Masatsune Yamaguchi

Surface Acoustic Wave Propagation Characterisation by Finite-Element Method and Spectral Domain Analysis

This paper proposes a method of deriving the discrete Green function for the analysis of surface acoustic wave (SAW) propagation and excitation under metallic-grating structures with finite thickness. The method uses the finite-element method (FEM) for the analysis of the grating electrode region, while the spectral domain analysis (SDA) is used for the analysis of the substrate region. This approach takes account of the mass-loading effect of grating electrodes as part of electrical quantities in a substrate, and makes it possible to employ Bltekjaer et al.s theory for rapid computation. Rayleigh SAWs and leaky SAWs propagating under metallic-grating structures on 128°YX- LiNbO3 and 36°YX- LiTaO3 (36-LT), respectively, were analysed. The dispersion relation calculated by the present method agreed very well with that obtained by the perturbation theory. It is also shown that the electromechanical coupling factor for leaky SAWs on 36-LT increases with the thickness of grating electrodes, which is primarily due to the change in the SAW energy concentration near the surface.

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.

Ultra-wideband surface acoustic wave devices using Cu-Grating/Rotated-YX-LiNbO3-Substrate structure

This paper discusses the application of Love mode propagating on Cu-grating/rotated YX-LiNbO3-substrate structure to the development of ultra-wideband and low-loss RF surface acoustic wave (SAW) filters. Theoretical analysis suggested that high performance resonators with very small capacitance ratio would be realised using Cu gratings with a thickness of several percent of wavelength. It was also suggested that in particular, on 15°YX-LiNbO3-substrate structure, the spurious response due to Rayleigh mode could effectively be suppressed. An IDT-type one-port SAW resonator and a ladder-type SAW filter were fabricated on the Cu-grating/15°YX-LiNbO3-substrate structure, and their high performances are demonstrated with discussion.

Tunable Radio-Frequency Filters Using Acoustic Wave Resonators and Variable Capacitors

In this paper, we describe possible configurations for tunable filters based on RF surface or bulk acoustic wave (SAW/BAW) technologies. The frequency tuning is made possible by variable capacitors (VCs) connected to SAW/BAW resonators in the ladder-type filter configuration. First, it is shown that the passband edges can be controlled by one VC connected to each resonator. Second, it is discussed that the width and location of a passband can be controlled flexibly by two VCs connected to each resonator both in parallel and in series. Finally, the SAW filters with the proposed configuration are fabricated on a Cu-grating/15°YX-LiNbO3 substrate structure, and the tuning capability is demonstrated.

Optimum leaky-SAW cut of LiTaO/sub 3/ for minimised insertion loss devices

The paper describes how the propagation loss /spl alpha/ of leaky surface acoustic wave (LSAW) is dependent upon the Al thickness h of grating electrodes and rotation angle /spl theta/ for rotated Y-X LiTaO/sub 3/. Since the energy leak of LSAW originates from the coupling of the slow-shear field component with other components through the surface boundary conditions, zero /spl alpha/ can be realised when the slow-shear component is decoupled. This means that the optimal /spl theta/ giving zero /spl alpha/ should change with h as well as the surface electrical boundary conditions. Since relatively large h of 0.07-0.1 wavelengths is needed for present LSAW devices, the optimal /spl theta/ shifts to 40-42/spl deg/ from the conventional value of 36/spl deg/. Thanks to the minimised propagation loss, experimental results showed that device performances are markedly improved only by increasing /spl theta/ to circa 42/spl deg/ from 36/spl deg/. We also describe the state-of-the-art of the performances obtainable in commercially available LSAW devices based on 42/spl deg/YX-LiTaO/sub 3/.

Optimal cut for leaky SAW on LiTaO/sub 3/ for high performance resonators and filters

The paper describes how the characteristics of leaky surface acoustic wave (LSAW) propagation depend on the thickness of Al grating electrodes on rotated Y-X LiTaO/sub 3/. It is shown that the propagation loss arising from leaky nature changes parabolically with both the grating electrode thickness and rotation angle and becomes zero when electrode thickness and rotation angle are properly determined. This means that even when thick grating electrodes are needed in device design, zero propagation loss is always realized by properly determining the rotation angle. When the grating electrode thickness is 0.07 to 0.1 in wavelength for example, LSAWs on 40-42/spl deg/Y-X LiTaO/sub 3/ give zero propagation loss without deteriorating other characteristics. Ladder-type filters for the 800-MHz range were fabricated, which essentially need thick Al grating electrodes of about 0.1 wavelength thickness. As predicted by theoretical calculation, experimental results showed that if the rotation angle is increased to circa 42/spl deg/ from a conventional value of 38/spl deg/, the insertion loss and shape factor are markedly improved compared with devices based on 36/spl deg/Y-X LiTaO/sub 3/. This is essentially a result of the minimized propagation loss.

Precise simulation of surface transverse wave devices by discrete Green function theory

The paper proposes a precise simulation method for devices employing surface-transverse-waves (STWs) which propagate under grating structure and possess strong dispersive nature. The method is based upon the coupling-of-modes (COM) theory, where four parameters required for the analysis, i.e., static capacitance, and self-coupling, mutual coupling and transduction coefficients are determined as a function of frequency by the discrete Green function theory. The method has applied to the simulation of STW resonator filters on quartz, and the result was in good agreement with experiments. It was shown that the passband shape as well as the resonance frequency are most dependent on the thickness and width of grating electrodes. This is because STWs on quartz with weak piezoelectric coupling are substantially guided close to the surface by mass-loading effect of the grating

Free software products for simulation and design of surface acoustic wave and surface transverse wave devices

The paper describes the free distribution of the computer softwares developed for surface acoustic wave (SAW) and surface transverse wave (STW) device simulation. The complete sets of the softwares including mathematical subroutines are distributed in the form of FORTRAN source codes, where the logs and outputs of the test run as well as the manuals are also attached. Functions and applications of the softwares are discussed in detail. Free delivery and maintenance including related announcements of the software are entirely carried out through Internet. The registered users may execute, modify, and analyse the softwares for their computer environment without any prior consultation.

Highly Piezoelectric Shear-Horizontal-Type Boundary Waves

This paper describes theoretical studies on piezoelectric shear-horizontal (SH) type boundary waves propagating along the surface of a separation between piezoelectric and non-piezoelectric materials. According to the guiding mechanism for this type of waves, it is expected that the application of highly piezoelectric materials results in a wide range of existence of combinations for various materials. Numerical analysis shows that SH-type leaky boundary waves exist for combinations of Si/LiNbO 3 , Si/LiTaO 3 and YAG/LiNbO 3 . The electromechanical coupling factor K 2 of 10.0% is obtainable for SH-type leaky boundary waves in [001]-Si(110)/175°YX-LiNbO 3 , in which the velocity is about 4,465 m/s and the attenuation due to leaky nature is substantially zero.

Wavenumber domain analysis of two-dimensional SAW images captured by phase-sensitive laser probe system

This paper is aimed at demonstrating how the wavenumber domain analysis of two-dimensional (2-D) images captured by phase-sensitive laser probe systems is applied in the characterization of RF SAW devices. Effectiveness is demonstrated through the selective characterization of spurious resonance modes and scattered, nonguided modes appearing in SAW resonators.