A highly sensitive humidity sensor based on DC reactive magnetron sputtered zinc oxide thin film

Nanostructured ZnO thin film was prepared by DC reactive magnetron sputtering and characterized by X-ray diffraction, SEM, AFM, FT-IR spectroscopy, UV–vis spectroscopy and photoluminescence measurements. Under the conditions employed, the sputtered ZnO film was found to be polycrystalline with grain size varying between 70 and 100 nm. The absorption and photoluminescence spectral data indicated the presence of defects in the form of zinc interstitials and oxygen vacancies which could promote adsorption of gaseous species. Impedance technique was used to confirm adsorption of water vapor onto the sensor film. The chemiresistor sensor showed nearly a four order variation in resistance in the relative humidity range between 6.3 and 84% with a response and recovery time of 3 and 12 s respectively. The device exhibited high stability offering scope for developing a practical humidity sensor.