GHz-Band Surface Acoustic Wave Devices Using the Second Leaky Mode on LiTaO₃ and LiNbO₃

Abstract

The propagation characteristics of a new high-phase-velocity leaky surface acoustic wave (SAW) mode, which is called the second leaky mode, were analyzed experimentally in a periodic structure on LiTaO 3 (90°, 90°, 31°) and LiNbO 3 (90°, 90°, 37°). As regards the mode on LiTaO 3 , the propagation loss is lowest when KH ( K =wave number, H =Al electrode thickness) is about 0.5. The higher mode of the second leaky mode is excited when KH is more than 0.7. As regards the mode on LiNbO 3 , the propagation loss exhibits no distinct minimum when plotted against KH . The higher mode of the second leaky mode is excited when KH is more than 0.6. A ladder-type band-pass SAW filter utilizing the second leaky mode on LiTaO 3 was designed and fabricated by applying the analysis extended results to the periodic structure. The pitch of the electrode fingers is 0.8 µ m. The center frequency of the pass band is 1.866 GHz. The minimum insertion loss is 3.3 dB. The width of the 1 dB pass band is 32 MHz. The attenuation at a center frequency of ±60 MHz is 25 dB. The measured characteristics of this filter are sufficient for practical mobile communication systems.