The High Sensitivity NO2 Surface Acoustic Wave Sensor with New Sensing Film Made by a Novel Method

Surface Acoustic Wave (SAW) sensors have received great attention because of their compact design and excellent sensing performance, including high sensitivity, low detection limits. However, SAW sensors generally suffer from low quality of the solid thin films which has a significant effect to the detection performance of the sensors. To solve this problem, three different methods (spin coating, drop coating and spray coating) for fabricating thin films have been investigated for gaseous nitrogen dioxide (NO2) SAW sensors in this work. Spray coating method showed its advantages in improving the solid film quality of the sensing layer and the performance of the sensors. SEM characterization shows that the spray coating films are more uniform and poly-porous. Sensors with spray coating film can detect NO2 range from sub ppm to hundreds ppm with high sensibility and stability. Its sensitivity is 42.31 Hz/ppm and its sensing limit is down to 57.2 ppb.