Advances and Perspectives in Magnetic-Integrated Inductors for RF ICs

This paper reviews advances in developing magnetic-integrated inductors for radio-frequency (RF) integrated circuits (IC). Magnetic integration is a promising way to reduce the footprint of on-chip inductors, which is the main roadblock towards realizing compact RF IC systems-on-a-chip (SoC) operating at GHz and beyond. In the past two decades, researchers have developed many ferromagnetic (FM) or ferrite thin films, laminations, and nanoparticle composites to overcome the frequency limit of the materials, hence, inductors, to GHz range by optimizing materials composition, structure and resistivity, device design, fabrication process, and integration method. The paper starts with reviewing key materials properties required for GHz inductor applications, followed by results of demonstrated magnetic-integrated on-chip inductors. The structural designs of materials and devices, fabrication processes, and the reported device performances of magnetic inductors are summarized. A unique, non-traditional vertical RF inductor with stacked-via magnetic core in CMOS is highlighted. RF IC design examples using magnetic-integrated inductors and emerging GHz tunable inductors are discussed. Future perspectives for compact, multiple-GHz magnetic-integrated inductors are outlined.