Touchscreens and multitouch technology make up a significant majority of Apple’s research into future user interface improvements, and the iPhone introduced some of those UI paradigm shifts into our increasingly mobile computing. Since almost all interaction with the iPhone—and presumably the hopefully imminent Apple tablet—involves a touchscreen, Apple hopes to improve on touchscreen technology by using each individual LCD pixel as a touch sensor.
Apple has filed a patent application, published today, for a “display with dual-function capacitive elements.” By mixing display and sensing functions into each individual pixel, it would make touchscreens thinner, lighter, and brighter than they currently are today.
The way current touchscreens found on most smartphones work is by overlaying a touch-sensitive panel on top of a traditional LCD panel. The touch-sensitive panel is essentially a grid array of capacitors, most commonly made from the transparent conductor indium tin oxide (ITO). When your fingertip comes in contact with the small magnetic fields present in the capacitors, it causes the voltage along those capacitors to fluctuate. A processor translates these fluctuations into touch positions.
The need for additional layers covering the LCD screen means it is thicker, and despite the fact that ITO is transparent, the touch layer does block some light coming from the LCD display underneath. Apple’s solution involves using each individual pixel as a capacitive sensor, eliminating the need for an additional layer for a separate touch sensor.
Part of the magic of Apple’s patent relies on forming an IPS LCD display using a low temperature polycrystalline silicon instead of the more common amorphous silicon. Materials engineering nerds may want to look at the patent for a more detailed explanation, but suffice it to say that the poly-Si allows for a much faster switching frequency for driving the individual pixels. (For those unaware, the individual pixels in an LCD panel switch on and off at a rate much faster than we can perceive—it’s this same switching that can cause eye fatigue from staring at your screen all day.)
Apple’s idea takes advantage of the faster switching of poly-Si to drive the pixels one instant, and use the capacitive properties of the individual pixels as touch sensors the next. The switching happens fast enough to give a clear, bright display, as well as responsive touch sensing. The elimination of the separate touch-sensing layer also makes for a thinner, lighter, brighter, and simpler touchscreen unit.
Apple proposes its solution for mobile devices, making references to iPhones, iPods, and even MacBooks, but don’t be surprised if such an innovation also makes its way into an Apple tablet.