High-performance soft magnetic composites for high-frequency power electronics: a review of insulating coating technologies

Abstract

The rapid commercialization of wide-bandgap silicon carbide (SiC) and gallium nitride (GaN) devices is pushing power electronics into the megahertz regime. Conventional ferrites have become a critical bottleneck because of their low saturation magnetization and sharply increasing high-frequency loss, whereas soft magnetic composites (SMCs) with high magnetic induction and low loss have therefore attracted increasing attention. The macroscopic magnetic performance of SMCs is governed by the microstructure and interfacial characteristics of the insulating coating on magnetic powders. This review summarizes recent progress in insulating coating technologies for SMCs intended for high-frequency power electronics. It first discusses the origin of high-frequency eddy-current loss and the key design requirements for insulating layers. It then traces the development of coating strategies from organic coatings to inorganic, composite, and nanoscale coatings, with emphasis on the process-structure-property relationships of phosphate, oxide, glass/ceramic, and atomic-layer-deposited (ALD) oxide systems. From the perspective of interface engineering, the review further examines how core-shell architectures suppress eddy currents while preserving acceptable permeability, highlighting the trade-offs among coating thickness, uniformity, adhesion, and magnetic dilution. Finally, the performance of representative coating routes is compared in terms of high-frequency loss reduction, thermal stability, and manufacturing feasibility, and future challenges and opportunities are discussed. This review provides a systematic framework for the rational design of next-generation high-performance SMCs for high-frequency power electronics.