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Will AMOLED Replace AMLCD?

Will AMOLED Replace AMLCD?

Mar 04, 2017

In recent years, a topic whether AMOLED (Active Matrix Organic Emitting Diode) will replace AMLCD (Active Matrix Liquid Crystal Display) becomes very popular, however, there is no conclusion so far. At present, AMLCD has a mature industrial chain, the cost of manufacturing a display is gradually declining. However, the application to Samsung as the representative of the Korean manufacturers are overall layout of AMOLED technology in the mobile phone screen, the screen will have its own mobile phone nearly 70% into the AMOLED screen, and even stopped the 7 generation AMLCD mobile phone panel production line of their own. In order to promote the development of AMOLED industry chain, Samsung also actively promote the use of Samsung AMOLED screen made in china.At present, OPPO, VIVO, Meizu, HUAWEI, ZTE and other domestic mobile phone has been used for Samsung AMOLED touch screen integration, AMOLED shipments continued to move up the screen. It is reported that in the second half of 2016, Samsung will continue to expand the scale of its investment in the AMOLED screen, and apple iphone8 mobile phone next year to debug new production lines. According to the prediction of the professional market research agency IHS, AMOLED display panel market share continues to increase, the proportion of shipments reached 11%, 2020 is expected to rise to 22%. In addition, Japan's Sharp and South Korea's LG is also in the study and promotion of large size AMOLED display. Sharp in the field of display 2012 important meeting SID reported its 13.5-inch resolution of 4K2K AMOLED display, LG reported on 2014 and demonstrated its full HD AMOLED TV prototype SID.

It can be seen that the AMOLED display is heady, compared to AMLCD, AMOLED has higher contrast, color gamut wider, lower power consumption and lighter, can view wider and faster response characteristics, outdoor readability etc.. The following from the technical point of view to compare the advantages and disadvantages of AMLCD and AMOLED.

First of all, introduce the principle of AMLCD light. AMLCD is the use of LCD photoelectric effect, through the thin film transistor (Thin Film, Transistor, TFT) circuit to control the transmissivity and reflectivity of liquid crystal cell, a flat panel display technology to produce different gray scale. As the liquid crystal material itself does not emit light, so AMLCD is a kind of passive light-emitting display, the need for backlight. The structure layer of AMLCD is shown in figure 1. The backlight module generates a white backlight, which is converted into a linear polarized light through a polarizing plate, and then through the TFT and the liquid crystal molecular layer. According to the different voltage TFT layer of liquid crystal layer will have different torsion angles, and polarization of linearly polarized light, on the vibration direction of torsion, then produce different colors through the filter, and finally through the second layer polarizer (perpendicular to the first layer), to achieve control of light intensity, different colors and final gray by red green and blue three colors light intensity combination.

Unlike AMLCD, AMOLED is a self luminous display that does not require a backlight, and its light-emitting components are Diode (Organic Light Emitting, OLED). Through the brightness control RGB OLED sub pixels can emit light of different colors, the brightness depends on the size of the current flowing through the OLED, the pixel grayscale control by controlling the current size can be through OLED. Figure 2 shows the structure of the AMOLED display. Since the AMOLED panel reduces the backlight module and the first polarizer, the AMOLED is lighter. The thickness of the AMOLED display is about 30% of AMLCD, the use of AMOLED phone because of its extreme ultra-thin has been loaded into the Guinness record.

Compared with LCD, AMOLED has higher contrast. In addition to the weight is not dominant, because of using the backlight layer, and backlight layer can not be completely closed, so there will be LCD screen light leakage phenomenon exists, so the contrast will be affected. For the AMOLED display, in theory, if there is no current flowing through the OLED, the brightness of the OLED can be zero, so the contrast is high. The test shows that the contrast of AMOLED is as high as 13000000:1, enough to show the image of the light and shade, to give a vivid sense of reality, especially in the night shooting, the difference is more obvious. In addition, due to the need to go through two AMLCD polarizer, the energy will be reduced, the maximum brightness is less than AMOLED. Figure 3 shows the comparison of AMLCD and AMOLED images, we can see that the AMOLED light is more bright and dark part of a more detailed. In addition, moderate brightness, AMOLED can not dazzling, minimum brightness display, not in the bedroom, the cinema lamp shadow looking for mobile phone glare and fatigue, can protect your eyes.

Lower power consumption of AMOLED. In the AMOLED panel, only the necessary pixel light, and the light generated by the OLED do not need to go through the filter, reduce light loss, therefore, lower power consumption, higher efficiency, power consumption saving about 30% times, so it can reduce mobile phone charging, charging can be once a day, eliminating the need to carry charging treasure the trouble.

AMOLED wider color gamut. AMOLED color gamut is about 1.4 times the width of the AMLCD, only AMOLED can really show the color of nature. Although LCD is also used in standard RGB levels, however, AMOLED can control a single sub pixel in a wider range, so it can be generated by mixing the main color of the wider color gamut. LCD vendors are also trying to make the LCD screen looks more beautiful in order to compete with the AMOLED in the market. However, often counterproductive, undermine the color balance. Figure 4 shows the nature of the AMOLED and color contrast with the AMLCD color chart.

AMOLED in the outdoor strong sunlight reflection still has a clear picture quality, its high brightness and wide color gamut can improve the outdoor readability. Figure 5 shows the contrast between the AMLCD and AMOLED in the outdoor sunlight color performance and readability. As can be seen, AMOLED can still be brilliant in the performance of the natural light.

In addition, because the AMOLED light-emitting device is a solid state OLED, the display is composed of solid state, so it can be easily made flexible display, but also can be made wearable and vehicle display. Samsung and Apple also announced that it will launch a folding phone recently, so flexible AMOLED has a huge market prospect. However, at present there is no mature technical team and technical route, its industrialization still need to wait and see.

AMOLED display screen is not perfect, the RGB pixel life cycle is different, so, with the increase in the use of time, there may be color drift, and LCD is not such a problem. Although, AMOLED in small and medium sized mobile phones, watches and other fields have a place, but there are still technical problems in the field of large-size tablet computers and television applications. This is because the OLED is a current mode device, the current flowing through the OLED determines the brightness of the. However, due to the driver (TFT), and light emitting devices OLED in long time under electrical stress will drift or space, resulting in different time or different positions, the same data voltage, the current through the OLED, this will cause the display unevenness, even display error. For small and medium size AMOLED display, Samsung and Sharp are used in pixel compensation scheme, so that changes in the electrical properties of TFT and OLED, the current through the OLED can still remain almost unchanged. However, due to the driving speed and a large area of panel TFT and OLED electrical characteristics in space or time the influence of uneven degree increases, the pixel compensation effect compensation scheme in large size AMOLED display is not ideal. At present, LG has also proposed a large size AMOLED display for the external compensation program, also gives the 55-inch AMOLED display prototype, but by the impact of manufacturing costs, its production still needs time. LCD has a mature production line, the cost is low, AMOLED is in the stage of market transformation, the panel will be willing to spend a lot of money to follow up the technology and production lines, is still unknown. It is worth mentioning that, because quantum dots emerge in recent years display technology can be used to improve the quality of the backlight source in AMLCD, this is also used in high-end LCD display panel, the AMLCD defenders in this field in smoke-free war seems to have seen the dawn of victory, AMLCD and AMOLED contest more whirling.

At present, AMLCD and AMOLED have their own advantages and disadvantages, with the continuous optimization of LCD technology and the continuous improvement of AMOLED technology, the gap between LCD and AMOLED will decrease in the high-end mobile phones. However, the advantages of AMOLED screen in power consumption, thickness and display effect is gradually highlighted, and the cost is gradually declining, it is more likely to become the future of mobile phone display screen. However, there are many problems to be solved in terms of technology and market size, the market is far away, AMOLED will eventually replace the AMLCD remains to be discussed, but also need to be tested by the market.