Researchers Cram 30,000 Energy-Harvesting Ultra-Tiny OWIC Sensors Onto a Single Penny

Researchers at Cornell University have mass-produced energy-harvesting sensors so small, 30,000 can fit on one side of a penny — and each individual sensor costs a tiny fraction of a penny to produce.

"In a certain sense, it’s an old idea, building tiny sensors like this," explains Professor Paul McEuen, who co-chairs the Nanoscale Science and Microsystems Engineering (NEXT Nano) Task Force at Cornell. "But we pushed it another order of magnitude down in size and made it mass fabricate-able. A lot of times when people would make these little doodads, they would wire them all together by hand. You didn’t get a million at a time. So we constrained ourselves and said we're not going to do it unless we can make them by the million."

The sensors are based on optical wireless integrated circuits (OWICs), and - despite requiring a microscope to see in any detail — contain solar cells for power and light-emitting diodes (LEDs) for communication. While mass production is possible — around a million sensors can be produced on a single eight-inch wafer, each sensor measuring just 100 microns in length - it's tricky: To get the gallium arsenide-based LEDs into the circuit required an assembly process with 15 layers of photolithography, 30 different materials, and over 100 individual steps.

"There are a lot of people working at larger scales where you can pick up things and see them with your eye and touch them. This is not that," says lead author Alejandro Cortese of the difficulty involved. "It's at a scale that you legitimately cannot see what you're doing unless you're under a microscope. So you really have to gain an intuition about the nanoscale and the microscale."

To prove that the technology works, an OWIC with on-board temperature sensor was produced and successfully embedded in brain tissue — though its surface needed to be exposed, both so the solar cell could gather energy from ambient light and so the on-board LED could be viewed to read back the resulting data.

"The circuits in this paper were quite simple," says Cortese. "But you can potentially fit thousands of transistors on one of these devices. And that means you can increase the range of things the device can sense, how the device communicates out, or it's ability to complete more complex tasks. We really developed this as a platform so that a lot of people have space to develop new devices, new applications."

The technology is to be commercialized under the company OWiC Technologies, beginning with OWIC-powered electronic product identification tags for inventory purposes. The team's paper, meanwhile, has been published in the journal Proceedings of the National Academy of Sciences (PNAS) under closed-access terms.