Published online 28 February 2007 | Nature | doi:10.1038/news070226-10

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Tiny transistor uses a single electron to turn off and on at room temperature.

Field of dreams: flat sheets of carbon could be etched into better transistors. Nature Materials

The latest contender to succeed silicon's throne is graphene. It has been used to make a truly tiny transistor that works at room temperature, offering hope for making faster, smaller electronics devices once silicon reaches its limits.

Graphene is a two-dimensional form of carbon, discovered just three years ago. It is very thin — just one atom thick — and highly conductive with minimal resistance, which has sent physicists and materials scientists into a frenzy to find applications that exploit these properties.

Andre Geim at The University of Manchester, UK, and colleagues made a device etched out of a sheet of graphene that acts as a single electron transistor (SET). The device has a tiny restriction, less than 10 nanometres wide, which can hold a single electron. If an electron is held and trapped here it creates what is known as a Coulomb blockade — no electrons can flow through the device when this electron is in the way.

As a result, the transistor can be turned on or off simply by shunting a single electron into and out of this restriction, which requires only a tiny amount of 'gate voltage' to accomplish. The upshot is that a very small change in voltage can cause a large change in current, making the devices very sensitive and fast. And also small: "The SET relies on controlling electrons one by one; by definition it has to be very small," says Geim.

Such devices have been made previously from conventional semiconductor materials, such as silicon, but these only worked at very low temperatures. At room temperature and at such small scales, silicon oxidizes and decomposes. Graphene, on the other hand, is stable at room temperature.

News of the tiny transistor is unveiled today in a review article1, and Geim has submitted more detailed results to the journal Physical Review Letters.

Ragged edge

Pablo Jarillo-Herrero, at Columbia University, New York, works with graphene and says that Geim's work is a useful proof of concept. But there are still problems to be overcome. Etching graphene leaves edges with dangling carbon bonds, he says, which can cause background electrons to scatter. This makes the transistor less efficient, although the full effect of the scattering isn't yet known. But the vast knowledge of carbon chemistry should hold the answer to how to overcome this kind of problem, he predicts, by chemically altering those edges.

Current industry predictions suggest that by 2020 silicon devices will have shrunk to about 20 nanometres and have reached their limit in size and performance. It is only after this that materials such as graphene will come into their own. And that gives scientists time to perfect the tricky fabrication methods to make such small devices.

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Geim's fabrication method has so far relied on luck: they can etch a very small gate, but it is only sometimes actually small enough to be blocked by a single electron. But he is confident that microfabrication techniques will have this problem cracked by the time silicon breathes its last breath.

"Graphene is not going to kill silicon," says Geim, but it has the most realistic promise of all materials investigated so far. "Graphene offers a glimpse of what is possible after silicon becomes unviable."

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