Nano switch hints at future chips

By Darren Waters Technology editor, BBC News website

Dr Leonid Ponomarenko shows off a device with the transistor embedded

Researchers have built the world's smallest transistor - one atom thick and 10 atoms wide - out of a material that could one day replace silicon.

The transistor, essentially an on/off switch, has been made using graphene, a two-dimensional material first discovered only four years ago.

Graphene is a single layer of graphite, which is found in the humble pencil.

The transistor is the key building block of microchips and the basis for almost all electronics.

Dr Kostya Novoselov and Professor Andre Geim from The School of Physics and Astronomy at The University of Manchester have been leading research into the potential application of graphene in electronics and were the first to separate a sheet of the material from graphite

Super material

Graphene has been hailed as a super material because it has many potential applications. It is a flat molecule, with only the thickness of an atom, and both very stable and robust.

The researchers are also looking at its use in display technology - because it is transparent.

The Manchester-based scientists have shown that graphene can be carved into tiny electronic circuits with individual transistors not much larger than a molecule.

Dr Novoselov told BBC News that graphene had many advantages over silicon because it could conduct electricity faster and further.

Silicon will be replaced by graphene Dr Kostya Novoselov

"These transistors will work and work at ambient, room temperature conditions - just what is required for modern electronics," he said.

Dr Novoselov said graphene was a "wonderful conductor", making it a perfect material for chip applications.

"It is already superior to silicon by an order of magnitude and comparable to the best samples of other materials.

"We believe we can increase this mobility of electron flow 10-fold."

Graphene is a hot topic among semiconductor researchers at the moment because it is an excellent conductor of electricity. Unlike silicon graphene transistors perform better the smaller they become.

Leak electricity

The global semiconductor business is currently built on sand; stamping out microchips from large silicon wafers.

Companies like Intel have a roadmap to reduce the size of circuits on the silicon wafer, down to about 10 nanometres - 10,000 times smaller than the width of a single human hair.

Many researchers believe that producing circuits smaller than 10 nanometres in silicon will be too difficult because they start to leak electricity at that size.

That current silicon roadmap is expected to end in 2020, making the race to find alternative materials potentially very lucrative.

Producing graphene sheets big enough to be used as wafers for chip production remained the biggest hurdle, said Dr Novoselov.

"We can control the cut down to 20 nanometres. And then when we have to scale down to one nanometre we use a bit of luck.

"The yield of the working devices is about 50%."

Many researchers around the world are working on creating large wafers of graphene.

In order to produce microchips wafers would need to be several inches across. The biggest wafer produced so far is 100 microns across, just a tenth of a millimetre.

Short and narrow constrictions in graphene can act as high-quality transistors

"I do believe we will find the technology to do this. And when we do silicon will be replaced by graphene," said Dr Novoselov.

Professor Bob Westervelt, in an assessment of the material and its future application in the journal Science, wrote: "Graphene is an exciting new material with unusual properties that are promising for nanoelectronics.

"The future should be very interesting."

Dr Novoselov added: "Given the material was first obtained by us four years ago, we are making good progress."

He said the process of using graphene to build circuits was very compatible with silicon technology.

"At the moment we use all the same steps to make a transistor as is done by the silicon industry. So once we have large wafers of graphene it should be straightforward to use the same process."

But it might be another 10 years before the first integrated circuits on graphene chips appear, he said.

Shorter term

In the shorter term graphene could be used in LCD displays to replace materials used to create transparent conductive coatings.

"The computer screen relies on good transparent conductors. But current materials are expensive and hard to produce.

"Graphene is only one atom thin so is absolutely transparent - it's a really wonderful conductor.

"We propose to use it as a transparent conductor, using small interconnecting graphene sheets all together."

The material is also being touted for use in solar panels, transparent window coatings and also for sensing technologies.

Dr Kostya Novoselov and Professor Andre Geim from The School of Physics and Astronomy at The University of Manchester presented their findings in the 17 April issue of Science.

Chaotic Dirac billiard in graphene quantum dots
L. A. Ponomarenko1, F. Schedin1, M. I. Katsnelson2, R. Yang1, E. H. Hill1, K. S. Novoselov1, A. K.Geim1
1Centre for Mesoscience and Nanotechnology, University of Manchester, Manchester M13 9PL, UK
2Institute for Molecules and Materials, University Nijmegen, 6525 ED Nijmegen, The Netherlands
We report on transport characteristics of quantum dot devices etched entirely in graphene. At large sizes,
they behave as conventional single-electron transistors, exhibiting periodic Coulomb blockade peaks. For
quantum dots smaller than 100 nm, the peaks become strongly non-periodic indicating a major
contribution of quantum confinement. Random peak spacing and its statistics are well described by the
theory of chaotic neutrino (Dirac) billiards. Short constrictions of only a few nm in width remain
conductive and reveal a confinement gap of up to 0.5eV, which demonstrates the in-principle possibility of
molecular-scale electronics based on graphene.