Slimline tonic

Researchers at Manchester University have used the world’s thinnest material to create the smallest transistor ever as well as super-fast electronic components that could speed up the development of drugs.

The transistor, just one atom thick and less than 50 atoms wide, could spark the development of a new type of super-fast computer chip.

Two years ago, Prof Andre Geim and colleagues at the university’s School of Physics and Astronomy discovered a new class of one atom thick materials.

One is graphene, a gauze of carbon atoms which resembles chicken wire.

The researchers believe that using this could allow the rapid miniaturisation of electronics — eventually replacing silicon when that reaches the point where it can no longer be used to make smaller and smaller devices.

As manufacturers have crammed more and more components on to integrated circuits, the number of transistors and the power of these circuits has roughly doubled every two years — the phenomenon known as Moore’s Law.

But the speed of this miniaturisation is now noticeably decreasing, and further reductions in size of electronics are to experience its most fundamental challenge in the next 1020 years

‘The number of applications being discussed is infinite,’ said Geim. ‘In my opinion, this is like the first stage after the discovery of polymers. No-one thought then that they would have so many applications, and graphene is the same.’

Though the team reported the first graphene-based transistor at the same time as the discovery of the material, it was very leaky, meaning electrical flow could not be turned off to zero.

This ruled out use in computer chips and other electronic circuits with a high density of transistors.

Noting that the material remained highly stable and conductive even when cut into strips just a few nanometres wide, the team has overcome this.

All other known materials — including silicon — oxidise, decompose and become unstable at sizes 10 times larger, forming a barrier to their use in future electronic devices, threatening to limit the future development of microelectronics.

Geim added that it may be possible to reduce the component down to just a single ring of carbon atoms, forming nanometre-sized circuits.

Future electronic circuits could then be carved out of a single graphene sheet and include the central element or ‘quantum dot’, semi-transparent barriers to control movements of individual electrons, interconnects and logic gates.

Geim’s team has proved this idea by making a number of single-electron-transistor devices that work under ambient conditions and show a high-quality transistor action.

The group is are currently limited by its inability to cut individual elements with nanometre precision, but is confident that this will be overcome as technology develops.

Graphene-based circuits are unlikely to be in general use before 2025. However, Geim believes that the material is ideal for replacing silicon.

‘Graphene combines most exciting features from carbon-nanotube, single-electron and molecular electronics, all in one,’ he said.

Together with researchers at Germany’s Max-Planck Institute, the Manchester group has also created a single atom thick membrane using the material.

They believe this could be used to sieve gases, make ultra-fast electronic switches and image individual molecules with unprecedented accuracy.

Beforehand, such materials were believed to be unable to exist in the free state, without being placed on top of other materials.

The team used a combination of microfabrication techniques of the sort used to manufacture microprocessors.

A metallic scaffold was placed on top of a sheet of graphene, on a silicon chip. The chip was then dissolved in acids, leaving the graphene hanging freely from the scaffold.

Geim and his team discovered this was possible as graphene is not perfectly flat but gently crumpled out of plane, which helps stabilise this ultra-thin matter.

They believe the membrane could also be used to make miniature electro-mechanical switches or as a non-obscuring support for electron microscopy to study individual molecules.

This would allow the rapid analysis of the atomic structures of bioactive complex molecules.

However, before the material can be widely used for such applications there are tow barriers to be overcome. ‘The real challenge is to make such membranes cheap and readily available for large-scale applications, said Geim.