Authors: E. Hynes, P. Elebert, M. O'Neill, H. Berney, W.A. Lane, G. Kelly and M. Hill
Affilation: Analog Devices, Iran, Islamic Republic of
Pages: 185 - 188
Keywords: pressure, sensor, FET, micromachine, finite difference
This paper presents the development and solution of a model to describe the behaviour of a surface micromachined FET pressure sensor. Initially an expression is developed to describe the radial deflection of the sensing diaphragm as a function of pressure. This is solved in MATLAB using finite difference methods for a range of applied pressures. The MATLAB code uses the solution for the diaphragm deflection to calculate the capacitance from diaphragm to substrate. The calculated capacitances for each applied pressure are used in the first order MOSFET equations to provide a full solution for FET output current versus applied pressure. The predictions are compared to measured results and the model is then used to predict the sensor behaviour for a different electrode design. The results suggest that electrode design can be used as a method of modifying the pressure to current transfer function while maintaining a single MEMS manufacturing process optimised for one diaphragm size and cavity height.