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Title: Non-hermetic protection of thin-film metallisation layers intended for implanted electronic medical devices
Author: Lamont, Callum Andrew Wallace
ISNI:       0000 0004 9348 6088
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2020
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available