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Single-Phase Unidirectional Surface Acoustic Wave Transducer Using Cu Electrode

This paper proposes the application of Cu electrodes to surface acoustic wave single-phase unidirectional transducers (SAW SPUDTs). Since SPUDTs require large and widely variable reflectivity obtained by relatively thin electrodes, Cu with large mass density is one of the candidate materials. First, SAW reflection characteristics of a Cu electrode on 128°YX-LiNbO3 were theoretically investigated. It is shown that Cu electrodes offer much larger reflectivity than Al electrodes. In addition, SAW velocity change with electrode width is quite moderate compared with other materials having large mass density such as Au. An SPUDT was fabricated employing Cu electrodes to discuss how effectively SAW reflectivity contributes, for example, to its unidirectionality. As a result, the obtained directivity for the Cu-SPUDT was about 16 dB, which was 10 dB larger than that for an SPUDT employing conventional Al electrodes.