School of Physics - Theses

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Author: Edalati, Khatereh × Type: PhD thesis × Subject: Diamond ×

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    Engineering Approaches to Active Brazing of Diamond Medical Implant Components
    Edalati, Khatereh ( 2023-12)
    This research aims to develop techniques for creating robust, hermetic joints and encapsulated structures using gold (Au) braze alloys and ceramic substrates for electronics and implantable medical devices. A major challenge is the poor wetting and adhesion typically observed between Au brazes and ceramics due to interfacial reactions and surface oxides. Without suitable adhesion layers, weak boundary joints prone to failure may result. We investigate processing methods involving thin film deposition, adhesion layer metals, brazing parameters, and joint analysis to overcome these adhesion issues with Au brazing on ceramics. A priority application is creating long-lasting, leak-proof packages for electronics in medical implants, which must meet strict encapsulation requirements for human use. Diamond demonstrates exceptional implantation lifetimes owing to outstanding biostability and biocompatibility but cannot be welded. One alternative is active braze alloys, containing carbide-forming elements that chemically bond to the diamond upon melting. However, biocompatible gold active braze alloys (Au-ABA) exhibit very poor wetting on diamond. I demonstrate that molybdenum (Mo) and niobium (Nb) interlayers significantly improve Au-ABA wetting, enabling excellent penetration into surface features. Optimal recipes for interlayer fabrication are determined, facilitating complex microstructures, hermetic electrical feedthroughs, and robust bonds. In laser-grooved diamond circuit boards, residual metal contamination resistant to etching and polishing was found to electrically short features after depositing Mo/Nb adhesion layers and Au-ABA brazing. Here, I reported an optimised reactive ion etching (RIE) process to remove this contamination and isolate fine circuit board features. Elemental and electrical testing verifies complete contaminant removal and restoration of electrically insulating diamond surface properties after RIE.