Research PaperMaterial and performance characterization of Z-shaped nickel electrothermal micro-actuators

- An electrothermal actuator based on an asymmetrical “Z” shape exhibits the relatively large displacement and the high exerting force.
- Electroplated nickel structure was achieved using a simple and low-cost fabrication technique through the deposition on a stainless steel substrate.
- Material properties of electroplated nickels from two kinds of electrolyte solution, i.e. nickel sulfamate and nickel sulfate, were compared.

The ultimate goal of this work was to develop a novel electrothermal micro-actuator, with ease of fabrication and low-cost, using a nickel electroplating technique. In this work, the properties of the nickel films deposited at an electroplating current density of 7.0 mA/cm2 using two electrolytes, i.e. nickel sulfate and nickel sulfamate solutions, were compared. From the material testing, the nickel sulfamate solution provided a nickel film with a rougher but softer surface; therefore, the solution was chosen in a process to fabricate the micro-actuators. The micro-actuators with a Z-shaped driving mechanism were designed with a variation in the gap between small and large arms. Within the range of experimental conditions, i.e. applying DC current of 3-5 A for 30 s, average temperature of the driving mechanism was less than 100 °C, at which the micro-actuator with the gap of 200 μm provided the largest displacement of around 250 ± 32 μm and the magnitude of the force higher than 4.5 ± 0.8 mN. All micro-actuators could appropriately respond to a driving frequency up to 1 Hz. In addition, no significant decrement of the magnitude of the exerting force was observed within 21,600 actuating cycles. Lastly, the micro-gripper was fabricated and tested. The successful gripping of an asymmetrical sesame seed was demonstrated.