Generation of micro-domains in AT-cut quartz by thermal processing and the effect on resonator modes

The fabrication of acoustic sensors with sol-gel selective coatings requires the deposition of thin films on quartz resonators using solution chemistry techniques. Oxide films are spin-cast, then heat treated. A variety of film compositions are deposited, requiring a variety of firing schedules. Network analysis of the untreated AT-cut quartz devices revealed a resonant frequency of 5.0 MHz, corresponding to a pure thickness-shear mode resonance. For devices that were rapidly fired to 400°C and rapidly air cooled, network analysis showed the shear-mode response at 5.0 MHz disappeared, while a predominantly compressional mode response at 7.3 MHz emerged. Structural analysis explored the crystal structure changes induced by processing which resulted in this new mode