Fabrication of Fe-based Nanocrystalline Spherical and Flake Powder Composite Magnetic Cores for Tens of MHz and their Application to Planar Power Inductor

Abstract

Two types of Fe-based nanocrystalline powder composite magnetic core for tens of MHz were fabricated and applied to the planar power inductor. One was Fe-Si-B-Nb-Cu-C spherical fine powder composite magnetic core for a closed magnetic circuit in the planar power inductor, which exhibited a relative permeability of 10 and loss factor tand of 0.004 at 10MHz. The other one was Fe-Si-B-Nb-Cu flake powder composite magnetic core for shielding the leakage magnetic flux from low permeability closed magnetic circuit, which exhibited a relative permeability of 150 and loss factor of 0.19 at 10MHz. The planar power inductor, with Fe-based nanocrystalline spherical fine powder composite magnetic core and flake powder composite magnetic core, had 4.8×3.2×1.84 mm in size, inductance of about 240nH, Q-factor of about 40 at 10MHz. The fabricated planar power inductor was implemented into a 24V input, 12MHz switching GaN-FET two-phase buck converter, and the converter exhibited efficiencies of 81% when 5V-3A output and 92% when 12V-2.5A output.