Laser-based Microfabrication Of Flexible ZnO-based Gas Sensor And Its Performance Study

Since the reform and opening up,the standards of China's industrialization and urbanization have been rising.When the economy vigorously develops,it has inevitably encountered some questions at the same time,namely environmental pollution,of which gas pollution is the major pollution source.The polluting gas nitrogen dioxide has attracted people's attention because of its diverse sources and great harm to the environment.The semiconductor material zinc oxide has been applied to the monitoring of nitrogen dioxide gas because of its high specific surface area,sensitive response to nitrogen dioxide,and low manufacturing cost.At present,the technology of using zinc oxide as a gas sensor sensitive material to monitor nitrogen dioxide is relatively mature,and there are some such commercial products on the market,but they basically have one thing in common:the working temperature of zinc oxide is very high(about 200-400?),subject to this shackle,most of these sensors have built-in micro heaters.On the other hand,with the continuous improvement of people's health awareness,in order to build a flexible smart sensor network with personalized diagnosis and environmental monitoring functions,there is a higher performance requirement for gas sensors:flexible and wearable.In response to the above requirements,this paper aims to conduct research on flexible zinc oxide-based gas sensors that can work at room temperature(?25?).The main work includes:(1)According to the needs of flexible gas sensor,we chose polyimide as the based material for preparing zinc oxide because of its high temperature resistance,high insulation and good flexibility.We used high-performance femtosecond laser direct writing technology to prepare a patterned carbon electrode on a polyimide film,which was used as a conductive material to connect the gas sensing element;Carbon-doped zinc oxide(C/ZnO)nanocomposite structure was prepared by local laser-based hydrothermal method on the patterned carbon electrode.The preparation process of general flexible gas sensors requires to grow sensing materials on a silicon-based substrate firstly,and then transfer it to a flexible substrate.But by the use of laser direct writing process and local laser-based hydrothermal method in this paper,the sensor could be realized directly on the flexible substrate rather than spending much time on patterning and steps of transferring substrate.(2)According to the requirements of gas sensing test,a gas sensor detection system mainly composed of vacuum chambers,vacuum pumps,electron microscopes,gas proportioners and other equipments was built.The prepared gas sensing element of C/ZnO nanocomposite structure grown on polyimide was used to detect nitrogen dioxide with the self-built gas detection system.The nitrogen dioxide gas concentration range was 50-1000 ppm(parts per million),and the experiment was conducted at room temperature(?25?).The experimental results showed that the sensor could respond regularly to the nitrogen dioxide gas with the concentration ranging from 50 to 1000 ppm.The sensor obtained the best detection effect when detecting 1000 ppm nitrogen dioxide.At this time,the sensor's sensitivity was 0.71%,and the response time and recovery time were 210 s and 350 s,respectively.In the subsequent stability experiment(30 days),the sensor also showed consistent performance,which allows people working in high concentration NO2 environments such as industrial furnaces,laboratories and electric welding to monitor the working environment.Even if the flexible substrate was bent and stretched with changing its radius of curvature from 22.34 to 4.16 mm,the sensor still had a relatively stable detection of NO2,which proved that the flexible gas sensor still had good stability under mechanical deformation.Unlike the traditional ZnO based gas sensor,the sensor in this paper presents the characteristics of p-type semiconductor through gas sensing tests,which could be attributed to the possible doping of C and low performing temperature.(3)Based on the gas sensing element prepared in the previous article,a gas sensor acquisition module based on the Arduino Mega2560 single-chip microcomputer was designed to detect the change in resistance of the gas sensing element in real time.Firstly,according to the principle of constant voltage method,after calculation and verification,the resistance value acquisition and conditioning circuit based on Wheatstone bridge and operational amplifier were designed.Then we selected the appropriate breadboard,wire,resistor and LED screen to successfully prepare a gas sensor dynamic detection system that could detect NO2 and display the value on the screen in real time.