Study On The Syntheses, Humidity Characteristics And Sensing Mechanisms Of Various Nano-Zirconia

Monitoring and controlling humidity have been widely used in industry, agriculture, daily life, meteorology and environmental protection which closely related to living of people and society development. Electric humidity sensors have been interested due to their connection with modern machines which can control, display and record. With the development of internet of things in industry, environment monitoring and intelligent community, higher requirement have to be needed for sensors. In view of humidity sensor, the main development views include higher humidity sensing properties (high sensitivity, rapid response time, good repeatability, long-term stability, etc.), integration and miniaturization of humidity sensors. Because of high surface area and oriented electron conduction of nanometer material, it is important to study sensitive materials with nanostructure for promoting the development of humidity sensors.A real-time test system has been developed for measuring humidity properties of humidity sensors. The testing system can be used to obtain electrical characteristics of humidity sensors at different humidity levels and measurement frequencies, such as impedance, phase angle, capacitance, dielectric loss, etc. Using the test system can improve the accuracy of experimental data and eliminates measurement errors caused by manual.Four kinds of humidity sensors based on zirconia have been mainly studied in the present dissertation, including CMOS process compatible ZrO2thin film humidity sensor, ZrO2:TiO2hierarchical hetero-nanofibers humidity sensor, alkaline doped nano-powder ZrO2thick film humidity sensor and Mg2+-doped nanofibers ZrO2thick film humidity sensor. Preparation and characterization of humidity sensing materials, fabrication and measurement of humidity sensors, and related theory on humidity sensing properties of sensor have been researched for the four kinds of humidity sensors. Crystal structure and growth mechanism of nano-ZrO2have been analyzed via using some important characterization technologies, including XRD, TG, DTA/DSC, FT-IR, etc. Morphologies of ZrO2have been characterized by SEM and TEM methods. The influences of micro structures of sensing materials on the humidity sensing properties of sensors have been discussed via BET and XPS technologies. In the present dissertation, the humidity properties of sensors include sensitivity, humidity hysteresis, response and recovery, temperature properties, and so on. High sensitivity, small hysteresis, rapid response and good thermal stability of the ZrO2humidity sensors have been exhibited, which will provide an important reference value for solving low sensitivity and poor stability issues of humidity sensors.Humidity sensing mechanisms of nano ZrO2humidity sensors have been discussed in view of dielectric properties, DC and AC characteristics. The bound charges contribute to the conduction of sensor in mean of polarization during the humidity sensing process, according to the dielectric loss properties of the sensors. And electronics and ions also play the conduction role by analyzing the DC transient characteristics of the sensors. The equivalent circuits with electrochemical elements CPE and Warburg have been created by using AC impedance method, which simulated and fitted using the complex impedance analysis software ZView perfectly. According to the afore-mentioned three characteristics of the sensors, it has been determined which kinds of charge play the major role in the conduction process of the sensor at low, medium and high humidity ranges. The influences of measurement frequency and measurement temperature on the impedances and complex impedances of the sensor have been discussed in different views.In the present dissertation, the adsorption models of the nano-ZrO2humidity sensors and the transmission mechanisms of proton among which have been also discussed.