RED display structures having dynamic hysteresis characteristics

Display structures based on reversible electrodeposition (RED) in organic solvent based electrolytes containing tetra-alkyl ammonium iodide, ammonium iodide, and silver iodide have been studied. Cells were made up with these electrolytes together with a mixed opacifier containing a semiconducting oxide (such as impure TiO2) and an insulator (such as a very fine zeolite powder). The cells develop bistable characteristics which permit operation with good contrast (between deep burgundy and white) at drive voltages of less than 2 V while operating at 0.5 Hz. Contrast ratio, optical density, efficiency, and memory time were measured. Probable mechanisms for the development of bistable characteristics and the nature of the deposits are discussed.