Vacuum-deposited TiNi shape memory film: characterization and applications in microdevices

Thin-film nickel-titanium shape memory alloy has been vacuum sputter deposited, characterized by crystallographic, electrical, and mechanical tests, and incorporated as an actuator in miniature devices. The composition and heat treatment of the film are critical as contamination by oxygen and other species affects the transition temperature. A variety of substrates have been utilized, with good adhesion. Shape memory behavior comparable to that of bulk TiNi has been observed in free-standing film. The work output per unit volume of TiNi is much greater than can be achieved with electrostatic or piezoactuators. Actuators in the few-micrometer size domain are feasible and have desirable characteristics for electrical and optical activation. Anticipated applications include miniature valves, bistable optical memory elements, and microactuators for silicon microelectromechanical devices.