In-plane surface phonon-polariton thermal conduction in dielectric multilayer systems

Nanoscale heat conduction is limited by surface scattering of phonons but can be enhanced by surface phonon-polaritons (SPhPs), which are the hybridization of photons and optical phonons in polar materials. Here, we analyze the dispersion of SPhPs in a multilayer system consisting of a silicon (Si) layer sandwiched between two silicon dioxide (SiO₂) nanolayers. We find that SPhPs generated in SiO₂ nanolayers couple with guided resonant modes and propagate mainly in the nonabsorbent Si layer for microscale Si thicknesses. This coupling yields an enhancement in thermal conductivity with Si thickness. In contrast, for nanoscale Si thicknesses, evanescent components of SPhPs couple inside the Si layer, resulting in a higher thermal conductivity for thinner Si layers. The transition between these two different coupling phenomena provides the minimum of the in-plane SPhP thermal conductivity at a Si thickness of approximately 1 μm. Our finding brings deeper insight into thermal management in electronics and semiconductors.