Microactuators Using R-phase Transformation of Sputter-deposited Ti-47.3Ni Shape Memory Alloy Thin Films

Actuation behavior of diaphragm-type microactuators utilizing Ti-47.3Ni shape memory alloy (SMA) thin films heat-treated at 773, 823, and 873 K is investigated. The microactuators heat-treated at 773 and 823 K are successfully actuated at room temperature by the R-phase transformation only. This is because the R-phase transformation start temperature is higher than room temperature while the martensitic transformation start temperature is below room temperature. The displacement (amount of actuation) decreases with decreasing heat-treatment temperature, indicating that the optimum heat-treatment temperature is 823 K. The temperature hysteresis for the R-phase transformation of the microactuator heat-treated at 823 K is only 3.2 K. The working frequency of the microactuator heat-treated at 823 K reaches 125 Hz without any decrease of displacement.