What is an in cell touch screen? Principle of in cell touch screen

Compared with the original method of setting the touch panel on the liquid crystal panel, the research on the integration of touch panel function and liquid crystal panel is becoming more and more popular. The integration of touch panel and liquid crystal panel includes “in cell” method and “on cell” method. In cell refers to the method of embedding touch panel functions into liquid crystal pixels. On cell refers to the method of embedding the touch panel function between the color filter substrate and the polarizer.

If the original external touch panel components can be integrated with the liquid crystal panel, it is possible to realize the thinness and lightweight of the panel. In addition, in the original way of placing the touch panel outside the liquid crystal, there is a physical space between the liquid crystal and the touch panel. Therefore, foreign light will be reflected between the upper part of the liquid crystal panel and the lower part of the touch panel, resulting in reduced visibility in bright environments such as outdoors. If the external touch panel components can be integrated, the reduction of visibility outdoors can be suppressed.

The proposal of in cell technology has been put forward before, but the practicability has not made progress because it is difficult to ensure the yield and display performance. The reason is that the touch sensor function needs to be embedded in the pixels on the TFT array substrate. Therefore, complex semiconductor manufacturing processes must be used, which has become a stumbling block to improve the yield. In addition, when the touch sensor is embedded in the pixel, the area available for display will be reduced, which is the main reason for the deterioration of image quality. According to sources, the yield of sharp and Toshiba in cell touch panels has improved

Advantages and disadvantages of in cell and on cell

Compared with the original method of setting the touch panel on the liquid crystal panel, the research on the integration of touch panel function and liquid crystal panel is becoming more and more popular. The integration of touch panel and liquid crystal panel includes “in cell” method and “on cell” method. In cell refers to the method of embedding touch panel functions into liquid crystal pixels. On cell refers to the method of embedding the touch panel function between the color filter substrate and the polarizer.

If the original external touch panel components can be integrated with the liquid crystal panel, it is possible to realize the thinness and lightweight of the panel. In addition, in the original way of placing the touch panel outside the liquid crystal, there is a physical space between the liquid crystal and the touch panel. Therefore, foreign light will be reflected between the upper part of the liquid crystal panel and the lower part of the touch panel, resulting in reduced visibility in bright environments such as outdoors. If the external touch panel components can be integrated, the reduction of visibility outdoors can be suppressed.

The proposal of in cell technology has been put forward before, but the practicability has not made progress because it is difficult to ensure the yield and display performance. The reason is that the touch sensor function needs to be embedded in the pixels on the TFT array substrate. Therefore, complex semiconductor manufacturing processes must be used, which has become a stumbling block to improve the yield. In addition, when the touch sensor is embedded in the pixel, the area available for display will be reduced, which is the main reason for the deterioration of image quality.

However, with the appearance of on cell technology, the integration of LCD and touch panel has ushered in a turnaround. Since it is only necessary to form a simple transparent electrode pattern between the color filter substrate and the polarizing plate, it is easy to ensure the yield. In addition, the area of the effective display area in the pixel will not be reduced, and the image quality degradation phenomenon will hardly occur.

If LCD integration technologies such as on cell mode are popularized, there is no need to use external touch panel components. The manufacturer of touch panel is likely to transform from the original external touch panel manufacturer to liquid crystal panel and color filter manufacturer. The original supply chain in which product manufacturers purchase external components from touch panel manufacturers will also be completely changed.

Now the on cell technology screen has been available for two years. The most widely used is Samsung super AMOLED screen. Thanks to this panel technology, the Samsung Galaxy S 2 has a thickness of 8.49mm and a weight of only 116g. The Galaxy S 3 has a thickness of 8.6MM and a weight of 133g. And both have the ability to replace batteries.

1、 IPhone 5 uses in cell touch technology

In the early morning of September 13, 2012 Beijing time, apple held a new product launch at the fangcaoping Art Center in San Francisco, and officially released its new generation product iPhone 5. IPhone 5 adopts the in cell touch screen as scheduled. The in cell panel is not only lighter and thinner, but also has higher touch sensitivity than the traditional touch panel.

In cell: integration of touch sensor and TFT

Touch technology can be divided into three categories according to the sensor position: in cell, on cell and out of cell (external type). Here, the cell can be understood as two glass substrates and the part sandwiched in the middle. In cell refers to that the sensor is inside the cell, both under the liquid crystal and on the same glass substrate as the TFT. On cell means that the sensor is on the cell, that is, on the glass substrate where the color filter is located and under the polarizer. Out of cell refers to the plug-in type. The touch module and panel are separated. At present, there are mainly GG, GFF / gfx, OGS and other schemes.

At present, the touch technologies that can make thin mainly include in cell, on cell, GFF / gfx and OGS. In 2012, thin and light mobile phones were popular. Due to the problems of OGS and in cell yield, in order to make mobile phones thin and light, many mobile phone manufacturers first adopted GFF / gfx under the out of cell technology school as the main transition technology scheme. The representative company of this technology in China is oufeiguang.

Where will the touch screen go in cell touch screen analysis

Classification diagram of touch technology

In cell technology is to realize the thinness and lightweight of touch function display components by integrating the original external touch panel components with the liquid crystal panel. The original combination links in the industry, such as panel manufacturers, touch sensor manufacturers, module manufacturers and fitting suppliers, are combined and directly completed by the panel factory in house.

Because in cell embeds the touch sensor into the liquid crystal pixel. That is, through the complex semiconductor manufacturing process, the touch sensor is embedded in the pixel on the TFT array substrate. Then embedding the touch sensor in the pixel will reduce the area available for display and reduce the display performance. In general, if in cell technology is adopted, LTPS TFT substrate with large opening rate will be selected to ensure light transmittance and display performance, rather than a-Si TFT substrate with small opening rate itself. Of course, if you must use in cell technology on a-Si TFT, it’s OK, but from the perspective of technical solutions, it seems a little nondescript. If the in cell technology is adopted, it is better to produce it on the LTPS (low temperature polycrystalline silicon) panel production line. However, there are few production lines that can supply LTPS panels in the world, which greatly limits the space for the promotion of in cell technology.   

  

2、 Thinness and competition among manufacturers are important reasons for Apple’s adoption of in cell technology

In cell: reduce the supply process and ensure the safety of supply while making it lighter and thinner

In fact, Apple’s first multi touch solution was in cell. It was just that it couldn’t be realized at that time, so it retreated to the second place and jointly developed plug-in solutions with CHENHONG. Now that in cell technology has developed and has obvious advantages, Apple will let it go and use in cell.

Contribute about 25% to the thinness of iphone5

One of the biggest highlights of the iPhone 5 is its lightness. The thickness of iphone5 is only 7.6mm, which is 1.7mm thinner than 9.3mm of iPhone 4S. By analyzing and comparing iPhone 4S and iphone5, it can be seen that the in cell architecture plays an important role in this thickness decline. The overall thickness of the panel module of the iPhone 4S using the traditional touch module is 2.98mm; For the iPhone 5 with in cell touch, ITO glass and a layer of bonding adhesive are missing. The bonding adhesive used will also be changed from optical adhesive to water adhesive, and the protective glass may be changed to 0.9mm, so as to increase the strength. Therefore, the total thickness of the panel module used in the iPhone 5 is estimated to be 2.54mm, and the thinning contribution is 0.44mm, accounting for about 25% of the thickness reduction of 1.7mm.

Improve screen display performance

The traditional touch screen is difficult to see the display content clearly in the sun. The reason is that there is a gap between the LCD and the touch panel. Therefore, the readability will be reduced and parallax will be caused. Due to the absence of plug-in touch pad, in cell will naturally have no parallax and the readability will be improved. In addition, due to the lack of a layer of glass or film compared with the traditional GG or GF scheme, the light transmittance is also improved and the screen display performance is improved.

Shorten the supply process to ensure supply security and ensure technical leadership in the screen

In the supply chain of traditional plug-in touch module, although the upstream and downstream series connection is complex, the role is clear, including surface glass processing, optical glue material, ITO target, copper foil soft flat cable, induction circuit substrate (glass or film), module bonding, control chip, etc.

With the in cell scheme, the process will be completed in the panel factory, which will shorten the operation time of the supply chain and improve the supply efficiency. The touch panel module includes the process program of TFT-LCD panel module, which can be reduced from 8 channels to 5 channels, and the process time can be shortened from 12-16 days to 3-5 days.

For in cell touch solutions, due to the high customization demand of small and medium-sized application terminals such as mobile phones and the short life cycle of consumer electronic products such as mobile phones, in cell touch solutions often “bundle” panels and touch chips, and may even include components such as panel driver chips, resulting in great customization difficulty. Therefore, from the perspective of brand procurement, the risk of a single supplier is high; But on the contrary, brand manufacturers will have the dominant power in the control of the supply chain. From the perspective of panel manufacturers providing in cell solutions, panel manufacturers may not be willing to customize unless brands can promise certain shipments. Therefore, it will be a win-win situation for suppliers and apple itself to adopt the in cell scheme for apple with few models but a large number of models. At present, only apple has the ability to integrate the capacity of in cell.

OGS: it’s just an upgrade rather than an innovation, and it won’t be the technical choice of Apple’s Pioneer products

OGS scheme is to coat the sensor originally plated on the glass or film substrate under the protective glass, so as to reduce one layer of glass or film and one-time bonding process, which not only reduces the thickness, but also reduces the cost. However, it is essentially a plug-in touch module. Compared with in cell, it has low technical difficulty and does not significantly shorten the supply process. For apple, which has always led the global technological innovation, OGS can only be regarded as a technology upgrade and cost reduction. Therefore, in last year’s series of reports, Apple has repeatedly expressed doubts about the use of OGS technology in the new generation of mobile phones. Judging from the choice of iPhone 5 in cell, apple still uses innovation in its pioneer products.

In addition, OGS has two main processes: sheet process and piece process. Sheet manufacturing process mainly includes strengthening, plating, cutting, printing and secondary strengthening. The production efficiency is high, but the edge strength is not good when cutting small size. The process flow of piece is mainly cutting, strengthening, printing and plating. Although the edge strength can be guaranteed, the plating efficiency of small pieces is low and the yield is poor. Therefore, in OGS, the first thing to rise should be the large-size touch module produced by sheet process. The large-size field is the advantage of OGS at present.

On cell technology is only available on AMOLED

On cell refers to the method of embedding the touch panel function between the color filter substrate and the polarizer. Therefore, one side of the substrate where the color filter is located is the color filter and the other side is the sensor. Due to process problems, whether the sensor or color filter is processed first, it will affect the other side of the processed, resulting in the decline of yield. In addition, since the sensor of on cell is made on the glass substrate of color filter, the thickness will also increase by about 0.3mm compared with in cell. Finally, due to the sensor, the glass substrate where the color filter is located cannot be thinned, and the overall thickness thinning space is limited in the future. Therefore, compared with in cell, on cell technology has not been favored by everyone.

However, when on cell is matched with AMOLED panel, the effect is significantly improved. Because AMOLED has no color filter (CF), there will be no process interference and other problems when making sensors on the glass substrate encapsulated with RGB three-color organic EL, and AMOLED also has advantages over LCD in thickness, so on cell and AMOLED will be a more suitable touch control scheme. However, since AMOLED technology is mainly monopolized by Samsung, if Samsung’s monopoly situation on AMOLED panel cannot be broken, on cell technology cannot be more popularized. Under the trend of “de Samsung” of apple, it is impossible for apple to take AMOLED as its own panel solution, so choosing in cell technology is also the only way for apple.

3、 Impact of iphone5 using in cell on touch industry

In cell has tight production capacity and will be exclusive to apple in the coming year

At present, there are only three iphone5 supply plants: Korean LGD, Japan display and sharp. Previously, it was estimated that the demand for iPhone 5 in the third quarter was about 12 million. From the current situation, the actual situation may meet expectations. Although the iPhone 5 has sold 2 million units in the first 24 hours of opening pre ordering, which has doubled compared with the previous sales record of iPhone 4S, the current distribution has also been extended from the previous two weeks to three to four weeks, which inevitably makes the market worried about the supply of iPhone 5. In addition, since the new iPod touch also adopts the in cell screen, it brings about a demand of about 6 million for Q4. The demand for Q4 is about 12 million in the third quarter and 50 million in the fourth quarter.

From the production capacity of in cell, according to DIGITIMES, the overall yield of in cell in the upstream supply chain in the third quarter has not been fully opened, and the shipment volume in August was less than 10 million pieces. The shipment volume in the third quarter should be about 16 million, and the output is expected to reach 48 million in the fourth quarter. Taken together, at present, the global in cell capacity is fully covered by apple, and it is impossible for the three manufacturers to supply other mobile phone manufacturers. According to the existing capacity, in cell will provide little or no capacity to other manufacturers in the next year.

Non Apple camp: AMOLED + on cell and OGS are positioned at the high end, and GF is positioned at the middle and low end

Thinness is the symbol of high-end. In terms of small-size touch control, AMOLED + on cell will occupy part of the high-end market driven by Samsung. OGS has advantages in technology maturity and mass production time, and will be the most cost-effective technology for high-end market models in the non Apple camp in the future. Due to the disadvantages in thickness and performance, and the fierce competition in the future, GF has a downward trend in price, and will face the medium and low-end market in the future.

Of course, OGS will first mainly capture the large-scale market. With the rise of ultrabook, it will drive the increase of OGS shipments, improve the yield of OGS, and gradually show its cost advantage, and then begin to occupy the small and medium-sized market. Due to its own technical yield, in cell has little probability of application in large-scale, and its main market positioning is in small-scale. In this sense, the further promotion of in cell technology has a relatively small impact on OGS, but a greater impact on the g-film camp.

In cell is Apple’s medium and long-term choice and is expected to transition to other products in the future

From Apple’s screen technology replication process, Apple will first use some new technologies on the iPhone, and then extend to other products. Taking the retina screen as an example, the iPhone 4 released on June 7, 2010 first adopted this technology, then extended to the new iPad released on March 7, 2012, and then extended to retina MacBook Pro released on June 11, 2012. In cell will be Apple’s medium and long-term choice. With the improvement of production capacity and yield and the maturity of technology, it is expected to transition to iPad series products in the future. As for Mac products, if the touch function is introduced in the future, the choice of touch technology mainly depends on the yield of in cell and the improvement speed of technology. In these unsatisfactory cases, it does not rule out the possibility of using OGS for Mac.

Leave a Reply

Your email address will not be published. Required fields are marked *