Investigation of anomalous losses in ferromagnetic spiral inductors using thick copper technology

Significant inductance enhancement over the air-core value using appropriate ferromagnetic thin film as flux amplifier is now possible that would allow RF designers to scale-down the air-core spirals. It was observed that by using high-Q air-core inductors with thick Cu metal trace, the integration of magnetic films results in lower Q. This paper examines the origin of the excess losses with respect to the air-core ones when associating high magnetization film with thick Cu spiral inductors. Results indicate that the origin of the anomalous losses is related to the multi-turn planar geometry. The basic mechanism behind current crowding directly depends on the amplitude of the B-field of adjacent turns in the inductor penetrating a trace normal to its surface.