Multilayered Ferromagnetic Polymer Composite Structures for High-Density Power Inductors

Abstract

This paper presents the modeling, design, processing, and characterization of a new class of multilayered ferromagnetic polymer composite structures for high-density power inductor applications. The multilayered composite structures comprise high-permeability, high saturation magnetization ( $M_{s} > 0.5$ T), and low-coercivity magnetic layers stacked with ultra-thin polymer adhesives. The adhesive acts as an an insulating layer to reduce eddy current losses while also enabling high permeabilities at higher operating frequencies. Fundamental material models were used to design the composite structures to achieve a permeability of above 500 in the frequency range of 1–10 MHz. A new adhesive coating and layering process was developed to achieve thicker composite structures in a single lamination step for increasing the inductance density and power handling. The frequency-dependent effective permeability of the composite structure was estimated from the measurement and analysis of $S_{11}$ parameters from a shorted strip transmission line using a vector network analyzer. The fabricated composite structures showed a permeability of $\sim 500$ , saturation magnetization of 0.6 T, and a coercivity of 4.4 Oe at 10 MHz. Such composite structures with excellent magnetic properties can be used to design power inductors in the 1–10-MHz frequency range.