Material and performance characterization of Z-shaped nickel electrothermal micro-actuators

Abstract

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 7.0mA/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 3–5A for 30s, average temperature of the driving mechanism was less than 100°C, at which the micro-actuator with the gap of 200μm provided the largest displacement of around 250±32μm and the magnitude of the force higher than 4.5±0.8mN. All micro-actuators could appropriately respond to a driving frequency up to 1Hz. 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.