High-Q polyimide-based spiral inductors with magnetic core for RF telemetry applications

This paper presents a new high quality factor (Q) and large inductance (L) stacked polyimide-based spiral inductor. Polyimide (PI) is used as the substrate and the insulation layer to provide good biocompatibility. To achieve multilayers, self-planarization of PI on the surface with 10μm steps was realized. Meanwhile, Ni₈₀Fe₂₀ was successfully electroplated to enhance the performance of inductors. The double-layer inductor shows a maximum Q of 12.7 and a large L of 7.078μH at 5.54MHz. Considering the area of the coil, the inductance density is as high as 62nH/mm². Based on this inductor, the wireless power transmission (WPT) system was built and tested. The minimum attenuation is -9.4dB at 1.8MHz. With the full IC-compatible fabrication process, this coil could be used in many implantable devices.