In situ stress measurements and mechanical properties of a composition range of NiTi thin films deposited at elevated temperature

A series of NiTi thin films of approximately 450 nm thickness, with a range of compositions from 48 to 51 at.% Ni, were magnetron-sputter deposited from elementary targets of Ni and Ti. The depositions were carried out at 450 °C. The crystal structure, surface morphology and mechanical properties were studied using X-ray diffraction, atomic force microscopy and nanoindentation. In situ wafer curvature measurements were performed to study the stress evolution during deposition of films. Depending on composition, different stress development is observed during film growth. In this work, we investigate the relation between the changeover in stress development and the onset of crystallization and subsequent grain growth. Measurement of substrate curvature, in situ and ex situ, yields thermal stress. From nanoindentation we obtained the elastic modulus of the NiTi films. From the obtained values of film thermal stress and elastic modulus the coefficient of thermal expansion for the composition range was determined.