Internal Stress in Ferrite Plated Thin Films

Abstract
Internal stress in ferrite plated films of Fe₃O₄ and Ni-ferrite was evaluated, and its dependence on the plating conditions was investigated. The internal stress was estimated to be 0.5~1.7x10⁹ dyn/cm² in tension. For Ni-ferrite films, the stress increased with increasing the atomic ratio of Ni/fe in reaction solution. The plated films were composed of columnarshaped grains of 0.2~0.3µm in size near the top surface as observed by SEM. Crystallinity of the films degraded with increasing Ni/Fe, and peaks of spinel structure were not observed by X-ray diffraction diagram for Ni/Fe=0.83. These results suggest that excess Ni ions in the reaction solution increase impurities in the films, which may increase the tensile internal stress. We found that the internal stress can be reduced by adjusting layout of sprays (i.e. changing the height of the nozzles from the table) in the spin-spray ferrite plating.