Thursday, June 14, 2007

Nanotube Circuits Made Practical

Continued from page 1

By Kate Greene

It's important to explore approaches such as these, says Naresh Shanbhag, professor of electrical engineering at the University of Illinois, Urbana-Champaign. "Nanotubes are considered to be a promising post-silicon device," he says. "Nanotube circuits need such techniques ... so that a circuit exhibiting reliable behavior can be designed."

The Stanford algorithm does not solve all the problems with carbon-nanotube transistors, however. In a typical batch of nanotubes, as much as 30 percent of them act as a metal, constantly conducting electricity (unlike a semiconductor), making them useless as transistors. Another issue, says Mitra, is that it's difficult to control the density of carbon nanotubes from one batch to the next. And if there isn't a sufficient density, then there simply aren't enough nanotubes to make logic gates for circuits.

Progress is being made on all these fronts, says Tom Theis, director of physical sciences at IBM's TJ Watson Research Center, in Yorktown Heights, NY. Researchers at IBM, for example, are developing ways to selectively remove unwanted nanotubes--metal nanotubes where semiconductor nanotubes are wanted, for example--to help pave the way for reliable devices. While the Stanford work doesn't resolve all the challenges facing nanotube electronics, Theis says that it's "an interesting piece of the puzzle."