Toward carbon circuits

Eventually, no matter how many improvements researchers make in the design of the computer chip, the conventional silicon-based CMOS scheme will have to be replaced. It may be 10 years, it may be 20, but everyone in the field realizes that at some point, the technology will reach fundamental limits. No one knows what approach will supplant it, but Phaedon Avouris, IBM Research Center, Watson believes that carbon nanotubes are a promising candidate.

“Nothing compares with the properties of
nanotubes,” Avouris says. They are very light, consisting mainly of open space–yet their mechanical strength is 10 times that of steel. And they are excellent conductors, about to carry current densities as much as 100 times higher than copper. Depending on their structure, nanotubes can act as either metals or semiconductors. 

Nanotubes are tiny tubes of pure carbon. In size, they range from 1 to 3 Nm, or, less than a tenth of the size of the smallest features on today’s silicon chips. The structure of a nanotube is much like a single sheet of graphite, with carbon atoms arranged in a hexagonal structure similar to a honeycomb, but the sheet is curved around to form a seamless tube. A nanotube’s conductivity and other properties vary depending on how wide it is, whether the sheet was twisted when it formed the tube, and whether the tube is attached to a surface that distorts its shape–a condition that allows the nanotube to be modified externally. 

Already Avouris and his co-workers have created a field-effect transistor–the basic component of computer chips–with a single 1.5 Nm wide nanotube serving as the channel for electrons flow from the source to the drain. By varying an external electric field, they were able to manipulate the current in the channel by five orders of magnitude, as is done with normal silicon transistors, even without trying to optimize the performance of the nanotube transistor.

If the information industry is to keep moving forward as it has for the past several decades, it will only be by remembering the importance of the physical stuff that embodies that non-material information.

Robert Pool

Excerpted from: Think Research, 1999

Courtesy: IBM