High-frequency ferromagnetic inductors covered by as-deposited FeCoAlO films with stress-induced uniaxial anisotropy

Nanocrystalline FeCoAlO films with composition gradients of Al and O were prepared by gradient sputtering (GS) method at room temperature. A uniaxial magnetic anisotropy (UMA) with high anisotropy field Hk up to 20.5 kA/m were achieved by controlling the composition gradient of doping elements Al and O. Experimental and calculated results revealed that the UMA can be attributed to the uniaxial stress gradient, which is resulted from the composition gradient. It is interesting to note that as-deposited GS films without magnetic annealing exhibited promising high-frequency ferromagnetic properties with resonance frequency over 3 GHz. The GS ferromagnetic films were used to fabricate magnetic inductors at room temperature. Significant enhancements of inductance L and Q factor were obtained in magnetic inductors covered by FeCoAlO GS films. Increments of L and Q are about 14% and 62%, respectively, at 2.4 GHz. The cut-off frequency of magnetic inductors was up to 4.6 GHz.