Integrated RF inductors with micro-patterned NiFe core

Integrated radio-frequency solenoids with micro-patterned magnetic cores for reduced dimensions and compatibility with CMOS/BiCMOS process technology are presented and discussed. It is demonstrated that the use of a ferromagnetic (FM) core leads to a more than 20-fold enhanced inductance per area. This is achieved by tailoring the anisotropy of the FM core and the design of the metal coil structure. Both a higher operating frequency and a larger inductance are obtained by increasing the shape aspect ratio of the FM core and by depositing the magnetic film under an external magnetic field. A reference to an optimum shape anisotropy has been created by measuring the FM core inductors with an external DC magnetic field. An optimum practical trade-off of inductance and operating frequency results from patterning of the FM core.