Laser-patterned quantum dot color conversion film for full-color mini/micro-LED displays

Abstract

The display industry is constantly improving the visual experience to meet the increasing demands for cutting-edge display applications, such as augmented reality (AR) and virtual reality (VR). Mini/micro-LED displays are now emerging as the most promising candidates to fulfill those demands owing to their excellent properties of high dynamic range (HDR), high resolution with ultra-fine pitch, and low power consumption. Mini/micro-LED displays can be realized with red, green and blue (RGB) LED chips. However, mini/micro-LED displays based on RGB LED chips suffer from several issues which have hindered the technology from being embraced by major vendors. A patterned quantum dot color conversion (QDCC) film with monochromatic blue LED backlight arrays has proven to be feasible alternative technology. As the technology to fabricate the monochromatic blue LED backlight arrays with down-scaled pixels has become more mature, achieving a patterned QDCC film with desirable converting lights has attracted increasing attention. However, saturated converting colors, adequate production efficiency and process stability are challenging to attain with traditional patterning methods of QDCC layers, such as photolithography or jet printing. This study proposes an innovative laser patterning approach for the QDCC film. The proposed laser patterning approach has been proven with the benefits of high production efficiency, a robust process, process scalability, and saturated converting colors, which can provide a feasible solution for the implementation of full-color mini/micro-LED displays. The first part of the thesis reports the preparation and characterization of the QDCC film. This part discusses the preparation of QD-polymer solutions with enhanced QD concentration and solution stability. The amphiphilic PEG-COOH QD ligands and the toluene solution have been proven feasible for enhancing the stability and QD concentration of chosen QD-photoresist (QD-PR) system. The QDCC film can be achieved by spin coating of QD-PR solution on a glass wafer, and the QDCC film with an optimized film thickness of around 20 μm has been prepared for subsequent patterning procedures. The second part of the thesis focuses on developing the QDCC subpixel arrays based on the laser patterning method. To get an ideal patterning quality, this part summarizes the laser-induced morphology of QDCC film after laser scribing with different parameters. A series of processing parameters that can achieve ideal patterning quality are suggested. Based on the identified laser scribing parameters, the process steps for patterning the red/green QDCC subpixel arrays are illustrated. The third part of the thesis describes the design and fabrication process of the full-color QDCC layer with an enlarged color gamut. This part presents an effective method to enhance the color gamut of QDCC film by direct depositing color filters on QDCC film. The full-color QDCC layer is achieved by the integration of red/green QDCC subpixel arrays. The final part of the thesis reports the implementation of the laser-patterned QDCC layer in full-color mini/micro-LED displays. A passive matrix of blue LED arrays is fabricated, serving as the backlight source for the laser-patterned QDCC layer. A prototype display is assembled, and the optical performance of the display is investigated. The optical crosstalk effect is studied by both simulation and experiments. The optical crosstalk reduction is accomplished by a silicon light confiner. The methods of controlling RGB color brightness to get a white balance are introduced. The strategy for achieving down-scaled full-color pixels using laser patterning technology is discussed.

Date of Award	2022
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Shi-wei LEE (Supervisor)