KAIST

< Professor Phil-Seung Lee (center), Master’s graduate Jun-han Bae (top left) >

The "crease," long considered the biggest weakness of foldable smartphones, has been pointed out as a major obstacle to market expansion, causing screen distortion and reduced durability over repeated use. A research team at KAIST has presented a solution to this problem, marking a turning point for foldables to leap forward as the standard for next-generation smartphones. Furthermore, the technology is expected to establish itself as a core component of the future mobile industry, expanding into various devices such as laptops.

KAIST announced on April 20th that a research team led by Professor Phil-Seung Lee of the Department of Mechanical Engineering has developed an original technology capable of fundamentally solving the crease issue that occurs at the folding area of foldable smartphone displays and has registered a patent for it. The team has secured global technological competitiveness by filing patent applications in the United States, China, and the European Union (EU), in addition to South Korea.

While global smartphone companies have attempted to solve this issue through massive R&D investments for years, they have yet to achieve the complete removal of the crease. Consequently, the industry has identified the crease problem as the single greatest barrier to the widespread adoption of the foldable smartphone market.

The research team began their study to resolve the inconveniences they personally experienced while using mobile foldable phones. After disassembling dozens of used foldable phones and repeating various experiments, they derived a solution by innovatively redesigning the "adhesive area" between the display and the supporting plate. The core of the design is ensuring that deformation is not concentrated in a specific folding area but is instead distributed to the surrounding sections. Through this, they perfectly demonstrated the feasibility of a "crease-free foldable" while maintaining normal smartphone functionality.

To verify performance, the team shone a straight-line LED light onto the screen. Unlike commercial products where the light refracts and the straight line appears curved at the fold, the prototype maintained a sharp, straight reflection without any distortion. Notably, no visual distortion appeared even under conditions sensitive enough to detect minute curves with a crease depth of less than 0.1mm.

< Display surface reflecting a straight-line LED lamp >

This technology presents a new design paradigm that surpasses the limitations faced by the current industry. It not only fundamentally suppresses the formation of creases but also ensures superior durability by minimizing deformation even after tens of thousands of folding cycles.

Furthermore, because the structure is intuitive and simple, it can be easily integrated into existing manufacturing processes. It is expected to have high industrial utility, as it can be expanded beyond smartphones to various foldable display devices, including tablets and laptops.

< Core idea of the invention: (a) Adhesive and non-adhesive areas of a conventional foldable smartphone, (b) Adhesive and non-adhesive areas in this invention, (c) Stress distribution in a conventional foldable smartphone display, (d) Stress distribution in a foldable smartphone display applying this technology >

Industry experts anticipate that the commercialization of this technology will encourage global companies—which have been hesitant to enter the market due to crease issues—to participate. This is projected to significantly improve consumer satisfaction and accelerate the growth of the stagnating foldable market.

Professor Phil-Seung Lee stated, "We have solved a challenge that global giants could not resolve, using a relatively simple and clear method. We expect this technology to spread across next-generation displays, including laptops and tablets, further strengthening Korea's technological competitiveness."

Meanwhile, this research was conducted with support from the "2022 Daedeok Innopolis Campus Project," and the patent for the related original technology was registered on September 9, 2025.