Research Of Humidity Sensitivity Characteristics Of Humidity Sensors Based On Alumina Film

The humidity sensors are regularly used to accurately monitor and control relative humidity(RH),which are currently applied in certain fields,such as weather forecasting,respiratory monitoring clinical diagnosis,food storage,automobile industry,agriculture and semiconductor manufacturing.In recent years,the synthesis methods of Nanoparticles have become more diverse,not only trying to control the morphology and structure of the particles,but also doping with various impurity elements.In this paper,we tried to prepare moisture-sensitive films by alumina nanoparticles,meanwhile,improved the moisture-sensitive properties of the films through two methods,increasing the number of hydrophilic groups on the surface of the films and changing the surface morphology of the films.Moreover,the film morphology and other characteristics were analyzed by employing the characterization methods of X-ray and SEM;the humidity sensitive performances of the sensors were tested by dynamic method.The specific research contents are as follows:1.Commercial?-Al₂O₃ nano-powders with particle size of 20 nm were selected as samples,and the films were prepared on the ceramic substrate using drop coating.After that,the sensors were handled by annealing treatment.The morphologies of the films were analyzed by characterization methods,such as SEM,XRD,FT-IR,etc.The electrochemistry measuring results showed that although the prepared humidity sensors is sensitive to humidity,the response to low humidity is small.The sensitivity is only 4.99%at around 20%RH.Then,the effect of the annealing temperature on the performance of the humidity sensor was also investigated,which results shows that when the temperature is 500?,the humidity sensing performance was best.Furthermore,in order to improve the humidity sensitive performance of the film,the hydrophilic treatment was carried out on the film surface by using hydrogen peroxide,trying to increasing the hydrophilic groups.It is obvious that the number of hydrophilic groups do increase from FT-IR spectrogram.Eventually,the performance of the modified sensors were tested,and the result showed that the property of the sensor had significantly improved,showing high linearity,and low humidity hysteresis.At 30%?80%RH,the sensitivity is improved by10?30 percent.2.Based on the previous experiments,an attempt was made to improve the performance of the humidity sensors by changing the morphology of the film.Mesoporous alumina nanoparticles with microfibers shape were synthesized by hydrothermal method.The effect of annealing temperature on decomposition products of synthesized precursor AACH was investigated characterized by XRD,SEM,etc.The results indicated that when the annealing temperature is 500°C,alumina with a crystal form of?can be obtained,and the fiber structure is prominent without obvious irregular particles and rod-like particles.By testing the different characteristic parameters(impedance and capacitance),the humidity sensors respond to the relative humidity range of 10?90%RH,and the sensitivity is 1.5%?22.6%;At 20%RH,the sensitivity of capacitive and impedance humidity sensors are 1.60%and 3.23%,respectively.Hence,the impedance humidity sensor is sensitive in low humidity environment.The capacitive humidity sensor has good stability in the low humidity range,and the error fluctuation is only 2%.