Fabrication of ultra-sensitive humidity sensors based on Ce-doped ZnO nanostructure with superfast response and recovery time

Abstract

In this study, the effect of cerium (Ce) concentration on humidity sensing performance of humidity sensors based on Ce-doped zinc oxide nanostructure was investigated. Undoped ZnO (uZnO) and Ce-doped zinc oxide (CZO) nanoparticles were synthesized by sol–gel method. X-ray diffraction analyzes revealed that all nanostructures have a hexagonal wurtzite crystal structure and preferential orientation along the (002) plane. Scanning electron microscopy micrographs showed that there are homogeneously and uniformly distributed nanosized grains and capillary-nanopores on the surfaces of nanostructures. The energy dispersive x-ray spectroscopy analyzes confirmed the presence of zinc, oxygen and Ce elements in the nanostructures. The relative humidity (RH) sensing performances of uZnO and CZO nanostructured sensors were determined by means of electrical resistance measurements in the range of 40–90% RH at room temperature. The humidity sensing performance of the zinc oxide (ZnO) nanostructured sensor was significantly increased by Ce doping. All of the CZO sensors showed very high sensitivity to humidity and very short response and recovery times were achieved. It has been determined that 3 mol% Ce-doped ZnO has the best crystallite quality, the highest humidity sensitivity with a ratio of 7490 in the range of 40–90% RH, and the fastest times with a response time of 0.8 s and a recovery time of 4.7 s. This study clearly showed that CZO nanostructures, which we produce easily and at low cost, have the ideal humidity sensor potential and therefore have a bright future for humidity sensor applications.