Thin film magnetics for integrated magnetic nano-structures

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Cronin, Darragh
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University College Cork
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The past decades have seen a surge in demand for highly miniaturised magnetic components which has been enabled by use of power circuitry high switching frequencies which require energy storage on a smaller scale. The optimal scale of this integration will be achieved with the complete integration of the power supply onto silicon. Hence there is a demand for soft magnetic materials for power conversion applications in the high MHz frequency range. These materials should exhibit crucial properties such as a low coercivity, high saturation magnetisation and a high resistivity for optimum performance. Methods to further optimise the intrinsic qualities of an ultra-soft magnetic material, CoZrTaB (CZTB) are presented. This includes methods to maintain in-plane, uniaxial magnetic anisotropy as well as efforts to produce composite soft magnetic materials such as CoZrTaB-N\textsubscript{2} via methods such as reactive sputtering. Furthermore Spin-Reorientation Transition in amorphous CZTB magnetic multilayers is investigated. This interesting phenomenon results from from a tuneable value of residual stress arising from a thermal shock effect at elevated temperatures, shifting the magnetic anisotropy from in-plane to out-of-plane. This study highlighted how external parameters such as stress and thermal effects can damage properties such as uniaxial magnetic anisotropy, essential for specific applications. Work on a novel soft magnetic composite – CoZrTaB-SiO\textsubscript{2} is also presented. This study involved the technique of co-sputtering to produce a composite amorphous magnetic and non-magnetic microstructure, comprehensively examining all aspects of the material and its vital properties resulting in an ultra-soft magnetic material. Moreover, this material exhibited an increased and tuneable resistivity, dependant on sputtering conditions. Finally, a detailed and systematic experiment to develop a low footprint inductor consisting of a 3-D vertical array of vertical copper cylinders (or pillars) coated in CZTB multilayers. This novel structure was designed for a low-footprint with high inductance-density values. This work focused precisely on the magnetic laminations and the techniques used to ensure vital properties were retained such as a low coercivity and a circumferential magnetic hard axis to correspond with the current induced magnetic field.
Magnetics , Materials Science , Physics , Inductors , Amorphous , Nanocrystalline , Magnetoelastic , Magnetic materials , Sputter deposition , Magnetic anisotropy , Thin films
Cronin, D. 2022. Thin film magnetics for integrated magnetic nano-structures. PhD Thesis, University College Cork.
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