Surface Acoustic Wave Duplexer Composed of SiO2/Cu Electrode/LiNbO3Structure Having Convex and Concave Portions

The transition bandwidth of 20 MHz between the transmission (Tx: 1850–1910 MHz) and the receiving (Rx: 1930–1990 MHz) bands of personal communication service (PCS) handy phones in the United States (US) is very narrow compared with those of other systems. We have already realized surface acoustic wave (SAW) duplexers with sizes of 5.0×5.0×1.7 and 3.0×2.5×1.2 mm 3 for PCS handy phones in the US with an excellent temperature coefficient of frequency (TCF) by using a shear horizontal (SH) wave on a flattened SiO 2 /Cu electrode/36–48° YX-LiTaO 3 structure and a Rayleigh wave on a SiO 2 /Cu electrode/120–128° YX-LiNbO 3 structure. Although the surface of the above-mentioned structures is flattened SiO 2 , we have also studied the shape of the SiO 2 surface. As a result, in addition to increasing the stop-band width, which corresponds to the reflection coefficient, the TCF and power durability have been improved by forming convex portions on the surface of the SiO 2 over the interdigital transducer (IDT) gaps.