Researchers from Cornell and the University of Pennsylvania built microscopic robots that consist of a simple circuit of silicon photovoltaics – essentially the torso and brain – and four electrochemical actuators that act as legs. When laser light is directed at the photovoltaics, the robots run. Photo credit: Cornell University
In 1959, former Cornell physicist Richard Feynman gave his famous lecture, “There’s a lot of space on the floor,” in which he described the possibility of shrinking technology from machines to computer chips to incredibly small sizes. Well the floor just got overcrowded.
In a collaboration led by Cornell, the first microscopic robots were developed that contain semiconductor components that can be used to control and operate using standard electronic signals.
These robots, roughly the size of Paramecium, provide a template for creating even more complex versions that use silicon-based intelligence, can be mass-produced, and one day can travel through human tissue and blood.
The collaboration is led by Itai Cohen, Professor of Physics, Paul McEuen, the John A. Newman Professor of Physics – both at the College of Arts and Sciences – and their former postdoctoral fellow Marc Miskin, who is now Assistant Professor at the University of Pennsylvania.
The paper of the team “Electronically integrated, mass-produced microscopic robots” published on August 26, 2020 in nature.
Building micrometer-sized robots is difficult, especially when developing small “actuators” – the motors that allow robots to move. Conventional actuators do not operate on such a small scale, and new actuators that do work use mechanisms such as magnetism and are difficult to integrate with conventional silicon-based microelectronics. Now a team of researchers has developed a new type of actuator that works electronically and can be layered directly onto the circuit that controls it. This opens the doors for the last 50 years of microelectronics research to be built into robots that are so small that they cannot be seen by the human eye.
The walking robots are the latest iteration and in many ways an evolution of Cohen and McEuen’s earlier nano-scale creations, from microscopic sensors to GraphOrigami machines.
The new robots are about 5 micrometers thick (a micrometer is a millionth of a meter), 40 micrometers wide, and between 40 and 70 micrometers long. Each bot is made up of a simple circuit made of silicon photovoltaics – which essentially functions as the torso and brain – and four electrochemical actuators that act as legs.
As simple as the tiny machines may seem, getting the legs done was an enormous achievement.
“In the context of the robot’s brain, in a sense, we’re just taking the existing semiconductor technology and making it small and solvable,” said McEuen, co-chair of the Nanoscale Science and Microsystems Engineering (NEXT Nano) task force. Part of the Provost’s Radical Collaboration Initiative and heads the Kavli Institute in Cornell for Nanoscale Science.
“But the legs didn’t exist before,” said McEuen. “There weren’t any small, electrically activated actuators that could be used. So we had to invent these and then combine them with the electronics. ”
The robots are about 5 micrometers thick, 40 micrometers wide and between 40 and 70 micrometers long – about the size of microorganisms like Paramecium. Photo credit: Cornell University
Using atomic layer deposition and lithography, the team constructed the legs from strips of platinum just a few dozen atoms thick, covered on one side by a thin layer of inert titanium. When a positive electrical charge is applied to the platinum, negatively charged ions from the surrounding solution adsorb on the exposed surface to neutralize the charge. These ions force the exposed platinum to expand, causing the strip to flex. The ultra-thinness of the strips allows the material to bend heavily without breaking. To control the 3D movement of the limbs, the researchers patterned rigid polymer plates on the strips. The gaps between the panels act like a knee or ankle, allowing the legs to bend in a controlled manner, creating movement.
The researchers control the robots by flashing laser pulses in various photovoltaic systems, each of which charges a separate set of legs. By moving the laser back and forth between the front and rear photovoltaics, the robot runs.
“Although these robots are primitive in their function – they’re not very fast, they don’t have a lot of computing power – the innovations we’ve made to make them compatible with standard microchip manufacturing open the door to these microscopic robots to make it intelligent, quick and mass producible, ”said Cohen. “This is really just the first shot over the bow that we can use to do electronic integration on a tiny robot.”
The robots are certainly high-tech, but they work with low voltage (200 millivolts) and low power (10 nanowatts) and remain strong and robust for their size. Since they are manufactured using standard lithography processes, they can be manufactured in parallel: around 1 million bots fit on a 4-inch silicon wafer.
Researchers are looking for ways to spice up the robots with more complicated electronics and on-board computation – improvements that could one day lead to swarms of microscopic robots crawling through materials and restructuring them, or sewing blood vessels or being sent en masse to examine large swaths of robots the human brain.
“Controlling a tiny robot is perhaps as close as possible to shrinking itself. I think machines like this will take us into all kinds of amazing worlds too small to see, ”said Miskin, lead author of the study.
Co-authors are David Muller, the Samuel B. Eckert Professor of Engineering; Alejandro Cortese, Ph.D. ’19, a postdoctoral fellow to the President of Cornell; Postdoctoral fellow Qingkun Liu; PhD students Michael Cao ’14, Kyle Dorsey, and Michael Reynolds; and Edward Esposito, a former college assistant and technician in Cohen’s laboratory.
“This research breakthrough offers exciting scientific opportunities to study new questions relevant to active matter physics and may ultimately lead to futuristic robotic materials,” said Sam Stanton, program manager of the Army Research Office, an Army element of the Combat Capabilities Development Command Research laboratory that supported the research.
Additional support was provided by the Air Force Office of Scientific Research, the Cornell Center for Materials Research, supported by the National Science Foundation’s Materials Research Science and Engineering Center program, and the Kavli Institute in Cornell for Nanoscale Science. The work was carried out in the Cornell NanoScale Science and Technology Facility.
Itai Cohen, Professor of Physics at the College of Arts & Sciences, speaks about interdisciplinary research between groups in Physics at the College of Arts & Sciences and groups at the College of Engineering. Photo credit: Cornell University
Reference: “Electronically Integrated, Mass-Manufactured Microscopic Robots” by Marc Z. Miskin, Alejandro J. Cortese, Kyle Dorsey, Edward P. Esposito, Michael F. Reynolds, Qingkun Liu, Michael Cao, David A. Müller, Paul L. McEuen and Itai Cohen, August 26th 2020, nature.
DOI: 10.1038 / s41586-020-2626-9
