From the outside, transistors seem so simple and straightforward. But inside, they're actually a mess. If you could watch them working at the level of atoms, you'd see the electronic equivalent of a game of bumper cars. Electrons moving through even the best transistor channel can't go in straight lines. Instead they're buffeted continually by a host of imperfections and vibrations, which together put a strict limit on speed and generate a lot of heat in the process.
The good news is that it doesn't have to be that way. By a quirk of quantum mechanics, electrons moving through atom-thick sheets of carbon—known as graphene—don't suffer much at all from these sorts of collisions. Instead, they behave like massless particles, speeding along in straight lines for long distances just like photons do. And just like light, these electrons can be made to bend or bounce back when they move from one medium to another.
What can you do with this light-mimicking behavior? Well, here's what we'd like to do: Replace the logic circuitry at the heart of every computer processor. Everyone today agrees that the days of the ever-shrinking CMOS transistor are numbered; the only disagreement is about what that number is. After 50 years of steady miniaturization, chipmakers have just about shrunk the device to its limits. The future gets hazy beyond 2020, but we know that to continue making faster, cheaper, and more energy efficient chips, we'll need a new technology.
In the United States, the hunt for novel computing devices that can start replacing CMOS transistors in the coming decade has crystallized into a massive effort called the Nanoelectronics Research Initiative, which includes many of the world's biggest chipmakers, state and federal agencies, and dozens of universities. Light-like graphene logic is just one of a half dozen or so possible successors to CMOS, but we think its combination of features makes it the heir apparent.
For one thing, graphene logic will be extraordinarily fast. Instead of manipulating information by turning the flow of current on and off through a transistor channel, graphene logic could perform calculations by bending, reflecting, focusing, and defocusing electrons moving at 1/300th the speed of light—about 10 times as fast as electrons in conventional silicon CMOS devices. Logic devices built from graphene will consume less power and take up far less real estate than CMOS or optical switches. And unlike any other technology being considered, graphene devices have the potential to simplify and speed up chips by creating truly reconfigurable logic. Such logic would be able to change its type on the fly: In response to electronic signals, an AND gate, for example, could be transformed into an OR gate and then back again. We have already shown that the fundamental physics of these graphene switches works just as theorists expected, and we are now on the verge of creating the very first reconfigurable devices.
As you might imagine, no ordinary semiconductor can be used to shuttle electrons around like beams of light. In the silicon CMOS transistors that make up today's chips, electrons can barely move a few nanometers before they bounce off an impurity or are buffeted by acoustic waves generated by the crystal. Other semiconductor materials aren't much better.