The team’s graphene device, grown on a silicon carbide substrate chip- Georgia Institute of Technology
A working, scalable semiconductor has been created from graphene for the first time, potentially paving the way for a new type of computer with greater speed and efficiency than today’s silicon chips.
Graphene is a material made from a single layer of carbon atoms that is stronger than steel at comparable thicknesses. It is an extremely good electrical conductor and is highly resistant to heat and acids. But despite its advantages, a working graphene semiconductor, which can be controlled to conduct or insulate electricity at will, has evaded scientists. Such semiconductors are key to creating the logic chips that power computers.
The problem has been the lack of what is known as a bandgap. Semiconductors have bands of higher and lower energies and a point – the bandgap – at which excited electrons can hop from one to the other. This effectively allows switching on and off of the flow of current, so it is either conducting or not conducting, creating the binary system of zeroes and ones used in digital computers.
While previous research has shown that graphene can be made to act like a semiconductor on a small scale, it had never been scaled up to sizes that would make a computer chip practical. Earlier work has shown that wrinkles, domes and holes in graphene sheets can have unusual effects on electrical flow, creating the possibility that logical chips could be made by creating the right landscape of flaws. But to date, nothing has scaled up.
Now, Walter de Heer at Georgia Tech in Atlanta and his colleagues have created graphene with a bandgap and even demonstrated a working transistor, an on/off switch that either prevents or allows current to flow through it. Their process should be more conducive to scaling up because it relies on techniques not dissimilar to those used to create silicon chips.
De Heer’s group used wafers of silicon carbide that were heated, forcing the silicon to evaporate before the carbon, effectively leaving a layer of graphene on top. De Heer wasn’t available for interview at the time of writing, but said in a statement that the electrical properties of a graphene semiconductor were far better than those of silicon chips. “It’s like driving on a gravel road versus driving on a freeway,” he said.
Silicon chips are cheap to make and are backed by enormous manufacturing infrastructure globally, but we are reaching the limits of what these chips can do. Moore’s law states that the number of transistors in a circuit will double roughly every two years, but the rate of miniaturisation has slowed in recent years as engineers reach circuit densities beyond which electrons cannot be reliably controlled. Graphene circuits could reinvigorate progress, but hurdles remain.
“The fact they’re using wafers is important because that’s really, truly scalable,” says David Carey at the University of Surrey, UK. “You can use all the technology that the whole semiconductor industry is totally comfortable with to scale up this process.”
But Carey is sceptical that the development means the world will soon shift from silicon to graphene chips, both because the new research needs lots of refinement in terms of transistor size, quality and manufacturing techniques, and because silicon has such a headstart.
“Most people who work on silicon are bombarded on a daily basis by new, wonderful materials that are about to replace it and none of it’s ever happened,” he says. “If you’re a silicon person, you’re quite happily sitting on top of the mountain. The idea that I’m going to replace my laptop with graphene is not quite there yet.”
