Characterization of TiNi shape-memory alloy thin films for MEMS applications

Thin film shape-memory alloys (SMAs) have been recognized as promising and high performance materials in the field of microelectromechanical systems (MEMS) applications. In this investigation, chemical composition, microstructure and phase transformation behaviors of sputter deposited TiNi films were studied. The surface and cross-section morphology of the deposited coating was analyzed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The results from the differential scanning calorimeter (DSC) showed clearly the martensitic transformation upon heating and cooling. X-Ray diffraction analysis (XRD) also revealed the crystalline structure changing with temperature. By depositing TiNi films on the bulk micromachined Si cantilever structures, micro-beams exhibiting a good shape-memory effect were obtained. Finite element simulation results of the deformation of micro-beam (using the measured NiTi thin film parameters) agree quite well with the measured behavior.