The breakthroughs in e-paper technology continue to come. First was a flexible device; now a touch screen display has been demonstrated at the Arizona State University Flexible Display Center (FDC). The device has been developed by FDC in collaboration with its military and industry partners and features the first flexible touch screen integrated with an active-matrix display, based on E Ink’s electrophoretic technology in the form of VizplexÔ Imaging Film.
Collaborative Effort
The Arizona State University FDC was set-up to provide complete flexible electronics capabilities to bridge the gap between innovation and product development in an information-secure environment. While that might sound simple, that aforementioned gap is both high risk and resource intensive-beyond the means of many individual companies to close successfully. The facilities include backplane electronics design, fabrication, test and integration capabilities, as well as dedicated Pilot Line toolsets for technology development and for technology demonstrator production. In this case, the collaboration was between E Ink, DuPont and the FDC.
Touch Screen Breakthrough
The device that was demonstrated uses plastic materials as a substitute for the glass found in conventional touch screens; the flexible Teonex® polyethylene napthalate (PEN) substrate was supplied by DuPont Teijin Films. It is powered by amorphous silicon thin-film transistors fabricated on the plastic substrate. While originally designed for military purposes, the touch screens could have a much wider application. Glass displays need a hard-shell casing; flexible screens open the door to larger format displays such as electronic newspapers and textbooks. However, the present screen may not be durable enough for consumer applications, which would find users navigating on-screen icons, then rolling up the e-paper for carrying and storage.
The new device is both rugged and extremely thin compared to traditional glass screens. Furthermore, its low power consumption eliminates the need for heavy lithium-ion batteries used for conventional LCD-based laptop computers. Like E Ink’s display, the touchscreen consumes power only when its contents are being changed. The device also includes a writing mode, where information can be sketched on the display. Such information can be stored before it is erased.
Significant Challenges
Touch screens are a significant breakthrough in e-reader technology and did not come without challenges, because most touch screen technologies are designed for a rigid screen. Resistive touch screens (used in the Nintendo DS games console) rely on making a point of contact between two separate conducting layers. “Flexing these layers can lead to false inputs,” says Jann Kaminski, display engineer at the FDC). “For resistive, you have an air gap that has to be maintained,” he says.
Capacitive touch screens (used in the iPhone) rely on conductive transparent films made out of indium tin oxide (ITO), a rigid, inflexible material. Likewise, touch screens that detect changes in light or vibrations across a screen don’t work because the signals become distorted when the material is flexed.
While inductive touch-screen technology solved the flex problem, it had its own difficulties. Inductive screens usually employ magnetized styluses to induce a field in a sensing layer at the back of the display; one not inherently sensitive to flexing. However, most flexible displays use a very thin stainless-steel backplane, which maintains enough rigidity to prevent damage, yet allows flexing of the display. These metallic backplanes act as a barrier to the electromagnetic fields needed for inductive touch screens to work.
The solution was Teonex® the alternative backplane material supplied by DuPont. Widely used in thin-film transistor manufacturing, the plastic offers support to the display while allowing the inductive touch layer to work. Moreover, the quality of the image is not degraded because the sensing is done behind the display. This is critical in a reflective display which depends on ambient light rather than backlight, which can consume high levels of energy.
The FDC estimates that the technology could be commercialized in approximately 18 months. With higher volumes that would come with consumer applications, manufacturing costs would be reduced. Given all recent developments on the e-newspaper front, it will be interesting to watch the news of flexible touch screens unfold. Will this be the final piece that will jettison e-paper readers into the mainstream, or will color challenges still hamper that penetration?
By Linda M. Casatelli
e-ink, fdc, flexible, touchscreen