Fifty years of Moore’s Law scaling in microelectronics have brought remarkable opportunities for the rapidly-evolving field of microrobotics. Electronic, magnetic, and optical systems now offer an unprecedented combination of complexity, small size, and low cost, and could readily be appropriated to form the intelligent core of robots the size of cells. But one major roadblock exists: there is no micron-scale actuator system that seamlessly integrates with semiconductor processing and responds to standard electronic control signals. We overcome this barrier by developing a new class of voltage-controllable electrochemical actuators that operate at low voltages (200 mV), low power (10 nW), and are completely compatible with silicon processing.
The key innovation enabling these microrobots is a new class of actuators that we call surface electrochemical actuators (SEAs). SEAs are made from nanometer-thick platinum and are fabricated using standard semiconductor technologies. We grow 7 nm thick layers of platinum using atomic layer deposition, cap the exposed surface with an inactive material, either graphene or sputtered titanium, and pattern them using lithography. Once released, the SEAs bend, both due to prestresses in the device and the difference in surface stress between the platinum and the capping layer. We use the latter for actuation: when biased relative to the surrounding aqueous electrolyte, ions adsorb/desorb from the platinum surface, changing the surface stress.
To demonstrate their potential, we developed lithographic fabrication and release protocols to prototype sub-hundred micrometer walking robots. Every step in this process is performed massively in parallel, allowing us to produce over one million robots per 4-inch wafer. These results establish a clear pathway to mass-manufactured, increasingly complex and functional, cell-sized robots.
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 leg’s 3D shape. The electronics in this case are simple circuits made from silicon photovoltaics and metal interconnects (Fig. A). Fig. B shows a side view of a robot after release. The microrobots walk when illuminated by a sequence of laser pulses (Fig. C). Each robot is comparable in size to many cells and microorganisms: a robot next to a paramecium is shown in Fig. D. All of the components are fabricated in parallel as part of the same integrated process. A chip, cut from a wafer, with thousands of robots on its surface is shown in Fig. E.
The robot uses their legs to walk on textured surfaces. We focus laser light onto photovoltaics that bias either the front or back legs in sequence. In this configuration, each leg acts as the counter electrode to the other: if one leg is positively biased, the other is negatively biased. We show the motion of the legs and a qualitative description of how they produce locomotion in Fig. A. The position and the velocity of the microrobot as a function of time are shown in Figs. B and C, respectively, with peak speeds approaching 30 μm/s and an average speed of ~1 μm/s.
Since the simple microrobots demonstrated here are compatible with standard CMOS processing, their capabilities can rapidly evolve. Future designs can immediately leverage fifty years of research in semiconductor electronics, manufacturing, packaging, and integration technologies, and complimentary optical, acoustic, magnetic, thermal or chemical strategies for micro-robotics. Such robots could autonomously explore a micro-environment or directly interact with biological systems using local sensory input and feedback. Furthermore, we estimate that such microrobots can be manufactured at a cost that is significantly less than a penny per robot using commercial silicon foundries. The new actuators and fabrication protocols presented here provide the key elements needed to realize this remarkable future, removing the final roadblocks to silicon-based, functional, highly-intelligent micro-robotic systems.
Check out the TED talk on tiny robots with giant potential!
These robots were featured in a Nature article and video: Robots smaller than the eye can see could revolutionise micro-robotics
Watch the Nature video here: March of the microscopic robots
For more information about these cell-sized robots, check out this video: Computer chips morph into tiny robots with medical applications
These robots hold the Guinness World Record for smallest walking robot: Guinness World Records
Watch Prof. Cohen explain how origami helps these microscopic robots walk: Itai Cohen explains the physics of origami
BBC News interview about this project: Scientists create a microscopic robot that ‘walks’
This project was featured on the following podcasts:
ASME TechCast: Engineers Make Microscopic Robots Walk
