Study On Electrical Model And Humidity Sensitive Characteristics Of Resistive Cnts Humidity Sensor

Since carbon nanotubes (CNTs) were discovered, they have been paid great attention due to their good chemistry stability, unique electrical property and special physics structure. Especially CNTs have huge specific surface area and multi-hole structure, which makes them sensitive to the environment humidity, and thus they will be the ideal materials for fabricating humidity sensors.In this paper, the physics structure of CNTs and the capillary condensation phenomenon of vapor in the holes of CNTs were researched firstly from adsorption aspect, and the polarization process and response ways of matter were introduced; the experimental sensor based on MWNT and SiO2 was designed and fabricated, and the process of fabrication included electrodes fabrication, slurry fabrication, silk screen printing, sinter and assembly; the equivalent model of sensor was built by means of analyzing the impedance characteristic and polarization mechanism of humidity sensor, and the conductance equations at different relative humidity were exported; the humidity characteristics of sensor were measured and explained by sensor's equivalent model and polarization theory.In the process of building model, the impedance graphs of sensor in humidity environment were compared with that of ideal circuit to confirm the basic modality of sensor's equivalent model. Then the polarization mechanism of sensor in different humidity was studied. There were interface polarization of MWNT-SiO2 and tropism polarization of water in sensor under the effect of alternating electric field. The measured conductance data was simulated by conductance equations associated with different polarization process to validate and confirm the equivalent model of sensor finally. It can be deduced that the interface polarization of MWNT-SiO2 plays an important role at low humidity and mainly happened at the frequency from 10Hz to 50kHz, and the tropism polarization of water plays an important role at high humidity and mainly happened at the frequency from 10kHz to 500kHz. In the process of studying sensor's characteristics, the sensor's sensitivity, humidity hysteresis, response/resume time, reiteration and impedance characteristic are researched. It is shown that the sensor has high sensitivity, good linearity and reiteration, and the response/resume times are 10s and 18s respectively. At the same time, the effects of measuring frequency and environment temperature are studied. These effects are explained by sensor's equivalent model and polarization theory, and it offers theory basis for improving sensor's characteristics.