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IEDM Boffins at MIT's Microsystems Technology Laboratories have developed the world's smallest transistor made of indium gallium arsenide, a substance they say could replace silicon as the go-to material for building tomorrow's ultra-fast, ultra-small microchips.

The tiny transistor is just 22nm in length, according to a report by MIT's in-house news agency, but it offers good logic performance.

But etching transistors much smaller than that using today's silicon-wafer processes will be tricky, because the smaller the transistors get, more difficult it is for them to handle current efficiently. Researchers believe we are fast approaching a "brick wall," after which point shrinking silicon transistors any further will be infeasible.

It should come as no surprise, then, that chip boffins have been searching high and low for practical alternatives to silicon. Graphene, gallium nitride, molybdenite, even carbon nanotubes – they're trying everything.

Indium gallium arsenide has long been a promising candidate, however, because its ability to conduct electrons is superior to silicon's at the nanometer scale – about five times better, in fact.

The material is already widely used in fiber-optic applications and in radar systems. The trick, however, has been figuring out how to create transistors with it that are small enough to be usable in microprocessors.

Jesús del Alamo and his team at MIT's Department of Electrical Engineering and Computer Science think they have found that method.

First, they used molecular beam epitaxy (MBE) to grow a thin layer of indium gallium arsenide. They then used a combination of electron beam lithography and a technique whereby evaporated molybdenum is fired at the wafer to create the three electrodes that make up the transistor: the gate, the source, and the drain.

Del Alamo says that although none of these techniques is really novel in the semiconductor industry, their use with non-silicon compounds has not been explored much so far, mainly because traditional applications of indium gallium arsenide don't require the tiny components that microchips call for.

"But when you are talking about integrating billions of tiny transistors onto a chip, then we need to completely reformulate the fabrication technology of compound semiconductor transistors to look much more like that of silicon transistors," he says.

According to del Alamo, the group's next step will be to try to shrink the size of the transistors it can produce even smaller than 22nm, with the ultimate goal of reducing them to below 10nm.

Should they succeed, however, there's still one hitch to overcome before chips based on the new material go mainstream; namely, that indium gallium arsenide – which is composed of the elements indium, gallium, and arsenic – is currently as much as 10 times as expensive as the equivalent amount of silicon. Those chips may be small, all right. But they'll cost you.

Del Alamo and his group will present their findings at the International Electron Devices Meeting, taking place this week in San Francisco. ®

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