Tiny injectable chips use ultrasound to monitor vitals

Researchers are increasingly interested in designing wireless, miniaturised implantable medical devices for in vivo and in situ physiological monitoring. These devices could monitor physiological conditions, such as temperature, blood pressure, glucose, and respiration for both diagnostic and therapeutic procedures.

To date, conventional implanted electronics have been highly volume-inefficient – they require multiple chips, packaging, wires, and external transducers, and they often need batteries for energy storage. A constant trend in electronics has been the tighter integration of electronic components, often moving more functions onto the integrated circuit itself.

With this, Columbia engineers report that they have built what they say is the world’s smallest single-chip system, consuming a total volume of less than 0.1mm³. The system is as small as a dust mite and visible only under a microscope; the researchers said. In order to achieve this, the team used ultrasound to both power and communicate with the device wirelessly.

“We wanted to see how far we could push the limits on how small a functioning chip we could make,” said Ken Shepard, a professor of electrical engineering and professor of biomedical engineering. “This is a new idea of ‘chip as system’ – this is a chip that alone, with nothing else, is a complete functioning electronic system. This should be revolutionary for developing wireless, miniaturised implantable medical devices that can sense different things, be used in clinical applications, and eventually approved for human use.”

Doctoral student Chen Shi designed the chip. And according to the researchers, Shi’s design is unique in its volumetric efficiency, the amount of function that is contained in any amount of volume.

Traditional radio frequency (RF) communications links are not possible for a device this small because the wavelength of the electromagnetic wave is too large relative to the size of the device. To tackle this, the engineers used ultrasound to both power and communicate with the device wirelessly as its wavelengths are much smaller at a given frequency because the speed of sound is so much less than the speed of light. They fabricated the 'antenna' for communicating and powering with ultrasound directly on top of the chip.

The chip, which is the entire implantable/injectable mote with no additional packaging, was fabricated at the Taiwan Semiconductor Manufacturing Company with additional process modifications performed in the Columbia Nano Initiative cleanroom and the City University of New York Advanced Science Research Center (ASRC) Nanofabrication Facility.

“This is a nice example of ‘more than Moore’ technology – we introduced new materials onto standard complementary metal-oxide-semiconductor to provide new function,” Shepard explained. "Here, we added piezoelectric materials directly onto the integrated circuit to transducer acoustic energy to electrical energy.”

Elisa Konofagou, a professor of biomedical engineering and professor of radiology, added: “Ultrasound is continuing to grow in clinical importance as new tools and techniques become available. This work continues this trend.”

The team’s goal is to develop chips that medical experts can inject into the body with a hypodermic needle and then communicate back out of the body using ultrasound, providing information about something they measure locally.