Electrodeposited anisotropic NiFe 45/55 thin films for high-frequency micro-inductor applications

Micro-inductors, with an electrodeposited nickel–iron core have been fabricated on silicon substrates, and have been characterized in the frequency range up to 100 MHz. The core consists of a nickel iron, 45:55 alloy which is deposited using pulse-reverse electroplating in the presence of a magnetic field to control anisotropy. The operation of the inductors with low loss at high-frequency critically depends on core thickness, which is used to control eddy-current loss as the frequency is increased. However, it is shown that the permeability of NiFe 45/55 has a dependency on thickness, and decreases with increasing thickness. For example, the permeability is measured to be approximately 1000 for a 1-μm-thick film, decreasing to approximately 400 for a 5-μm-thick film. In order to correctly design micro-inductors for operation up to 100 MHz, it is important that this characteristic of the material is taken into account.