Nanotubes on plastic speed circuits

Many groups of researchers are working to make plastic electronics that are as fast as today's silicon electronic components. Powerful plastic electronics promise to enable flexible, inexpensive and very-large area computer screens.

Researchers from the U.S. Naval Research Laboratory and Applied Nanotech, Inc. have moved a step forward with an electronic material that is a mix of carbon nanotubes and polymer, or plastic. Carbon nanotubes are rolled-up sheets of carbon atoms that can be narrower than a single nanometer. A nanometer is one millionth of a millimeter, or the span of ten hydrogen atoms.

Key the potential usefulness of the researchers' material is its electron mobility -- a measure of how quickly electrical current moves through the device. Organic thin film transistors have electron mobilities under 10 square centimeters per volt second. The single-crystal silicon used in computer chips has a mobility of 1,500. The researchers' carbon nanotube/polymer mix has an electron mobility of 150, according to the researchers.

The material promises to enable lightweight unbreakable displays and inexpensive large-area screens, according to the researchers.

To make the material the researchers suspended nanotubes in a liquid, put the liquid on a polyimide surface, and dried the liquid to leave a random tangle of nanotubes. The researchers are working out ways to print the material onto surfaces rather than using conventional microfabrication. This would make it possible to manufacture large, inexpensive sheets of electronics.

The material's electron mobility could be boosted close to that of single crystal silicon thin-film transistors if only semiconducting rather than a mix of semiconducting and metallic nanotubes were used, according to the researchers.

The material could be used practically in five to ten years, according to the researchers. The work appeared in the January 17, 2005 issue of Applied Physics Letters.