Micro humidity sensors based on ZnO–In2O3 thin films with high performances

Micro humidity sensors are fabricated by radio-frequency sputtering ZnO and In2O3 thin films on SiO2/Si substrates with interdigitated Pt signal electrodes. By adjusting the sensing film form, the micro sensors with a tiny area (1.36 mm × 0.55 mm) exhibit controllable humidity sensing properties. The best sample is obtained by sputtering two times of ZnO and one time of In2O3 on sensor active area (0.63 mm × 0.55 mm). The corresponding impedance changes by more than four orders of magnitude over the whole testing humidity range (from 11% to 95% relative humidity), and the response and recovery times are about 15 s and 40 s, respectively. High stability and good consistency are also observed based on the as-fabricated sensors. The improved and excellent humidity sensing properties are explained by the hetero junctions between ZnO and In2O3 thin films. High sensor performance and large-scale fabricating potentiality demonstrate that the micro humidity sensors are very promising devices for humidity detection which could be produced at industrial level.