Wiry transistors aim for 60GHz

Researchers in Sweden have used self-forming nanowires to put transistors made of indium arsenide onto a wafer of silicon, with the aim of building devices able to switch at 60GHz or more.

“This kind of transistor should be able to reduce energy consumption in mobile phones and computers. What’s more, it can pave the way for communicating in frequencies that are too high for today’s technology,” claimed Professor Lars-Erik Wernersson of Lund University.

The team used indium arsenide to improve electron mobility over silicon. Building the nanowires vertically make it easier to wrap a gate around the transistor channel and to control its length. It should be possible to design transistors with very short gate lengths as that is controlled by the rate at which the insulating gate oxide that wraps around the wire is grown. The experimental devices have a gate length of around 50nm but the team believes this can be shrunk.

Laterally, the design is bigger than a conventional transistor because the team is using arrays of nanowires to improve the current flow through an aggregate device. However, the move towards shorter gates should improve switching frequency, although the team has yet to publish figures on the switching speed of the current device. The hope is to reach 60 GHz.

“With 60 GHz you can only communicate across short differences and not through walls, for instance. But this new frequency range can rationalise wireless communication in the home, for example when you download a film or communicate between TVs and projectors. We know for sure that such electric appliances will be integrated more and more in the future,” said Wernersson.

The transistor has been partly developed in collaboration with the spin-off company QuNano.

Image: The transistor uses a vertical wire of indium arsenide surrounded by hafnium oxide that acts as the gate dielectric

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