IBM shrinks circuit with nanotube

IBM researchers have built a complete integrated circuit by combining standard silicon methods with a carbon nanotube molecule.

Researchers at IBM have taken a large step toward creating nano-scale processors. They have built an electronic integrated circuit by combining conventional silicon technology with a carbon nanotube molecule.

The resulting hybrid circuit is still slower than a conventional component, but it is an important proof of concept, said Joerg Appenzeller, research staff member at IBM's Thomas J. Watson Research Center in Yorktown Heights, New York.

IBM released the news Thursday in a paper published in the journal Science.

The research could have a large impact on the design of faster processors. Forty years after Intel cofounder Gordon Moore predicted that the number of transistors on a chip would double every two years, engineers are finding it hard to keep up with "Moore's Law."

Industry leader Intel has announced plans to move from 65-nanometer chip geometry to a 45-nanometer plan by 2007. But many engineers warn that chips cannot get much denser without running into problems like overheating. A hybrid processor would avoid that problem because electrons flow through nanotubes at high speed and low friction.

Analysts said IBM's achievement was an important step toward reaching the goal. "Given that they're looking at a 10-to-15 year time horizon until this can become a game-changer in the industry, there is a tremendous amount they have accomplished," said Vahe Mamikunian, an analyst with Lux Research.

Many researchers have noticed the great physical attributes of carbon nanotubes before, such as offering higher speed, lower power consumption and higher densities, he said.

One company, Nantero, is using nanotubes to create high-density nonvolatile memory. Other scientists are using the thermal conduction properties of nanotubes to draw heat away from processors. That work is happening at Fujitsu and NanoConduction.

"IBM's work is different, because no one has really looked at using carbon nanotubes as a replacement for silicon," Mamikunian said. "Now they have to scale that up to gigahertz and terahertz levels. They haven't found a switching speed limit yet, so theoretically it shouldn't be a problem."

A nanotube is like a straw built of carbon atoms, frozen in a form between a crystal and a molecule. That allows it to be very small, 50,000 times thinner than a human hair. The IBM team took a carbon nanotube and attached standard wires to it, sticking out like the teeth of a comb. That allowed them to use a single molecule as the base for all components in the circuit, using standard semiconductor processes.

"So we've combined the nanotube with standard architecture, similar to what's used today in a silicon chip. The difference is that this would be smaller and faster," Appenzeller said.

The resulting circuit is called a ring oscillator, a tool used by silicon engineers like a speedometer to measure the performance of a transistor. The IBM researchers used it to measure the speed of their nanotube using alternating current (AC) power.

They reached a top speed of 50MHz, which is 100,000 times faster than anything done previously with nanotubes in a circuit.

"It is still not as fast as today's silicon chips, but we can make it orders of magnitude better," said Appenzeller. "We have a very clear picture of how to move on. Developing the first car is much harder than making a car that can go faster."

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Ben Ames

IDG News Service
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