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P-cap tech opens new possibilities for ITO touch sensing

Posted: 21 Feb 2012 ?? ?Print Version ?Bookmark and Share

Keywords:p-cap? touch sensing? ITO?

Projected capacitive (p-cap) touchscreens have witnessed overwhelming success in the consumer portable space over the last few years, being specified into highly popular products such as Apple's iPad and iPod Touch, as well as Samsung's Galaxy and Blackberry's Torch smartphones. People are now starting to perceive touch as the only way to interact with technology and this is leading to demands for comparable functionality to be incorporated into the small screen devices used in far more challenging settings. However, there are issues as to how this can be done.

ITO's widespread proliferation in the consumer sector
Touchscreens based on a mutual capacitive sensing mechanism and utilizing conductive Indium tin oxide (ITO) have proved highly attractive for bringing touch functionality to small format displays. This metal compound has several attributes that make it highly suitable for touchscreen manufacture. As well as being both electrically conducting and near optically transparent (with the ability to easily be etched into micro-fine structures that do not inhibit display visibility), in small screens it offers improved durability and performance levels coupled with the economies of scale needed to serve mid/high volume touchscreen designs, while supporting more compelling features, such as multitouch operation, which allow device manufacturers to create user interfaces that will differentiate their products from the competition.

Market breakdown

Figure 1: Touch sensor market breakdown (2009-2016).
Source: 2010 Touch market analysis, DisplaySearch

The existing widespread use of ITO in several other touch technologies has accelerated the adoption of p-cap touch sensing and has enabled its meteoric growth in the small display consumer sector (If this predicted growth is to be fully realized though, then new market opportunities for ITO must be found, both inside and outside established consumer application areas. One such opportunity exists where manufacturers seek to replace traditional mechanical keypads and switches with more intuitive control methods. In order for ITO-based p-cap touchscreens to migrate into these and other demanding industry sectors and applications, such as medical diagnostic tools, domestic appliances, handheld test equipment, warehousing data entry terminals and vehicle telematics, there are certain technical challenges which need to be addressed. These highlight some of the limitations of the "conventional" mutual capacitive sensing mechanism used in consumer electronic devices, and, as we will see, call for a whole new perspective to be taken.

Current ITO touch sensing technology issues
Mutual capacitive sensing using ITO as the conductive medium is relatively insensitive, and consequently it is difficult to detect touch through more than 1 or 2mm of glass. This means that although scratch-resistant screens can be made, they lack the rigidity necessary to protect the underlying display from moderate to severe impacts thereby reducing operational longevity in many non-consumer applications. However, this issue can be overcome if a self-capacitance approach is followed instead. While mutual capacitance touch sensing measures capacitance between two electrodes, self-capacitance touch sensing measures capacitance of single electrode to ground, utilizing the field generated from the user to induce minute changes within the sensors field.

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