Ultra-Compact Power Conversion Based on a CMOS-Compatible Microfabricated Power Inductor with Minimized Core Losses

A CMOS-compatible microfabricated inductor is presented. The inductor consists of a planar spiral coil optionally sandwiched between upper and lower magnetic core layers. Core materials investigated include ferrite-filled polymer and electrodeposited nickel-iron permalloy (Ni_0.80Fe_0.20).Four core constructions were investigated: air-core (i.e., no magnetic material); lower permalloy core with upper air core; lower permalloy core with upper ferrite polymer core; and lower and upper permalloy core. In all cases with magnetic cores, a nominal magnetic air gap of 2 microns was utilized. As expected, the all-permalloy construction yielded the highest inductance. Inductors were characterized both by impedance analysis as well as in a prototype buck DC-DC conversion circuit. When the converter was operated at 5 MHz, peak efficiency of 82% and an efficiency of 80% at a load current of 2.5 A and output voltage of 2 V was obtained.