Zero TCF ZnO/quartz SAW structure for gas sensing applications

A zero TCF SAW device was developed for a temperature selfcompensated gas sensor. The device is based on the combination of a ZnO film and a quartz substrate with the appropriate cut and propagation angle. The developed structure IDT/ZnO/quartz, using ST-cut 35° X propagation quartz, presents a zero power flow angle, a very low temperature coefficient of frequency (TCF) value, and a relatively high electromechanical coupling factor. In this structure, the ZnO film is used simultaneously as gas sensitive layer and as TCF compensation layer. As ZnO is a very promising material for the application as gas sensor, the main interaction mechanisms between the acoustic wave and gaseous species (CO₂, ethanol, butanol) are reviewed. Detailed results for the sensitivity of different acoustic modes are presented.