Soft magnetic properties of Fe-(Si3N4, Al2O3) thin films

We have studied the structure and soft magnetic properties of Fe-ceramic(Si3N4, Al2O3) thin films fabricated by an rf magnetron sputtering apparatus using a composite target. The concentration of solute in the film increases linearly with the area fraction of ceramic pieces in the target. In the case of Si3N4, the concentration of O increases largely with the Ar pressure, especially at high Ar pressures of more than 20 mTorr. In Al2O3, the composition of Al and O exhibits a maximum at the Ar pressure of 20 mTorr. As the area fraction of the ceramic increases, the structure of the film changes from a crystalline phase to an amorphous phase. The electrical resistivity increases significantly with increasing area fraction of the ceramics. The saturation magnetization decreases inversely with the logarithm of the electrical resistivity. The gradient of the decrease in saturation magnetization against electrical resistivity is lower in the Al2O3 system than that in the Si3N4 system. The Ar pressure dependences of the electrical resistivity and the saturation magnetization are similar to that of the thin film composition. Fe-Si3N4 films exhibited a saturation magnetization of about 8 kG, a hard-axis coercivity of 0.2 Oe, an electrical resistivity of about 800 mu Ohm-cm and a permeability(100 MHz) of higher than 400.