Magnetron Sputtered TiNiCu Shape Memory Alloy Thin Film for MEMS Applications

TiNiCu films were successfully prepared by co-sputtering of a TiNi target and a separate Cu target. Surface and cross-section microstructures of the deposited coating were analysed using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). Results showed that the deposited coating had fine grain size of about 300 to 400 nm and fully martensitic structure under room temperature. X-Ray Photoelectron Spectroscopy (XPS) indicated that there was an adherent and stable TiO₂ oxide film on TiNiCu film surface, which can prevent Ni element from delamination. The deposited TiNiCu film has relatively strong (11 1) and (111) and relatively weak (010) texture. Results from Differential Scanning Calorimeter (DSC), in-situ X-Ray Diffraction (XRD) and curvature measurement revealed clearly martensitic transformation of the deposited TiNiCu films upon heating and cooling. Freestanding TiNiCu thin film showed clearly pronounced “two-way” shape memory effect, which is quite applicable to develop thin film micro-actuators. By depositing TiNi films on the bulk micromachined Si cantilever structures, micro-beams exhibiting good shape-memory effect were obtained. This type of cantilever structure can be further fabricated as a micro-gripper which can be used as the end-manipulator for micro-assembly in industry, minimally invasive surgery for medical application, and handling of small particles in hazardous environment for military application.