Nanotube makes metal transistor

The field-effect transistors that underlie electronics are made from semiconducting materials rather than conductors like metals because it is possible to use an electric field to block or allow the flow electricity in semiconductors, and thus turn the transistor on or off.

It's difficult to make tiny semiconductor devices that conduct efficiently, however. Metals are much more efficient at conducting electricity but the flow of electricity through a metal is not easy to shut off because the flow is not ordinarily sensitive to electric fields.

Researchers from the University of Illinois at Urbana-Champaign have found a way to produce a field effect in a metallic single-wall carbon nanotube that conducts electricity 40 times more efficiently than copper. Carbon nanotubes are rolled-up sheets of carbon atoms that can be smaller than a single nanometer in diameter and are either metallic or semiconducting. A nanometer is the span of 10 hydrogen atoms.

The metal field effect transistor has the potential to consume less energy, operate at higher frequencies, and dissipate heat more readily than traditional semiconducting field effect transistors, according to the researchers.

The researchers took advantage of the nanotubes' small size and a special type of electric field to produce the effect. They made the electric field highly irregular, which breaks the nanotube's molecular symmetry, thereby changing the tube from conducting to semiconducting.

The metal transistor could be used in practical applications in five to ten years, according to the researchers. The work appeared in the April 19, 2004 issue of Applied Physics Letters.