Fabrication of cylindrical micro actuator by etching of TiNiCu shape memory alloy tube

In this paper, we describe the fabrication of a cylindrical micro actuator from a TiNiCu shape memory alloy (SMA) tube. Ternary TiNiCu SMA is a favorable material for micro actuators with good flexibility and considerable force generation. We proposed a novel fabrication process based on an electrochemical etching and a chemical etching of the TiNiCu SMA tube. The electrochemical etching in LiCl–ethanol electrolyte solution was successfully used for fine patterning of the TiNiCu tube with a high etch factor (etched depth/under-cut). After the fine patterning by using the electrochemical etching, a chemical etching process was used for wall thinning and wall-through etching from the TiNiCu tube inside. The composition of the chemical etchant of mixture of hydrofluoric acid and nitric acid was optimized. Using the etching processes, the TiNiCu SMA cylindrical actuator, in which three meandering-shaped actuators are formed in the tube with an outer diameter of 1 mm and a wall thickness of 30–40 μm, was fabricated successfully. The fabricated SMA meandering actuator could be elongated to 60% without out-of-plane deformation. The single meandering actuator unit could generate a tensile force of 75 mN when it was heated at a current of 90 mA (23 mW).