystals and erbium-doped silicon oxide can be incorporated into the same layer of a standard silicon wafer by means of ion implantation.

‘Conventional silicon chips can process information much faster than they can transfer data in and out,’ says Halsall. ‘This is because the copper wiring on the board has a limit of around one gigabit per second. These chips would remove the bottleneck, he says, because they would work at around 40GB/s.

The project has a UK industrial partner – Qinetiq – that will help create the device. Halsall expects to commercialise the technology   with a university spin-off company, which should begin life at the start of next year. ‘We are looking for interest from large chip-making companies,’ he says.

Work is also beginning to explore other potential applications for this technology, including biosensors and solar cells. The biosensor chips are likely to use erbium-doped silicon dioxide, but the solar cells may use neodymium to generate near-infrared light. The team is also looking at how metamaterials might improve performance.

‘The ultimate aim in this field is to converge photonics and electronics,’ says Halsall.