Fabrication of a Zn Ferrite Thick Film Planar Power Inductor for DC-DC Converter LSI Package

摘要

In order to realize a point of load (POL) DC-DC converter for LSIs, a Zn ferrite thick film power inductor embedded in an LSI package has been fabricated and evaluated in this study. A 10-μm-thick spin-sprayed Zn ferrite film with a high saturation magnetization of 0.57 T was introduced to the magnetic core for a planar power inductor consisting of a 20-μm-thick, 650-μm-square, two-turn inner copper spiral coil sandwiched between top and bottom magnetic cores. The Zn ferrite film had a natural resonant frequency of 500 MHz and a static relative permeability of 80. The planar power inductor with a footprint of 850 × 850 μm exhibited a 10-nH inductance and a quality factor of 20 at 100 MHz. The degradation of inductance owing to the superimposed DC current of 2 A was 17%. The planar power inductor will be applied to a low-voltage converter with a switching operation at hundreds of megahertz in the future.