Investigation of Proximity Effects in Ferromagnetic Inductors with Different Topologies: modeling and solutions

Abstract

“ Proximity effects” could be the superior mechanism responsible for lowering the quality factor (Q) of ferromagnetic spiral inductors, apart from ferromagnetic resonance considerations. In this paper, a model extraction from previous measurements is described. In particular, the extracted series resistance Rs is discussed with regards to skin depth and current crowding contributions in the metal traces. Comparing air-core and ferromagnetic spirals, it is shown that“ proximity effects” are enhanced with magnetic materials leading to a much stiffer increase in Rs with frequency (f² instead of √ f). This points out Q being naturally always lowered at the same frequency with ferromagnetic spirals, even if an adequate high FMR is realized. Thus, it is necessary to reconsider the design of spirals when using magnetic materials and some solutions are suggested at the end of this paper.