In yet another step toward making nanotech transistors from graphene nanoribbons, chemically-prepared graphene nanoribbons less than 10 nm wide were found to be uniformly semiconducting, room-temperature, field-effect transistors. From Stanford University news service via PhysOrg.com “Carbon nanoribbons could make smaller, speedier computer chips“:
Stanford chemists have developed a new way to make transistors out of carbon nanoribbons. The devices could someday be integrated into high-performance computer chips to increase their speed and generate less heat, which can damage today’s silicon-based chips when transistors are packed together tightly.
For the first time, a research team led by Hongjie Dai, the J. G. Jackson and C. J. Wood Professor of Chemistry, has made transistors called “field-effect transistors”—a critical component of computer chips—with graphene that can operate at room temperature. Graphene is a form of carbon derived from graphite. Other graphene transistors, made with wider nanoribbons or thin films, require much lower temperatures.
“For graphene transistors, previous demonstrations of field-effect transistors were all done at liquid helium temperature, which is 4 Kelvin [-452 Fahrenheit],” said Dai, the lead investigator. His group’s work is described in a paper published online in the May 23 issue of the journal Physical Review Letters [abstract; arXiv preprint].
The Dai group succeeded in making graphene nanoribbons less than 10 nanometers wide, which allows them to operate at higher temperatures. “People had not been able to make graphene nanoribbons narrow enough to allow the transistors to work at higher temperatures until now,” Dai said. Using a chemical process developed by his group and described in a paper in the Feb. 29 issue of Science [abstract], the researchers have made nanoribbons, strips of carbon 50,000-times thinner than a human hair, that are smoother and narrower than nanoribbons made through other techniques.
David Goldhaber-Gordon, an assistant professor of physics at Stanford, proposed that graphene could supplement but not replace silicon, helping meet the demand for ever-smaller transistors for faster processing. “People need to realize this is not a promise; this is exploration, and we’ll have a high payoff if this is successful,” he said.
Dai said graphene could be a useful material for future electronics but does not think it will replace silicon anytime soon. “I would rather say this is motivation at the moment rather than proven fact,” he said.
Different graphene nanostructures are being explored for use in nanoelectronic circuits. Six weeks ago we cited progress from a group at the University of Manchester that used high-resolution electron-beam lithography to carve graphene quantum dots that showed promise as transistors, but which could not be reliably fabricated. This Stanford University group is using a chemical method to prepare “ultrasmooth graphene nanoribbon semiconductors” somewhat larger than the smallest graphene quantum dots, but more reliably fabricated. Which, if any, of these structures end up in practical nanoelectronic circuits remains to be seen.
—Jim
