14 DAY TRIAL // While today's technology is made up of a variety of device and component classes, each aimed at a specific set of tasks, what they have in common is their use of silicon-based field-effect transistors (FETs). So far, silicon has been central to computing because of its very high carrier mobility, However, IBM Research has been striving to implement a new type of FETs based on graphene, which has an even higher carrier mobility.
IBM previously reported that it was successful in lowering the noise level of graphene FETs through the use of a bi-layer architecture. However, it was unable to insulate the graphene channel from its high-k grade dielectric with a polymer. Nevertheless, a more recent advancement enabled the researchers to use a dual-gate by-layer architecture to achieve this effect, thus setting the stage for graphene-based FETs that can match or, eventually, outmatch complementary metal oxide semiconductors.
While the carrier mobility of graphene is high, transistors based on it have, until recently, been suffering from a very low on-off ratio. This was caused by the graphene's lack of band gap. What IBM succeeded in doing was open up this bandgap, even enabling an on-off current ratio of around 100 at room temperature, with 2,000 when the device was cooled.
"Graphene doesn't naturally have a bandgap, which is necessary for most electronic applications," said IBM Fellow Phaedon Avouris, who oversees the company's carbon-based materials efforts. "But now we can report tunable electrical bandgaps of up to 130meV for our bi-layer graphene FETs. And larger bandgaps are certainly feasible."
Avouris added that this breakthrough opened up numerous possibilities for graphene to be used in fields such as optoelectronics and digital electronics. The next step will be to scale down the thickness of the insulating layers so as to bring about higher electric fields. The research will be focused on further opening the band gap in order to improve graphene FET current ratios.