GHz-band surface acoustic wave devices using the second leaky mode on LiTaO3 and LiNbO3

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 LiTaO3 (90 degrees, 90 degrees, 31 degrees) and LiNbO3 (90 degrees, 90 degrees, 37 degrees). As regards the mode on LiTaO3, 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 LiNbO3, 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 LiTaO3 was designed and fabricated by applying the analysis extended results to the periodic structure. The pitch of the electrode fingers is 0.8 mu 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 Biter are sufficient for practical mobile communication systems.