Characteristics Of Surface Acoustic Waves Research Articles

Optimum cut orientation of piezoelectric substrate and propagation direction of SAW for rotation rate sensor

The effect of Coriolis and centrifugal forces on the propagation characteristics of surface acoustic waves (SAW) on a rotating piezoelectric substrate can be utilized for sensing rotation rate. In this paper, the relationship between SAW phase velocity and the rotation rate of the substrate is analyzed theoretically and numerically based on the coupling wave equations on anisotropic piezoelectric substrate with rotation effect. Partial wave theory and surface effective permittivity method are employed. Using LiNbO 3 as an example, some quantitative results of SAW rotation rate sensor, including free and metalized interfaces between substrate and free space in X-cuts, Y-cuts, and Z-cuts, are obtained. Furthermore, by considering comprehensively SAW rotation rate sensitivity with SAW excitation efficiency and beam steering, the optimum cut orientation of piezoelectric substrate and propagation direction of SAW for rotation rate sensor are presented. The research findings can provide theoretical guidance and simulation basis for the experimental research on SAW rotation rate sensor.

Effect of Metal Buffer Layer on Surface Acoustic Wave in AlN/Diamond Structure

This study investigates the propagation characteristics of surface acoustic waves in interdigital transducer/AlN/Mo/diamond structures using the finite element method. Propagation characteristics in AlN/thin metal film/diamond and AlN/diamond structures are also evaluated for comparison. Results indicate that by adding the Mo layer at the AlN/diamond interface, the maximum coupling coefficient can be upgraded to 2.24%, which is 5% and 81% higher than that of AlN/thin metal film/diamond and AlN/diamond structures, with a very high phase velocity of 10745 m/s. The effects of electrodes on surface acoustic waves in interdigital transducer/AlN/Mo/diamond structures are also discussed.

Design of Double Mode SAW Filters Using IDT/(100) ZnO/(111) Diamond Structure

Propagation characteristics of surface acoustic waves (SAWs) in interdigital transducers (IDT)/(100) ZnO/diamond structures are investigated in this study using the finite element method. The effects of electrodes on phase velocity, coupling coefficient, and reflectivity of SAWs in the layered structures are illustrated. The extracted coupling-of-mode parameters are then applied to calculate frequency responses of double mode SAW filters using the transmission matrix method. Simulation results show a tailored filter applicable for wideband code division multiple access systems can be achieved.

The viscous effects on shear horizontal surface acoustic waves in semi-infinite superlattices

In this paper, by a semi-analytical method, the propagation characteristics of shear horizontal surface acoustic waves in semi-infinite superlattices containing viscous materials are investigated. The factors that influence the attenuation and phase velocity of the surface waves are analyzed in detail. The results may be useful for the design of acoustic wave devices.

Effects of metal buffer layer on characteristics of surface acoustic waves in ZnO/metal/diamond structures

The interdigital transducer (IDT)/ZnO/metal/diamond structure is investigated for use in the design surface acoustic wave (SAW) devices in the super-high-frequency (SHF) band. Simulation results indicate that adding a metal buffer layer with a finite thickness significantly increases the coupling coefficient. In the Sezawa mode, the coupling coefficient is 4.71% when an Al interlayer is applied. This coupling coefficient is 75% and 77% larger than those in the IDT/ZnO/diamond and IDT/ZnO/shorted surface/diamond structures, respectively. The results in this study are useful in designing SAW devices using diamond-based structures with a large coupling coefficient in the SHF band.

Propagation Characteristics of Surface Acoustic Waves in AlN/128° Y–X LiNbO3 Structures

In this study, propagation characteristics of surface acoustic waves in a layered piezoelectric structure (AlN/128° Y–X LiNbO3) are investigated. The phase velocity and coupling coefficient of the layered structure with interdigital transducers (IDTs) and/or thin metal films deposited at various interfaces are calculated numerically. The effects of the polarity of 128° Y–X LiNbO3 on SAW characteristics are illustrated. The calculated phase velocity and coupling coefficient of SAWs in the IDT/ZnO/128° Y–X LiNbO3 structure are also demonstrated for comparison. The simulation results obtained in this study can be applied to the design of SAW devices using AlN/128° Y–X LiNbO3 structures.

Propagation characteristics of shear horizontal surface acoustic waves in (11 2 0) ZnO film/silica glass substrate structures

This paper presents the propagation characteristics of the shear horizontal surface acoustic wave (SH-SAW) in ZnO (0deg, 90deg, psi) (11 2macr 0) textured ZnO films. ZnO (0deg, 90deg, 0deg) film/interdigital transducer (IDT) electrode/silica glass substrate structures were fabricated by RF magnetron sputtering. Experimental results demonstrate that SH-SAW was clearly excited in these structures. We also theoretically estimated the electromechanical coupling coefficient K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the ZnO (0deg, 90deg, psi) film/silica glass substrate structure. The theoretical results show that the IDT electrode/ZnO (0deg, 90deg, 55deg) film/silica glass substrate structure had a relatively high K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> value of 3.4%. Moreover, the shear horizontal displacement component of the SH-SAW in this structure is much larger than the transverse and longitudinal displacement components. This structure could be used in SH-SAW sensors for evaluating the electrical properties of liquids.

On the propagation of elasto-thermodiffusive surface waves in heat-conducting materials

The present paper deals with the study of the propagation of Rayleigh surface waves in homogeneous isotropic, thermodiffusive elastic half-space. After developing the formal solution of the model, the secular equations for stress free, thermally insulated or isothermal, and isoconcentrated boundary conditions of the half-space have been obtained. The secular equations have been solved by using irreducible Cardano's method with the help of DeMoivre's theorem in order to obtain phase velocity and attenuation coefficient of waves under consideration. The motion of the surface particles during the Rayleigh surface wave propagation is also discussed and found to be elliptical in general. The inclinations of wave normal with the major axis of the elliptical path of a typical particle have also been computed. Finally, the numerically simulated results regarding phase velocity, attenuation coefficient, specific loss and thermo-mechanical coupling factors of thermoelastic diffusive waves have been obtained and presented graphically. Some very interesting and useful characteristics of surface acoustic waves have been obtained, which may help in improving the fabrication quality of optical and electronic devices in addition to construction and design of materials such as semiconductors and composite structures. Therefore, this work finds applications in the geophysics and electronics industry.

1J2a-1 Measurement model for propagation characteristics of leaky surface acoustic waves by the line-focus-beam ultrasonic material characterization system(Measurement techniques)

1J2a-1 Measurement model for propagation characteristics of leaky surface acoustic waves by the line-focus-beam ultrasonic material characterization system(Measurement techniques)

Anisotropy-induced polarization mixture of surface acoustic waves inGaN∕c-sapphire heterostructures

The characteristics of surface acoustic waves (SAWs) in GaN layers grown on $c$-plane sapphire are investigated. Besides Rayleigh mode, Sezawa and Love modes, which are confined in the nitride layers, arise because of the slow sound propagation in GaN compared with the substrate. In addition, pseudo-SAWs leaking into the bulk are observed. The trigonal crystal symmetry of sapphire not only leads to an anisotropic propagation of the SAWs in the heterostructures, despite the isotropic elastic properties in the $c$-plane GaN, but also mixes their polarization even for the propagation along high-crystal-symmetry directions. Love modes, which are normally piezoelectrically inactive, can be excited by interdigital transducers through this polarization mixture. The nonzero value of the elastic coefficient ${c}_{14}$ of sapphire is indicated to be the origin of the coupling of sagittal and shear horizontal displacements.

Propagation Characteristics of Surface Acoustic Waves on K3Li2Nb5O15

The contour maps of the phase velocity vf, the temperature coefficient of delay (TCD), the electromechanical coupling coefficient K2, and the power flow angle (PFA) of surface acoustic waves (SAWs) on K3Li2Nb5O15 are presented for Euler angles (φ, θ, ψ) with φ=0, 10°, 20°, 30°, and 40°, and -180° ≤φ, θ< 180°. These maps computed by Campbell and Jonnes' method reveal that SAWs on K3Li2Nb5O15 with Euler angles (4°, 49°, 92°), (33°, 76°, 126°), and (30°, 86°, 151°) have vf of 3255 m/s, 3383 m/s, and 3728 m/s, K2 of 0.0115, 0.0147, and 0.0045, the values of first-order TCD of 0.02 ppm/°C, 0.05 ppm/°C, and 0.04 ppm/°C, and PFAs of 0.005°, 4.7°, and 5.1°, respectively.

Confinement of surface acoustic waves in AlN∕GaN∕γ-LiAlO2 acoustic wells

We numerically investigate the characteristics of surface acoustic waves (SAWs) in AlN∕GaN∕γ-LiAlO2 heterostructures. The markedly large sound velocity in AlN in comparison to that in GaN leads to an expulsion of SAWs from the top AlN layer and their resultant relocation to the middle GaN layer in the short-wavelength regime. The SAW velocity in the limit of zero wavelength is given by a bulk sound velocity of GaN, owing to the capping by the AlN barrier layer. The extra confinement of the SAW power in the acoustic well is advantageous in manipulating the operation of GaN-based devices by SAWs. The threshold velocity for the appearance of guided Rayleigh-like modes is found to be smaller than the bulk transverse sound velocity in the substrate. The present system exhibits furthermore unusual bowing behavior in the SAW dispersion.

The effect of electrical boundary conditions on the characteristics of surface acoustic waves propagating in potassium niobate

The study of the effect of a perfectly conducting plane placed at a certain distance from the surface of a potassium niobate crystal on the characteristics of the generalized Rayleigh and Gulyaev-Bleustein surface waves is continued. In addition, the effect of an infinitely thin conducting layer applied to the surface of the piezoelectric on the characteristics of these waves is analyzed. It is found that a variation in the conductance of this layer can produce a result that completely differs from the result obtained when a perfectly conducting plane is moved toward the surface, although the extreme states of these actions (electrically open and short-circuited surfaces) are identical. A possible physical explanation of this difference is proposed.

Development of an improved calibration method for the LFB ultrasonic material characterization system

We investigated standard specimens for accurately calibrating the line-focus-beam ultrasonic material characterization (LFB-UMC) system without system dependencies. We evaluated several types of lithium tantalate (LiTaO3) substrates using two LFB-UMC systems with different device/system characteristics to measure and calibrate the propagation characteristics of the leaky surface acoustic waves (LSAWs), and analyzed the variations between the calibrated results. We concluded from this analysis that, by selecting materials with the cut surfaces and propagation directions of standard specimens that are identical to the objects to be calibrated, calibration errors resulting from different performance characteristics between the two systems could be nearly eliminated. Also, analytical errors caused by the effects of spectra with two close peaks (another propagation wave mode), one of the most common problems of characterization in the past, could be eliminated at the same time by this method.

Highly anisotropic dispersion of surface acoustic waves in M-plane GaN layers grown onγ−LiAlO2(100)

The characteristics of surface acoustic waves (SAW's) in M-plane GaN and AlN layers grown on $\ensuremath{\gamma}\ensuremath{-}{\mathrm{LiAlO}}_{2}(100)$ are investigated. The SAW velocities in the (100) plane of bulk $\ensuremath{\gamma}\ensuremath{-}{\mathrm{LiAlO}}_{2}$ are virtually identical along the [010] and [001] directions and are significantly larger than those in the M-plane bulk GaN. Despite these velocity relations, the SAW velocity in $\mathrm{G}\mathrm{a}\mathrm{N}/\ensuremath{\gamma}\ensuremath{-}{\mathrm{LiAlO}}_{2}$ heterostructures increases steadily along the $\mathrm{GaN}[112\ifmmode\bar\else\textasciimacron\fi{}0]$ direction with increasing the SAW wavelength, whereas it decreases along the GaN [0001] direction. A guided Rayleigh mode is observed solely for the propagation along the $\mathrm{GaN}[112\ifmmode\bar\else\textasciimacron\fi{}0]$ direction. These experimental results are compared with numerical simulations. Velocity bowing is indicated to govern the dispersion in the heterostructures.

Slowness curves and characteristics of surface acoustic waves propagating obliquely in periodic finite-thickness electrode gratings

The computation of the diffraction of surface acoustic waves (SAWs) on piezoelectric materials is complicated by the anisotropy of their propagation, and requires their slowness curves to be known precisely. In addition, in actual devices these slowness curves are strongly affected by the massive electrodes used for SAW generation. We investigate the characteristics of SAWs propagating obliquely in periodic finite-thickness electrode gratings, with the mass-loading effect taken into account. The velocity of the surface waves, as well as the attenuation, piezoelectric coupling and beam steering are obtained as a function of the propagation angle with respect to the grating axis. The slowness curves for SAWs propagating under periodic electrode gratings are compared with the slowness curves for the same SAWs propagating under a thick homogeneous metallic layer. Numerical examples are presented for the SAWs of 42.75°YX quartz and X112.2°Y lithium tantalate, and the leaky SAWs of 36°YX lithium tantalate.

Guiding characteristics of surface acoustic waves visualized using photoluminescence quenching

We restrict the surface acoustic wave (SAW) propagation on a GaAs surface within a waveguide by means of reduction of the SAW velocity realized by metal gratings. The spatial variation of the SAW amplitude is evaluated by mapping the efficiency of the quenching of photoluminescence by the SAWs. Confinement of the SAWs is accomplished at a frequency of 1.4 GHz when the angle of SAW incidence with respect to the waveguide boundary is kept less than ∼10° for SAW velocity reduction of 4%. Mapping also reveals interference stripes associated with the SAWs bounce at the waveguide boundary.

The characteristics of surface acoustic waves on AlN/LiNbO 3 substrates

The characteristics of surface-acoustic-wave (SAW) devices on various substrates were measured by a network analyzer in the temperature range from 0 to 80 °C. Based on the structure of IDT/AlN/LiNbO3, it was revealed that the magnitude of the temperature coefficient of frequency (TCF) of a SAW on a LiNbO3 substrate was significantly decreased due to the thickness increase of AlN thin film deposited on the LiNbO3 substrate. The TCF of a SAW on an AlN/LiNbO3 device was measured to be about -51 ppm/°C at h/λ=0.1, where h is the thickness of the AlN film and λ is the wavelength of the SAW. This indicates that the deposition of an AlN film on a LiNbO3 substrate could improve the temperature stability, as compared with that of a SAW on a LiNbO3 substrate (-73 ppm/°C). The SAW device on the ST-X quartz is shown to have a positive TCF as the AlN thin film is deposited on the surface of the ST-X quartz. In addition, the phase velocity (Vp) of the SAW on an AlN/LiNbO3 substrate was significantly increased by the increase of AlN thickness (h/λ).

High-accuracy standard specimens for the line-focus-beam ultrasonic material characterization system.

We prepared standard specimens for the line-focus-beam ultrasonic material characterization system to obtain absolute values of the propagation characteristics (phase velocity and attenuation) of leaky surface acoustic waves (LSAWs). The characterization system is very useful for evaluating and analyzing specimen surfaces. The calibration accuracy of these acoustic parameters depends on the accuracy of acoustical physical constants (elastic constants, piezoelectric constants, dielectric constants, and density) determined for standard specimens. In this paper, we developed substrates of nonpiezoelectric single crystals (viz., gadolinium gallium garnet [GGG], Si, and Ge) and an isotropic solid (synthetic silica [SiO2] glass) as standard specimens. These specimens can cover the phase velocity range of 2600 to 5100 m/s for Rayleigh-type LSAWs. To determine the elastic constants with high accuracy, we measured velocities by the complex-mode measurement method and corrected diffraction effects. Measurements of bulk acoustic properties (bulk wave velocity and density) were conducted around 23 degrees C, and bulk wave velocities were obtained with an accuracy of within +/-0.004%. We clearly detected differences in acoustic properties by comparing the obtained results with the previously published values; the differences were considered to be due to differences of the specimens used. We also detected differences in acoustic properties among four SiO2 substrates produced by different manufacturers.

Leaky Surface Acoustic Waves on Langasite with Thin Dielectric Films

The propagation characteristics of leaky surface acoustic waves on rotated Y-cut langasite with a thin dielectric film, such as those of tantalum pentoxide (Ta2O5) and silicon dioxide (SiO2), are investigated theoretically and experimentally, mainly in terms of the attenuation. The theoretical analysis showed that, for a certain range of the cut angle, the attenuation can be reduced by choosing the appropriate material and thickness of the film. In fact, the estimated propagation loss of the leaky surface acoustic wave on (0°, 140°, 42°)-cut langasite with RF-sputtered Ta2O5 film decreased to approximately one-tenth that of the sample without the thin film.