A Microcantilever-based Gas Flow Sensor for Flow Rate and Direction   Detection
  The purpose of this paper is to apply characteristics of residual stress that causes cantilever beams to bend for manufacturing a micro-structured gas flow sensor. This study uses a silicon wafer deposited silicon nitride layers, reassembled the gas flow sensor with four cantilever beams that perpendicular to each other and manufactured piezoresistive structure on each micro-cantilever by MEMS technologies, respectively. When 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 sensor upstream and downstream beam deformation was made, thus the airflow direction can be determined through comparing the resistance variation between different cantilever beams. The flow rate can also be measured by calculating the total resistance variations on the four cantilevers. 
Y.-H. Wang, Tzu-Han Hsueh, Rong-Hua Ma, Chia-Yen Lee, Lung-Ming Fu,   P.-Ch. Chou, Chien-Hsiung Tsai