The design, fabrication and development of micromechanical integrated optical pressure sensors for aerospace

Abstract

This thesis concerns pressure sensors based on silica-on-silicon integrated optical devices, fabricated using flame hydrolysis deposition, micromachining and Small Spot Direct Ultraviolet Writing (SSDUW). Device performance, fabrication methods and experimental testing have all been designed to meet the requirements of aerospace fuel systems.
Specifically, to this work, the investigation of Bragg grating based integrated optical sensors has been explored. This is covered in terms of evaluation of theoretical performance, investigating cleanroom and non-cleanroom based scalable fabrication, validating operational performance in aerospace-like pressure environments, subjecting samples to long term jet fuel exposure and routes for expanding the design space to include integrated optical fibre. Critically both single and dual diaphragm pressure measurements with thermal corrections were demonstrated using device fabrication process developed and implemented by the author. For the proposed devices, a theoretical full scale accuracy of 0.007% was found and exceed the requirements outline by Parker Aerospace. Good progress towards achieving this target was made although the highest accuracy achieved for fabricated devices by the end of the project was 0.24%. In terms of pressures, for the case of a 2.85 by 2.75 mm diaphragm, a pressure resolution of 280 Pa was demonstrated with routes for reducing this further outlined.
Through this work, numerous findings are made such as; improved Bragg grating pressure response, new wafer level cleanroom and non-cleanroom fabrication routes, enhanced photosensitivity through annealing in a hydrogen atmosphere, improvements to SSDUW into rough surface samples, lowering of glass consolidation temperatures through sodium doping, thermal regeneration of SSDUW written Bragg gratings and tilted gratings in integrated optical fibre.

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Identifiers

ORCID for Peter Smith: orcid.org/0000-0003-0319-718X

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