The Improvement of High-Frequency Performances and the Inductance of Micro-Inductors by Tuning the B-Gradient in Composition Gradient Sputtered FeCoB Thin Films

The static and dynamic magnetic properties of 50 nm thick iron-cobalt-boron (FeCoB) soft magnetic films, fabricated using a composition gradient sputtering (CGS) method on intrinsic Si (100) substrates, are studied as a function of the B composition gradient. By optimizing the B composition gradient, larger stress is induced, resulting in an increase of the uniaxial magnetic anisotropy field ${H} _{k}$ from 229.7 to 720.1 Oe and an increase in ferromagnetic resonance (FMR) frequency from 5.8 to 9.27 GHz. These are attributed to the B doping, which eliminated magneto-crystalline anisotropy, with the stress induced by the composition gradient becoming the dominant factor. The film was then integrated as a magnetic core into a planar spiral inductor, resulting in a 24.6% increase in inductance, demonstrating the potential of this film as a material for magnetic cores in high-frequency electronic components.