  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.
