Kookmin University researchers develop integrated micro-LED assembly technology
Schematic illustration of an integrated platform for micro-LED assembly, repair and transfer / Courtesy of Kookmin University
Single platform combines assembly, repair, transfer processes
A Kookmin University research team has developed an integrated assembly technology critical to the commercial production of micro-light emitting diode (micro-LED) displays.
The university said Wednesday that the technology enables micro-LEDs, key components of next-generation displays, to be precisely assembled at desired positions and in desired orientations.
Led by chemistry professor Do Young-rak, the team has developed a method that integrates several manufacturing processes considered critical to the commercialization of micro-LEDs — including mass assembly, chip orientation control, defective-pixel repair and mass transfer — on a single alignment platform.
The findings 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.” The study was also selected for the Front Cover of an upcoming print issue.
Eo Yoon-jae of the university’s department of chemistry was the first author, while Do was the corresponding author.
The research was supported by the National Research Foundation of Korea.
The university noted that micro-LEDs offer advantages such as high brightness, energy efficiency, fast response times and long lifespans.
However, large-area, high-resolution displays require a vast number of micro-LED chips to be precisely placed at their designated pixel positions.
Even with a high transfer yield through fluidic assembly, some chips may still be misplaced or incorrectly oriented, making effective repair technology a key challenge.
To address these challenges, the research team developed a technology called dielectrophoretic injection-suction printing (DEP-ISP) for fluid assembly of micro-LED chips.
The key to the technology is precisely controlling the dielectrophoretic forces and torque exerted on micro-LED chips by an electric field, as well as the fluidic forces generated during the injection and suction processes.
This method reduces the consumption of the chip-containing solution, controls chip orientation using the DEP field, positions chips through subpixel grooves, and enables repair of misaligned chips.
Using dielectrophoretic forces, the team moves chips to their desired subpixel positions and uses rotational torque to control their orientation and distinguish their front and back sides.
By combining dielectrophoretic forces with injection-suction printing, the process can selectively remove unnecessary or misplaced chips while retaining those that are correctly aligned.
In particular, correctly oriented chips are held in place by dielectrophoretic forces, while misoriented chips are removed by fluidic forces generated during the suction process, after which the vacant positions are refilled.
This self-correcting repair process enables assembly, orientation control, defect removal and reassembly to be performed continuously within a single process.
Repeated validation tests showed an average post-repair assembly yield of 99.8 percent, with an orientation alignment yield of 100 percent.
Going forward, the team plans to automate the manual injection-suction process by integrating pumps, valves and multi-nozzle dispensers and to expand the technology to large-area substrates.