Improved Sensitivity of MEMS-based Piezoresistive Pressure Sensor using Silicon Nitride Diaphragm

In this paper, Piezoresistive Pressure Sensor (PPS) with four Polysilicon piezoresistors on Si3N4 diaphragm with improved sensitivity is successfully designed by using MEMS technology. Sensing is accomplished via deposited polysilicon resistors like metal resistors. The analytical model of PPS is optimized for location and geometry of the piezoresistors and the sensors based on different aspect ratios (both square and rectangular) have been investigated. The performance parameters like maximum deflection, maximum induced stress on the diaphragm have been compared using ANSYS and MATLAB simulation programming based on mathematical model. By interpreting the proper selection of the geometry of a thin Si3N4 diaphragm, the maximum deflection, maximum induced stress and highest sensitivity for this sensor are obtained for the diaphragm when aspect ratio is minimum. It has been found that sensitivity of the sensor is achieved when the piezoresistors are symmetrically placed at 65 m from the edges of the diaphragm. The analysis describes that the sensor based on square diaphragm is more sensitive than the rectangular one. It is influenced more powerfully by diaphragm thickness. The applied pressure range is considered from 0.5 kPa to 40 kPa. From the simulation results, the shape and the sensor design can be optimized for a highly sensitive PPS.