A research team led by Professor Do Young Rag of the Department of Chemistry at Kookmin University (President Jeong Seung Ryul) has developed an integrated assembly technology capable of precisely positioning micro-LEDs—key components for next-generation displays—in desired locations and orientations, repairing misplaced components, and transferring them to other substrates.

This research proposed a method to integrate multiple manufacturing processes—including mass assembly, chip orientation control, defective pixel repair, and mass transfer, which are considered major challenges in the commercialization of Micro-LEDs—onto a single physical alignment platform.

Micro-LEDs offer advantages such as high brightness, energy efficiency, fast response times, and long lifespan. However, to realize large-area, high-resolution displays, a vast number of Micro-LED chips must be placed at precise pixel locations. In particular, even if high transfer yields are achieved during the fluid-based assembly process, chip misplacement or orientation errors can still occur; therefore, developing technology to effectively repair these issues remains a critical challenge.

△ Photo: Integrated platform for “assembly, repair, and transfer” of micro-LEDs

To address this issue, the research team developed a “dielectrophoresis-based injection-suction printing (DEP-ISP)” technology that combines dielectrophoresis (DEP) with injection-suction printing (ISP). The key to this technology lies in the precise control of the dielectrophoretic forces and rotational torque acting on the micro-LED chips due to an electric field, as well as the fluid forces generated during the injection and suction processes.

Dielectrophoretic forces are used to move the chips to the desired subpixel positions, while rotational torque is used to control the orientation of the chips’ front and back sides. By combining this with injection-suction printing, the technology enables the selective removal of only unnecessary or misaligned chips while retaining those that are properly aligned. In particular, the team implemented a self-correcting repair process in which chips aligned in the correct orientation are secured by dielectrophoretic forces, while misaligned chips are removed using the fluid forces generated during the suction process, after which the empty positions are refilled. This enables assembly, orientation alignment, defect removal, and reassembly to be performed continuously within a single process.

Repeated verification results showed that, following repair, the average assembly yield was 99.8% and the orientation alignment yield was 100%. The research team formed SiO₂ layers on the sides and top of the micro-LEDs to control the chips’ dielectric properties and optimized the interaction between dielectrophoretic forces and rotational torque to improve orientation selectivity. This approach can be extended to designing the structure of the micro-LEDs themselves to facilitate not only future light-emitting characteristics but also assembly and transfer processes.

Unlike conventional fluid-based assembly methods, injection-suction printing allows for the injection of a small amount of chip solution only into the required areas, followed by its recovery. By using dielectrophoretic forces to hold chips in the desired positions while removing unwanted chips via suction fluid forces, the team confirmed the potential to reduce chip and solvent consumption through the repeated use of the same chip solution.

High precision was also achieved in the transfer process. The research team performed PDMS-based transfer while suppressing chip movement using dielectrophoretic forces, achieving a 100% transfer yield with minimal positional displacement. Subsequently, by fabricating an actual micro-LED array and verifying its light emission, they validated the potential for application in device fabrication processes.

This research goes beyond simply positioning chips rapidly during the micro-LED manufacturing process; it demonstrates the potential for an integrated process that can improve yield throughout the entire manufacturing process—from precision assembly to orientation control, defect repair, reassembly, and transfer—by precisely controlling the dielectrophoretic forces, rotational torque, and hydrodynamic forces acting on the chips. Future research will focus on automating the currently manual injection-suction process by integrating pumps, valves, and multi-nozzle dispensers, as well as scaling it up to large-area substrates.

Dr. Eo Yun-jae from the Department of Chemistry at Kookmin University served as the first author of this study, which was led by Professor Do Young Rag as the corresponding author. The research results were published online in the international journal *Advanced Functional Materials* under the title “Dielectrophoretic Assembly, Repair, and Transfer Technology for Micro-LED Display Boosted by Injection-Suction Printing” and were selected as the front cover for the upcoming print issue. This research was conducted with support from the National Research Foundation of Korea.