A new publication from Opto-Electronic Science discusses the application of lasers in the fabrication of high-efficiency full-color micro-LED displays.
Micro-light-emitting diode (micro-LED) displays with a size smaller than 50 × 50 μm2 has been regarded as the next-generation display technology. Compared with liquid crystal displays and organic LED technology, micro-LEDs has many advantages such as long lifetimes, high efficiency, etc. Micro-LEDs also present great potential in many fields, such as virtual reality (VR)/augmented reality (AR) and smart watches. However, there remain multiple challenges to their commercialization. For example, the mass transfer yield of pixels in micro-LED displays should achieve 99.999%; researchers should develop nano-processing technologies with higher efficiency and accuracy; it is urgent to optimize the efficiency and accuracy of the defective detection and repair processes for micro-LED modules; the performance of the quantum dots color conversion layers (QD-CCFs) should be improved. In conclusion, the low cost, high precision, and high efficiency technologies for full-color micro-LED displays are essential to be developed.
For the advantages of lasers in brightness, directivity and monochromaticity, it is considered as as “the fastest knife”, “the most accurate ruler” and “the brightest light”. Recently, laser-based technology has attracted attention for their application in the manufacturing process of micro-LED full-color displays, such as chip dicing, geometric shaping, lift off, defective repair, mass-transfer and QD-CCFs modification. With the widespread application of lasers, the commercialization of full-color micro-LED displays could be vigorously promoted.
The research group of Rong Zhang / Tingzhu Wu from Xiamen University and Hao-Chung Kuo from Yang Ming Chiao Tung University reviewed the application of lasers during the fabrication processes of micro-LEDs, including nano-processing, defective detection and repair, mass transfer, and QD-CCFs, as shown in Fig. 1. In addition, the difference between laser-based technologies and traditional technologies are discussed, and the research status and application prospects of laser technologies during the fabrication processes of micro-LED full-color displays are introduced in detail, these results provide a reference towards low-cost fabrication of high-efficiency full-color micro-LED displays.
Traditional diamond dicing and plasma dicing technologies still face many challenges during the wafer dicing processes of micro-LEDs, thus the UV-laser dicing technology with high precision has attract great attention. For the limit of accuracy, traditional wet etching and plasma etching is only suitable for processing the geometry shape of micro-LEDs, thus the laser-based technologies such as laser drilling or laser scribing with high precision could be used for processing the nanostructures of micro-LEDs. In addition, instead of nanosecond lasers, people have used ultrafast lasers to reduce the thermal damage during LLO processes, the schematic and physical mechanism of the LLO processes is depicted in Fig. 2(a–d), and the laser machining setup is illustrated in Fig. 2 (e). As shown in Fig. 2(f), by using the high-energy pulsed laser beam to penetrate the sapphire substrate and to evenly scan the interface between the sapphire substrate and the epitaxial GaN material, the separation of the substrate and chips could be achieved. Moreover, the application of micro-LEDs in many fields still faces the challenges of high-efficiency detection, location, and removal of defects. Therefore, the PL defect detection technique using lasers with the advantage of no contact and ultrahigh detection efficiencies has attracted attention.
High-efficiency full-color micro-LED displays
The mass-transfer yield requirement for micro-LEDs should exceed 99.999%, related technological breakthroughs are the key to achieving low-cost fabrication of high-efficiency full-color micro-LED displays. As shown in Fig. 3(a-d), many technologies such as stamp transfer printing, Roll-to-Roll transfer, fluid self-assembly (FSA) mass transfer, two-dimensional materials-based layer transfer and laser-induced forward transfer (LIFT) have been proposed. For the noncontact advantages of laser-assisted mass transfer, we summarized the principle and differences of LIFT, laser direct writing (LDW), thermomechanical selective laser-assisted die transfer (tmSLADT), and selective laser lift-off (SLLO) mass-transfer technologies, as shown in Fig. 3(e).
There are many advantages of using QD-CCFs for full-color micro-LED displays. However, the stability of QD-CCFs should be enhanced in the application of displays. In addition to the calibration of the inkjet-printing system, laser-based technologies could also be used to regulate the defect density, phase transition, grain size and other aspects of the perovskite QD-CCFs, thereby improving the performance of the micro-LED full-color displays.