Air annealing regulates the environmental stability in transparent and conductive performance of TCO films
摘要
To enhance the environmental stability of transparent conductive oxide (TCO) films for wearable electronic device applications, In2O3, ZnO and SnO2 films were deposited on glass substrates via magnetron sputtering. The effects of air annealing on the morphological, structural, optical and electrical properties of the films, together with their resistance to sweat corrosion and mechanical wear, were investigated. Air annealing considerably decreased the surface roughness, increased the particle size and enhanced the crystalline quality of the films by promoting grain growth and coalescence. X-ray photoelectron spectroscopy analysis indicated that air annealing substantially decreased the concentration of oxygen vacancies and increased the concentration of lattice oxygen in the films. The effect was attributed to oxygen diffusion from the environment into the lattice during annealing. Optical analyses indicated that the film transmittance increased after annealing and the band gap exhibited a slight redshift. However, the carrier concentration sharply decreased from the order of 1021–1022 to 1015–1021 cm−3, resulting in an increase in sheet resistance. This behaviour was ascribed to the substantial decrease in the oxygen vacancy concentration in the films after air annealing, which increased the stoichiometric ratio and subsequently decreased the index. The figure of merit of the In2O3 film decreased from 9.52 × 10−3 to 2.86 × 10−3 Ω−1, whereas the index of the ZnO and SnO2 films considerably reduced to the order of 10−7 Ω−1. In terms of environmental stability, the TCO films featuring low surface roughness, large particle diameters and high crystallinity exhibited effective resistance to acidic and alkaline artificial sweat (except for the ZnO film). Furthermore, the optical and electrical indices of the films remained within the same order of magnitude as those of the as-deposited state. Air annealing enhanced the mechanical hardness and modulus of the films, improving their wear resistance; however, the index decreased by one order of magnitude following 12 h of wear treatment. Considering the optical and electrical properties as well as wear and corrosion resistance, the In2O3 film satisfies the application requirements of external display screens for intelligent wearable electronic devices.