Steve Bush

Georgia Tech predicts graphene will skip FETs and jump straight to quantum devices.

The forecast follows the creation of nanometre conductors with smooth – ballistic – electron flow.

“This means that the way we will be doing graphene electronics will be different,” said Georgia Professor Walt de Heer. “We will not be following the model of using standard field-effect transistors, but will pursue devices that use ballistic conductors and quantum interference. We are headed straight into using the electron wave effects in graphene.”

Taking advantage of the wave properties will allow electrons to be manipulated with techniques similar to optical control, for instance switching may be carried out using interference – separating beams of electrons and then recombining them in or out of phase to switch the signal.

That said, the university is to continue to research on graphene transistors, which it makes using similar techniques, and speculates these may eventually operate at THz.

De Heer’s research team hopes to demonstrate a rudimentary quantum interference switch within a year.

“There are going to be a lot of surprises as we move into these quantum devices and find out how they work,” he said.

The ballistic conductors are made by what the university has dubbed ‘templated growth’, which replaces an electron beam cutting technique that left rough edges on conductors and consequently scattered electron flow.

Templated growth begins by etching contours into a silicon carbide surface.

Heating the contoured wafer to 1,500°C initiates melting that polishes any rough edges left by etching.

Established techniques are then used for growing graphene from SiC by driving silicon atoms out of the surface.

“Instead of producing a consistent layer of graphene across the entire surface of the wafer, the researchers limit the heating time so that graphene grows only on portions of the contours,” said the university.

The width of the resulting ribbon-like conductors is proportional to the depth of the contour, providing a way to controlling the ribbon dimensions.

Multiple etching steps can be carried out to create complex templates.

“This technique allows us to avoid the complicated e-beam lithography steps that people have been using to create structures in epitaxial graphene,” said de Heer. “We are seeing very good properties that show these structures can be used for real electronic applications.”

Ribbons 15 to 40nm wide that conduct current with almost no resistance have been made, said the university.

“These narrow ribbons become almost like a perfect metal. Electrons can move through them without scattering, just like they do in carbon nanotubes,” said de Heer. “We expect to be able to do everything we need with the size ribbons that we are able to make right now, though we probably could reduce the width to 10nm or less.”