Carbonyl-Iron/Epoxy Composite Magnetic Core for Planar Power Inductor Used in Package-Level Power Grid

Our research objective is to realize the basic technology for a next generation package-level power grid (PLPG) for plural application large scale integrated circuits (LSIs). In this study, a carbonyl-iron powder (CIP)/epoxy composite magnetic core, for large-current power inductor used for the main dc-dc converter in the PLPG, has been fabricated and evaluated. 54 vol.%-CIP/epoxy composite core made by screen-printing had a relative permeability of 7.5 and loss tangent of about 0.03 at 100 MHz. The planar power inductor using composite core was fabricated and evaluated, which had a quasi closed magnetic circuit consisting of low permeability composite core and embedded 35-μm-thick, two-turn copper spiral coil. The fabricated inductor with a 1-mm-square in size had 5.5 nH inductance, Q-factor of 15 at 100 MHz, and 18 mΩ dc coil resistance. Inductance was constant even when the superimposed dc current increased up to around 5.5 A.