Joji Fujiwara

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.

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.

Study of Spurious Response near the Fast Shear Wave in SiO2/Al/LiNbO3 Structure

The shear horizontal (SH) mode on the SiO2/Al/LiNbO3 structure is studied because of its sufficient electromechanical coupling factor (K2) and good temperature coefficient of frequency (TCF). The authors proposed a method of suppressing the spurious response of the Rayleigh mode and the transverse mode for narrow duplex gap applications. For the narrow duplex gap application, the SiO2 thickness must be increased to achieve good TCF characteristics. However, another spurious response appears near the fast shear wave with increasing SiO2 thickness. In this paper, we discuss the suppression mechanism of the spurious response near the fast shear wave.

Reduction of Transverse Surface Acoustic Wave Leakage in Resonator on Al/42° YX-LiTaO3 Substrate for High-Frequency Applications

In this paper, we propose a new structure for reducing the extent of transverse surface acoustic wave (SAW) leakage for the SAW resonator on a 42° YX-LiTaO3 substrate. Such leakage occurs from the interdigital region toward the busbar region in the SAW resonators. The new structure has a Ta2O5 film outside the interdigital region. This structure can make the SAW velocity in the busbar region lower than the velocity in the interdigital region. Therefore, the new structure could reduce the extent of leakage, and contribute to confine the SAW energy in the interdigital region. This structure was applied in SAW resonators and ladder-type SAW filters fabricated on a 42° YX-LiTaO3 substrate. The insertion loss could be improved by suppressing transverse SAW leakage. This technique could be applied to the fabrication of the filters and duplexers using leaky SAW on a 42° YX-LiTaO3 substrate, and the SAW devices could exhibit excellent performance.

Suppression Technique of fast-shear-wave spurious responses in SAW resonators on SiO 2 /Al/LiNbO 3 structure

SH mode on SiO2/Al/LiNbO3 structure is studied because of their sufficient electromechanical coupling factor (K2) and good temperature coefficient of frequency (TCF). Authors proposed the suppression method of the spurious response of the Rayleigh mode and the transverse mode for the narrow duplex gap application. For the narrow duplex gap application, SiO2 thickness must be increased to achieve the good TCF characteristics. However, another spurious response is appeared near the fast-shear-wave as increasing the SiO2 thickness. This paper discusses the suppression mechanism of the spurious response near the fast-shear-wave.