Look out silicon here comes graphene

By Elizabeth Latham, Journalist
Tuesday, 10 April, 2007

Graphene, a form of bonded carbon, may become the next buzz word in electronics over the next 10 to 20 years if the current rate of miniaturisation continues.

With manufacturers trying to cram more and more components into integrated circuits, they are reaching the physical limits of silicone that becomes unstable at nanoscale levels.

The response could be a fundamental change in direction for the industry if they use graphene to create what they believe is the world's smallest transistor. Using this carbon has allowed Prof Andre Geim and Dr Kostya Novoselov, of the School of Physics and Astronomy at Manchester University in Britain, to build these devices that are one atom thick and only 50 atoms wide.

Silicone transistors cannot be made smaller than about 10 nm, while graphene can go down to about one molecule or 1 nm, says Geim.

However, the end of silicon transistors in equipment such as computers is not nigh. Researchers have found that graphene semiconductors are very 'leaky', making them quite unsuitable for this use.

After further research, the Manchester team found that graphene remains highly stable and conductive even when it is cut into strips of only a few nanometres wide, whereas all other known materials - including silicon - oxidise, decompose and become unstable at sizes 10 times larger.

The poor stability of these materials has been the fundamental barrier to their use in electronic devices and has threatened to limit the future development of microelectronics.

"We have made ribbons only a few nanometres wide and cannot rule out the possibility of confining graphene even further - down to maybe a single ring of carbon atoms," said Geim.

"Making very narrow ribbons makes graphene transistors both small and non leaky."

The research team suggested that future electronic circuits could be carved out of a single graphene sheet. Such circuits would include the central element or 'quantum dot', semitransparent barriers to control movements of individual electrons, interconnects and logic gates - all made entirely of graphene.

Geim's team has proved this idea by making a number of single-electron-transistor devices that work under ambient conditions and show a high-quality transistor action.

Dr Leonid Ponomarenko, who is leading this research at the university, pointed out that no technology can cut individual elements with nanometre precision, and that the researchers rely on chance by narrowing ribbons to a few nanometres in width. This means that some of them were too wide and did not work properly, whereas others were over-cut and broken.

But Ponomarenko is optimistic that this proof-of-concept technique can be scaled up.

"To make transistors at the true-nanometre scale is exactly the same challenge that modern silicon-based technology is facing now. The technology has managed to progress steadily from millimetre-sized transistors to current microprocessors with individual elements down to 10 nanometres," Ponomarenko said.

"The next logical step is true nanometre-sized circuits and this is where graphene can come into play because it remains stable - unlike silicon or other materials - even at these dimensions."

Geim predicts we won't see these graphene chips any earlier than 2020 - more likely around 2025 - and that until then, silicon technology will remain dominant. He believes graphene is probably the only viable approach after the silicon era comes to an end.

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