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. 2020 May 11:9:83.
doi: 10.1038/s41377-020-0268-1. eCollection 2020.

Micro-light-emitting diodes with quantum dots in display technology

Zhaojun Liu #  1 , Chun-Ho Lin #  2 , Byung-Ryool Hyun  1 , Chin-Wei Sher  3   4 , Zhijian Lv  1 , Bingqing Luo  5 , Fulong Jiang  1 , Tom Wu  2 , Chih-Hsiang Ho  6 , Hao-Chung Kuo  4 , Jr-Hau He  7
Affiliations

Micro-light-emitting diodes with quantum dots in display technology

Zhaojun Liu et al. Light Sci Appl. .

Abstract

Micro-light-emitting diodes (μ-LEDs) are regarded as the cornerstone of next-generation display technology to meet the personalised demands of advanced applications, such as mobile phones, wearable watches, virtual/augmented reality, micro-projectors and ultrahigh-definition TVs. However, as the LED chip size shrinks to below 20 μm, conventional phosphor colour conversion cannot present sufficient luminance and yield to support high-resolution displays due to the low absorption cross-section. The emergence of quantum dot (QD) materials is expected to fill this gap due to their remarkable photoluminescence, narrow bandwidth emission, colour tuneability, high quantum yield and nanoscale size, providing a powerful full-colour solution for μ-LED displays. Here, we comprehensively review the latest progress concerning the implementation of μ-LEDs and QDs in display technology, including μ-LED design and fabrication, large-scale μ-LED transfer and QD full-colour strategy. Outlooks on QD stability, patterning and deposition and challenges of μ-LED displays are also provided. Finally, we discuss the advanced applications of QD-based μ-LED displays, showing the bright future of this technology.

Keywords: Inorganic LEDs; Quantum dots.

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Conflict of interest statement

Conflict of interestThe authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
Pixels per inch roadmap of µ-LED displays from 2007 to 2019
Fig. 2
Fig. 2
Positional relation between leakage spots and defect states. The emission microscopy measurement shows a strong relation between a leakage spots and b etch pits (~1 μm size), confirming the importance of defect control during epitaxy. The dashed line and circles indicate the mesa edge and leakage spots, respectively. Reproduced from ref. with permission from AIP Publishing
Fig. 3
Fig. 3
Size reduction effect on μ-LED performance. EQE of GaN μ-LED as a function of LED size. Data compiled from ref.
Fig. 4
Fig. 4
Sidewall passivation effect in μ-LEDs. a Schematic of the μ-LED structure with ALD deposited SiO2 for sidewall passivation. b Electroluminescence images of the μ-LEDs (sizes from 10 μm to 100 μm) before and after sidewall passivation. c The EQE distribution of different device sizes with and without KOH treatment and ALD sidewall passivation. Reproduced from a, b ref. with permission from OSA and c ref. with permission from Copyright (2019) The Japan Society of Applied Physics
Fig. 5
Fig. 5
Strain relaxation in small LEDs observed by Kelvin probe force microscopy. Topographic and CPD distribution of μ-LEDs with a 10-μm and b 40-μm diameters. The central bright region is the LED mesa. Reproduced from ref. with permission from OSA
Fig. 6
Fig. 6
μ-LED mass transfer techniques. Schematics of a elastomer stamping, b electrostatic/electromagnetic transfer, c laser-assisted transfer and d fluid self-assembly. Reproduced from a ref. with permission from Springer Nature, c ref. with permission from MDPI and d ref. with permission from IOP Publishing
Fig. 7
Fig. 7
μ-LED monolithic integration techniques. Schematics of a metal wiring, b flip chip bonding, c microtube bonding and d adhesive bonding. Reproduced from a ref. with permission from Elsevier, b ref. with permission from AIP Publishing, c ref. with permission from John Wiley and Sons and d ref. with permission from RSC Publishing
Fig. 8
Fig. 8
Process flow of the full-colour µ-LED display with photoresist mould design. a The structure of the µ-LED arrays. b Aligning the mould to the UV µ-LED array. c–e Consequently jetting the RGB QDs inside the mould window to form the full-colour pixels. Reproduced from ref. with permission from Chinese Laser Press
Fig. 9
Fig. 9
Förster resonant energy transfer nanohole design in LEDs. a Schematic representation, b cross-sectional, and c top scanning electron microscope images of a photonic nanohole LED hybridised with QD colour converters. d Time-resolved photoluminescence decays of LED with pure MQW (black line) and MQW-QD contact (red line) structures. Reproduced with minor editing from ref. the Optical Society under the terms of the Creative Commons Attribution 4.0 License
Fig. 10
Fig. 10
Full-colour QD-NR μ-LED display design and performance. a Epitaxial wafer. b Three subpixels of a green μ-LED, a blue NR μ-LED, and a red QD-NR μ-LED. c Deposition of transparent conducting oxide film and p-n electrodes. d Covering DBR filter. e Full-colour QD-NR μ-LED display. f Cross-sectional view of a single RGB pixel. g EL spectra of a QD-NR μ-LED display. h Colour gamut of a QD-NR μ-LED display, NTSC, and Rec. 2020. Reproduced from ref. with permission from Chinese Laser Press
Fig. 11
Fig. 11
Perovskite QDs for wide colour gamut conversion. a Colloidal CsPbX3 (X = Cl, Br, I) QD solutions in toluene under a UV lamp and b their representative PL spectra. c CIE chromaticity coordinates (dark points) from the emissions of CsPbX3 QDs compared with those of commercialised LCD TVs (dashed white line), reaching 140% of the NTSC colour standard (solid white line). Reproduced from ref. with permission from ACS Publications
Fig. 12
Fig. 12
Strategies for improving the stability of perovskite QDs. a A-site or B-site doping. b Surface engineering. c Encapsulation with a polymer or oxide matrix. d More efficient device packaging (i.e., remote-type design can enhance the stability of QDs compared with the prototype structure). Reproduced from a ref. with permission from RSC Publishing, b ref. with permission from AAAS, c ref. with permission from John Wiley and Sons, and d ref. with permission from RSC Publishing
Fig. 13
Fig. 13
Requirements for µ-LEDs in typical applications. Reproduced from ref. with permission from MDPI
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