Modeling Microinductors With Thin-Film Alloy Magnetic Cores

Abstract

This paper presents a compact nonlinear frequency-dependent circuit model for microinductors with magnetic thin-film cores. The model captures saturation, high-frequency eddy currents in the conductors and core, and capacitive effects. A modeling extraction algorithm is proposed that generates a passive and accurate circuit from current-biased small-signal impedance measurements. These measurements are wafer-level compatible and can readily be made using an impedance analyzer or vector network analyzer. The model is applicable to the most common microinductor topologies, including toroidal, stripline, and racetrack used for integrated power electronics applications. We demonstrate the model performance of these three different microinductor geometries with commercially available field solvers as well as actual device measurements for switched mode power supply applications. Field-solver simulations show that the model captures ac power loss significantly better than traditional models and captures the current waveforms within 4.5% error. Comparison of the model to device measurements results in an RMS error less than 7.1% in current waveform for a device transitioning in and out of saturation due to a 10-MHz rectangular pulse.