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

概要

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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 ($3.8\times 3.8$ 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 ($3\times 2.5$ mm2) SAW duplexer having a low insertion loss and a good TCF has been realized for the first time.
2007-07-30