GHz Permeability of Soft Magnetic Co-Fe-B Films with High Anisotropy Fields

Co-Fe-B films with a thickness of 0.5μm were fabricated by synchronous dual RF magnetron sputtering a while rotating cylindrical electrode. A magnetic thin-film core for GHz applications was obtained with a large anisotropy field Hk and large saturation magnetization 4πMs, and these permeability characteristics and micro-structures investigated. The as-deposited film, with Hk of 390 Oe were and 4πMs of 17.6 kG, exhibited high ferromagnetic resonance (FMR) frequencies of up to 6 GHz in permeability characteristics. The film has an amorphous-like structure including atomic ordering within the range of several angstroms, which leads to good soft magnetic properties with an electrical resistivity of 100μ Ω cm. The large Hk of the films fabricated by the sputtering method is effective for attaining higher frequency characteristics with lower FMR loss.