Ajou University Develops Foldable 3D Electronic Device Technology

Next-Generation Wearables Expected with Flexible Structures

Researchers at Ajou University have developed a new technology that simultaneously addresses the decline in conductivity and durability limitations that occur at the folding areas of electronic devices. This breakthrough is drawing attention as a key technology to accelerate the commercialization of next-generation display and wearable devices that can be freely folded and unfolded from a 2D flat state into 3D structures.

A schematic of an origami electronic device that embeds nylon fibers into a flexible polymer electrode device (PEDOT:PSS), maintaining high durability even after multiple folds and stretches. It illustrates the folding stability due to the intermolecular network structure of the polymer electrode device and the tear resistance against tensile forces provided by the embedded nylon fibers. Ajou University

On November 12, Ajou University announced that the research team led by Professor Han Seungyong of the Department of Mechanical Engineering has succeeded in developing a fiber-reinforced origami electronic device with high strength and flexibility. This research was supported by the National Research Foundation of Korea's Nano Material Technology Development Program and the Mid-career Researcher Program.

Origami, meaning "paper folding," has recently gained attention as a technology that enables the transformation of flexible electronic devices into three-dimensional shapes by folding and unfolding. As a result, there have been active attempts to apply origami structures to electronic devices such as displays. Just as thin and lightweight 2D sheets of paper can be folded in various ways to create a wide range of 3D structures, applying origami techniques aims to realize electronic devices that are as light and compact as possible.

If electronic devices can be created using flexible materials that allow for unrestricted folding and unfolding, or even crumpling and flattening, like "paper folding," they could be applied not only to next-generation displays but also to fields such as the space industry, wearable devices, and soft robotics.

Currently, the display technology available to consumers is limited to foldable phones with two folding points, allowing only inward folding (infolding), while outward folding (outfolding) remains challenging. However, the method developed by the Ajou University research team enables both infolding and outfolding with complete flexibility.

The main reason this technology has not yet been applied to actual products is the change in conductivity and decrease in durability at the folding areas that occur when transforming a two-dimensional plane into a three-dimensional structure. During repeated folding and unfolding, electrodes may tear or experience a sharp drop in conductivity, resulting in unstable performance, and the repeated deformation significantly reduces durability. This has been considered a critical issue that must be resolved for planar electronic devices to evolve into three-dimensional structures.

To overcome these limitations, the Ajou University research team focused on using fibers, particularly nylon, to address these problems. The team applied a composite material that embeds tear-resistant nylon fibers into a flexible polymer-based electrode (PEDOT:PSS). The flexible electrode developed by the team minimizes bending stress and suppresses changes in conductivity during the folding process of display devices, fundamentally solving the performance degradation issues caused by repeated folding in existing technologies. The nylon fibers complement the flexible material, preventing tearing and enhancing durability.

The research team confirmed that the newly developed electronic device maintains stable mechanical and electrical properties even after more than 20,000 cycles of repeated folding and unfolding. They also directly demonstrated the application potential of various origami structures as displays with freely transformable shapes, including: △ the "Flasher" structure, which maximizes portability by reducing the display area by up to 25 times using fiber-reinforced, high-strength, and highly flexible electronics; and △ the "Kresling" structure, which transforms into a three-dimensional cylindrical shape like a ring and can be used as a wearable touch panel.

Professor Han Seungyong stated, "The biggest hurdle preventing the commercialization of origami-based electronic devices has been the instability of conductivity and reduced durability at the folding areas. Through this research, we have found a solution that addresses both issues simultaneously, and it is expected that this approach can be extended to fibers other than nylon."

Meanwhile, the results of this research were published this month in the international journal 'npj Flexible Electronics' under the title "Fiber-Reinforced Origami Electronics with High Rigidity and Flexibility for Display Applications." Doctoral student Gong Dohyun and master's students Hwang Suhyun and Kang Minji from the Department of Mechanical Engineering at Ajou University participated as first authors, and Professor Han Seungyong served as the corresponding author.