Research Powerful and stretchable micro-electronics for wearables and implants

Related Vendor

Wuxi InfiMotion Technology Co., Ltd.

Researchers at Stanford have developed soft integrated circuits that are powerful enough to drive a micro-LED screen and small enough to accommodate thousands of sensors on a single square centimeter.

Small portable or implantable electronic components could help monitor our health, diagnose diseases, and create opportunities for improved autonomous treatments. To achieve this without injuring or harming the cells in their vicinity, this electronics not only have to flex and stretch with our tissue, but also be soft enough not to scratch and damage the tissue.

Researchers at Stanford have been working on skin-like, stretchable electronic devices for over a decade. In a report published in 'Nature', they now present a new design and manufacturing process for skin-like integrated circuits that are five times smaller and operate at a thousand times higher speed than previous versions.

The researchers demonstrated that their soft integrated circuits are now capable of driving a micro-LED display or recognizing a Braille field, with the ICs being more sensitive than human fingertips.

"We have made a significant leap forward. For the first time, stretchable integrated circuits are now small enough and fast enough for many applications," said Professor Zhenan Bao in Stanford, and the main author of the research work. "We hope this will make wearable sensors and implantable nerve and bowel probes more sensitive, operate more sensors, and potentially use less power."

2,500 sensors and transistors on one square centimeter

The heart of the circuits are stretchable transistors made of semiconducting carbon nanotubes and soft elastic electronic materials developed in Bao's lab. Unlike silicon, which is hard and brittle, the carbon nanotubes have a fishnet-like structure amongst the elastic materials, allowing them to continue to function even when stretched and deformed. The transistors and circuits are applied to a stretchable substrate along with stretchable semiconductors, conductors, and dielectric materials.

"This is the result of years of material and technique development," said Bao. "We not only had to develop new materials, but also the circuit design and fabrication process for the circuits. There are many layers that are stacked on top of each other, and if one layer doesn't work, we have to start everything from scratch."

In a demonstration of their new stretchable electronics design, the researchers managed to accommodate more than 2,500 sensors and transistors on one square centimeter, thus creating a tactile active matrix that is more than ten times as sensitive as human fingertips. The researchers demonstrated that the sensor array can recognize the position and orientation of tiny shapes or recognize entire words in Braille script.

"Normally, with Braille, you perceive one letter at a time," says Donglai Zhong, a postdoctoral researcher in Bao's laboratory and co-author of the study. "With such high resolution, you could sense an entire word or possibly an entire sentence with just one touch."

The researchers also used their stretchable circuits to drive a microLED display at a refresh rate of 60Hz, which is the typical refresh rate of a computer or television screen. Earlier versions of the stretchable circuits were not fast enough at small dimensions to generate enough current to achieve this.

"We are very pleased with these performance improvements as they open up many new opportunities," says Can Wu, Postdoctoral Fellow in Bao's lab and co-first author of the study. "Preliminary results show that our transistor can be used to drive commercial screens that are used, for example, in computer monitors."

"And for biomedical applications, a high-density, soft, and adaptable sensor array could enable us to capture signals from the human body, such as from the brain and muscles on a large scale and fine resolution. This could lead to next-generation brain-machine interfaces that are both powerful and biocompatible."

"Soft circuits for the future."

The researchers have deliberately developed materials and processes that work with the existing manufacturing tools so that the circuits can more easily make the leap to commercial manufacturing. Their process is based on similar manufacturing techniques to the current production of screens, even if it is completely different materials. Manufacturers would not be able to manufacture these circuits without additional fine tuning, but the tools are already available, says Bao.

Of course, there are still more hurdles before these stretchable and soft integrated circuits can reach market maturity. Body and tissue movements can still lead to deviations in the electrical properties of the circuits - Bao and colleagues are working on new designs that could reduce these effects - and the components need some form of soft moisture protection before they can be used.

"There are still challenges for the future of this technology, but these recent developments open up some very exciting biomedical applications for wearable and implantable electronics," said Bao. "And there are also applications in soft robotics that give robots a sensory functionality that is close to human and makes work safer for people."

This research work was funded by SAIT, Samsung Electronics Co, Ltd, the Army Research Office, the CZ Biohub-San Francisco, the Stanford Wearable Electronics Initiative and the National Science Foundation. (mbf)

* Henning Wriedt is a freelance specialist author.

Link: Source: Stanford University