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° Y X -LiNbO 3 is large (3.8 × 3.8 mm 2 ) and its TCF is not good (-80 ppm/°C). When a SiO 2 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 SiO 2 film/Cu electrode/substrate structure to improve the TCF, Y X -LiNbO 3 substrate to obtain a large coupling factor, and flip-chip bonding to miniaturize the duplexer, a small (3 × 2.5 mm 2 ) SAW duplexer having a low insertion loss and a good TCF has been realized for the first time.
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Kadota et al. (2007) studied this question.
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