Fujitsu touts carbon nanotubes for chips

Due to reporting errors, the story "Fujitsu touts carbon nanotubes for chip wiring," which ran on the wire Tuesday, mischaracterized the way in which Fujitsu Ltd. plans to use carbon nanotubes in some future chips.

The story also mischaracterized Fujitsu's level of commitment to the technology, and did not explain accurately the problem it may be able to solve with carbon nanotubes.

The story on the wire has been corrected, with changes made throughout. It now reads as follows:

Fujitsu Ltd. believes it may have the answer to a major technology problem that will confront chip makers in the future -- using carbon nanotubes to replace some of the copper wires used to connect layers of integrated circuits in chips.

As chips become more powerful, the density of electrons traveling through circuits becomes so high that the electrons hit against each other, causing copper atoms to move. The problem, known as electro-migration, is likely to cause problems for the production of some high-end chips some time after 2010, 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.

Fujitsu is exploring the use of carbon nanotubes as one option for overcoming the problem in vertical copper wires used to connect layers of circuitry within chips. The vertical wires are known as "vias."

Carbon nanotubes are made by manipulating carbon atoms to form hollow cylinders. The nanotubes that Fujitsu is developing, known as "multi-wall" nanotubes, are 5 nanometers to 10 nanometers in diameter. They can vary in length up to several hundred nanometers 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 electro-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 Road map for Semiconductors, a trade group that helps set chip industry standards.

Fujitsu is considering the use of carbon nanotubes for some of its 45-nanometer process chips made after 2010, and for 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 may be able to develop the technology sufficiently to use it in high-end processors 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 in place of copper vias, 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 Corp. and IBM Corp. 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.

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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