Nanotubes tied to silicon circuit

Many research teams are working to make electronics that include carbon nanotubes -- rolled-up sheets of carbon atoms that have useful electrical properties and that can be as narrow as the span of four hydrogen atoms.

Researchers from the University of California at Berkeley and Stanford University have fabricated a circuit that combines carbon nanotube transistors and traditional silicon transistors on one computer chip. Connecting minuscule nanotube transistors to traditional silicon transistors enables the atomic-scale electronics to communicate with existing electronic equipment.

Such integrated nanotube-silicon circuits could enable super-sensitive sensors that distinguish among thousands of chemical or biological agents and ultra-high-density memory chips that store 100 times the information of today's state-of-the-art memory chips, according to the researchers.

The researchers grew carbon nanotubes on portions of a silicon chip that contained connections made from molybdenum, a metal able to withstand the high temperatures needed to grow the nanotubes. The prototype chip contains thousands of silicon transistors and hundreds of nanotube transistors.

The silicon transistors were configured in an 11-level binary tree that allowed for individual access to all the nanotube transistors using only 22 input signals.

The researchers' chip is designed to rapidly evaluate the electrical properties of large numbers of nanotubes, which will help researchers optimize nanotube growth processes. It can be used for that purpose now. More broadly practical carbon nanotube-silicon transistor chips could be built in five to ten years, according to the researchers.

The work appeared in the January, 2004 issue of Nano Letters.