Microbots smaller than an ant’s head can move autonomously and untethered

Tiny bots can walk autonomously without being externally controlled.
Ayesha Gulzar
Alejandro Cortese, Ph.D. ’19 displays a silicon-on-insulator wafer that contains finished CMOS “brains.”
Alejandro Cortese, Ph.D. ’19 displays a silicon-on-insulator wafer that contains finished CMOS “brains.”

Cornell 

In a new development in the field of micro and nanoelectronics, scientists at Cornell University developed microbots smaller than an ant's head yet capable of walking autonomously. The solar-powered robot, invisible to the naked eye, has a tiny microprocessor "brain" onboard that allows it to walk without being externally controlled.

Building an autonomous robot is no easy task. Until now, scientists have developed microscopic robots that require special wire harnesses or an external stimulant, like focused laser beams, to generate mobility. Currently featured in Science Robotics, a new type of microchip allows for onboard control in untethered robots only a tad bigger than the width of a human hair.

"Before, we literally had to manipulate these 'strings' in order to get any kind of response from the robot. 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," said Itai Cohen, professor of physics in the College of Arts and Sciences.

Brain on Board

The new electronic brain-powered microbot is only 100 - 250 micrometers in size. It consists of three major systems: An integrated circuit for control and direction, a power source, i.e., a photovoltaic cell capable of harnessing energy from a light source, and a set of hinged legs capable of providing motion greater than 10 micrometers per second.

Autonomous control comes from complementary metal-oxide-semiconductors, also known as CMOS. These semiconductors consist of thousands of transistors, diodes, capacitors, and resistors responsible for electronic device control. The motion is actuated using phase-shifted square wave frequency signals. The robot legs are made of platinum-based actuators. Both the electronic circuit and limbs of the device are powered via photovoltaics.

The team created three robots to demonstrate the CMOS integration: a two-legged Purcell bot, a more complicated six-legged antbot that walks like an insect, and a four-legged dogbot that can vary the speed.

The new technology opens many opportunities in terms of applications of these micro machines. Autonomous micromachines are predicted to significantly increase the diagnostic and therapeutic methodologies in medicine. Self-driven microbots can be deployed to track specific bacteria, locate toxic chemicals, tackle pollutants, integrate with microsurgery, and help clear arteries by removing plaque.

The novelty of this electronic fabrication lies in its utility of extremely low-powered electronics. With the new fabrication technique at Cornell Nanoscale Science and Technology Facility, the researchers have assembled many more electronics onto a single silicon wafer than through traditional semiconductor fabrication processes. This, in turn, enabled them to utilize a single circuit to control the whole body effectively.

While this is a significant leap towards autonomous micro-robotics, the device is fairly simple, with only having to perform a gait without any actual communication with the user for the sense of directionality. However, the limitation of the intelligence of the device can be explained by using a large silicon fabrication process — 180 nanometers — whereas the top industrial applications use sub-10-nm processes. In the future, the fabrication of nano-circuits will allow for a lot more electronics to be fitted inside a smaller space, thus allowing for far more intelligent structures.

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