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Non-Hermetic Protection of Thin-Film Metallisation Layers Intended for Implanted Electronic Medical Devices

Lamont, Callum Andrew Wallace; (2020) Non-Hermetic Protection of Thin-Film Metallisation Layers Intended for Implanted Electronic Medical Devices. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Ensuring the reliability of implanted medical devices is critical for their clinical usefulness. The current gold-standard for achieving this reliability is hermetically sealing the sensitive electronics in a water impermeable casing. However, such an approach faces challenges with the growing requirement for device miniaturisation, higher electrode count, and proximity of electronics to the site of action. As a result, non-hermetic packaging technologies, such as polymer and inorganic coatings, have received increased attention. Of these, the only approach that has demonstrated long-term clinical reliability is silicone encapsulation. With recent advances in circuit manufacture, including new materials, deposition processes and reduced feature sizes, there remains a requirement to verify the ability of silicone encapsulation to enable long lifetimes for modern-day implanted devices. This thesis provides a useful preliminary investigation towards this goal through the use of accelerated ageing experiments. Establishing realistic lifetime predictions from long-term in vitro ageing tests poses a number of difficulties. As a consequence, initial work focused towards the validation of an apparatus for ageing and measuring large numbers of samples. Using this apparatus, experiments analysing the effect of material selection and ageing conditions were performed on thin-film test structures. The primary finding from these was that silicone encapsulation, in combination with an inorganic thin film passivation layer, provided excellent protection to underlying aluminium metallisations. The benefits of Bayesian statistical analysis are discussed, with a suitable procedure applied to the current results to provide a statement about the lower-bound for expected device reliability.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Non-Hermetic Protection of Thin-Film Metallisation Layers Intended for Implanted Electronic Medical Devices
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
Keywords: Medical devices, Reliablilty, Neuroprostheses
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences > Div of Surgery and Interventional Sci
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences > Div of Surgery and Interventional Sci > Department of Ortho and MSK Science
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng
URI: https://discovery.ucl.ac.uk/id/eprint/10100135
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