Graphite pencilled in for circuits

Graphite could be the basis for a new class of nanometre-scale electronic devices that have the properties of carbon nanotubes but could be produced using established microelectronics manufacturing techniques.

Using thin layers of graphite known as graphene, researchers at the Georgia Institute of Technology in the US, working with the Centre National de la Recherche Scientifique (CNRS) in France, have produced proof-of-principle transistors, loop devices and circuitry. Ultimately, the researchers hope to use graphene layers less than 10 atoms thick as the basis for revolutionary electronic systems that would manipulate electrons as waves rather than particles, much like photonic systems control light waves.

"We expect to make devices of a kind that don't really have an analogue in silicon-based electronics, so this is an entirely different way of looking at electronics," said Walt de Heer, a professor in Georgia Tech's School of Physics. "Our ultimate goal is integrated electronic structures that work on diffraction of electrons rather than diffusion of electrons. This will allow the production of very small devices with very high efficiencies and low power consumption."

Graphene is already used in carbon nanotubes, which conduct electricity with virtually no resistance, but present difficulties in the manufacturing process and can produce excess heat at junctions. "Using narrow ribbons of graphene, we can get all the properties of nanotubes because those properties are due to the graphene and the confinement of the electrons, not the nanotube structures,“ said de Heer.

De Heer and his colleagues make the circuitry with a wafer of silicon carbide, a material made up of silicon and carbon atoms. By heating the wafer in a high vacuum, they drive silicon atoms from the surface, leaving a thin continuous layer of graphene.

Next, they spin-coat onto the surface a photo-resist material of the kind used in established microelectronics techniques. Using optical lithography or electron-beam lithography, they produce patterns on the surface, then use conventional etching processes to remove unwanted graphene. Using this method, they have created feature sizes as small as 80 nanometres.

So far, they have built an all graphene planar field-effect transistor. The side-gated device produces a change in resistance through its channel when voltage is applied to the gate. However, this first device has a substantial current leak, which the team expects to eliminate with minor processing adjustments.

The researchers have also built a working quantum interference device, a ring-shaped structure that would be useful in manipulating electronic waves.