Achieving Isotropic Permeability for Integrated Inductors

Partially perpendicular anisotropy in Permalloy thin films was found to produce reliably isotropic permeability in the plane of the film. Isotropic permeability is especially desirable for integrated closed-loop magnetic solenoid inductors in order to create an efficient return path for the flux. Material properties for the Permalloy were verified through hysteresis loop, permeability, and magneto-optic Kerr effect microscopy and utilized to simulate the behavior of the inductor. Laminated Permalloy films with partially perpendicular anisotropy yielded a relatively high permeability value of 860 isotropically in-plane. Simulation results indicate that, depending on the permeability, in-plane closure can yield 2× the inductance or more compared with a rectangular magnetic core with the same permeability. The enhancement due to closure was seen to depend heavily on permeability, increasing at a rate of 6.8 per unit permeability.