A collaborative effort has installed electronic “brains” on solar-powered robots that are 100 to 250 micrometers in size — smaller than an ant’s head — so that they can walk autonomously without being externally controlled.
While Cornell researchers and others have previously developed microscopic machines that can crawl, swim, walk and fold themselves up, there were always “strings” attached; to generate motion, wires were used to provide electrical current or laser beams had to be focused directly onto specific locations on the robots.
“Before, we literally had to manipulate these ‘strings’ in order to get any kind of response from the robot,” said Itai Cohen, Professor of Physics in the College of Arts and Sciences. “But now that we have these brains on board, it’s like taking the strings off the marionette. It’s like when Pinocchio gains consciousness.”
The project brought together researchers from the labs of Cohen, Alyosha Molnar, Associate Professor of electrical and computer engineering in Cornell Engineering; and Paul McEuen, the John A. Newman Professor of Physical Science (A&S), all co-senior authors on the paper.
The “brain” in the new robots is a complementary metal-oxide-semiconductor (CMOS) clock circuit that contains a thousand transistors, plus an array of diodes, resistors and capacitors. The integrated CMOS circuit generates a signal that produces a series of phase-shifted square wave frequencies that in turn set the gait of the robot. The robot legs are platinum-based actuators. Both the circuit and the legs are powered by photovoltaics.
“In some sense, the electronics are very basic. This clock circuit is not a leap forward in the ability of circuits,” Cohen said. “But all of the electronics have to be designed to be very low power, so that we didn’t have to put humungous photovoltaics to power the circuit.”
The low-power electronics were made possible by the Molnar Group’s research. Former postdoctoral researcher Alejandro Cortese, Ph.D. ‘19, worked with Reynolds and designed the CMOS brain, which was then built by a commercial foundry, XFAB.
The finished circuits arrived on 8-inch silicon-on-insulator wafers. At 15 microns tall, each robot brain — essentially also the robot’s body — was a “mountain” compared to the electronics that normally fit on a flat wafer, Reynolds said. He worked with the Cornell NanoScale Science and Technology Facility (CNF) to develop an intricate process using 13 layers of photolithography to etch the brains loose into an aqueous solution and pattern the actuators to make the legs.
The team created three robots to demonstrate the CMOS integration: a twolegged Purcell bot, named in tribute to physicist Edward Purcell, who proposed a similarly simple model to explain the swimming motions of microorganisms; a more complicated six-legged antbot, which walks with an alternating tripod gait, like that of an insect; and a four-legged dogbot that can vary the speed with which it walks thanks to a modified circuit that receives commands via laser pulse.
The new robots are approximately 10,000 times smaller than macroscale robots that feature onboard CMOS electronics, and they can walk at speeds faster than 10 micrometers per second.
“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.
The innovation sets the stage for a new generation of microscopic devices that can track bacteria, sniff out chemicals, destroy pollutants, conduct microsurgery, and scrub the plaque out of arteries.