Design of Piezoresistive MEMS Absolute Pressure Sensor

MEMS pressure sensors are one of the most widely commercialized microsensors in the MEMS industry. They have a plethora of applications in various fields including the automobile, space, biomedical, aviation and military sectors. One of the simplest and most efficient methods in MEMS pressure sensors for measuring pressure is to use the phenomenon of piezoresistance. The piezoresistive effect causes change in the resistance of certain doped materials when they are subjected to stress, as a result of energy band deformation. Piezoresistive pressure sensors consist of piezoresistors placed over a thin diaphragm which deflects under the action of the pressure to be measured. The result of this deflection causes the piezoresistors to change their resistance due to the stress experienced by them. The change is converted into electrical signals and measured in order to find the value of applied pressure. In this work, a high range ( 30 Bar) pressure sensor is designed based on the principle of piezoresistivity. The inaccuracies in the analytical models that are generally used to model the pressure sensor diaphragm have also been analysed. Thus, the Finite Element Method (FEM) is adopted to optimize the pressure sensor for parameters like sensitivity and linearity. This is achieved by choosing the proper shape of piezoresistor, thickness of diaphragm and the position of the piezoresistor on the pressure sensor diaphragm. For the square diaphragm, sensitivity of 5.18 mV/V/Bar and a linearity error of 0.02% are obtained. For the circular diaphragm, sensitivity of 3.69 mV/V/Bar and a linearity error of 0.011% are obtained.