Material Properties for High Thermal Interface Conductance

<b><u>Material Properties for High Thermal Interface Conductance</u></b><br/>S. Khan¹, F. Angeles¹, W. Peng¹, J. Wright², S. Vishwakarma³, Depdeep Jena², H. Grace Xing², David J. Smith³, Richard Wilson¹ <br/>¹University of California, Riverside, ²Cornell University, ³ Arizona State University<br/> <br/>The materials science of interfacial heat transfer in wide- and ultra-wide bandgap material systems is not well understood. There are gaps in knowledge about what types of materials can form thermally conductive interfaces with ultrawide band gap semiconductors and why. Understanding the physics of interfacial thermal transport is important because thermally resistive interfaces limit the maximum power before failure in an electrical device and hinder device reliability. In this talk, we discuss which material properties are most important for forming thermally conductive interfaces in wide- and ultra-wide band gap material systems. We performed a series of experiments designed to identify how three phenomena govern how thermally conductive ultra-wide band gap semiconductor interface can be. These three phenomena are (i) the vibrational similarity of the materials forming the interface, (ii) the complexity of the material’s unit cells, and (iii) the interfacial structure. We report time-domain thermoreflectance (TDTR) measurements of the interface conductance between nitride metals (TiN, HfN) and group IV (Diamond, SiC, Si, Ge) as a function of temperature. We also measure interface conductance between nitride metals and group III-V crystals (AlN, GaN, cubic BN). The nitride metals, group IV and group III-V materials we study have systematic differences in acoustic properties. These systematic differences allow us to test how vibrational similarity between the nitride-metal and substrate affects interfacial transport. At room temperature, we observe interface conductances range between 150 and 900 MW m^-2 K^-1. We find that even vibrationally dissimilar materials can form thermally conductive interfaces. The most thermally conductive interfaces are formed between vibrationally stiff materials with high phonon frequencies. Finally, to investigate how interfacial structure effects heat-transfer, we measure the interface conductance of a series of TiN/AlN samples prepared in different ways. We use TEM to image interfacial structure. Our findings on how bulk vibrational properties, crystal unit-cells, and interfacial morphology govern interfacial transport will aid ongoing efforts to engineer ultra-material heterostructures with thermally conductive interfaces.<br/> <br/><i>Research supported as part of ULTRA, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award # DE-SC0021230</i>.