Bistable shape memory thin film actuators

Abstract

Shape memory alloys (SMA) are able to provide high work output when they undergo the martensitic transformation. Therefore, they present a favorable actuation mechanism for microsystems, e.g. for microvalves, switches or microgrippers. Sputter deposited thin SMA films are already in use as free-standing films or as composites in combination with a substrate. In the case of a composite, the substrate works as a bias spring and enables the SMA actuator to show a two way behavior. To enlarge the potentialities of shape memory based actuators a bistable principle is presented. This is realized by the combination with a polymer exhibiting a glass transition temperature (T_g) between the hysteresis loop of the shape memory composite. The fabrication of this composite is described with a special emphasis on the development of suitable polymer samples.