Fujitsu finds copper-bottomed solution to chip problem

Fujitsu claims to have answered a major technological problem of the future for chip makers by using carbon nanotubes to replace copper wires in circuits.

Chips to be made around 2010 will have connecting wires made of copper that will be so thin that electrons will tend to migrate and leak out of the wires, said Yuji Awano, a research fellow at Fujitsu Laboratories' Nanotechnology Research Center.

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.

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 diametres between about 0.4 nanometres and 1.8 nanometres and can vary in length up to several hundred nanometres long, depending on how they are made. A nanometre is one-billionth of a metre.

"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-nanometre 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-nanometre process and around 2013, on a 32-nanometre 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-nanometre process chips and most or all of its 32-nanometre 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.