Precessional dynamics of Ni45Fe55 thin films for ultrahigh frequency integrated magnetics

Abstract

Future monolithic point of load switched mode power supplies will be expected to meet the energy requirements of miniaturized, high functionality electronic devices. Recently, Ni45Fe55 has emerged as a potentially important material choice for use as a soft magnetic core material within high frequency integrated passive magnetic components. The operating frequency range of the integrated passives which form a key part of the point of load power supply must increase to allow for inductor/transformer miniaturization to become monolithic with power integrated circuits. In this work, an analysis of the high frequency permeability spectra of an electroplated Ni45Fe55 thin film has been carried out to quantitatively analyze the material’s high frequency performance. Complex permeability spectra of the film have been investigated at frequencies up to 9 GHz to identify both the film’s spectroscopic splitting factor (g) and its effective dimensionless damping parameter (α). The Kittel equation is utilized to identify g as 2.128, while α is determined to be approximately 0.045. The critically damped condition for the film is also examined to extract α in the critically damped case under a range of externally applied bias fields. It is concluded that for monolithic power inductors, improved device performance can be achieved when the ferromagnetic core is in an underdamped state up to a critical frequency.