Residual stress-loaded titanium-nickel shape-memory alloy thin-film micro-actuators

Residual stress in titanium-nickel thin films has been exploited as a force load for thin-film shape-memory alloy micro-actuators, thus eliminating the need for providing 'external' force load for device training and operation. Thermal cycling during device operation is accomplished using electrical current-induced Joule's heating for temperature ramp-up and thermal conduction/convection-induced cooling for temperature ramp-down. In response to thermal cycling, hysteresis loops in both the displacement and electrical resistance of the micro-actuator have been observed - thus demonstrating the existence of shape-memory effect in the micro-actuators. Elimination of manual training of individual devices makes it possible to operate large arrays of shape-memory alloy micro-actuators realizable using micro-fabrication techniques.