Optically Black and Electrically Insulating Ag-Fe-O-Based Thin Films for Touch Panel Displays

Apart from transparent conductors, the demand for nontransparent black insulators in the electronic display industry is significant. The development of these dark insulators requires sophisticated material designs. This study shows that narrow-gap-oxide-based nanoscale cermets with nonequilibrium phases which decompose into metal and oxide phases have both the insulative character and a stronger and less-dispersive absorption than graphite throughout the visible range. Herein, the cases of pulsed-laser-deposition-derived Ag-Fe2O3 and Cu-Bi2O3 systems are shown. The combination of the interband absorption of the narrow-gap oxides and the plasmonic absorption of the metals provides strong optical absorption throughout the visible range. Because they create diffusion at the edge of the interband absorption and the peaks of the plasmonic absorption, the nonequilibrium phases make the absorption less dispersive. By preventing the mutual contact of the metal grains, they also make the cermets electrically insulative. This new approach has the potential to produce excellent black and insulating optical coatings using a variety of combinations of metals and ceramics for touch panel displays.