The patent for a “Touch screen liquid crystal display” details several methods of integrating the touch-sensing elements of the touchscreen within the LCD.
The in-cell tech integrates the touch sensors directly into the display rather than using a separate layer.
AppleInsider reports that the iPhone 4S uses “on cell” technology, which is a layer of touch-sensitive glass placed between the Gorilla Glass layer and the unit’s top glass.
What in-cell does is that it merges the two layers, allowing for the “same electrodes used for display updating to also be used for touch sensing.”
By merging those layers, the screen size is reduced by half a millimeter.
The patent filing reads:
“By integrating the layered structure of an LCD and a touch sensor, a variety of benefits can be achieved. This integration can include combining or interleaving the layered structures described above. Integration can further include eliminating redundant structures and/or finding dual purposes (e.g., one purpose for the touch function and another for the display function) for particular layers or structures. This can permit some layers to be eliminated, which can reduce cost and thickness of the touch screen LCD, as well as simplify manufacturing.”
The patent was filed in 2007, before the launch of the first iPhone.