Bistable Thin-Film Shape Memory Actuators for Applications in Tactile Displays

Bistable shape memory actuators were fabricated by microsystem technology processes and characterized with regard to their use in tactile graphic displays. The actuators were realized as sputter-deposited buckled metallic thin-film carriers, having structured Ti-Ni-Cu and Ti-Ni-Hf shape memory alloys on the top and at the bottom, respectively. They were sputtered on wavy-structured substrate and had lateral dimensions ranging from 2.2 to 3.5 mm in width and from 1 to 3 mm in length. The actuators were switched with voltages in the range of 0.2 to 0.8 V and with currents in the range of 0.2 to 0.8 A. A force of 2.2 mN with a displacement of 0.7 mm was reached. To improve the performance further, a special test setup was developed. The bistable actuators in it were sputtered on a planar substrate with lateral dimensions ranging from 6 to 8 mm in width and from 3 to 6 mm in length. These actuators were switched with actuation voltages in the range of 0.6 to 1.6 V and with currents in the range of 0.6 to 1.8 A. Thus, a force of 16 mN with a displacement of 1.2 mm was reached.