Study On Tin Oxide Composite Material And Thin Film Heteroi Unction Gas Sensitive Properties

Gas sensor,as the basic device for gas detection,has been widely applied in industrial production and daily life.Among them,tin oxide gas sensor with high sensitivity,good response and recovery features and low cost,is one of the most popular gas sensors currently.However,with the development of technology,the demand for gas sensor performance is increasing.Therefore,it still needs the further optimization research on gas sensors.In this dissertation,firstly,a tin oxide composite material is obtained and doped with palladium chloride and graphene,and a gaseous ethanol sensor which can work at a near room temperature is completed.Tin oxide powder is prepared by chemical precipitation and shows porous surface,and the powder is composed by 10-20 nm nanoparticles.By adding different proportion of palladium chloride and graphene,the working temperature was reduced and the sensitivity and response speed was increased.Especially,the sample of 0.1 wt%rGO/3 wt%PdCl₂/SnO₂ can working at 40?,and the response is 4.6,the response time is 93 s and the recovery time is 130 s.Besides,the sensor shows good stability and linearity.The performance improvements depend on the promoting effect of anion adsorption by palladium ion and the carrier transport ability by graphene at low temperature.Then,a SnO₂ thin film gas sensor prepared by MEMS technology was designed and fabricated.Micro heating plate was analyzed by a finite element analysis software,and it proved the structure can provide the high temperature about 375? with 80mA heating current.The tin oxide thin film was grown by RF magnetron sputtering,and the SEM and AFM images show that the thin film is composed of nanoparticles and its surface is compact and flat.The response of the 100 nm tin oxide thin film gas sensors for 100 ppm gaseous ethanol is 3.1 at 250?,but the resistance of this sensor cannot fully recovered under this temperature.Besides,among the 100 nm,200 nm,300 nm tin oxide film gas sensor,it is also found that with the increase of the thickness,the response of the sensor is reducedThen,the 100nm SnO₂ thin film gas sensor is modified by a heterojunction structure,and the material is nickel oxide and tungsten oxide,respectively.It is found that using the heterojunction structure improves the response significantly,and makes the resistance recovery features better.Especially,the 5 nm NiO/100 nm SnO₂ gas sensor shows the high response of 7.9 at 250'C,which is increased by 155%compared to the pure tin oxide film gas sensor.In addition,this sensor can measure the ultra-low concentration of gaseous ethanol,and the concentration can be as low as 100 ppb.