This investigation studies fringe field between laterally adjacent electrodes in a reverse-emulsion electrophoretic
display (REED). The display consists of a nanodroplet ink and a porous matrix that serves as the "paper" between
planar electrodes. One relative advantage of this type of electronic paper display is that it can be produced with lowcost
materials and manufacturing processes. A concern for image resolution, however, is the fringe field effect that
occurs in the gaps between neighboring electrodes. Ideally the dye-containing nanodroplets in the ink move in a
direction that is strictly perpendicular to the opposing pairs of electrodes. However, nanodroplet saturation and
potential gradients from neighboring electrodes may result in lateral displacement of the nanodroplets as well.
Accordingly, this study examines how fringe field between neighboring electrodes is affected by lateral spacing and
applied voltage. Transient and steady-state effects were studied by fabricating and testing devices that were
patterned with different lateral spacing between electrodes, and switching under different voltage levels. Relative
luminance was extracted from digital microscope images, captured in the vicinity between neighboring electrodes.
Measurements were recorded for electrode spacing of 20 μm, 40 μm, 60 μm, and 80 μm with devices switched at
±1.5 V and ±2.5 V. Gradients in luminance overlapped at lateral distances below 60 μm, and became distinct for
left and right electrodes spaced by at least 80 μm. Higher applied voltage resulted in steeper transition between light
and dark states, but exhibited distortion at electrode edges.