Determining the effective permeability of a laminated CoZrTaB (CZTB) film, through consideration of demagnetisation effects and eddy-displacement currents

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Date
2024-11-08
Authors
Murphy, Ruaidhrí
Wei, Guannan
Masood, Ansar
O’Mathúna, Cian
Pavlovic, Zoran
McCloskey, Paul
O’Driscoll, Séamus
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Institute of Electrical and Electronics Engineers (IEEE)
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Abstract
Multi-laminated thin film inductors are a key emerging technology to enable highly integrated, on-chip, voltage regulators. The permeability of a magnetic core at high frequency is a key determiner of inductance density. In this paper, a multi-lamination magnetic core made up of alternate CZTB amorphous, uniaxially anisotropic magnetic films and AlN dielectric layers is investigated. The individual films are approximately 200 nm thick, appropriate for operation at over 100 MHz, but the laminated structure and overall thickness of several micrometres mean that analytical methods are impractical for computing demagnetisation. Magnetostatic Finite Element Analysis (FEA) is used to model the magnetic core demagnetisation, accounting for various length/width dimensions, magnetic film thicknesses and dielectric thicknesses. At higher frequencies, the dielectric layers, which are included in the structure to suppress induced eddy-currents allow displacement currents to flow through the dielectric layers and lead to increased eddy currents circulating around the overall core structure and thus further increasing loss and reducing permeability. Eddy-current FEA simulations which include the displacement currents, and an analytically derived Equivalent Circuit Model (ECM) are used to model the real and imaginary (loss) components of permeability spectra. The work, therefore determines the combined contributions of both demagnetisation effects and eddy-displacement currents to the reductions in real permeability and the increase in loss components for thicker multi-laminated magnetic cores. Permeameter measurements on fabricated cores, having ten laminations, and with various AlN thicknesses (10, 20, 40 and 60 nm) gave excellent agreement with the predicted effective permeability through the approach of combining the FEA and ECM models, over the 10 MHz to 1 GHz frequency range. It was shown, that at 100 MHz, for multi-laminated cores with thin or higher k dielectric layers, that displacement-eddy currents are dominant, giving a power loss an order of magnitude higher than would be for magnetically induced eddy currents alone.
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Thin-film magnetic , CZTB , Multi-laminated , AlN , Dielectric layer , Displacement-eddy , Demagnetisation , Effective permeability , Inductor-on-silicon , Magnetic skin effect , Integrated voltage regulator
Citation
Murphy, R., Wei, G., Masood, A., O’Mathúna, C., Pavlovic, Z., McCloskey, P. and O’Driscoll, S. (2024) 'Determining the effective permeability of a laminated CoZrTaB (CZTB) film, through consideration of demagnetisation effects and eddy-displacement currents', IEEE Transactions on Magnetics. https://doi.org/10.1109/TMAG.2024.3494675
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