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Fifty years of Moore's law scaling in microelectronics have brought remarkable opportunities for the rapidly evolving field of microscopic robotics1-5. Electronic, magnetic and optical systems now offer an unprecedented combination of complexity, small size and low cost6,7, and could be readily appropriated for robots that are smaller than the resolution limit of human vision (less than a hundred micrometres)8-11. However, a major roadblock exists: there is no micrometre-scale actuator system that seamlessly integrates with semiconductor processing and responds to standard electronic control signals. Here we overcome this barrier by developing a new class of voltage-controllable electrochemical actuators that operate at low voltages (200 microvolts), low power (10 nanowatts) and are completely compatible with silicon processing. To demonstrate their potential, we develop lithographic fabrication-and-release protocols to prototype sub-hundred-micrometre walking robots. Every step in this process is performed in parallel, allowing us to produce over one million robots per four-inch wafer. These results are an important advance towards mass-manufactured, silicon-based, functional robots that are too small to be resolved by the naked eye.
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Figure 1a shows a microscopic robot still attached to its substrate and Fig. 1b shows a side view of a robot after release. Each robot consists of two main parts: a body containing standard silicon electronics, and legs consisting of our newly developed actuators and panels that set the legs' three-dimensional shape. The electronics in this case are simple circuits made from silicon photovoltaics and metal interconnects. These microscopic robots walk when illuminated by a sequence of laser pulses, shown schematically in Fig. 1c and in a real micrograph sequence in Fig. 1d. Each robot is comparable in size to larger microorganisms: a robot next to a single-celled Paramecium is shown in Fig. 1e. All of the components are fabricated in parallel as part of the same integrated process. A chip, cut from a wafer, with thousands of microscopic robots on its surface is shown in Fig. 1f.
The key innovation enabling these microscopic robots is a new class of actuators that we call surface electrochemical actuators or SEAs (Fig. 2). SEAs are made from nanometre-thick platinum and are fabricated using standard semiconductor technologies. We grow 7-nm-thick layers of platinum (Fig. 2b, Extended Data Figs. 1, 2) using...