Color-converted full-color Micro QLED microdisplay technology

Metaverse is a platform to connect digital and physical realities, enabled by immersive technology of augmented reality (AR) and virtual reality (VR). As crucial components of AR technology, microdisplay panels have attracted a great number of attentions. To date, there are a few of methodologies to achieve microdisplay panels, including liquid crystal on silicon (LCos), organic light emitting diode on silicon (Micro-OLED), and micro light emitting diode (Micro-LED). However, there are still great challenges to meet the requirements of high resolution and high brightness of AR technology, due to the brightness limitation of LCos and Micro-OLED and the full color limitation of Micro-LED. QLED are emerging as an alternative microdisplay technology due to their high brightness and solution-processed ability. Therefore, it is important to develop high-resolution patterning processing for fabricating high-resolution Micro-QLED, especially the full color panels.

 

In the previous works, the fabrication of Micro-QLEDs strongly relies on the patterning of quantum dots (QDs), motivating the developments of inkjet printing, transfer printing, and direct photolithography of QDs. After a decade of efforts, great successes have been made in patterning process of QDs, resulting in the fabrication of high resolution and full color QDs patterns. To our knowledge, only a few works have evaluated electroluminescence (EL) devices of patterned QDs, due to the challenges of processing compatibility and current leakage between pixels with QLED fabrication process. Therefore, developing simple-process, high-resolution full-color fabrication technology is an urgent requirement for the advancement of Micro-QLED micro-display technology.

 

In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Haizheng Zhong from Beijing Institute of Technology proposed a color-converted full-color Micro-QLED technology route and fabricated a high-resolution full-color prototype. They developed a novel photolithography template assisted processing (PTA) for fabricating Micro-QLEDs, successfully producing blue-emitting Micro-QLED devices with pixel sizes ranging of 2 - 20 μm. Furthermore, they fabricated a high-resolution full-color color-converted Micro-QLED prototype by combining blue Micro-QLED device and dual-color red-green QDCC. The prototype demonstrated an outstanding performance with 1184 ppi resolution and brightness more than 10 000 cd m⁻². This route provides a simple and low-cost fabrication method, promising to accelerate the development of micro-display technology.

 

“The color-converted full-color Micro-QLED structure comprises two key components: blue-emitting Micro-QLED device and patterned red/green quantum dot color conversion arrays (Figure 1). We develop a photolithography template-assisted process for the fabrication of high-resolution Micro-QLED. The workflow consists of three critical steps: (1) Fabrication of the lithography template; (2) Spin-coating of the blue Micro-QLED; (3) Photolithography fabrication of the red/green color conversion arrays.”

 

“Using above fabrication process, we achieve high-resolution blue-emitting Micro-QLED device (Fig. 2) with uniform electroluminescence distribution and a pixel size of 2 - 20 μm. Furthermore, we fabricate a high-resolution full-color color-converted Micro-QLED prototype by combining blue Micro-QLED device and dual-color red-green color conversion arrays. The prototype demonstrated an outstanding performance with 1184 ppi resolution and brightness more than 10 000 cd m^-2.” they added.

 

“QLED is a new lighting emitting device using quantum dots as emitter. By adapting the fabrication processing of lithography or inkjet printing, it can not only produce or large or medium-size display panels such as TV and monitors, but also have potential to fabricate high-resolution micro display panels. Leading display companies like TCL, Samsung, BOE, and Sharp have made significant achievement in developing QLED prototypes. Table 1 summarizes the reported QLED prototypes. Compared with reported routes, the PTA fabrication not only break the resolution limitation of quantum dots patterning, but also avoid materials degradation in the UV exposure. ” they added.

 

“In principle, the resolution of PTA fabrication depends on the Mask Aligner and photoresists. Therefore, the resolution can be further improved to 10,000 ppi using an advanced Mask Aligner. This method will be a “game changer” for microdisplay” the scientists forecast.

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