A Smart Flow Sensor for Flow Direction Measurement

The purpose of this paper is to apply MEMS techniques to manufacture a gas flow sensor that consists with an airflow rate and airflow direction sensing units for detection of airflow states. This study uses a silicon wafer as a substrate which is deposited silicon nitride layers. To form the airflow rate sensing unit, a micro heater and a sensing resistor are manufactured over a membrane that released by a back-etching process. The airflow direction sensing unit is made of four cantilever beams that perpendicular to each other and integrated with piezoresistive structure on each micro-cantilever, respectively. As the cantilever beams are formed after etching the silicon wafer, it bends up a little due to the released residual stress induced in the previous fabrication process. As air flows through the airflow rate sensor, the temperature of the sensing resistor decreases and the evaluation of the local temperature changes determines the airflow rate. On the proposed sensor, the airflow direction can be determined through comparing the resistance variation caused by different deformation of cantilever beams at different directions.