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IBM proves nanotubes can beat silicon

IBM has improved its carbon nanotube (CNT) transistors to the point where they can outperform the most advanced silicon transistors in prototype today.

CNTs are tube-shaped molecules made of carbon atoms, one nanometer (around three atoms) thick and 50,000 times thinner than a human hair, IBM Research Scientist Shalom Wind said in an interview.

They are expected to replace silicon when chip development hits the physical barrier where silicon just can't be made any smaller, in about 10 to 15 years' time, IBM said.

IBM scientists have achieved the highest transconductance - a measure of current-carrying capability - of any CNT transistor to date, and more than twice the transconductance, per unit width, of the top-performing silicon transistors available."

The research involved creating carbon nanotube field-effect transistors (CNFETs) with a similar structure to conventional metal-oxide semiconductor field-effect transistors (MOSFETs). That allowed the CNTs to be compared with their silicon equivalent, IBM said.

The devices showed excellent electrical characteristics, turning on and off easily and conducting well at low voltages. Previous attempts at CNT transistors needed high voltages of up to 20 volts to turn on and off, Wind said, compared with the 1 volt used for silicon.

These previous transistor attempts were based on a silicon wafer, using the silicon itself as the gate or switch to control the flow of electricity. That worked, but all of the transistors had to be turned on and off at the same time, he said.

The new structure puts the gate on top of the nanotube with a thin insulating layer of silicon dioxide in between, "so that it looks just like a silicon transistor, but with a narrow nanotube instead of a flat sheet of silicon," Wind said.

This research takes carbon nanotube technology a step closer to becoming a viable option for replacing silicon, Wind said.

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