The era of flexible screens is approaching, how will TP technology evolve? From the "Big Brother" that can make phone calls and self-defense, to the bulletproof Nokia that is unbreakable, reproduced in various full-screen hyperbolic screens, the development of mobile phones is simply plugged in with the wings of light, and it has even been called "New Human Organs".
The touch screen greatly reduces the threshold for people to operate electronic devices
With the advent of the smart phone era, we have a sensitive and fast full-color touch screen, and the sense of experience and interaction is gradually enriched. You can click on the screen with your finger from the 99th to the first time. , Controlling APP, playing games, handwriting input, and realizing a series of specific commands. This seemingly basic function is actually not simple. It depends on the existence of TP in the mobile phone.
Classification of TP
TP is the abbreviation of Touch Panel, which is a part of touch technology. Our common touch screens can be divided into two categories: resistive screens and capacitive screens.
Resistive screens use the pressing of fingers and other contact objects to generate a potential difference to calculate the coordinate position of the contacts, while capacitive screens use a finger to touch the surface of the screen to transfer a certain amount of charge to the human body. In order to recover these charge losses, the charge is added from the wiring. TP can calculate the position of the touch point through various IC algorithms according to the amount of charge supplemented by each trace and the charging time, so as to control the system.
Because capacitive screens support multi-touch, high accuracy, high durability, and the price is decreasing day by day, capacitive screens are often used in smartphones.
Classification of TP process
The TP process technology is constantly updated with the development of the market. At present, the TP process of OLED screens is mainly Out-Cell and On-Cell. The two technologies can be said to have their own characteristics:
The principle of Out-Cell is similar to that of mobile phone film. The thickness of ordinary TP is about 60 microns. It needs to be laminated with glue. Because the bonding is affected by the environment and temperature, there is a risk of separation of the neutral layer. The accuracy of the combined precision will affect the yield and structure to a certain extent, but the technical requirements are simple and the cost is relatively low.
The On-Cell process is to complete the Touch Sensor directly on the encapsulation layer (TFE) through a low-temperature process. There is no need for an additional layer of external film. On the one hand, the number of layers is directly reduced, and the thickness is reduced accordingly, and the number of layers is increased. The less, the more controllable, the calculation amount and the risk of instability will be correspondingly reduced. On the other hand, this process can reduce the possibility of separation between layers when performing dynamic actions such as folding and curling. In terms of cost, the On-Cell process requires new equipment. Although the cost will increase in the short term, in the long term, only the metal grid is required in terms of material cost. After the process is stable and the technology is mature, the equipment cost can be shared. On the whole, it is a more advanced TP process that is more suitable for flexible screens.
Flexible TP commonly used materials
With the continuous development of OLED technology, many OLED manufacturers have successively mass-produced flexible OLED screens. For OLED manufacturers, how to implement flexible TP technology on flexible screens will be a new challenge. Compared with rigid TP, flexible TP needs to achieve three aspects of thinness, bending resistance, and embedded type. The main requirements are several indicators. It is flexible, good in light transmission, easy to process, and supports multi-touch.
First of all, according to the material properties, the commonly used flexible TP materials can be divided into Metal Mesh, ITO, nano silver wire, graphene and so on.
Metal Mesh
Metal Mesh is a technology that uses metal grids with a line width of less than 4um to make transparent electrodes. The advantage is that it is extensible and is more suitable for flexible touch. The disadvantage is that metal has a greater impact on light, and it is easy to block the light of the light-emitting layer. To reflect the light of the external environment, a more suitable solution is to make the metal grid narrower and thinner to minimize the impact of the metal grid on the light.
ITO
The advantage of ITO is that it has good light transmittance but strong brittleness and is not suitable for dynamic flexibility, but it can be used for solid-state bending.
Nano silver wire
Nano silver wire is also metal, and its distribution order is slightly worse than that of Metal Mesh, and its optical performance is poor.
Graphene Carbon Nanotubes
The graphene process is still immature, and it is currently in the research and development stage, and the actual production process is rarely seen.
Now the more mature On-Cell process is MM-on-TFE. This solution uses a low-temperature process on the packaging layer (TFE) to directly etch the metal into a metal grid to complete the production of the Touch Sensor. Multiple advantages such as substrate, no pressure layer, softer, narrow frame, and one-time binding.
Out-Cell and On-Cell structure comparison
The OLED screen with built-in TP is thinner, more suitable for dynamic flexible display, and can be applied to a wider range of terminals and scenarios. It is expected that through continuous accumulation and innovation, China's OLED companies will have more technologies and products with independent intellectual property rights, open up the application fields of smart terminals, and have a more amazing performance in the consumer market.
