Micro LED technology, namely LED miniaturization and matrix technology. It refers to a high-density micro-sized LED array integrated on a chip. For example, each pixel of LED display screen can be addressed and driven separately, which can be regarded as a scaled-down version of outdoor LED display screen, reducing the pixel distance from millimeter level to micron level.
The micro LED display screen is an LED display driving circuit made by normal CMOS integrated circuit manufacturing process at the bottom, and then the LED array is made on the integrated circuit by MOCVD machine, so as to realize the micro display screen, that is, the micro version of the LED display screen.
Outstanding advantages
The advantages of Micro LED are obvious. It inherits the characteristics of inorganic LED, such as high efficiency, high brightness, high reliability and fast reaction time, and has the characteristics of self-luminous without backlight, which is more energy-saving, simple in mechanism, small in size and thin.
In addition, another major feature of Micro LED is its ultra-high resolution. Because it is ultra-small, the resolution of performance is particularly high; It is said that the resolution of Apple iPhone6S can easily reach 1500ppi if micro LED is used, which is 3.75 times higher than the original retina display screen of 400PPi.
Compared with organic light-emitting diodes, its color is easier to debug accurately, and it has the advantages of longer luminous life, higher brightness, better material stability, long service life and no image branding. Therefore, it is another display technology with light weight and power saving advantages after organic light emitting diodes. What it has in common with OLED is that it also needs to be driven by TFT backplane, so the technical level of TFT is IGZO, LTPS and oxide.
Existing shortcomings
1, costs and disadvantages of large-scale application. Depending on the single crystal silicon substrate as the driving circuit, according to the patent published by Apple, there is a step of transferring LED from sapphire substrate to silicon substrate, which means that making a screen requires at least two sets of substrates and independent processes. This will lead to an increase in cost, especially when it is applied in a large area, and it will face great challenges in yield and cost. (For monocrystalline silicon substrates, one or two inches is already a large area, refer to the price of full-width and larger CMOS sensor products. Of course, from a technical point of view, it is feasible for LuxVue to convert the driving circuit substrate into timing or glass to reduce the cost of large-area applications, but it also takes time. Compared with the mature LTPS+ organic light emitting diode scheme of AMOLED, the cost has no advantage.
2. The luminous efficiency advantage is threatened or even surpassed by PHOLED. The efficiency of organic light-emitting diode phosphorescent organic light-emitting diode has been obviously improved. UDC's red and green PHOLEDs have also been commercialized on the panels of Samsung GalaxyS4 and subsequent models, and the panel power consumption has been equal to or slightly better than that of high PPI TFT-LCD. Once the lifetime problem of blue light materials is solved and commercialized, the efficiency of inorganic LED will not be cheap.
3. Brightness and longevity are threatened by QLED. QLED research is very hot now. According to the data provided by QD Vision, both efficiency and life span are very promising, and many large companies are engaged in this research. Of course, QLED is also a strong competitor of OLED.
4. It is difficult to make a curled flexible display. The flexible display prospect of organic light emitting diodes and QLED is very good, and many prototypes have been displayed, but LuxVue is difficult to make them curly and flexible. If you want to make products like iWatch, it is not beautiful to have a certain curvature on the screen.
condition
Speaking of the development status of micro LED, as CandiceBrown-Elliott, the current CEO of Nouvoyance and the founder of P-arranged pixels in Samsung OLED panel, said, before Apple acquired LuxVue, only a few people knew and engaged in this field, and now many people have begun to discuss this technology.
Two experts in Micro-LED technology also said last year that it is still difficult to apply this technology to produce various practical screen panels, and it is unlikely to see this screen technology in iPhone, iPad or iMac products in the near future. However, for smaller display screens, Micro-LED is still a feasible choice, such as small screen applications such as Apple Watch.
In fact, since LuxVue was accepted by Apple, VerLASE has announced that it has obtained a breakthrough patent for color conversion technology, and can make full-color MicroLED arrays suitable for near-eye displays. Since then, there has been no relevant report. Recently, LEDinside got the news from the recent solid-state lighting seminar held in Taiwan Province Province. At the seminar, Leti, Texas Tech University and PlayNitride all showed their research and development achievements on microLED.
Leti deduced the iLED matrix, with blue EQE of 9.5% and brightness of 107Cd/m2. The green EQE is 5.9%, and the brightness can reach 108Cd/m2. Full-color display is realized by quantum dots with a pitch of only 10um, and the future goal is 1um. Leti's short-range plan is to start with intelligent lighting, enter the HUD and HMD markets in 2-3 years, and grab the VR/AR craze. The long-term goal is to cut into large-size display applications within 10 years.
And the PixeLEDTM display technology, which is also based on gallium nitride and published by Playride in Taiwan Province Province, is now transferred to the panel through transfer technology, and the transfer yield can reach 99%!
It can be seen that many companies have followed the Micro LED technology, and the development speed is also accelerating. But as far as Apple itself is concerned, this technology belongs to Apple's laboratory stage technology, and Apple itself has bet on many emerging industries, so it remains to be seen whether mass production will be introduced in the future.
Development bottleneck
In fact, the core technology of Micro LED is the transportation of nano-LED, not the technology of making LED itself. Due to lattice matching, LED micro-devices must be grown on sapphire substrate by molecular beam epitaxy. In order to manufacture the display, it is necessary to transfer the LED light-emitting micro-devices to the glass substrate. Because the size of sapphire substrate of LED micro-device is basically the size of silicon wafer, the size of glass substrate of display is much larger and needs to be transported many times.
It is especially difficult to transport micro-devices for many times, and it is even more difficult to use them in products that pursue high-precision display. From the patent list published after Apple acquired Luxvue, it can be seen that most of them use electrical means to complete the transshipment process, so this is the key core technology of Luxvue.
Li Yunli, CEO of Taiwan Province Chuangchuang, also said recently: "There are two keys to the success of Micro LED: First, the will of brand factories such as Apple and Samsung; The second is chip moving technology, which carries millions of ultra-small LED chips at a time, and there are thresholds to overcome. "
In fact, Micro LED is also facing the third problem, that is, full color, yield and wavelength consistency. Monochrome micro-LED arrays can be realized by flip-chip packaging and driving IC bonding, but RGB arrays need to transfer red, blue and green chips many times and embed hundreds of thousands of LED chips, which requires higher light efficiency, wavelength consistency and yield of LED chips. At the same time, the cost of Ning Bin is also a technical bottleneck that hinders mass production.