In the “coming soon” category of “gee-whiz” devices, few things create as much buzz or excitement as flexible, touch-sensitive displays that mimic the traits of paper. Corporate and university research teams have already developed working units that are leading to even further advances that consumers will see in new generations of portable devices.
E Ink of Cambridge, MA, is already supplying displays for the Amazon Kindle and Sony Reader that are readable in direct sunlight and consume much less power than the plasma screens or LCD panels that CRE rents. Of course, they are much smaller and are in a different market segment than these. The company’s design has a layer of “microcapsules” loaded with black and white particles smaller than one micrometer, thus creating a low-power but high-reflectivity screen.
Of course, the ultimate goal is to have displays that are flexible and touch-sensitive. Rumors suggest that the first such electronic paper products will launch sometime in late 2009 or early 2010 with roll-out displays using E Ink’s technology and produced by a Dutch firm. Still, the developers at E Ink and other firms have to overcome a number of challenges to add touch sensing to these kinds of screens. The methods used in existing touch screens require a rigid surface, such as seen on tablet PCs and high-end smartphones. There are two major technologies at work here, resistive touch and capacitive touch.
The Nintendo DS game console uses the former technology, resistive touch, which relies on two separate “conducting layers” being forced together at specific touch points. If these layers were to flex, there would a big problem with false inputs. Early on, researchers at the Flexible Display Center (FDC) of Arizona State University, co-developer of E Ink’s new display approach, realized the limitations of resistive technology as far as touch-sensitivity goes. The air gap between the layers has to be maintained, making flexibility problematic.
The capacitive touch screens used in Apple’s iPhone use transparent, conductive film manufactured from indium tin oxide (ITO). This is a superior technology that is used in the CyberTouch Orion LCD monitor that CRE rents. A brittle and ceramic-like material, ITO is wholly incapable of doing what roll-up, folding and flexing displays will require. Even touch screens using other technologies, ones that detect light changes or screen vibrations, are not up to this futuristic task, since those types of signals can become distorted.
The answer? For now, it appears to be something called “inductive touch-screen technology,” although there are still some challenges to overcome. This technology requires the use of a magnetized stylus to create “fields” on a sensing layer in the rear portion of the display. The problem is that most flexible displays use stainless-steel backplanes to allow flexibility while retaining the rigidity needed to prevent damage, and those backplanes interfere with the electromagnetic fields at the heart of the inductive touch technology.
The FDC team has proposed an alternative material for the backplane, a thin-film DuPont plastic called polyethylene napthalate (PEN). Already used by thin-film transistor manufacturers, it would provide sufficient support for a display while letting the inductive touch layers work. This approach should not degrade the image quality since the sensing will be accomplished behind the display, an essential consideration as E Ink technology uses ambient light reflection instead of energy-eating backlights.
Prototypes are currently going through rigorous testing and military applications will likely be the first for these new displays. The tough battlefield scenarios where such portable displays would be deployed require that the screens do not shatter, meaning the glass backplanes in touch- and non-touch-sensitive consumer monitors like the Apple Cinema Displays are completely out of the question. Once the military gets their lightweight displays that are both rugged and low-powered, the rest of us will start seeing the real fruits of this amazing research, with capabilities and sensitivity far beyond the first consumer products trickling into the marketplace.