PDP (Plasma Display Panel, plasma display panel in Taiwan) is a display technology that uses gas discharge, and its working principle is very similar to that of fluorescent lamps. It uses a plasma tube as a light-emitting element. Each plasma tube on the screen corresponds to one pixel. The screen uses glass as a substrate. The substrates are separated by a certain distance, and the surrounding is sealed by airtightness to form a discharge space. The discharge space is filled with a mixed inert gas such as helium or neon as a working medium. A metal oxide conductive film is coated on the inner side surfaces of the two glass substrates as an excitation electrode. When a voltage is applied to the electrodes, a plasma discharge phenomenon occurs in the mixed gas in the discharge space. The gas plasma discharge generates ultraviolet light, the ultraviolet light excites the fluorescent screen, and the fluorescent screen emits visible light to reveal an image.
Plasma display is also known as a plasma display in Taiwan. Although the translation name is different, the meaning is the same. To understand the plasma display, you need to know what a plasma is.
From a physics point of view, plasma refers to the fourth substance; but when placed in medical science, plasma refers to plasma; in addition, plasma can also be interpreted as protoplasm or protoplasm, that is, including nuclear and cytoplasm Place. In the world of Plasma Display Panels (PDPs), plasma is the phenomenon of discharge.
The plasma display is composed of two front and back glass panels. The front panel is composed of a glass base layer, a transparent electrode, an auxiliary electrode, an electric conductor layer and a magnesium oxide protective layer, and covers the transparent dielectric layer (Dielectric Layer) on the electrode and prevents the ions from striking the MgO layer of the dielectric layer; the rear plate The glass has a Data electrode, a dielectric layer, and a strip-shaped partition wall (BarrierRib), and sequentially applies red, green, and blue phosphors on the inner side of the middle partition wall, and after combining, nitrogen, helium, and the like are respectively implanted to form a plasma. panel.
At present, each plasma display panel factory is mainly produced by a 42-inch VGA (16:9) plasma screen, so the size of each cell body is about 0.36 mm. However, when the resolution is increased from VGA to XGA, the size of the cell body will be reduced to 0.24mm, which will be accompanied by changes in other elements such as the size of the partition, the size of the electrode, the thickness of the dielectric film, and the phosphor. The thickness and shape will also change. Generally, a high-definition change, that is, a high-density structure, relatively causes a decrease in luminance and a doubling of IC cost.
Pioneer and Fujitsu's fine plasma display panel products have a resolution of up to SXGA, but still exhibit high brightness. Gradually high-quality digital broadcasting is beginning to take place around the world, and plasma display screens are gradually entering the TV market. Therefore, improving the picture quality will be the current priority of the new plasma display.
Principle of illumination
The plasma display can be said to put a lot of tiny fluorescent tubes in a mother body, which is controlled by traditional methods, one is direct current (DC-) and the other is alternating current (AC). In 1964, the University of Illinois at the University of Illinois developed an AC-type plasma display panel. After years of technological reforms, plasma technology is now using AC, because its simple structure can extend the life of plasma displays.
The phenomenon of discharge is to introduce AC conductance into the display. The basic technology of the panel is to form a plurality of sealed spaces between the two glass substrates and the partition walls to allow active movement of ions and electrons, and to inject rare gases and helium into the sealed spaces. In addition, the electrodes (positive and negative electrodes) on the upper and lower devices of this sealed space cause the particles to collide with the gas at a high speed to generate a high energy state. When these particles calm down, the energy will slowly dissipate, thereby emitting ultraviolet rays, and the discharge phenomenon is formed in this way. Ultraviolet light can irritate red, green, and blue phosphors. Each cell body can independently generate a discharge phenomenon, and each cell's switch is controlled along with the video source.
The next step is to talk about the technique of producing hue. To make the color of the plasma display dazzling, each of the three primary color cell bodies must be manipulated independently. In the past, the picture tube was played from left to right, from top to bottom, and scanned by an electron beam. But the plasma uses a completely different method. Since the display is fully illuminated at the same time, the screen is alternately displayed from top to bottom in 60 seconds. However, during this period, the previous data remains on the screen, so the screen It is in a state of constant illumination.
In terms of the color of the image, it is not possible to adjust the amount of electron beam as in the case of a picture tube. Since both the ultraviolet light and the visible light are already saturated, it is impossible to use the control of the current to control the brightness. Even if the current changes, the brightness of the picture will not change. Therefore, the plasma uses PCM (Pulse Code ModulaTIon) technology to control the pulse in each area, which can change the brightness of the picture.
First, the image is composed of 60 frames per second. Secondly, each frame is divided into 8 sub-regions, and the relative brightness of each sub-region is determined according to the appropriate pulse law. The small fluorescent lights in each area are illuminated and extinguished in response to the imagery; finally, these sub-areas are combined to display 256 shades. Combining the total number of colors is 256 & TImes; 256x 256 = 16,777,216 colors.
This method can be said to be very complicated, and it also brings out a serious shortcoming. The generation of afterimages "In order to solve this problem, the plants of various plasma display panels are also actively researching countermeasures, such as clearing the driving method or using screen savers. The problem is finally solved.
Brightness improvement technology
Since the plasma display is fully illuminated, the power consumption must be large, but with the improvement of technology, the power consumption of the plasma has gradually dropped below 300W. But it is not forgotten that under the increase of brightness, it still needs high brightness to enhance the image quality. In the past, the energy efficiency of plasma should be only 1.4%, and the luminous efficiency is only 1.11m/W, so there must be improvement. Scientists have adopted two improvements, one is to start from the cell body's aperture ratio structure; the other is to improve the material.
In terms of general plasma structure, the most direct method to increase the luminosity is to increase the aperture ratio of the cell body and increase the space for discharge. The aperture ratio of the discharged cell body is related to the Barrier Rib structure in the plasma, and the partition wall is made thinner by a new manufacturing method to increase the discharge space. The general plasma partition is manufactured by the Screer, PrinTIng, SanfCiilUSt or PhrWesist methods, but the new manufacturing process, such as TORAY's PhotosensiTIve film paste or Kyocera's Press Method, can reduce the space occupied by the partition walls. Thereby increasing the aperture ratio.
In addition, Pioneer changes the RGB arrangement of the general panel from a stripe to a well-shaped shape, and uses a T-shaped transparent electrode to prevent the fluorescent material from leaking light and increase the light-emitting area of ​​the fluorescent material, thereby improving the luminous efficiency by 20%. However, in the case of a well-shaped partition wall, the Sand-Blust1- method is still used, so it is difficult in the manufacturing process.
Since the plasma is generated by a rare gas discharge to generate vacuum ultraviolet rays, the illuminating phosphor powder emits light. Its luminous efficiency depends on the discharge efficiency and the conversion efficiency of the luminescent powder. Because the discharge space is small, the discharge efficiency is naturally low, and the energy conversion efficiency of the phosphor powder is only 20%.
If UV radiation and various absorption factors are added, the current luminous efficiency of the plasma display panel is less than 0.4%, and the lumen efficiency is less than 1.11 m/W. If compared with the high-definition PDP 51 m/WAWO efficiency requirement, there are still A distance. In order to improve the discharge efficiency, in addition to thinning the partition wall to increase the discharge space, the mixing ratio of the discharge body and the gas optimization; the discharge ultraviolet red shift and the increase of the AC sustain discharge time are all feasible solutions.
Plasma display manufacturing process
The production process of the plasma display screen has a manufacturing process of the front stage and the back stage, and the front stage process includes the front base layer manufacturing and the back base layer manufacturing. The latter process involves joining, heating, venting, and injecting pure gases such as nitrogen and helium, and finally the inspection process.
At the current stage of the production of plasma display screens, the most difficult part is the production of the rear partition walls. Since the function of the partition wall is to prevent adjacent atomic ends, a discharge interference problem may occur in the process. Therefore, the precision of the partition wall needs to be very high to avoid the existence of open holes, etc. If there are open holes such as holes, after the panel is used for a period of time, the partition wall may cause the voltage value at the atomic end due to the interference generated therein. change.
In addition, the production method of the phosphor can be divided into four ways, and the manufacturing method is to sequentially apply the three primary colors of red, green and blue, so the precision of the partition wall is also very high. If the interval precision is not high, and electricity is generated in the atom, the phosphor powder will be excited together and there is no light, so that the panel color cannot be controlled. At present, the production methods commonly used by manufacturers are printing method and sand blasting method. The printing method is limited by the problem that the precision is not precise enough, and the use thereof is frequent, which is likely to cause unevenness and asymmetry of the partition walls; Because of the long time spent on sand blasting, the uniformity of each blasting must be strictly monitored, and the process is quite complicated.
In the connection process of the drive circuit board in the back-end process, since the plasma display screen adopts the direct-discharge discharge to emit the fluorescent light to control the gray-scale change and is controlled by the gas discharge method, the factor that needs to be determined is the discharge. The characteristics, luminous efficiency, contrast of the panel brightness, and power consumption, on the one hand, increase the resolution and brightness, while not affecting the discharge stability, these are the winners of individual manufacturers.
Advantages and disadvantages of plasma
Let me talk about the advantages of the plasma display. The most obvious one is of course the large and thin picture. Whether it is a wall or a floor, it can give the living room a more ideal visual effect. In the past, the size of a CRT TV increased with the size of the screen. It felt that it was both stupid and blunt, and it was impossible to have a wall-mounted design. This is because the electron ejector is biased and has to leave a certain distance between the electron gun and the screen. This can only be said to be helpless. However, with the increase of the screen in the plasma display, the development of the fuselage has become thinner and thinner, from the initial thickness of 6 inches to the current thickness of only 3 to 4 hours. At the moment, the display of the knocker is basically no longer thin. This is because the thickness has reached the limit in terms of current technology.
Another advantage of the plasma display is that the picture has a strong focus, no chromatic aberration, and low distortion. Unlike a CRT TV, a picture tube scans the entire picture by an electron beam, so the central part of the picture quality is usually better, but the surrounding position is prone to errors, such as bias, focus error, and picture distortion. Plasma technology does not suffer from these errors, but it works better on natural images and text displays. The reason is that the illuminating method of the plasma phosphor, in addition to the image quality of the picture tube, the focusing ability is more ideal, which is necessary for the plasma to record the work of the entire screen.
Another advantage is that the plasma is easy to make a large size picture. Because plasma can apply the screen printing technology to plasma panels, the size of the printer, and the size of the plasma. In contrast, the picture tube is much worse, and the 36-inch is almost the limit.
There are advantages, of course, there is a lack of silence. Of course, the biggest reaction for everyone is its expensive price and maintenance cost. A 42-hour plasma TV needs 30,000 to 40,000, and 60-inch or more needs more than 100,000. How can it not be ordered? People are at a loss! And its maintenance cost is about 10% of the display, ranging from 4,000 to 10,000, can be said to be a very expensive thing. Another shortcoming is the quality of the picture. The quality of the plasma display on the market is uneven. The black spots with poor quality are only seen in black and white, and the images appear severely jagged and cold. Cold and awkward, if you buy it wrong, it’s a headache!
Also, you have to spend more on electricity to own a plasma TV. This is due to the fact that the entire screen is lit, so the plasma consumes a lot of power. Plasma TVs also have the phenomenon of afterimages, but this problem has now been solved by various factories.
Another global flat panel market display technology for large-scale applications and mature markets is PDP plasma display technology. The display technology accounts for 20% of the global market for large-size color TV products. Although it is difficult to become a strong competitor of OLEDs without LCD, OLED will eventually replace PDP technology, because OLED is more perfect in many aspects.
From the display effect, PDP plasma technology is superior to LCD technology: contrast, color, response time are higher than LCD products, and even achieve the possible display effect of OLED. However, OLED display products are still significantly ahead of PDP technology in terms of display density, angle, and unit energy consumption brightness, especially in the ideal thickness of the product, less than one-tenth of the PDP. . Therefore, the overall display effect OLED is significantly stronger than the PDP, and the PDP is significantly stronger than the LCD. The defect of OLED compared with plasma PDP is still reflected in the lifetime.
From the applicability of the product, the PDP is a gas small capsule structure, and a glass (ceramic) screen frame with a certain thickness must be used. The screen must have a protective structure, otherwise it is easily broken under the influence of collision, temperature and pressure, and the PDP It is seriously backward in high-resolution technology and cannot produce small-sized high-definition products. In contrast, OLEDs are solid-state displays that are simple, lightweight, and lightweight, and can be characterized by a flexible or transparent substrate. OLED products are prepared to meet the practical needs of various special conditions and special conditions. Conventional applications do not require special protection, meet different sizes of high-definition display, and are suitable for use in combination with a variety of other film structures (resistive touch screens).
From the point of view of manufacturing cost, OLED and PDP are almost equal in terms of large-size display. However, in the construction of the production line, the cost of OLED is significantly higher than that of the PDP, which may reach several times or even 10 times the investment in the construction of the PDP product line. This is a major bottleneck in the mass production of OLED products.
Although the investment in the preparation of OLED products is even greater, PDP products still have no advantage in the market. Because LCD products, which are also more expensive than PDPs, have gained market advantages for PDP's main large-size display devices. This advantage will be fully inherited by the OLED technology that can inherit the LCD production line. Or, it can be said that the success of LCD today has helped OLED to complete the first step of investment. The conversion and upgrade of LCD to OLED is inevitable, and the scene of LCD victory over PDP will be inherited by OLED in the near future.
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