Noise suppression effect of nanogranular Co based magnetic thin films at gigahertz frequency

Noise suppression effect of Co-Pd-Al-O nanogranular thin films, which have considerably high permeability up to gigahertz range, was investigated. The films with large variety of electrical resistivity (ρ) from 10² to 10⁷ μΩ·cm were prepared by reactive sputtering method and by changing both target compositions and deposition conditions. The films with ρ less than 10³ μΩ·cm are ferromagnetic, and the films with ρ more than 10⁶ μΩ·cm are superparamagnetic. A microstrip line with granular films placed on its top was used to evaluate conduction noise suppression. The result of transmission and reflection measurements reveals that these nanogranular soft magnetic Co-Pd-Al-O thin films have high potential for noise suppressors in the gigahertz range. In particular, the broad maximum of power loss (P_loss/P_in) about 0.6 at 6 GHz has been obtained in Co-Pd-Al-O films with ρ around 10⁴ μΩ·cm.