Miniaturization of Shape Memory Actuators

Actuation on small scales has been an issue since the early nineties, where MEMS technology has been still in its infancy. Silicon is not a transducer material. Therefore additional materials have to be introduced for conversion of energy into mechanical work. Among the various transducer materials shape memory alloys (SMAs) offer a number of unique properties including thermoelasticity, superelasticity, actuation at highest work densities up to 10(exp 7) Jm(exp -3) and self-sensing. Their characteristic of being a "smart material" becomes particularly advantageous upon miniaturization, as technology constraints pose severe limitations on the number, geometry and size of functional structures. This review addresses the ongoing miniaturization of SMA actuators from miniature SMA wire-based actuators to SMA foil- and film-based microactuators down to novel SMA nanoactuators. Key processing technologies for fabrication of functional SMA micro- and nanodevices are presented and selected demonstrators are discussed. Potential applications and the transfer to commercial products are highlighted.