Tetsuya Tsurunari

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.

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.

Zero Temperature Coefficient of Frequency Surface Acoustic Wave Resonator for Narrow-Duplex-Gap Application on SiO2/Al/LiNbO3 Structure

In this paper, we describe a zero temperature coefficient of frequency (TCF) surface acoustic wave (SAW) resonator on a SiO2/Al/LiNbO3 structure. We studied the dependence of TCF and electromechanical coupling factor (K2) of shear-horizontal (SH) SAW on SiO2 thickness, where the SiO2 shape control technique is applied to suppress spurious responses caused by the Rayleigh mode. As a result, we could realize a high performance SAW resonator having moderate K2 (8%) and zero TCF with complete suppression of the Rayleigh-mode spurious response. We demonstrated that the SiO2 shape control technique is effective for suppression of the Rayleigh-mode spurious response in the SAW resonator using the SiO2/Al/LiNbO3 structure for a wide range of SiO2 thicknesses. We also revealed the applicability of the SiO2/Al/LiNbO3 structure to SAW duplexers with a narrow duplex gap.

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.

Transverse-Mode Spurious Suppression Technique for Surface Acoustic Wave Resonator with Zero Temperature Coefficient of Frequency on a SiO2/Al/LiNbO3 Structure

In this paper, we describe a suppression technique of transverse-mode spurious responses for a surface acoustic wave (SAW) resonator with a near zero temperature coefficient of frequency (TCF) on a SiO2/Al/LiNbO3 structure. We investigated the thinning of SiO2 on the dummy electrode region and studied how the transverse-mode responses change with remaining SiO2 thickness h on the dummy electrode region. As the results, we clarified that the remaining SiO2 thickness h on the dummy electrode region has an optimum value and could suppress the transverse-mode spurious responses completely when H and h are set at 0.35 λ and 0.20 λ, respectively. It was demonstrated that the selective SiO2 removal technique is effective to suppress transverse-mode spurious responses for SAW resonators employing the SiO2/Al/LiNbO3 structure for a wide range of SiO2 thicknesses, provided that the SiO2 thickness at the dummy electrode region is adjusted properly.

Good temperature coefficient of frequency SAW resonator on a SiO 2 /Al/LiNbO 3 structure

This paper describes a good temperature coefficient of frequency (TCF) surface acoustic wave (SAW) resonator on a SiO<inf>2</inf>/Al/LiNbO<inf>3</inf> structure. We studied the dependence of TCF and electromechanical coupling factor (K²) of shear-horizontal (SH) SAW on the SiO<inf>2</inf> thickness, where the SiO<inf>2</inf> shape control technique is applied to suppress spurious responses caused by Rayleigh-mode. As the results, we could realize high performance SAW resonator having moderate K² (8%) and zero TCF with complete suppression of the Rayleigh-mode spurious response. It was demonstrated that the SiO<inf>2</inf> shape control technique is effective for suppression of the Rayleigh-mode spurious response in the SAW resonator using the SiO<inf>2</inf>/Al/LiNbO<inf>3</inf> structure with wide range of SiO<inf>2</inf> thicknesses. We also revealed applicability of the SiO<inf>2</inf>/Al/LiNbO<inf>3</inf> structure to SAW duplexers with narrow duplex gap.

Suppression of transverse-mode spurious responses for zero temperature coefficient of frequency SAW resonator on a SiO 2 /Al/LiNbO 3 structure

This paper describes a suppression of transverse-mode spurious responses for zero temperature coefficient of frequency (TCF) surface acoustic wave (SAW) resonator on a SiO₂/Al/LiNbO₃ structure. We investigated to use thinning of SiO₂ on the dummy electrodes and studied how the transverse-mode responses change with remaining SiO₂ thickness h on the dummy electrode region. As the results, we could realize high performance SAW resonator with complete suppression of the transverse-mode spurious responses when h is set at 0.20λ. It was demonstrated that the selective SiO₂ removal technique is effective to suppress transverse-mode spurious responses for SAW resonators employing the SiO₂/Al/LiNbO₃ structure for wide range of SiO₂ thicknesses, provided that the SiO₂ thickness at the dummy electrode region is adjusted properly.

Reduction of transverse leakage for SAW resonators on LiTaO 3 substrate

This paper proposes a new structure to reduce the transverse SAW leakage for the SAW resonator on a 42° YX-LiTaO3 substrate. The leakage occurs from the inter-digital region toward the bus-bur region in the SAW resonators. The new structure has the Ta2O5 film on the outside of the interdigital region. In this structure, the SAW velocity in the bus-bur region becomes slower than the velocity in the inter-digital region. Therefore, the new structure could reduce the leakage, and contribute to confine the SAW energy in the inter-digital region. This structure is applied to the SAW resonator and the Ladder-type SAW filter fabricated on a 42° YX-LiTaO3 substrate. The insertion loss could be improved by reducing the transverse SAW leakage. This technique could be applied to the filters and duplexers using the leaky SAW on 42° YX-LiTaO3 substrate, and the SAW devices could exhibit the excellent performances.

Small-sized SAW duplexer on non-flat SiO 2 /Al/LiNbO 3 structure for UMTS Band I system

This paper describes the SiO2/Al/LiNbO3 structure for the SAW duplexer. Although this structure has large electromechanical coupling coefficient, it also supports unwanted spurious responses. They are categorized into two types of the Rayleigh-mode and transverse-mode. We have developed the novel spurious suppression techniques for these spurious; the SiO2 shape control technique for Rayleigh-mode and the scattered dummy electrode weighting for transverse-mode. We applied the proposed techniques to the balanced-type SAW duplexer for UMTS Band I system. The developed SAW duplexer was installed into a 2.5×2.0×0.5 mm3 package, and exhibited low insertion loss and high out-of-band rejection. The insertion losses in the Tx and Rx bands are 1.3dB and 2.0dB, respectively. The rejections in the Tx and Rx bands are 54 dB and 48 dB, respectively.