Micro LED technology, namely LED miniaturization and matrix technology. Refers to a high-density and small-sized LED array integrated on a chip. For example, each pixel of an LED Display can be addressed and individually driven to light up. It can be regarded as a miniature version of an outdoor LED display. The pixel distance is from millimeters. The level is reduced to the micron level.

What is Micro-LED?

Micro LED technology, namely LED miniaturization and matrix technology. Refers to a high-density and small-sized LED array integrated on a chip. For example, each pixel of an LED Display can be addressed and individually driven to light up. It can be regarded as a miniature version of an outdoor LED display. The pixel distance is from millimeters. The level is reduced to the micron level.

For Micro LED Display, the bottom layer uses normal CMOS integrated circuit manufacturing technology to make an LED display drive circuit, and then uses a MOCVD machine to make an LED array on the integrated circuit, thereby realizing a micro display, which is the so-called LED display. A reduced version of the screen.

 Analysis of the processing process of the full-color light emission of quantum dots based on the micro LED display

LuxVue active matrix Micro LED display applied for patent

Highlighted advantages

The advantages of Micro LED are obvious. It inherits the high efficiency, high brightness, high reliability and fast response time of inorganic LEDs. It also has the characteristics of self-illumination without backlight, more energy saving, simple structure, small size, Advantages such as thinness.

In addition, another major feature of Micro LED is its super high resolution. Because of its ultra-small size, the performance resolution is extremely high; it is said that if the Apple iPhone 6S uses micro LED, the resolution can easily reach 1500ppi or more, which is 3.75 times higher than the 400ppi of the original Retina display.

Compared with OLED, its color is easier to adjust accurately, has a longer light-emitting life and higher brightness, and has better material stability, long life, no image burn-in and other advantages. Therefore, it is another display technology that has the advantages of lightness, thinness and power saving after OLED. The commonality with OLED is that it also needs to be driven by a TFT backplane, so the TFT technology level is IGZO, LTPS, and Oxide.

 Analysis of the processing process of the full-color light emission of quantum dots based on the micro LED display

Existing disadvantages

1. The disadvantages of cost and large-area applications. Relying on the single crystal silicon substrate as the driving circuit, and from the patents published by Apple before, there are steps to transfer the LED from the sapphire substrate to the silicon substrate, which means that at least two sets of substrates and Independent crafts. This will lead to an increase in cost, especially when it is applied in a larger area, it will face huge challenges in yield and cost. (For a single crystal silicon substrate, one or two inches is already a large area, refer to the price of full-frame and larger medium-format CMOS sensor products) Of course, from a technical point of view, LuxVue converts the driving circuit substrate into quartz or Glass is feasible to reduce the cost of large-area applications, but it also takes time. Compared with AMOLED’s mature LTPS+OLED solution, there is no cost advantage.

 Analysis of the processing process of the full-color light emission of quantum dots based on the micro LED display

2. The advantage of luminous efficiency is threatened or even surpassed by PHOLED. Phosphorescent OLED (Phosphorescent OLED, PHOLED) efficiency improvement is obvious to all. UDC’s red and green PHOLED materials have also begun commercial use on the panels of Samsung Galaxy S4 and subsequent models, and the Panel power consumption has been leveled with the high PPI TFT-LCD. Or a slight advantage. Once the life issue of blue PHOLED materials is solved and commercialized, inorganic LEDs will not take advantage of the efficiency.

3. Brightness and lifespan are threatened by QLED. QLED research is very hot now. From the data provided by QD Vision, both efficiency and life expectancy are very promising, and there are many large companies engaged in this research. Of course, QLED is also a strong competitor of OLED.

4. It is difficult to make a curled and flexible display. OLED and QLED flexible display prospects are very good, and there have been many prototype displays, but it is more difficult for LuxVue to make curling and flexible. If you want to manufacture products such as iWatch, the screen does not have a certain curvature, which is less aesthetic.

status quo

Speaking of the development status of micro LED, just as Candice Brown-Elliott, the current CEO of Nouvoyance and the founder of P-array pixels in Samsung OLED panels, said, before Apple acquired LuxVue, only a few people knew about and engaged in this field, and now there are many people. Start discussing this technology.

Two Micro-LED technology experts also said last year that it is still difficult to apply and produce various practical screen panels with this level of technology. It is unlikely that this screen technology will be seen in iPhone, iPad or iMac products in the near future. But for smaller displays, Micro-LED is still a viable option, such as Apple Watch and other small screen applications.

Analysis of the processing process of quantum dot full-color light emission based on micro LED display

VerLASE’s MicroLED array in the near-eye display (NED) application

Analysis of the processing process of the full-color light emission of quantum dots based on the micro LED display

In fact, since LuxVue was acquired by Apple, VerLASE has announced that it has obtained a breakthrough color conversion technology patent, which can make full-color MicroLED arrays suitable for near-eye displays. There has been no related reports since then. Recently, LEDinside got news from the recent Taiwan Solid State Lighting Seminar. LeTI, Texas Tech University and PlayNitride all presented their micro LED research and development results at the seminar.

LeTI launched the iLED matrix. Its blue light EQE is 9.5%, and the brightness can reach 107 Cd/m2; the green EQE is 5.9%, and the brightness can reach 108 Cd/m2. Quantum dots are used to achieve full-color display, and the pitch is only 10 um. To 1 um. LeTI’s short-term plan is to start from smart lighting, and enter the HUD and HMD market in the mid-range 2-3 years to grab the VR/AR craze. The long-range goal is to cut into large-size display applications within 10 years.

And Taiwan’s Play Nitride announced the PixeLEDTM display technology, which is also based on gallium nitride. The company is currently transferring to the panel through the transfer technology, and the transfer yield rate can reach 99%!

It can be seen that many companies have followed up Micro LED technology, and the development speed is also accelerating. But as far as Apple itself is concerned, this technology is at the Apple laboratory stage, and Apple itself has bet on many emerging industries, so it remains to be seen whether it will be introduced into mass production in the future.

Development bottleneck

In fact, the core technology of Micro LED is the transfer of nano-level LEDs, not the technology itself of making LEDs. Due to lattice matching, LED micro-devices must first be grown on a sapphire substrate by molecular beam epitaxy. To make a display, it is necessary to transfer the LED light-emitting micro-devices to a glass substrate. Since the size of the sapphire substrate for making LED micro-devices is basically the size of the silicon wafer, while the size of the glass substrate for making the display is much larger, it will inevitably require multiple transfers.

The technical difficulty of multiple transportation of micro-devices is particularly high, and it is even more difficult to use in products pursuing high-precision displays. It can be seen from the list of patents obtained after Apple’s acquisition of Luxvue that most of them use electrical methods to complete the transfer process, so this is the key core technology of Luxvue.

Li Yunli, CEO of Taiwan’s Rchuang, said recently: “There are two keys to the success of Micro LED: one is the willingness of brands such as Apple and Samsung; the other is chip handling technology, which can handle millions of ultra-small LED chips at a time. overcome.”

In fact, Micro LEDs still face the third problem, namely, full-color, yield, and light-emitting wavelength uniformity. Monochrome Micro LED arrays can be realized by flip-chip packaging and driver IC bonding. However, RGB arrays need to be reposted with red, blue, and green dies in stages, and hundreds of thousands of LED dies need to be embedded. The requirements for particle light efficiency, wavelength consistency, and yield are higher, and the cost of binning is also a technical bottleneck hindering mass production.

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