MEMS based fabrication of high-frequency integrated inductors on Ni–Cu–Zn ferrite substrates

Abstract A surface micro-machining process is described to realize planar inductors on ferrite (Ni 0.49 Zn 0.33 Cu 0.18 Fe 2 O 4 ) for high-frequency applications ( 8  Ω m) 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~367 nH (DC resistance~1.16 Ω and Q-value>14 at 30 MHz) and ~244 nH (DC resistance~0.86 Ω and Q-value~18 at 30 MHz) at 1 MHz for elongated racetrack (10.75 nH/mm 2 ) and racetrack inductors (12.5 nH/mm 2 ), 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.