Microfabrication of Soft Millirobots Propelled by Low Voltage Electrohydraulic Actuators

Micron‐ and millimeter‐scale soft actuators with high energy density and rapid response are an essential step toward highly functional untethered millirobots. Scaling down electrohydraulic actuators, such as HASELs, from cm‐scale to mm‐scale requires a complete change in manufacturing methods, switching from laser patterning and film lamination to MEMS‐like cleanroom processes. Here, we introduce a versatile wafer‐level microfabrication strategy for soft electrohydraulic actuators at the millimeter and sub‐mm scales. Scaling down such actuators leads to thinner films and hence to lower drive voltages but requires adapting MEMS processes optimized for rigid materials to be compatible with the polymers and liquid‐filled cavities needed for electrohydraulics. Our wafer‐level process integrates Parylene‐sealed mm‐long microcavities into multilayer architectures from flexible µm‐thick polymer–metal layers. The resulting actuators operate below 300 volts, a substantial reduction from the 1–5 kV typical of similar macro‐scale actuators. This microfabrication approach enables monolithic integration of actuators in robots, combining repeatability and precision. We realized a 20 × 20 mm 2 sized swimming robot incorporating two embedded actuators to drive a pair of pectoral fins. This work establishes a pathway toward untethered electrohydraulic robots at millimeter scale and below.