High-Electromechanical-Coupling-Coefficient Surface Acoustic Wave Resonator on Ta2O5/Al/LiNbO3 Structure

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In this paper, we describe a high-electromechanical-coupling-coefficient ($K^{2}$) surface acoustic wave (SAW) resonator on a Ta2O5/Al/LiNbO3 structure for wide duplex gap applications. We analyzed the responses of a SAW resonator on a Ta2O5/Al/LiNbO3 structure by finite element method (FEM)/spectrum domain analysis (SDA). We have clarified that the optimum Ta2O5 thickness at which the high-performance SAW resonator without the Rayleigh-mode spurious response could be realized. The results of the simulation were in good agreement with those of the experiment. Also, the Ta2O5 film has the advantage of decreasing the film thickness over the SiO2 film. The developed SAW resonator shows excellent characteristics, namely, a low insertion loss and a high $K^{2}$ of 23%. By applying the SAW resonator in the filters, a ladder-type filter and a longitudinally-coupled double-mode SAW (DMS) filter with a low insertion loss and a large bandwidth were realized. We have therefore shown the feasibility of applying devices with a wide duplex gap such as Band I, IV, and X duplexers and a wide pass-band filter using the Ta2O5/Al/5°YX-LiNbO3 structure.
2010-07-25