Permeability Measurement of Soft Magnetic Films at High Frequency and Multilayering Effect

This paper reports a new method for the measurement of permeability at high frequencies (1 MHz to 1 GHz). An inductance line with a magnetic/conductive/magnetic layer structure was used to estimate the permeability. The inductance line made it possible to measure frequency characteristics of the permeability up to the GHz range because of a low stray capacitance and high resonance frequency. The magnetic film pattern was designed so as to eliminate de-magnetizing field effects, and the permeability was estimated based on analysis of the magnetic circuit. Using this method, NiFe/SiO2 and (Fe/SiO2)/SiO2 multilayer films were confirmed to show superior frequency characteristics by a factor of 20 over those of NiFe single-layer film. Also, ferromagnetic resonance (FMR) was observed in these multilayer films at 650 and 750 MHz.