A New Distortion-Free Substrate Beats the Poisson's Ratio for Future Flexible, Stretchable Displays

Researchers from the Korea Institute of Science and Technology, Seoul National University, Korea University, and Chung-Ang University have developed a transparent substrate that, they say, can be stretched without distortion — and which could be used in next-generation flexible displays.

"This research proposes a new method to develop a distortion-free and completely transparent stretchable substrate by precisely controlling the nanostructure, and the shear-rolling process to implement it can be easily applied to mass production and industrialization," claims team lead and co-corresponding author Jeong Gon Son of the project. "We are currently conducting research to realize a real display device with no distortion even when tensile by transferring display light-emitting devices using this substrate."

Flexible substrates for display devices aren't new — curved and foldable devices have been available commercially for a number of years now, and rollable devices are beginning to appear — but stretchable displays are a bigger challenge. The main issue: a high Poisson's ratio, the ratio by which stretching the display in one direction causes corresponding shrinkage in another. It's a problem for more than just displays, too: skin-contact electronics that stretch to follow the wearer's movement can wrinkle and pinch due to the same effect.

The team's substrate, though, improve things dramatically: rather than a Poisson's ratio of 0.4 to 0.5, as with rival materials, the substrate designed by the team has a ratio of 0.07 or less — delivering almost no shrinkage and reducing distortion. Coupled with a shear-rolling process that aligns nanostructures evenly across the substrate, the finished material exhibits little to no shrinkage even when stretched vertically by over half its length. When applied to an actual display, the team found that the substrate was able to fix image distortion — evenly spacing each row and column as it stretched to maintain image quality.

"Future work could explore broader applications," the researchers claim, "including wearable electronics, stretchable or deformable displays, and soft robotics, leveraging the unique mechanical and optical properties of shear-rolled substrates to advance the field of stretchable electronics. Additionally, further investigations into scalability and integration with various device architectures will be crucial for the practical realization of these advancements."

The team's work has been published in the journal Advanced Materials under open-access terms.