A bistable SMA microactuator with large work output

The design, fabrication and performance of a bistable shape memory alloy (SMA) microactuator is presented comprising large contact force and stroke at low power consumption. The switching mechanism consists of two antagonistically coupled SMA microbridges. The end positions are maintained by ferromagnetic attraction using integrated soft-and hard-magnetic structures with optimized geometry. The problem of 3D integration of SMA and magnetic components on the wafer scale is solved by introducing a new two-step SMA transfer bonding process and the technology of electroplating of soft-magnetic layers directly on SMA layers. Demonstrators of 7times7times4 mm³ overall size show contact forces of 30 mN and a stroke of 84 mum.