Pre-stressed Diaphragm based Capacitive Pressure Sensor for Blood Pressure Sensing Application

The paper presents Micro-electro-mechanical system (MEMS) based clamped circular capacitive pressure sensor with pre-stressed diaphragm made of polysilicon material with compressive residual stress. The residual stress affects the mechanical performance of material thereby influencing the performance of the device. The used polysilicon material is assumed to have a Young's modulus of elasticity, Possion ratio and residual stress as 160GPa, 0.22 and -80 MPa, respectively. The simulations of diaphragm deflection (according to small deflection theory), capacitance variation with respect to pressure application and capacitive sensitivity for blood pressure sensing application has been carried out using MATLAB
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program and results have been presented. For simulation results, mathematical formulations have also been performed. The deflection, capacitance variation due to pressure application from 1.0 - 1.4 bar (blood pressure range) and sensitivity are obtained for various diaphragm thicknesses after optimization. In optimization, maximum possible diaphragm radius is obtained for a particular thickness of diaphragm, keeping small deflection theory of plates and pull-in under consideration.