Thermal conductance measurements of a silicon nitride membrane at low temperatures

Silicon nitride membranes are used for thermal isolation in various devices , such as bolometric millimetre-wave detectors and lattice microrefrigerato rs. We have measured the thermal conductance of a 1.5 mu m thick silicon ni tride membrane, between 0.1 and 0.3 K. At these temperatures, thermal trans port in such thin films is believed to be dominated by phonon surface scatt ering, and not by bulk behaviour. We compare our results with theory, as we ll as experiments using films with different thicknesses. (C) 2000 Elsevier Science B.V. All rights reserved.