revolutionary atom-sized transistor

12 février 2009

Thursday, February 12, 2009 - Guardian Newspapers

The GuardianHow UK scientists made revolutionary atom-sized transistor (2)
By Sam Ejike Okoye

WHEN the transistor was first unveiled to the public in the Spring of 1948, it received little attention in both the popular press and the scientific community. But in the 1950s it was quickly adopted for industrial and military applications and, of course, the transistor radio.

Nevertheless, the transistor became the key to advances in technology. The transistor allowed information to be easily processed and transmitted to the ends of the Earth, the miniaturisation of electronics made possible human exploration of space and the advent of the microchip ushered in the age of the PC and the Internet. The three inventors could hardly have known the outcome when they made their discovery in 1947 - that they were going to change the world.

In the global race to make ever more powerful computer chips, designers have for years been shrinking parts and wires and creating circuits that are both faster and smaller. Today, the standard circuit line is about one micron wide, a hundred times thinner than a human hair, allowing millions of transistors to be crammed onto a computer chip.

On the horizon, with considerable work lie diameters of 0.1 micron or so, which might yield devices with billions of transistors. This level of complexity has long been viewed as the likely end of the conventional electronics race, since finer transistors would burn up if subjected to requisite currents.

But the dream for ever smaller chips may well be within reach with the report that UK scientists have made a transistor one atom long and 10 atoms wide. In a research report published in the journal Science, Dr. Kostya Novoselov and Professor Andre Geim from The School of Physics and Astronomy at The University of Manchester, have described how they created some of the smallest transistors ever made, measuring only one atom by 10 atoms.

The transistors are made out of graphene (a type of carbon sheet), which has the potential to replace silicon in the never-ending hunt for smaller computer technology components. Although there are other kinds of prototype transistors in this size range, they usually need super-cooling using liquid gas, says Novoselov.

The new graphene devices work at room temperature. Such prototypes are typically made by building one atom at a time or, wiring up individual molecules. Those approaches are complex and impractical, Novoselov says. By contrast, the graphene transistors were made in the same way that silicon devices are, by etching them out of larger pieces of material. "That's their big advantage," he said.

The transistor has been made by the Manchester researchers 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. 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. 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.

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

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 per cent," he said.

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.

"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 writes: "Graphene is an exciting new material with unusual properties that are promising for nanoelectronics. The future should be very interesting."

But according to Dr. Novoselov: "Given the material was first obtained by us four years ago, we are making good progress." He said that 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.

In the shorter term, graphene could be used in liquid crystal displays (LCDs) to replace materials used to create transparent conductive coatings. As Dr. Novoselov noted: "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 is 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."

The prognosis for the future of electronics may lie in graphene rather than silicon. Electricity conduction through graphene is about 100 times greater than that of silicon and could offer many improvements to things like computer chips and biochemical sensors. Graphene, a single-atom-thick sheet of graphite, is a new material which combines aspects of semiconductors and metals.

A team of researchers led by Physics Professor Michael S. Fuhrer of the University of Manchester's Centre for Nanophysics and Advanced Materials, and the Maryland NanoCentre said that the findings were the first measurement of the effect of thermal vibrations on the conduction of electrons in graphene, and showed that thermal vibrations had an extraordinarily small effect on the electrons in graphene.

Concluded.