Ferrofluid-core S-RuM microelectronic inductors

Abstract

Integrated planar inductors suffer from the performance limitations of their thin film cores, including eddy current losses, hysteresis losses, and low ferromagnetic resonance frequencies. Despite past and potential magnetic material advances, the utilization of these materials is poor given the architecture and fabrication technology for integrated inductors. As power module miniaturization innovation requires inductor components that operate at high frequencies, inductor technology has lagged due to the fundamental positive scaling of a solenoid’s inductance with loop area. The integration of ferrofluids as a core material for the Self-Rolled-up SiNx Membrane (S-RuM) platform circumvents and alleviates these problems, realizing the advantages of magnetic nanoparticles in this application. The S-RuM inductor platform uniquely provides a cylindrical cavity through which the device’s magnetic field flows, ideal to host a fluid core stabilized by capillary force. Ferrofluids are colloidal suspensions of magnetic nanoparticles, which display superparamagnetism and whose magnetization can rapidly rotate spontaneously under sufficient thermal conditions according to their Néel relaxation time. In this work, the performance characteristics of S-RuM power inductors filled with two different ferrofluids, a commercial ferrofluid and custom-synthesized ferrofluids, are compared, and the engineering physics of a ferrofluid specialized for the proposed application are considered.