Microfabricated Thin-Film Inductors for High-Frequency DC-DC Power Conversion

Microfabricated V-groove inductors targeted to operate above 10 MHz are investigated. Multilayer nano-granular Co-Zr-O/ZrO2 magnetic thin films are used as the core material of the inductors to improve the magnetic performance of the films deposited on the sidewalls of V-grooves and to control eddy-current loss in the core, which goes up very quickly as frequency increases. A loss model is developed to estimate eddy-current loss in multilayer magnetic thin films considering the effect of displacement current at high frequencies, and the model is applied in the design of V-groove inductors.;V-groove inductors using multilayer magnetic thin films are co-optimized with power MOSFETs for 7-V to 3.3-V, 1-A DC-DC buck converters to maximize power handling capability per unit substrate area for given efficiencies. Prototype V-groove inductors are fabricated based on the optimization results, and measured and predicted performance of the inductors match well. The prototype inductors are a promising candidate for high-power-density high-efficiency DC-DC converters. The 7-V to 3.3-V, 1-A converters using prototype V-groove inductors are expected to exhibit power density of 2.5 W/mm2 and efficiency of 86% at 100 MHz, and power density of 0.36 W/mm2 and efficiency of 91% at 11 MHz.