High-resistive (CoFeB)-(SiO/sub 2/) soft magnetic amorphous film for micro-cores in a few MHz range

Highly resistive (CoFeB)-(SiO/sub 2/) amorphous films were deposited on glass substrates and polyimide sheets by synchronous dual-rf magnetron sputtering. SiO/sub 2/ volume fraction dependence of magnetic properties and resistivity was investigated. The as-deposited films for SiO/sub 2/ volume fraction /spl upsi/=20 vol.% had low coercivities of H/sub c/=0.2-0.3 Oe, together with high resistivities of 1500-2200 /spl mu/ /spl Omega/ cm. The film exhibited an anisotropy field 40 Oe, a relative permeability of 200 and a saturation magnetization of 7.3 kG. The core loss of the films was 1-1.5 J/m/sup 3/ at 1 MHz for maximum flux density B/sub m/=0.1 T. The loss was found to be as low as those of Co-based ultra-thin ribbons. The films are useful as thin film cores in the micromagnetic elements which work in the MHz range.