Thermal conductivity measurements on diamond films based on micromechanical devices

Abstract

An accurate technique to measure the thermal conductivity k(T) of CVD diamond based on new micromechanical devices is presented. The thermal conductivity parallel to the surface of films with thicknesses ranging from 2 to several hundred μm can be determined over a wide temperature range. The diamond films were patterned by RIE in an oxygen plasma to achieve accurate device dimensions. The silicon was completely removed from a defined area leaving diamond membranes and free standing diamond cantilevers. A thin film heater generated a temperature profile which was measured using several thermoresistors. Shape and dimensions of the structures were optimized using computer simulations (FEA). The effects of thermal radiation, additional metallization and insulation layers were minimized. Measurements on CZ silicon show a very good agreement with literature results. The thermal conductivity of diamond films with thicknesses between 3.6 and 8 μm grown on a silicon substrate by the hot filament technique with different methane concentrations were measured between −195 and 300 °C. The measured values range between < 1 and 5 W cm −1 K −1.