With their capability to slim down the profile of smartphones and tablets, touch sensors that are directly integrated into either the cover glass or the display panel are gaining traction in the market. Apple has pioneered the in-cell approach with its iPhone 5, where touch sensors were integrated directly into the thin-film-transistor backplane glass. Rival Samsung, on the other hand, advocates the on-cell approach via its Galaxy SIII and later models, with sensors assimilated into the top side of the encapsulation of the display panel.
The portion of mobile phones shipped with in-cell LCD technology will grow to 14.8 percent this year, up from 7.5 percent in 2012. In comparison, phones with either on-cell LCD or on-cell OLED will rise to a combined 19.2 percent in 2015, up from 12.0 percent in 2012. The majority of phones will still employ the traditional projected capacitive approach, wherein the cover glass, touch sensors and display panel occupy three separate layers. However, shipment share for those devices will decline gradually in time.
Integrated technologies have been known for years, but only recently have in-cell and on-cell mechanisms taken off as understanding of the technologies improved.
From the outset, there was no clear differentiation of in-cell and on-cell. Conventionally, the sensors patterned on the upper glass were called “on-cell,” while sensors that were included in the LCD backplane glass were deemed “in-cell.”
However, some suppliers offer sensors embedded with a black matrix and labeled them “in-cell.” Others have placed X-Y electrodes on the upper and backplane glass, respectively, as is the case in so-called “hybrid in-cell.”
Since 2015, there has been a new definition: On-cell now means the sensor is patterned on the top side, facing users, of the encapsulation or color filter glass of the display. If at least one electrode is positioned inside the open cell or display component—that is, between the bottom of the display panel and the glass at the topmost layer—then the sensors qualify as being in-cell.
Regardless of the technology, deploying in-cell or on-cell touch results in a thinner smartphone or tablet, as it eliminates the third layer otherwise found in older display technologies. Another benefit is more saturated color, because light passes through fewer layers.
Overall, in-cell technology is more complicated and is used in fewer phones, with large-scale adoption by panel makers except Apple not likely for now. On the other hand, some display makers like Samsung are known to favor the on-cell approach, as they can directly integrate the sensors—which in many cases they also produce—cutting out touch-sensor suppliers and thereby saving costs.
Calvin Hsieh is research director, IHS Technology