Enhancement of SO₂ gas sensing performance using ZnO nanorod thin films: the role of deposition time

In this study, a sensor with a controllable thin film of zinc oxide (ZnO) nanostructures with different deposition times is successfully synthesized over alumina substrates by chemical bath deposition methods. The seed of ZnO is grown using the dip-coating method, and ZnO thin film is grown by chemical bath deposition (CBD) using the precursor of Zn(NO₃)₂·4H₂O. Chemical bath deposition was done three times to investigate the role of deposition time toward gas sensing properties. Structure, morphology, and composition of the ZnO thin films are characterized using X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy, respectively. From the morphology characterization, the ZnO nanostructure from two-times CBD and three-times CBD process shows different sizes and densities of nanorods compared to the ZnO thin film from one-time CBD process. Increasing thickness of thin film is also observed in two-times CBD of ZnO. The gas sensor characterization test results show that the ZnO thin films from two-times CBD can improve the sensing response to be 93% for SO₂ gas at 70 ppm of concentration at working temperature of 300 °C, which is an increase of 15% compared to ZnO thin films from one-time CBD. At different operation temperatures, the response of two-times CBD ZnO nanorod increases 20–40% over one-time CBD ZnO nanorod. The three-times CBD ZnO nanorod showed non-order and high-density nanostructure yielding low resistance value and cause low sensor response.