Recent developments in shape memory thin film technology

In recent years, new developments have been made concerning the fabrication and characterization of shape memory alloys (SMAs). Part of the research work has been carried out in the field of thin film SMAs. The main focus has been set on the improvement of their material properties. SMA films have to reveal high ductility to enable the actuators to perform work. Anisotropic grain growth might provide superior properties like the deposition of films with high purity. Parallel to the development of the materials, mechanisms have been developed to use the shape memory effect more effectively. The combination of metallic SMAs with polymers allows the switching of SMA actuators in a bistable manner in order to reduce energy consumption and to avoid excessive heat-flow to the adjacent structures. Beyond it, the appropriate combination of SMAs with different hysteresis widths leads to actuators with wave-like behaviour, convenient for the peristaltic motions of microrobots and for active surfaces designed for drag reduction. The contribution includes a general survey over the state of the art and illustrates the applicability of thin film composites by several demonstrators.