Fujitsu Laboratories has created a thin flexible adhesive sheet thermal interface material for heatsinking that achieves up to 100W/mK thermal conductivity.

“Unlike previous technologies, the carbon nanotube adhesive sheets are also flexible, making them easy to cut and handle for use on variety of surfaces,” according to the lab. “This technology promises to deliver practical improvements and cost-effectiveness for power modules for electric vehicles.”

Carbon nanotubes have high thermal conductivity along their length, but poor thermal conductivity across their width, requiring them to be aligned through the thickness of a layer if it is to be used to conduct heat from one face to the other.

Fujitsu has developed a technique for laminating vertically aligned multi-walled carbon nanotubes, while maintaining high thermal conductivity and flexibility. The result can be handled and cut for use.

This follows on from work in 2017 when the lab created a rigid carbon nanotube thermal sheet by moulding and scintered at 2,000°C. While highly thermally conductive, it could not be used between uneven surfaces.

FujitsuLabs-CNT-thermal-interface-material-diagThe new structure is a sandwich of vertical nanotubes between thin protective sheets.

“Carbon nanotubes are difficult to use as heat dissipating materials because they easily lose their shape,” said Fujitsu. “However, this technology protects the carbon nanotubes themselves with a laminate layer, making them stable in shape and making cutting and handling easier, which was difficult with conventional technologies.”

These protective sheets are bonded to the ends of the nanotubes with a polymer adhesive layer several microns thick.

“Because even a small amount of resin can cause large thermal resistance, it has become an issue that must be solved to achieve both adhesiveness and thermal conductivity,” said Fujitsu. “Thus, by optimising three or more correlation parameters, such as the density of carbon nanotubes, the type and thickness of the resin, and the bonding conditions, utilising knowledge of thermal resistance at the interface between carbon nanotubes and resins cultivated over many years, it becomes possible to bond carbon nanotubes while maintaining sufficient adhesive properties without impairing thermal conductivity.”

Fujitsu is aiming to license the use of its thermal conductor.