Operation characteristics of a buck/boost converter using a layered inductor with high resistive Fe(CoFe)-M-O (M=Hf,Zr,rare-earth) films

Fe(CoFe)-M-O (M=Hf,Zr,rare-earth) films have excellent soft magnetic properties at a high frequency for their high electrical resistivity. Layered inductors using the magnetic films have a low loss at a high frequency. Accordingly, the DC-DC converter using these layered inductors exhibit a high efficiency for the high frequency drive. A layered inductor using nanocrystalline Fe/sub 61/Hf/sub 13/O/sub 26/ film and Co/sub 44/Fe/sub 19/Hf/sub 15/O/sub 22/ film exhibit the Q of 8.4 and 12.3 at 5 MHz. The micro DC-DC converter using nanocrystalline Fe/sub 61/Hf/sub 13/O/sub 26/ film and Co/sub 44/Fe/sub 19/Hf/sub 15/O/sub 22/ film exhibit the maximum efficiency of 83.5% and 86% in the boost converter driving at 5 MHz. Furthermore, thin film inductor using Fe/sub 55/Hf/sub 11/O/sub 34/ film which size of 3.5 mm/sup 2/ exhibits L of 950 nH and Q of 6.6 at 5 MHz. Then, they are evident that high resistive nanocrystalline, Fe(CoFe)-Hf-O films are effective for the high frequency micro DC-DC converter.