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

TL;DR

This paper models and simulates a composite membrane capacitive pressure sensor using analytical and FEM methods, demonstrating close agreement and analyzing sensitivity and non-linearity for intraocular pressure measurement.

Contribution

It introduces a novel composite membrane design for capacitive pressure sensors and compares analytical and FEM simulations to validate performance.

Findings

Deflection variation between analytical and FEM is about 7.19%.

Capacitance variation between methods is approximately 2.7%.

Non-linearity of the sensor is around 4.25%.

Abstract

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, high sensitivity), capacitive pressure sensors are the 2nd largest useable MEMS-based sensor 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, SiO2 and Si3N4. The membrane deflection, capacitance variation, mechanical sensitivity, capacitive sensitivity and non-linearity 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 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 non-linearity is about 4.2492% for the proposed sensor for fabrication using surface micro-machining process.