Thermal transport across a transition metal oxide-insulator interface

Thermal resistance between metals and semiconductors or insulators has become a major factor that affects the heat dissipation and cooling of high-power devices. Multiple mechanisms are involved, including electron-phonon coupling in the metal, phonon-phonon coupling across the interface, and direct coupling of electrons in the metal and phonons in the dielectric oxide. Here, we consider a unique metal oxide, VO₂, whose electronic structure can be tuned by either doping or temperature to modulate electron density by orders of magnitude, essentially transitioning from metal-like to insulating behavior. To quantitatively determine the contribution from each thermal mechanism, a first-principles method along with the Atomistic Green's function method is applied to VO₂-Al₂O₃ interfaces. Two VO₂ structures, a low-temperature monoclinic phase and a high-temperature rutile phase, are investigated. Electrical band structure and phonon dispersion are calculated, showing a transition from semiconductor to metal phase, accompanied by a pronounced change in thermal transport characteristics. Calculated thermal boundary conductances are compared to pump probe experiments before and after the phase transition on highly controlled VO₂-Al₂O₃ interfaces. The spectrally resolved phonon transmission is also compared to experimental data obtained from phonon spectral mapping.