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Large-size touch panel production technology and application trends

2018-01-02 00:40:00 Editor:MICRON 4

In the past, large-size screens could only be used with low-cost resistive or high-cost acoustic and external optical designs; in the past, limited by the bonding yield, they could only be used in small and medium-sized mobile devices. The projected capacitive multi-touch technology, with the proficiency of G/G, in-cell and other process technologies, and the evolution of touch-sensing ICs, it is currently available in 10 to 12 inch flat panels, 13 to 17 inch thin/electric Competitive laptops, 20-22 inch AIO all-in-one computers have appeared, and larger size (32-42 inch) Internet-connected TVs and electronic whiteboards are also gaining momentum...

  Big size and multi-touch

  From ATM cash machines, mutual assistance navigation systems in institutions, to electronic whiteboards in department stores, these devices that require touch applications are moving towards large-size trends just like mobile phones and tablets.


Large-size touch screen is divided into inCell&on-Cell

At present, Apple only introduces projected capacitive multi-touch technology in small and medium-sized iPhone/iPod/iPad, and only began to introduce trackpad feedback force in the desktop and laptop parts, and there is no design plan to introduce a large number of touch applications; But in the non-Apple camp, from Android phones and tablets to mainstream notebook computers of 12 to 17 inches, projected capacitive multi-touch technology is introduced, and even some 20-inch desktop computers or computer dining tables, electronic whiteboards , Also began to use multi-touch technology.

   In the early days, the resistive touch technology, which was more common in 15 inches or more, used a finger or a stylus to touch the ITO Film to cause the ITO film to sink and produce a voltage change, and then the A/D conversion calculation process was used to obtain the positioning position. Due to its early debut, it has advantages in terms of material and technology costs; however, resistive touch technology will have a resistive film that affects the light transmittance of the screen, and the pressure-sensitive mechanical structure will cause service life under frequent use and long-term heavy pressing. Reduction.

   Infrared and surface acoustic wave touch technologies are currently common technologies for large-size touch screens. The infrared type is equipped with a large number of infrared transmitters and receivers on the four sides of the screen, and the coordinate position of the touch is calculated by blocking the infrared light source when the finger is selected. The advantage is that the applicable size is quite large (6-167 inches), the response speed is fast, the positioning is accurate, and it is quite durable; the disadvantage is that the infrared module cannot achieve high resolution due to the volume of the infrared module, the cost is high, and the dust and ambient light will fall in the future. Interference is also the bottleneck of this technology.

The surface acoustic wave type is to install a surface acoustic wave transmitter and a receiver in the three corners of the screen, using the characteristics of the absorption of sound wave energy when the finger touches the screen, and calculate the coordinates of the energy change. Its application size is only 10-32 inches, but it has the advantage of high resolution compared to infrared type. However, because the reflective antenna around the screen needs to be customized and the yield is not high, the overall cost is relatively high.

   A more cost-effective solution for multi-point touch screens

When users have become accustomed to the multi-touch experience of smartphones and tablets, many industry players are also actively developing multi-touch application solutions for medium and large screens. This also enables large-scale touch screens with low-cost resistive technology in the past. Technology, or costly sound wave, external optical touch design is facing certain challenges.

For medium and large touch screens larger than 10.1 inches, in the past, a transparent film or glass touch sensing layer was placed between the cover glass and ITO (TFT Array) or AMOLED panels. The manufacturing method was changed from the past GFF (Glass Film Film), G The /G (Glass to Glass Structure) structure shifts to two designs built in the ITO pixel layer (In-Cell) or externally mounted (Out-Cell).

In the case of In-cell, there are currently existing LCD screen integration solutions for different forms of VA/IPS/TN. The design solution of In-cell for large screens with cover glass can achieve good results in products with large display ranges. The screen effect can also maintain the thinness of the screen material, which is more suitable for high-end Ultrabook or deformed laptop products that emphasize the thin design of the product.

Jian Yang Co., Ltd. (iDTi), which settled in the Hsinchu Science Park in 2003, has directly used the In-Cell process to add a set of light sensors to the TFT Array through the cooperation with the panel factory on the process. Array (Photo detector), by detecting the subtle light source changes caused by objects approaching or touching on the TFT pixel layer, the touch IC of the touch control circuit board (TCB) captures 120 frames per second for comparison and comparison After arithmetic processing, the number of touch points and the force of touch are calculated. This technology is suitable for LCD panels ranging from 1 to 100 inches, supports 10-point touch, stylus, laser pen and other diversified applications, and has obtained Windows 10 touch certification.

In the Out-cell plug-in solution, G/G is used for touch products larger than 10 inches. In the larger size (17 inches), it is limited by the thickness limitation of G/G's inherent structure. Manufacturers are used to Simple OGS (One Glass Solution) as a solution for large-size touch screens.

   ITO alternative materials

The main characteristic of ITO (Indium Tin Oxide) is its combination of "electrical conduction" and "optical transparency". It is suitable for use as a material for the touch sensing layer. However, because ITO materials are expensive and the ITO layer is relatively fragile and lacks flexibility, It is impossible to make flexible panels; in order to seek complete flat or curved/flexible panels, as well as large-size touch panel applications, related industries have also introduced many ITO alternative material solutions, such as Silver Nanowires, Metal Mesh, PEDOT/Conductive Polymers, Graphene, Carbon Nanotubes, ITO inks and other technologies.

   "Nanosilver wire" technology is now mature. Its flexibility is better than ITO, its color shift is lower than ITO, and its light transmittance is higher. The patented ClearOhm material, such as Cambrios, has ultra-high light transmittance (>98%) and high conductivity of 30 to 150 ohms per square foot. In addition, Carestream, BlueNano, and Industrial Technology Research Institute also have such products, which are one of the promising ITO substitutes in the market.

The "metal grid" technology is like a barbecue grill composed of extremely thin metal wires. The advantages of making it into a touch application are low impedance (less than 10 ohms), better transparency than ITO, the best light transmittance, and high flexibility. And the capital expenditure is very low, and the manufacturing cost is slightly lower than that of ITO.

However, in the "metal grid" process of thinning metal lines (must be less than 5 microns), the support of many touch ICs is reduced due to the reduction of touch sensing area. At the same time, in order to solve the problems of metal reflection and material oxidation, the process cost is Follow to improve. Whether to introduce a metal grid depends on the manufacturer's process technology and touch integration technology. Currently, there are Korean MNTech (available at the end of 2012), Atmel’s XSense (launched in the first half of 2013), Fujifilm (Fujifilm, the second quarter of 2013), UniPixel’s UniBoss (launched in the second half of 2013), 3M, PolyIC, and mainland China The manufacturer goes public.

   "Conductive polymer" has the advantages of good ductility and material price, and has become one of the technologies that have attracted attention in the market. Suppliers include Agfa (Agfa), Fujitsu, Molex, Oji Paper, etc. Carbon nanotubes have the best ductility, the lowest color shift, and the material price is lower than ITO. They are also one of the promising ITO alternatives in the market. Suppliers include Eikos, Canatu (Carbon nanobuds carbon ball mixture), Manufacturers such as SWeNT, Unidym, Sinai Materials, Industrial Technology Research Institute, Innolux, etc. are also promoting.

As for "graphene", the thin and hard nanomaterial in the world today, it only absorbs 2.3% of light and is almost completely transparent. Its resistance value is lower than that of copper or silver. It is an ITO alternative material and heat dissipation material with good overall performance. It is expected that the price will be significantly reduced to below US$200 per kilogram in 2016, increasing its promotion. At present, Samsung, Sony, and Taiwan's Graphage are promoting mass production.

   Combining the advantages of the above various ITO alternative solutions, it is estimated that by 2019, the global touch panel industry will change 50% of the PCAP sensing layer to ITO alternatives. ITO Film Nitto Denko has not only made every effort to reduce the resistance value of ITO film, but also significantly reduced the price to 25USD/m2. Several ITO Film alternative material suppliers that have just established a foothold in the market have faced severe price war threats.

  Large size touch panel faces the challenges of manufacturing process and 4K UHD

In the design and process development of large-size touch panels, manufacturing processes such as silver circuit printing and baking, laser etching, protective layer coating, anti-glare coating, high temperature baking, Tali hot pressing, linear testing and calibration have been added: It also needs to face many problems such as linear accuracy, noise processing, large substrate handling and transportation problems, and overall cost increase of testing and packaging.

  Jianyang exhibited its shooting simulation system with an 86-inch LCD screen using in-cell optical touch technology and standard a-SI process at the Taipei International Computer Show in June 2014. At the 2015 Taipei International Computer Show, Wanda Optoelectronics Technology (Higgstec, Inc) exhibited a 42-inch projected capacitive multi-touch technology touch screen. Through breakthroughs in technology, manufacturing processes, materials, and equipment, these suppliers have expanded projected capacitive touch products to 84-86 inches in one fell swoop, making up the last piece of the puzzle in the market for large-size projected capacitive touch needs.

   The next breakthrough is the touch screen with 4K UHD (3840x2160) or 5K UHD resolution. The current refresh rate of 4K UHD and 5K displays is only 60Hz at most, making the delay effect caused by dragging and scribing with fingers on the screen more easily noticeable by the human eye. Therefore, the industry is increasing the refresh rate of 4K UHD and 5K displays, and at the same time actively improving the computing performance of the touch IC, and the integration with other display driving and display circuits.