Measurement of the in-plane thermal conductivity of SiO2 thin films due to surface phonon-polaritons

Abstract : Reduction of the phonon thermal conductivity of thin films as their thickness is scaled down raises a lot of difficulties for the thermal management of nanodevices used in microelectronics or optics. In this work we aim to experimentally prove that the thermal conductivity of silicon dioxide thin films can be enhanced by taking advantage of surface effects, through the propagation of surface phonon-polaritons. The strengthening of these effects for increasingly thinner films enables to offset the decrease of their thermal properties. Periodically laser-heating method is used to measure the in-plane thermal diffusivity of suspended silicon dioxide thin films with strong surface resonances. The thermal conductivity is then determined through a simple relation. Plasma-enhanced chemical vapour deposition (PECVD) and dry oxidation techniques are used to produce thin films with thicknesses from 2 pmi to 50 nm. Purity and surface quality are controlled using a scanning electron microscope and energy-dispersive X-ray spectroscopy. Based on our theoretical results we expect a total in-plane thermal conductivity of about 2 W/(m.K) for a 50 nm-Thick glass thin film at room temperature.