Achieve Next Generation Full Color Micro-LED Pixel Array by Innovative Nanotechnology

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Professor Hao-Chung Kuo and his students take a photo with the CTO of EPISTAR after winning the science competition.

Recent research conducted by Professor Hao-Chung Kuo’s research team (Department of Photonics, National Chiao Tung University) in collaboration with SIJ Technology Inc. showcased the application of nanostructure stress modulation and high-precision quantum dot spray coating on nanostructure and the cooperative development of monolithic integrated RGB Micro-LED components. The research results have demonstrated that mass transfer could be simplified for manufacturing full-color Micro-LEDs display, and the above results have correspondingly been published in the internationally renowned scientific journal Scientific Reports [1] and Photonics Research [2]. The related research results also win the champion of the 2019 EPISTAR science competition.

As blue and green LEDs use InGaN as the active material which has piezoelectric properties due to its crystal structure, their strong built-in electric fields affect the light emission wavelength and the carrier recombination efficiency. This effect is known as the quantum-confined Stark effect (QCSE), which is one of the main factors that impede LED light emission efficiency. Using the nature of the QCSE, the team of researchers developed a novel nanostructure on green epi-wafers to release stress from the LED active region, which in turn successfully modulated the light emission wavelength from green to blue. Light intensity reduction due to the nanostructure sacrificing parts of the light-emitting area along with the reduction in Micro-LED size has also increased the scale of the effects of the side surface defects on the chip that further lowers the luminous efficiency. As a result, Professor Hao-Chung Kuo and his team integrated the atomic layer deposition (ALD) thin-film passivation protective technology to replace traditional plasma-enhanced chemical vapor deposition (PECVD) methods. Using the ALD passivation layer’s properties of high reproducibility, step coverage, and effectively repairing defects, the team has successfully avoided carriers being trapped by surface defects and, as a result, enhanced the component’s luminous intensity and efficiency.

In this work, the dimensions of every RGB subpixel prepared were only 3´10 μm2, precise quantum dot material spray coating on small areas have also become one of the biggest highlights of the research. As shown in the figure below, the high-precision quantum dot spray coating technology by which the research team implemented was able to uniformly spray coat line widths of 1.65 μm, satisfying the requirement of the experiment.

In conclusion, the research collaboration team led by Prof. Kuo has developed a brand new Micro-LED that supports full-color micro-display. They implemented ALD technology to improve the luminous efficiency of the Micro-LED, while simultaneously using the non-radiative energy transfer mechanism to enhance quantum dot color modulation efficiency. This research also probes into preparation processes of quantum dots and nanostructure Micro-LED technology, creating a new path and trend of thought for Micro-LED full-color display.

[1]        S. Wang et al., "Wavelength tunable InGaN/GaN nano-ring LEDs via nano-sphere lithography," Scientific Reports, vol. 7, p. 42962, 2017.

[2]    S.-W. H. Chen et al., "Full-color monolithic hybrid quantum dot nanoring micro light-emitting diodes with improved efficiency using atomic layer deposition and nonradiative resonant energy transfer," Photonics Research, vol. 7, no. 4, pp. 416-422, 2019.

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