Anisotropic Composite Core Material for Inductor-based Fully Integrated Voltage Regulator

Miniaturization of efficient integrated voltage regulators is critical in order to fully benefit from dynamic voltage and frequency scaling. A major challenge to this is the high parasitic loss of inductor cores at switching frequencies in the MHz range. In this study, we report on a novel soft magnetic core material with anisotropic magnetic properties. This composite core is fabricated using magnetic field directed assembly of magnetic particles in an epoxy matrix. Various experimental conditions were explored, and subsequent image analytics of the resulting samples was used to optimize the process parameters, in order to yield the desired morphology. Magnetic measurements revealed improved magnetization, lower coercivity and higher permeability along the percolation axis of the magnetic particles when compared to isotropic composites with the same particle loading. In addition, the permeability of the anisotropic composites remained close to constant up to 100 MHz. Finally, a funicular “necking” structure with nano-sized particles assembled around contact points of micro-sized particles in the composite was achieved via a bi-modal particle distribution, resulting in further improvements in magnetic properties. Our anisotropic composite core materials are attractive candidates to establish highly efficient power inductors.