Development of TiNi shape memory alloy film deposited by sputtering from separate Ti and Ni targets

A separate-target sputtering process has been applied to fabrication of TiNi shape memory alloy (SMA) for microelectromechanical systems (MEMS). This process employs separate Ti and Ni sputtering targets and independently controllable RF power source for each target. Since RF power ratio can change the composition of the films as required, the shape memory properties can be better controlled. This process would enable efficient batch production of MEMS devices and components similarly to the LSI batch process. This process is expected to be a more appropriate method for mass production than other techniques such as machining from bulk SMA sheets or wires and deposition of SMA films from a single TiNi alloy target. The TiNi SMA films in the present study were fabricated by co-sputtering from two separate targets and vacuum-annealing for crystallization. The phase transformation behavior of the crystallized films was observed by differential scanning calorimetry (DSC) and x-ray diffractometry (XRD). DSC showed exothermic/endothermic peaks corresponding to phase transformations: martensitic transformation around at 345 K and reverse martensitic transformation around at 365 K. The transformations of crystal structure were also examined by temperature-controlled XRD analysis. The formed films were confirmed to show shape memory effect (SME) by these results.