Thermal Boundary Conductance at High Temperatures

Understanding the physics of thermal boundary conductance is essential for thermal management of semiconductor devices. Thermal boundary conductance between two materials has been shown to depend on atomic scale details like interfacial bonding, interfacial roughness, and interfacial layers. The intrinsic vibrational properties of the materials at the interface also affect thermal boundary conductance¹. Surprisingly, only a few experimental studies of thermal boundary conductance at high temperatures exist. This prevents testing of theories for how inelastic processes contribute to thermal conductance^2,3. Inelastic processes at the interface between dissimilar materials are expected to be most important, and more noticeable at high temperatures. In this study, we present results of time domain thermoreflectance (TDTR) measurements of the thermal boundary conductance for nitride-metal/group-IV-semiconductor interfaces between 80 and 800 K. The nitride-metals (TiN and HfN) and group-IV-semiconductors (Ge, Si, SiC, and diamond) have systematic differences in bulk vibrational properties. By comparing the conductance vs. temperature of these systems, we determine the effect of vibrational similarity on inelastic scattering processes. We show that the average probability for interfacial energy transmission increases significantly with temperature by comparing the measured conductance values to theoretical predictions for the elastic and inelastic limits of the constituent materials. In diamond systems, the transmission probability of thermal energy triples from 20% at 300 K to 60% at 900 K. Our findings fill an important gap in the literature for how interfacial conductance evolves at high temperatures, and tests burgeoning theories^2,3 for the role of inelastic processes in interfacial thermal transport.<br/> <br/><b>References</b><br/>(1) Khan, S.; Angeles, F.; Wright, J.; Vishwakarma, S.; Ortiz, V. H.; Guzman, E.; Kargar, F.; Balandin, A. A.; Smith, D. J.; Jena, D.; Xing, H. G.; Wilson, R. Properties for Thermally Conductive Interfaces with Wide Band Gap Materials. <i>ACS Appl Mater Interfaces</i> <b>2022</b>, <i>14</i> (31), 36178–36188. https://doi.org/10.1021/acsami.2c01351.<br/>(2) Guo, Y.; Zhang, Z.; Bescond, M.; Xiong, S.; Nomura, M.; Volz, S. Anharmonic Phonon-Phonon Scattering at the Interface between Two Solids by Nonequilibrium Green’s Function Formalism. <i>Phys Rev B</i> <b>2021</b>, <i>103</i> (17). https://doi.org/10.1103/PhysRevB.103.174306.<br/>(3) Sääskilahti, K.; Oksanen, J.; Tulkki, J.; Volz, S. Role of Anharmonic Phonon Scattering in the Spectrally Decomposed Thermal Conductance at Planar Interfaces. <i>Phys Rev B</i> <b>2014</b>, <i>90</i> (13), 134312. https://doi.org/10.1103/PhysRevB.90.134312.