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A concern regarding the electromagnetic interference (EMI) issue with a short wavelength of the 5G frequency band has been increasing. Hence, EMI shielding materials with low reflection and high absorption...

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We demonstrated the radio-frequency (rf) noise suppressor using soft magnetic films on a coplanar transmission line from 0.1 to 20 GHz. The coplanar transmission line is composed of magnetic film/polyimide/Cu transmission line/seed layer (Cu/Ti)/glass substrate with the dimension of 50 μm width of the signal line and 3 μm thickness (characteristic impedance: 50 Ω). The magnetic films (CoPdAlO, CoZrO, and CoNbZr) as a noise suppressor are prepared by rf sputtering. The saturation magnetization of each magnetic film is about 10 kG. The magnetic anisotropy field and the ferromagnetic resonance frequency are 230, 89, and 6 Oe and 4.2, 2.5, and 0.7 GHz, respectively. The power loss of the coplanar line with magnetic films is significantly larger than without magnetic and nonmagnetic films due to ferromagnetic resonance losses.

Owing to high resistivity and high inplane uniaxial anisotropy, granular films are known to exhibit high permeability at radio frequencies. But this granular resistivity is not high enough to suppress eddy current when they are used at gigahertz frequencies. Recent developments to solve this problem are described. One is patterning the granular films. It is effective to control the inplane anisotropy and to suppress inplane eddy current. Another is deposition of granular films by evaporation. A peculiar fiber structure is formed for which very high resistivity and anisotropy are realized. Finally, a study of using these films as near-field electromagnetic noise absorbers is described, and it is demonstrated that they have high potential as micrometer-scale noise absorbing elements in the gigahertz frequency range.