Introduction to OLED from LG Display's official website
OLED compares the advantages and disadvantages of traditional LCD screens
From the official website of LG Display
Do "thin", do "bend". Since OLED does not require a large area of backlight layer and liquid crystal layer, it has a natural advantage over LCD in thickness, and can achieve a very thin form, which is also in line with the needs of current smart phones, smart wearable devices, super TVs, and displays. In addition, because OLED does not necessarily need a "glass substrate" as the bottom layer, the upper layer of the material, so it can become bent, in recent years, the folding mobile phone is used in this technology, with soft PI plastic as the substrate to achieve a large angle of bending.
OPPO Find N, image from Pacific Computer Network
"Black" is pure, compared to the backlight technology used in LCD, when displaying black, you can only try to cover it up, OLED if you show black, that is, directly cut off the voltage transmission, so that the photon is no longer produced, there is no longer a trace of light, so that black is more pure. At the same time, due to the pure blackness, it also makes its contrast and LCD screen have a qualitative gap, the contrast ratio of OLED desktop monitors is often 100,000 to 1, and the desktop monitor of LCD screens is often only 1000 to 1 on average.
"Color is enchanting", OLED organic materials in the luminous can often emit a very pure three primary color light to combine into different colors, and LCD screen is subject to backlight technology and passive color display, in terms of color gamut is not as rich as OLED.
"Bright evenly", because the LCD display requires backlight as a support, and most of the backlight is "side-in", so the irradiation uniformity is more general. OLED is much better in this regard, because each pixel can emit its own light, it is easy to achieve uniformity and control in brightness uniformity, so that the screen looks more complete and unified.
"Fast action", the difference with the LCD screen display necessary liquid crystal molecule deflection takes time, so in the grayscale time (response time), OLED this way of using voltage to control the pixel point is many times faster, theoretically OLED screen can do 0.1ms level of response delay, and LCD screen The fastest e-sports fast IPS screen response time is about 5ms.
So is OLED invincible? Does OLED have no drawbacks at all? Of course not.
"Burn-in screen" Because the color of OLED comes from organic matter, it has to consider the problem of organic matter loss and short life, and because the service life of the same area size of red, green and blue tricolor sub-pixels is not the same, which leads to accelerated loss once one of the colors (blue life is the shortest), it will make the normal display content have a serious color cast, and even compose a certain graphic by the loss area, which is the burning screen, which is why some OLED mobile phones, The cause of yellowing of the TV after prolonged use.
The picture comes from the network, and the status bar at the bottom is still visible on the pure white background, which is the OLED burning screen phenomenon.
"Low fineness at the same resolution", in order to solve the above-mentioned screen burning problem, OLED manufacturers will generally use the adjustment of the size and position and number of red, green and blue three sub-pixels to control their life is almost equal. In the early stages of the OLED market, the Pentile arrangement was used, and the Pentile arrangement reduced the number of pixels by one-third compared to the standard RGB arrangement, and the degree of fineness was 2/3 of that of the LCD screen of the same resolution. Although with the development of the times, the sub-pixel arrangement of OLED has undergone new changes, such as Samsung's diamond arrangement, Huaxing Optoelectronics' pearl arrangement, so that the density of OLED pixels has increased, but the highest is only about 83%, and there is still a certain gap with the standard RGB vertical arrangement.
The image comes from the network, with the RGB standard arrangement on the left and the Pentile arrangement on the right
"High-frequency flash" IN recent years PMW dimming has been well known because of some mobile phone circle news, especially the new iPhone released last year, because it is equipped with high-frequency PMW dimming technology and many users complain that they can't stand it for a long time. So what is PMW dimming? PMW dimming is a pulse dimming technology, the principle is more cumbersome, simply take the lamp as a metaphor, the normal adjustment of the brightness of the lamp to rotate the knob to adjust the size of the voltage, resistance to achieve (DC dimming); and PMW dimming is by switching the lamp in a very short period of time, using the human eye for the light retention phenomenon to control the brightness. This is due to the fact that olED screens are not uniformly displayed at low brightness.
OLED luminescence principle
OLED (English name: Organic Light-Emitting Diode, Chinese literal translation: organic light-emitting diode) is a light-emitting technology of organic materials, first developed by the French in the 1950s, and then evolved by Kodak in the United States and Cambridge University in the United Kingdom, and mass production began in the 21st century by companies such as Sony in Japan and Samsung and LG in South Korea.
The most typical structure of OLED is the "sandwich-like" type, which consists of a thin and transparent indium tin oxide (ITO) with semiconductor characteristics, connected to the positive electrode of electricity, and another metal cathode to form three structures: the electric hole transmission layer (HTL), the light emitting layer (EL) and the electron transport layer (ETL). When a certain voltage is given, the electrons of the anode and the cathode will meet and combine in the light-emitting layer to produce photons. The luminous layer has a special organic material (O in OLED) that, along with the photons, becomes the primary colors of red, green, and blue.
OlED basic structure:1. Cathode ( ); 2. Emissive Layer (EL); 2. The anode cavity and the cathode electrons combine in the light-emitting layer to produce photons;4. 5. Conductive Layer; Anode (+), from Wikipedia.
To use an easy-to-understand metaphor, the principle of OLED is like "electrocution" of organic materials, and as soon as the cathode anode is energized, the organic material is "electrically illuminated". Since the red, green and blue primary color points in each pixel can be controlled by a separate voltage to emit light, no large area of backlight is required as the "bright source" of the screen, so this technology is also known as self-illumination technology.
From the principle of OLED emission, we can see that it is much simpler at the principle level than LCD technology. At the same time, OLED has many advantages over traditional LCD screens. Although there are some shortcomings, it is still flawed. The most important definition of a good screen should be to be able to restore the real colors of the world as much as possible, and OLED can certainly do a good job in this regard. But is OLED the ultimate answer? You can take a look at the following two technologies.
Mini LED和Micro LED
Among them, Mini LED technology we have already talked about in the previous issue, the principle is to change the original LED backlight board to be composed of thousands of individual LED lamp beads, of which multiple LED lamp beads constitute an LED backlight matrix, each backlight matrix can be turned into a separate light control area. Take a top-of-the-line Mini LED gaming screen on the market as an example, which has 4096 LED lamp beads, and every two of them can form a light control area, that is, it has 2048 separate light control areas.
The advantage of this is that the Mini LED also has the same ultra-high contrast as OLED and a more refined, adjustable local brightness, because when displaying the black area, the lamp beads in the area are in a state of extinction, so theoretically its contrast is equal to the OLED display, and there is no risk that the OLED display will burn the screen for a long time. Mini LED also has a big advantage is that its independent area lamp beads can be stimulated in a short period of time to produce a larger brightness, in some excellent Mini LED can achieve the highest brightness of 2000 nits in the local area, the common Mini LED can basically pass the HDR1000 certification, which makes the Mini LED very friendly to HDR content, in the HDR content display of high-quality Mini LED can be comparable to OLED.
But at present, Mini LED is still only a newly perfected screen type, but also can not get rid of the LCD screen inherent poor viewing angle and narrow color gamut problem, if you want to solve the problem of narrow color gamut, you have to add another layer of quantum dot film (QLED technology) in the Mini LED display to pull up the color gamut, but doing so will make the cost of the display greatly increased, more than worth the loss. At present, the display of high-end Mini LED can already achieve the level of high-end OLED, and there is still an advantage of about 15% in cost control.
Thanks to the domestic screen factory's offensive attitude towards the Mini LED market, in the next five years, Mini LED backlight technology will gradually become the mainstream backlight technology of high-end displays, and its technology will continue to improve, the number of lamp beads has been improved, and the technology of partition control has also been continuously improved.
Apple's new Macbook Pro series, released last year, is powered by a Mini LED screen
At present, although OLED has occupied most of the market of self-illuminating screens, Mini LED is ready to move, but there is a "new emperor" has been conceived, and its "king" atmosphere has made the first two feel threatened, it is Micro LED.
Micro LED (English: Micro Light Emitting Diode Display, Chinese literal translation for light-emitting diode display) Its display principle is to thinn, miniaturize and array the LED structure design of the red, green and blue primary colors, so that its size is only about 1 to 10 microns; then the micron level LED batch transfer to the circuit substrate, and then install the circuit and transistor under each micron LED. Not to finish with a simple Micro LED display.
Each pixel of the Micro LED contains three LED subpixels of RGB that can be self-emitting and independently controlled. Take Sony's first Micro LED product Crystal LED launched in 2012 as an example, the display has an area of 55 inches, 1920 * 1080 resolution, its number of micron LEDs is 1920 * 1080 * 3 = 6220800 pieces. Compared with the high-end Mini LED display area of about 20,000 lamp beads, micro LED technical difficulty increased by more than a little and a half.
Introduction to Micro LED from Samsung Display's official website
Because Micro LED uses a self-emitting individual micron-level LED, it is outstanding in color expression ability, micron LED luminescence spectrum its main wavelength of half-height full-width FWHM is only about 20nm, can provide extremely high color saturation, usually greater than 120% NTSC. This is almost consistent with the color gamut that today's top OLED displays can provide. At the same time, due to the stability of LED inorganics, the color can maintain consistency and stability no matter how much time it is used, which is unmatched by OLED. At the same time, Micro LED also takes into account the characteristics of displaying pure black, and it is pure black at the pixel level, which is more direct and pure than the partition backlight control of Mini LED.
Another point that Micro LED can achieve is power saving and ultra-high brightness, in the traditional LCD TV, the display efficiency is about 3%, the loss of TFT in the LCD is very small, because it is voltage driven. However, due to the energy loss in color filters, polarizers and LC materials, the efficiency of LCDs is very low. Due to the simple structure, small energy consumption, Micro LED has a higher photoelectric conversion efficiency, power consumption can be as low as 10% of LCD, 50% of OLED, while greatly reducing the unit of electricity consumption while allowing higher energy for direct luminescence, so that the highest brightness can go to nearly 2000 nits.
Micro LED almost all the advantages of OLED and LCD, taking into account high brightness, high color gamut, high contrast, but also can achieve long life, power saving, flexible screen. It can be said that it is the master of the future screen, so why does Micro LED have so many advantages and has not yet been popularized?
It can be said that the success of Xiao He also Xiao He, the advantage of Micro LED is from its million-level micron LED, and the difficulty also appears on this. At present, Micro LED mainly has three technical difficulties and problems, quantum efficiency Droop effect (limited effective luminous surface, low efficiency of red LED), driving capacity matching problem (requiring high current, low power consumption drive material), huge transfer problem (high process requirements, high accuracy requirements, high cost). The most important problem is the problem of huge transfers.
Schematic diagram of a large amount of transfer
Huge graft technology is currently the mainstream and ideal manufacturing technology of Micro LED, because Micro LED is a diode in micron-level units, which needs to be manufactured on silicon wafers, rather than directly on the screen substrate. So this requires the micron LEDs produced on the silicon wafer to be transplanted to the substrate of the screen. The transfer technology in this is called giant transplantation. Because the micron LED chips to be transferred, about 1/10 of the hair, require high precision fine operation; a transfer needs to move tens of thousands or even hundreds of thousands of LEDs, the number is very large, requiring a very high transfer rate, which makes the realization of the technology difficult to have a higher challenge.
Schematic of a large amount of transfer, from eeNews
At the same time, the cost of manufacturing a large number of micron LEDs is also more expensive, to a 2K resolution Micro LED screen for example, it takes 11.05 million micron LEDs to achieve, in the current manufacturing difficulty, it determines the cost and price of Micro LED is certainly not cheap. At present, in the civilian field, Micro LED has no formal mass production products, the last product relatively close to us is Samsung's The Wall commercial screen, Samsung's The Wall TV uses 806.4×453.6mm Micro LED panel module composition, each module has 960×540 resolution, bezel-less design, can be perfectly spliced. Each module has a brightness of 250 - 2000 nits, a contrast ratio of about 10,000:1, a color depth of 16 bits, and a refresh rate of up to 100/120 Hz. The screen size can be freely combined through the stitching of the module, and up to 292 inches of products can be selected. It also sells for a staggering $100,000.
Although Micro LED still has a lot of difficulties in technology and cost and manufacturing, it does not prevent major screen manufacturers and big brands from eager for it. Apple, one of the world's most successful technology brands, began laying out Micro LEDs in 2020, and Apple partnered with Taiwan PROVINCE LED producer Jingyuan Optoelectronics and Taiwan Province LCD panel manufacturer AUO Optoelectronics to build a new factory, which will be located in the Longtan branch of Hsinchu Science Park, and Apple's total investment is estimated at NT$10 billion (US$334 million). Apple said in a public report: "Like OLED, Micro-LED is also self-emitting. However, compared to OLED, Micro-LEDs can support higher brightness, higher dynamic range, and a wider color gamut, while enabling faster update rates, wider viewing angles, and lower power consumption, which are all qualities favored by Apple. ”
After the popularization of Micro LED, it is believed that it will become the first choice for future screen materials, and its modular assembly method can allow the screen to be customized according to the user's wishes, so that the screen can also enter the "DIY era".
Summary: In this issue of "Hardware Chronicle", we analyze and summarize the implementation technology and advantages and disadvantages of the three major product lines of the current self-illuminating screen camp (OLED, Mini LED, MIcro LED). The current self-illuminating screen is more mature, the market acceptance of high products for OLED, but OLED will not dominate the self-luminous screen camp for a long time, because Mini LED will achieve corner overtaking in these years, after the partition backlight technology and control chip mature, its long life, no attenuation, no burning screen advantages will be highlighted. Micro-LED is the next 20 years of the development of the screen trend, modular, miniaturized product form, high brightness, wide color gamut, high contrast, power saving, fast response characteristics make it can laugh to the end.