High reflectivity electrofluidic pixels with zero-power grayscale operation

Abstract

Electrofluidic display pixels are demonstrated with zero-power grayscale operation for 3 months and with >70% reflectance. The color of the pixel is changed as electrowetting moves the pigment dispersion between a top and bottom channel. When voltage is removed, a near zero Laplace pressure and a hysteresis pressure of 0.11 kN/m2 stabilizes the position. For 450 μm pixels, an electromechanical pressure of 1.4 kN/m2 moves the pigment dispersion at a speed of ∼2650 μm/s. The predicted switching speed for ∼150 μm pixels is consistent with video rate operation (20 ms). The geometrically sophisticated pixel structure is fabricated with only simple photolithography and wet chemical processing.

Bright e-Paper by transport of ink through a white electrofluidic imaging film

“…Therefore, equating this threshold pressure for splitting with the electrically applied pressure in the other channel, it is determined that the spacer must be designed such that l42h. By allowing the ink to freely merge or split in either channel, these specialized spacers also completely eliminate the need for ink microencapsulation [6][7][8] or pixel borders, a novelty compared to all previous pixel approaches that move a colourant [2][3][4][5] . The spacers can be straight or, as shown in this work, slightly bowed between 120 and 1401 for an R H that is initially slightly positive to provide a small starting volume of oil.…”

“…Readers interested in additional details on the electromechanical pressure (electrowetting) control are encouraged to read previous work on electrofluidic displays 4,5 .…”

“…1) with equal thickness, h, which are hydrophobic such that R V ¼ h/2 and have a value of h such that R V ooR h , the Laplace pressure for the ink in both the upper and lower channel can be approximated as DP ¼ 2g/h. To achieve movement, electromechanical pressure locally reduces the pressure as predicted 4 by DP ¼ À CV 2 /h, where C is the capacitance of the hydrophobic dielectric and V is the voltage applied to the electrode towards which the ink will move 5,9 . The minimum V for movement can be very low, but practically ranges from 5 to 30 V depending on C and/or the required switching speed.…”

“…Grayscale was not characterized in this preliminary work, but simple experiments showed achievable intermediate reflectance (grayscale) using pulse-width modulation 1,5 . In theory, analogue control (Q ¼ CV) is also possible.…”

“…Unique from the dozen or more existing e-Paper technologies 1 , an ink is electromechanically transported to the viewable front, or hidden in the back, of a highly engineered porous film. This film is a first for all types of electrowetting-style displays by allowing nonaligned lamination fabrication [3][4][5] . Furthermore, the film is able to efficiently split merged fluid and therefore eliminate the need for ink microencapsulation [6][7][8] or pixel borders needed in other displays that also move a colourant [2][3][4][5] .…”