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Graphene interconnects outperform copper

Posted: 11 Jun 2009     Print Version  Bookmark and Share

Keywords:grapheme  on-chip interconnects  transistor  copper interconnects 

The unique properties of thin layers of graphite – known as graphene – make the material attractive for a wide range of potential electronic devices.

Georgia Institute of Technology researchers have now experimentally demonstrated another potential application for graphene: replacing copper for interconnects in future generations of ICs.

In a paper published in the June 2009 issue of the IEEE journal Electron Device Letters, the researchers report detailed analysis of resistivity in graphene nanoribbon interconnects as narrow as 18nm.

The results suggest that graphene could outperform copper for use as on-chip interconnects – tiny wires that are used to connect transistors and other devices on ICs. Use of graphene for these interconnects could help extend the long run of performance improvements for silicon-based IC technology.

Raghunath Murali (left) and graduate student Kevin Brenner are shown with a test station used to study the properties of graphene.

Raghunath Murali (left) and graduate student Kevin Brenner are shown with a test station used to study the properties of graphene.

"As you make copper interconnects narrower and narrower, the resistivity increases as the true nanoscale properties of the material become apparent," said Raghunath Murali, a research engineer in Georgia Tech's Microelectronics Research Center. "Our experimental demonstration of graphene nanowire interconnects on the scale of 20nm shows that their performance is comparable to even the most optimistic projections for copper interconnects at that scale. Under real-world conditions, our graphene interconnects probably already outperform copper at this size scale."

Beyond resistivity improvement, graphene interconnects would offer higher electron mobility, better thermal conductivity, higher mechanical strength and reduced capacitance coupling between adjacent wires.

"Resistivity is normally independent of the dimension – a property inherent to the material," Murali noted. "But as you get into the nanometer-scale domain, the grain sizes of the copper become important and conductance is affected by scattering at the grain boundaries and at the side walls. These add up to increased resistivity, which nearly doubles as the interconnect sizes shrink to 30nm."

The research was supported by the Interconnect Focus Center, which is one of the Semiconductor Research Corporation/DARPA Focus Centers, and the Nanoelectronics Research Initiative through the INDEX Center.

A graphene material sample that was tested for its properties is shown against an image in a test station.

A graphene material sample that was tested for its properties is shown against an image in a test station.

Murali and collaborators Kevin Brenner, Yinxiao Yang, Thomas Beck and James Meindl studied the electrical properties of graphene layers that had been taken from a block of pure graphite. They believe the attractive properties will ultimately also be measured in graphene fabricated using other techniques, such as growth on silicon carbide, which now produces graphene of lower quality but has the potential for achieving higher quality.

Because graphene can be patterned using conventional microelectronics processes, the transition from copper could be made without integrating a new manufacturing technique into circuit fabrication.

"We are optimistic about being able to use graphene in manufactured systems because researchers can already grow layers of it in the lab," Murali noted. "There will be challenges in integrating graphene with silicon, but those will be overcome. Except for using a different material, everything we would need to produce graphene interconnects is already well known and established."

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