Integrated thin film magnetics in advanced organic substrates

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Jordan, Declan.
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University College Cork
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This thesis investigates the challenges of integrating thin film magnetics into advanced organic substrates for Power Supply in Package (PwrSiP) applications. The surface conditions of the substrate on which the thin films were deposited was found to play a critical role in terms of the magnetic performance and efficacy of the material used as the magnetic passive component. Whence, planarization of the underlying substrate, or a release process with which the magnetic core could be deposited, and later liberated from a polymer layer spun on smooth Si were developed in order to address the issue of surface roughness of the underlying substrate. \newline\newline The released magnetic thin films were incorporated into advanced organic substrates by three methods, as follows: 1) the integration of the released magnetic core using wirebonds; 2) the embedding of the released magnetic material using a Flip-Chip approach; 3) fully embedding the released magnetic material between the prepreg layers in the PCB stack. \newline\newline Finally, methods for the modelling and characterisation of the magnetisation dynamics of thin film magnetics were developed. The modelling of the magnetisation dynamics comprises two approaches: 1) development of software which enables large scale numeric modelling of the magnetic thin films using graphical processing units; 2) development of analytical models to characterise the magnetisation dynamics of magnetic thin films. Both the analytic and numeric methods were developed in order to characterise the issue of surface roughness in magnetic thin films, which was found to result in severely degraded magnetic performance. Furthermore, the thickness dependent multimodal behaviour of amorphous CZTB films spanning thickness 80nm – 500nm were investigated using Brown’s continuous diffusion model of magnetic spins. It was found that there is a critical film thickness whereat there is a breakdown in the induced uniaxial anisotropy within the film, and hence, that thickness should be considered the maximum useful thickness of the material in ultra-low loss PwRSiP applications.
Integrated magnetics , Embedded inductors , Magnetic thin films , Power supply in package
Jordan, D. 2021. Integrated thin film magnetics in advanced organic substrates. PhD Thesis, University College Cork.