Structural, electrical, optical properties and reliability of ultra-thin tin doped indium oxide films for touch panels

Ultra-thin ITO films with thickness of 4-56 nm were deposited on glass by dc magnetron sputtering using 5 wt% SnO2 doped ITO target. The effect of film thickness on the structural, electrical, optical properties and reliability was investigated for its application to touch panels. The 4 nm thick ITO film shows amorphous structure and other films present polycrystalline structure and the (222) preferred orientation. The ultra-thin ITO films show smooth surface with low Ra surface roughness smaller than 1 nm. The sheet resistance and visible transmittance of the ITO films decrease with the increase in film thickness. The 4 nm thick ITO film shows the highest resistivity (3.08 x 10(-3) Omega cm) with low carrier density and Hall mobility, and other films have excellent conductivity (< 4.0 x 10(-4) Omega cm). The ITO films show high transmittance (> 85 %) in visible light range and do not generate interference ripples between film and substrate interface. The ITO films with thickness of 18-56 nm show stable reliability under high temperature, high temperature & high humidity and alkaline environmental conditions. The only electrical degradation corresponds to the increase of sheet resistance in the ITO films with thickness of 4-12 nm.