The effect of post annealing temperature on grain size of indium-tin-oxide for optical and electrical properties improvement

Abstract

Background (Problem): Indium tin oxide (ITO) is a transparent conductive oxide (TCO) thin film used as a transparent electrode. Given its high demand for the manufacture of transparent electrodes (high visible light transmittance, low resistance) in applications such as liquid crystal displays, touch screens, light emitting devices and solar cells, ITO thin films have attracted immense research interest. Objectives: This study determines the effect of grain size on the optical and electrical properties of the ITO thin films under different annealing temperatures. Materials and methods: ITO thin film was deposited at room temperature by a high frequency magnetron sputtering method using a target composed of In2O3 and SnO2. The structural, optical and electrical properties of the thin films annealed at 250 °C, 350 °C, 450 °C and 550 °C for 1 h were then analyzed. Results: The research shows the grain size of indium-tin oxide thin films is strongly related to annealing conditions. The grain size was found to increase with increasing annealing temperature, although the crystal structure did not change for all the samples. It was observed that the lowest resistivity (500 × 10−4 Ω-cm) and highest optical transmittances (90–98%) of ITO films were obtained at annealing temperature of 450 °C. At low annealing temperatures, the measured resistivity is dependent on the effect of grain size, where it decreases with increasing grain size. Conclusion: This work showed that the grain size of ITO thin films is strongly influenced by post annealing technique and conditions applied, thus providing a tool for enhancing the optical and electrical properties of the film. Keywords: ITO grain size, Annealing, Optical properties, Structure, Resistivity