A thin porous matrix using SU-8 bonded ceramic particles for reverse-emulsion electrophoretic displays

Thin porous layers of ceramic particles were developed to improve display performance for reverse-emulsion electrophoretic displays (REED). Titanium dioxide (TiO₂) particles on the order of 5-microns were bonded together using a polymeric SU-8 negative photoresist. The TiO₂ porous layers were fluidized by the SU-8 solvent to enable mechanical compaction and shearing in order to form 10-micron layers between glass plates. The working device was a single-pixel display with indium tin oxide (ITO) electrodes to switch the dark electrophoretic ink within the white TiO₂ matrix. A factorial experiment was performed to determine the effects of the concentration of SU-8 bonding agent, ITO plasma treatment, and TiO₂ surface treatments on porosity of the ceramic layers. The porosity was characterized based on the volumetric flow rate of the ink through the layer. The display performance was then evaluated in terms contrast, spatial uniformity, and bistability. Optical microscopy was used to measure flow rate and to evaluate display performance by image analysis.