Metal mesh touch and Advance in cell touch technology

Metal mesh touch and Advance in cell touch technology

  Study of the issues of metal mesh touch

•    Because metal mesh is opaque, so to achieve 95%~99% transmittance means to pick off 95%~99% sense area. When touch sensor area remaining 1-5%, the amount of the touch sensing signal that touch circuit received will also be reduced by 20 to 100 times, in this condition is there any touch IC can support this metal mesh touch panel.

•    For avoiding the human eyes to see, the width of a metal line must be less than 5 microns, Existing touch panel plant’s lithography equipment is impossible to implement, we must use the LCD panel plant’s high level photolithography equipment to do the job, if you replace the photolithography process by the printing method to print less than 5 micron metal wire, even the most sophisticated letterpress printing techniques, yield issues remain difficult to overcome. The cost of stencil will be high, durability of stencil, stencil cleaning cost; all will significantly affect the cost of the metal mesh touch panel.

•    Using roll-to-roll production equipment in high speed and high tension conditions, how to keep the wire less than 5 micron continue line without broken, also a challenge for the equipment manufacturers.     

•    In addition to the characteristics of the metal opacity but also high reflectivity, it is necessary to add opaque material or anti-reflective material to solve reflection problem, and therefore to impact on the manufacturing process, increasing the difficulty and cost of production.

•    Using silver, aluminum or copper as a metal mesh material, must face with oxidation problem, how to add surface treatment material to prevent oxidation, also increases the difficulty and cost of the production process.

•    When we successfully overcome the above problems later, could we remain convinced that the metal mesh has a cost advantage?

      

 Metal mesh touch technology's success key point is the touch IC

Currently the hottest topic in the touch industry "metal mesh touch"; new technologies and new materials to replace ITO materials in order to reduce the cost of touch panel is gaining momentum, and many friends of the industry have also focused on this. Metal mesh is opaque material, but has to use at a transparent purposes, this is bound to the balance between product optical consideration and user acceptance issues. Transmittance, reflectance, interference caused by the phenomenon of Newton's rings are in a test of user acceptance. The higher quality requirement needs to use the finer metal wire, the finer metal wire the smaller sensor area and much more difficult to produce also increase the production costs, the tiny sensor area will challenge the detecting ability of the touch controller IC. So that the existing touch IC industry cannot cross this technical threshold and therefore metal mesh touch technology's success key point is the touch IC, but not production technology of the panel firms.

Metal mesh sensor should not use mutual capacitance technology

•    First, driving electrodes Tx and the receiving electrode Rx overlap area is a non-effective region, therein the electric flux lines can take the shortest distance route, so when the finger touches the region cannot affect changes in the electric flux lines and no mutual capacitance change induced. Second, the smaller overlapping area the smaller mutual capacitance, the closer the two layers the larger the mutual capacitance; these two parameters can be adjusted to get the desired mutual capacitance value.

The size of the mutual capacitance is inversely proportional to the value of its capacitive impedance, of the impedance of the mutual capacitance becomes larger, then the touch sensing current will become smaller, thus, the design trick is to pick the best measureable induced current as a necessary condition, and to make overlapping area the smaller the better.

To achieve greater finger touching capacitance change, the adjacent but non-overlapping regions between Tx electrode and Rx electrode are the larger the better, thus there are more electric flux lines overflow through the substrate to react with the finger. When a finger approximates or touches, it can block and absorb those overflowed electric flux lines, so the blocked electric flux lines cannot reach Rx electrode caused the mutual capacitance reduction. That’s why Apple applies larger Tx electrode and smaller Rx electrode to her mutual capacitance double-layer structure.

•    How reasonable arrange both the size of non-touch mutual capacitance and touch mutual capacitance change, which challenge to the skill of design of touch panel plant. Since mutual capacitance is reduced when touch occurs , the lowest limit is that the mutual capacitance change to 0, so the key point is that, where a fundamental value from which began to change, this is the non-touching mutual capacitance values we want. Someone would say the bigger the better, so have enough space to change, it is not true, we have to take the sensing circuit and amplification method into account, the larger reserved space in the front the more unfavorable for sensing signal amplification, the quality of signal amplification directly impact on the touch sensitivity, so different touch circuit is suitable to different touch panel specifications. If you choose the correct touch IC, the touch panel design will be very simple and flexible, contrary to disastrous consequences.

•    When we use metal mesh replace ITO sensing electrode, what places changes along with? First, because the area of Tx and Rx becomes smaller, so the overlapping area becomes very small and the capacitive impedance increases dramatically, thus sensing current becomes very tiny, but the background noise still remains the same condition, and therefore SNR deteriorates seriously. Second, because the non-overlapping region becomes smaller, so only very few electrical flux lines overflow to outside to react with touch finger, thus touching mutual capacitance change becomes very small, causes SNR deterioration more serious. Although the metal mesh could reduce the sensor resistance to benefit sensing sensitivity, but the very limited scope for improvement is not sufficient to remedy the deterioration of SNR, so the use of mutual capacitance technology for metal mesh, whether to do it at the LCD internal or external, the chances of success are not much, only the self-capacitance technology is feasible.

Metal mesh in cell touch

Metal mesh concept may seem simple, but difficult to do well. However there is always an opportunity, open your mind to change the ideas may make a big difference. Putting the metal mesh in invisible positions of the LCD inside, all optical problems can be solved at once; we call this method "Metal mesh in-cell touch". The first to propose this view is not the author, but veteran Apple in 2007 proposed an advanced embedded touch patent Apple's US Patent No. 8,243,027; In this patent, Apple suggested ​​two revolutionary concepts;

First, The common electrode (Vcom) inside the LCD is patterned as touch sensing electrodes, so you can solve the great self-capacitance due to the sensing electrodes inside the LCD thus too close to common electrode. Both Sony's Pixel eyes technology and Synaptics’s TDDI technology are derived therefrom, but since Apple's US8, 451,244 B2 "Segmented Vcom" Patent certified, panels with  Pixel eyes or TDDI's in cell panel structure would infringement concerns.

Second, take advantage of the internal LCD unseen locations to build a metal mesh touch sensor, neither observable issues nor metal wire reflection and glare problems, one solution to solve all optical problems. Samsung TW 201217863 patent application is to follow this idea. Of course, LGD, AUO, Innolux, Hannstar, CPT, Wintek, Sharp, JDC, also has similar patent applications.

A battle of whether to make the metal mesh inside or outside the LCD, that is pulling touch panel and LCD panel plants plate movements, it is interesting that the key factor of victory or defeat is not the two major forces in this war but touch IC technology and touch panel patent portfolio.

Touch measurement techniques don't measure capacitance, "perturbation resonance" on stage

Currently the touch industry measure capacitance touch the way, nothing more than to input represents the charges voltage or current, then accumulate it as a reading value, and use a software algorithms to process many recorded readings, as a basis to judge the touch signal amount. These cumulative actions must to measure the approximate steady-state charge movements, and the results will be accurate, I would classify it the "steady-state measurements method" or "Static Measurement Method".

 In addition to measuring the charge accumulated, there are also other changes can be measured, for example, analyzing the voltage or current state of change with time, behind the nature of the changes, whether there exist a particular Pattern, I call it "Transient Measurement Method" or "Dynamic Measurement Method".

When many of the components interact with each other and produce feedback reaction, it already has the basic elements of complexity theory, complex state has no periodicity, no regularity, unpredictable and other features, it is difficult to use analysis and inductive method to deal with. But when the various environmental factors under certain conditions then the complex will enter a "chaos" state, at this moment, it will present a great order of something, similar to the "Things always reverse themselves after reaching an extreme", and "perturbation resonance" the touch of new technologies, is the use of this principle.

Perturbation resonance touch technology doesn’t measure capacitance, it predominates the environmental conditions to induce "chaotic state" occurrence, in other words, these chaotic touch signals (including noise), make it into a real "chaotic state", once into the chaotic state, the touch signal and noise will blend together to become the new touch signals which is sufficient for touch judgment, therein this new touch signal will be endless, endless, and disturbing noise has also become an important element of the touch signals, like we often hear of the "butterfly effect" is the same reason. This new touch change signal in comparison with the prior art measuring the accumulated change of charge, even hundreds of times to thousands of times bigger, it can be regarded as the revolutionary new touch technology.

Super C-Touch is a touch industry pioneer, the world's first applied "chaos theory" in measuring changes of touch, probably is the world's first successfully achieved practical application by a chaotic state, so whether in physics or touch the field of history have left footprints.

For touch design and production, no longer need to measuring capacitance is really a godsend.

•    No longer worry about optical adhesive to induce uneven thickness or thickness error problem in lamination process. Slight difference in thickness is sufficient to cause the capacitance value difference which is larger than capacitance difference caused by finger touch, so thickness problem is the number one enemy of lamination process.

•    Never worry about different material of substrate.

•    Never worry about the touch pattern on the bit offset issue in alignment process.

•        Never worry about ITO resistance and capacitance values too large problem.

•        Never worry about touch Sensor area is too small to induce insensitivity issue.

Basically as long as there is no open or short problem and no visual defect, then the touch panel is qualify to sell, thus substantially increase the lamination yield and touch Sensor production yield, more importantly, remove the obstacles to enter in-cell touch domain, touch industry becomes very simple since there is no barrier to entry, then touch the industry will enter a mature stage, since the touch industry enter its final stage, so most of existing firms will gradually be forced to exit the stage, and only remains a few firms to dominate the industry.

Slip through the net: Touch in-cell metal mesh structure of AMOLED

Spent a lot of time searching for information about the in cell AMOLED touch patent and only very few can be found. Even Samsung have not patent applied, only found several patent proposal related in-cell touch are also the same with earlier, using the substrate deformation caused by a short circuit or change in capacitance caused by proximity to detect touch. Or else that apply generally embedded LCD touch when the way to expand the scope of claim to the OLED field, basically all are not invented for AMOLED.

Inferences about the following three reasons, (1) most people do not understand the principle structure of the AMOLED, so could not do. (2) Experts familiar with the AMOLED found it impossible to cross a major obstacle, so they cannot design a feasible in-cell touch structure of AMOLED. (3) Just using the touch sensing glass as a cover glass of AMOLED could achieve on-cell touch, while the existing Sensor glass is very cheap, if done in cell touch to cause any yield losses on its costs are higher than the cost of the touch sensor glass, so the development of in-cell AMOLED touch is pointless.

After discussing with the friends of Samsung, reached a consensus that the main reason is the aforementioned third point, when there is not enough attractive interests, whoever waste of time to do this research and development. But one incident made me change my opinion, to accept a unit's invitation to participate in a seminar on mobile devices thinner forum. We discuss what is the thinnest combination of touch structure with display panel, very naturally mentioned to in cell, on cell and OGS, etc., their structure is actually little different. Among these was an ITRI analysts mentioned a quite creative argument, he said that no matter in cell, on cell and OGS have three glass to form, two to the LCD with the outside plus a protective glass, but if you are using a AMOLED when there may range from three glass becomes two glass. Simply replace on-cell's touch sensor by OGS to achieve it, very reasonable, I pushed it a step further, if a flexible AMOLED (foldable AMOLED) attached to the OGS and it is turned into only one glass on completion.

Whether two or one glass structural needs OGS touch to match, while the cost of OGS is much higher than touch sensor only, and therefore the in-cell touch can reduce many of the costs. Also you can make flexible AMOLED touch the best way is in-cell metal mesh structure of the touch, because the ITO material is brittle and considerably difficult to be folded, however the metal materials do not have this problem is folding the best option.

Conclusion

 To produce an In-cell touch screen is very simple, just use the touch sensor glass to make the LCD color filter glass, then adhere it to an Array glass, pouring the liquid crystal in and finish. There are over one hundred patents that use of this concept all over the world, but the drawback is no cost savings and a large capacitance is formed between the touch sensor and the Vcom, thus all touch control ICs cannot work normally.

The second method is to pattern the Vcom as sensors, therefore to solve the above-mentioned deficiencies, no more difficulties for touch control IC, and this is the method used in iPhone 5, but Apple’s patent is an exclusive monopoly, to be heading in this direction will be infringement concerns.

The last way is to make the metal mesh as sensors inside the LCD panel, currently the world about the amount of related patent applications is still limited, it is more possible development areas; In addition, in AMOLED in-cell touch territory, in fact, there is still quite a large part of the development space, Since in addition to Samsung's AMOLED with the separated RGB, there are LGD as the representative of the white light AMOLED. It is the same as LCD panel that the white light AMOLED needs to use the color filter glass, thus, it cannot use the sensor glass as on-cell touch and its touch cost is higher, and therefore, there is a greater incentive to introduce the in-cell touch technology.