Ken Matsunami

Miniature Surface Acoustic Wave Duplexer Using SiO2/Al/LiNbO3 Structure for Wide-Band Code-Division Multiple-Access System

In this paper, we describe the development of a miniature surface acoustic wave (SAW) duplexer for Band I in the standard of the Third-Generation Partnership Project (3GPP) at a 2 GHz band. We employed a shear-horizontal SAW on a SiO2 overlay/thick Al electrode/5°YX-LiNbO3 structure, which offers a high electromechanical coupling coefficient (K2) as well as a small temperature coefficient of frequency (TCF). This feature is crucial for the realization of a wide duplex gap between the transmitting and receiving bands in the Band I specification. We investigated experimentally that the spurious response caused by the Rayleigh-mode could effectively be suppressed by controlling the cross-sectional shape of a SiO2 overlay on interdigital transducer (IDT) electrodes. In addition, the result also showed how this spurious response depends on IDT design parameters, i.e., electrode pitch and metallization ratio. The developed SAW duplexer was installed in a 2.5×2.0 mm2 package, and exhibited a low insertion loss, a high out-of-band rejection and a small TCF.

6E-1 A Small-Sized SAW Duplexer on a SiO2/IDT/LiNbO3 Structure for Wideband CDMA Application

A small-sized SAW duplexer for Wideband CDMA (W-CDMA) application at 2 GHz band has been developed. The W-CDMA application has a wide duplex gap between transmitting (Tx) band and receiving (Rx) band. To realize a small-sized SAW duplexer, a substrate with high electromechanical coupling coefficient (K2) and small temperature coefficient of frequency (TCF) is needed. Our W-CDMA SAW duplexer was fabricated on a SiO2/IDT/5degYX-LiNbO3 structure. Using this structure, an appropriate high K2 and small TCF could be achieved, but the spurious caused by Rayleigh-mode would occur. This spurious appears at lower side than the resonance frequency of SAW resonator, and degrades performances of the duplexer. We have successfully developed the technique to suppress the spurious by controlling a shape of SiO2 film on IDT electrodes. And, the spurious dependences of IDT designs, pitch and metallization ratio, were cleared. The spurious suppression technique has been applied to the W- CDMA SAW duplexer. The duplexer has excellent performance of low insertion loss, high attenuation and small TCF. The Tx and Rx insertion loss are 1.2 dB and 1.9 dB, respectively. The size of the duplexer could be miniaturized to 2.5times2.0 mm2. Additionally, the duplexer has sufficient power durability by using the multi-layer electrodes of AlMgCu/Ti. These techniques could be applied to the other wide-band SAW applications for realizing good performances.

Suppression of transverse mode spurious in SAW resonators on an SiO 2 /Al/LiNbO 3 Structure for wideband CDMA applications

The wideband CDMA (W-CDMA) system at 2 GHz has a wide duplex gap between transmitting (Tx) and receiving (Rx) bands. When developing a small-sized SAW duplexer for this application, one needs a substrate with a large electromechanical coupling factor (K2) and good temperature coefficient of frequency (TCF). An SiO2/Al/LiNbO3 structure meets these two requirements, it also supports a large electromechanical coupling factor (K2). However, certain number of unwanted spurious responses. They are categorized into two types; one is caused by the Rayleigh mode and the other by the transverse mode. This paper proposes a new technique to suppress the transverse mode spurious appearing in the SAW resonators on the SiO2/Al/LiNbO3 structure. In the technique, the dummy electrodes are only length-weighted in the form of a triangle, which selectively scatter higher-order transverse mode spurious. In addition, the SiO2 overlay is selectively removed from the dummy electrode region for enhancing the SAW energy confinement in the active electrode region. This technique was applied to an SAW resonator fabricated on a 5deg Y-X LiNbO3 substrate. We applied the proposed technique to the development of a miniature W-CDMA duplexer with the packaged size of 2.5 mm times 2.0 mm. The duplexer exhibited the excellent performance.