Japanese company Toyoda Gosei is making waves in the world of tiny displays, announcing progress on a new type of monolithic Micro LED screen that could eventually power brighter augmented reality glasses and other next-gen gadgets with lower costs and higher resolutions. The displays, created by stacking layers of indium gallium nitride (InGaN), achieves red, green, and blue (RGB) three-color emission.

Currently, many micro-displays is engineered with OLED technology, which often struggles to produce enough brightness, especially if they are used outdoors in sunlight – a major problem for applications like AR glasses. The proposed monolithic InGaN Micro LEDs can deliver the necessary brightness for these kinds of applications.

Fig. 1: (a) Cross-sectional structure of Toyoda Gosei’s full-color monolithic Micro LED. (b) Electroluminescence (EL) image of sub-pixels without inter-sub-pixel isolation. (c) EL image of sub-pixels with inter-sub-pixel isolation. (d) Photograph of the fabricated monolithic micro-LED chip.

While the proposed method requires a regrowth process—which is often seen as complex and costly—the researchers argue it might be more practical. Conventional approaches involve using quantum dots or complex ways of connecting different colored layers, which might require specialized equipment.

The team has successfully built a small display with 96x96 pixels, crammed into a display area of around 3mm by 3mm. Initial tests show it can produce red, green, and blue light, the building blocks of full-color display. However, the red light is not as efficient as the green and blue. The color gamut is also much narrower than the researchers’ previous efforts, but they believe that it can be improved by adjusting the red-light-emitting layer.

The research team even showed off a 4-bit grayscale RGB image of a colorful cardinal tetra fish on their tiny screen. While the red in the image was not perfect, it hints at the potential of this technology.

Fig. 2 A cardinal tetra fish displayed on the 3mm Micro LED screen

Indeed, there are still hurdles to overcome, like making the red color brighter and more accurate, but Toyoda Gosei’s progress suggests that brighter, more efficient micro-displays for future technologies like AR and VR might not be too far off. This development could pave the way for sharper and more immersive visual experiences in smaller, more power-efficient devices.

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Release: 31 May / 30 November 2024
Language: Traditional Chinese / English
Format: PDF
Page: 160-180

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