Hiroki Kamiguchi

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

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 (K2) 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 2.5×2.0×0.5 mm3. Additionally, the SAW duplexer has sufficient power durability owing to the use of multilayer electrodes of AlMgCu/Ti.

Small-sized SAW duplexers with wide duplex gap on a SiO 2 /Al/LiNbO 3 structure by using novel Rayleigh-mode spurious suppression technique

This paper describes the novel Rayleigh-mode spurious suppression technique for SAW duplexers with wide duplex gap on a SiO2/Al/LiNbO3 structure. We have cleared the optimum shape of SiO2 with taking account of the difference of the electrode thickness. The shape of SiO2 which can suppress the spurious depended on the thickness of Al electrode. By controlling the shape of SiO2, the Rayleigh-mode spurious of both Band I and Band IV duplexers can be suppressed. The small-sized SAW duplexers for Band I and Band IV systems were realized by employing this technology and optimizing the thickness of Al electrode. Our duplexers show the excellent performances for actually use. Insertion loss of transmitting band for Band I and for Band IV are 1.2 dB and 1.3 dB. And, the TCF is about -30 ppm/degC. The size of these duplexers is 2.5 mm times 2.0 mm. Additionally, the duplexers have sufficient power durability by using the multi-layer electrodes of AlMgCu/Ti.