Abstract
We try to design gas sensors by theory of surface acoustic waves and do some research about that. A surface acoustic waves gas sensor includes substrate, interdigital transducers and coating. The convenient generation of a surface acoustic wave requires a substrate material which is piezoelectric. An interdigital transducer is used to apply the electric field to the piezoelectric substrate. The operating frequency is determined by the spacing between the interdigital electrodes. The coating is chose by what we want this sensor to detect. In my research, I choose ST cut quartz be the substrate of gas sensor. This special material has low temperature coefficient and high electromechanical coupling coefficient.Then, I design the interdigital electrode for low frequency and high frequency measurement. About the coating, I choose three kinds of thin film as the coating of gas sensor. They are palladium, tin oxide and polyimide. Palladium is for detecting hydrogen. Tin oxide is usually used to detect carbon monoxide. Polyimide is for humidity measurement. We just need the technology of thin film deposition and photolithography process to make this gas sensor. Then we do some low frequency and high frequency measurement about the characteristic of this gas sensor. From the result of measurement, we can observe and get the relation between the change of mass of the coating and the change of operating frequency. We can prove the theory and the sensor are correct and practicable. In future I hope to keep on the research of this surface acoustic waves gas sensor. We can reach objective of gas sensor array by linking different kinds of gas sensor. We even can combine the field of biology and medical science to reach the target of completing the electronic noses.