A flow direction sensor fabricated using MEMS technology and its simple interface circuit

A thermal flow direction sensor was fabricated using MEMS technology. A new structure was suggested to improve the detection of airflow in any direction and its interface circuit was realized with simple OP amp circuits. Pt was used as resistive material because of its very stable physical properties and linearity of TCR. Pt was sputtered on a silicon wafer and patterned by a lift-off process. In addition, a silicon diaphragm was fabricated on the back of the pattern by backside etching. The structure of the sensor is circular-type to generate uniform output regardless of the variation of airflow direction. The sensor consists of one heater at the center and four detectors surrounding the heater. The designed sensor operates based on the relative output difference of the four detectors in response to temperature variations induced by airflow. Therefore, flow directions can be easily detected by amplifying and calculating each output signal of the four detectors. As a result, the interface circuit could be realized with simple circuits. It was designed with popular instrumentation amplifiers and OP amps and integrated into ASIC chips using CMOS technology. The fabricated sensors were tested at 5 and 10 m/s. The response time was about 10 s and the maximum angle difference compared to flow angle was 5°. The results demonstrate that the suggested structure of sensors could be applied to the detection of flow directions.