Smart MEMS Flow Sensor: Theoretical Analysis and Experimental Characterization

This paper presents analytical and experimental studies of a new microelectromechanical system (MEMS) smart flow sensor for the measurement of gas flow. The flow sensor has an array of curved-up cantilever beams that are surface-micromachined with two layers of deposition under two sets of different process parameters. The differential residual stress between the two layers of the polysilicon deposition causes the beams to curve upward from the substrate surface when the sacrificial layer is released. Each beam of the array of beams of different lengths vibrates successively as the flow rate increases, enabling more accurate sensing and identification of range of flow rates based on the vibration characteristics, thus making this a smart sensor design. Design and fabrication of these sensors are discussed. Experiments were conducted on this MEMS flow sensors to characterize the deflection of the curved cantilever beams with respect to flow rates. In addition, backflow tests were also conducted separately. Results of the analytical study are presented to investigate the cause of vibration of beams when subjected to flow. Finite-element analyses of vibration of the sensors comply with the experimental observation. Based on the analysis of fundamental natural frequencies, possible arrangement for the distribution of lengths of the beams is proposed to enhance its functionality as a sensor. Future work and plan of the on-board capacitive metrology and other practical issues are discussed