Noble magnetic films for effective electromagnetic noise absorption in the gigahertz frequency range

To meet the requirement that radio-frequency (RF) electromagnetic noise absorbers must be very thin to be installed in extremely integrated electronic components, we studied a new type of granular film deposited by coevaporation. The films have a peculiar nanostracture that exhibits a magnetic anisotropy with the easy axis perpendicular to the film plane. In this paper, practical noise suppressing features and advantage of this peculiar nanostructure film are investigated, comparing with a conventional noise suppression sheet made of a composite magnetic material. First, measurements are performed using the microstrip line method, and second with a prototype of digital circuit driven at 50 MHz that produces higher harmonic current noise at frequencies over 1 GHz. In both cases, the films exhibit remarkable ability of noise absorption that suggests high possibility of a thin film absorber which works effectively to suppress noise radiation and transmission from high-speed IC leading to appreciable improvement of RF performance of various electronic components. Numerical analysis based on the finite-difference time-domain (FDTD) method was also performed assuming the noise suppression sheet placed over a microstrip line. The analysis confirmed that re-radiation of electromagnetic noise from the sheet is negligible and it is absorbed mainly by magnetic loss of the sheet material.