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随着显示技术的不断发展, 高度微型化和集成化成为显示领域主要的发展趋势. 微米发光二极管(light-emitting diode, LED)显示是一种由微米级半导体发光单元组成的阵列显示技术, 在亮度、分辨率、对比度、能耗、使用寿命、响应速度和稳定性等方面相比于液晶显示和有机发光二极管显示均具有巨大的优势, 应用前景十分广阔, 同时也被视为下一代显示技术. 目前商用的5G通信技术与显示领域的虚拟现实、增强现实和超高清视频等技术的结合, 将进一步推动微米LED显示产业的发展. 在面临发展机遇的同时, 微米LED显示领域也存在着一些基础科学技术问题需要解决. 本文主要总结了微米LED显示从2000年以来的一些研究进展, 重点介绍了微米LED显示在外延生长和芯片工艺两方面存在的主要问题和可能的解决方案. 在外延生长方面主要介绍了缺陷控制、极化电场控制和波长均匀性等研究进展, 芯片工艺方面主要介绍了全彩色显示、巨量转移和检测技术等进展情况, 并对微米LED显示在这两方面的发展趋势进行了讨论.The continuous miniaturization and integration of pixelated devices have become a main trend in the field of display. Micro light-emitting diode (micro-LED) display is composed of an array of LEDs that are sub-50-micrometers in length. It has huge advantages in brightness, resolution, contrast, power consumption, lifetime, response speed and reliability compared with liquid crystal display (LCD) and organic LED (OLED) display. Consequently, micro-LED display is regarded as the next-generation display technology with high potential applications, such as virtual reality (VR), augmented reality (AR), mobile phones, tablet computers, high-definition TVs and wearable devices. Currently, the combination of commercial 5G communication technology with VR/AR display, ultra high definition video technologies will further prompt the development of micro-LED display industry. However, some basic scientific and technological problems in micro-LED display remain to be resolved. As the chip size shrinks to below 50 μm, some problems that are not serious for large-sized LEDs appear for micro-LEDs. These problems include crystalline defects, wavelength uniformity, full-color emmision, massively tranferring and testing, etc. In the past two decades, various solutions to those problems have been proposed, which have greatly promoted the progress of micro-LED display. In this paper, an overview of micro-LED display since 2000 is given firstly, which includes the main research results and application achievements. Secondly the issues involved in the wafer epitaxy and chip process of micro-LEDs and possible solutions are discussed based on the display application in detail. The surface state induced by the dangling bonds and dry etching damages are concerned for the nonradiative recombination at a low injection level. The remedies are provided for those surface states, such as atomic-layer deposition and neutral beam etching. Some methods to reduce the threading dislocation and suppress the polarization field are summarized for micro-LED epitaxial growth. Moreover, the GaN-based LEDs on Si (100) substrate are also introduced for the future integration of micro-LEDs into the Si-based integrated circuits. As to the wavelength uniformity, the MOCVD equipment and growth technology including the laser treatment are discussed. In the chip processing part, the full-color display, mass transfer and effective inspection technology are discussed. Assembling RGB individual LEDs, quantum dot phosphor material and nanocoloumn LEDs are different routes for full-color display. Their trends in the future are provided. The pick and place, laser lift-off technologies, are strengthened in the massively transferring for micro-LEDs. In the massively and rapidly inspection technologies, the photoluminscence combined with Raman scattering, the electroluminescence combined with digital camera are discussed. Finally, the summary and outlook in these issues are also provided.
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Keywords:
- micro light-emitting diodes/
- display/
- epitaxy/
- chip process/
- inspection
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Year Substrate Pixel size/μm Pixel pitch/μm Array Wavelength Group Reference 2001 Sapphire 12 50 10 × 10 Blue Jiang H X, et al. [5] 2004 Sapphire 20 30 64 × 64 UV Dawson M D, et al. [6] 2011 Sapphire 12 15 640 × 480 Green/Blue Jiang H X, et al. [13] 2013 Sapphire 50 70 60 × 60 RGB/UV Liu Z J, et al. [7] 2014 Sapphire 15 ~20 256 × 192 Blue Lau K M, et al. [8] 2014 Si 45 100 10 × 10 Blue Dawson M D, et al. [14] 2015 Sapphire 35 40 128 × 128 RGB Kuo H C, et al. [10] 2017 Si 2 3 — Blue Templier F, et al. [11] 2017 Sapphire 5 10 873 × 500 Green/Blue Templier F, et al. [15] 2019 Si — 40 64 × 36 Blue Lau K M, et al. [16] 2019 Sapphire 3 × 10 — — RGB Kuo H C, et al. [17] 2020 Sapphire 3.6 5.6 — Green Wang T, et al. [12] -
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