Carbon nanoribbons could lead to smaller, speedier computer chips

Washington, May 29 : Chemists at Stanford University have developed carbon nanoribbons made of graphene, for making computer chips that are speedier and generate less heat, which can damage today's silicon-based chips when transistors are packed together tightly.

The team of researchers led by Hongjie Dai, the J. G. Jackson and C. J. Wood Professor of Chemistry, have for the first time developed transistors called "field-effect transistors"-a critical component of computer chips-with graphene that can operate at room temperature. 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.

The researchers successfully made graphene nanoribbons less than 10 nanometers wide, enabling 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," said Dai.

Researchers used a previously developed chemical process to make nanoribbons, strips of carbon 50,000-times thinner than a human hair that are smoother and narrower than nanoribbons made through other techniques.

Field-effect transistors are the key elements of computer chips, acting as data carriers from one place to another. They are composed of a semiconductor channel sandwiched between two metal electrodes. In the presence of an electric field, a charged metal plate can draw positive and negative charges in and out of the semiconductor, enabling electric current to either pass through or be blocked, which in turn controls how the devices can be switched on and off, thereby regulating the flow of data.

From what the researchers predict, graphene could soon replace silicon chips. However, 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 also said that while researchers have shown that carbon nanotubes outperform silicon in speed by a factor of two, the main hitch is that, not all of the tubes, which can have 1-nanometer diameters, are semiconducting.

"Depending on their structure, some carbon nanotubes are born metallic, and some are born semiconducting. Metallic nanotubes can never switch off and act like electrical shorts for the device, which is a problem," he said.

Also, researchers have demonstrated that all of their narrow graphene nanoribbons made from their novel chemical technique are semiconductors.

"This is why structure at the atomic scale-in this case, width and edges-matters," he said.

His group's work is described in a paper published online in the latest issue of the journal Physical Review Letters.

ANI