Cooling microprocessors with carbon nanotubes

Posted by TG Daily Staff

“Cool it!” That’s a prime directive for microprocessor chips and a promising new solution to meeting this imperative is in the offing. Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a “process friendly” technique that would enable the cooling of microprocessor chips through carbon nanotubes.

Frank Ogletree, a physicist with Berkeley Lab’s Materials Sciences Division, led a study in which organic molecules were used to form strong covalent bonds between carbon nanotubes and metal surfaces.

This improved by six-fold the flow of heat from the metal to the carbon nanotubes, paving the way for faster, more efficient cooling of computer chips. The technique is done through gas vapor or liquid chemistry at low temperatures, making it suitable for the manufacturing of computer chips.

“We’ve developed covalent bond pathways that work for oxide-forming metals, such as aluminum and silicon, and for more noble metals, such as gold and copper,” says Ogletree, who serves as a staff engineer for the Imaging Facility at the Molecular Foundry, a DOE nanoscience center hosted by Berkeley Lab. “In both cases the mechanical adhesion improved so that surface bonds were strong enough to pull a carbon nanotube array off of its growth substrate and significantly improve the transport of heat across the interface.”

Ogletree is the corresponding author of a paper describing this research in Nature Communications. The paper is titled “Enhanced Thermal Transport at Covalently Functionalized Carbon Nanotube Array Interfaces.” Co-authors are Sumanjeet Kaur, Nachiket Raravikar, Brett Helms and Ravi Prasher.

Overheating is the bane of microprocessors. As transistors heat up, their performance can deteriorate to the point where they no longer function as transistors. With microprocessor chips becoming more densely packed and processing speeds continuing to increase, the overheating problem looms ever larger.

The first challenge is to conduct heat out of the chip and onto the circuit board where fans and other techniques can be used for cooling. Carbon nanotubes have demonstrated exceptionally high thermal conductivity but their use for cooling microprocessor chips and other devices has been hampered by high thermal interface resistances in nanostructured systems.