News from Nanotechjapan

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Fujitsu Laboratories Develops Pure Carbon-Nanotube Sheets with World's Top Heat-Dissipation Performance

 On November 30, 2017, Fujitsu Laboratories Ltd. announced the successful development of a high-thermal-conductive carbon-nanotube (CNT) sheet with the world's top heat dissipation performance. The sheet is composed of perpendicularly oriented pure (no binder materials included) CNTs, resulting in exceptional thermal conductivity and heat resistance. Details were presented at the 2017 Workshop on Innovative Nanoscale Devices and Systems (WINDS2017)*.

 Reduction of greenhouse gas emission has been heavily demanded for the sustainable development of the world. Power electronics is expected as an enabling technology for this challenge. Semiconductor power devices made from silicon and silicon carbide, for example, are going to be key devices in automobiles to drive them by electricity. Reliable and efficient operation needs to keep the moderate temperature of these devices, and heat dissipation is important design criteria.

 CNT is featured for high thermal conductivity along its axis and a promising material for heat dissipation. However, it has been difficult to grow dense, uniform arrays of perpendicularly oriented CNTs as a robust sheet. Researchers in Fujitsu challenged this difficulty and succeeded in developing a highly-thermal-conductive CNT sheet.

 The success was resulted by two innovative technologies : (1) multi-walled CNT growth control with respect to the metal-particle catalyst, and the feedstock gas so that a dense, uniform array of CNTs grew perpendicularly : (2) CNT sheet formation all over the surface of a 200-mm diameter silicon substrate by heat treatment at temperatures above 2000℃ without using binder materials such as resin and rubber.

 The CNT sheet thus made showed high thermal conductivity of 80 W/m・K to be compared to 25 W/m・K of conventional resin sheet and thermal resistance up to over 700℃ against 200℃ of the resin. 

 *Shinichi Hirose,"High Thermal Conductivity of Carbon Nanotube Sheets for Future Thermal Interface Materials", WINDS 2017(2017 Workshop on Innovative Nanoscale Devices and Systems, Poster Session, P-7, 30 Nov. 2017