HIGH-FREQUENCY SOFT-MAGNETIC PROPERTIES OF NANOCRYSTALLINE FE-(CO)-HF-O FILMS WITH HIGH ELECTRICAL-RESISTIVITY AND THEIR APPLICATION TO MICRO DC-DC CONVERTER

We have developed nanocrystalline Fe-(Co)-Hf-O films which exhibit hig h electrical resistivity (rho) more than 4 mu Omega m as well as high magnetization (Is)more than 1T and also good soft magnetic properties even in as-deposited states. Furthermore, real part of complex permeab ility mu' of these films exhibit more than 1000 up to 100 MHz by annea ling in an uniaxial magnetic field. The layered inductor using nanocry stalline Fe-61-Hf-13-O-26 film and Co-44-Fe-19-Hf-15-O-22 film show th e Q of 8.4 and 12.3 at 5 MHz. The micro DC-DC converter using the nano crystalline Fe-61-Hf-13-O-26 film and Co-44-Fe-19-Hf-15-O-22 film indu ctor show the maximum efficiency of 83.5% and 86% in the boost convert er driving at 5 MHz. So, it was evident that high resistive nanocrysta lline Fe-(Co)-Hf-O films were effective for the high frequency micro D C-DC converter. (C) 1998 Acta Metallurgica Inc.