Thermal conductivity measurements on thin films based on micromechanical devices

A new, highly accurate technique to measure the thermal conductivity k(T) of thin films (thickness ranging from 2 mu m up to several hundred micrometres) parallel to the surface over a wide temperature range is presented. The silicon substrate on which the films were deposited is completely removed in a defined area leaving membranes or free standing beams. A thin-film heater generates a temperature profile which is measured by several thermoresistors. The shape and dimensions of the structures have been optimized using computer simulations (FEA). The measurement is carried out in a vacuum chamber. First measurements on etched silicon membranes show a good agreement with literature values for bulk silicon. Measurements on polycrystalline diamond films show a maximum value of the thermal conductivity of 4 W cm(-1) K-1 between 100 and 200 degrees C, which can be explained by the theory for thermal conductivity as an effect of the small grain size of the diamond film.