Since they were discovered in 1991, carbon nanotubes—tube-shaped molecules composed of carbon atoms—have had the potential to sustain almost super-conducting speeds at room temperature. In fact, carbon nanotubes, which are 50,000 times thinner than a strand of human hair, are stronger and more conductive than any other known fiber. Recent breakthroughs have made good on its incredible promise and have pushed carbon nanotubes closer to supplanting silicon transistors in devices.

Perhaps the most astonishing of recent advancements in carbon nanotube technology is IBM Corp.'s creation of the best-performing nanotube transistors to date. IBM recently announced that its nanotube transistors not only demonstrated the greatest transconductance—current carrying capability—of any nanotube transistor to date but they also outperformed the best silicon transistor prototypes available today. In fact, IBM researchers say that by testing different device structures, they have more than doubled the transconductance per unit width of leading silicon transistor prototypes. "Proving that carbon nanotubes outperform silicon transistors opens the door for more research related to the commercial viability of nanotubes," says Phaedon Avouris, nanoscale science manager in the IBM Research organization. Their high transconductance means that the nanotube transistors can run faster and enable the production of more powerful integrated circuits. According to Avouris, "carbon nanotubes are already the top candidate to replace silicon when current chip features just can't be made any smaller, a physical barrier expected to occur in about 10 to 15 years."

IBM's recent achievement follows a string of major breakthroughs in its use of carbon nanotubes in small electronic devices. Last April, IBM researchers developed an innovative technique to produce arrays of carbon nanotube transistors, sidestepping the painstaking process of separating metallic and semiconducting nanotubes. Last August, IBM introduced the world's first logic circuit within an individual nanotube. Moreover, IBM is not alone in its groundbreaking nanotube discoveries.

Carbon nanotubes are not only highly conductive, but long strands of it can be easily created for electronic devices, researchers at Rensselaer Polytechnic Institute have demonstrated in a recent breakthrough. Using chemical vapor deposition (CVD), the standard way to fabricate semiconductors, researchers produced high yields of wires as long as eight inches—making these fibers the world's longest carbon nanotubes. This was the first time the CVD process was able to grow them long enough to be used as bus interconnects across or even between chips, says Rensselaer associate professor Pulickel Ajayan. Past efforts using CVD have produced tangled wires, since the fibers have a tendency to clump together like protein strands. Ajayan's solution was adding a sulfur compound in the presence of hydrogen, resulting in long, untangled nanowires.

Another Rensselaer finding hints at the possibility of other uses for these fibers. Researchers recently discovered that carbon nanotubes could be restructured using light. Ajayan exposed the tubes to light from an ordinary photographic flash lamp and found that in response the tubes rearranged themselves into horn-shaped configurations. This behavior was surprising since carbon bonds require temperatures between 1,500 degrees C and 2,000 degrees C to break and reform. Some possible applications for this effect are already being examined, says the Rensselaer group, and these include being utilized as a microscopic fuel source for microelectromechanical systems (MEMS) and as a means to ignite material remotely.

Recent advancements in carbon nanotube technology have made it not just a viable, but a likely replacement for silicon transistors in the near future. Utilizing carbon nanotubes, devices could be twice as fast, significantly more powerful and even more compact. In addition, the implications for these nanowires' response to light are only starting to be considered.

Sources: IBM says Carbon Nanotube Transistors Could Double Speed of Silicon Devices
Semiconductor Business News, May 20, 2002
http://www.siliconstrategies.com/story/OEG20020520S0012

Light Flash Restructures Carbon Nanotubes
Chappell Brown
EE Times, April 30, 2002
http://www.eetimes.com/story/OEG20020430S0014

Researchers Lengthen Carbon Nanotubes
R. Colin Johnson
EE Times, May 14, 2002
http://www.eetimes.com/story/OEG20020514S0024