Germanium transistor could increase speed of computers

An experimental design for electronics components made from conventional materials could provide a new way to increase the speed of computers.

Researchers from the Massachusetts Institute of Technology’s (MIT’s) Microsystems Technology Laboratories (MTL) have developed a type of transistor that is twice as fast as previous experimental models and almost four times as fast as the best commercial equivalent.

The new p-type transistor is made from germanium, alloys of which are already found in commercial microchips, so germanium transistors could be easier to integrate into existing chip-manufacturing processes than those made from more exotic materials.

The transistor also features what’s known a trigate design, which could solve some of the problems that currently plague computer circuits at extremely small sizes.

A p-type transistor is a kind of switch that controls the flow of ‘holes’ — the gaps created in an atomic structure as electrons move around. (An n-type transistor controls the flow of electrons and is typically easier to improve.)

The researchers achieved the high speeds by ‘straining’ the germanium in the transistor — forcing its atoms closer together than they’d ordinarily find comfortable.

To do that, they grew the germanium on top of several different layers of silicon and a silicon-germanium composite. The germanium atoms naturally try to line up with the atoms of the layers beneath them, which compresses them together.

‘It’s kind of a unique set of material structures that we had to do, and that was actually fabricated here in the MTL,’ said research leader Prof Judy Hoyt in a statement. ‘That’s what enables us to explore these materials at the limits. You can’t buy them at this point.’

Graduate student James Teherani added: ‘These high-strain layers want to break. We’re particularly successful at growing these high-strain layers and keeping them strained without defects.’

Another crucial aspect of the research was developing the trigate design. A transistor works by opening and closing a kind of gate to control the flow of electrons or holes (charge carriers) through a channel.

Transistors have become gradually smaller over the years but they can only be miniaturised so far before the gates become too small to reliably control the flow.

In the MIT trigate design, the channels rise above the surface of the chip — like trains on a track — and the gate is wrapped around the channel’s three exposed sides, allowing greater control.

The MIT researchers’ work was supported by the US Defense Advanced Research Projects Agency (DARPA) and the Semiconductor Research Corporation.