Microsensors Developed Using Optical Wireless ICs to Increase Sensing and Communication Range
Researchers at Cornell University have mass-produced tiny energy-harvesting sensors, 30,000 of which can fit on one side of a penny.
The sensors are based on optical wireless integrated circuits (OWICs) and contain solar cells and LEDs that allow them to harness light for power and communication. And because up to 1 million can be fabricated on an 8-inch wafer, the research team claims that each sensor costs a fraction of a penny.
Designed with Space to Develop New Applications
The researchers claim that, in theory, thousands of transistors could be placed on one of these OWIC devices, increasing the range of things that the device can sense and its ability to carry out more complex tasks.
“We really developed this as a platform so that a lot of people have space to develop new devices, new applications,” said Alejandro Cortese, a Cornell Presidential Postdoctoral Fellow.
"In a certain sense, it’s an old idea, building tiny sensors like this," explained Professor Paul McEuen, who co-chairs the 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."
An illustration provided by Cornell researchers showing a size comparison of the voltage-sensing OWIC on the back of a penny and a schematic of an OWIC's components. Image credited to Alejandro Cortese
A Difficult Process
Although mass production at this level is possible, it is a difficult process. To get the gallium arsenide-based LEDs onto the chip involves 100 different steps alone. This is because it requires 15 layers of photolithography and 30 different materials. There is also the size problem—the fabrication process is at a scale where “…you legitimately cannot see what you’re doing unless you’re under a microscope,”
Essentially, these OWICs are paramecium-size smartphones that can be specialized with the use of apps. Rather than rely on radio frequency technology; however, the researchers looked towards light as a potential power source communication method, this is where the solar cells and LEDs come in.
To prove their concept, the researchers used an OWIC with an on-board temperature sensor and successfully embedded in brain tissue. However, the OWIC’s surface needs to be exposed so that the solar cell can gather energy from ambient light and so the on-board LED could be viewed for data collection. Once the OWICs are released from their substrate of silicon, they can be used to measure inputs in hard-to-reach environments, such as inside living tissue.
I’ve been waiting for light connected chips for over ten years. I understand the power and space problems, but it looks like they may be overcome soon. Still, I have to question the viability of a sensor that needs light for power and needs a clear path for optical communication in the context of “hard to reach environments, such as inside living tissue.”