CONTROL OF 2ND-ORDER TEMPERATURE COEFFICIENTS OF DELAY-TIME FOR SAW PROPAGATING IN THIN-FILM LAYERS

In a surface acoustic wave substrate with a ''piezoelectric thin-film/ substrate'' configuration, the temperature coefficients of the acousti c constants of the Ta2O5 and ZnO thin films were determined by means o f the least square method based on the experimental values of the temp erature coefficients of the acoustic constants. Also, with regard to t he two-layered model of a ''piezoelectric thin-film/piezoelectricthin- film/substrate'' configuration, the surface acoustic wave speed, elect romechanical coupling coefficient and temperature characteristics were computed and the combinations of the film thicknesses were derived fo r a first-order zero-temperature coefficient. Further, it is recognize d that the ZnO thin film and the Ta2O5 thin film have second-order del ay time temperature dependences with opposite signs and then a method is proposed for controlling the first- and second-order temperature co efficients in a two-layered substrate. It is found experimentally and theoretically that there exists a highly stable substrate which exhibi ts a third-order characteristic at an appropriate film thickness.