Abstract
Magnetically isotropic (CoFe-AlN)n/(AlN)n+1 multilayer films, in which the number of CoFe-AlN magnetic layers n ranged from 1 to 27, were prepared by radio frequency sputtering to achieve noise suppression at gigahertz frequencies. The soft CoFe-AlN magnetic layers consisted of nanometer-sized CoFe ferromagnetic grains embedded in an insulating AlN amorphous matrix, while the insulating AlN layers comprised AlN columnar crystals. All films showed a similar frequency dependence of permeability and ferromagnetic resonance of 1.7 GHz. Noise suppression was evaluated using a microstrip line as a noise source by determining the in-line conductive loss and the near-field intensity picked up by magnetic field detective probes. High noise suppression effects were observed in every direction in the film plane. Maximum noise suppression values amounted to 60% for the in-line conductive loss and −20 dB for the magnetic near-field intensity at around 1.7 GHz in the 27-layer film. These high-frequency noise suppression levels may be attributed to eddy current losses and ferromagnetic resonance.
Highlights
Gigahertz in every direction of the film plane, in addition to high noise suppression effects, these multilayer films required time-consuming and intensive fabrication processes
The soft CoFe-AlN magnetic layers consisted of nanometer-sized CoFe ferromagnetic grains embedded in an insulating AlN amorphous matrix, while the insulating AlN layers comprised AlN columnar crystals
High noise suppression effects were observed in every direction in the film plane
Summary
Gigahertz in every direction of the film plane, in addition to high noise suppression effects, these multilayer films required time-consuming and intensive fabrication processes. Isotropic Co-AlN granular films prepared by sputtering have shown high permeability at frequencies reaching a few gigahertz.[7]. The absence of uniaxial magnetic anisotropy in these films may facilitate noise suppression. Along with high noise suppression in every direction in the film plane, it is expected to enhance noise suppression owing to ferromagnetic resonance at gigahertz level frequencies. Ferromagnetic resonance is clearer in these isotropic films than in soft magnetic films exhibiting uniaxial magnetic anisotropy, as explained by the LLG equation. The study aims to achieve high noise suppression effects at gigahertz level frequencies using magnetically isotropic (CoFe-AlN)n/(AlN)nþ[1] multilayer films. Magnetic resonance effects on in-line conductive noise and inductive radiated noise are qualitatively investigated
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