Surface Acoustic Wave Gas Sensor Based On SnO₂ Colloidal Nanowires Sensitive Film

Gas sensors,which can identify the type and concentration of gases,have been successfully applied to many fields.Among of many kings of gas sensors,surface acoustic wave（SAW）-based gas sensor has the advantages of high resolution,powerful anti-jamming performance and good reproducibility,which is also suitable for the development of system digitized and integrated system.At present,SAW-based H₂S gas sensors run into problems that operating as such relatively high temperature.Therefore,it is of great importance to develop SAW-based gas sensor for room temperature H₂S gas detecting,which can take full advantage of wireless passive of SAW sensors,meeting the needs of specific usage scenariosTin dioxide（SnO₂）colloidal nanowires have shown excellent gas sensing performance at room temperature due to their large specific surface area,solution processable and good compatibility with a variety of substrates.In this paper,SAW-based H₂S gas sensor was prepared to operate at room temperature by morphological control of SnO₂ colloidal nanowires,structure optimization of SAW devices,as well as improvement of film forming process.Firstly,based on Density functional theory（DFT）calculation,the materials were designed,and gas sensitivity of the material was improved by controlling the reaction time for regulating crystal face morphology,which aimed to expose more（110）planes that increased the specific surface area of the material.Then,combining with the characteristics of the colloidal nanowires,the structure of the SAW device was optimized by COMSOL software modeling,and fabricated by stripping method based on the simulation parameters.Finally,the thin film preparation process of SnO₂ colloidal nanowires on the SAW delay line structure was improved.In addition,Cu（NO₃）₂ salt solution was used for ligand treatment to remove the organic long chains coated on the surface of the colloidal nanowires,then the SAW gas sensor,based on SnO₂ colloidal nanowires sensitive film,was successfully obtained.The room-temperature response and recovery characteristics of the SAW sensor toward H₂S gas was tested.For 10 ppm H₂S,the frequency change of the sensor is about 6000 Hz,the response and recovery time is about 248 s and 327 s,respectively.Further,it has been found that the frequency change of the sensor is mainly caused by the acoustic-electrical effect.In other words,when the H₂S gas adsorb onto the sensitive film,the frequency decreases owing to the resistance alteration of the film.This study provides the theoretical basis and experimental methods for the design and preparation of wireless passive,high-performance and low-power consumption SAW-based gas sensors.