In-depth analysis of the next generation display technology Micro LED

Source: Content from Southwest Electronics ,Thanks.

1. Micro LED, the next generation display technology

Micro LED, or LED miniaturization technology, refers to the process of arraying and miniaturizing traditional LEDs and then transferring them to a circuit substrate in large quantities to form ultra-small pitch LEDs. It further miniaturizes the millimeter-level LED length to the micron level to achieve ultra-high pixels and ultra-high resolution. In theory, it can adapt to screens of various sizes.

Micro LED has the characteristics of self-luminescence without the need for backlight, which is similar to OLED. However, compared with OLED, Micro-LED color is easier to adjust accurately, has a longer luminous life and higher brightness. Therefore, it is another display technology with the advantages of lightness, thinness and power saving after OLED, and may become the next generation display technology after OLED.

Micro LED is subject to production capacity and cost constraints, and it will take time to complete commercialization. Now major manufacturers are making plans, and key technologies are progressing rapidly. It is expected that it will be commercialized in three years.

2. Micro LED Technology Path

Micro LED mainly uses the miniaturization process technology to miniaturize, array, and thin film the traditional LED crystal film, and then transfers the crystal film to the circuit board in batches through the mass transfer technology, uses physical deposition to make a protective layer, and finally completes the packaging. The key core technologies mainly include two steps: miniaturization process technology and mass transfer technology Technology .

2.1 Micro-scaling process technology

Micro-scaling technology refers to shrinking the original millimeter-level length of LED chips to about 1~10μm. Currently, the size of LEDs is mostly 10~30mil, that is, 250~750 μm, and the minimum size of a single chip is 100μm. Micro-scaling technology can break this limit. The industry estimates that the size of indoor displays must be at least 5μm. Currently, the industry level of LED chip size has generally reached 50μm. Apple is strong enough to achieve the 10μm level. Mikro Mesa's laboratory can already produce 3μm size.

There are three main ways to implement miniaturization process technology: Chip Bonding, Wafer Bonding, and Thin film transfer.

Source: LEDinside

The three technical paths each have their own advantages and disadvantages. Among them, thin film transfer technology can break through size limitations and complete batch transfer. The manufacturer Mikro Mesa has taken the lead in completing 3um-sized wafers in the laboratory. The theoretical cost is relatively low and it may become the main implementation path in the future.

2.2 Mass Transfer Technology

After the epitaxy is completed, the lit LED crystal film needs to be directly transferred to the driver backplane without packaging. This technology is called mass transfer. There are two technical difficulties:

1) Only the epitaxial layer of the already lit LED crystal is transferred, and the original substrate is not transferred. The handling thickness is only 3%. At the same time, the size of MicroLED is extremely small, requiring more sophisticated operating technology.

2) One transfer requires moving tens of thousands or even hundreds of thousands of LEDs, which is a huge number and requires new technology to meet this requirement.

Currently, major manufacturers are showing their unique skills in overcoming this technical difficulty. Companies have applied for more than ten patents in total for mass transfer technology. It is expected that this technical threshold will be overcome quickly.

Luxvue transfer technology related patent image Image source: Patent

2.3 Drive system

After the LED wafers are transferred to the circuit board in large quantities, the brightness and contrast can be improved by integrating the microlens array. The Micro LED array connects the positive and negative electrodes of each Micro LED through vertically staggered positive and negative grid electrodes. Through the sequential power supply of the electrode lines, the Micro LED is lit up through scanning to display the image.

Micro LED structure diagram epoxy resin electrode electrode Source: LEDinside

2.4 Micro LED Technology Bottlenecks

Micro LED still has many technical and process issues to be resolved, and there are many challenges from the implementation path to cost yield.

In the process of Micro LED transfer, the transportation of nano-scale LEDs is one of the core issues . Micro LEDs grown on sapphire substrates need to be transferred to glass substrates. Due to the mismatch in size, multiple transfers are required. The technical difficulty of multiple transfers of micro devices is particularly high, and it is even more difficult to use them in products that pursue high-precision displays. Luxvue mainly uses electrical methods to complete the transfer process.

The problem of wafer uniformity also needs to be solved . After the LED is cut from the wafer into chips, each LED chip will not present a perfectly consistent wavelength. Different wavelengths present different colors. For traditional LEDs, the display requirements can be met by binning and matching. However, the number of Micro LED wafers is huge, and the traditional binning method is inefficient and the equipment investment cost is too high, which is not conducive to large-scale production. There are two solutions to this problem: one is to use the existing wafer technology to make Micro LED applications small in size and high PPI, such as wearable devices, and the small size has relatively low requirements for precision. However, this solution limits the market space for Micro LED. Another solution is to directly control uniformity by improving the production process or equipment during the epitaxial stage.

Luxvue capture diagram Source: Patant

It is relatively simple to achieve single color in Micro LED, which can be achieved through flip-chip packaging and driver IC bonding, but it is relatively complicated to achieve full color. The traditional RGB three-color array needs to transfer red, blue, and green crystals in batches, embed hundreds of thousands of LED crystals, and have higher requirements for the light efficiency, wavelength consistency, and yield of LED crystals. There are currently three ways to achieve the color problem of the final screen: RGB three-color LED method, UV/blue light LED + 2 luminous medium method, and optical lens synthesis method.

Source: LEDinside

To solve various technical bottlenecks, various manufacturers have shown their unique skills: VerLASE has a patent for color conversion technology, which can make full-color MicroLED arrays suitable for near-eye displays; Leti uses quantum dots to achieve full-color display and launched iLED matrix, whose blue light EQE is 9.5%, brightness can reach 107Cd/m2; green light EQE is 5.9%, brightness can reach 108Cd/m2, Pitch is only 10um, and the future goal is to achieve 1um. Taiwan Play Nitride announced the PixeLEDTM display technology based on gallium nitride. The company is currently transferring it to the panel through transfer technology, and the transfer yield can reach 99%. It is expected that Micro LED may begin the commercialization process in 3-5 years.

3. Beyond OLED, with broad application prospects

3.1 Micro LED has broad application prospects

At present, if we consider the existing technical capabilities, Micro-LED has two major application directions. One is the wearable market, represented by Apple. It is rumored that Apple will use Micro-LED technology in the new generation of Apple Watch and iPhone, and is expected to launch Micro LED wearable devices in 2018. The other is the ultra-large-size TV market, represented by Sony. This year, the Micro-LED cledis displayed by Sony at CES has excellent performance in resolution, brightness and contrast.

In the short term, the Micro-LED market is concentrated in ultra-small displays. In the medium and long term, the application areas of Micro-LED are very broad, spanning wearable devices, ultra-large indoor display screens, head-mounted displays (HUD), head-up displays (HUD), taillights, wireless optical communications Li-Fi, AR/VR, projectors and other fields.

3.2 Advantages of Micro LED

• High brightness, low power consumption, ultra-high resolution and color saturation. The biggest advantage of Micro LED comes from its biggest feature, the micron-level spacing, each pixel can be addressed and controlled and driven to emit light at a single point. Compared with other LEDs, MICRO LED currently has the highest luminous efficiency and still has room for significant improvement; MICRO LED has the highest luminous energy density and still has room for improvement. - The former is conducive to energy saving of display devices, and its power consumption is about 10% of LCD and 50% of OLED; the latter can save the limited surface area of ​​display devices and deploy more sensors. The current theoretical result is that compared with OLEDD, MICRO LED only needs about 10% of the coating area of ​​the latter to achieve the same display brightness. Compared with OLED, which is also a self-luminous display, the brightness is 30 times higher than that, and the resolution can reach 1500 PPI (pixel density), which is equivalent to 5 times the 300 PPI of Apple Watch using OLED panels.

• Long life. Since Micro-LED uses inorganic materials, has a simple structure, and consumes almost no light, its life is very long. This is something that OLED cannot compare to. As an organic material, OLED has its inherent defects - namely, life and stability, which are difficult to match with inorganic QLED and MICRO LED.

• Better material stability and no image burn-in.

• The nanosecond-level high-speed response characteristics make Micro LED displays suitable not only for three-dimensional (3D) display, but also for high-speed modulation and signal carrying, serving as a visible light wireless communication function for smart displays.

• Able to adapt to various sizes.

• There is a lot of room for cost reduction. Currently, micro-projection technology is mainly based on three technologies: Digital Light Processing (DLP), reflective silicon substrate liquid crystal display (LCoS), and micro-electromechanical system scanning (MEMS Scanning). However, these three technologies all require the use of external light sources, making it difficult to further reduce the size of the module and the cost is also higher. In contrast, the use of self-luminous Micro LED micro-displays does not require external light sources and has a simpler optical system. Therefore, it has advantages in miniaturization of module size and cost reduction.

• Seamless stitching.

• Wide range of applications. Micro LED solves several major problems. One is that 80% of the energy consumption of consumer tablets, including smartphones and wearable devices, is in the display. Low-energy Micro LED displays will greatly extend battery life. For the application of Micro LED displays, due to its self-luminous display characteristics and a simple structure with almost no light-consuming components, it is easy to achieve low-energy or high-brightness display design. The second is the problem that the image on the display is white and the recognition is poor due to strong ambient light. Micro LED high-brightness display technology can easily solve this problem, making its application scope wider.

3.3 Next-generation display technology

Compared with LCD, OLED and Micro LED have significant advantages in various functional indicators (PPI, power consumption, brightness, thinness, color rendering index, and flexible panel adaptability). Although LCD panels have been used for a long time, have a higher supply chain maturity, and have price advantages, they will definitely be replaced by OLED and Micro LED in the future.

OLED and Micro LED are both future-oriented display technologies. There is a big gap between the two from the perspective of industrial practice. Micro LED is superior to OLED in performance. Micro LED is a mass transfer of micron-level Micro LEDs to a substrate, similar to a miniature outdoor LED display. Each Micro LED is addressed and can be driven and lit individually. Compared with OLED, it is more power-saving and has a faster response speed. OLED is thinner than LCD and has a clearer display, but if you want to save power, you have to reduce high-brightness display and white screen, which will affect the visual performance. Micro LED technology has broken through the limitations of OLED, and its brightness and saturation are higher in comparison. In addition, OLED materials are organic light-emitting diodes, and their service life is naturally incomparable to organic light-emitting diodes such as Micro LED. Micro LED is more competitive in application areas that require life when used, such as automotive head-up displays and large-screen projections.

From the perspective of the industrial chain, about 70% of all OLED display technologies can be shared or absorbed by Micro LED, which means that after the breakthrough of Micro LED technology, it will not be difficult for the entire industry to turn around, laying the foundation for replacing OLED in the future.

Differences between LCD/OLED/Micro LED Source: LEDinside

4. Many manufacturers are accelerating the layout of Micro LED

• SONY launches Micro LED display CLEDIS: In June 2016, Sony exhibited the Micro-LED large-screen product "cledis" at the IFA exhibition in Germany. This Micro-LED large-screen display successfully combines three single pixels of RGB to form a large-size LED screen that can be used in digital signage, public large screens, showrooms, automotive design reviews, etc.

• Apple acquires LuxVue and may apply MicroLED to Apple Watch: Apple acquired LuxVue in 2014 and began to develop Micro LED technology. In July 2016, Apple ignited the "6 FHDMicro-LED" pilot project and is said to be developing Micro-LED technology models for future Apple Watches.

Micro LED, as a new application that may become the next generation of display technology, has attracted the attention of major international giants. Currently, there are nearly 100 manufacturers and institutions involved in Micro LED. Now Micro LED has been first commercialized by Sony, and the pace of development will be further accelerated in the future.

From the perspective of the specific industrial chain, Taiwanese and mainland factories are actively making plans. Many equipment manufacturers of Taiwan Epistar have already begun to develop Micro-LED production equipment, which is expected to enter the factory this year, and some production capacity may be released next year; MikroMesa has successfully developed a 3umx3um light-emitting area, which is the smallest size in the world; MikroMesa cooperated with Chongqing HKC Jinyu Optoelectronics to jointly establish the first MicroLED laboratory on both sides of the Taiwan Strait. The laboratory is expected to be completed in the fourth quarter of 2017 and develop full-color MicroLED products in 2018. According to the Micro-LED academic salon opened by SID at Shanghai University, mainland companies have already made plans to develop Micro-LED chips. At present, Micro-LEDs in the research and development of mainland manufacturers can reach 15um, and the follow-up speed is very fast, with promising prospects.

5. Micro LED market is expected to reach tens of billions of dollars

Considering the characteristics of MicroLED, wearable devices and indoor display screens will be the first areas to enter. If these two areas adopt MicroLED display in the future, it will consume nearly 50% of the global LED chip production capacity. The market size can reach 30-40 billion US dollars.

In the field of Micro-LED applications, consumer panels including smartphones, wearable devices, TV screens, as well as automotive displays, public displays including outdoor super large screens are all the future development trend of Micro-LED. So can Micro-LED completely replace the existing screens LCD and OLED? We think it is very likely. At present, Apple has announced that all Apple displays will adopt OLED in 2018. The advantage of OLED lies in mature mass production technology, while the production cost of Micro-LED is too high due to quantitative transfer technology. However, once Micro-LED breaks through the technical difficulties of mass production, the cost will be greatly reduced. It will create a new era of LED with its unique high resolution, low loss and high definition. It is very important that the transition from LCD/OLED to Micro-LED is not as difficult as the fight between plasma screens and LCD screens. They all use FTF backplanes, and a large part of the resources can be shared. Therefore, it is less difficult for manufacturers to transform. With the obvious advantages of Micro-LED, we have reason to believe that Micro LED is very likely to completely replace LCD screens. If estimated based on the scale of completely replacing the components of existing LCD displays, including backlight modules, liquid crystals, polarizing plates, etc., the potential market size of Micro LED in the future can reach approximately US$30 billion to US$40 billion.

6. Micro LED belongs to the future, Sanan Optoelectronics is the first choice

Micro LED is an application of the future. Judging from the development of the equipment supply chain, many equipment manufacturers have developed Micro LED production equipment, and leading manufacturers may start mass production in 2018.

Micro LED commercialization process Source: LEDinside

As a major LED chip manufacturer, Sanan Optoelectronics is already in the process of developing Micro LED and is expected to catch up with the first wave of Micro LED commercialization. It is the biggest beneficiary of the new technology and is highly recommended!

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