Miniature Surface Acoustic Wave Duplexer with Wide Duplex Gap on SiO2/Al/LiNbO3 Structure

概要

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In this paper, we describe the development of a miniature surface acoustic wave (SAW) duplexer for a Band IV system in the universal mobile telecommunication system (UMTS). We employed the SiO2/Al electrode/5° YX-LiNbO3 structure, which has a high electromechanical coupling coefficient ($K^{2}$) and a small temperature coefficient of frequency (TCF). It is necessary to suppress the Rayleigh mode spurious response to apply this structure to the duplexer. We clarified experimentally the relationship between the SiO2 shape and the thickness of the Al electrode in the SiO2/Al/LiNbO3 structure to suppress the spurious response. Furthermore, we determined the condition to reduce the bulk radiation for the transmitting band of the Band IV duplexer. The developed SAW duplexer has the optimum structure for the Band IV system. The SAW duplexer exhibits excellent performance for practical use. In addition, the TCF is about $-30$ ppm/°C. The SAW duplexer is $2.5\times 2.0\times 0.5$ mm3. Additionally, the SAW duplexer has sufficient power durability owing to the use of multilayer electrodes of AlMgCu/Ti.
2009-07-25