"Graphene transistors aren’t just fast; they’re lightning fast. The speediest one to date clocked in at some 427GHz. That’s orders of magnitude more than what you can tease out of today’s processors. The problem with graphene transistors though is that they aren’t particularly good at turning off. They don’t turn off at all actually, which makes it hard to use them as switches.

Now, Guanxiong Liu and a team of researchers at University of California, Riverside have come up with a practical, highly technical solution. It boils down to “don’t treat graphene like it’s silicon”."
http://www.gizmodo.com.au/2013/08/scientists-just-figured-out-how-to-make-lightning-fast-graphene-cpus/

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MIT Technology Review: "How to Save the Troubled Graphene Transistor"

"The problem with graphene is that it has no band gap; electrons can flow at any energy. So the major focus of graphene engineers has been to find ways of creating an artificial band gap using methods such as applying electric fields, doping with atoms or by stretching and squeezing the material.

These approaches have met with modest success. Practical digital circuits require a band gap on the order of 1 eV at room temperature. But the best efforts with graphene have produced modest band gaps in the few hundred meV.

Even then this has come at a serious cost. The best graphene transistors are hugely fast but they dissipate energy like there’s no tomorrow and leak current like water through a sieve.


Now Liu and co have come up with an entirely different approach. “We intentionally avoid any attempt to artificially induce an energy band, which would make graphene “more-silicon-like”, they say. Instead they rely on a different phenomenon called negative resistance to create transistor-like behaviour.

Negative resistance is the counterintuitive phenomenon in which a current entering a material causes the voltage across it to drop. Various groups, including this one at Riverside, have shown that graphene demonstrates negative resistance in certain circumstances.

Their idea is to take a standard graphene field-effect transistor and find the circumstances in which it demonstrates negative resistance (or negative differential resistance, as they call it). They then use the dip in voltage, like a kind of switch, to perform logic.

In fact, the main contribution of this paper is to show how several graphene field-effect transistors can be combined and manipulated in a way that produces conventional logic gates.

And the results are promising. Liu and co demonstrate the effectiveness of their approach by designing a graphene-based circuit that can match patterns and show that it has several important advantages over silicon-based versions.





http://www.technologyreview.com/view/518426/how-to-save-the-troubled-graphene-transistor/

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"Graphene-Based Non-Boolean Logic Circuits"

http://arxiv.org/abs/1308.2931

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