Permeability Measurements of Magnetic Thin Films using Shielded Short-Circuited Microstrip Lines

摘要

A method to measure wideband permeability was developed for 5-mm-square magnetic thin film from 0.1 to 10 GHz by using a shielded short-circuited microstrip line as the test fixture. The S_(11) parameters of the test fixture were measured with a vector network analyzer (VNA). The permeability was derived, based on the lumped element approximation, by comparing S_(11s) with S_(11os) which corresponded to without and with a strong magnetic field parallel to the microwave magnetic field caused by the microstrip line. In this case, the influence of substrate on which the thin film prepared could not be neglected due to the small gap between the microstrip line and the substrate. We introduced a method to derive an effective permittivity ε_e caused by the substrate by comparing S_(11o) of blank fixture with S_(11os) of fixture with sample under a strong static magnetic field. We also propose a method of determining whether the lumped element approximation is valid or not.