Detectors & Imaging

Prototype electrophoretic display is faster and whiter—two advantages for e-readers

Oct. 7, 2010

A new type of electrofluidic pixel developed by researchers at the University of Cincinnati and Gamma Dynamics could lead to e-readers with zero-power grayscale-image storage, a video-rate capability, and a white state as bright as that of ordinary paper.

John Wallace

Cincinnati, OH--A new type of electrofluidic pixel developed by researchers at the University of Cincinnati and Gamma Dynamics could lead to e-readers with zero-power grayscale-image storage, a video-rate capability, and a white state as bright as that of ordinary paper (even the best commercial E-Ink electrophoretic displays, such as in the Amazon Kindle, appear grayish in their white state).¹

In each pixel of the new device, electrowetting forces move a blob of pigment between a top and bottom channel, enabling continuous variation of the pixel color from dark to bright. When the voltage is turned off, the fluid stays in its exact grayscale position (unlike previously developed electrowetting pixels); the stability of the powered-off pixels was tested for three months with the pixel array put in many different orientations, with no change in the pixel grayscale shades.

The pixel-refresh rate of the 0.45 mm pixels in the test array was 6 Hz; scaling the pixels down in size by a factor of three should boost the refresh rate to 50 Hz, say the researchers. The reflectance of the pixels' white state approached 75%, or as bright as white paper. The prototype has a dark-state reflectance of 25% due to lack of black pixel borders and such in the device; this figure can be cut way down with attention paid to the border design in the next version.

More details to come soon in Laser Focus World.

REFERENCE

1. S. Yang et al., Applied Physics Letters 97, 143501 (2010).

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About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.