Research On NO₂ Gas Sensor Based On Threedimensional Reduced Graphene Oxide Field Effect Transistors

Nitrogen dioxide?NO₂?is one of the major atmospheric pollutants and belongs to the air quality monitoring projects prescribed by China.This paper proposed a NO₂ gas sensor based on three-dimensional?3D?reduced graphene oxide?r GO?field effect transistors?FETs?.In order to enhance the responsivity of the sensor,the r GO material was modified with silver nanoparticles?Ag NPs?.Compared with the traditional planar two-dimensional?2D?gas sensors,the 3D microtubular AgNPs/rGO FET NO₂ gas sensor significantly reduced the chip area,and maintained the large r GO-gas reaction area simultaneously.In addition,the 3D structure is beneficial to avoid doping and contamination of the gas-sensitive films by particulate impurities.Therefore,the 3D AgNPs/rGO FET can be used a novel high-performance NO₂ gas sensor with high responsivity,miniaturization,easy integration,and low cost.Firstly,silicon nitride?SiNx?stress layers were deposited on an aluminum?sacrificial layer?/silicon substrate,then,2D AgNPs/rGO FETs were fabricated on the Si Nx stress layers using the MEMS?Micro-Electro-Mechanical System,MEMS?technology,where the AgNPs/rGO hybrid film acted as the conductive channel of the FET as well as the sensitive layer of NO₂ gas.Secondly,the aluminum sacrificial layer was selectively etched away,so that the Si Nx stress layers rolled-up the 2D AgNPs/rGO FETs into 3D microtubular FETs.Thirdly,the morphology,physical and chemical properties of 2D and 3D AgNPs/rGO FETs were characterized by scanning electron microscope,Raman spectrometer and other equipment.Furthermore,the electrical properties of 2D and 3D AgNPs/rGO FETs,such as the transfer and output characteristics,were investigated and compared with each other,using a semiconductor parametric apparatus.Finally,the NO₂ gas sensing performance of the 3D AgNPs/rGO FET chip was carefully tested.Experimental results demonstrated that the response of the 3D AgNPs/rGO FET to NO₂ gas with a concentration of 20 ppm reached 10.72% at room temperature.Besides,the responsivity of the sensor can be further improved by applying a very small gate voltage or increasing the source-drain bias voltage.At present,gas sensors are developing towards the direction of miniaturization and integration.The size reduction of the 2D gas sensor inevitably leads to a reduction in the gas reaction area,thus the responsivity of the sensor will be decreased.The 3D gas sensor proposed in this paper can fundamentally solve the problem.It can achieve ultrahigh responsivity,miniaturization and ease integration simultaneously,which can be used in many important fields such as indoor health and safety testing,atmospheric environment monitoring,and industrial pollution monitoring.