P2H-4 Small (3x2.5mm²) Surface Acoustic Wave Duplexer for W-CDMA with Good Temperature and Frequency Characteristics

Small sized surface acoustic wave (SAW) duplexer for wide band code division multiple access (W- CDMA) system with a good temperature coefficient of frequency (TCF) and good frequency characteristics has been required. However, the size of conventional SAW duplexer for W-CDMA using Al-electrode/50-70degYX- LiNbO₃ is large (3.8x3.8 mm²) and its TCF is not good (-80ppm/degC). So, this duplexer can´t satisfy its severe specifications in the all temperature range from -30 to 85degC. When SiO₂ film is deposited on this substrate to improve the TCF, the frequency characteristics is deteriorated by convex portions on the SiO₂ surface caused by SiO₂ sputtering. This time, by applying a flip chip bonding process, a fiattened-SiO₂/Cu- electrode/substrate structure, and a YX-LiNbO₃ substrate, a small sized (3x2.5x1.2 mm³) SAW duplexer having good characteristics (such as low insertion loss and large attenuation) and good TCF has been realized for the first time. Here, the SiO₂ film is used to improve the TCF, the flattened-SiO₂ to obtain high Q, the thick Cu- electrode to obtain the large reflection coefficient, and the YX-LiNbO₃ substrate to obtain the large coupling factor and not to generate Rayleigh wave which causes spurious at the SiO₂ of 0.3lambda and the Cu-electrode of 0.05lambda.