Magnetic Thin-Film Inductors With Induced Radial Anisotropy for Improved Inductance Density

This letter presents the design and electrical performance of integrated power inductors based on thin-film magnetic cores with radial anisotropy induced by in situ magnetic annealing. The magnetic anneal uses an additional coil, as part of the CMOS interconnect below the core, to simultaneously apply a biasing magnetic field and act as a resistive heater. Following annealing, devices demonstrated inductance enhancements as high as 8.8 times the original as-fabricated value, a peak inductance-to-dc resistance $(L/R_{{\rm{dc}}})$ of 348 nH/Ω, a peak volumetric inductance density of 935 nH/mm 3 , and a peak areal inductance density of 33.4 nH/mm 2 . Additional improvements in inductor and bias coil design should further improve device $L/ R_{{\rm{dc}}}$ ratios to greater than 450 nH/Ω.