Micro LED es una nueva generación de tecnología de visualización que es más brillante y luminosa que la tecnología OLED existente, pero consume menos energía. En mayo de 2017, Apple comenzó el desarrollo de una nueva generación de tecnología de visualización. En febrero de 2018, Samsung lanzó televisores Micro LED en CES 2018.
Características de los microLED
Micro LEDs are brighter and more efficient than existing OLED technologies, but consume less power. The excellent properties of MicroLED will make it available on TVs, iPhones, and iPads.
Historia de los micro LED
Speaking of Micro LED, we must start with the application of display TFT-LCD backlight module. When TFT-LCD began to flourish in the 1990s, some manufacturers used LEDs as backlights because of their high color saturation, power saving, and thinness. However, due to factors such as high cost, poor heat dissipation, and low photoelectric efficiency, it has not been widely used in TFT-LCD products.
Until 2000, the process, efficiency, and cost of white LED technology with blue light LED chips stimulated phosphors began to mature; when entering 2008, white LED backlight modules showed explosive growth, almost completely replacing CCFL in a few years. The application field extends from mobile phones, tablet computers, desktop monitors to TVs and so on.
However, due to the non-self-luminous display principle of TFT-LCD, its open cell transmittance is about 7 percent or less, resulting in low photoelectric efficiency of TFT-LCD; and the color saturation provided by white LED is still not as good as that of three-primary LED. , Most TFT-LCD products are only about 72 percent NTSC; in addition, in the outdoor environment, the brightness of TFT-LCD cannot be increased to more than 1000nits, resulting in low image and color recognition, which is a major application defect. Therefore, another technology of LED Display or Micro LED Display that directly uses three primary color LEDs as self-luminous display dot pixels is also under development.
Principio de la tecnología Micro LED
The display principle of Micro LED Display is to make the LED structure design thin, miniaturized and arrayed, and its size is only about 110 μm; then the Micro LED is transferred to the circuit substrate in batches, and the substrate can be rigid, soft It is a transparent and opaque substrate with good properties; and then the physical deposition process is used to complete the protective layer and the upper electrode, and then the upper substrate can be packaged to complete a MicroLED display with a simple structure.
In order to make a display, the surface of the wafer must be made into an array structure like an LED display, and each dot pixel must be addressable and controllable and individually driven to light up. If it is driven by a complementary metal oxide semiconductor circuit, it is an active addressing driving structure, and packaging technology can be passed between the Micro LED array chip and the CMOS.
After the pasting is completed, the Micro LED can improve the brightness and contrast by integrating the microlens array. The Micro LED array is connected to the positive and negative electrodes of each Micro LED through vertically staggered positive and negative grid electrodes. The electrodes are energized in sequence, and the Micro LEDs are lit by scanning to display images.
The typical structure of Micro LED is - PN junction diode, which is composed of direct energy gap semiconductor material. When a forward bias is applied to the upper and lower electrodes of the Micro LED, causing the current to pass through, the electrons and holes recombine in the active region, emitting a single color of light. The FWHM of the dominant wavelength of the Micro LED spectrum is about 20nm, which can provide extremely high color saturation, usually reaching 120 percent NTSC.
And since 2008, LED photoelectric conversion efficiency has been greatly improved, and more than 100lm/W has become a mass production standard. Therefore, for the application of Micro LED display, due to its self-luminous display characteristics, with a simple structure with almost no light-consuming components, a display design with low energy consumption or high brightness can be easily realized.
This can solve the two major problems of current display applications. One is that more than 80 percent of the energy consumption of wearable devices, mobile phones, tablets and other devices is on the display, and low-power display technology can provide longer battery life; the second is ambient light. The problem is that the image on the display is whitened and the recognition is poor, and the high-brightness display technology can make its application range wider.
Ventajas de los microLED
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 pitch, each pixel can be addressed and controlled and driven to emit light at a single point. Compared with other LEDs, in terms of luminous efficiency, Micro LED is currently the highest, and there is still room for significant improvement; in terms of luminous energy density, Micro LED is also the highest, and there is still room for improvement. The former is conducive to the energy saving of display devices, and its power consumption is about 10 percent of LCD and 50 percent of OLED; the latter can save the limited surface area of display devices and deploy more sensors. The current theoretical result is that Micro LEDs Compared with OLED, to achieve the same display brightness, only about 10 percent of the coating area of the latter is required. Compared with OLED, which is also a self-luminous display, the brightness is 30 times higher, and the resolution can reach 1500PPI (pixel density), which is equivalent to 5 times the 300PPI used by the Apple Watch.
long life. Because Micro LED uses inorganic materials, and has a simple structure, it has almost no light consumption, and its service life is very long. This point is incomparable to OLED. As an organic material and organic substance, OLED has its inherent defects, namely lifespan and stability, and it is difficult to compare with QLED and MICROLED of inorganic materials.
There is a lot of room for cost reduction. At present, the micro-projection technology is mainly based on three technologies: Digital Light Processing (DLP), reflective liquid crystal display on silicon substrate (LiquidCrystalonSilicon, LCoS), and MEMS scanning (MEMS Scanning), but these three technologies must use external The light source makes it difficult to further reduce the volume of the module, and the cost is also high. In contrast, the self-illuminating Micro LED microdisplay does not need an external light source, and the optical system is simpler, so it has advantages in miniaturization of the module volume and cost reduction.
Wide range of applications. Micro LED solves several major problems. One is that 80 percent of the energy consumption of consumer tablets, including smartphones and wearable devices, is on the display. Micro LED displays with low energy consumption will greatly extend battery life. For the application of Micro LED display, due to Its self-luminous display characteristics, combined with a simple structure with almost no light-consuming components, can easily realize low-power or high-brightness display design. Second, the strong ambient light causes the image on the display to be whitened and the recognition degree deteriorates. The high-brightness display technology of Micro LED can easily solve this problem and make its application range wider.
¿Cómo es la cadena de la industria Micro LED?
For a Micro LED display product, its basic components are TFT substrate, ultra-micro LED die, and driver IC. The three have a common feature, that is, a large number of inheritance from the existing LCD and LED industries. Therefore, Taiwan Industrial Research Institute believes that they have the advantage of the entire industry chain.
However, regions with the same industrial base also include South Korea, mainland China, and Japan. Among them, Japan's leadership and perfection in upstream materials and equipment far exceed that of Taiwan in China. However, Japanese colleagues' interest in Micro LED is not as high as the Taiwanese industry.
Why are other regions with comparable or better industrial bases less enthusiastic about Micro LED than Taiwan? The answer is divided into two levels: the first is that the display companies in mainland China, South Korea and Japan are currently the busiest thing to do is OLED. Second, Micro LED has a difficult process that other electronics industries rarely use - mass micro-transfer (also called mass transfer). One of the biggest moves in Taiwan's Micro LED industry is the establishment of a "massive micro-transfer" industry alliance in December 2016 with the Taiwan Industrial Technology Research Institute as the lead unit.
What kind of technology is "mass transfer"? Simply put, on the TFT circuit substrate the size of a fingernail, according to the necessary specifications of optics and electricals, three to five hundred or even more red, green and blue three primary color LED micro-chips are evenly welded, and the allowable process failure rate is only hundreds of thousands. one part.
For the process of Micro LED, many people believe that experience can be learned from traditional LED screens. However, Micro LED is very different from traditional LED display products. Compared with the traditional LED display, the main differences of Micro LED are: 1. The degree of precision is improved by dozens of times; 2. The integration process has changed from direct insertion, surface mount, COB packaging, etc. to "mass micro-transfer"; 3. Defect repairability is almost zero; 4. The backplane has changed from a printed circuit board to a TFT substrate used in liquid crystal and OLED displays, or a single crystal silicon substrate used in CPU and memory.
That is, compared with traditional LED displays, Micro LEDs are different in every aspect, such as die, packaging, integration process, backplane, and driver. Therefore, it can be seen that the popularity of Micro LED products has not gained any traditional LED large screen. manufacturer's statement.
In fact, in addition to the "element components" such as die, TFT backplane, and IC, which are inherited from LED die (such as Sanan), semiconductor display (such as BOE), and IC design companies (such as Accumulation, Qijing), etc., The real core of Micro LED is "how to integrate these components", that is, "mass transfer" technology. The latter is the lifeblood of the entire industry. If there is a company that wants to lead Micro LED products, the most important thing is to start from here.
In this regard, the more accurate news is that in February this year, Mikro Mesa and Chongqing Huike jointly built the first Micro LED panel laboratory on both sides of the Taiwan Strait. The lab is scheduled to be completed by the end of this year, with full-color Micro LED samples manufactured in 2018. Mikro Mesa currently has leading RD technology in LED micro-die, and it is rumored that it can achieve 3UM. Huike has built an A-SILCD production line and has technical resources such as TFT backplane. The purpose of the cooperation between the two is to use the resources as readily available as possible to break through the "mass transfer" technology.
However, even for such a relatively in-depth project, its expectations for the Micro LED industry timetable are not optimistic: the realization of full-color samples in 2018, it is still difficult to say how far away from the real commercial application. Taking OLED as an example, it has taken more than 20 years to achieve full color and the current large-scale recognition in the mobile phone industry. In addition, Huike and Mikro Mesa are both newcomers to the display circle. Their attention to Micro LED is quite an attempt to overtake in corners.
To sum up, from the perspective of components, Micro LED is not difficult in TFT, IC, and LED die; however, from the perspective of technology and industrial process, the huge transfer lies between the vision and reality of Micro LED, and it is difficult to completely transfer in the short term. span.
Micro LED tiene amplias perspectivas de aplicación
At present, if considering 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 on the new generation of Apple Watch and iPhone, and it is expected to use Micro LED technology in 2018. Launched Micro LED wearable devices. The second is the super-sized TV market, represented by Sony. The Micro LED cledis displayed by Sony at CES this year has excellent performance in terms of resolution, brightness and contrast.
In the short term, the Micro LED market is concentrated in ultra-small displays. In the medium and long term, Micro LED has a wide range of applications, spanning wearable devices, large indoor display screens, head-mounted displays (HUDs), head-up displays (HUDs) ), taillights, wireless optical communication Li-Fi, AR/VR, projectors, etc.
