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

Abstract

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.

Heat-Resistant Black Insulative Thin Films for Flat-Panel Displays in Al-Doped Ag–Fe–O Systems

“…This trend is evidence that the absorption coefficient at a short wavelength range depends on the interband absorption of the matrix phase and that at a long wavelength range depends on the plasmon absorption. Even though the standard deviation values are slightly higher than those of Ti 0.33 Ni 0.67 O 2– x , W–Ti–O–N and that reported for Ag–Fe–O ( x = 0), the absorbance attained for the Al-doped Ag–Fe–O thin films was remarkably flat and strong. For the composition with Ag fixed at 60 mol %, high absorption intensity and flat absorption were obtained for the Fe-free x = 1 sample, but by adjusting the amount of Ag, the absorption intensity and flatness of the Fe-containing sample can also be improved.…”

“…ADF-STEM images of (a) 60 mol % Ag–40 mol % Fe–O ( x = 0), (b) 60 mol % Ag–40 mol % (Fe 0.5 Al 0.5 )–O ( x = 0.5), and (c) 60 mol % Ag–40 mol % Al–O ( x = 1.0).…”

“…(a) Wavelength dispersion of absorption coefficients and (b) sample appearances, (c) wavelength at which the minimum absorption coefficient attained, and (d) wavelength of plasmonic absorption of 60 mol % Ag–40 mol % (Fe 1– x Al x )–O thin films deposited at 300 °C. For comparison, the absorption coefficients of Ag and Fe 2 O 3 are also displayed.…”

“…The substrates were heated to 300 °C by means of an infrared heating lamp. This temperature was chosen because of the superior absorption properties and electric resistance attained for Ag–Fe–O films in a previous study . The distance between the substrate and the target was maintained at 50 mm in all cases.…”

“…Even though these materials show promising absorption properties, they are electrically highly conductive due to their metallic band structures. Another material design concept is to use insulative oxides with dispersed metal particles: black insulators consisting of nanocermet materials in Ag–Fe–O and Bi–Cu–O systems have been reported . These composite-type black matrices show superior absorption and insulation properties due to their unique microstructure that allows the conduction path of dispersed Ag metal particles to be interrupted by the insulative oxide matrix.…”