Electronic Design

Atom-Sized Transistor Ready For Use In Chips

Measuring less than 50 atoms wide and one atom thick, Andre Geim's graphene transistor may represent the best hope yet for delaying the expiration of Moore's Law. "Silicon will run out of steam in about 20 years," predicts Geim, a professor of condensed matter physics at England's University of Manchester. "We have to meet the challenge of keeping up with Moore's Law."

A little over two years ago, Geim and fellow University of Manchester professor Kostya Novoselov discovered a new material class: a two-dimensional crystal, representing a single sheet of atoms. The material, graphene, is a gauze of carbon atoms resembling chicken wire and has become one of the hottest areas in physics research.

"Until our discovery, this chicken wire was presumed not to exist in the real world," Geim says.

The Manchester team reported the first graphene-based transistor at the same time as its materials discovery. The new transistor is a two-dimensional giant molecule that’s still only as thick as a single atom. Other researchers have since reproduced the team's result, but these first-generation graphene transistors were very "leaky," meaning their electrical flow could not be switched off to zero.

This limitation restricted the devices' potential use in high-density electronic circuits. But earlier this year, Geim and his team announced they had worked their way around the problem and can now produce graphene transistors that suit use in microprocessors and other chips.

Geim notes that in his team's experiments, the graphene remains highly stable and conductive even when it is sliced into strips as narrow as a few nanometers wide. All other known semiconductor materials, including silicon, eventually oxidize, decompose, and become unstable at sizes tens of times larger than Geim's graphene strips. Such poor stability has been the major barrier blocking conventional materials' use in ever-denser electronic devices, threatening to stall future microelectronics development.

"We have created ribbons just a few nanometers wide and cannot rule out the possibility of confining graphene even further, perhaps even down to just a single ring of carbon atoms," says Geim.

The team's research suggests that electronic circuits could someday be sliced out of a single, slightly crumpled, graphene sheet. Geim notes that the sheet's "waviness" may be responsible for its unexpected stability. In any event, circuits carved from the sheet could include semitransparent barriers to control the movements of individual electrons, interconnects, and logic gates all made out of graphene. Geim's team proved this concept by creating a series of single-electron-transistor devices that work under ambient conditions while showing a high-quality transistor action.

"This material promises terahertz transistors," Geim claims.

While enthusiastic about his discovery, Geim doesn't believe that graphene-based circuits will become widely available before 2025. Until then, silicon should continue on as the dominant semiconductor material. Nevertheless, Geim believes that graphene will likely emerge as the only viable approach to increase circuit density after the silicon era inevitably ends.

"Graphene is a unique material in that it is the only material in which electrons travel micron distances without scattering," Geim says. "Ballistic transistors, a holy grail of electronic designers, are possible with this material."

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