The industry defines different LED technologies according to the size of the LED chip. For example, when the size of the LED chip is less than 150 μm, it is called a mini LED; and when the size of the LED chip is less than 50 μm, it is called a micro LED. As the size of backlight LED chips becomes smaller and smaller, the structure of the display panel also changes accordingly.
When the size of the LED chip is as small as the pixel level, each pixel corresponds to a micro LED chip. Since the micro LED can emit light by itself, it can control the brightness, brightness and color. Compared with the traditional LCD screen, the micro LED can save the liquid crystal layer and filter structure.
The screen structure of micro LED is close to that of OLED, and both have the characteristics of self-illumination of pixels, simple structure and high luminous efficiency. However, the material life of micro LED is much higher than that of OLED, and its stability is also stronger.
From the perspective of technological maturity, micro LED is still a certain distance from the real large-scale mass production, and its mass production cost is still high. In fact, OLED also went through this period in the early years. Although the cost of large screen of OLED is still much higher than that of LCD, it has reached the range that can be accepted by ordinary home users.
Judging from past experience, as micro LED technology matures, will OLED and LCD (mini LED belong to the LCD category) be replaced? Perhaps the answer is not that simple.
Micro LEDS Are Still a Long Way from Making Big Screens
First of all, it needs to be clear that it is difficult to apply micro LEDs to large panels in the early stage of development. Just like OLED, the micro LED large panel process is greatly limited by yield and cost.
LED chips are getting smaller, and the value it brings is greater than everyone expected. If you look at the manufacturing process of the micro LED, it grows from the wafer and eventually needs to be transferred to the back plane of the screen. If the resolution of a screen is 1,920 × 1,080, the number of pixels on the screen exceeds 2 million, and each pixel consists of three sub-pixels of red, green and blue. If it is a micro LED screen, it means that there are 6 million micro LED chips on this screen.
With contemporary semiconductor manufacturing processes, it is not difficult to grow 6 million micro LED chips on a wafer, the difficult thing is to transfer these 6 million micro LED chips to the backplane. The industry calls this transfer process a mass transfer. Even the high-end mini LED screens on the market, such as the 2021 iPad Pro 12.9", have only 10,000 mini LEDs in the backlight layer. Therefore, mass transfer is a major difficulty in micro LED manufacturing.
Different solutions exist on the market for the mass transfer problem. Among them, the two main categories are: whole-piece transfer and batch pick-and-place. Whole-chip transfer is suitable for small-sized screens, because the screen panel is small enough, so it can be transferred as a whole; the technology of picking and placing in batches is more difficult, and large screens can only use this solution to achieve mass transfer.
Mass transfer isn't the only technical hurdle in micro LED panel manufacturing, but it's the watershed that constrains micro LED manufacturing for large and small screens - of course, how big a screen can be depends largely on cost, as demonstrated for the first time by Samsung and Sony Micro LED large-screen TVs all cost over a million US dollars.
At the display technology exhibitions in recent years, the micro LED products displayed by manufacturers have become more pragmatic. At this year's SID Display Week, the micro LED products displayed by Tianma Microelectronics, AUO, Chitron Technology and other manufacturers are all aimed at small screen applications such as automotive dashboards and electronic paper. Of course, even if the display is a large-screen application, the current parameter advantages have not greatly surpassed OLED/LCD.
Opportunities At This Stage
The obvious advantages in structure determine the characteristics of micro LED's high pixel density, high brightness, high contrast, and fast response. High pixel density, high brightness and high contrast can be significantly perceived from the structure. In previous prototype product demonstrations, manufacturers have demonstrated displays with tens of thousands of ppi (pixels per inch) pixel density.
Since the micro LED chip is small at the pixel level, it can display true black with no light from a single pixel. At the same time, ultra-small LEDs in micro LED displays are more efficient in converting electricity into photons, and micro LEDs are brighter than OLEDs and LCDs; based on higher electron mobility, micro LEDs can switch at nanoseconds (ns). )grade. Due to the limitations of the manufacturing process, micro LED is only suitable for small screens in the early stage, for example, it is especially suitable for AR/VR applications, including goggles for entertainment.
AR/VR's requirements for display brightness, contrast, pixel density and response are much higher than those of mobile phone consumer electronics products. It is technically difficult for LCD and OLED to meet the needs of such applications. Many consumers have reported that the current AR/VR applications are prone to dizziness and lack of immersion. In fact, this is largely limited by the technology itself of LCD and OLED. The application of micro LED in the field of AR/VR has significantly overcome this problem. Perhaps the key to the future development of AR/VR depends on the breakthrough of micro LED technology.
In addition, the miniaturization of micro LED chips is conducive to the softness and transparency of the panel. Chitron Technology has demonstrated a soft + transparent screen. "Softness", "transparency", and "foldable" are the hotspots of screen display technology in the past two years, and to some extent are the keys to achieving industrial breakthroughs.
ESMC analysts learned from LED chip manufacturers upstream in the panel supply chain that the early application of micro LEDs will focus on wearable devices, AR, VR, and automotive small screen products, which is a logical thing from a technical point of view.
It is worth mentioning that although micro LED has many technical advantages over LCD/OLED, some of these advantages are still in the theoretical stage. A more representative one is the external quantum efficiency (EQE) - which can be understood as the luminous efficiency. Compared with LCD, the screen structure of micro LED display removes the liquid crystal, color filter, and polarizer. Compared with OLED, it does not require complex packaging technology. In theory, the luminous efficiency of micro LED display is much higher than the latter two.
However, the extremely small size of micro LEDs makes the chip very susceptible to sidewall effects - an engineering issue that arises in the manufacturing process, so the actual EQE of micro LEDs is extremely low, and may not even be comparable to LCD or OLED. The existence of sidewall effects also makes it more difficult for micro LEDs to produce ideal large-screen applications. Therefore, the existing micro LED solutions on the market are far from reflecting the technical advantages of micro LED itself.
Complementary Application with LCD/OLED
Various technical challenges of micro LED are difficult problems that many market players are trying to solve. The technical characteristics of micro LEDs also determine the changes in the structure of the display industry chain in the future. The miniaturization of micro LEDs will further tilt panel manufacturing towards semiconductor technology.
CMOS is limited to small size screens. CMOS will also face cost issues when producing large-size screens. Therefore, amorphous silicon and low temperature polysilicon TFTs are still the necessary technologies for the manufacture of large-screen micro LEDs.
Early observations of micro LEDs from Hendy Consulting suggest that there may be a value shift in the micro LED supply chain. This is determined by its technical characteristics. As micro LEDs gradually move closer to IC manufacturing, they challenge the status of traditional panel manufacturers.
It is expected that there will be four possibilities in the future industry chain: the first is that traditional display industry players (such as Samsung, LG) are still in the center, but the value will be diluted; the second is that manufacturers with vertical integration capabilities, such as Apple- acquired LuxVue and Google-invested Glo AB will occupy a dominant position in the micro LED world; the third is the composition of the new industrial structure, and the industrial value may be transferred to LED chip manufacturers, semiconductor manufacturers and enterprises holding key IP ( or multi-party cooperation) transfer; the fourth is that micro LED may not become the mainstream of the market.
Judging from the market trends of South Korea, Taiwan and China in the past two years, micro LED related investments are increasing on a large scale, and upstream and downstream companies in the industry chain are also actively cooperating. Before 2018, the market players of micro LED were independent, and different companies had different technical directions, and these technical directions were very different.
Considering that micro LED manufacturing technology may need to be application-oriented, to customize a systematic manufacturing process - this is very different from LCD/OLED. The situation of independent management is not conducive to the market development of micro LED, and there are different technical directions and no common standards for a certain type of technology, which is just the performance of the industry in the early stage of development. Beginning in 2020, there has been a lot of cooperation in the industry, which is a sign that micro LEDs are maturing.
The market variables are very large, and ESMC analysts believe that the industry development direction analyzed by Hendy Consulting may be too simplistic. In his view, it is not only the changes in market investment and cooperation trends in the past 1-2 years, but also the possibility of long-term development of micro LEDs in the future.
Just as OLED did not completely replace LCD in the past, as a technology with development potential in small screens and AR/VR in the early stage, micro LED is very likely to coexist with OLED and LCD for a long time. It's just that the application directions of the three are different. For example, micro LED focuses on the small screen and AR/VR market, and eats up part of the value of OLED and LCD in the high-end market. Although the market size of OLED and LCD will shrink, the three will form a subtle complementary relationship in terms of technology and market, rather than micro LED replacing OLED or LCD.
