High-Q 3D Microfabricated Magnetic-core Toroidal Inductors for Power Supplies in Package

Integration of power inductors is a roadblock in realizing highly miniaturized power supply in package (PSiP) and power supply on chip (PwrSoC). Inductors in such power system are used for energy storage and filtering, but they dominate in size and loss. This paper presents a novel 3D insilicon through-silicon via (TSV) magnetic-core toroidal inductor for PSiP. The magnetic powder based core is embedded into TSV air-core inductor using a casting method. The unique air-core inductor design with a hollow core and suspended windings enable a complete core filling with microscale magnetic powders. The proposed casting method is simple, scalable, and generic for a wide range of magnetic powders. TSV magnetic-core inductors are fabricated in a compact size of 2.4 x 2.4 x 0.28 mm with the core content varying from 63 to 88 weight percent of soft ferrite NiZn powders. The TSV magnetic-core toroidal inductors are fabricated and electrically characterized. Small-signal measurements show a three-fold higher inductance of 112 nH and a 30% higher quality factor of 14.3 at 12.5 MHz for magnetic core inductors compared to similar TSV air-core inductors. The small-signal measurement results are verified by the modelled results. The total core loss is characterized by large-signal measurements. A suitable inductor is implemented in a 12-MHz buck converter that operates in a zero-voltage-switching mode. The converter achieves a peak efficiency of 71.6 % and the output power of 2.4 W converting 12 to 5 VDC.