IBM Milestone Could Lead to Smaller Chips

Reaching a long-sought goal in computing research, scientists have created a computer circuit based on a single molecule, which could lead one day to far smaller and faster computer chips that use less power.

IBM Corp. said Sunday that its researchers have built a logic circuit--a set of electronic components that performs a processing function--based on a a tiny cylindrical structure made up of carbon atoms that is about 100,000 times thinner than a human hair.

The breakthrough is IBM’s second this year using the molecules called carbon nanotubes as semiconductors, making them an increasingly viable alternative to silicon, which forms the base of current chips, IBM said.

“Carbon nanotubes are now the top candidate to replace silicon when current chip features just can’t be made any smaller,” said IBM’s Phaedon Avouris, lead scientist on the project. “Such beyond-silicon nanotube electronics may then lead to unimagined progress in computing miniaturization and power.”

Scientists are looking for a replacement for silicon because in the next 10 to 15 years they expect it will no longer be possible to reduce the size of chips using silicon, which will limit improvements in chip size and speed.

Since Intel Corp. introduced its 386 microprocessor in 1985, computer chips have made exponential advances in both speed and size, increasing the number of transistors on a chip more than 152 times.

That’s what’s behind Moore’s Law, named after Intel founder Gordon Moore, who predicted in 1965 that the number of transistors, or electronic switches, on a chip would double every 18 months.

Avouris wasn’t able to quantify how chips built of nanotubes would compare in speed with silicon ones, but nanotubes are expected to at least match the improvements Moore’s Law dictates for today’s silicon chip.

In a couple of years, IBM expects to start working on ways of building the new chips and will know how the size of the elements in the nanotube chip compare with those of silicon chips.

Although researchers had already found a way to form nanotubes into transistors, IBM’s latest achievement showed that a nanotube can be used to make a logic circuit, the key to computing.

A carbon nanotube is a single molecule that’s about 500 times narrower than the silicon used in today’s processor and is about 10 atoms across. A nanotube creates less heat than silicon and uses less power and space.

IBM scientists used a nanotube to make a “NOT” gate, which has both a positive and negative transistor, meaning that the entire circuit can perform the processing functions critical to computing.

A NOT gate is essentially an open or closed switch that changes a “1” to a “0” and a “0” to a “1.” Previously, nanotube transistors were only positive and didn’t process information.

IBM said a nanotube circuit’s signal output is strong enough to drive other gates or circuits, which means that more complex circuits could be built using a single nanotube. These complex circuits are the next step toward molecular computer chips, IBM said.

The discovery comes about four months after the IBM team said it had built the first array of transistors out of carbon nanotubes. Prior to that, nanotubes had to be positioned one at a time or by random chance. That achievement was a step toward eventual mass production of computer chips.

In New York Stock Exchange trading Friday, IBM closed at $106.99, up $3.99 for the day.