Effect of pressure and gas type on the response of thermal flow sensors in low flow regime

The dependence of integrated gas flow sensor response on pressure variations and gas type has been investigated. The devices are based on the differential temperature principle and were fabricated by applying two post-processing steps to standard microelectronic chips. The structure is made up of a polysilicon heater on a suspended SiO2 membrane placed between an upstream and a downstream thermopile used as temperature probes. Flow rates below 200 sccm were investigated for three different gases, namely Ar, Xe and N2, at pressures in the range 10-100 kPa