Laser Annealing of Amorphous Ni-Ti Shape Memory Alloy Thin Films

Shape memory alloy (SMA) thin films, especially those based on Ni-Ti, have received considerable attention since it was demonstrated that they can undergo a nearly perfect shape memory effect [1-7]. When SMA films are used as actuators in MEMS devices, biasing springs are generally needed to restore the initial state in order to achieve a twoway shape memory effect. As a result, use of SMA actuator in MEMS has been limited mainly to bimorph-like mechanisms. Recently, laser annealing of shape memory alloys (LASMA) emerged as a promising approach for the fabrication of planar mechanisms [8,12]. This technique has the advantage that shape memory properties can be spatially distributed: material crystallized by laser irradiation has shape memory properties and can be used as an actuator, while untransformed material is passive and provides a restoring force. In this paper, we present the results of an experimental study of the laser annealing process for NiTi thin films, along with a computational model.