Modeling and FEM-Based Simulations of Composite Membrane Based Circular Capacitive Pressure Sensor

In Micro-electro-mechanical Systems (MEMS) based pressure sensors and acoustic devices, deflection of a membrane is utilized for pressure or sound measurements. Due to advantages of capacitive pressure sensor over piezoresistive pressure sensors (low power consumption, less sensitive to temperature drift, higher dynamic range, and high sensitivity), capacitive pressure sensors are the second largest useable MEMS-based sensors after piezoresistive pressure sensors. We present a normal capacitive pressure sensor, for continuous sensing of normal and abnormal Intraocular Pressure (IOP). The composite membrane of the sensor is made of three materials, i.e., Si, SiO_2, and Si₃N₄. The membrane deflection, capacitance variation, mechanical sensitivity, capacitive sensitivity, and nonlinearity are discussed in this work. Mathematical modeling is performed for analytical simulation, which is also compared with Finite Element Method (FEM) simulations. MATLAB^® is used for analytical simulations and CoventorWare^® is used for FEM simulations. The variation in the analytical result of deflection in membrane w.r.t. FEM result is about 7.19%, and for capacitance, the variation is about 2.7% at maximum pressure of 8 kPa. The nonlinearity is about 4.2492% for the proposed sensor for fabrication using surface micro-machining process.