Nano-Switches Could Yield Even Smaller Gadgets

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Researchers hope that it might eventually be possible to replace standard silicon transistors with much smaller versions fashioned from carbon nanotubes.

Rao and his colleagues at Clemson University figured out how to make the Y-shaped nanotubes by adding metal particles during the formation process. When a particle is trapped in a half-formed nanotube, the tube branches.

Prabhakar Bandaru, a materials scientist at the University of California, San Diego, heard the news and started thinking: The new tubes had three prongs—just like a traditional transistor.

"I was curious whether there could be some transistor-like properties" in the nanotubes, Bandaru said.

Bandaru and his colleagues borrowed some nanotubes from Rao and performed a series of experiments. They noticed that applying a current to one prong of the Y-shaped nanotube affected a separate current that was already running between the other two prongs.

Regardless of which prong they used to apply current, they could manipulate the current in the other prongs as if they were opening and closing a gate.

"We created a completely new kind of transistor," Bandaru said. "There's no silicon at all."

From Lab Bench to Laptop

"The gate modulates the current between the source and the drain," commented Jia Chen, an IBM research scientist in Yorktown Heights, New York. "That's the basic element of a transistor."

But consumers shouldn't expect to find carbon transistors in their electronics any time soon. Chen and Bandaru agree that commercial applications are still years away.

To make a working chip, engineers would need to assemble millions of evenly spaced, predictably shaped nanotube transistors.

"We don't know yet how to assemble these in a regular fashion," Bandaru said. Even making tidy arrays of standard cylindrical nanotubes has been a challenge. "There have been a lot of attempts, but nothing that is economically feasible."

The new Y-shaped nanotubes also don't perform nearly as well as current silicon-based transistors. According to Chen, the gate in the carbon nanotube couldn't completely halt the flow of electrons as it would in a true transistor. "There was leakage," she said.

As a material for making transistors, carbon "is probably not going to catch silicon in [the next] 10 to 20 years," Chen predicted. "At this stage nothing really competes."

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