Anemometric air flow sensor on Silicon membrane

This paper reports the design, realization and preliminary testing results of an integrated air flow sensor based on micromachined technology. Tha mass airflow sensor architecture consists of microelectronic thermal (hotwire) anemometer design: two separate photomask sets were developed using L-EditTM software (by Tanner Research), with different layout for the two different splitting projected, one for the polysilicon resistor process and the other one for the gold resistor process. The working mode of the system is very simple: when there is no flow, the temperature profile around the hot resistor on the membrane is symmetrical. When gas flows, the symmetry is perturbed and we can measure this by controlling the difference in the resistance of the heaters. A flow rate can then be correlated to this differential change in temperature. The advantages are: the very small sensor size, the low power consumption, the velocity measurement range, the good accuracy, the very low signal to-tnoise rations, the excellent frequency response, the operational simplicity, a continuosanalog output signal and the low cost of the sensor device. We realised a micro air flow sensors prototype, fabricate with MEMS technologies. Preliminary electro-mechanical tests were carried on demonstrating the high performances of this device.