Sputter-deposited Sma Thin Films: Properties and Applications

Shape memory alloy (SMA) thin films formed by sputter deposition have attracted considerable attention in the last decade. Current intensive research demonstrated that thin films' unique fine microstructure is responsible for superior shape memory characteristics in films, compared to that of bulk materials. Simultaneously, much effort has been taken in the development and fabrication of microdevices actuated by SMA thin films. This article reviews the research to date on shape memory behavior and mechanical properties of SMA thin films, in connection with the peculiar microstructures. Furthermore, promising applications such as microvalves are demonstrated, along with the focused discussion on process-related problems. All the results indicate that thin films shape memory actuators are ready to contribute to the development of microelectromechanical systems. 3 Introduction In the last decade, shape memory thin films formed by sputtering have been attracting great interest as powerful actuators in microelectromechanical systems (MEMS) such as micro valves, micro fluid pumps and micromanipulators, since the shape memory thin films (SMA thin films) possess a large force and displacement compared with the other type actuators including electrostatic, electromagnetic and piezoelectric ones. (Typically, the available stress and elongation limits for SMA actuators are 600 MPa and 5% as compare to 40 MPa and 0.1 % for piezoelectric ones). Originally, SMA actuators have an advantage of large output as the size decreases 1 (Figure 1). Besides, the response