Small Surface Acoustic Wave Duplexer for Wide-Band Code-Division Multiple Access Full-Band System Having Good Temperature Characteristics

Abstract

A small surface acoustic wave (SAW) duplexer for a wide-band code-division multiple access (W-CDMA) system with a good temperature coefficient of frequency (TCF) has been required. However, the conventional SAW duplexer for W-CDMA using Al electrode/50–70° YX-LiNbO3 is large (3.8×3.8 mm2) and its TCF is not good (-80 ppm/°C). When a SiO2 film is deposited on this substrate to improve its TCF, good frequency characteristics cannot be realized. Thus, by using a new structure such as a flattened SiO2 film/Cu electrode/substrate structure to improve the TCF, YX-LiNbO3 substrate to obtain a large coupling factor, and flip-chip bonding to miniaturize the duplexer, a small (3×2.5 mm2) SAW duplexer having a low insertion loss and a good TCF has been realized for the first time.