Investigation of the effects of AR layers on the structure and properties of transparent conductive oxide thin films

Antireflective (AR) layers, i.e., a SiO2 overcoat and an Al2O3 undercoat were added to an ITO film to improve its visible transmittance. The microstructure and optical, electrical, and mechanical properties of the ITO films with and without AR coatings were systematically investigated. It is found that: 1) while the SiO2 overcoat has little impact on the microstructure of the ITO layer, the Al2O3 undercoat decreases the lattice parameter and grain size of the ITO layer; 2) while the carrier mobility for the ITO films with and without AR coatings is quite similar, the carrier concentration for the ITO film is little affected by the SiO2 overcoat, and it is increased by 31% with the Al2O3 undercoat; 3) the ITO film with AR layers shows significant improvement in scratch resistance, which is attributable mainly to the increased value of H/E and H3/E2 (where H and E are the hardness and elastic modulus respectively) and decreased residual stress; 4) the increased ratio H/E for the ITO film sandwiched structure over the ITO single layer indicates that there is a possibility to tailor the mechanical properties of a material by making multilayer composite.