MEMS based Fabrication of High Frequency Integrated Inductors on Ni-Cu-Zn Ferrite Substrates

A surface micro-machining process is described to realize planar inductors on ferrite (Ni0.49Zn0.33Cu0.18 Fe2O4) for high-frequency applications (<30MHz). The highly resistive nature (~108Ωm) of the Ni–Cu–Zn substrate allows direct conductor patterning by electroplating of Cu windings through a photoresist mold on a sputtered seed layer and eliminates the need for a dielectric layer to isolate the windings from the bottom magnetic core. Measured inductances~367nH (DC resistance~1.16Ω and Q-value>14 at 30MHz) and ~244nH (DC resistance~0.86Ω and Q-value~18 at 30MHz) at 1MHz for elongated racetrack (10.75nH/mm2) and racetrack inductors (12.5nH/mm2), respectively show good agreement with simulated finite element method analysis. This device can be integrated with power management ICs PMICs for cost-effective, high-performance realization of power-supply in package (PSiP) or on-chip (PSoC). This simple process lays the foundation for fabricating closed core ferrite nano-crystalline core micro-inductors.