Shulou(Shulou.com)11/24 Report--

Original title: "how does Micro-LED unlock HD No Code?" "

Five years ago, Apple's iPhone X was equipped with OLED (organic small molecule electroluminescent display) screens, and in 2021, Apple introduced a new display technology on its new MacBook Pro: Mini-LED (submillimeter light emitting diodes). But the Mini-LED is not a terminal, and another reserve technology Apple is involved in, the rookie Micro-LED (micron light emitting diode) display technology, may be expected to unify.

The reason for upgrading the display technology is to see more clearly and restore the real world. But at present, products equipped with Micro-LED technology are too expensive, such as Samsung's 110in Micro-LED TV, the price has exceeded one million yuan, ordinary people simply do not enjoy it. When will the price of Micro-LED products be close to the people, and when will the phone tablet be on the Micro-LED screen?

Display technology that changes human life simply put, you can think of Micro-LED as a new display technology that zooms LED to a very small size. Its future applications are expected to involve display, television, mobile phone flat panel display, augmented reality / virtual reality / hybrid reality (AR / VR / MR), space display, flexible transparent display, wearable / implantable optoelectronic devices, optical communication / optical interconnection, medical detection, intelligent car lights and other fields.

The industry uses two methods to define the technical specifications of Micro-LED.

First, by defining the chip size, the LED chip can be called Micro-LED chip if it is scaled to less than 100 μ m (some scholars also think that it should be limited to 50 μ m). Depending on the viewing distance and the limit resolution of the human eye, the requirements for chip size are also different:

The viewing distance of VR / AR application is about 5cm, the pixel density is about 1800PPI, and the size of Micro-LED chip is 3'5 μ m.

The 10-inch to 12-inch plate should be at least as dense as the pixel density of 300PPI, and the corresponding chip size is 20-30 μ m.

A 75-inch TV requires only 43PPI, and the chip size is often about 200 μ m. [1]

Different applications on the size of the Micro-LED chip requirements, tabulation? fruit shell hard science and technology reference materials ("special equipment for the electronic industry" [2] the other is defined by the process, because the size of the Micro-LED chip is very small, its length and width is even smaller than the height of the chip, resulting in the chip height greater than the solid surface size, which is not conducive to the chip fixed on the substrate, so it will be one more step than the traditional LED laser peeling chip substrate operation.

Throughout the display industry, technologies continue to emerge. At present, the mainstream technologies in the market include TFT-LCD (thin film transistor liquid crystal display), AMOLED (active matrix organic light emitting diode display), QD-OLED (mixed OLED and QLED technology), QNED (QD-OLED display with blue LED as light source), Mini-LED, Micro-LED, Micro-OLED.

The current display technology can be simply divided into four categories: LCD, OLED, QLED and Micro-LED, and other technologies are improved or transitional versions on this basis. Micro-LED is considered to be an ideal display technology and the ultimate goal of a new display era, and is expected to replace LCD and OLED, which are widely used at the present stage.

From black and white to high-definition color, CRT technology meets a generation's dream of influencing the world. From thick and heavy to flat panel displays, LCD and OLED meet people's requirements for being thin, portable and vision-friendly. At this stage, the only next-generation display technology that can be closer to reality, or even deceive the human eye, is Micro-LED. [3]

People in the industry believe that when a variety of display technologies break out, only one or two technologies may eventually dominate the market, and there is no doubt that the most promising is Micro-LED. [1]

Classification of mainstream display technology, mapping? fruit shell hard science and technology reference materials? "Micro LED display Research report (2019)" [4], "Electronic Industry Professional equipment" [2] how can Micro-LED get such a high rating? Because it not only has most of the advantages of LED, but also has the characteristics of high brightness, high resolution, high response speed, low power consumption, small size, easy to disassemble, high flexibility, no stitching and so on, it can cover most of the display application scenarios [5]. At the same time, its response speed can reach dozens of nanoseconds, there is no residual image and there is no life problem. [3]

In addition, compared with LCD, OLED, QLED and other predecessors, the main performance parameters of Micro-LED are excellent.

Comparison of modern display technology [1] transition technology has been commercialized on a large scale. Micro-LED also has a close relative: Mini-LED, which can be understood as the transition technology between LED and Micro-LED. Because the technical principles are very similar, the industry generally boils down to the two in the same route, and some cases will also be called MLED.

As a preorder technology, Mini-LED mainly solves the problem of chip size fault, and the development of related technology can be used for reference to Micro-LED, and its chip size is generally 75 μ m ~ 300 μ m.

LED panorama [6] Mini-LED is much easier to achieve than Micro-LED. It is not only easier to achieve in chip size, but also has no scientific problems in materials. It has been put into the market by mass production. Apple, Samsung, TCL and other brands have achieved large-scale mass production.

However, Mini-LED and Micro-LED have different application scenarios. On the market, Mini-LED generally appears as a LCD backlight, combined with quantum dot technology to achieve high dynamic range display, while Micro-LED is directly used to make display pixels [7]. To put it simply, the commercial Mini-LED display is essentially a foil to the LCD, while the Micro-LED display is a direct luminous imaging. [8]

Since 2018, panel manufacturers have released prototypes that use Mini-LED as backlight, and the product size has reached 152.4mm~685.8mm (6x 27 inches). So far, Mini-LED backlit displays have models such as 1398mm (55 inch), 1651mm (65 inch), 1905 mm (75 inch) and 2159 mm (85 inch), which can reach 8K resolution and 120Hz refresh rate, and can increase the contrast of the existing display from 10000 ∶ 1 to 1000000 ∶ 1. [9]

Mini-LED industrialization behavior is clear, has a certain volume of shipments. In 2021, global shipments of medium-sized Mini-LED backlit panels reached 7.4 million pieces. By 2023, smart cars will become the new frontier of Mini-LED. [10]

Based on the development route of Mini-LED backlit products [9] as an intermediate transition, the Mini-LED industry is thriving, while Micro-LED is still a minority, so what is the difficulty of making Micro-LED out of the circle?

If you want to build it, it's not that easy to Micro-LED anything, but it's expensive. The reason is that there are many problems in the manufacturing process, which leads to the difficulty of mass production and low yield, which leads to rising prices.

On the surface, the Micro-LED chip only miniaturizes the LED chip, but the actual situation is far more difficult than expected. The essence of the conversion process from millimeter to micron is LED miniaturization, thin film and matrix. in this process, material growth, device preparation, driving technology, production process and other steps have changed, resulting in qualitative change. [11]

Micro-LED uses the RGB (red, green and blue) color standard. Because it is a self-luminous element, if you want Micro-LED to show the image, you have to make three primary colors of light-emitting chips to form pixels.

Different colors of Micro-LED chips can be prepared with different materials, such as InGaN / GaN-based materials for green / blue light Micro-LED arrays, AlInGaP / GaAs-based materials for red light Micro-LED arrays, and epitaxial layers on sapphire, gallium arsenide and silicon substrates to prepare Micro-LED arrays. [12]

From substrate to product, Micro-LED display will go through four processes: epitaxial growth, chip manufacturing, mass transfer and performance testing.

Micro-LED device manufacturing process [2]

Brief introduction and difficulties in Micro-LED device manufacturing, tabulation? fruit shell hard science and technology reference materials "Progress in Laser and Optoelectronics" [13], "Professional equipment in Electronic Industry" [2] from a technical point of view, the materials and equipment related to chip preparation are relatively mature, and the symptom of the problem lies in the manufacturing process. specifically, the barriers to Micro-LED include the following:

It's all small trouble. for chips, the smaller the size, the more difficult it is to make, and so is the Micro-LED. The size of Micro-LED chip is so small that the influence of small size should be considered when making it into all kinds of display devices.

In order to obtain a small size of Micro-LED, it is necessary to use microprocess technology to miniaturize the LED chip to meet the application requirements. Microfabrication technology includes chip welding, wafer welding and film transfer. The better the technology is implemented, the higher the pixel density will be.

There are three paths for the realization of microprocess technology, tabulation, hard science and technology reference materials for fruit shells, "Micro-LED Technology Roadmap (2020 version)" [6], there is also a fatal problem that has to be faced with the deletion and modification of Micro-LED: sidewall defects often occur in the process of miniaturization. For example, with the same error defect of 2 μ m, the remaining utilization rate is 97% on the LED of 250 μ m × 250 μ m, but only 4% on the Micro-LED of 5 μ m × 5 μ m. [14]

Error defects lead to a significant reduction in chip utilization [14] not only that, the smaller the size of the Micro-LED chip, the greater the ratio of the volume of the inductively coupled plasma (ICP) etching region (sidewall) to the active region, and the higher the proportion of defects caused by etching damage [15]. As a result, the proportion of non-radiation recombination increases gradually, and the luminous efficiency and service life decrease. If the size is reduced from 400 μ m to 20 μ m, the luminous efficiency of current density can be reduced by 50% [7]. This will also lead to the increase of non-radiative recombination probability of Shockley Redhall (SRH) in the active region, the decrease of radiation recombination probability and luminous efficiency, and the introduction of new leakage channels to aggravate the reverse leakage of the device. These problems are particularly obvious in Micro-LED with a size of less than 10 μ m. [16]

Chip size problems also make it difficult to improve the efficiency and stability of driver integration with Micro-LED arrays. In short, the process of mass production of LED or Mini-LED may no longer be applicable to Micro-LED.

The dilemma of huge transfer each pixel of LED display is composed of lattice, and the spacing of the array composed of small LED chips is basically the same. The same goes for Micro-LED. After manufacturing the chip, it is also necessary to transfer a large number of Micro-LED chips to the circuit substrate at a fixed point. This process is called "mass transfer".

Different from the traditional LED, the huge transfer of Micro-LED not only has higher requirements for the control of transfer accuracy, transfer rate and color uniformity, but also has a larger number of transfers. 4K Micro-LED displays need to flip more than 20 million Micro-LED chips, while 8K has reached hundreds of millions. [17]

At present, there are a variety of technical solutions for mass transfer technology, including precision pickup technology, laser release technology, fluid self-assembly technology and roller transfer technology and so on. Different technologies have different characteristics, but they all have some disadvantages.

Mass transfer mode of Micro-LED chip [2] specifically, precision pickup technology requires extremely high accuracy and stability of transfer equipment; laser release technology may damage the chip surface and reduce yield in the implementation process, in addition, laser equipment is expensive; fluid assembly technology takes three times to complete transfer, and the efficiency is low. Roller transfer technology can be transferred on a flexible substrate, but it also needs 3 transfers to complete a large amount of transfer. [17]

Some of the methods can reach 99.99% yield in the laboratory, but there is a big gap compared with the industrialization requirement of at least 99.9999% yield. The industry is looking for a technical solution that is easy to implement, high yield and cheaper. [18]

The challenge behind the colorful color why can the display be so colorful? Because the RGB (red, green and blue) color system is widely used in the display world, most of the colors visible to the naked eye can be realized through the superposition of the three primary colors of RGB. Want Micro-LED to correctly depict the picture, it is necessary to do a good color scheme, that is, full color.

There are mainly two solutions for Micro-LED colorization: one is the blue source color conversion scheme, but the color conversion materials have some problems such as coating uniformity and reliability, so they are rarely used. The other is to directly use the RGB tricolor scheme of LED, but for Micro-LED, this scheme is not easy to use and needs to adjust the size of LED accordingly. In addition, due to the difference of wavelength uniformity of each color, it will also face the problem of insufficient light efficiency and yield. [14]

Different color technologies [17] the difficult problems in the industrial chain to create a Micro-LED chip does not mean the end, in order to make it really appear in front of people, there must be a breakthrough in a number of technical fields.

Like other chip technologies, Micro-LED will also involve huge industrial chain and raw material problems, from raw materials to lighting the screen, divided into upstream, middle and downstream, each link is closely related to the final product, among which the key technologies include driving IC, driving backplane and packaging. [19]

Mirco-LED display industry chain [19] the industry is ready for development as the ultimate goal, Micro-LED is undoubtedly the star in the display field.

Since 2000, professors at Texas Tech University put forward the concept of Micro-LED, and Kansas State University prepared Micro-LED based on Ⅲ nitrides [20]. Since then, there has been a wave of research in academic circles. Especially after 2006, it began to grow exponentially. Google academic data show that so far, there have been nearly 6000 articles in the field of Micro-LED.

Research institutions and manufacturers around the world have also invested in Micro-LED research, under the influence of consumer electronics giants, the initial industrialization of Micro-LED.

In 2012, Sony released the 55-inch HD Micro-LED TV panel Crystal LED, the first product to appear as a commercial product.

In 2014, Apple acquired Lux Vue and entered the technical research of Micro-LED. This technology really began to enter the public eye. So far, Apple has not only continued to promote the development of Micro-LED technology, but also released a number of Mini-LED-related products.

In 2018, Samsung unveiled the world's first 146in Micro-LED TV "The Wall" at CES.

Samsung sells 110in Micro-LED TVs in December 2020

In January 2021, Vuzix released the first commercial Micro-LED AR smart glasses. [17]

From the perspective of patents, the total number of Micro-LED patent applications from 2002 to 2014 is relatively small. Since 2017, the number of applications has increased sharply. [21]

Development course of Micro-LED [12] due to many technical problems, the overall market size of Micro-LED is limited at this stage. It is expected that Micro-LED will be commercialized on a large scale in 2024. [22]

According to Research And Markets, the global market size of Micro-LED is US $1 billion in 2020 and is expected to grow at a compound annual growth rate of 77.1% by 2027 [23]. According to the LED Research Institute of High Engineering Industry and Research (GGII), the global market will exceed US $3.5 billion in 2025 and is expected to exceed US $10 billion in 2027 [24]. On the domestic side, it is expected to impact the market size of 80 billion yuan after large-scale commercial use. [22]

Micro-LED Technology Roadmap [6] at present, Micro-LED applications on the market side are divided into two major directions, one is the wearable market represented by Apple, and the other is the super-large TV market represented by Samsung and Sony. In the short term, the market will focus on ultra-small displays, while in the medium to long term, Micro-LED will span wearable devices, large indoor and outdoor display screens, head-up displays (Head-Up Display,HUD), taillights, AR / VR / MR, projectors and other fields. [25]

The enterprises that promote industrialization mainly include three categories: the first category is traditional LED chip and packaging enterprises, such as Nippon and Crystal Lumens; the second category is new display enterprises such as TFT-LCD and OLED, such as BOE; and the third category is terminal enterprises, such as Sony, Samsung and LG.

In the form of industrialization, cooperation is the main form, and customized design is the main form of Micro-LED, coupled with higher technical requirements, the industry shows a highly integrated trend, panel, chip, huge transfer and drive IC and other manufacturers group development. [26]

Internationally, the relevant financing also rises one after another, and the goal is to point to large-scale industrialization.

From January to mid-November 2022, the international related financing of Micro-LED is incomplete, and the tabulation of fruit shell hard technology Micro-LED is also popular in China, with a continuous tilt in policy and frequent investment and financing actions. According to the White Paper on 2022 Mini / Micro LED display Industry, from January to August 2022 alone, more than 30 domestic enterprises have invested, involving a total of 41.5 billion yuan. [10]

Enterprises in the upstream and downstream of China's industrial chain have also carried out technical cooperation in key technologies such as LED, mass transfer, colorization, detection and repair, forming three camps of "BOE + Huacan Optoelectronics", "San'an + Huaxing Optoelectronics", "Fucai + Yuanchuang + Youda + Qunchuang" [27]. At the same time, domestic research and development and trial production of wearable display, high-definition mobile display, vehicle display, high-definition large-size display, super-large size spliced commercial display prototype have been carried out. [18]

From January to mid-November 2022, the relevant domestic financing statistics of Micro-LED are incomplete. For the industry, the future road of Micro-LED is either black or white. From a positive point of view, the market prospect is bright. From a bad point of view, it is a game of sales volume in a short time.

On the one hand, the market is down, the panel industry is the first "victims" of the storm of cutting orders, consumer electronics demand is weak, I do not know whether this situation will be alleviated in large-scale commercialization.

On the other hand, for ordinary consumers, they pay more attention to the performance, function and price of the product, and do not care too much about which technology is adopted. For display manufacturers, perhaps the most important thing is to think about how to make more ordinary consumers feel the changes that Micro-LED brings to their lives.

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This article comes from the official account of Wechat: fruit Shell hard Technology (ID:guokr233), author: Fu Bin, Editor: Li Tuo

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