A double heater integrated gas flow sensor with thermal feedback

An integrated thermal sensor for flow rates below 200 sccm, consisting of two central heaters and two thermopiles, located downstream and upstream with respect to the heaters, is presented. The sensor, fabricated by post-processing chips produced with a standard microelectronic process, is operated in closed loop configuration through a single operational amplifier, in such a way that the flow-induced temperature difference between the two thermopiles is cancelled by applying a power mismatch to the two heaters. The output signal is proportional to the heater power unbalance. Static and dynamic electrical characterization of the sensor is performed. The response to nitrogen flow rates has been measured for various gas pressures.