MicroLED technologies and applications: characteristics, fabrication, progress, and challenges

Micro light-emitting diode (microLED) technology is expected to be used in next-generation displays and other applications due to its many advantages. This paper categorizes, reviews, and analyzes the main challenges and technical solutions in the microLED displays manufacturing process, covering epitaxial growth, wafer fabrication, mass transfer, control circuit, and panel. In the overview section, the comparison between microLED, liquid crystal display, and organic light-emitting diode displays, as well as the various applications of microLEDs, are reviewed. In the same part, the specific challenges of microLED manufacturing are also discussed, including full-color operation, reduced external quantum efficiency (EQE), low-efficiency and low-yield mass transfer, and structure and process design from a system perspective. In the epitaxial growth section, the requirements, problems, and technical developments of epitaxial growth, especially the growth of AlInGaN red LED, have been reviewed. The microLED chip characterization and fabrication section present the reasons for the low EQE of microLEDs and the methods to overcome this problem. This section also includes the unique characteristics and theories of microLEDs, compared with those of traditional broad-area LEDs. Various mass transfer technologies are summarized in the mass transfer section. The design and operation mechanism of the microLED control circuit is discussed in the control circuit and panel section. This section also introduces the manufacturing and performance improvement of the backplane and the panel. The best way to use this review is to read the overview section first, get a big picture of microLEDs, read the chip section to learn about their special features and reasons behind them, and then go to the parts you are interested in.