Polymer optimization for the development of low-cost moisture sensor based on nanoporous alumina thin film

Sol–gel processed alumina (Al₂O₃) thin film has been investigated for sensing moisture. The sensor was based on ordered nanoporous Al₂O₃ thin film, which consisted of gold electrodes on both sides of the film forming parallel plate capacitor. Alumina substrate was used for supporting thin film moisture sensor. Hydrophilicity was achieved by controlling the surface energy of the substrate and polymer (polyvinyl alcohol (PVA)) optimization was done for developing rigid thin film over it. A high change in capacitance was observed as the moisture level increased from 5 ppmV to 500 ppmV. Scanning electron microscopy (SEM) results revealed that pores were distributed uniformly throughout the sample, which enhanced the adsorption of water molecule over the film. X-ray diffraction (XRD) study clearly confirmed the gamma (γ) phase of alumina thin film. It was found that the sensitivity of our sensor was suitable for commercial application.