|dc.description.abstract||Silicon micromachining techniques were developed and used to batch fabricate a new type
of heavily doped p-type (or p") silicon etch stop structure on glass that could be suitable for
implementation of a condenser microphone. This involved study, development and use of
techniques such as mask design, lithography, oxidation, diffusion, thin film deposition,
electrostatic bonding, many different etching techniques, freeze drying, packaging/interfacing
The condenser microphone structure consisted of a thin conductive diaphragm suspended
above a back plate electrode in order to form a capacitive device. A narrow gap between the
two plates constituted the capacitor plate separation and the air occupying the gap was the
dielectric material. Two versions of this condenser microphone structure were fabricated with
over all dimensions of 2mm2
x 8-12 Jlm, air gap sizes of 0.5-1.5 Jlm and lum thick
diaphragms. The first design utilised a square diaphragm with an area of lrnm" while the
second incorporated a circular diaphragm with a diameter of lrnm. Fabrication of the back
chambers was implemented with an innovative double thermal oxidation technique.
Signals of up to ImVIPa were obtained in the audio range for one of the circular p+ silicon
microphone structures, but the frequency response measured was not consistent with the
desired frequency response for a condenser microphone.
Thin film thicknesses, silicon etch rates and electrode metallisation conductivity were
characterised using specially designed test structures and innovative electrical and opticalmeasurement techniques so that fabrication accuracy and reproducibility could be monitored.
As a result of the investigations carried out to develop novel p" silicon microphone
structures, this thesis also identifies important areas which warrant further research, and
provides a foundation, in terms of theory and fabrication, for future development of more
advanced and appropriate p + microstructures for application as condenser microphones.||en