Fabrication of a Zn ferrite thick film planar power inductor for DC‐DC converter LSI package

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. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(4): 53–60, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10425