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Thermal Expansion in Bonded Carbon Nanotube Forest Interfaces
Keywords: Thermal Interface, Thermal Expansion, Carbon Nanotube
Carbon nanotubes (CNTs) possess an ideal combination of thermal and mechanical properties for thermal interface materials (TIMs). They have been measured to have a thermal conductivity as high as 3000 W/m-K along their axis, and due to their large aspect ratios are extremely flexible. TIMs comprised of forests of nominally vertically aligned CNTs attempt to utilize the high thermal conductivity of CNTs to efficiently conduct heat across an interface and their mechanical flexibility to accommodate mismatches in thermal expansion between the materials on either side of the interface. However, it has been found that the effective thermal conductivity of CNT forests is considerably lower (~10-100 W/m-K) than that of a single CNT and that high thermal contact resistance on either side of the CNT forest limits the thermal effectiveness of CNT TIMs. As a result, most research on CNT forest TIMs has focused on improving thermal transport. Studies on the in-plane mechanics of CNT forests, parallel to the interface and along the direction of thermal expansion, have been limited to a few measurements of elastic modulus. Whether or not CNT forests can accommodate mismatches in thermal expansion, especially when bonded using a metal or polymer, remains largely unstudied. We study the capacity of CNT forests TIMs, bonded using a variety of methods, to accommodate mismatches in thermal expansion. Specifically, the thermal resistance of CNT forest TIMs bonded between silicon and silver substrates with polystyrene, indium, and gold is measured before and after several cycles of baking at high temperature.
John H. Taphouse, Graduate Research Assistant
Georgia Institute of Technology
Atlanta, GA

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