Characterization of Metallically Bonded Carbon Nanotube-Based Thermal Interface Materials Using a High Accuracy 1D Steady-State Technique

The next generation of Thermal Interface Materials (TIMs) are currently being developed to meet the increasing demands of high-powered semiconductor devices. In particular, a variety of nanostructured materials, such as carbon nanotubes (CNTs), are interesting due to their ability to provide low resistance heat transport from device to spreader and compliance between materials with dissimilar coefficients of thermal expansion (CTEs). As a result, nano-Thermal Interface Materials (nTIMs) have been conceived and studied in recent years, but few application-ready configurations have been produced and tested. Over the past year, we have undertaken major efforts to develop functional nTIMs based on short, vertically-aligned CNTs grown on both sides of a thin interposer foil and interfaced with substrate materials via metallic bonding. A high-precision 1-D steady-state test facility has been utilized to measure the performance of nTIM samples, and more importantly, to correlate performance to the controllable parameters. Nearly 200 samples have been tested utilizing myriad permutations of such parameters, contributing to a deeper understanding and optimization of CNT growth characteristics and application processing conditions. In addition, we have catalogued thermal resistance results from a variety of commercially-available, high-performance thermal pads and greases. In this paper, we describe our material structures and the parameters that have been investigated in their design. We report these nTIM thermal performance results, which include a best to-date thermal interface resistance measurement of 3.5 mm²-K/W, independent of applied pressure. This value is significantly better than all commercial materials we tested and compares favorably with the best results reported for CNT-based nTIMs in an application-representative setting.