Effect of aging on transmittance, and effect of annealing temperature on CO2 sensing of ZnO thin film deposited by spin coating

Investigations have been made on the structural, morphological, optical, sensing, and aging characteristics of ZnO thin films created on glass substrate using the sol-gel spin coating process. Zinc acetate (ZnAc), ethanol, and stearic acid were employed as the starting materials, solvent, and stabilizer, respectively, to deposit the ZnO thin films on the blue star glass substrate. An UV–visible spectrophotometer is used to study the optical characteristics. With the aid of XRD and FESEM characterization techniques, the structural and morphological properties are studied. The results showed that the characteristics of ZnO thin films were strongly dependent on the annealing temperature. The XRD measurement indicated that the deposited film shows the hexagonal structure and preferential orientation along the (002) crystal plane with a grain size of 78.99 nm. The transmittance value of the ZnO films was relatively high up to 90 %. The result showed that the transmittance value is strongly dependent on the aging time of the sample. The SEM images show that morphology and texture are dependent on the annealing temperature. The SEM image also contains a foreign object or xenolith. The V-I characteristics show nonlinear behavior, and the resistance of the thin film is between 2800 and 5000 MΩ. The CO2 sensing at 450 °C is far better than that of at 750 °C. The response time at 450 °C is 20–40 s, the recovery time is better at 750 °C.