How 'in-cell' technology could make the next iPhone ultra-thin

We're all familiar with Apple's love affair for thin devices. Although the third-generation iPad surprised many by gaining about half a millimeter of thickness, it looks like Apple could be back to trimming product dimensions by using a new kind of display technology in the next iPhone.

Instead of using a display comprising a number of separate layers, Apple could use in-cell touch display technology, according to a Friday report from Digitimes. The report says Apple would be sourcing its in-cell displays from Toshiba and Sharp.

"The advantage of in-cell is that you're streamlining the manufacturing process, so in time you should be able to drive efficiencies and reduce cost," IHS analyst Rhoda Alexander told Wired. "Additionally, by reducing the number of layers, you reduce the size and thickness of the device, making it thinner and lighter."

If the iPhone has a larger 4- to 4.3-inch display, as some reports expect it to, that extra glass could add a bit of heft to the iPhone's weight. Thus, Apple would need to find new ways to keep the phone from gaining too much weight.

Currently, the iPhone's "on cell" display is layered a bit like a sandwich (or if you're feeling like dessert, think of a trifle). At the very bottom, you've got the back light. Directly above that, the LCD section, which houses the red-, green-, and blue-colored pixels of the display. Then there's a layer of glass.

On top of that is the capacitive touch layer, which is then topped off by a tough layer of Gorilla Glass. The middle layer of glass separates the liquid crystal portion of the display from the touch portion.

In-cell display tech eliminates that middle layer of glass, combining the LCD and touch sections of the display into a single layer.

One way this can be successfully accomplished is by "multiplexing" the electrodes normally used to relay touch input -- that is, using the same electrodes to handle the signals for both touch control and the pixels of the LCD, according to a 2010 IHS report on touch-screen displays.

In-cell technology isn't currently deployed in any shipping cellphones. And it shouldn't be confused with the similar-sounding "Super" technologies from Samsung. Super AMOLED and Super LCD screens use on-cell technology rather than in-cell.

Right now, in-cell touch displays are still an emerging technology. So while the core technology promises long-term benefits, yield rates could be a problem in the shorter terms, Alexander says.

But that's the deal with any new technological process, isn't it? In the months before the new iPad was announced, yield rates for Apple's Retina display were a huge question mark.

So is in-cell really something Apple would pull the trigger on? "We do believe that the next iPhone display will implement in-cell touch," DisplaySearch's Paul Semenza told Wired via e-mail. But of course, we'll have to wait and see how it pans out when the next iPhone actually debuts