Enhanced Magnetic Permeability Through Improved Packing Density for Thin-Film Type Power Inductors for High-Frequency Applications

This study investigates methods to enhance the permeability of metal magnetic composites, crucial for the performance of thin film power inductors in high-frequency applications, such as those in contemporary smartphones operating in the MHz range. Traditional reliance on ferrite magnetic materials is eschewed in favor of metal magnetic materials combined with epoxy to create novel composites aimed at optimizing packing density and significantly increasing magnetic permeability. The impact on permeability is explored using four different metal powders: pure iron (FE), Fe-Si (FS), Fe-Si-B-C-Cr (AM), and Fe-Si-B-Nb-Cu (NC). The FE sample is produced using carbonyl iron powder, resulting in a particle size (D50) of 2.1 μm. The FS sample, produced through gas atomization, has a particle size of 17.5 μm, while the AM and NC samples, produced via water atomization, yield particle sizes (D50) of 19.4 μm and 23 μm, respectively. Analyses using X-ray diffraction (XRD) and Mösbauer spectroscopy reveal that FE and FS samples have crystalline structures, whereas AM and NC are amorphous. Scanning electron microscopy confirms the spherical shape of particles in all samples. Theoretical calculations, based on Ollendorff’s theory of permeability and Suzuki and Oshima’s models on packing fraction, suggest that a composite with a ratio of 8:1.2:0.8 and particle sizes of approximately 25 μm, 1.5 μm, and 0.1 μm, respectively, could achieve a permeability value of up to 138.1. This demonstrates the potential for achieving high permeability at MHz frequencies through strategic packing of voids with submicron and nanopowders, marking a significant advancement in the field of thin film power inductors.

Graphical Abstract