Study On Stability Of The Mwnts Humidity Sensor

Along with the scientific and technical development and improvement of living standards, people request more advanced techniques for detection and control of environmental humidity. Carbon nanotubes(CNTs), discovered by Iijima in 1991, possess good performances such as large surface area, outstanding mechanical properties and specific conductivity. CNTs can easily adsorb vapor because of the good adsorption capability, and therefore could be used as humidity sensing material. Humidity sensors with CNTs sensing material have advantages of high sensitivity and fast response and become the research hotspot currently.Firstly, the complex pore structure and large specific surface area of multi-walled carbon nanotubes(MWNTs) were described, and the adsorption properties of carbon nanotubes was explained with good reason in this thesis. Analysis of humidity sensing mechanism of the sensor's resistance and capacitance signal at DC or low working frequency was made, based on the humidity interaction between CNTs film and water molecules adsorbed.Thereafter, MWNTs humidity sensor with interdigital electrodes was designed and fabricated. It carried out using MWNTs pretreated by nitric acid oxidation. Aluminum electrode layer was carved into interdigital pattern using photolithography after deposited on glass substrate by evaporation. MWNTs composite sensing film was coated on electrode surface by screen printing and fabrication of the sensor was complete after sintering processing.With a number of comparative experiments the optimized sensor process parameters were confirmed.Tests and analysis on the sensor achieve results as follow: MWNTs sensor features high capacitive sensitivity and linearity of resistive humidity sensing behavior is better; the sensor has good repeatability, with response and recovery time of 8s and 16s respectively; after acid treatment, the sensor shows obvious semiconducting features and high sensitivity, but has some temperature drift.This paper focuses on factors of stability of MWNTs humidity sensor. Impact of testing frequency and testing voltage on the working sensor were studied. By introduction of dielectric relaxation effects in dielectric physics and the electron tunneling effect in quantum mechanics, the experiment results of the relationship between sensor sensitivity and stability features and the testing frequency and voltage were analyzed. Preliminary interpretation was given against the influence of the testing frequency and testing voltage on the stability of the sensor, which provides an experimental and theoretical basis for stability advancement of the CNTs humidity sensor.