What is a flexible AMOLED touch panel and how do you touch an AMOLED screen?

- May 19, 2020-

The flexible panel can be divided into three levels: "Bendable", "Foldable" and "Rollable". The bendable state is the easiest state for a flexible screen. The display screen is bent at a fixed angle, while the foldable and bendable screens can be bent at will on one surface and any surface. These two forms of bending lead to The manufacturing process and materials of the display screen have higher requirements, among which there are new requirements for panel touch technology.


The flexible AMOLED touch panel is a flexible AMOLED panel based on touch technology. Conventional LCD screen-based touch technology has a big difference from the flexible AMOLED screen in terms of substrate materials, packaging materials and the process difficulty of the overall multilayer light-emitting device, so the touch technology of the AMOLED flexible screen will not simply copy the traditional The way. Thin film materials are expected to be reused and developed rapidly in the era of AMOLED flexible screens due to their inherent "flexibility" and "flexibility".


"What is a flexible AMOLED touch panel"


AMOLED flexible screen cannot use glass as the substrate and packaging material, leading to changes in the touch solution


Touch technology can be divided into plug-in and embedded. Out-cell touch technology (Out-cell) is dominated by touch manufacturers, the technology can be divided into glass mode and film mode. The mobile phones that come out now are getting thinner and thinner, leading panel manufacturers to introduce in-cell touch technology that integrates panels and touch units. The embedded touch technology can be divided into On-cell and In-cell. The touch control solutions of high-end mobile phones have gradually shifted from external to embedded, such as Apple iPhone's In-cell TFT-LCD. Compared with the glass method and the film method, the In-cell and On-cell solutions save the glass cost and paste cost, making the module lighter in weight and high in light transmittance, and better meet the quality requirements of high-end mobile phones.


In 2016, global shipments of touch screens were 1.47 billion, of which 820 million were embedded shipments, accounting for 55.6%, surpassing external touch modules for the first time. Whether it is a plug-in type or a built-in type, it is a touch technology suitable for LCD display, and the manufacturing process has been developed and mature.


The glass-type external touch technology is to make all touch sensors on a layer of ITO glass, and the film method is to replace this ITO glass with ITO film. For the glass method, the ITO glass and the glass cover can be integrated into a piece of glass, and the touch sensor is directly placed on the piece of glass. This solution is also called "single glass solution" -OGS. The In-cell touch method is to build the touch module into the liquid crystal panel, while the On-Cell touch method is to place the touch sensor externally above the liquid crystal module and under the polarizer.


The AMOLED screen is divided into a hard screen and a flexible screen. The material of the hard screen is a glass substrate and a glass cover plate, and the glass is brittle. The flexible screen is encapsulated by a flexible polymer substrate and a thin film. Then the two have different choices for touch solutions.


Except that the In-cell method is not applicable, the selection of touch technology is similar to that of the LCD screen. Since In-Cell needs to embed the touch sensor and the associated touch integrated circuit into the pixel at the same time, it is easy to have wrong touch sensing Signals or excessive noise, this process is very complicated and difficult.


The liquid crystal layer in the LCD adopts the printing coating method, and the yield is high; while the organic layers in the OLED are all deposited by the vapor deposition method, which has high technical requirements and difficulty, so the yield is also low. Adding another layer of touch IC to the evaporation structure will definitely affect the yield. The yield of OLED process has been low, if In-Cell is used, it will lead to a lower yield. Therefore, there is currently no In-cell touch solution for AMOLED screens.


At present, the touch technology adopted by Samsung AMOLED hard screen is the On-cell solution. Since Samsung uses RGB three-color pixel technology, no filter is required under the encapsulation glass. It can be coated with touch-sensing electrodes first, and then package the OLED light-emitting device. Samsung ’s On-cell touch solution is technically very difficult. Samsung has an advantage in this research, and its panel production yield can be controlled between 70% and 85%. For other panel manufacturers, the difficulty of adopting the On-cell touch solution will be very large, and most of them will switch to the plug-in GF / GG / OGS solution with a higher yield.


"Touch Technology Used in Samsung AMOLED Hard Screen"


AMOLED flexible screen needs a touch solution based on thin film materials


On-cell: The light-emitting device in the AMOLED flexible screen currently uses thin-film encapsulation. The touch-sensing electrode cannot be like a glass encapsulation. Instead, all the sensing electrode needs to be deposited before the light-emitting device, which increases the difficulty of yield. . Moreover, evaporation, etching and other processes will also damage the packaging film. Therefore, for AMOLED flexible screen, On-cell is very difficult to achieve.


"Bendable" flexible screen: The device substrate and packaging materials use flexible materials, but the outermost cover plate uses 3D glass. However, if the GG scheme is used, another piece of 3D sensing layer glass is required to vaporize the touch sensing electrodes, which undoubtedly increases the technical difficulty; while the OGS scheme requires the vapor deposition of the touch sensing electrodes directly to the inside of the cover glass, due to the fixed curved surface The heat treatment of 3D glass has been carried out, there is a possibility of fragile, if further thermal processing such as vapor deposition, the probability of problems is greater. Therefore, the flexible sensing film GF is a suitable touch technology solution for this type of screen.


"Foldable" and "bendable" flexible screens: The need to fold and bend excludes the GG / OGS solution related to glass. At the same time, because the outermost glass cover is replaced by a flexible protective cover, the GF solution is not necessary, just leave this layer of touch sensing film to match the flexible display.