Surrey researchers use tunnelling electrons to speed up electronics

Electronics based on amorphous materials, such as amorphous semiconductors, are the key to making low-cost driver circuitry for flat-panel displays. But to date, the operating speed of such electronics has been hampered by the difficulty electrons have moving through the disordered amorphous materials, which are non-crystalline.

The key to speed is negative differential resistance, in which current is actually a decreasing function of the voltage. Up until now, it had only been successfully realised in highly ordered crystalline semiconductors such as gallium arsenide.

"This work extends the potential of amorphous carbon electronics to high-speed switching at gigahertz rates," said Ravi Silva, lead investigator of the Surrey team. "It follows our earlier demonstration of room-temperature processing of carbon electronics on plastic."

Applications of the research run from large-area display drivers to high-speed electronics for mobile communications. The devices also could be used in combination with plastic electronics.

The scientists reported their work in the January 2006 issue of Nature Materials. The breakthrough the scientists claim is that they can make devices with layers that are only a few nanometres thick. Electrons can pass through the layers using a phenomenon called quantum-mechanical tunnelling.

In a three-layer structure, the composition and thickness of the layers control the energies at which the electrons can tunnel, and thus produce the region of negative resistance. This reportedly is the first successful attempt to realise negative resistance in non-crystalline devices.

The work was sponsored by the Carbon Based Electronics Programmes of the Engineering and Physical Sciences Research Council in the UK, which contributed £202,000 over three-and-a-half years, and a £6.1-million Portfolio Partnership Award in Integrated Electronics.

The university also has invested £4 million in equipment for nanofabrication from the Higher Education Funding Council of England's Science Research Investment fund.

Surrey has a number of patents in the production and application of carbon-based materials for electronics, sensors and photovoltaics, said Jeremy Allam, deputy director of the Advanced Technology Institute at the University of Surrey.

Allam added that further development of the work is under way at the university, which is seeking research funding that will allow it to determine the potential of amorphous carbon nanoelectronics.