Abstract

Shape memory thin film composites consisting of at least one shape memory thin film component are of special interest as microactuators since they provide two-way shape memory behavior without any training of the shape memory material. Furthermore, they allow the realization of novel concepts like bistable or phase-coupled shape memory actuators. The potential of shape memory thin film composite microactuators is discussed in view of possible applications.

Introduction

The availability of suitable actuators is of particular importance for the advanced development of novel micro- or nanosystems. An attractive approach is based on smart materials that directly transduce electrical into mechanical energy, e.g., materials exhibiting a shape-memory effect, piezoelectricity or magnetostriction. Actuator mechanisms on these smart materials allow easy down-scaling to the micrometer or even nanometer range and can be realized by a cost-effective fabrication technique compatible with micro- or nanosystem technology using thin-film technologies. As shape memory alloys combine high output forces with large motions and can be controlled by Joule heat in a microelectronic-compatible way, they are of increasing interest for microactuator applications as long as only low frequencies or slow response times are required. Due to smaller grain sizes compared with those of bulk materials, magnetron sputtered shape memory thin films can be fabricated between approximately 1 and 50 μm in thickness with properties not affected by the film thickness.

In this chapter the mechanism, fabrication and features of shape memory thin film composite microactuators are discussed in view of special designs (bistable, phase-coupled actuators) and applications.