Technological advances have given rise to numerous ultra-advanced display technologies that shine in different fields. Micro OLED, known as a fusion of semiconductor and OLED technologies, allows displays to be thinner and more energy saving. Particularly, the application of Micro OLED in AR/VR is highly promising, but what is the difference between this novel technology and the aforementioned Micro LED?

Before comparing the two technologies, we should first know what exactly OLED is and whether Micro OLEDs are simply miniatures of OLEDs.

OLED has been developed for a long time. Using mostly organic materials, the technology does not require backlight modules, as each pixel of an OLED display can independently emit a specific color of light and be switched on and off. OLEDs can therefore facilitate the presentation of amazingly deep blacks with excellent contrast and have lower power consumption compared with traditional LEDs and LCDs.

▲ Countless OLEDs (Source: shutterstock)

Unlike OLED that has already been used in smartphones and TVs, Micro OLED, despite having only an additional “Micro” in its name and being based on OLED, is actually a more complex technology with a completely different target market, namely the market of AR/VR displays.

A Micro OLED comprises an organic luminescent material sandwiched between two electrodes, where the diode emits light when a current flows through. Subsequently, the required colors are generated through color filters. A Micro OLED light source module is produced by attaching OLEDs to a substrate using vapor deposition. To produce a silicon-based OLED module, for example, OLEDs are attached to a silicon substrate (i.e., semiconductor wafer). In addition to their self-illuminating nature like OLEDs, Micro OLEDs help create thinner, smaller, and more energy-saving panels. Their shorter response time and greater luminous efficacy also enables production of high PPI (pixel per inch) monitors.

Micro OLED happens to meet the requirements of AR/VR headset screens and mirrors. Despite being developed for years, AR/VR products are subject to problems of motion sickness, low resolution, large size, and costliness due to immature technology. To avoid motion sickness, specifically, panel resolution must be increased from the existing 500 PPI to 2,000 PPI.

This is where Micro OLED can fit in. Indeed, like its OLED counterpart, Micro OLED is not suitable for large-size displays due to problems of low brightness and uneven aging. However, Micro OLED has a great advantage in the small-size display market. As the application of AR/VR displays gradually shifts from gaming and military fields to medical, education, and retail scenarios with expanded markets, demand for resolution and input lag avoidance will increase. Under such circumstances, next-generation display technologies with high resolution, high luminance, high contrast, and quick response will be developed. Presently, Micro OLED has been used for military, industrial, medical purposes as well as commercial smart glasses.

Don’t Confuse Micro OLED with Micro LED, They Are Different Things

When mentioning Micro OLED, Micro LED—another advanced display technology also starting with “Micro”—is often discussed. Although the two technologies both boast ultra-fine pitch, high resolution, high reliability, and short response time, they largely differ from each other from production processes to applications; only a part of their applications are overlapped.

A Micro LED is defined as a diode measuring ≤ 75μm without a sapphire substrate, of which the epitaxy process differs from that of Micro OLEDs. Because of its high-density, small-size LED arrays integrated on chips, Micro LED can be widely applied to different fields, including wearables, headset displays, AR/VR displays, and even phototherapy. Moreover, because Micro LEDs are composed of inorganic materials, the components tend to be brighter and more stable than OLEDs.

The biggest problems now for Micro LED are how to accurately transfer millions of tiny LEDs to a backplane (i.e., mass transfer) and perform subsequent tests and packaging; the technology is still costly.

By contrast, the size of a Micro OLED is not limited to 75μm; the size of each pixel is defined during the OLED process. Micro OLED mainly adopts the vapor deposition technique; therefore, how to precisely and evenly deposit organic materials (which are easily affected by oxygen and water ) on the target substrate—along with designs of vacuum coating machines, and fine metal masks—are key process factors.

Numerous suppliers are developing Micro OLED, a technology combining CMOS technology (for IC design) with OLED and using monocrystalline silicon as the active-matrix backplane. As Nikkei Asia reported in March, Apple has asked TSMC, its long-term chip supplier, to co-develop an ultra-advanced Micro OLED display.

China and South Korea have never overlooked Micro OLED. Since 2018, the Chinese electronic components producer BOE has worked with its joint venture Kunming BOE to develop Micro OLEDs. An ELEC report indicates that BOE plans to launch a commercial Micro OLED display targeting the AR/VR market in 2Q21, of which the vapor deposition equipment is provided by the South Korean supplier Sunic Systems.

APS Holdings, a South Korea-based display and semiconductor equipment supplier, revealed in May that the South Korean government has assigned it a Micro OLED display project. APS will work with other companies to develop a pair of 4,000-PPI AR glasses by 2024.

In 2020, the French company MicroOLED announced that it received a growth investment of €8 million from two pan European high-tech investors, Cipio Partners and Ventech, facilitating the development of integrated AR modules.

The target of Micro OLED is clearly the small-size display market. Despite its narrow application compared with OLED and Micro LED, Micro OLED has become a popular research topic in recent years, and has been sought after by various manufacturers to strengthen their production capacity and satisfy requirements of different fields. Micro OLED will be a crucial driver of the development of AR/VR technologies and human–machine systems in the next decade. In fact, various Micro OLED products were showcased at display exhibitions in 2020; some of them even feature more than 3,000 PPI.

By 2024, global Micro display production is expected to reach 50 million units, including AR/VR, smart glasses, headset, and head-up displays.

(This article is reposted by TechNews, source of first image: shutterstock)