Abstract
A buck-converter using a multilayered micro-inductor with Fe (Co-Fe)-Hf-O-based soft magnetic films was investigated. Fe (Co-Fe)-Hf-O films have excellent frequency characteristics with a low loss factor in a frequency range exceeding 100 MHz owing to their high electrical resistivity. Consequently, a micro-inductor using these films exhibited maximum values of the quality factor (Q) of 12.0 at 5 MHz and 17.1 at 10 MHz for Fe-Hf-O and Co-Fe-Hf-O films, respectively. The highest output power, 1 W, and the highest efficiency, 70%, were simultaneously obtained for a buck-converter with Co-Fe-Hf-O films. These values are higher than those for a 1 MHz-driven converter using a Co-Ta-Hf amorphous alloy film. As the operation of the converter depends more strongly on the equivalent resistance (R) and Q values than the inductance (L), a Fe (Co-Fe)-Hf-O film reactor with a very small value of R is suitable for a micro dc-dc converter with higher switching.
