Thermal characterization of surface-micromachined silicon nitride membranes for thermal infrared detectors

The aim of this work is to provide a thorough thermal characterization of membrane structures intended for thermal infrared detector arrays. The fabrication has been conducted at temperatures below 400°C to allow future post processing onto existing CMOS readout circuitry. Our choices of membrane material and processing technique were plasma enhanced chemical vapor deposited silicon nitride (SiN) and surface micromachining, respectively. The characterization gave for the thermal conductance (G) and thermal mass between the membrane and its surroundings 1.8·10^-7 W/K and 1.7·10^-9 J/K, respectively, which are close to the best reported values elsewhere. From these results the thermal conductivity and specific heat of SiN were extracted as 4.5±0.7 W/m.K and 1500±230 J/kg.K. The contribution to G from different heat transfer mechanisms are estimated. A model describing the pressure dependence of G was developed and verified experimentally in the pressure interval [5·10^-3, 1000] mbar. Finally, the influence of the thermal properties of the membrane on infrared detector performance is discussed