Residual stress and thermal stability of the Fe–Ni–Cr/Invar bimetal membrane used for microactuation

Abstract

The residual stress and Young's modulus of Fe–Ni–Cr (FNC)/Invar bimorph, FNC, and Invar single-layered polycrystalline thin films were evaluated by the load–deflection method. It is found that the residual stress, microstructure, and sheet resistance are clearly correlated. The thin film stresses, determined by the bulge test, depend strongly on the working pressure and change from highly compressive to highly tensile in a narrow pressure range. The residual stress of both bilayers and single-layers can reduce to a relatively low level and can be stabilized with an annealing treatment. Thus, a bimorph wrinkle (or buckle) free membrane with low residual stress level and stable mechanical properties can be fabricated. These fabricated units may be used for microactuation devices.