"Proving that carbon nanotubes outperform silicon transistors opens the door for more research related to the commercial viability of nanotubes," said Phaedon Avouris, manager of nanoscale science in the IBM Research organization. "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."

The development, reported in today's issue of the Applied Physics Letter, demonstrates the highest transconductance of any carbon nanotube transistor to date, according to IBM researchers. The high transconductance--or the measurement of current carrying capability--implies that transistors can run faster, which could lead to more powerful integrated circuits, IBM said.

IBM researchers also said they have discovered that the carbon nanotube transistors produced more than twice the transconductance per unit width of top-performing silicon transistor prototypes. IBM said it is taking carbon nanotubes--the strongest and most conductive fibers known--another step closer to becoming a viable option for replacing silicon transistors in future devices. Nano

Scientists in IBM's T.J. Watson Research Center made single-wall carbon nanotube field-effect transistors (CNFETs) in a structure that resembles conventional metal-oxide-semiconductor field-effect transistors (MOSFETs). These CNFETs have gate electrodes above a conduction channel separated from the channel by a thin dielectric. The researchers said they used these devices to study the performance improvements achieved by reducing the gate-to-channel separation.

The research team reported that the top gate devices exhibited excellent electrical characteristics, including steep sub-threshold slope (measure of how well a transistor turns on and off) and high transconductance at low voltages. The devices exhibited a significant improvement over previously reported CNFETs, which used the silicon wafer as a gate and a thick gate dielectric, IBM researcher said.

Scientists said they were able to fabricate both hole (p-type) and electron (n-type) transistors. The top-gate design allows independent gating of each transistor, making it possible to generate CMOS circuits that have a simpler design and consume less power, researcher said.

The CNFET structure enabled IBM researchers to compare the performance of the carbon nanotube transistors to that of conventional silicon-based MOSFETs. The nanotube devices were not optimized, but they still outperformed prototype silicon transistors, according to the scientists. IBM researchers said they have concluded that decreases in CNFET gate length and gate oxide thickness will enable these devices to dramatically outperform experimental silicon transistors.