Firstly, review its progress last year. In 2019, progressive alliances and cooperation, as well as more display companies announcements to invest in R&D, were the most important progress last year. Although a small number of new entrepreneurs claim to have obtained new massive transfer technologies, they have not yet achieved the results of mass production, so they are still in the early stages of development.

However, these alliance strategies and the input of new players mean that the feasibility of the Micro LED has been confirmed, and it is no longer an "under evaluation" project, but a commercial project that requires real investment in capital. For example, Ritdisplay and PlayNitride in Taiwan jointly develop Micro-LED wearable products. ITRI cooperated with MACROBLOCK, Unimicron, and PlayNitride to launch collage-type small-pitch Micro LED displays. Epistar and China Leyard establish Li-jing joint venture that develops display solutions for Mini and Micro LED.

Also, Japan's JDI has announced to enter the Micro LED market and locked the display applications of automobiles. LG also demonstrated its Micro LED application for the first time. China's Konka released a series of Micro LED large display products.

Solving the Mass Transfer, Micro LED to mass production in 2022

Although they are all prototype demonstrations and strategy announcements, with more capital and investment from the industry, the development progress of the Micro LED has become more evident. We can tell the situation from the announcements of several industry players last year. For example, AUO said that they could go mass-produce Micro LED in about two years; Epistar also believed that it could enter mass production after 2021; LG planned to mass-produce after two years.

Summarizing the progress of these players, the most likely time for large-scale mass production will be in 2022.

The time for mass production is clarified, which means there are ways to cope with the challenges of mass production. In other words, the mass transfer process of the Micro LED is no longer a problem, and they only need to improve the yield rate. More specifically, at this stage, it is necessary to focus on the production equipment construction and the adjustment of production parameters. The method of mass transfer has been found.

Currently, several commercial potential mass transfer technologies are using stress force to transfer Micro LED dies to PCB, like electrostatic interaction force and Van der Wall's force. Although the number of LED dies is less in one transfer cycle, but this approach can support small die size and more accurate. If it operates by a scalable mechanism, it will have a high chance to enter commercial production.

Such as Lextar, not only minimized the size of LED itself, the company has developed self-own mass transfer technology. According to the Lextar, it uses electrostatic interaction force to pick up Micro LED from the substrate then proceed transfer afterward.

Taiwan’s ITRI demonstrated a scalable Micro LED display module in the CES 2020, which was assembled by new RGB Micro LED mass transfer technology with a high yield rate of 99%. The technology was developed by CIMS, which also a stress-force-based technology.

Rohinni, a startup for the US, is one of the notable Micro LED technology providers. The company not only collaborated with the BOE to establish a joint venture in China but also co-boosted innovative applications of Micro LED with other companies from different domains. The most eye-catching achievement of the company is a patented high speed, and high volume attaches technology.

Mikro Mesa Technology, a Taiwanese startup, announced last year that they had developed a new mass transfer technology successfully, which can transfer 3um of the diameter of Micro LED. According to their announcement that they use a technique named “Pressureless Low-temperature Bonding,” which can improve the yield rate and lower cost. The size of the transfer board is about 4 inches and can transfer millions of Micro LED chips each time. Also, it can proceed patch and multi-color transfer to increase the productivity of large size Full-color monitors. The company is working with CEC-Panda, a Chinese LCD panel maker, scheduled to release their products in two years.

The others like AUO, PlayNitride, Epistar, LG, Seoul Semiconductor, Samsung were all had announced to develop mass transfer technology by themselves and had demonstrated related prototype. Seoul Semiconductor has begun small scale mass production via its subsidiary Viosys. Generally speaking, these companies are all using the method of absorption and attachment, which shows that basic stress-force based transfer technologies can meet the needs of the development of equipment and yield rate in terms of mass production.

Figure 1 : Micro LED mass production schedule of major players.

Large size display come first; Automotive and wearable will be later

Regarding end-user applications, base on current progress, engaged in the large-size outdoor and commercial display had become a common understanding in the industry, especially traditional display providers. Like Samsung, LG, Sony had launched their super large-size commercial, and outdoor Micro LED display solutions.

Strictly speaking, this kind of display solution cannot be classified as the “Micro LED” level. It is a modular LED display. It splices modular LED displays one to another with a small pitch distance, which makes it looks seamless, and to fit the outdoor and commercial display purpose.

The size of the LED of this spliced display is around 50~100um with 100 um of pitch distance. The resolution is not excellent, but it contains the same features of high lightness and high refresh rate. If you look at it from a distance, this product shows competitiveness and easy to deploy in most scenarios by using spliced module design.

Samsung, for example, the size of its second generation of “The wall” showcased at the CES 2020 to reach 292-inch, and total resolution up to 8K. Nevertheless, Samsung had released glass backplane equipped 75-inch and 93-inch active Micro LED display products. Most importantly, the size of the LED itself is keeping shrinking.

The size of LG’s “Real Micro-LED Display” reached 145-inch and spliced with 48 pieces of LPTS display panel. LG claimed that the size of its LED was 50µm. For Sony, they demonstrated a 220-inch display product with a resolution of 4K.

Figure 2 : Schematic diagram of the die size of the Micro LED.

The Micro LED display module from Taiwan’s ITRI was also using a spliced architecture, but it is the industry’s first Micro-LED module, which assembled by mass transfer process that bonding Micro LED chips to PCB directly. It uses 15 small-sized Micro LED modules (100 μm RGB chips) to splice into a 30 x 30 cm Micro LED display with a resolution of 480 x 480 pixels.

Thinking highly of the high lightness and wide-angel view features, many display solution providers are working on developing automotive Micro-LED display products. Its main application scenarios are a car infotainment system. Including Taiwan’s AUO, Innolux, JDI of Japan are all doing R&D of related technologies. AUO and Innolux had demonstrated their prototype products, and AUO even estimated to enter mass production within five years.

Different from the longer seeing distance of large-size display, the automotive Micro-LED need to have a higher resolution. Therefore, it is more challenging to enter mass production. Meanwhile, it takes longer R&D time. Related personnel forecasted that there would be a more transparent commercial schedule after 2023.

In addition to automotive display, wearable devices and other innovative display applications will be the touchstone of Micro LED. Currently, Ritdisplay and Luumii have stepped into this domain. Ritdisplay focuses on smartwatch and wristband display, and Luumii sees itself in the niche consumer display application market.

For wearable devices such as smartwatches and bracelets, Micro LED's most significant advantage is its high brightness characteristics that are comparable to sunlight, and its extremely thin and light display structure. Also, it is only used for displaying information and does not require excellent chromaticity and high resolution. Therefore, as long as the overall production cost can meet the needs of system manufacturers, Micro LED has the opportunity to enter the wearable device market.

There are many applications for Micro LED displays that are worth exploring. It is not necessary to follow the traditional display scenario. Rohinni and KoJa ’s joint venture Luumii uses Micro LED for notebook computer keyboard backlight and logo lighting Application. Through the small size and low power consumption of Micro LED, system product developers can have different explicit design considerations.

Figure 3 : Taiwan Industrial Technology Research Institute adopts the splicing concept on its Micro LED display module. It is the world's first Micro LED display module which directly transferred to the PCB board with the Micro LED chip.

Conclusion

"The revolution in display technology is just beginning," an industry leader said, and this sentence is right in Micro LED technology. However, after several years of evolution, Micro LED is still in its infancy. But is it qualified to be called a revolution? It is the question we have to ask.

If viewed from the process point of view, Micro LED is a revolutionary technology, because it is almost impossible to manufacture and combine tens of millions of micron-level LED die perfectly. But now it seems that there is a chance to do it.

But from an application point of view, Micro LED does not have any revolutionary. Because it only follows the current display thinking, coupled with better specifications, and does not add other new ideas, especially the current mainstream LCD and OLED display technology is very mature. It is not a reasonable idea to push Micro LED firmly with a very high layout cost.

Therefore, looking for innovative applications and differentiation will be the next crucial subject of Micro LED display technology. If there is no broader and more breakthrough application thinking, then Micro LED may only stay in minimal areas. The vision expected by the Taiwanese display industry will be challenging to realize.