New e-paper displays full-motion video

An electronic-paper display developed by QUALCOMM can deliver high-quality video images, making the technology usable for applications like mobile phones, portable electronic readers and display signs, the “MIT Technology Review” reported.

The new e-paper display employs microscopic mechanical switches that turn pixels on and off at rates fast enough to display video.

Early versions of the display will be monochrome. The first application was released recently in an Audiovox Bluetooth headset. A two-color display will be used next year in a phone made by the Chinese phone company, Hisense, with full-color versions to follow, the MIT publication said.

Like ordinary paper, e-paper displays are designed to be reflective, making them much easier to view in a range of different lighting conditions, such as bright sunlight, than are traditional displays, such as backlit LCDs.

They are also bi-stable, meaning that once they have been switched to a state, they will hold that state without requiring an electrical current. The benefit of this is that they use considerably less power.

In most e-paper displays, however, pixels switch on and off too slowly to display video, said James Cathey, vice president of business development for QUALCOMM MEMS Technologies, based in San Diego. Such slow switching can lead to “ghosting,” in which moving subjects blur.

In contrast, MIT said, pixels in the new display can switch in just tens of microseconds — a speed fast enough to produce sharp video images.

To produce color, the report said, each pixel consists of several color-specific cells that mimic the film of oil on water. Each cell is made up of two reflective layers, one on top of the other. The top layer is only partially reflective, allowing some light to pass through it and bounce off the second surface.

In each cell, the gap between these surfaces is spaced so that constructive interference occurs for only one specific range of wavelengths, causing them to amplify a single primary color while canceling out other colors. To create a full-color display, each pixel is made up of three different types of cells, each having a different-size gap between the layers that reflect red, green, or blue.

By combining different sets of colored cells as subpixels, researchers can get any color of the spectrum, the report said. MEMS devices are very robust and have been demonstrated to be reliable for more than 12 billion cycles.