Structural and Ferromagnetic Properties of Sputtered FeCoB/AlN Soft Magnetic Multilayers for GHz Applications

Abstract

Owing to their large saturation magnetization and low hysteresis loss, soft magnetic layers based on amorphous alloys currently receive great attention for their potential for gigahertz frequencies applications. In this paper, we studied the structural and magnetic properties of amorphous FeCoB/AlN multilayered thin films with in-plane uniaxial magnetic anisotropy based on the Fe-28%Co-20%B (at. %) alloy, deposited on 8” Si/200 nm-thermal-SiO2 wafers in an industrial, high-throughput magnetron sputtering system. Depending on the process conditions and hardware configuration, the multilayers exhibit structural anisotropy consisting of surface ripples elongated perpendicular to the incident flux direction, which replicate through the entire multilayer stack. By varying the AlN interlayer thickness and sputter process parameters the anisotropy field $H_{k}$ of these films was tuned in the range of 25–130 Oe, while the coercivity along the magnetic easy axis $H_{c}$ was kept low, 0.2–0.3 Oe. The ferromagnetic resonance frequency of the multilayered structures was ~2 GHz, and the experimental behavior of the magnetization dynamics was described by the classical Landau–Lifschitz–Gilbert model. Magnetic domain imaging confirmed a strong coupling between the adjacent FeCoB layers, in agreement with the edge-curling wall model.