Graphene challenges future of silicon

A collaborative research project claims to have brought the world a step closer to producing a new material on which future nanotechnology could be based.

Researchers across Europe, including Britain’s National Physical Laboratory (NPL), have demonstrated how a material, graphene, could hold the key to the future of high-speed electronics, such as microchips and touch-screen technology.

Graphene has long shown potential, but has previously only been produced on a very small scale, limiting how well it could be measured, understood and developed.

A paper published in Nature Nanotechnology explains how researchers have, for the first time, produced graphene to a size and quality where its electrical characteristics can be practically developed and successfully measured. These breakthroughs overcome two of the biggest barriers to scaling up the technology.

Graphene is a relatively new form of carbon, made up of a single layer of atoms arranged in a honeycomb-shaped lattice.

Despite being one atom thick and chemically simple, graphene is extremely strong and highly conductive, making it suitable for high-speed electronics, photonics and beyond.

It is a strong candidate to replace semiconductor chips. Moore’s Law observes that the density of transistors on an integrated circuit doubles every two years, but silicon and other existing transistor materials are thought to be close to the minimum size where they can remain effective.

Graphene transistors can potentially run at faster speeds and cope with higher temperatures. They could be the solution to ensuring computing technology continues to grow in power while shrinking in size, extending the life of Moore’s law by many years.

Large microchip manufacturers, such as IBM and Intel, have openly expressed interest in the potential of graphene as a material on which future computing could be based.

Graphene also has the potential for innovations such as touch-screen technology, LCDs and solar cells. Its unparalleled strength and transparency make it suitable for these applications and its conductivity offers an increase in efficiency on existing materials.

Until now, graphene of sufficient quality has only been produced in the form of small flakes of tiny fractions of a millimetre, using painstaking methods such as peeling layers off graphite crystals with sticky tape.

Producing usable electronics requires much larger areas of material to be grown. This project saw researchers, for the first time, produce and successfully operate a large number of electronic devices from a sizeable area of graphene layers (about 50 mm²).

The graphene sample was produced epitaxially - a process of growing one crystal layer on another - on silicon carbide. Having such a significant sample not only proves that it can be done in a practical, scalable way, but also allows the scientists to better understand important properties.

The second key breakthrough of the project was measuring graphene’s electrical characteristics with unprecedented precision, paving the way for convenient and accurate standards to be established.

For products such as transistors in computers to work effectively and be commercially viable, manufacturers must be able to make such measurements with incredible accuracy against an agreed international standard.

The international standard for electrical resistance is provided by the Quantum Hall effect, a phenomenon whereby electrical properties in 2D materials can be determined based only on fundamental constants of nature.

The effect has, until now, only been demonstrated with sufficient precision in a small number of conventional semiconductors.

Furthermore, such measurements need temperatures close to absolute zero, combined with very strong magnetic fields and only a few specialised laboratories in the world can achieve these conditions.

Graphene was long tipped to provide an even better standard but samples were inadequate to prove this. By producing samples of sufficient size and quality, and accurately demonstrating Hall resistance, the team proved that graphene has the potential to supersede conventional semiconductors on a mass scale.

Furthermore, graphene shows the effect at much higher temperatures. This means the graphene resistance standard could be used much more widely as more labs can achieve the conditions required for its use.

In addition to its advantages of operating speed and durability, this would also speed the production and reduce costs of future electronics technology based on graphene.

NPL’s Prof Alexander Tzalenchuk, and the lead author on the Nature Nanotechnology paper, says:

“It is truly sensational that a large area of epitaxial graphene demonstrated not only structural continuity but also the degree of perfection required for precise electrical measurements on par with conventional semiconductors with a much longer development history.”

The research team is hoping to go on to demonstrate even more precise measurement, as well as accurate measurements at even higher temperatures. They are currently seeking EU funding to drive this forward.

Dr JT Janssen, an NPL Fellow who worked on the project, says:

“We’ve laid the groundwork for the future of graphene production and will strive, in our ongoing research, to provide greater understanding of this exciting material.

“The challenge for industry in the coming years will be to scale the material up in a practical way to meet new technology demands.

“We have taken a huge step forward and, once the manufacturing processes are in place, we hope graphene will offer the world a faster and cheaper alternative to conventional semiconductors.”

The research was a joint project carried by the National Physical Laboratory, Chalmers University of Technology (Göteborg, Sweden), Politecnico di Milano (Italy), Linköping University (Sweden) and Lancaster University in Britain.

National Physical Laboratory
http://www.npl.co.uk/