Micro Humidity Sensor with High Sensitivity and Quick Response/Recovery Based on ZnO/TiO₂ Composite Nanofibers

ZnO/TiO₂ composite nanofibers are synthesized by an electrospinning method and characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A micro humidity sensor is fabricated by spinning the precursors of these nanofibers on a ceramic substrate with Ag-Pd interdigitated electrodes. Humidity sensing investigation reveals that this micro sensor offers high sensitivity and quick response/recovery at an operating frequency of 100 Hz. The corresponding impedance changes more than four orders of magnitude within the whole humidity range from 10% to 90% relative humidity (RH), and the response and recovery times are about 4 and 12 s, respectively. The maximum hysteresis is around 2% RH. The humidity sensing mechanism is also discussed based on the nanofiber structure and morphology.