FMR Effects on Integrated Ferromagnetic Thin-Film RF Inductors
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0984-MM15-02
FMR Effects on Integrated Ferromagnetic Thin-Film RF Inductors Weiping Ni, Jinsook Kim, and Edwin Kan ECE, Cornell Univ., Ithaca, NY, 14853
ABSTRACT Ferromagnetic inductors with various geometries and permalloy thin film patterns were fabricated on the standard silicon substrate with a fully CMOS compatible process. The ferromagnetic resonance effects on the inductors were studied with the applied magnetic fields in different orientations. It showed that with the properly applied magnetic field, the ferromagnetic resonance for the patterned permalloy thin films can be pushed higher and the maximum quality factor for the ferromagnetic inductors can be improved. However, because the relative permeability decreases with increasing applied field, the trade-off between the effective inductance and the quality factor needs to be optimized for the practical designs. INTRODUCTION Ferromagnetic materials have been studied in the radio-frequency (RF) monolithic integrated inductors recently to enlarge the effective inductance for the given area. Permalloy, Ni80Fe20, has been used in our study, because it has a relatively high permeability (µr) and is ready to be integrated into a CMOS compatible process. The ferromagnetic inductor can exploit the large µr of permalloy to achieve a high effective inductance, which however, vanishes at the ferromagnetic resonance (FMR) frequency, due to the reduction of the real part of µr and the increase in the imaginary part. In this study, the FMR effects on the performance of the ferromagnetic inductors with various permalloy patterns and DC magnetic-field orientations are investigated to provide a practical guidance in the ferromagnetic inductor design. MAGNETIC PROPERTIES OF PERMALLOY THIN FILMS The performance of the ferromagnetic inductors strongly depends on the magnetic properties of the incorporated permalloy thin films. Magnetic anisotropy is one of the most fundamental properties of ferromagnetic materials, for it influences other properties such as hysteresis loop, coercivity, remanence, and saturation field [1]. A number of magnetic anisotropies can exist in magnetic materials and give rise to the uni-axial magnetic anisotropy in a preferred direction, usually called the easy axis, along which the magnetization tends to lie. For the magnetic thin films with their thicknesses much smaller than the in-plane dimensions, the easy axis is usually in the plane. The in-plane shape magnetic anisotropy is often negligible for thin films with large area. However in small patterns, it can be significant due to the element shape and the magnetostatic interactions [2]. Therefore, we can engineer the magnetic properties of the patterned micron-size magnetic materials by the shape of the constituent elements [3].The magnetic shape anisotropy and FMR are discussed below.
Table I Geometries and magnetic properties for the patterned permally arrays Hc Sample Aspect Length Width Spacing Num Num 4πMS µr per NO. ratio of (KGauss) (Oe) (µm) (µm) (µm) rows row #1 250 500 2 10 4 252 11
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