SAW characteristics in a layered ZnO/GaAs structure for design of integrated SAW filters

In this paper, characteristics of the lowest order SAW mode in a ZnO film on a GaAs structure are studied. Velocity and coupling coefficient (K²) are calculated versus film thickness, film polarity orientation, and interdigital transducer (IDT) location. It is found that velocity varies with the product of the frequency and film thickness (fh), K² increases nearly monotonically with fh when the IDT´s are located on the upmost surface with an interface free of metallization. When the interface is metallized, K² exhibits a maximum value of 1% for fh=230 m/s and a minimum value of 0.5% for fh=750 m/s. Burying the IDT at the interface gives rise to a higher K² (1.5% for fh=1500 m/s). These results are obtained using a (+Z)-oriented ZnO film, those with a (-Z)-oriented one are also given for comparison. Also given is the SAW displacement-potential ratio directly involved in the determination of the inter-electrode reflectivity