Fujitsu touts carbon nanotubes for chip wiring

Fujitsu wants to use carbon nanotubes in its future chips, ahead of other chip vendors, and is readying the technology for implementation around 2010.

Fujitsu believes it has the answer to a major technology problem that will confront chip makers in the future -- using carbon nanotubes to replace copper wires in chip circuits.

For chips scheduled to be made around 2010, connecting wires made of copper will become so thin and their volume so small that the electrons will tend to migrate and leak out of the wires, said Yuji Awano, a research fellow at Fujitsu Laboratories' Nanotechnology Research Center, in an interview at the Japan Nano Tech 2005 exhibition held in Tokyo Feb. 23 to Feb. 25.

Because copper transmits electrons relatively inefficiently, the wires heat up and will become unusable as the electrons get pushed out of the tiny copper threads, according to Awano. Such problems will only worsen for the more advanced chips with even smaller circuits planned after 2010, he said.

Carbon nanotubes will become essential to replace copper in chips that are expected to be about a third of the size of those today, according to Awano.

Fujitsu, he said, is the first manufacturer to commit to using carbon nanotubes in place of copper wires in chips.

Carbon nanotubes are made when carbon atoms form hollow, open-ended cylinders. They have diameters between about 0.4 nanometers and 1.8 nanometers and can vary in length up to several hundred nanometers long, depending on how they are made. A nanometer is one-billionth of a meter.

"If you make a smaller chip, you need thinner wiring," Awano said. "We have to solve the electron migration issue, and to do this we need thicker wiring -- but we can't make thicker wiring because the chip size will become bigger."

Carbon nanotubes can carry about 1,000 times the current density, or the current per unit area, compared to copper, according to Awano. In addition, they transmit electrons about 10 times faster and dissipate heat much more readily -- characteristics that allow them to replace copper, he said.

Many of today's advanced chips are made on a 90-nanometer process. The measure refers to the average size of features on a chip built using that process.

Around 2010, chips will be made on a 45-nanometer process and around 2013, on a 32-nanometer process, according to the International Technology Roadmap for Semiconductors, a trade group that helps set standards for the chip industry.

Fujitsu will use the carbon nanotubes on some of its 45-nanometer process chips and most or all of its 32-nanometer chips, Awano said.

The manufacturer is already making carbon nanotubes to standard lengths that conduct electricity in the required way. It should be able to mass-produce them and develop the technology to put them in complex chips by the end of the decade, Awano said.

Fujitsu has already made test chips in which it has connected two layers of circuitry with about 1,000 connections using the carbon nanotubes as wires, he said.

"This is real, and it's a real challenge," said Makoto Okada, a manager at the company's public and investor relations division.

In addition to Fujitsu, several major technology companies, including NEC and IBM have announced breakthroughs in chip production processes and in their understanding of how carbon nanotubes work.

IBM, which pioneered the use of copper for connections in chips in the late 1990s, has yet to announce its plans, said Glen Brandow, a company spokesman.

Intel did not respond to questions on the subject.

NEC is also considering carbon nanotubes, but has not yet committed to the technology, said Toshio Baba, senior manager of NEC's Fundamental and Environmental Laboratories.

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Paul Kallender

IDG News Service
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