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.
