With the help of mini/micro led technology, the LED display industry is opening up a new application space: 1. Mini led backlight application similar to Apple IPAD, 2. Facing the 4k/8k era, direct LED display, indoors 0.x-150 inches , Micro led smart display large screen in handheld and near-eye applications.
"These will be two future markets that will bring LED technology to hundreds of billions of dollars a year!" This will certainly attract the attention of more and more industry giants. For example, Leyard and TCL Huaxing reached a strategic cooperation in March, and the two parties established a collaborative innovation office. The areas of cooperation include the development of Mini LED backlight modules and new Micro LED products in the COG/MIP mode.
This is the "friendship" between the world's second largest LCD display company and the world's number one brand of small-pitch LED displays. Its strategic impact cannot be said to be insignificant. Prior to this, China Star Optoelectronics has also established a joint laboratory with San'an Optoelectronics, the world's largest LED upstream company. Behind the giants working together is the LED display miniaturization technology, especially the COG/MIP mode TFT-Micro LED products are leaping towards the market!
(COG is an integration process of ultra-fine IC components on TFT glass substrates. The production process of COG products requires a cleanliness level of 1000. MIP refers to Memory-In-Pixel pixel memory technology, which has the advantage of adding traditional liquid crystal display devices. The opening rate is higher and it is more energy-efficient. MIP has a larger application scale on mobile display devices.)
"Solving industry pain points", TFT glass substrate combined with LED large screen
2021 is the first year of mini-led backlight display products. The industry predicts that the application of this new technology will grow 20 times in color TV products alone. However, perhaps many people have found that color TV products using mini-led backlights, "most of the thickness has increased." Why is this?
At present, the increase in the thickness of mini-led backlight color TVs mainly comes from the use of PCB boards in the backlight, and its backlight drive power supply and control system. Because, mini-led backlight means that the display device backlight lamp beads ten times, a hundred times, or even a higher order of magnitude increase. It has higher quality and quality requirements for the driving circuit structure behind it. This has become the fundamental reason for the increased thickness of the final product under the background of its more complex backlight structure and higher stability and redundancy requirements.
However, some products also use mini-led backlight technology driven by TFT glass substrates. The thickness change of this product is even smaller. This is obviously due to the long-term "ultra-thin technology accumulation" in the TFT drive structure of LCD TV products: Although the cost has increased temporarily, the advantages of TFT technology compared with PCB boards are still obvious.
For example, in addition to the thickness issue, the TFT structure is naturally "more suitable for more sophisticated Micro LED display products" technology. Compared with PCB products, if you want to apply Micro LED technology backlight to computer monitors or handheld devices, or even direct Micro LED display technology, integrate tens of thousands of LED crystals, or even tens of millions, on a 10-inch diagonal size. The precision, strength, flexibility, redundancy and cost required for LED crystals and PCB boards are all facing high tests.
Of course, there was also an idea of "silicon-based driving Micro LED" products before. However, the cost, flexibility, and large size limitations of the monocrystalline silicon driver board are the biggest obstacles to its commercialization in conventional display applications, such as mobile phones, PC monitors, and digital car rearview mirrors. Silicon-based driving Micro LED is more suitable for combining with near-eye display, namely VR and other applications.
Another natural benefit of the TFT glass substrate drive structure is that it is "especially suitable for'mass transfer technology'". The reason is very simple, the surface of the TFT glass substrate is smooth; and the surface of the PCB substrate has a convex structure of circuit copper foil. This difference determines that in Micro LED display applications, whether it is direct display or backlight products, when evolving to a more refined and high-density LED particle integration process, TFT glass substrate is currently the most ideal technology choice. "Huge transfer" is the "biggest obstacle" in the mature development of Micro LED display technology. Compared with PCB, glass substrates can reduce the difficulty of this technology. This is enough to determine that there will be more and more head Micro LED brands in the market. Entered the COG/MIP model product market for TFT substrates.
In addition to the above three advantages, the application of TFT glass substrates to display products such as Micro LEDs also has another advantage that is generally not noticed: that is, the PCB board is mainly driven by PM, and the TFT board is driven by AM.
PM drive mode, this passive drive adopts a circuit structure where the horizontal and vertical scanning lines are crossed and lighted, and the LED crystals on the driving pixels are operated in a "flicker" mode. This leads to two problems, 1. The flicker problem, the traditional solution is that the higher frequency flicker is imperceptible to the eyes; 2. To achieve a continuous constant brightness output, the peak brightness of the LED crystal should be higher when it is actually working (usually The constant brightness value is more than 3 times), which does not use smaller size LED crystal particles.
AM drive mode, each Micro-LED pixel has its corresponding independent drive circuit, and the drive current is provided by the drive transistor. When the scanning line finishes scanning the pixel points, the pixel points can still be in the lighted state through the power supply of the driving capacitor. This means that the LED crystal is naturally in the constant brightness state required. AM drivers naturally do not have stroboscopic problems. Compared with PM driver products, smaller LED crystals can be used at the same constant brightness output; or higher brightness output can be achieved on the same LED crystal.
The industry believes that AM-driven TFT backplanes have many advantages in Micro-LED products. Active site selection has a stronger driving capability, which can achieve a larger area of driving, and active site selection has better brightness uniformity and contrast. , Active site selection can achieve low power consumption and high efficiency, pixels with high independent controllability, avoid driving pixel crosstalk, adapt to higher PPI pixel density display...
From the advantages of thickness and volume, to being more suitable for mass transfer, to higher pixel density, and more advantages of AM driving, the inherent advantages of glass substrate in transparent display, etc., it can be said that when small-pitch LED displays When products enter the mini/micro era, and when they enter the P0.X structure and even Micro-LED direct display applications in mobile, automotive, 8K large-screen TVs and other fields, TFT glass substrate technology and upstream capacity resources are becoming a “necessary A place of contention". This is the secret of the "marriage" between Leyard and China Star Optoelectronics.
"Technology coexistence period", PCB and TFT glass are division of labor
"Glass-based AM LED display" has made great strides in the industry. In August and October 2020, TCL China Star successively demonstrated the world's first a-Si-driven Mini LED array product, and the world's first 142-inch IGZO glass-based active MLED display screen. This proves that various TFT technologies can "good support for LED" display to enter a new evolutionary stage.
However, this does not mean that glass substrates and PCB substrates have established a clear "substitution relationship." In fact, the glass substrate still has its "cost problem." Typically in the market with a pitch above P1.0, the cost of using glass substrates for LED display products will be significantly higher than that of PCB substrates. The cost issue is the key threshold for the "market acceptance" of new technologies. The industry believes that P1.0 will be the first dividing line between PCB and glass substrate.
At the same time, on P0.5-p1.0 products, whether the advantages of TFT substrates can well cover its cost disadvantages is questionable. If the cost of PCB high-precision boards continues to drop, and these products do not necessarily need to use a massive transfer process, then PCB board products will still have a competitive advantage. At the same time, if the terminal manufacturers of products with pitches above P0.5 turn to TFT glass substrates, it means that the "equipment and production conditions" will be turned upside down, which is also an important cost consideration.
However, if the backlight or direct display device based on micro-led technology enters the pitch below P0.5, especially in smaller size markets such as handheld devices, and mass transfer technology becomes a process that must be selected, the advantages of TFT glass substrates will be Zoom in further. And under the condition of smaller size and higher precision, the feasibility and cost advantage of PCB board will also be lost. These products will also be completely aimed at application fields that are not related to traditional LED large screens. Manufacturers need to establish completely new production conditions and purchase equipment. Manufacturers will also prefer technologically advanced route choices.
In addition to the above-mentioned spacing indicators, whether to use glass substrates is also related to the LED crystal transfer method: that is, if you decide to apply mass transfer technology, then the TFT glass substrate may have a natural advantage—that is, direct display The massive transfer of LED screens will basically be dominated by TFT glass substrates in the future. For example, Leyard revealed the new COG/MIP model of Micro LED products. The primary goal will be to face the LED direct display market (although there is no corresponding product available for the time being, this is obviously an important forward-looking technology investment direction).
Not all products require massive transfers, and not all products require glass substrates. "At the same time, there are also some products that "must use TFT glass substrates. Even VR Micro LED products may be the best drive choice for monocrystalline silicon CMOS substrate products." Industry insiders pointed out that when LED display products face a variety of completely different applications, their LED crystal packaging and transfer technology, LED board drive materials and process technology must be different. This is the "division of labor" relationship between market segmentation needs.
In summary, because of the potential growth space and technological advancement requirements of the LED display market, the "degree of attention" of TFT glass substrate technology in the industry is increasing. This has almost integrated the LCD and LED displays into a community of destiny with both internal competition and inevitable cooperation. The investment in TFT glass substrate technology LED display will determine the future positioning of some display companies. Those brands whose goal is to continue to advance to the high-end and strive for more market-take-all brands, obviously must enter the field of TFT glass substrate LED display. After COB, P0.X and massive transfers, TFT glass substrates are becoming a new high ground for competition in the LED display industry.
