When the hottest technology bottleneck breaks thro

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Breaking through the technical bottleneck one by one, the commercialization process of micro LED is approaching

when Apple released the apple watch with OLED display technology as the display panel, it really brightened the eyes of Apple fans, and praised the high saturation of OLED display color, especially the panel size adopted by the latest Apple watch is larger than that of the previous generation, which has attracted the attention of countless Apple fans. The latest news is that Apple will invest the display technology of a new generation of products, which is also made of metal, in micro led, so that the display industry, which has already set off a hot research, will no longer spare no effort and hope to be in the leading position in the commercialized mass production

Apple watch will use micro led

micro LED display. The LED size used is micron level, which has the characteristics of pixel independence, low power control, independent light-emitting control, high brightness, low power consumption, ultra-high resolution and high color. If combined with nano wiring, it can make micron level subminiature led achieve the characteristics of flexible soft display

because micro LED display has a high color saturation similar to OLED, adopts the principle of self illumination, and consumes less than one tenth of the power of LCD panel. In addition, apple and Sony both announced that they hope to adopt micro LED display panel as the display of portable products in 2018, micro LED display technology has become one of the hottest technical topics in the industry, Therefore, apple acquired luxvue, which mainly developed micro LED display technology, in 2014

luxvue has patents for various applications in the field of micro LED display technology. For example, in 2015, it applied for "using LEDs with both luminous ability and sensing function as display panels", which has both sensing function and attracts the attention of the industry. Just like the recently released iPhone x, instead of using physical sensors for fingerprint recognition, it uses sensors hidden in the screen for face scanning and recognition

in addition, like the new generation development of BMW, some breakthrough design concepts were boldly adopted in the 3 series, and then the 5 series were introduced. Apple watch is also the first to use OLED as the display screen, and the next generation iPhone X and iPhone 8 released this year will continue to be used. The new generation of Apple watch is expected to use micro LED display as the screen, so the public in the industry began to boldly predict whether the future iPhone will follow Apple watch to use micro LED display as the screen, just like OLED

no matter in the display industry, intelligent industry, large-scale TV industry, OLED display industry and so on, they are all looking forward to and concerned about when the high-profile micro LED display can be commercialized, and they are also fully engaged in specific fields with the continuous promotion of micro LED display technology

150 μ M micro LED will appear in 2018

according to a micro LED display research report published by ledinside in July 2017, the biggest bottleneck for micro LED displays to enter the actual mass production at present is how to transfer a large number of micron sized LED chips to the circuit substrate, which is often called mass transfer in the industry. Although micro LED display technology has attracted the active participation of major display industry, semiconductor industry and LED industry all over the world, for the above-mentioned bottleneck of mass production of micro LED displays - massive transfer, they have also stepped up the development of unique technology to improve the hourly production capacity (UPH; the number of units that can be produced per hour), the yield of massive transfer and the best and applicable LED chip size, We hope to lead the group into the stage of mass production and take the lead in the market (Figure 1)

Figure 1: Micro LED display technology attracts industry players in major related fields around the world, hoping to lead the group into the stage of mass production and win the market. (source: ledinside)

in this report, the size of micro LED chip is defined as 100 μ M or less, but at present, the mainstream size of micro led development in the industry is still 150 μ m. The development of massive transfer technology is also based on 150 μ M is the target, so it is believed that the LED size of the first generation micro LED display and projector module on the market will fall below 150 μ m。 After that, with the improvement of market acceptance and the expansion of production capacity, we will have the opportunity to expect further investment from relevant competitors and develop 100 μ M or size ratio 100 μ M smaller LEDs and massive transfer technology

however, for the manufacturing and mass production technology of micro LED displays, the massive transfer technology is only one of the four key technologies in the mass production process, and there are still many other difficulties that need to be overcome one by one. At present, for large-scale transfer technology, how to achieve low investment and high efficiency needs to be observed in several aspects, including the improvement of equipment accuracy, the reduction of defect rate during transfer, the shortening of production time, highly reliable detection methods and equipment, the handling and utilization of defective products, the reduction of mass production costs and smarter mass production methods. The progress speed of these seven main areas

breaking through the technical bottlenecks one by one

it is not only the technology with huge transfer that is the most difficult. For example, it is also very difficult to achieve the red light part of RGB trichromatic micro led and how to improve the brightness of LED in the micron level, which is a relative test of the technical ability of LED epitaxial industry

in addition, even the suppliers of LED chips, semiconductor manufacturers, and the overall supply chain of displays should join in and cooperate to develop, such as luxvue, elux, vuereal, x-celeprint, French CEA leti, Sony and Chong electric industry, neptunium Chuang, Taiwan Industrial Research Institute, mikro mesa, TSMC, etc., which can make micro LED displays enter all kinds of production equipment, mass production materials Testing standards and manufacturing technology. However, there are still considerable differences and capabilities among various industries, so it is more necessary to throw away their prejudices, improve the technical level in their respective fields, and work together wholeheartedly to overcome technical obstacles. Of course, this also requires a considerable amount of capital, manpower and time

for example, in terms of materials, in April 2017, monocrystal, the world's largest supplier of Sapphire Wafers, Russia, also published ultra clean grade sapphire epitaxial wafers for future micro led needs. Monocrystal uses the latest cleaning technology to make sapphire wafer surface 1 μ The pollutants below m are removed to about 20-50. Ultra clean grade Sapphire Wafers do not need to carry out front-end cleaning work when carrying out the patterned sapphire substrate (PSS) process. As a result, the yield of PSS operators can be increased to 95% - 99%, thereby reducing consumption and costs. This is a great help to the LED chip manufacturers who are starting to develop micro LEDs (Figure 2)

Figure 2: monocrystal's new generation of high-purity Sapphire Wafers will significantly improve the process yield

further, at present, the decisive point for mass production of micro LED displays can be achieved if the industrial process has 6 standard deviations (6 σ) From the point of view, ledinside believes that the yield of large-scale transfer process must reach 4 standard deviation levels (4 σ), Only then has the opportunity to commercialize. However, to this extent, the cost of detection and defect repair is still quite high. Therefore, if we expect to make mature commercialized micro LED display products and reach the mass production cost with market competitiveness, ledinside believes that the mass transfer yield of micro LED displays should reach at least 5 standard deviations (5 σ) Above

commercialization key of micro led

there are several solutions for the huge volume transfer process under development, including application market, equipment investment, hourly production capacity (UPH), mass production cost and other technologies, but one of them will eventually be selected as the breakthrough point for commercialization. In addition, the process ability and yield control of various industries are also the key to product development

according to the current development situation, ledinside believes that it is defined as 100 μ Micro LED displays below m will be first used in large indoor display devices and wearable products, such as smart watches, smart bracelets, etc. At present, it is still very difficult to complete the mass production technology of large-scale transfer, so most of the current operators still use the existing wafer bonding process equipment as a solution for research and development. However, at present, the number of pixels required by each application product is different, so in order to shorten the time of R & D and mass production, we may first take the product application with less pixel demand as the early development goal

so far, the only one who has developed micro LED display technology to commercialization is Sony (Sony), which uses micro LED display technology to develop the display into a large-scale TV wall and named it as clips (Figure 3)

Figure 3: Sony uses micro LED display technology to develop the display into the type of large TV wall, which is named clips

sony adopts the self-developed led, which is smaller than the general led, with an area of about 20 μ M square RGB ultra fine LED chips, and a large number of LED chips are packaged on a black substrate. And each substrate is tiled to form a large 8K x 2K display with a width of 9.7 meters x a height of 2.7 meters, so that the screen can be scaled at will. At the beginning, Sony targeted the market areas of industrial design and simulation applications, and also spread the target group of customers to hotels and enterprises that need to display

sony's clips uses packaging to make a single RGB LED chip form a pixel, because the luminous ability of LED depends on the characteristics of the material itself. Generally speaking, the LED chip of green light and blue light uses sapphire, silicon carbide (SIC) or gallium nitride (GAN) wafer as the substrate to complete the light-emitting layer, while the part of red light uses gallium arsenide (GaAs) wafer to carry out the process operation. Basically, it is impossible to complete the LED light-emitting structure of red light, blue light and green light on the same material substrate at the same time

technical problems of RGB LED chips

because the clips is used as a TV wall, its size is large, so there is no requirement for too tight packaging spacing of RGB LED chips. However, once faced with applications such as apple watch, under the extremely small panel size, if micro LED display is required to be able to reach a higher level in diversified applications and high-precision display capability, it is quite expected to complete the processing technology and materials of single-chip RGB LED chip on the same wafer material, as well as ultra-high-density packaging technology, but this is also the biggest bottleneck of micro LED display at present

but it is not impossible to complete a single RGB LED chip on the same wafer material. At present, some technologies have been proposed and discussed to complete RGB LED chip on the same wafer, such as wavelength conversion technology using thin film, or micro (nano) wire led chip... And so on

using thin films for wavelength conversion

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