Application of nanocrystalline Fe(or Co-Fe)-Hf-O magnetic films with high electrical resistivity to micro DC-DC converters

High resistivity magnetic films, such as reactive sputtered Fe-Hf-O and Co-Fe-Hf-O, were applied to multilayered micro reactors for high frequency operation dc-dc converters. For a comparison, an amorphous Co-Ta-Hf film with good soft magnetic properties was also investigated. The micro reactor had the highest quality factor (the lowest loss) when using Co-Fe-Hf-O film with the highest resistivity. In 5 MHz operation of dc-dc converters using these micro reactors, the highest conversion efficiency was obtained when using Co-Fe-Hf-O film.