Research Background
Micro-light-emitting diodes (Micro LEDs) are electroluminescent devices fabricated from inorganic epitaxial materials such as gallium nitride, with sizes typically smaller than 50 micrometers. Due to their excellent performance in brightness, integration, and stability, Micro-LEDs are heralded as key light-emitting units for next-generation display technologies. Currently, while Micro-LED monochrome microdisplay technology is relatively mature, full-color microdisplays still face numerous technical challenges, including difficulties in transferring tiny pixel sizes and complex vertical stacking integration processes. Recently, color conversion technology has proven effective for achieving full-color Micro-LED displays, necessitating the integration of color conversion materials into blue Micro-LED chips. However, existing reports on full-color Micro-LED microdisplay devices primarily encounter issues such as significant “blue backlight leakage” and low “color pixel integration yield,” which serve as bottlenecks hindering industry development.
Article Introduction
Professors Anlian Pan and Ziwei Li, along with Dr. Jianhua Huang, from Hunan University, collaborated with Hunan Normal University, Noshit Technology, and Jingneng Optoelectronics to develop a Micro LED full-color integration process based on quantum-dot color conversion pixels. This innovation achieved ultra-high brightness and pixel density in Micro LED full-color microdisplay chips. The team utilized ligands with chlorosulfonyl and silane groups as synthetic ligands and surface treatment materials for quantum dots, enhancing the stability of quantum dot photoresists and the interface adhesion of quantum dot pixels, thereby realizing a high-density array integration of sub-5 micrometer quantum dot pixels. The fabricated 0.39-inch microdisplay can dynamically display images and videos, with a peak brightness exceeding 400,000 nits and a pixel density of 3300 PPI, achieving a color gamut of 130.4% NTSC and an effective operational lifespan of over 1000 hours at ultra-high brightness, surpassing commercial OLED performance. These results advance mature integrated circuit technologies into microdisplay manufacturing and clarify the path toward industrializing full-color Micro LEDs, with related findings published in Advanced Materials.
Research Content
1. High-Efficiency Quantum Dot Photoresists
To effectively mitigate blue backlight leakage issues, it is crucial to enhance blue light absorption within the limited thickness of the color conversion layer, thereby improving the light absorption and photoluminescence conversion efficiency of quantum dots. In the synthesis of perovskite quantum dots, the research team optimized the use of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CES) as the surface ligand. Compared to traditional surface ligand materials, CES features a functional group (S=O) with higher electronegativity, facilitating the formation of chemical bonds with precursor perovskite small molecules for protection. This results in the synthesis of small-sized (average size of 10 nm), highly uniform quantum dots. Steady-state fluorescence spectral tests and transient absorption tests indicated that CES-ligand-passivated perovskite quantum dots exhibit higher fluorescence quantum yields, longer exciton lifetimes, and superior photoluminescence efficiency.
2. Quantum Dot Color Conversion Pixel Stacking Process
During the integration of sub-5 micrometer quantum dot pixel lithography, insufficient interfacial adhesion can lead to uncontrolled “delamination” of pixels, severely impacting manufacturing yield. The research team developed a surface pretreatment process by spin-coating CES ligand molecules on blue Micro-LED matrix pixels. Under UV lithography exposure, these ligand molecules form chemical covalent bonds with quantum dot photoresists, significantly enhancing the adhesion at the pixel interface and achieving wafer-scale patterning for sub-5 micrometer pixel integration with a yield of up to 100%.
3. Micro-LED Full-Color Monolithic Integration Technology with Quantum Dot Pixels
The full-color Micro-LED monolithic integration manufacturing process necessitates the development of a series of semiconductor integration techniques. The research team employed silicon-based gallium nitride wafers as light-emitting chips, first integrating the light-emitting chip with an IC driver chip, followed by micro-nano processing to fabricate blue light-emitting pixels. By depositing a mixed metal “isolation wall” microstructure between pixels, effective isolation of optical crosstalk was achieved, and light efficiency of the color conversion pixels was enhanced. A layer of quantum dot color conversion pixels, measuring 5-6 micrometers, was fabricated within a 5×5 µm blue light-emitting pixel area, achieving 100% blue backlight absorption and resulting in ultra-high brightness red and green pixel arrays.
4. 0.39-Inch Micro-LED Full-Color Microdisplay Chip
The research team optimized the lithography process and achieved stacked arrays of red and green quantum dot pixels through multiple alignment exposures, producing a 0.39-inch Micro-LED full-color microdisplay chip. Within a physical size equivalent to a quarter of a coin, the display achieved controllable dynamic display of 1024×780 high-density pixels. By connecting the display to a computer or smartphone via a video data line, dynamic images were displayed. The microdisplay showcased performance advantages such as a wide color gamut, high color purity, and stability. Compared to Micro-LED devices based on gallium nitride, perovskite-based light-emitting devices, and quantum dot color conversion integrated light-emitting devices, this microdisplay far surpasses existing technologies in green and red color brightness, achieving a record for color screen brightness in the microdisplay industry.
Summary and Outlook
In conclusion, this article presents a scalable production strategy for Micro-LED full-color display monolithic integration, achieving extremely high peak brightness and effective operational lifespan. The quantum dot pixel-stacked Micro-LED full-color microdisplay chip demonstrates excellent dynamic display functionality, with a high pixel integration density of 3300 PPI, a color gamut of 130.4% NTSC, and a peak brightness of 400,000 nits. This achievement represents a milestone breakthrough in microdisplay technology, exploring a pathway for the industrial production of microdisplay chips.
Acknowledgments
We thank the National Key Research and Development Program, the National Natural Science Foundation, and the Hunan Provincial Natural Science Foundation for their support.
Authors: Jianhua Huang†, Ziwei Li†, Youliang Zhu†, Liuli Yang, Xiao Lin, Yi Li, Yizhe Wang, Yazhou Wang, Yi Fu, Weidong Xu, Ming Huang, Dong Li, Anlian Pan
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