Fabrication And Properties Of Non-balance Electric Bridge Ethanol Gas Sensor Based On A Single ZnO Microwire

Zinc oxide（Zn O）,as one of the most important wide-band gap semiconductors,has been widely used for its non-toxicity and low-cost,which has a direct wide band gap（3.37 eV）and a strong exciton binding energy（60 meV）at room temperature.For its special electrical,optical and catalytic properties,ZnO provides extensive possible applications in sensors,piezoelectric and photoelectric devices,solar cells,light emitting diodes and catalysis.ZnO nano/microwire have become a research hotspot as materials for gas sensing because of the large surface-to-volume ratio and high surface activity.At present,the ZnO-based gas sensor has a relatively high operating temperature.Working at a high temperature may cause damage to the device and increase the instability of the device.In this paper,we report the synthesis and characterization of ultra-long and large-sized ZnO microwires by chemical vapor deposition（CVD）method.A non-balance electric bridge ethanol gas sensor based on a single ZnO microwire was fabricated and its ethanol gas sensing property was studied.The main research contents of the thesis are as follows:（1）Ultra-long and large-scale ZnO microwire arrays were grown by chemical vapor deposition method without using metal catalyst.The surface morphology,crystal structure and optical properties of ZnO microwire were researched.The surface of the ZnO microwire is very smooth,with no particles or clusters attached to it.The length of the microwires was about 1–2.5 cm.The EDS analysis was showed that the molar ratio of Zn to O close to 1:1.Furthermore,the intensity ratio of the UV and visible emission was increased with increasing Sb contents in the photoluminescence spectrum.In addition,a strong ultraviolet（UV）luminescence and a weak green luminescence were observed in the micro-area photoluminescence spectrum.The higher UV intensity was indicated that the ZnO microwires have good optical quality.（2）Utilizing principle of non-balance electric bridge,the ethanol gas sensor based on single ZnO microwire non-balance electric bridge type with the single ZnO microwire was used as one bridge arm R₄ and other three fixed-value resistors R₁,R₂ and R₃ were prepared.The experimental results showed that the gas sensor has good repeatability,high sensitivity,short response and recovery time at room temperature（25°C）.When the ethanol concentration is 90 ppm,the response of ethanol gas sensor can reach 93%,the response time is about 0.3s,and the recovery time is about 0.7s.The sensitivity of the sensor to 90 ppm ethanol was about 93%and the response and recovery times are 0.3 and 0.7 seconds,respectively.The traditional resistive gas sensor of a single ZnO microwire has very small gas response at room temperature.Therefore,ethanol gas sensor based on non-balance electric bridge can obviously enhance gas sensing characteristics,which provides a feasible method for the development of high performance ZnO based gas sensor.