Investigating Non-Equilibrium Effects Due to Electron-Phonon Interaction at Metal-Insulator Interfaces

With the miniaturization of electronic devices, denser interfaces can lead to significant thermal resistance, impeding heat dissipation. Among these, metal-insulator interfaces involve complex interactions among multiple heat carriers, which are not yet fully understood. Insulated electrons and partially transmitted phonons can create strong non-equilibrium distributions near the interface, leading to additional thermal resistance. Non-equilibrium distributions relax via scattering at different length scales, depending on the electron/phonon mean free paths. The Boltzmann’s H-theorem dictates the entropy generation and thermal resistance upon the relaxation by scattering processes. In this work, we discuss the carrier non-equilibrium and resulting additional thermal resistance near metal-insulator interfaces. To capture the complex transport phenomena involving the advection and scattering of electrons and phonons, we present the solution of coupled Boltzmann transport equations using ab initio inputs for interfaces of two semi-infinite leads. The results show that the interfacial thermal resistance is substantially different from the resistance based on Landauer’s formalism which does not consider the carrier non-equilibrium. We also found that the spatial decay of carrier non-equilibrium is not an intrinsic property of the lead material but strongly depends on the paired lead material in the opposite side. Lastly, we discuss the role of normal phonon-phonon scattering, which is often a dominant scattering mechanism in high thermal conductivity insulators, on the relaxation of carrier non-equilibrium and contributions to the excessive thermal resistance. This presentation is in memory of Dr. Natalio Mingo.