Apple: pixels as touch sensors for brighter, thinner screens
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, it does absorb 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.
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