Iron and Permalloy based magnetic monolithic tunable microwave devices

We fabricated a series of magnetic monolithic tunable microwave notch-filters and phase shifters. In contrast to previous work with molecular beam epitaxy grown metallic ferromagnets, our devices were created by magnetron sputtering. Single crystal GaAs (001) was used as a substrate. Iron and Permalloy were used as magnetic materials in a coplanar waveguide geometry. The transmission characteristics of the filters were observed to depend on substrate quality, film deposition parameters (Argon pressure, growth rate, power, etc.), and grain size. In addition we observed a substantial increase in the resonance frequency for the Fe based notch-filters. This increase in the resonance frequency is due to a growth-induced uniaxial anisotropy field of 40 kA/m in the Fe films. This is an unexpected and important result especially because the observed anisotropy is growth and not field induced. The resonance frequency shifted from 9.3 GHz at zero applied magnetic field to 15 GHz for an applied static magnetic field as low as 72 kA/m (0.9 kOe). The Fe based notch filter attenuation was greater than 35 dB/cm over the whole applied field range at the resonance condition. The phase shift of the Fe structures was up to 100degrees/cm at 8 GHz. The Permalloy based filters show, over the same magnetic field range, a shift in the resonance frequency from 2 to 9 GHz. The attenuation of the Permalloy filters at resonance (6 dB/cm) is substantially lower than in the Fe based filters. (C) 2003 American Institute of Physics.