Wafer-scale manufacturing of robust trimorph bulk SMA microactuators

N. Sandström (a), S. Braun (a), T. Grund (b), G. Stemme (a), M. Kohl (b), W. van der Wijngaart (a)
a Microsystem Technology Lab, KTH - Royal Institute of Technology, Stockholm, SWEDEN
b Institut für Mikrostrukturtechnik, Forschungszentrum Karlsruhe GmbH, Karlsruhe, GERMANY

Abstract

This paper demonstrates the concept of wafer-level fabrication and integration of robust bulk SMA microactuators based on adhesive bonding of cold-rolled SMA sheets to silicon wafers. Contact printing of an adhesive polymer ensures a selective bonding when transferring full SMA sheets to silicon structures on a patterned wafer. The induced stress of a thin dielectric film deposited on top of the SMA sheet ensures a stable and built-in reset mechanism of the actuators. The trimorph microactuators can be actuated by indirect resistive heating through a thin metal film. We report on the successful wafer-scale fabrication of actuator cantilevers and their characteristics. First test cantilevers show a cold-state deflection of 300 μm which, however, is limited by the silicon substrate. Upon heating, the cantilever shows a stroke of approx. 80 μm.