Development, fabrication and characterization of soft-magnetic thin films for high frequency applications

This submitted manuscript describes the development, fabrication and characterization of soft-magnetic thin films for high frequency applications up to GHz frequencies. These high frequency suitable films were investigated with the prospective use as magnetic core material, for the assembly of micro inductors or micro sensors for the micro electronic and micro system technology. Within the scope of this work amorphous CoB and FeCoBSi films as well as nanocrystalline FeTaN films were deposited by means of magnetron sputtering and characterized regarding their film constitution and film properties. The main development goal was the realization of films with high ferromagnetic resonance frequencies, low eddy current losses and suitable hf-permeabilities up to the GHz range. As a concept for the realization of high frequency suitable film systems the direct deposition of films with a uniaxial anisotropy was traced. The film fabrication was carried out by means of magnetic field deposition table (substrate holder), which induced a magnetic field within the film plane. As film materials initially amorphous thin films were deposited with different sputtering targets (Co79B21, Fe67Co18B14Si1 und Fe60Co15B15Si10) with a target diameter of 75 mm. By varying the deposition conditions (Ar sputtering pressure and hf-sputtering power) an optimization of the film fabrication was carried out with respect of the deposition of films with low internal stress. These optimized amorphous films show a strong uniaxial anisotropy within the film plane. With a saturation magnetization (μ0Ms) of 1.8 T and an anisotropy field (μ0Hk) of 3.5 mT Fe68Co18B13Si1 films reach the highest values (Co84B16: μ0Ms = 1.2 T, μ0Hk = 1.5 mT, Fe58Co18B12Si12: μ0Ms = 1.2 T, μ0Hk = 1.5 mT). Along the easy axis direction these films exhibit high permeabilities (Co84B16: 2340, Fe58Co18B12Si12: 1825, Fe68Co18B13Si1: 3340) which were damped at higher excitation frequencies in the kHz range. Along the hard axis direction the permeabilities of the films are lower (Co84B16: 690, Fe58Co18B12Si12: 830, Fe68Co18B13Si1: 520) but stay constant for the hole frequency range. For thin films (0.1 μm) permeabilities up to the GHz range (Co84B16: 1.3 GHz, Fe58Co18B12Si12: 1.5 GHz, Fe68Co18B13Si1: 2.3 GHz) are observed along the hard axis direction. These experimentally determined permeabilities and ferromagnetic resonance frequencies are in good agreement with the theoretically calculated values using the static magneti2 Chemical Composition in At.-%.