Large Format Multi Touch Screen Technology PCT | Zytronic
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`Self Capacitive Sensing Brings Touch to Large-Screen Products
`
`Monday 10th June 2013 10:44am
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`By Ian Crosby, Sales & Marketing Director, and Dr. Andrew Morrison, Technical Director, Zytronic
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`The widespread adoption of projected capacitive (p-cap) touch sensing has contributed to one of the largest consumer electronics revolutions in recent
`years. As devices such as smartphones and tablets have proliferated, so a durable, sensitive touch-enabled user interface has become an almost
`mandatory feature for product designers in every field.
`
`The vast majority of these devices are now based around a p-cap sensor, driving a phenomenal growth rate in this part of the touchscreen sector.
`Figures from leading industry analyst DisplaySearch show that, though still relatively new, p-cap has rapidly risen to become the most widely used
`touch sensing technology in the global market, overtaking the long established and increasingly commoditized resistive sensing technology.
`
`This fast uptake has been driven by a compelling feature set, including an effectively unlimited lifespan conferred by a resistant all-glass surface, edge-
`to-edge design capability (with no requirement for bezels) and high levels of sensitivity. However, as original equipment manufacturers (OEMs) seek
`to incorporate touch interactivity with a similar style and performance outside the portable consumer domain, there becomes a realization that touch
`screens which satisfy different set of design criteria are required.
`
`Two choices of technology
`
`OEMs can choose between two distinct types of p-cap touch sensing methodologies. The most common now, is mutual capacitance. This uses two
`separate conductive layers, one of which contains the sensing cells through which the position of the touch event can be identified, while the other has
`the driving cells through which an electrical signal passes. The cells are usually interlocking and each is connected to the control electronics. When the
`screen is touched, there is an alteration of the charge held within the local electric field, reducing the mutual capacitance built up between the two
`layers. This alteration is picked up by the cells in the sensing layer. Detection algorithms within the controller electronics determine the individual cells
`with the greatest change in charge, and output a corresponding X-Y co-ordinate to the host system.
`
`The second “flavor” of p-cap sensing uses the principle of self-capacitance. In contrast to mutual capacitance, this technique employs a separated X-Y
`grid of open ended conductive lines connected to a controller containing the detection algorithms. The charge held on the lines is altered by human
`body capacitance, as the user’s finger comes closer to the touchscreen surface. The X and Y lines with the peak change in charge are detected and the
`touch co-ordinate is output to the PC.
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`http://www.zytronic.co.uk/news/white-papers/self-capacitive-sensing-brings-touch-to-large-screen-pr...
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`TPK 2007
`Wintek v. TPK Touch Solutions
`IPR2013-00567
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`

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`Large Format Multi Touch Screen Technology PCT | Zytronic
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`Page 2 of 5
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`There are a number of reasons behind the adoption of the mutual capacitance approach in consumer electronics. The technology is particularly capable
`of providing multi-touch functionality assuming sufficient cell density and controller IC power is available. The high density of individually connected
`cells makes it possible to gather and interpret the large amounts of touch data required to separate multiple independent touches.
`
`However, conventional mutual capacitive screens can suffer major drawbacks when a designer attempts to move to larger form factors. In order to
`accurately track multiple touch points, the controller must capture data from each of the small individual cells. The bigger the screen, the larger the
`amount of information that need to be captured. Eventually the size of the data set becomes overwhelming. In practical terms once the touch display
`size reaches 15 inches (approx. 380 mm), the number of cell intersections that must be connected to and monitored by the controller becomes a major
`challenge. The increased complexity in the control electronics and connectivity also adds to the bill of materials and increases the required integration
`time and effort.
`
`For those weighing between mutual and self-capacitive techniques, practical manufacturing issues also take on increasing importance as display size
`grows. Mutual capacitance solutions are generally based on a matrix of cells made of Indium Tin Oxide (ITO), a conductive, near-transparent material
`that is deposited and patterned on glass or film using a semiconductor-style photolithographic manufacturing process. ITO is widely used in
`applications requiring mass produced, small touch displays (such as portable consumer electronic devices), where the volume-friendly production
`process is a plus. However, if volumes are lower (and this often goes hand in hand with larger screen sizes such as those used in public, self-service
`applications for example ), the relative inflexibility of the ITO process and the high one-off cost of photo masks become more problematic.
`
`Finally, in addition to manufacturing complexity and cost, there is a question of touch performance to be considered. For all its benefits, ITO has a
`relatively high resistivity. This means that as the display area increases, and the distance between cell and controller grows, the signal to noise ratio
`decreases rapidly, resulting in progressively lower touch sensitivity and in the worst case an inoperable device.
`
`A self-capacitive alternative
`
`Zytronic’s proprietary Projected Capacitive Technology (PCT™) is a self-capacitive system that has been proven in deployments all over the world in
`the last 10 years, particularly in situations where larger screen size is required. Based on an X-Y matrix of micro-fine capacitors, embedded within a
`laminated glass substrate, PCT uses frequency modulation to detect minute capacitance changes within the conductive tracks.
`
`A key attribute of this technology is its high sensitivity. It can detect a touch through very thick overlays, protective glass and even heavily gloved
`hands and therefore has an unsurpassed level of Z-axis sensitivity and control. This makes it eminently suitable for industrial and public access
`applications, and even for outdoor use. Because PCT requires unique detection algorithms running within the control electronics, Zytronic has also
`developed its own touch controller hardware and firmware, designed specifically to work with its PCT sensors. The latest controller will output two
`separate touch co-ordinates, making it capable of supporting most gesture recognition and multi-touch software.
`
`Two variants of PCT sensors are currently available. An ITO-based solution suits higher volume applications that require a rugged interface with a
`relatively small screen size, such as white goods and industrial vehicle telematics. Although this senses in the self-capacitive style, it uses the same
`basic manufacturing processes as mutual capacitive sensors designed for consumer electronic applications. For large format and lower volume
`applications, a solution based on copper is offered. Here, the capacitive matrix within the sensors is made of 10 micron diameter copper electrodes.
`One advantage of this material is its extremely low resistivity (10 times less than ITO) allowing touch detection without noticeable degradation of
`sensitivity, even on screens larger than 80 inches. Another advantage of using copper electrodes is that they can be deposited directly onto the rear
`glass surface without the need for photo masks – this means that new designs can be quickly created, tested and manufactured with minimal effort.
`
`Furthermore, the ductility of copper means it can also be applied onto curved planes. Microsoft ® Corporation made good use of this capability when
`developing a touchscreen for its Envisioning Lab (at the corporation’s global headquarters in Redmond, WA). A wrap-around ZYBRID® touch sensor
`was supplied for its conceptual 10 display multi-monitor workstation, called the Spatial Desk, operated through a single PCT touch-enabled surface and
`used to demonstrate the latest Microsoft technologies to key customers.
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`http://www.zytronic.co.uk/news/white-papers/self-capacitive-sensing-brings-touch-to-large-screen-pr...
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`Large Format Multi Touch Screen Technology PCT | Zytronic
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`Figure 1: PCT-based touchscreen applied to Microsoft’s Spatial Desk
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`With a choice of materials and of mutual or self-capacitive sensing p-cap methodologies, OEM interface designers have a toolkit at their disposal that
`allows them to create a touch screen for any application, depending upon factors such as the deployment environment, touch performance, physical
`screen size and volume required.
`
`An example of an unusual application solved by p-cap sensing occurred when advanced user interface specialist Sunvision Technology was asked to
`create interactive dining tables for exclusive Taipei restaurant Mojo. For this project, it was necessary to make the wooden tables touch sensitive. This
`required a technology with extremely high levels of Z-axis sensitivity and the capability to detect touch through the wooden surface of the dining table.
`With this challenging brief, Sunvision chose to embed Zytronic’s 22-inch ZYBRID PCT sensors behind each table top, linking each to a computer-
`controlled projector mounted above the table presenting interactive menus on the touch-enabled surface. With the touch sensors hidden from view,
`when coupled with software specifically written for Mojo by Sunvision, diners are now able to interact with projected images, scrolling through dining
`options, placing orders, playing games and messaging diners at other tables.
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`http://www.zytronic.co.uk/news/white-papers/self-capacitive-sensing-brings-touch-to-large-screen-pr...
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`Large Format Multi Touch Screen Technology PCT | Zytronic
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`Page 4 of 5
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`Figure 2: PCT brings multi-touch table service to Mojo restaurant
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`The ability of PCT to enable far larger screens than can be realized using conventional mutual capacitance alternatives is demonstrated by its increasing
`use by digital signage specialists such as Infinitus. Here a 65-inch version of the ultra-rugged ZYTOUCH® product was specified for the iMotion®
`high-definition digital signage systems designed for use in outdoor, public environments (such as ski resorts, plazas and amusement parks).
`
`Figure 3: Zytronic touch sensors specified by Infinitus for large format digital signage application
`
`Design engineers in a broad range of markets outside of consumer electronics, are increasingly keen to adopt similar levels of touch interactivity
`already enjoyed in the latest hand held tablets and smart phones. In the process, the limitations of conventional mutual capacitance techniques become
`apparent. The nature of the materials used and their manufacturing processes (with resulting economies of scale) normally employed in the production
`of mutual capacitive p-cap screens mean they will probably remain best suited to small format, high volume designs.
`
`In more demanding, ruggedized applications, which require volume flexibility and large form-factors, alternative approaches are essential. As a result,
`p-cap sensors derived from advanced self capacitance sensing such as PCT are likely to remain at the forefront of such applications as industrial
`controls, self-service terminals and medical devices. This technology is already delivering touch interaction in products that simply would not have
`been possible using other methodologies and has the potential to enable further innovation in the future.
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`http://www.zytronic.co.uk/news/white-papers/self-capacitive-sensing-brings-touch-to-large-screen-pr...
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`Large Format Multi Touch Screen Technology PCT | Zytronic
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`The continued improvement in p-cap controller ICs coupled with sensor developments using printable conductive inks and nano-materials are likely to
`extend the capability and use of this versatile touch technology family further still.
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