Wednesday, 28 November 2012

Graphene: The Future of Computers?

Hannah Bruce Macdonald

Graphene is a one atom thick sheet of pure carbon, with a hexagonal pattern much like graphite. Its structure causes graphene to allow very rapid movement of electrons across the sheet, and it is this property that has caused graphene to be flagged for use in ultra-fast computers. However, the nature of transistors require them to be semi-conductors like Silicon, allowing the circuit to be turned on and off by a band gap in the material. A band gap is a difference in energy between the energy of the electrons and the energy required to conduct, with the band gap being bridged only when the correct amount of external energy is applied. Graphene does not have a band gap and therefore does not semi-conduct. 

Computer chip with over 1 billion transistors
A band gap has been introduced into Graphene before, allowing the application of Graphene to transistors. This has been done using techniques such as adding an insulating layer to the Graphene, reducing its conductivity, or through carving the Graphene into ribbons, where the altered structure allows the current to be turned off more easily. Both these previous techniques have been successful, but are limited in their scope as they only work in transistors above a certain size, as the edges of the ribbons become roughly cut at small sizes, allowing the band gap to disappear.

New research carried out at the Georgia Institute of Technology has found that graphene sheets designed with a rippling surface could be used for transistors. The troughs in the rippled surface mimic the ribbon, but as it is made of one continuous sheet, the issue of the edges of the ribbons has been bypassed. The parallel trenches are 18nm deep and have a band gap of 0.5 electron volts. This development has opened up the opportunity for graphene to replace silicon in transistors in the future, but there is still plenty of research to be done into the band gap, to produce the ideal sized graphene ripple. This potential shift from silicon to graphene transistors could push Moore’s Law to its limits, as the law states that processor speeds and the number of transistors on a computer chip would double every two years.

Will rippling the surface of graphene make them the ultimate transistor?