Computer chips give new spin on saving energy

MICROCHIPS that process information without moving electrons could lead to a new generation of ultra-low-power computers. That is the promise behind a processor that uses waves rather than current to crunch digital data.

In conventional computer chips, information is processed in the form of electric charges and transmitted by physically moving electrons from one place to another. This approach has been hugely successful, with engineers packing ever-increasing numbers of transistors onto a single chip.

But Moore's law, as this trend is called, is set to come up against a barrier. As transistors become smaller, tiny variations in the structure of the materials they are made from can influence the electron flow. This makes it hard to guarantee that neighbouring transistors are identical.

Physicists have been studying another way to process data that may overcome this problem. In addition to their charge, electrons have a property called spin, analogous to the spin of a basketball, that can also carry information. Electron spin can be made to represent a 0 or a 1 of digital code by aligning it with or against a magnetic field.

Instead of physically moving the electrons, the information can be sent in the form of a "spin wave" that travels through the sea of electrons in a conductor like a ripple moving across a pond. The snag so far has been to find a suitable way of processing the data carried by the spin waves.

Now a team led by Kang Wang at the University of California, Los Angeles, has built the first logic gate a few micrometres long that can process the data carried by spin waves. To generate the waves, electrons are zapped with a magnetic field. The waves then flow along transmission lines buried in the chip and are processed by making them interfere, says Wang.

Wang's logic gates have the potential to work on a much smaller scale than conventional transistors because they do not rely on a flow of electrons. Also, as no electrons actually move in this device, less energy should be lost as heat, says Wang. This could help when it comes to packing large numbers of these devices onto a microchip, resulting in ultra-low-power computers.
Spin wave logic gates could work on a smaller scale than today's transistors

Wang's group faces numerous challenges in turning the logic gate into a commercially viable processor. One hurdle is to find a way to split the signals from one gate so that several gates can be connected together to form a transistor.

"The spin wave logic device is very elegant from a physical point of view, but whether it will really make a device is very difficult to say," says Del Atkinson from Durham University in the UK.

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