One chip, many functions

Researchers from King Abdullah University of Science and Technology (KAUST) have managed to combine sensing, energy-harvesting, current-rectifying and energy-storage functions into a single microchip.

Described in the journal Advanced Materials, the team’s work is believed to mark a significant advance in the quest to perfect the tiny, self-powered sensors that will expand the Internet of Things, with a broad range of potential applications from monitoring personal health indications directly from the human body to environmental and industrial sensing.

“Previously, researchers had to use bulky rectifiers that converted intermittent harvested electrical energy into steady direct current for storage in electrochemical microsupercapacitors,” said KAUST research scientist Mrinal K Hota, lead author on the study.

Hota explained that the key to integrating everything into a single chip was the development of ruthenium oxide (RuO₂) as the common electrode material connecting all devices in the microcircuits. The ruthenium-oxide contacts are laid onto a glass or silicon substrate to connect sensing, energy-harvesting and current-rectifying electronics with one or more electrochemical microsupercapacitors that store the electrical energy.

This creates a tiny system that can operate without any battery power. Instead it uses available body movement or machinery vibrations as a continual source of energy.

“Unlike a battery, electrochemical microsupercapacitors can last for hundreds of thousands of cycles rather than just a few thousand,” Hota said. They can also deliver a significantly higher power output from a given volume, he added.

A key to creating electrode material suitable for connecting all devices was to make optimal ruthenium-dioxide surfaces with controlled roughness, defects and conductivity. These features enabled the team to use RuO₂ for both electronics and electrochemical microsupercapacitors.

Another crucial innovation was to use a gel that, after application, solidifies into the supercapacitors’ electrolyte. This is a material that transports electric charge in the form of ions. The solidified gel was chosen to avoid any damage to rectifiers and thin-film transistors.

The researchers now plan to work to optimise the RuO₂ electrodes further and explore linking many different types of sensors into their chips. They also want to investigate adding wireless communication into the device, which would allow biosensors and environmental sensors to send data remotely to any wireless receivers — including mobile phones and personal computers.

“Our achievement simplifies device fabrication and realises significant miniaturisation of self-powered sensor devices,” said project leader Husam Alshareef.

Image caption: A thin-film chip with the energy-storing microsupercapacitors arrayed along top and bottom of the chip. Image ©2019 KAUST.

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