Cornell researchers integrated a CMOS circuit on solar-powered microbots, allowing them to walk autonomously. (Image Credit: Cornell University/YouTube)
Previously, Cornell developed tiny robots with crawling, swimming, walking, and folding capabilities. However, these typically required wires to deliver electrical current or laser beams targeted on certain areas of the bot to generate motion. Cornell researchers recently integrated electronic brains on solar-powered microbots measuring 100 to 250 micrometers, allowing them to walk autonomously without external control. This could pave the way for microscopic devices designed to track bacteria, detect chemicals, eliminate pollutants, perform microsurgery, and cleanse plaque from human arteries.
These robots have a metal-oxide-semiconductor (CMOS) clock circuit, which operates as the bran, containing a thousand transistors along with an array of resistors, capacitors, and diodes. The CMOS circuit produces a signal, which generates a series of phase-shifted square wave frequencies that set the robot's gait. Photovoltaics provide power to the platinum-based actuators (robotic legs) and the CMOS circuit.
The circuits are inside 8-inch silicon-on-insulator wafers. Standing 15 microns tall, the robot's brain towers over the electronics. Each brain was etched into an aqueous solution using 13 photolithography layers, which also patterned the actuators that formed the legs.
"One of the key parts that enables this is that we're using microscale actuators that can be controlled by low voltages and currents," said Itai Cohen, professor of physics at the College of Arts and Sciences. "This is really the first time that we showed that, yes, you can integrate that directly into a CMOS process and have all of those legs be directly controlled by effectively one circuit."
The team developed three robots to test the CMOS circuit. They started with a two-legged Purcell bot, named after physicist Edward Purcell, who came up with a similar design to help explain the microorganisms' swimming motions. The second bot, a complex six-legged antbot, walks with an alternating tripod gait. Lastly, the four-legged dogbot can change its walking speed due to a modified circuit receiving commands via laser pulse.
"Eventually, the ability to communicate a command will allow us to give the robot instructions, and the internal brain will figure out how to carry them out," Cohen said. "Then we're having a conversation with the robot. The robot might tell us something about its environment, and then we might react by telling it, 'OK, go over there and try to suss out what's happening.'”
These robots are 10,000 times smaller than macroscale bots featuring CMOS electronics. Additionally, they walk faster than 10 micrometers per second. The new fabrication process can be used by other researchers to integrate their apps, such as chemical detectors and photovoltaic eyes, on microscopic robots.
“What this lets you imagine is really complex, highly functional microscopic robots that have a high degree of programmability, integrated with not only actuators, but also sensors,” Reynolds said. “We’re excited about the applications in medicine – something that could move around in tissue and identify good cells and kill bad cells – and in environmental remediation, like if you had a robot that knew how to break down pollutants or sense a dangerous chemical and get rid of it.”
Earlier, the researchers installed the CMOS circuits on artificial cilia, which were developed with platinum-based, electrical-powered actuators, allowing them to manipulate the movement of fluids.
“The real fun part is, just like we never really knew what the iPhone was going to be about until we sent it out into the world, what we’re hoping is that now that we’ve shown the recipe for linking CMOS electronics to robotic actuating limbs, we can unleash this and have people design low-power microchips that can do all sorts of things,” Cohen said. “That’s the idea of sending it out into the ether and letting people’s imaginations run wild.”
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