*Invited* Formation and Actuation Properties of Ti-Ni-Cu/Polyimide Composite Films

Recently, we reported the deposition of a crystalline Ti-Ni-Cu film on a polyimide film heated at 543K and demonstrated that this polyimide/SMA composite film can be used as a simple actuator by cutting out an appropriately shaped piece with scissors and then connecting the two edges to a battery. In the previous study, the deposition of a Ti-Ni-Cu alloy film was performed using a multi-target sputtering apparatus with three pure metal targets. In the present study, we deposited alloy films on polyimide films using a conventional sputtering apparatus with a single alloy target and found that this simple fabrication facilitates the mass production of Ti-Ni-Cu/polyimide composite films and thereby makes these films cost-effective. Ti₄₉Ni₃₃Cu₁₈ films with various thicknesses (0.8~13μm) were prepared on two kinds of polyimide films (Kapton EN and H) of various thicknesses (25~125μm) to investigate the design parameters of composite-film actuators. The actuation stroke and power of the composite films were found to be significantly dependent on the thickness ratio of Ti-Ni-Cu and polyimide films and the coefficient of thermal expansion of a polyimide film. It was also found that constrained heating of composite films changes the shape of the composite-film actuator. By optimizing the design parameters such as a thickness ratio, Ti-Ni-Cu/polyimide composite-film actuators showed a large actuation stroke and a high response speed of 3Hz, and a large force of 0.1N, respectively.