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

• High-frequency microinductors have been fabricated on Ni-Cu-Zn substrates.
• High-resistive ferrite substrates assist direct conductor patterning on the surface.
• Uniform inductances ~365 nH over 30 MHz frequency have been achieved.
• High Q-values (>18 at 30 MHz) attained are applicable for high-frequency DC–DC conversion applications.
• The described process lays the foundation for fabricating closed core ferrite nano-crystalline core.

A surface micro-machining process is described to realize planar inductors on ferrite (Ni0.49Zn0.33Cu0.18 Fe2O4) for high-frequency applications (<30 MHz). The highly resistive nature (~108 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/mm2) and racetrack inductors (12.5 nH/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.

Material Characterization of Ni–Cu–Zn ferrite substrate and process developed for on-ferrite integrated micro-inductor fabrication.Figure optionsDownload as PowerPoint slide