Shipments of flexible AMOLED panels will exceed rigid OLED panels in 2020

According to the research and analysis of IHS Markit, the shipment of flexible AMOLED panels is expected to reach 335.7 million in 2020, breaking through the shipment of 315.9 million rigid AMOLED panels. Flexible AMOLED panels are expected to account for 52% of total AMOLED panel shipments, compared with 38.9% in 2018.

Figure 1: Statistics and forecast of the proportion of global flexible AMOLED mobile phone shipments (data source: IHS Markit)

Review of traditional touch control schemes

In the flexible panel, it can be divided into “bendable”, “foldable” and “rollable”. The bendable state is the most easily realized state of the flexible screen, and the display screen is bent at a fixed angle, such as Samsung edge series mobile phones; The foldable and bendable screen can bend freely on one surface and any surface, so these two forms of flexible panel will put forward new requirements for the manufacturing process and materials of the display screen, including the re selection of touch technology scheme. The traditional touch technology based on LCD screen is quite different from AMOLED soft screen in terms of substrate material, packaging material and manufacturing difficulty of overall multilayer light-emitting devices. Therefore, the touch technology of AMOLED soft screen will not simply copy the traditional way. Due to its inherent “flexibility” and “flexibility”, thin film materials are expected to be reused and developed rapidly in the era of AMOLED flexible screen.

Figure 2: three categories of flexible panels

AMOLED soft screen cannot use glass as substrate and packaging material, resulting in the change of touch scheme

Touch technology can be divided into plug-in and embedded. External touch technology (out cell) is dominated by touch manufacturers. This technology can be divided into glass mode and film mode. Later, due to the thinner and thinner mobile phones, panel manufacturers launched embedded touch technology, integrating panels and touch units. Embedded touch technology can be divided into on cell and in cell. The touch control scheme of high-end mobile phones has gradually shifted from plug-in to embedded, such as Apple’s iPhone’s in cell TFT-LCD. Compared with the glass mode and film mode, the in cell and on cell schemes save the glass cost and fitting cost, make the module light weight and high light transmittance, and better meet the quality requirements of high-end mobile phones.

As early as 2016, the global touch screen shipped 1.47 billion pieces, including 820 million embedded pieces, accounting for 55.6%, surpassing the plug-in touch module for the first time. Whether external or embedded, it is a touch technology suitable for LCD display screen, and the manufacturing process has been developed and mature.

Figure 3: Glass mode plug-in touch technology GG (left) and film mode plug-in touch technology GF (right)

Figure 4: structure diagram of GG / GF touch technology

The external touch technology of glass mode is to make all touch sensors on a layer of ITO glass, while the film mode is to replace this ITO glass with ITO film.

  

Table 1. Comparison between glass mode and film mode

For the glass mode, ITO glass and glass cover plate can also be integrated into one piece of glass, and the touch sensor can be directly placed on the piece of glass. This scheme is also known as “single glass solution” – OGS.

Figure 5: single glass solution OGS and its structure diagram

In cell touch mode is that the touch module is built into the LCD panel, while on cell touch mode is that the touch sensor is externally placed on the LCD module and under the polarizer.

Figure 6: structure diagram of in cell (left) and on cell (right) embedded touch technology

Figure 7: structural diagram of OLED hard screen (left) with glass as substrate and encapsulated with glass or metal cover plate and OLED soft screen (right) with flexible polymer material as substrate and encapsulated with single-layer or multi-layer film material

For AMOLED screen, the hard screen adopts glass substrate and glass cover plate, while the flexible screen adopts flexible polymer substrate and film packaging due to the brittleness of glass. Then, the choice of touch scheme is also different between the two.

Except that the in cell method is not applicable, the selection of touch technology is similar to that of LCD screen. This is because when in cell embeds the touch sensor into the pixel, it must also embed the supporting touch integrated circuit, otherwise it is easy to lead to wrong touch sensing signal or excessive noise, which means that the complexity and difficulty of the process will increase. The liquid crystal layer in LCD adopts printing coating method, which has high yield; The organic layers in OLED are attached by evaporation method, which has high technical requirements and great difficulty, so the yield is also low. Adding another layer of touch IC in the evaporation structure will affect the yield. The process yield of OLED has been low. If in cell is used, it will lead to lower yield. Therefore, there is no in cell touch scheme for AMOLED screen at present.

At present, the touch technology adopted by Samsung AMOLED hard screen is on cell scheme. Because Samsung adopts RGB three-color pixel technology, there is no need for color filter under the packaging glass. It can be used to coat the touch sensing electrode first, and then package the OLED light-emitting device. Samsung’s on cell touch scheme is technically very difficult. It benefits from Samsung’s deep cultivation in the field of AMOLED display for many years, and its panel production yield can be controlled between 70% – 85%. The probability that other panel manufacturers adopt the on cell touch scheme is not high due to the influence of yield, but switch to the plug-in GF / GG / OGS scheme with high yield. AMOLED screen makes the plug-in touch module pulled down from the altar get the attention of the market.

Figure 8: structural diagram of Samsung “hard screen” embedded on cell touch scheme

AMOLED soft screen needs a touch control scheme based on thin film materials

On cell: because the light-emitting devices in AMOLED soft screen are packaged in thin film, the touch sensing electrode cannot be coated on the glass first and then taken back for packaging as in glass packaging. Instead, the sensing electrode needs to be evaporated in front of the light-emitting devices at one time, which will increase the challenge of yield again. And evaporation. Etching and other processes will also damage the packaging film. Therefore, at present, for AMOLED soft screen, on cell is probably not an alternative.

“Bendable” flexible screen: Although the device substrate and packaging materials are replaced with flexible materials, the top cover plate is still made of 3D glass. However, if the GG scheme is adopted, another piece of 3D sensing layer glass is required to evaporate the touch sensing electrode, which undoubtedly increases the technical difficulty; In the OGS scheme, the touch sensing electrode needs to be directly evaporated with the inner side of the cover glass. Due to the heat treatment of the fixed curved 3D glass, there is a problem of fragility. If the thermal processing such as evaporation is carried out on it, its brittleness will be deteriorated. Therefore, the flexible sensing film GF is a more suitable touch technology solution for this kind of screen.

“Foldable” and “bendable” flexible screens: the characteristics that need to be folded and bent exclude the GG / OGS scheme related to glass. At the same time, because the outermost glass cover plate needs to be replaced with a flexible protective cover plate, the GF scheme will no longer exist, but this layer of touch sensing film needs to be retained to cooperate with the flexible display.

  

Table 2. Comparison of touch technology schemes between AMOLED hard screen and soft screen

  

Touch manufacturers affected by AMOLED soft screen touch film technology

If the capacitive touch screen is the most far-reaching invention in the era of smart phones, the flexible touch screen will continue to write a new chapter in the brilliant history of the smart phone industry together with the flexible display. With the gradual development of flexible intelligent terminal products, plug-in touch screen, especially the flexible touch products represented by nano silver and metal grid, has attracted the attention of more and more people in the industry because of its highly competitive price, performance and production capacity. As an industry wind vane for the development of global touch applications, materials and equipment. 2018 Shenzhen International full touch and display exhibition will focus on 5g, Internet of things, industry 4.0 and other industry hotspots and carefully build an exclusive platform to present the whole industry chain product exhibition from materials, equipment and solutions to R & D and manufacturing. Among them, the special area of flexible touch and display will focus on the whole industry chain resources such as flexible touch display technology products, materials and equipment, TPK, Xinlun technology, kelistv, Qianhe optoelectronics, Runde, global Tongchuang Well known brands such as genesis, Enrique, Sike, saibel, Liande equipment, Yongquan automation and Baode automation will show the audience the latest technologies and products. At the same time, the second 2018 China flexible display technology (materials) International Forum will also be held, which will deeply explore the development of materials, components and equipment under different technology industrial chain routes, and jointly explore the road of optimal solutions for flexible products.

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