Bistable Display

What distinguishes a bistable display from other display types (e.g., LCD) is that after power is removed from the display, whatever is currently showing on the display remains until the next time the power is restored and the image refreshed. In short, the image is bistable; stable in two (or maybe more) states.

The fast color bistable display is a sort of holy grail for portable computer display developers. Since computer displays are often static for long periods of time, power could be turned off to the display during those periods conserving battery life since the active display is one of the largest consumers of power in any portable computer system.

For the moment, bistable displays in common use are typically black and white and are used for such things as retail store signage where the store can change displayed prices from a central location and avoid posting errors.

There are a number of different approaches to achieve bistable displays.

E Ink

E Ink has worked with Royal Philips Electronics to develop a bistable display based on electrostatic charges used to affect tiny spheres suspended in a plane. The spheres are electrostatically charged with a black half carrying the negative charge and a white half carrying the positive charge. Two electrodes surround the plane; the front one transparent. When a charge is placed across the electrodes the spheres rotate to align with the front-to-back charge gradient. Because the spheres are suspended in a semi-solid when the power is removed, they remain in that position and the display continues to show whatever design or text it showed before power was removed. This sort of display is used in the LIBRIé e-book reader from Sony.

Kodak and Microcup

Both Kodak and Microsup electronic paper from SiPix use a roll-to-roll manufacturing process which produces a sort of electronic paper that is thin and flexible. The Kodak process uses a liquid-crystal dispersed in a polymer while the SiPix process uses a microcup structure to hold electronic ink stable.

NTERA

NTERA uses a NanoChromics technology where nanostructured semiconducting metal oxide films that have a layer of viologen molecules creates black and white high contrast images.

Other manufacturers are working the liquid-crystal technology in an attempt to get grey-scale or color bistable displays.

ZBD

ZBD has created the Zenithal bistable display which uses a simple micro-structured grating surface as a way to control liquid crystal alignment. At present, black and white are the only two stable orientations for the molecules in the display.

Nemoptic

BiNem is an acronym that comes from Bistable Nematic, a development of Nemoptic. This combination has produced a black and white display. Nemoptic has also announced a 32,000-color bystable LCD using a grayscale device and LCD color filters.

Kent Displays

Working with Panasonic, Kent Displays has shown an e-book reader with VGA monochrome bistble cholesteric LCD technology. A prototype color cholesteric LCD is under development.

(Cholesteric is a spiral crystal LCD technology that reflects almost all the image light cast on it while attenuating most of the ambient light to produce a bright reflected display.)

More Information

• Zenithal bi-stable display
• Nemoptic BiNem Bistable Nematic display
• Components in Electronics article: Plastic technologies go on display