Date of Award


Document Type

Master Thesis

Degree Name

Master of Engineering (Research)


Mechanical & Manufacturing Engineering

First Advisor

Dr. Ger Kelly


This thesis is concerned with the electro-mechanical characterisation of MEMS capacitive pressure sensors and the determination of models to describe their behaviour.

The finite element software package ANSYS is validated as a tool for the examination of the electro-mechanical behaviour of capacitive pressure sensors. It is then used to incorporate the effects of applied load, voltage and residual stress into a model of the sensor structure. The capacitive pressure sensor is modelled both in 3D and also in 2D axis-symmetric modes. The error between the 2D and 3D models is quantified.

The behaviour of structures under electrostatic actuation is investigated. A means of extracting the capacitance from the sensor structure is developed and also a m.eans of modelling contact between structural entities in the system is proposed. The optical profiling method. Scanning White Interferometry is introduced and utilised to measure the behaviour of sample capacitive pressure sensors under electrostatic actuation.

The behaviour of classical structures under electrostatic actuation is investigated and the electrostatic pull-in behaviour of fixed-fixed beams is investigated using both analytical and TEA methods. The output from the ANSYS models developed is also compared to the commercially available numerical analysis software packages SUGAR and Coventorware. Capacitance and the effect of fringing fields are also addressed to a lesser extent.

A sensitivity analysis was also conducted on the geometric structure of the sensor and the critical dimensions such as diaphragm diameter and thickness were investigated. The capacitance output range for the sensor was found to be non-linear and in the region of 390 to 415 femto Farads in a pressure range from 0-0.14 MPa.


Submitted to HETAC for the degree of Master of Engineering - 2003.

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