When Apple Computer released OLED display technology as an APPLE WATCH display panel, Apple's eyes really lit up, and praised the highly saturated OLED display color saturation, especially the latest APPLE WATCH panel size used Larger than the previous generation, but also attract the attention of countless Apple fans the latest message is that Apple Computer more a new generation of display technology to the MICRO LED, it is to have set off a research and development of the hot display industry, all without exception Full, hoping to take the lead in the status of commercial mass production (Figure 1).
Figure 1: The use of OLED display technology as APPLE WATCH let Apple fans eyes bright.
APPLE WATCH will use Micro LED
Micro LED displays are available in micron-scale LED sizes, with independent control of the pixels, independent glow control, high brightness, low power consumption, ultra-high resolution and high chromaticity, and more if combined with nanowire routing Micron-level ultra-small LED flexible display to achieve the characteristics of a flexible.
As the Micro LED display with similar high degree of color saturation with the OLED, the use of self-luminous principle, the power consumption of only less than one-tenth of the LCD panel power and so on the advantages of features, coupled with Apple and SONY are published With the introduction of the Micro LED display panel as a display for portable products in 2018, the Micro LED display technology has become one of the hottest technical topics in the industry, allowing Apple Computer to acquire Micro LED display technology in 2014 Based LuxVue.
LuxVue already holds patents for a wide range of applications in the field of Micro LED display technology. For example, "Using LEDs with both light-emitting capability and sensing functions as display panels" applied in 2015, LuxVue has a combination of sensing functions Is attracting the attention of the industry just as the recently released iPhone X is the elimination of the use of physical sensors for fingerprint recognition, and switched to the screen built-in sensor for face scan identification.
In addition, like the new generation of BMW development, bold adoption of some breakthrough design concepts in the Series 3 followed by the introduction of the Series 5. APPLE WATCH is also the first to use OLED as a display screen, followed by this year's new release A generation of iPhone X and iPhone 8 continue to use.And a new generation of APPLE WATCH is expected to Micro LED display as a screen so the industry began to boldly predict whether the future of the iPhone will be the same as OLED, APPLE WATCH with Micro LED display As a screen.
Micro LED display for the attention of the time when it can be commercialized, whether it is display industry, or smart phone industry, the large television industry, OLED display industry, etc. are all with the expectations and care, and are also Micro LED display Technology continues to advance, each in full swing in a particular area in progress.
150μm Micro LED will appear in 2018?
According to LEDinside in a July 2017 Micro LED display research report pointed out that the current Micro LED display into the actual production of the biggest bottleneck is how to transfer a large number of micron-size LED chips to the circuit board (Backplane) , Which is commonly referred to in the industry as the Mass Transfer (Mass Transfer) .Although Micro LED display technology to attract the world's major display industry, semiconductor industry and LED industry to actively join, but for the above Micro LED display production bottleneck - giant Volume transfer, but also to step up the unique technology to improve hourly capacity (UPH; unit per hour hour in the number of units that can be produced), mass transfer yield and the best and applicable LED chip size, Hope to be able to lead the heroes into mass production stage, pull the top spot in the market (Figure 2).
Figure 2: Micro LED display technology to attract the world's major players in related fields, hoping to lead the herd of mass production stage, the market leader (Source: LEDinside)
In this report, the size of the Micro LED chip is defined as below 100μm. However, at present, the mainstream size of the Micro LED for development is still 150μm. The development of huge amount of transfer technology is also carried out with the goal of 150μm. Therefore, It is believed that the LED sizes of the first generation of Micro LED displays and projector modules on the market will fall below 150μm and the subsequent acceptance of the market and the expansion of production capacity will give the opportunity to look forward to further investment by the relevant competitors, And development of 100 μm or smaller LEDs with a size smaller than 100 μm as well as mass transfer technology.
However, for the production of Micro LED display manufacturing technology, mass transfer technology is only one of the four major production process key technology only one, there are many other difficulties need to overcome one by one.Currently, the giant For quantitative transfer technology, how to achieve low investment and high output efficiency depends on several aspects of observation, including the improvement of equipment accuracy, reducing the transfer rate of non-performing, shortening the production time, high reliability of detection methods and equipment, Process utilization, reduce production costs and smarter production methods, these seven major areas of progress.
Breakthrough in technical bottlenecks
It is not only the technology of huge amount of transfer is the most difficult, just like the red part of the RGB primary color Micro LED and how to improve the brightness of the LED in the micron level, the difficulty is also very high, which is relatively testing LED epitaxy industry Technical ability.
In addition, even suppliers including suppliers of LED chips, semiconductors, and the overall supply chain of displays have to join and collaborate on such products as LuxVue, eLux, VueReal, X-Celeprint, France CEA-Leti, Sony and OKI Industrial, Intel, ITRI, Mikro Mesa, TSMC, etc., allow Micro LED displays to go into production equipment, production materials, test standards and manufacturing techniques needed for real production, but as the industry There are still quite different differences and abilities. Therefore, it is even more necessary to put aside their respective prejudices, upgrade their technical levels in their respective fields, and work together wholeheartedly to overcome technical obstacles. Of course, this also requires considerable investment Funding, manpower and time.
In material terms, for example, April 2017, the world's largest supplier of sapphire wafer, Monocrystal, a Russian manufacturer, has released Ultra Clean grade sapphire wafers for future Micro LEDs. Monocrystal utilizes the latest cleaning technology , The sapphire wafer 1μm below the surface of the contaminants removed to about 20 to 50. Ultra Clean grade sapphire wafers in the graphical sapphire wafer substrate process (PSS; Patterned Sapphire Substrate), there is no need for the front section Wash operation, so that the yield of the PSS industry can be increased to 95% to 99%, thereby reducing wear and tear and reduce costs.This is for the LED chip manufacturers are starting to develop Micro LED is no different from A considerable boost (Figure 3).
Figure 3: Monocrystal's new generation of clean sapphire wafers will dramatically increase process yields.
Further, at present, LEDinside considers the yield of mass transfer processes to be up to 4 standard deviation levels (6 sigma for industrial processes) at the point where mass production of Micro LED displays can now be achieved 4σ), there is a chance to commercialize, but at this level, the cost of detection and the cost of defect repair are still quite high. Therefore, it is expected to make mature and commercialized Micro LED display products and achieve market competitive mass production Costs, LEDinside believes Micro LED displays have a mass transfer yield of at least 5 standard deviations (5σ) or more.
MicroLED commercialization of the key
There are several solutions for the mass transfer process currently under development, including various technologies such as application market, equipment investment, hourly throughput (UPH), and volume production costs, but eventually one of them will be chosen as the entry into the product The breakthrough point, in addition to the process of manufacturing capacity and yield control, but also the key to product development.
Judging by the current development status, LEDinside believes that the Micro LED displays defined below 100μm will be the first to be applied to indoor large-scale display devices and wearable products such as smart watches, smart bracelets, etc. Due to the huge amount currently being completed Transfer of mass production technology is still very difficult, so most of the current investment practitioners still use the existing wafer bonding process equipment (Wafer Bonding Process) as a program to carry out research and development, but now the number of applications required by the pixel are Not the same, so in order to shorten the R & D and production of the schedule, perhaps the first pixel less demand for product development as a pre-development goals.
So far, the only SONY (SONY) technology that has made Micro LED display technology commercially available has been developed using the Micro LED display technology into a large video wall and named CLEDIS (Figure 4).
Figure 4: SONY Micro LED display technology used to develop the monitor into a large TV wall type, and named CLEDIS.
SONY uses its own RGB Ultra Fine LED chips, which are smaller than the average LED size and have an area of about 20μm square, 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, a height of 2.7 meters and a scalable display of the screen. SONY initially targeted the market for industrial design and simulation applications Field, and will also target customers across the hotel and the need to showcase the business.
SONY CLEDIS is the use of packaging to make a single RGB LED chip form a pixel, because the LED's light-emitting ability will depend on the material itself .Generally, the green and blue LED chip is the use of sapphire, silicon carbide ( SiC) or gallium nitride (GaN) wafer as the substrate to complete the light-emitting layer, while the red part is the use of gallium arsenide (GaAs) wafer processing operations, it is basically not possible in the same piece of material The substrate simultaneously completes the red, blue and green LED light-emitting structures.
RGB LED chip technical problems
Because CLEDIS is used as a TV wall, so its size is larger, so in the RGB LED chip package spacing is not too tight on the requirements, but once faced such as APPLE WATCH such applications, in a very small panel Size, if the requirements of the Micro LED display in a wide range of applications and high-definition display capabilities to the next level, the same piece of wafer material to complete the process of single-chip RGB LED chip technology and materials, and ultra-high density Packaging technology is expected to be quite, but this is also the biggest bottleneck Micro LED display.
However, it is not impossible to complete the monolithic RGB LED chip on the same wafer material. Currently, there are some technologies that have been proposed to complete the RGB LED chip on the same wafer. For example, To carry out wavelength conversion technology, or Micron (Nano) Wire LED chip .... and so on.
The idea of thin film for wavelength conversion is published by VerLASE Technologies in 2015. VerLASE Technologies calls it Chromover Wavelength Conversion, a key thin film conversion layer that uses gallium selenide, tungsten disulfide, Molybdenum disulfide, and the like to form a sheet-like film on graphene, the technology VerLASE Technologies has acquired a technology patent in the United States.
Chromover wavelength conversion technology is in the blue LED chip array, the resonator surface surrounded by the semiconductor quantum wells, and then in the same material on the wafer to transform the thin film layer, you can in the film when the excitation of blue light, For green and red light conversion.The idea is to replace the current idea of using phosphors and quantum dots to change the luminescence color (Figure 5).
Figure 5: VerLASE Technologies hopes to replace the idea of using phosphors and quantum dots to make color changes.
The other Micron (Nano) Wire LED chip technology was developed by Aledia in France and Glo in Sweden, etc. To put it simply, the nano-level columnar three-dimensional process on the wafer Each column has a light-emitting layer formed by such three-dimensional processing of the LED produced, its brightness will be higher than the average process to LED, and can reach the same wafer, or even on the same chip can be excited The ability to multi-color (Figure 6).
Figure 6: Aledia, France, uses a three-dimensional process to create a light-emitting layer on each column.
Taiwan catches up
In Taiwan, the major display industry is also unlikely to miss this LED display R & D event, including the largest LED chip industry wafer optoelectronics, LCD panel dual leader AU Optronics and Innolux and other companies are also actively involved in Micro LED display Related technology development.In addition to these three companies, the KT Technology and ITRI have also invested in the development of Micro LED display technology in the global arena, Samsung Electronics, LG Electronics, Nichia, Sharp, SONY, LuxVue , X-Celeprin, which was founded independently from the University of Illinois Research Laboratory, etc., are all on the Micro LED display research and development road.
Epistar vice president and spokesman Zhang Shixian once said in 2016, although the wafer optoelectronics, in the epitaxial and grain part of the process, Micro LED high probability of success, as to whether the volume production in 2017, But also very hard.As the Micro LED small size, epitaxial, grain process also need to cooperate with the transfer of equipment and system applications such as joint development plant.
The AU Optronics is the combination of its Lunda Optoelectronics to carry out the development of Micro LED displays, Micro LED display experimental line in Luanda Optoelectronics installed in 2016 to complete and carry out related research and development projects. Innolux also Micro The growth potential of LED displays is quite awaited. Under the same group, Innolux will develop Micro LED displays by a subsidiary company Hon Hai (AOT), a precision investment company.
In addition to supporting Quantum to develop Micro LED displays, Hon Hai Precision also joins hands with Sharp, which is already considered a member of the group, to invest in eLux, a Micro LED display development company in the United States.
However, unlike the Hon Hai Group's investment in capital, Sharp is using its 21 patents in display manufacturing, assembly, and cost reduction as the benchmark for about $ 7 million in eLux While Hon Hai invested in eLux, part of its group of companies, and 45% of Cyber Agent Ventures registered in the British Virgin Islands, while Sharp is 31.82%, under the group of a photoelectric and Wing Chong energy were 13.64% and 9.09% .In proportion, Hon Hai Group, the company took a total of 54.55% of the shares, which also represents Hon Hai Although indirect, but it Is essentially controlling eLux's operations.
Taiwan in addition to acquiring overseas Micro LED display companies to accelerate the development of technology, because Astronomical is scheduled to begin production of Micro LED displays in the second half of 2017 Micro LED chips, therefore, on the other hand the market also came out, South Korea's Samsung Electronics Intends to 150 million acquisition of Taiwan's Chuangchuang technology if Samsung can really wish and schedule the successful acquisition of Chuangchuang technology there is a considerable opportunity to meet Apple is expected in 2018 using the Micro LED The display serves as the supply chain for the APPLE WATCH screen panel, though Samsung does not anticipate that Micro LEDs will replace OLEDs, but for unexpected changes Samsung is still preparing for the Micro LED display market.
In addition to LED miniaturization, LED lighting to enhance capacity to overcome the huge amount of transfer issues .... and other existing bottlenecks, on the other hand, Taiwan is also working hard to Micro LED display technology needed to develop a relatively Driver chips. Based on the expectation that Micro LED displays will exhibit higher resolution and color saturation, a large number of LEDs smaller in size must be placed in a single backplane, and the mass transfer technology becomes Very important, but also as a key cost of successor but how to make such a large number of LED can be independently controlled, independent of light, which must rely on faster processing, higher throughput, higher reliability, power consumption A new generation of lower driver chips to complete.
From the original long-term operation of LED display and LED lighting products in the accumulation of science and technology, combined with the strength of ITRI, the development of Ultra Fine Pitch LED display driver chip, to make up for the incomplete Micro LED display technology.
As early as 2014, Gadget Technology has released and sold driver chips for Ultra Fine Pitch LED displays. However, for the more challenging Micro LED display needs, it has to overcome the bottleneck points of prior art capabilities and overcome them. Therefore, Accelerating the development of Micro LED display driver ICs based on existing technology of accumulation technology becomes an issue that can not wait.
Integration of domestic and foreign resources
At present, the display industry is very concerned about the development status and progress of the Micro LED display. Whether the Micro LED display can have the potential of rapid and huge growth predicted and expected by various media (such as market research institutes) Figure 7), or whether it can be difficult to break through the production of Micro LED display in the face of difficulties, which overcome the difficulties and bottlenecks but not single or single business can be done alone.
Figure 7: Market Forecast Micro LED display applications will grow rapidly.
Looking at the technological capabilities of enterprises in different countries, they all have their own strengths and abilities. So far, none of the enterprises in a single country can cover all technical capabilities. In Taiwan, the research and development, production and cost-saving capabilities of LED and displays , Are leading other companies in other countries, and Apple is also optimistic about Taiwan's ability to set up Micro LED display R & D plant in Longtan, but Taiwan in the materials and equipment part but not enough, so at this stage more need to combine Taiwan's automation equipment and The introduction of a large number of foreign materials industry, and invested, manpower together in the development of the Mileage LED display mileage, become a member of the leading group.