Using conventional e-beam lithography, IBM has successfully fabricated graphene FETs with very narrow nanoribbon channels. FETs are field-effect transistors. So far, the bandgaps opened were relatively small, compared with the excellent properties of nanotubes. This IBM attributes to the imperfections in its method of cutting the nanoribbons. However, by supercooling the device the researchers were able to prove the concept. Next, they plan to further narrow the nanoribbons to achieve room temperature operation.
The first applications of the nanoribbon FETs will be for RF devices in Darpa’s Carbon Electronics for RF Applications (CERA) program. The high electron mobility of graphene makes it an excellent candidate for analog ultra-high-frequency oscillators and switches.
“We think analog graphene devices will have wide applicability in communications, radar and other areas requiring very-high-frequency operation,” said Avouris.
IBM used the mechanical exfoliation method to place graphene atop a silicon wafer for its current device; in the future, they plan to also pursue growing graphene on silicon-carbide wafers. By heating a silicon-carbide wafer in a high vacuum to evaporate the silicon atoms from the top layer, it is possible to leave behind a monolayer of pure carbon in graphene’s crystalline lattice.
The graphene FET’s performance is not quite as good as carbon nanotubes, but graphene’s electron mobility is at least an order of magnitude [10X] greater than silicon
The graphene FET’s could achieve ten times the speed of ordinary CMOS transistors. If the graphene FET’s are made smaller with nanometer features then they could have corresponding better speed to CMOS of the same dimensions.
Future graphene-chip technologies, meanwhile, could borrow many of the methods already used for creating silicon chips. Many scientists are seeking ways of chiseling narrow strips, called nanoribbons, out of graphene sheets. Graphene electronics is far from proved as a viable candidate for the postsilicon era. As yet, graphene transistors are slower than silicon ones and much slower than transistors made with competing materials such as carbon nanotubes.
No one is ready to make promises, especially in light of the experience with carbon nanotubes. “Carbon nanotubes promised so much and so far [have] delivered so little, and we should naturally be cautious about promising too much for graphene,” Geim says.
Cees Dekker of Delft University of Technology in the Netherlands, who a decade ago created the first nanotube transistor (SN: 5/9/98, p. 294), says that scientists’ excitement about graphene gives him a feeling of déjà vu. “Sometimes, people are enthusiastically rediscovering the properties of graphene which were already heavily discussed 10 years ago in conjunction to nanotubes,” he says.