Small-sized SAW duplexer on non-flat SiO2/Al/LiNbO3 structure for UMTS Band I system

This paper describes the SiO2/Al/LiNbO3 structure for the SAW duplexer. Although this structure has large electromechanical coupling coefficient, it also supports unwanted spurious responses. They are categorized into two types of the Rayleigh-mode and transverse-mode. We have developed the novel spurious suppression techniques for these spurious; the SiO2 shape control technique for Rayleigh-mode and the scattered dummy electrode weighting for transverse-mode. We applied the proposed techniques to the balanced-type SAW duplexer for UMTS Band I system. The developed SAW duplexer was installed into a 2.5×2.0×0.5 mm³ package, and exhibited low insertion loss and high out-of-band rejection. The insertion losses in the Tx and Rx bands are 1.3dB and 2.0dB, respectively. The rejections in the Tx and Rx bands are 54 dB and 48 dB, respectively.