A study of heat process by using direct electric current heating for reversible SMA thin film actuators

Reversible shape memory alloy (RSMA) (TiNi alloy) thin film actuators have many advantages for micromachines; for example, the films have three functions; (1) a frame of the arm, (2) a joint of the arm and (3) an actuator of the arm; also the films could actuate the arm without friction with low driving electrical voltage. To develop a micron sized actuator system with RSMA on silicon substrates, the sputter deposition technique and the wet etching process were used. However, the same heat treatment as the method for bulk TiNi alloy was reported to be unsuccessful for crystallizing the sputtered amorphous thin films because the thin films were stripped off from the silicon substrates. In this study, to solve the problem, a heat treatment method by Joule heating of direct electrical current through the TiNi alloy thin films on the silicon wafers was proposed. Reversible shape memory effects of TiNi thin films treated by direct Joule heating and conventional furnace heating were evaluated