High sensitivity capacitive humidity sensors based on Zn_1−xNi_xO nanostructures and plausible sensing mechanism

Zn_1−xNi_xO (X = 0%, 1%, 3%, 5%, 10%) nanowires were synthesized by the hydrothermal method, and the prepared materials were characterized and analyzed by XRD, SEM and XPS. Then, the materials were positioned on the pre-designed Ti/Au interdigital electrode to fabricate humidity sensors by the dielectrophoresis method. The humidity sensitive characteristics of the sensors were studied by combining complex impedance spectroscopy and theory of multilayer adsorption. The results show that the surface oxygen vacancies concentration can be regulated by Ni doping process. Under the combined action of Ni ions and oxygen vacancies, the performance of humidity sensors has been improved significantly. Especially, 5% Ni doped ZnO humidity sensor shows a high capacitance sensitivity, which is varied by more than four orders of magnitude with increasing the relative humidity from 11 to 95%, respectively. Moreover, the response time and recovery time are reduced to 27 s and 2 s, which is much better than undoped ZnO humidity sensor. The results indicate that the doping of Ni elements play an important role in the sensing property improvement of ZnO humidity sensor.