OLED, or Organic Light-EmitTIng Diode, also known as Organic Electroluminesence Display (OELD), is a solid-state semiconductor light-emitting technology that should have organic materials. Although the term "laser" is mentioned in the name "Organic Electroluminesence Display", in essence, OLED technology is quite different from the single-optical and high-convergence laser technology in our usual concept. In many cases, the data does not consider OLEDs to belong. Laser field.
The organic light-emit TIng diode (OLED) is a patented display technology developed by Kodak that uses organic polymeric materials as a semiconductor material in light-emitting diodes. The polymeric material may be natural or synthetic, and may be very large in size or small in size. Proteins and DNA are examples of organic polymers.
OLED display technology is widely used in mobile phones, digital video cameras, DVD players, personal digital assistants (PDAs), notebook computers, car stereos and televisions. OLED displays are thin and light because they don't use backlights. The OLED display also has a wide viewing angle of up to 160 degrees, and its operating voltage is two to ten volts (volt, expressed in V). A new OLED-based technology is Soft Organic Luminescence Display (FOLED), which has the potential to enable highly portable, folded display technologies in the future.
OLED driving methodThe driving methods of OLEDs are divided into active driving (active driving) and passive driving (passive driving).
1, active drive (AM OLED)
Each pixel of the active driving (AMOLED) is equipped with a low-temperature polysilicon thin film transistor (Low-Temperature Poly-SiThin Film Transistor, LTP-SiTFT) with a switching function, and each pixel is equipped with a charge storage capacitor, and the peripheral driving circuit and the display array are integrated in the same system. On the glass substrate. The same TFT structure as the LCD cannot be used for OLEDs. This is because the LCD is driven by voltage, and the OLED is driven by current. The brightness is proportional to the amount of current. Therefore, in addition to the address TFT that performs the ON/OFF switching action, the on-resistance that allows sufficient current to pass is required. Low small drive TFT.
The active drive is a static drive with a memory effect that can be driven with 100% load. This drive is not limited by the number of scan electrodes and can be independently adjusted for each pixel. The active drive has no duty cycle problem, and the drive is not limited by the number of scan electrodes, making it easy to achieve high brightness and high resolution. Active driving is more advantageous for OLED colorization because it can independently perform gray scale adjustment driving on the red and blue pixels of brightness.
AMOLEDs consume less power than PMOLEDs because TFT arrays require less power than external circuits, making AMOLEDs suitable for large displays. AMOLED also has a higher refresh rate and is suitable for displaying video. The best use of AMOLEDs is computer monitors, large screen TVs, and electronic signage or billboards. However, the active driving method requires complicated built-in circuits, built-in transistors, and external ICs. These components are complicated in manufacturing process, high in cost, and difficult to achieve higher yield. Therefore, production cost and yield are the key technical bottlenecks for the large-scale promotion of active-driven OLED technology, especially for large-size display products.
2. Passive drive (PM OLED)
Passive drivers are further divided into static drive circuits and dynamic drive circuits.
(1) Static driving mode: On a statically driven organic light emitting display device, generally, the cathodes of the respective organic electroluminescent pixels are connected together, and the anodes of the respective pixels are separately led out, which is the connection mode of the common cathode. To make a pixel glow, as long as the difference between the voltage of the constant current source and the voltage of the cathode is greater than the pixel illumination value, the pixel will be illuminated by the constant current source. If a pixel does not emit light, its anode is connected. On a negative voltage, it can be turned off in reverse. However, cross-effects may occur when there are many changes in the image, in order to avoid the need for us to adopt the form of communication. The static drive circuit is generally used for the drive of the segment display.
(2) Dynamic driving method: On the dynamically driven organic light emitting display device, the two electrodes of the pixel are made into a matrix structure, that is, the electrodes of the same nature of the horizontal group of display pixels are shared, and the vertical group of display pixels The other electrode of the same nature is shared. If the pixels can be divided into N rows and M columns, there can be N row electrodes and M column electrodes. The rows and columns correspond to the two electrodes of the illuminating pixel, respectively. That is, the cathode and the anode. In the process of driving the actual circuit, it is necessary to illuminate line by line or to illuminate the pixels column by column, usually by progressive scanning, line scanning, and the column electrodes are data electrodes. This is achieved by cyclically applying pulses to each row of electrodes while all column electrodes give a drive current pulse for the row of pixels, thereby enabling display of all pixels in a row. The row is no longer in the same row or the same column of pixels is added to the reverse voltage so that it is not displayed to avoid "cross-effect". This scanning is performed line by line, and the time required to scan all the lines is called the frame period.
The selection time for each line in a frame is equal. Assuming that the number of scanning lines of one frame is N and the time for scanning one frame is 1, the selection time occupied by one line is 1/N of one frame time. This value is called the duty ratio coefficient. At the same current, an increase in the number of scanning lines will lower the duty ratio, thereby causing an effective drop in current injection on the organic electroluminescent pixel in one frame, which degrades the display quality. Therefore, as the number of display pixels increases, in order to ensure display quality, it is necessary to appropriately increase the driving current or to employ a dual-screen electrode mechanism to increase the duty ratio coefficient.
In addition to the common cross-effect of the electrodes, the mechanism of positive and negative charge carriers combined to form luminescence in an organic electroluminescent display allows any two luminescent pixels to be directly connected to any one of the functional films that make up their structure. The two illuminating pixels may have mutual crosstalk, that is, one pixel emits light, and the other pixel may emit weak light. This phenomenon is mainly caused by the poor uniformity of the thickness of the organic functional film and the poor lateral insulation of the film. From the perspective of driving, in order to mitigate this unfavorable crosstalk, it is also an effective method to take the reverse cut-off method.
Display with grayscale control: The grayscale of the display refers to the brightness level between black and white for black and white images. The more gray levels, the richer the image is from black to white, and the more detailed the details. Grayscale is a very important indicator for image display and colorization. Generally, the screens for grayscale display are mostly dot matrix displays, and the driving thereof is mostly dynamic driving. Several methods for realizing grayscale control are: control method, spatial grayscale modulation, and time grayscale modulation.
PMOLEDs are easy to manufacture, but they consume more power than other types of OLEDs, mainly because they require external circuitry. PMOLED is the most efficient for displaying text and icons, and is suitable for making small screens (2-3 inches diagonally), such as those that people often see on mobile phones, palmtops, and MP3 players. Even with an external circuit, the passive matrix OLED consumes less power than the LCDs currently used in these devices.
Full color display is an important indicator to verify whether the display is competitive in the market. Therefore, many full-colorization technologies are also applied to OLED displays. There are usually three types of panel types: RGB pixel independent illumination, color conversion (Color) Conversion) and color filter (Color Filter).
RGB pixels independently illuminated
Independent illumination with luminescent materials is currently the most widely used color mode. It uses a precise metal shadow mask and CCD pixel alignment technology. First, it prepares the red, green and blue primary color illuminating centers, and then adjusts the color mixing ratio of the three color combinations to produce true color, so that the three-color OLED elements are independently illuminated. One pixel. The key to this technology is to improve the color purity and luminous efficiency of the luminescent material, while the metal shadow mask etching technology is also crucial.
The organic small molecule luminescent material AlQ3 is a good green light emitting small molecular material, and its green color purity, luminous efficiency and stability are very good. However, the best red light-emitting small molecule material of OLED has a luminous efficiency of only 31 mW and a lifetime of 10,000 hours. The development of blue light-emitting small molecule materials is also very slow and difficult. The biggest bottleneck faced by organic small molecule luminescent materials is the purity, efficiency and longevity of red and blue materials. However, by doping the host luminescent material, blue light and red light with good color purity, luminous efficiency and stability have been obtained.
The advantage of the polymer luminescent material is that it can be adjusted by chemical modification. It has been obtained from blue to green to red in various colors covering the entire visible range, but its lifetime is only one tenth of that of small molecule luminescent materials. Therefore, for high molecular polymers, the luminous efficiency and lifetime of the luminescent materials need to be improved. Continuous development of luminescent materials with excellent performance should be an arduous and long-term issue for material developers.
With the colorization, high resolution and large area of ​​the OLED display, the metal shadow mask etching technology directly affects the quality of the display panel image, so more stringent requirements are placed on the dimensional accuracy and positioning accuracy of the metal shadow mask.
Light color conversion color conversion is based on blue OLED combined with color conversion
In the film array, a device for emitting a blue OLED is first prepared, and then a red light and a green light are obtained by using the blue light excitation color conversion material to obtain full color. The key to this technology is to improve the color purity and efficiency of the light color conversion material. This technology does not require a metal shadow mask alignment technology, and only needs to evaporate blue OLED components, which is one of the potential full colorization technologies for large-size full-color OLED displays in the future. However, its disadvantage is that the light color conversion material easily absorbs blue light in the environment, resulting in a decrease in image contrast, and the light guide also causes a problem of reduced picture quality. Japan's Idemitsu Kosan Co., Ltd., which has mastered this technology, has produced 10-inch OLED displays.
Color filter film
This technology utilizes a white light OLED combined with a color filter film to first prepare a device for emitting a white light OLED, and then obtains three primary colors through a color filter film, and then combines the three primary colors to realize color display. The key to this technology is to obtain high efficiency and high purity white light. Its production process does not require metal shadow mask alignment technology, and can adopt the color filter film making technology of mature liquid crystal display LCD. Therefore, it is one of the potential full-colorization technologies for large-size full-color OLED displays in the future, but this technology can cause up to two-thirds of the light loss caused by the color filter film. Japan's TDK Corporation and the US Kodak Company use this method to make OLED displays.
RGB pixel independent illumination, light color conversion and color filter film three manufacturing OLED display full color technology, each has advantages and disadvantages. Can be determined according to the process structure and organic materials.
At present, LCD is the first choice for small device displays, and large screen TVs are also common. Conventional LEDs can be used to form numbers on electronic watches and other electronic devices. OLEDs have many advantages that LCDs and LEDs do not have:
Compared to the crystal layer of an LED or LCD, the organic plastic layer of the OLED is thinner, lighter and more flexible.
The luminescent layer of the OLED is relatively light, so that its base layer can be made of a flexible material without using a rigid material. The OLED base layer is made of plastic, while the LED and LCD use a glass base layer.
OLEDs are brighter than LEDs. The OLED organic layer is much thinner than the corresponding inorganic crystal layer in the LED, and thus the conductive layer and the emission layer of the OLED can adopt a multilayer structure. In addition, LEDs and LCDs require glass as a support, while glass absorbs some of the light. OLEDs do not require the use of glass.
OLEDs do not need to use a backlighting system in the LCD. The LCD selectively blocks certain backlight areas during operation, allowing the image to appear, while the OLED is illuminated by itself. Because OLEDs do not require a backlighting system, they consume less power than LCDs (most of the power consumed by LCDs are used in backlighting systems). This is especially important for battery powered devices such as mobile phones.
OLEDs are easier to manufacture and can be made in larger sizes. OLED is made of plastic material, so it can be made into a large-area sheet. It is much more difficult to use so many crystals and flatten them.
OLEDs have a wide field of view, up to 170 degrees. While the LCD is working to block light, there are natural obstructions at some angles. The OLED itself can emit light, so the field of view is also much wider.
OLED problemsOLED seems to be a perfect technology for all types of displays, but it also has some problems:
Lifespan: Although red and green OLED films have a long life (10,000-40,000 hours), the life of blue organics is much shorter (only about 1000 hours) according to current state of the art.
Manufacturing: The cost of OLEDs is still relatively high.
Water: If the OLED is in contact with water, it will easily be destroyed.
OLED applicationFirst, the application of OLED in the field of head-mounted display
Head-mounted displays with video glasses and portable cinemas have become more and more widely used and developed. It has excellent advantages in digital video, virtual reality, virtual reality games, 3G and video glasses fusion, ultra-portable multimedia devices and video glasses.
Compared with LCD and LCOS, OLED has great advantages in the application of head-mounted display: clear and bright full-color display, ultra-low power consumption, etc., is a major driving force for the development of head-mounted displays.
The first to apply OLEDs to video glasses is the US eMagin. It provides an excellent near-eye solution for both consumer and industrial applications as well as military applications. As a result, video glasses using European ultra-micro OLED displays were introduced to the market. In China, iTheater is the first to introduce the world's first high-definition ultra-micro OLED display video glasses with its strong R&D capabilities; it has successfully entered the domestic military field with the background of its full intellectual property rights, and is the construction of Chinese digital soldiers. make an effort.
Second, the application of OLED in the field of MP3
As a digital walkman, MP3 has become the protagonist of fashion entertainment in the market. It has received wide attention from its functions, capacity, price, etc. It is also the focus of the eyes of various manufacturers, but for the eyes of MP3. The screen is rarely involved.
In addition to video and audio products, whether it is Flash or HDD MP3, most of them use black and white monochrome LCD panels, just staying on the simple requirements of listening to music. But nowadays, in addition to this most basic function, MP3 is based more on people's psychology of individuality and fashion, and expresses a concept of life. Therefore, in the design of the panel, a colorful backlight design appeared, which is the "7-color backlight" product that is often heard. Based on this development, it has been used in regional color OLED panels (such as 16-color scales in areas such as yellow and blue), such as the Joybee 180 and iRiver N10 from BenQ.
OLED (Organic Light EmitTIng Display), an organic light-emitting display, is a newly emerging category in the field of MP3 screen applications, and is known as the "dream display." It does not require a backlight, but "active illumination." Taking the OLED LCD screen of BenQ Joybee180 as an example, it eliminates the shortcomings of the traditional LCD. Each pixel can emit light by itself, no matter what angle or light, it can display a clearer picture than the traditional LCD display, and the darker the environment, the more the screen Bright, like the nighttime fairy spirit.
MP3 consumers are mostly young people. For them, MP3 has a little bit of flaming color in addition to its basic functions. On the quiet street at night, listening to music while walking, watching the blue light of the OLED screen beating, the beating of the notes accompanied by the beating of the footsteps and the ups and downs of the mood, there is a different feeling. Or on the party where friends are gathering, the bokeh of blue light will make you the protagonist of the party.
In addition to bringing a new visual experience, OLEDs have many advantages that LCD panels cannot match. For example, the MP3 can be made lighter and thinner, has a larger viewing angle, and can significantly save power. However, the application of OLED must be matched with the overall design of MP3 to show its charm. The listed BenQ Joybee180 can be said to be a model for combining LCD applications with overall design. The Joybee180 is stylish, simple and generous. The whole machine is square in shape and looks like a delicate and small tote bag. The essence is like a gorgeous watch. Moreover, using the popular elements of the strap to replace the traditional wearing method, providing a series of different panels, can be replaced according to the different styles of clothing, changing the past unchanging matching scheme, show your fashion mix, show your unique mood.
The application of OLED to MP3 products not only increases the beauty of the products, but also adds to the expression of graphic information, which will undoubtedly become the mainstream of MP3 display panels.
Third, potential applications
The main advantage of OLED technology is active illumination. Red, green, and blue OLEDs are available. In the past few years, researchers have been developing OLED applications ranging from backlights to low-capacity displays to high-capacity displays. Below, the potential applications of OLEDs will be discussed and compared to other display technologies.
The first commercialization in 1999, the technology is still very new. Used in some black and white / simple color car radios, mobile phones, handheld electric game instruments. Both belong to high-end models.
Engaged in the commercial development of OLED, more than 100 manufacturers around the world, OLED technology development direction is divided into two categories, Japan, South Korea and Taiwan tend to Kodak's low-molecular OLED technology, European manufacturers are mainly PLED. In addition to the KODAK alliance, another major group of polymers, Philips, which is based on high-molecular polymers, has joined forces with companies such as EPSON, DuPont and Toshiba to develop their own products. The output value of the global OLED market in the second quarter of 2007 has reached $123.4 million.
In terms of Chinese enterprises, as early as 2005, Tsinghua University and Visionox decided to start the construction of OLED large-scale production lines, and finally built a large-scale OLED production line in Kunshan; Guangdong Province also actively launched the OLED project, as of December 2009, There are 5 OLED production line projects that have been built, under construction and under construction in Guangdong. They are Shanwei Xinli small-size OLED production line, Foshan Zhongxian Technology's low-temperature polysilicon TFT (thin-film field effect transistor) AMOLED production line project, and Dongguan Hongwei's OLED display screen. Demonstration production line project, Huizhou Maoqin Optoelectronics AM (active) OLED optoelectronics project, Rainbow OLED production line project in Foshan. According to research firm DisplaySearch, the global OLED industry's output value in 2009 was 826 million US dollars, an increase of 35% over 2008. China has become the world's largest market for OLED applications, with China's mobile phones, mobile display devices and other consumer electronics products producing more than half of global production.
Fourth, the development of "transparent aircraft" in the aviation field
At the end of October 2014, the British technology company plans to develop a "transparent aircraft", allowing passengers to sit in the cabin and enjoy the 360-degree panoramic view, just like flying in the sky.
The Centre for Process InnovaTIon (CPI) recently published a new concept for passenger aircraft design, which will use OLED (Organic Light-Emitting Diode) technology on the aircraft fuselage, not only It allows passengers to view the scenery outside the window and even turn into a touch screen, allowing passengers to fully enjoy the machine.
The British Process Innovation Center envisions a windowless aircraft with an OLED display. The enhanced illumination of the cabin lighting comes from the bulkhead lighting wall, creating a unique travel atmosphere for passengers. The flexible screen with OLED technology is extremely thin and light, high quality and flexible embedded in the fuselage and seat backing lining, organically integrated, eliminating the heavy outer casing and allowing high-definition display to capture images captured from external cameras. This optimizes the space and weight of the aircraft, not only reduces costs, but also makes the body lighter, stronger, and more spacious, reducing fuel consumption.
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