Material characterization of electroplated nanocrystalline nickel-iron alloys for micro electronic mechanical system

Nickel-iron nanocrystalline layers with thicknesses ranging from 34.6 to 44.6 μm were DC-plated using a widely available sulfamate-based electrolyte on an evaporated Au/Cr substrate. The deposited nickel-iron alloys at mean current densities of 2 and 4 A/dm² had a (200) crystalline preference orientation at Fe 5.28 and Fe 0.20 wt%, whereas respectively at Fe 10.76 and 8.80 wt%, the (111) texture was observed locally. Such a structural characteristic was confirmed by Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images of etched sections. The nickel/iron atom ratio of the deposits was analyzed by energy dispersion spectroscopy (EDS). The hardness of the alloys was evaluated using a Vickers hardness indenter. The internal stress of the deposits was measured by thin film stress measurement using Stoney's formula. Our study revealed that the mechanical properties and microstructures of the deposits could be related to a crystalline preference orientation changed by different iron contents. With increasing iron content, the hardness and internal stress of the deposits increased. An excellent correlation between the increase in the internal stress or hardness and the loss of the (200) texture or the predominance of the (111) texture was found.