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.
The microstructures and the phase transformation temperatures of sputtered titanium-nickel (TiNi) thin films, both free-standing and attached on different underlying multi-layer substrates, have been studied. Differences in the microstructures, such as the lattice constants and relative concentrations of TiNi, Ti 2 Ni and TiNi 3 phases, have been observed among the free-standing and the attached films, among the films attached on different underlying multi-layers and among the films with different relative orders of ageing and release. Not surprisingly, the corresponding phase transformation temperatures are also different. It is proposed that both process-and substrate-induced stresses affect the microstructures, hence the phase transformation characteristics, of the resulting shape-memory thin films.
The micro-structures and the phase transformation temperatures of sputtered titanium-nickel (TiNi) thin films, both free-standing and attached on different underlying multi-layer substrates have been studied. Differences in the micro-structures, such as the lattice constants and the relative concentrations of TiNi, Ti2Ni and TiNi3 phases, were observed (1) among the free-standing and the attached films, (2) among the films attached on different underlying multi-layers and (3) among films with different relative orders of aging and release. Not surprisingly, the corresponding phase transformation temperatures are also different. It is proposed that both substrate- and process-induced stress significantly affect the micro-structures, hence the phase transformation characteristics, of the resulting shape-memory alloy thin films.
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