High-Performance Humidity Sensors Based on Double-Layer ZnO-TiO₂ Nanofibers via Electrospinning

ZnO and TiO₂ nanofibers are synthesized via electrospinning methods and characterized by x−ray diffraction, scanning electron microscopy, and transmission electron microscopy. Humidity sensors with double-layer sensing films are fabricated by spinning the ZnO and TiO₂ nanofibers on ceramic substrates sequentially. Compared with sensors loading only one type of nanofiber, the double-layer sensors exhibit much better sensing properties. The corresponding impedance changes more than four orders of magnitude within the whole humidity range from 11% to 95% relative humidity, and the response and recovery times are about 11 and 7 s, respectively. Maximum hysteresis is around 1.5% RH, and excellent stability is also observed after 180 days. The humidity sensing mechanism is discussed in terms of the sensor structure. The experimental results provide a possible route for the design and fabrication of high performance humidity sensors based on one-dimensional nanomaterials.