1.9-GHz-band surface acoustic wave device using second leaky wave 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, in a periodical structure on LiTaO3 (90 degrees,90 degrees,31 degrees) and LiNbO3 (90 degrees,90 degrees,37 degrees) were analyzed experimentally. As for the mode on LiTaO3, the propagation loss is the lowest when the KH (K = wave number, H = Al electrode thickness) parameter is about 0.5. The higher mode of the second leaky mode is excited when the KH parameter is larger than 0.7. As for the mode on LiNbO3, the propagation loss does not have an evident minimum value on the KH parameter. The higher mode of the second leaky mode is excited when the KH parameter is larger 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 results to the periodical structure. The pitch of the electrode fingers is 0.8 mu m. The center frequency of the pass band is 1.938 GHz. The minimum insertion loss is 3.3 dB. The attenuation at the center frequency +/- 100 MHz is 25 dB. The measured characteristics of this filter are sufficient for practical mobile communication systems.