Effect of buffer layers in ZnO/ langasite and SnO2/langasite SAW gas sensors

Oxygen gas sensors have previously been reported using ZnO sensing layers deposited on langasite surface acoustic wave devices. The reported gas response exhibited aging effects that may have been due to grain growth in the ZnO or reactions with the langasite substrate. In addition the kinetics of the gas response is complex. We have examined the effect of silicon oxynitride buffer layers on sensor aging and the gas response kinetics. We find that a 100 nm oxynitride layer improves the response stability and reduces the sensor response time. We also report experiments using SnO2 sensing layers where the sensor response has been correlated with the measured resistivity of the sensing layer.