Ion beam sputtering of Fe-Hf-O ferromagnetic thin films of EMI shielding applications

Ferromagnetic thin films can be used to improve the shielding effectiveness (SE) of plastic substrates against the electromagnetic field in the radio frequency range. In order to obtain good shielding performances, the ferromagnetic thin film is required to have a high AC permeability over the spectral range of interest. Actually, the magnetic permeability of common ferromagnetic alloys and ferrites decreases very rapidly to one above a few hundred megahertz. In this work, Fe-Hf-O thin films have been deposited on plastic substrates by ion beam co-sputtering of two Fe and HfO₂ adjacent targets. Multi-layered structures containing the ferromagnetic film have also been deposited in order to enhance the shielding performance of the coating. The electric conductivity of the layers has been measured by using the four-print probe method. Simulated and measured shielding effectiveness of the films have been compared in order to derive the dispersion characteristics of the ferrite. Good adhesion between the multilayer and the substrate has been observed for both poly-vinyl-chloride and polycarbonate substrates.