Investigation of electrothermal properties of indium-tin-oxide thin films

Abstract

Transparent conductive oxide (TCO) thin films are highly sought-after for their unique characteristics of conducting electricity and transmitting visible light, making them ideal conductive coating materials for electronic devices. We carried out a comprehensive analysis of the deposition, optical, electrical, and structural properties of ITO and Ag/ITO thin films on glass substrates in this study. The weight ratio of the deposited metals was 1:10, 2:10, and 4:10[Formula: see text]wt.% (Sn:In) for ITO films and 1:1:10[Formula: see text]wt.% (Ag:Sn:In) for Ag–ITO film. The films were annealed at 300°C using a program controller furnace. We employed infrared cameras to analyze the surface temperature profiles of these thin films under external voltage supply. We also investigated the resistivity behavior of both ITO and Ag–ITO films, analyzing them with regard to Mott’s variable range hopping (VRH) model and the fluctuation-induced tunneling model. Scanning electron microscope images revealed that adding Ag increased the grain size of ITO thin films. The average grain size for ITO thin film was determined as 186[Formula: see text]nm, while it was found to be 270[Formula: see text]nm for Ag–ITO thin film. Furthermore, incorporating Ag into the ITO thin film resulted in a reduction of 21.5% in transmittance over the complete visible range of the electromagnetic spectrum when compared to the ITO thin film without Ag as measured by ultra-visible spectrophotometer. The figure of merit was obtained as [Formula: see text] for ITO and [Formula: see text] for Ag–ITO thin films. However, the resistance of the ITO thin film was calculated to be 9.58[Formula: see text]k[Formula: see text], while that of the Ag–ITO film was found to be 6.99[Formula: see text]k[Formula: see text]. The ITO thin film that included Ag exhibited a lower electrical resistivity due to the larger grain size caused by doped Ag atoms in the structure, leading to less electron scattering at the grain boundaries and a resulting decrease in resistivity as determined by four-point probe system. Thermal imaging camera measurements revealed that the surface temperature of the ITO thin film decreased with the addition of Ag under high voltage application, but not under low voltage. When a voltage of 350[Formula: see text]V and 250[Formula: see text]V was applied to the thin films, the ITO film exhibited a surface temperature of 73.9°C and 50.4°C, whereas under identical conditions, the Ag–ITO film showed a surface temperature of 62°C and 44.1°C, respectively. Furthermore, both films exhibited exponentially increasing surface temperature behavior under a certain voltage, suggesting that they have potential for transparent heaters and high-voltage/low-current applications.