High-resistive, high-saturation inductive soft magnetic amorphous fluorine modulated (CoFe)BF films

Abstract

(Co0.5Fe0.5)BF amorphous films with modulated F content were investigated and such multilayered films have ceramic spacers to increase permeability at high frequencies. Modulated films having alternate F-poor layers (15 nm thick) and F-rich layers (5–10 nm thick) within an F content of 2–10 at. % were prepared by a sputtering technique. High-saturation induction (Bs) of 1.6–1.8 T, low coercivity (Hc) less than 1.0 Oe, permeability (μ′) of 800–1000, and enhanced high frequency response were obtained in the case of a modulated film having alternating layers: 15-nm-thick layers, 2 at. % F, ρ=150 μΩ cm and 10-nm-thick layers, 10 at. % F, ρ=800 μΩ cm. The number of periods was variable. Auger-electron spectroscopy and secondary-ion mass spectroscopy depth profiles clarified the periodicity of the modulated films. Multilayered films with four layered F modulated films (0.55 μm/layer) and SiO2 spacers (0.24 μm/layer) exhibited an excellent frequency response of μ′=1500 in the range of 1–100 MHz. The coexistence of high ρ, high Bs, and low Hc in these films may be attributed to the oscillatory resistivity resulting from a compositional modulation in F and B.