Abstract
MicroLED displays have been in the spotlight as the next-generation displays owing to their various advantages, including long lifetime and high brightness compared with organic light-emitting diode (OLED) displays. As a result, microLED technology1,2 is being commercialized for large-screen displays such as digital signage and active R&D programmes are being carried out for other applications, such as augmented reality3, flexible displays4 and biological imaging5. However, substantial obstacles in transfer technology, namely, high throughput, high yield and production scalability up to Generation 10+ (2,940 × 3,370 mm2) glass sizes, need to be overcome so that microLEDs can enter mainstream product markets and compete with liquid-crystal displays and OLED displays. Here we present a new transfer method based on fluidic self-assembly (FSA) technology, named magnetic-force-assisted dielectrophoretic self-assembly technology (MDSAT), which combines magnetic and dielectrophoresis (DEP) forces to achieve a simultaneous red, green and blue (RGB) LED transfer yield of 99.99% within 15 min. By embedding nickel, a ferromagnetic material, in the microLEDs, their movements were controlled by using magnets, and by applying localized DEP force centred around the receptor holes, these microLEDs were effectively captured and assembled in the receptor site. Furthermore, concurrent assembly of RGB LEDs were demonstrated through shape matching between microLEDs and receptors. Finally, a light-emitting panel was fabricated, showing damage-free transfer characteristics and uniform RGB electroluminescence emission, demonstrating our MDSAT method to be an excellent transfer technology candidate for high-volume production of mainstream commercial products.
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Data availability
The data that support the plots in this study are available in figshare with the identifier https://doi.org/10.6084/m9.figshare.21992711.
Code availability
No custom code or mathematical algorithm was used in this study.
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Acknowledgements
We would like to thank all the engineers of the Materials & Devices Advanced Research Center involved in this work for their contribution.
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Authors and Affiliations
Contributions
W.C. conceived and designed most of the simulations and the experiments. W.C. also wrote the manuscript. J.K. supervised the self-assembly processes and all simulations. M.K. designed and conducted all simulations. M.K. analysed the high-speed video images and fabricated the RGB microLED panel. M.W.L. contributed the theoretical aspects of this work. G.K. performed and analysed all the self-assembly processes. G.K. also measured the electroluminescence and the I–V characteristics of the RGB microLED panel. M.K., C.H.L. and S.H. fabricated the RGB microLEDs. J.C. fabricated the assembly substrates and carried out the literature review. Y.H.M. analysed data related to the fabrications and the self-assembled structures of the microLEDs. K.J. supervised the overall results of this work. J.K. and S.K. supervised the fabrication and the characterization of the RGB microLED panel. Y.-H.C. provided notable revisions of the manuscript. Y.-H.C. and J.S.L. supervised the project and advised on the overall results in the manuscript. All authors discussed the results.
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Extended data figures and tables
Extended Data Fig. 1 Schematic cross-sectional view of microLEDs.
a, Schematic of the GaN-based microLED. A ferromagnetic material (nickel) is embedded in a half-moon shape of n-contact metals (Cr/Ti/Ni/Ti). The sidewalls and top are surrounded by a 500-nm-thick SiO2 layer. A titanium metal layer is included on the bottom. The thin layers of multiquantum wells are not shown because they were not applied in the COMSOL simulations. b, Schematic of the AlGaInP-based microLED. A ferromagnetic material (nickel) is embedded in the ring-shaped n-contact metals (AuGe/Au/Ti/Ni/Ti). The separation between the Ni layer and the edge of the microLED is indicated by the dashed lines; this separation prevents the microLEDs from adhering together owing to magnetization after magnetic manipulation (figure not drawn to scale).
Extended Data Fig. 2 Transfer yield under the optimal voltage (12 Vpp).
Transfer yield from 15 repeated experiments on a 75 mm × 75 mm assembly substrate. The average of the 15 transfer yield values is 99.99%.
Extended Data Fig. 3 Transfer yield of FSA with element size.
The data from previous studies are categorized into capillary force (open circles) and surface tension (open triangles). The respective reference numbers are provided in square brackets. The yield in this work is marked with a closed circle.
Extended Data Fig. 4 Microscope image of RGB microLEDs and the DEP force from COMSOL simulations.
Microscope image of AlGaInP-based red LED with a microLED size of 38 μm diameter (a), GaN-based green LED with a microLED size of 45 μm × 31 μm (b) and GaN-based blue LED with a microLED size of 52 μm × 24 μm (c). All scale bars denote 20 μm. d, Change in the DEP force with frequency at a fixed value (12 Vpp) of the applied voltage. e, Change in the DEP force with frequency at a fixed value (12 Vpp) of the applied voltage with modified RGB microLEDs that have a metal layer (titanium) on the bottom surface.
Extended Data Fig. 5 Schematic diagram of a 3D model for COMSOL simulations and variation of the DEP force with three factors.
a, Schematic diagram illustrating three factors (gap ratio, LED chip size and dielectric layer) that influence the DEP force. The gap ratio is defined as the ratio of the distance between the two assembly electrodes to the diameter of the LED. Change in the DEP force as a function of gap ratio, LED chip size and a dielectric layer of SiO2 (b) or Si3N4 (c), respectively.
Supplementary information
Supplementary Video 1
MDSAT method. Video of MDSAT assembled with 12 Vpp and 100 kHz of an applied voltage.
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Chang, W., Kim, J., Kim, M. et al. Concurrent self-assembly of RGB microLEDs for next-generation displays. Nature 617, 287–291 (2023). https://doi.org/10.1038/s41586-023-05889-w
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DOI: https://doi.org/10.1038/s41586-023-05889-w
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