Design and Fabrication of VHF Tapped Power Inductors Using Nanogranular Magnetic Films

The design and fabrication of coupled inductors with low profile, low cost, and high power density for tapped-inductor high-step-down dc-dc power converters in the very-high-frequency (30-300 MHz) range are presented. The inductor consists of a multilayer thin-polyimide printed circuit board with nanogranular thin-film magnetic material deposited on both sides and on beveled cuts to form a fully linked closed core. The magnetic material Co-Zr-O has good soft magnetic properties, high resistivity, and high flux density capability. Multilayer Co-Zr-O/ZrO₂ thin films are used to improve the performance of the magnetic core. A winding loss model of this coupled inductor is presented. Coupled inductors with turns ratios 2 and 10 for several different converter applications have been designed, fabricated, and measured. Loss in the magnetic material is investigated. Small-signal and large-signal measurements show good performance of the fabricated components with high-frequency, high-field excitation.