Tuning the thermal boundary conductance at metal-dielectric interfaces by varying interlayer thicknesses

Interfaces play a significant role in the heat transport across boundaries at sub-micron length scales. Interfacial adhesion and phonon matching are important factors in determining the thermal boundary conductance, and the addition of an interlayer can be used to tune the heat dissipation. In this study, we analyze the modification of the thermal boundary conductance at metal-dielectric interfaces by insertion of metal interlayers with varying thicknesses from 2.5Å to 100Å. We show that the insertion of a tantalum interlayer at Al/Si and Al/sapphire interfaces hinders the phonon transmission across the interfaces and it plateaus at ~20Å. We found that the addition of a nickel interlayer significantly increased the thermal interfacial conductance at both the Al/Si and the Al/sapphire interfaces. The nickel interlayer, having an intermediate Debye temperature as compared to the Aluminum layer and the substrates, increases the phonon transmission across the boundary. Thermal property measurements were performed through time domain thermo-reflectance, and are in good agreement with a formulation of the diffuse mismatch model based on real phonon dispersions, accounting for anharmonic phonon scattering and phonon confinement within the interlayer.