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  Date:1st Nov 2011

Sensor-on-cover and in/on-cell are emerging tech in capacitive touch panels

DisplaySearch has announced its latest research study on capacitive touch panels. The release from DisplaySearch states In-cell and on-cell sensors are typically integrated during the display manufacturing process, whereas sensor-on-cover involves coordination between touch sensor and cover glass makers. While Apple products use glass-based sensors with ITO (indium tin oxide, the typical transparent conductor) layers on both sides, most sensors use one or two layers of ITO on the same side of the glass; this is required for sensor-on-cover because the outer side is the exterior of the product, said in the release.

Jennifer Colegrove, PhD, Vice President of Emerging Display Technologies for DisplaySearch says "Two approaches are emerging to simplify projected capacitive sensor designs,". "One is sensor-on-cover and the other is in/on-cell."

The other research finding shared by DisplaySearch includes:

Capacitive touch screen shipments grow by more than 100% Y/Y, cover glass has become a key component in touch screens. Regardless of the type used-sensor-on-cover or in/on-cell-cover glass is a must for projected capacitive touch for both cosmetic and protection purposes.
Cover glass finishing is very labor-intensive and, depending on the processes required and specifications, has yield rates in the 70% range. Process challenges will be an increasingly strategic issue for the industry. Depending on the technology and supply chain, cover glass finishers and touch module makers will be working together by contract or informal relationship, while tier-one touch module makers are integrating and expanding their in-house cover glass finishing capacities.
The touch screen supply chain is evolving differently in each region, based on variations in technologies and supply chain variables. Although sensor patterning and lamination processes are mostly automated, manpower is still necessary, especially for inspection. Japan, with high labor costs as well as a complex supply chain, tends to have the highest cost structure. China offers the lowest prices for mature mobile phone sensors, and Taiwan has lower prices for tablet PC sensors. This is due to greater availability of glass and better access to Gen 4.5 and larger equipment for sensor deposition and photolithography.

For popular mobile PC sizes (9.7" and 10.1"), average selling prices (ASPs) per unit are in the range of $1.00-1.50 per inch; however, DisplaySearch anticipates ASPs will fall as popularity increases. ASPs of regular notebook sizes (>11.6") are still higher due to challenges in scaling production.

Curved or shaped cover glass-referred to as 2.5D if along one axis and 3D if along both axes-is a new design trend. Many touch-enabled smart phones look very similar, so brands are looking to use curved cover glass to differentiate their products. Due to its more complicated processes and costs, DisplaySearch expects curved cover glass to be used primarily in high-end models.
While touch module makers are likely to outsource larger-sized sensors if volumes increase, DisplaySearch expects tier-one touch module makers to integrate cover glass finishing because it is critical for sensor-on-cover production and for decreasing substrate weight and thickness.
Moving into the holiday season, DisplaySearch forecasts that the tablet PC market will be increasingly important for the touch panel industry, particularly as lower-priced products, like the Amazon Kindle Fire, enter the market.

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