Friday, October 03, 2008

Simpler Flexible Displays

A new approach avoids flexible electronics.

By Kurt Kleiner

Flexible image: Stills from an animated cartoon, projected by a 635-nanometer scanning laser at eight kilohertz onto three different flexible plastic screens. The screens fluoresce blue, green, and yellow-red, and could eventually be combined to create a full-color display. Credit: Institute of Physics, Sony, Max Planck Institute for Polymer Research

Multimedia   Click here to watch a video of the new screen in action.

Flexible displays that are bigger, brighter, and cheaper could be made using a new approach that involves exciting fluorescent chemicals embedded in the screen with an infrared laser.

Researchers are exploring a range of flexible-screen technologies because they could have a range of applications, from electronic advertisements that can be pasted on a wall to laptops and electronic books that can be rolled up and tucked into a backpack. One approach is to use organic LEDs on top of a flexible substrate. Another is to use electronic "ink" consisting of tiny colored particles that can be controlled electrically. E-Ink, based in Cambridge, MA, has even created electronic "paper" that is used in a number of commercial products. However, both approaches require some form of flexible electronics to control the displays.

The new approach, developed by researchers in Germany--at Sony Deutschland Gmb, in Stuttgart, and the Max Planck Institute for Polymer Research, in Mainz--avoids the complications caused by flexible electronics. Their device consists of a chemical layer sealed between plastic sheets. Under normal light, the screen is transparent. But when exposed to infrared light, the chemicals in the screen fluoresce.

To create images, the researchers used a red or infrared laser to quickly scan across the screen, from either in front or behind, causing different parts to fluoresce in sequence to produce a fast-moving image. This is similar to the way that a cathode-ray tube uses an electron beam to make images. In a demonstration, the researchers made a cartoon image move around on their screen.

Tzenka Miteva, a researcher at Sony who coauthored a paper on the technology, published today in the New Journal of Physics, says that the screens use specially-matched combinations of chemicals to "upconvert" light--that is, absorb light of longer wavelengths and emit light at shorter wavelengths. This means that the researchers were able to use a red or infrared laser to generate colors in the visible spectrum. "Red or infrared lasers are cheap and very much available on the market," Miteva says. "And because it works at very low intensities, we can use them without problems with the viewers."