While developing this method of organizing nanotube transistors is an important step, much work remains to be done before commercial processors will be available. For one thing, exploiting the full potential of nanotube transistors will require improving the leads, possibly by using nanotubes in place of the palladium wires.
But perhaps a more pressing problem is finding reliable and inexpensive ways to isolate different types of carbon nanotubes. Current fabrication techniques produce a mix of nanotubes with different sizes and electronic properties, not all of which will work well in integrated circuits.
Because of these challenges, the first applications of carbon nanotube transistors will probably not be as high-performance processors, Hannon says, but highly sensitive sensors that work even with a mix of different nanotubes.
Meanwhile, others are developing devices that don’t rely on nanotubes’ high-end electrical properties, but rather on features such as their strength and flexibility. This skirts the need both to sort and to individually arrange the nanotubes. The Woburn, MA-based company Nantero, for example, takes advantage of nanotubes’ strength and flexibility to make memory devices. “We use [nanotubes] as electromechanical devices, so we just bend them up and down to represent zeros and ones,” says Nantero CEO Greg Schmergel. In this application, clusters of nanotubes rather than single tubes can be used, so they can be patterned using lithography.
Eventually, Schmergel says, nanotubes could replace every part of semiconductor devices by using all of the tubes’ features. “Nanotubes have quite a number of unique properties all combined in one material. They can replace memory, logic, the interconnect, ultimately they can replace everything in the chip, so it definitely makes sense to pursue all of those angles,” he says.