Linewidth distribution of various inkjet printing technologies
Currently, two mainstream display technologies, liquid crystal display (LCD) and organic light-emitting diode (OLED), have been applied to near-eye displays (NEDs) and head-mounted displays (HMDs). However, the development of new display technologies has been accelerated due to disadvantages such as low conversion efficiency, color saturation, and rapid aging and short lifespan.
With excellent optical performance and long lifespan, Micro LED is considered to be the ultimate next-generation display technology. The minimum pixel size reaches tens of microns, and the high pixel density makes it possible for it to be used in AR/VR.
With the rapid development of artificial intelligence, image recognition and 5G communication technologies, augmented reality (AR) and virtual reality (VR) technologies are developing at an alarming rate. In the context of the new crown epidemic, telecommuting and remote consumer interactions are increasing, and the market has once again turned its attention to AR/VR, and investment in technology applications has increased.
According to IDC, from 2020 to 2024, the market size of the global AR and VR industries will grow from 28 billion yuan and 62 billion yuan to 240 billion yuan, respectively. One of the main reasons for the market explosion is the breakthrough of new display technology with excellent performance. As the basic element of AR/VR, display devices should have ultra-high pixel density and fast refresh speed in addition to light weight and small size.
This paper first introduces the research progress of AR/VR technology, and then discusses the research progress of Micro LED display technology and its adaptability in AR/VR, as well as the advantages of preparing Micro LED color conversion layer by inkjet printing technology. The non-radiative energy transfer mechanism and the effect of the thickness of the color conversion layer on the color conversion efficiency; the superiority of SIJ in resolution compared to other printing technologies is introduced.
Letters and school crest logo printed by SIJ technology
In addition to high pixel density, full color is also a key element to realize Micro LED in AR/VR. Among them, color conversion scheme is an effective method to achieve full color. Quantum dots are deposited on blue or ultraviolet Micro LED chips by inkjet printing technology. Three-color luminescence is achieved, while avoiding giant quantitative transfer.
In recent years, technologies such as piezoelectric/thermal inkjet printing, aerosol inkjet printing, electrohydrodynamic inkjet printing, and super inkjet printing have been used to deposit color conversion layers, showing great potential for realizing full-color Micro LEDs . Recently, the team of Prof. Zhang Rong from Xiamen University, in cooperation with Prof. Guo Haozhong from Taiwan Chiao Tung University, published a paper entitled "Principle of Inkjet Printing Technology and Its Application in AR/VR Microdisplays" in Opto-Electronic Advances Issue 5, 2022 "A review article.
The second part introduces the printing principles of various inkjet printing technologies, and two key issues: the optimization of rheological parameters of ink and the solution to the coffee ring effect.
The rheological parameters of ink suitable for each printing technology and the influence of rheological parameters on the printing effect are introduced. Two solutions to the coffee ring effect and specific improvement methods are reviewed. Finally, some potential problems associated with color conversion layers are highlighted, including optical crosstalk, blue light absorption, and self-absorption effects.
Micro LED paves the way for the commercialization of AR/VR, and the manufacture of full-color Micro LED with high pixel density is one of the bottlenecks. The color conversion layer scheme is an effective way to realize full-color Micro LED, and the development of inkjet printing technology provides technical support for the preparation of high-resolution color conversion layers.
Post time: Aug-22-2022