Microdisplay: Inkjet printing principle and its application in AR/VR microdisplay

CINNO Research Industry Information, with the rapid development of artificial intelligence, image recognition and 5G communication technology, augmented reality (AR) and virtual reality (VR) technologies are developing at an astonishing speed. Against the backdrop of COVID-19, the current remote office and consumer interaction market is increasing. At present, more and more market participants are turning their attention to AR/VR technology and continuously increasing their investment in the application of this technology.

According to foreign media web3byts, in fact, one of the main reasons for the explosive growth of this part of the market is the advancement of new display technologies with excellent performance. As the core component of AR/VR applications and devices, display devices must have ultra-high pixel density and fast refresh rate, and the structure must be small and light. At present, the two main display technologies, liquid crystal display (LCD) and organic light-emitting diode (OLED), have been widely used in near-eye displays (NED, Near-Eye Display) and head-mounted displays (HMD, Helmet Display). However, due to low conversion efficiency and color saturation, fast aging and short life, these solutions still have many areas that need to be improved, which is actually one of the reasons for the accelerated development of new display technologies.

Micro-LED display devices have excellent optical properties and very long life, and have been considered as the next generation and latest display technology. This technology can support designs with a minimum pixel size of tens of microns, and the high pixel density corresponding to this size makes it very suitable for AR/VR applications. In addition to high pixel density, full-color display is also one of the key points for Micro-LED technology to realize AR/VR applications. At present, color conversion scheme is an effective way to realize full-color Micro-LED scheme.

Using inkjet printing technology to deposit quantum dots on ultraviolet or blue Micro-LED chips to achieve the goal of three-color full-color luminescence can well circumvent the bottleneck of mass transfer. In recent years, inkjet printing technology has shown great application potential in the field of micro-manufacturing with its advantages such as digitization, pattern making, additive manufacturing, low material waste and large-area printing. In particular, the emergence of super inkjet (SIJ, Super Inkjet) printing technology can achieve ultra-high resolution pixel printing with the smallest printing line width at the submicron level. It provides a direction for Micro-LED to achieve full-color display, especially the manufacture of high-resolution color conversion layers for augmented/virtual reality.

Recently, researchers from Xiamen University published a paper in the journal Optoelectronics, reviewing the principles of inkjet printing technology and its application in AR/VR microdisplays. The paper first introduces the progress of AR/VR technology, and then discusses the adaptability of Micro-LED display technology in AR/VR, and the advantages of using inkjet printing technology to print color conversion layers for Micro-LEDs. Then, the paper also discusses the effect of non-radiative energy transfer mechanism and color conversion layer thickness on color conversion efficiency, as well as the advantages of super inkjet printing technology SIJ in resolution presentation compared with other printing technologies.

The second part of the paper introduces the printing principles of various inkjet printing technologies, as well as two key issues: the optimization of ink rheological parameters and the improvement of coffee ring effect. In this part, the author first introduces the ink rheological parameters suitable for various printing processes and the effect of rheological parameters on printing effects. Then, two solutions to the caffeine ring effect and specific enhancement methods are reviewed. Finally, the author separately proposed some potential problems related to the color conversion layer, including optical crosstalk, blue light absorption, and self-absorption effects. This journal paper provides a reference for inkjet printing technology, full colorization of Micro-LEDs, and their applications in AR/VR.