Influence of geometrical parameters on performance of MEMS thermopile based flow sensor

Abstract

The aim of this work is to study how performance of thermal flow sensors depends on variation of specific geometrical parameters. Self-developed 1D analytical model was applied at a MEMS sensor based on Seebeck effect. The main elements of the analysed structure are: p+ Si/Al thermocouples, p+ Si heater, thermally and electrically isolating membrane and residual n-Si layer in membrane area. Two thermopiles consisting of N thermocouples are placed symmetrically at both sides of the heater. In this type of flow sensor output signal is obtained as a difference between the Seebeck voltages generated at the downstream and upstream thermopile. It was assumed that sensor is placed in the constant air flow. Several parameters of interest were calculated including flow induced temperature difference established between the downstream and upstream thermopile, output voltage and sensitivity. Simulations were performed in order to analyse dependence of these parameters on residual n-Si layer thickness (dnSi), distance between the hot thermopile junctions and the heater (Δl) and thermocouple width (wTP) and length (lTP). Simulation results show that sensitivity of the thermal flow sensor is improving with increasing Δl and lTP. On the other hand, performance of the sensor will also increase if dnSi or wTP are decreasing.