As electronic devices with unique form factors, such as rollable phones, are on the verge of commercialization, a domestic research team has developed a 3D display source technology that can express information that is difficult to implement with existing flat displays.

A joint research team led by Kim Dae-hyung, deputy research director (Professor, Department of Chemical and Biological Engineering, Seoul National University) and Hyun Taek-hwan, director (Distinguished Professor, Department of Chemical and Biological Engineering, Seoul National University) of the Nanoparticle Research Group at the Institute for Basic Science (IBS, President Noh Do-young) succeeded in developing a 3D quantum dot light-emitting diode (QLED) that can be freely folded like paper.

QLED, which uses quantum dots as a light-emitting material, does not require bulky elements such as backlights, unlike conventional liquid crystal displays (LCDs), allowing for the production of displays with a much thinner thickness.

The IBS Nanoparticle Research Group also developed an ultra-thin QLED with a thickness of 3 μm, about 1/30th the thickness of a human hair, in 2015 and produced it in the form of a wearable display.

In this study, we went further and created an ultra-thin QLED that can be freely folded into any desired shape, like origami. Based on this, we succeeded in producing a 3D foldable QLED with complex structures such as a butterfly, airplane, and pyramid.

To achieve this, the research team developed a new "selective laser etching process," using a carbon dioxide laser to partially etch the epoxy film deposited on the QLED surface. The etched area is relatively thinner than the surrounding area, making it susceptible to deformation when external forces are applied.

In origami, it is about making a 'folding line'. At this time, there is a thin etch-preventing layer made of silver and aluminum alloy between the QLED and the epoxy film, which effectively prevents damage to the inside of the QLED caused by the laser.

Through this process, the research team succeeded in precisely controlling the radius of curvature of the foldable QLED, and succeeded in producing a foldable QLED with an extremely small radius of curvature of less than approximately 50 μm.

When the radius of curvature becomes smaller than several tens of μm, it appears to the naked eye as a sharp fold rather than a bend.

Additionally, all light-emitting surfaces, including the corners, operated stably even after repeated folding over 500 times.

Through this, the research team created QLEDs with complex 3D shapes such as butterflies and airplanes, and in particular, the pyramid-shaped 3D foldable QLED consisting of 64 pixels showed the possibility of developing a display that can be freely folded into the shape desired by the user as it can freely transform between 2D and 3D structures.

“Thanks to the development of a laser process utilizing an etch-preventive layer made of an alloy, we were able to create a 3D foldable QLED that can be folded freely like paper,” said Kim Dae-hyung, deputy head of the research team. “Beyond the 64-pixel display created in this study, we will be able to create QLED displays with more complex form factors in the future.”

Director Hyun Taek-hwan said, “It will be particularly useful in places that require customized small displays, such as electronic paper, newspapers, and tablets,” adding, “It is significant in that it opens up the possibility of manufacturing customized displays.”

The research results were published on September 24th in the world-renowned journal in the field of electrical and electronic engineering, Nature Electronics (IF 33.686)..