The principle of inkjet printing and its applications on AR/VR microdisplays

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 alarming rate. Against the backdrop of the COVID-19, the remote office and consumption interaction are increasing. The market is refocusing on AR/VR and increasing its investment in technology applications.

One of the main reasons for the breakout in the market is the breakthrough of new display technology with excellent performance. As a basic element of AR/VR, display devices must have an ultra-high pixel density and a high refresh rate, in addition to a low weight and small volume. At present, liquid crystal display (LCD) and organic light-emitting diode (OLED), two common display technologies, have been applied to near-eye displays (NEDs) and head-mounted displays (HMDs). Due to the low conversion efficiency and Color saturationrapid aging and short life, the development of new display technology has accelerated.

Micro LED has excellent optical performance and long life, which is considered the next generation and ultimate display technology. The minimum pixel size reaches tens of microns and the high pixel density makes it suitable for AR/VR. In addition to high pixel density, full color is also the most important element to realize Micro-LED in AR/VR and the color conversion scheme is an effective method. Quantum dots were inkjet deposited on blue or ultraviolet micro-LED chips printing technology to achieve tricolor luminescence while avoiding mass transfer technology. In recent years, inkjet printing technology has shown great potential in microfabrication due to the advantages of digitization, patterning, additive manufacturing, low material waste and large area printing. In particular, the emergence of super inkjet (SIJ) printing technology can achieve ultra-high-resolution printing with a minimum line width of printing that falls in the sub-micrometer range. It sheds light on the fabrication of a high-resolution color conversion layer for micro-LED to realize full color reproduction, and in particular for the augmented/virtual reality (AR/VR).

The authors of this article published in Optoelectronic Advances overview of the principle of the inkjet printing technique and its application to microdisplay for AR/VR. This review first introduces the advancement of AR/VR technologies, followed by a discussion of the adaptability of micro-LED display technology in AR/VR and the benefit of printing a color conversion layer for micro-LED using inkjet printing technology. The mechanism for energy transfer without radiation and the influence of the thickness of the color conversion layer on the efficiency of the color conversion are discussed. The advantages of SIJ over other printing technologies in resolution are introduced.

In the second part, the printing principle of different inkjet printing technologies were introduced, as well as two important issues: the optimization of ink rheological parameters and the reduction of coffee ring effects. The rheological parameters of ink suitable for each printing technology and the influence of rheological parameters on the printing effect were introduced. Two solutions for the caffeine ring effect and specific enhancement methods were evaluated. Finally, some potential problems associated with the color conversion layer are highlighted, including light crosstalk, blue light absorption, and self-absorption effect. This review article serves as a reference for the areas of inkjet printing technologies, micro-LED full colorization and its application in AR/VR.

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