Leaky Surface Acoustic Wave Velocity Research Articles

Evaluation of SiO2 Thin films on piezoelectric substrates using line-focus-beam ultrasonic material characterization system

SiO2 thin films deposited on LiNbO3 and LiTaO3 using RF magnetron sputtering were evaluated using a line-focus-beam ultrasonic material characterization (LFB-UMC) system. From the measured velocity of a leaky surface acoustic wave (LSAW), c11 and c44 for a SiO2 film were determined to be 0.755 × 1011 and 0.289 × 1011 N m−2 assuming that the density and dielectric constant of the thin film were bulk values. The measured LSAW velocities are in good agreement with values calculated using determined values. The acoustical loss was evaluated from the difference between the measured propagation attenuation and the calculated leakage loss into water. However, the differences were 0.02–0.27 dB/λ, which were considered to be too large for the acoustical loss of SiO2 thin films. By accurately measuring the density of a thin film and determining its elastic constant, it is possible that the acoustical loss of a thin film can be evaluated using an LFB-UMC system.

Relationships among chemical composition, lattice constants, and acoustic properties for Ca3Ta(Ga1−xAlx)3Si2O14 single crystals

The relationship among lattice constant a, Al content, and acoustic properties were experimentally examined using a plate specimen perpendicular to Y-axis prepared from Ca3Ta(Ga0.75Al0.25)3Si2O14 [CTGAS(0.25)] single crystal grown by Czochralski method. As the acoustic properties, leaky surface acoustic wave (LSAW) velocities with different propagation directions, X- and Z-propagations, and longitudinal wave velocity propagating along Y-axis direction were measured by the line-focus-beam/plane-wave ultrasonic-material-characterization (LFB/PW-UMC) system. The measured results of LSAW velocity distributions revealed inhomogeneity in radial direction of the crystal ingot exhibiting lower velocity area at the center of the ingot. In addition, the distributions of lattice constant a and chemical composition (especially Al content) were measured along the radial direction. Abnormal changes suggesting existence of residual stresses concentrated on the central part of the crystal ingot other than the effect of chemical composition change were detected from the relationships among the measured parameters.

Evaluation of Acoustic Properties for Ca3Nb(Ga0.75Al0.25)3Si2O14 Single Crystal Using the Ultrasonic Microspectroscopy System.

Acoustically related physical constants were experimentally determined for Ca3Nb(Ga0.75Al0.25)3Si2O14 (CNGAS) single crystal for the first time. Several plate specimens of the X-, Y -, Z -, 40.24 ° Y -, and 144.98 ° Y -cut were prepared from a CNGAS single crystal ingot grown by Czochralski technique. Elastic constants, piezoelectric constants, and their temperature coefficients for CNGAS were determined from longitudinal wave and shear wave velocities at around room temperature, measured by the ultrasonic microspectroscopy system. Dielectric constants, density, and coefficients of thermal expansion were also measured. It was demonstrated that the determined constants could provide calculation accuracy within ±0.12% in leaky surface acoustic wave velocity. The piezoelectric constants for CNGAS were a 7.2% increase in e11 and a 1.7% decrease in e14 due to Al-substitution effect, compared with those of Ca3NbGa3Si2O14. The appropriate cut angle for thickness-shear mode resonator with zero temperature coefficient of velocity was estimated to be around 150 ° Y -cut from calculations using the determined constants of CNGAS exhibiting electromechanical coupling factor k2 of 3.19% and power flow angle of -1.70°.

Chemical composition characterization of Ca3Ta(Ga0.5Al0.5)3Si2O14 single crystal by the line-focus-beam ultrasonic material characterization system

A new method for evaluation of homogeneity of Ca3Ta(Ga0.5Al0.5)3Si2O14 (CTGAS) single crystals was established based on leaky surface acoustic wave (LSAW) velocity measurements performed by the line-focus-beam ultrasonic material characterization (LFB-UMC) system. Three plate specimens cut perpendicular to X-, Y-, and Z-axes were prepared from the CTGAS crystal ingot and LSAW velocity distributions were examined for these specimens. LSAW velocity changes due to Al-substitution effect were successfully extracted by using a relationship between two LSAW velocities propagating along different directions for Ca3TaGa3Si2O14 (CTGS) and Al-substituted CTGS. Comparison of measured LSAW velocities and the results of chemical composition analysis performed by electron probe microanalysis (EPMA) demonstrated that LSAW velocity is mainly affected by Al-content change in CTGAS. Maximum velocity variation was observed in radial direction of the crystal ingot through the Z-axis propagating LSAW velocity measurements for Y-cut CTGAS specimen corresponding to Al-content change of 0.226mol%. Accuracy of evaluation of Al content by velocity measurement for Y-cut Z-propagating LSAW is estimated to be ±0.0047mol% and is superior to that by EPMA.

Czochralski growth of 2 in. Ca3Ta(Ga,Al)3Si2O14 single crystals for piezoelectric applications

Growth of 2-in. diameter Al-substituted Ca3TaGa3Si2O14 crystals by Czochralski method is reported. The crystals were grown from the melt of Ca3TaGa1.5Al1.5Si2O14 composition and had langasite structure. No inclusions of secondary phases were detected in these crystals. The Ca3Ta(Ga,Al)3Si2O14 mixed crystals produced using non-substituted Ca3TaGa3Si2O14 seeds were defective. They had cracks and/or poly-crystalline structure. However, those grown on the seed of approximately Ca3TaGa1.5Al1.5Si2O14 composition were defect-free. Phase diagram of the Ca3TaGa3Si2O14–Ca3TaAl3Si2O14 pseudo-binary system and segregation phenomenon are discussed in some details. Homogeneity of the crystals was evaluated by measuring 2D-mapping of leaky surface acoustic wave (LSAW) velocities for Y-cut Ca3TaGa1.5Al1.5Si2O14 substrate. Although some inhomogeneities were observed due to slight variations in chemical composition, the crystal had acceptable homogeneity for applications in acoustic wave devices exhibiting the LSAW velocity variation within ±0.048%.

Acoustical physical constants around room temperature for Ca 3 TaGa 1.5 Al 1.5 Si 2 O 14 single crystal

A full set of acoustical physical constants was determined for Ca3TaGa1.5Al1.5Si2O14 (CTGAS) single crystal from bulk wave velocities measured by the ultrasonic micro-spectroscopy method. Several plate specimens were cut perpendicular to the X-, Y-, Z-, 35.25°Y-, and 139.74°Y-directions from a CTGAS single crystal ingot grown by Czochralski technique. Following measurements of dielectric constants and density, elastic constants, piezoelectric constants, and their temperature coefficients were determined from longitudinal wave and shear wave velocities measured for the CTGAS specimens at around room temperature. It was demonstrated that the as found constants could provide calculation accuracy within ±0.15% in leaky surface acoustic wave velocity. The determined constants were used for numerical calculation of the cut angle, at which the temperature coefficient of shear wave velocity becomes zero. This angle corresponded to 147.9°Y-cut substrate that had electromechanical coupling factor of k 2 = 3.2%. This parameter is about four times greater than that of AT-cut α-quartz.

Design, Fabrication of Line-focus Lens-less Polyvinylidene Fluoride Transducers and Applications on Measuring Surface Acoustic Waves with V(f, z) Analytical Method

Line-focus-beam ultrasonic material property characterization system enables accurate measurements on the phase velocities of leaky surface acoustic waves(LSAW) or rayleigh-type leaky surface acoustic waves.But in view of the lens of the conventional acoustic microscopy is expensive and difficult to produce,new method of design and fabrication of two line-focus lens-less polyvinylidene fluoride(PVDF) transducers is presented for acoustic microscopy system utilizing a 40 ?m thick piezoelectric PVDF film to construct the active element.The transducers introduced here centre around 5 MHz and 11 MHz respectively.Different from high cost of equipments and measuring the oscillation period on an operation of tone-burst mode,an improved V(f,z) method based on tow-dimensional Fourier transform is developed for the broadband measurements.A defocusing system for measuring surface acoustic waves is established and a non-contact immersion experiment of a polished fused quartz is carried out.The LSAW velocity extracted by V(f,z) analytical technique is compared with the theoretical one and they both are in good agreement.

Wave propagation model for acoustic evaluation of polymeric thin films.

Polymeric thin films are fabricated on crystalline wafers to serve as a photoresist in lithography processes of semiconductors or MEMS. Essentially these film structures are viscoelastic layers on anisotropic substrates. Acoustic evaluation for these material structures requires an appropriate wave propagation model. This paper presents a leaky surface acoustic wave (LSAW) model for the evaluation of polymeric film integrity. Scanning acoustic microscopy (SAM) operating at relative high-frequency above 100 MHz is utilized to measure the LSAW velocity. For the use of SAM, the model modifies the pre-existing anisotropic layered model by employing hysteretic absorption in viscoelastic polymer and water-loading. The model produces the mean reflectance function and mean dispersion curve, which are specialized for spherical acoustic lenses. The predicted mean dispersion shows good agreement with LSAW velocities measured at several frequencies with spherical lenses.

Ultrasonic Microspectroscopy of ZnO Single Crystals Grown by the Hydrothermal Method

A new set of acoustical physical constants for ZnO was obtained by ultrasonic microspectroscopy (UMS) using very conductive and resistive (001), (100), and (101)ZnO specimens, grown by the hydrothermal method. The specimens were selected from a lot of small ZnO crystals evaluated with the velocity of leaky surface acoustic waves (LSAWs) on a water-loaded specimen surface, in order to identify proper specimens or proper measurement positions for bulk-wave velocity measurements. The constants were determined with measured bulk-wave velocities, according to the determination procedures developed previously. Their accuracies were estimated by comparing the measured LSAW velocities with the calculated ones using the determined constants, within 3.1 m/s. We observed LSAW velocity distributions and bulk-wave velocity dispersions for some specimens that were related to the resistivity distributions on the specimen surfaces and inside the specimens. We established experiment procedures to apply our UMS technology to ZnO crystals in this study. This ultrasonic method is useful for further understanding ZnO crystal growth processes in the hydrothermal method. This application is extended to other class-6mm crystals.

Procedures for determining acoustical physical constants of class 6mm single crystals by ultrasonic microspectroscopy technology

We theoretically and numerically investigated procedures for accurately determining the acoustical physical constants of piezoelectric hexagonal (class 6mm) crystals, taking ZnO as an example, using bulk-wave velocities and leaky surface acoustic wave (LSAW) velocities acquired by ultrasonic microspectroscopy technology. Selection of appropriate propagation modes and directions for eight velocity measurements to facilitate accurately determining five elastic constants (c11E, c12E, c13E, c33E, and c44E) and three piezoelectric constants (e15, e31, and e33) was discussed in addition to measurements of two dielectric constants (ε11S and ε33S) and the density (ρ). Several determination procedures were obtained. Using only bulk-wave velocities measured for Y-cut, Z-cut, and several rotated Y-cut crystalline plane specimens provided the best determination accuracies for constants c13E, c33E, e31, and e33. Favorable determination accuracies were also achieved using several sets of two rotated Y-cut crystalline plane specimens such as (101) and (102). Conductive specimens of (001) and (102) with a resistive (103) specimen made the bulk-wave measurements simpler, resulting in greatly improved determination accuracies. The additional use of LSAW velocity with one conductive (001) specimen enabled the determination procedures to be simplified, resulting in acceptable accuracy for c13E. Measurements of bulk-wave velocities and LSAW velocities for just two resistive Y-cut and Z-cut specimens could determine all the constants, albeit with some deterioration in accuracy, especially for e31 and e33. This will be useful for preliminary determination of the constants for precious crystals.

Analysis and Suppression of Side Radiation in Leaky SAW Resonators

This paper discusses side acoustic radiation in leaky surface acoustic wave (LSAW) resonators on rotated Y-cut lithium tantalite substrates. The mechanism behind side radiation, which causes a large insertion loss, is analyzed by using the scalar potential theory. This analysis reveals that side radiation occurs when the guiding condition is not satisfied, and the LSAW most strongly radiates at the frequency in which the LSAW velocities in the grating and busbar regions approximately correspond to each other. Based on these results, we propose a "narrow finger structure," which satisfies the guiding condition and drastically suppresses the side radiation. Experiments show that the resonance Q of the proposed structure drastically improves to over 1000 by suppressing the side radiation, which is three times higher than for a conventional structure. Applying the proposed resonators to the ladder-type SAW filters, ultra-low-loss and steep cut-off characteristics are achieved in the range of 800 MHz and 1.9 GHz.

Numerical Analysis of Ultrasonic Beam of Variable-Line-Focus-Beam Film Transducer

In this study, the characteristics of an ultrasonic beam radiated by a variable-line-focus-beam transducer were numerically calculated by finite-difference time domain (FDTD) method and liquid-elastic wave reflection theory. The interference ripple caused by a leaky surface acoustic wave (SAW) was observed in the lens width vs received intensity curve. Reasonable results, the true-circle-arc-lens in the literature, were obtained. As in the conventional V(z) curve, the ripple changed according to the attenuation parameter α and the leaky SAW velocity. Unlike for the conventional true-circle-arc-lens, the ripples caused by the leaky SAWs are observed at both sides of the focal point.

Evaluation of Rolling Fatigue Damage in Deep Groove Ball Bearings by Divided-Type Focusing Ultrasonic Transducer

To evaluate quantitatively the damage caused by rolling fatigue in deep groove ball bearings, we used a method in which the wave velocity of a leaky surface acoustic wave (SAW) propagating on the race surface of bearings was measured. The wave velocity was directly measured from the change in the propagation time by defocusing a focusing ultrasonic transducer. A new focusing ultrasonic transducer was developed by molding a piezoelectric copolymer into a concave-shaped film. To fabricate ultrasonic transducers with a lower frequency characteristic, the films were stacked and composite backings made from epoxy resin and tungsten were used. The electrode of the transducer was divided into three areas to receive direct reflection waves and leaky SAW independently without any interference. Two of these electrodes were used for the excitation and reception of leaky SAW, and the shape of the electrodes was designed so that leaky SAW might propagate only on the raceway surface of the inner ring of the bearings. Moreover, in order to suppress the effects caused by edge waves, the shape of the electrodes for leaky SAW was considered. The availability of this method was evaluated by measuring the leaky SAW velocity in the bearings whose worked hours differed. As a result, a small difference in leaky SAW velocity was detected according to the worked hours of the bearings, and it was demonstrated that this method would be useful for non-destructive soundness evaluation of bearings.

Accurate Velocity Measurement of Periodic Striae of TiO2–SiO2 Glasses by the Line-Focus-Beam Ultrasonic Material-Characterization System

The evaluation of periodic striae layers in TiO2–SiO2 ultra-low-expansion glasses, formed during production, is discussed through the measurement of leaky surface acoustic-wave (LSAW) velocities by the line-focus-beam (LFB) ultrasonic material-characterization system. The averaging effect associated with an LSAW propagation region interacting with periodic striae on a specimen surface was examined at 225 MHz, taking several specimens prepared with inclination angles of θ=0, 2, 5, 10, 20, and 90° to the plane of striae layers with a periodicity of 0.16 mm. LSAW velocities corresponding to TiO2 concentrations in the glass were properly measured for the specimens with θ less than 10°, and the perpendicular specimen (θ=90°) was suitable for accurate determination of the striae periodicities for LSAW propagation perpendicular to the striae plane.

Ultrasonic Characterization of Residual Stress in Shot Peened AI 7075 Alloy Using Acoustic Signature

We attempted to estimate the residual stress which evolved during the shot peening of Al 7075 alloy using leaky surface acoustic wave (LSAW). Shot peening was conducted to produce a variation in the compressive residual stress with the depth from the surface at a shot velocity of 30m/s. The LSAW velocity was measured using a scanning acoustic microscopy (SAM). The Vickers hardness profile obtained inwards from the surface showed significant work hardening of the near surface layer with a thickness of about 0.3mm. The variation in the LSAW velocity through the shot peened surface layer was in good agreement with the distribution of the residual stress measured by X-ray diffraction.

Evaluation method of TiO/sub 2/-SiO/sub 2/ ultra-low-expansion glasses with periodic striae using the LFB ultrasonic material characterization system

Experimental procedures and standard specimens for characterizing and evaluating TiO2-SiO2 ultra-low expansion glasses with periodic striae using the line-focus-beam (LFB) ultrasonic material characterization system are discussed. Two types of specimens were prepared, with specimen surfaces parallel and perpendicular to the striae plane using two different grades of glass ingots. The inhomogeneities of each of the specimens were evaluated at 225 MHz. It was clarified that parallel specimens are useful for accurately measuring velocity variations of leaky surface acoustic waves (LSAWs) excited on a water-loaded specimen surface associated with the striae. Perpendicular specimens are useful for obtaining periodicities in the striae for LSAW propagation perpendicular to the striae plane on a surface and for precisely measuring averaged velocities for LSAW propagation parallel to the striae plane. The standard velocity of Rayleigh-type LSAWs traveling parallel to the striae plane for the perpendicular specimens was numerically calculated using the measured velocities of longitudinal and shear waves and density. Consequently, a reliable standard specimen with an LSAW velocity of 3308.18 +/- 0.35 m/s at 23 degrees C and its temperature coefficient of 0.39 (m/s)/degrees C was obtained for a TiO2-SiO2 glass with a TiO2 concentration of 7.09 wt%. A basis for the striae analysis using this ultrasonic method was established.

Experimental Study for Evaluating Striae Structure of TiO2–SiO2 Glasses Using the Line-Focus-Beam Ultrasonic Material Characterization System

Striae configurations in TiO2–SiO2 ultra-low-expansion glasses caused by variations in TiO2 concentration were investigated through measurement of leaky surface acoustic wave (LSAW) velocities by the line-focus-beam (LFB) ultrasonic material characterization system. LSAW velocity distributions were measured on the surface of a specimen substrate prepared from a large circular plate glass ingot produced by the direct method using a flame hydrolysis process. A subsequent procedure that included polishing the surface of the specimen to reduce the specimen thickness by 40 µm and measuring the LSAW velocity distributions on the surface was repeated five times in order to examine at least one period of the striae. TiO2 concentration variations were clearly observed in the deposit direction of the glass ingot and in its radial direction. The maximum LSAW velocity difference over the whole examined region was 11.7 m/s, corresponding to 0.70 wt % TiO2 concentration. The three-dimensional striae structure revealed that the striae plane in the examined region was almost parallel to the substrate surface but gently curved down in the radial direction. The plane had a slightly convex-shaped cross section layered with a striae periodicity of about 0.16 mm and a curvature radius of about 440 mm, and also existed in a circular form with a curvature radius of about 450 mm. The ultrasonic method will contribute to improvement of characteristics and homogeneity of glass associated with production-process conditions.

Accurate Calibration Line for Super-Precise Coefficient of Thermal Expansion Evaluation Technology of TiO2-Doped SiO2 Ultra-Low-Expansion Glass Using the Line-Focus-Beam Ultrasonic Material Characterization System

We obtained an accurate relationship between the leaky surface acoustic wave (LSAW) velocities and TiO2 concentrations. Such a relationship is needed for the line-focus-beam ultrasonic material characterization (LFB-UMC) system as a new technology for evaluating the coefficient of thermal expansion (CTE) of ultra-low-expansion glasses with extremely high precision. Using commercially available TiO2–SiO2 glass with periodic striae, averaged velocities for LSAW propagation parallel to the striae plane at 225 MHz and averaged TiO2 concentrations by X-ray fluorescence analysis were measured on the surface of seven specimen substrates prepared perpendicular to the striae plane. The obtained sensitivity of LSAW velocity to TiO2 concentration was -0.0601 wt %/(m/s), and the measurement resolution was estimated to be ±0.0084 wt % for ±2 σ (σ: standard deviation) from the LSAW velocity measurement resolution of ±0.14 m/s. The TiO2 concentration for the standard TiO2–SiO2 glass specimen with a LSAW velocity of 3308.18 m/s for system calibration was determined to be 7.09 wt %. This ultrasonic technology will contribute greatly to the development of the ultra-low-expansion glasses needed for extreme ultraviolet lithography (EUVL) systems.

Improvement of Velocity Measurement Accuracy of Leaky Surface Acoustic Waves for Materials with Highly Attenuated Waveform of the V(z) curve by the Line-Focus-Beam Ultrasonic Material Characterization System

Measurement accuracies of leaky surface acoustic wave (LSAW) velocities for materials with highly attenuated waveforms of V(z) curves obtained by the line-focus-beam ultrasonic material characterization (LFB-UMC) system are investigated. Theoretical investigations were carried out and experiments were performed for TiO2–SiO2 glass (C-7972), Li2O–Al2O3–SiO2 glass ceramic (Zerodur®), and (111) gadolinium gallium garnet (GGG) single crystal as specimens. Waveform attenuations of V(z) curves for C-7972 and Zerodur® are greater than those for the (111) GGG single crystal. Frequency dependences of the waveform attenuations were calculated for each specimen by considering the propagation attenuation of LSAWs. The theoretical results revealed that the waveform attenuation dominantly depends upon the acoustic energy loss due to the water loading effect on the specimen surface, and that the waveform attenuation becomes smaller with decreasing frequency. Significant improvement of the measurement precision of LSAW velocities was demonstrated for each specimen using three LFB ultrasonic devices with different curvature radii R of the cylindrical acoustic lenses: R=2.0 mm at 75 MHz, R=1.5 mm at 110 MHz, and R=1.0 mm at 225 MHz; for C-7972, the precisions were improved from ±0.0053% at 225 MHz to ±0.0020% at 75 MHz.

Determination of the true congruent composition for LiTaO/sub 3/ single crystals using the LFB ultrasonic material characterization system

The true congruent composition for LiTaO3 single crystals was determined by measuring the velocities of leaky surface acoustic waves (LSAWs) with the line-focus-beam ultrasonic material characterization (LFB-UMC) system for two 42 degrees YX-LiTa3s crystal ingots. The congruent composition determined here was 48.460 Li2O-mol%, corresponding to the LSAW velocity (42 degrees YX-LiTaO3) of 3125.3 m/s, and the absolute relationship between the LSAW velocity and chemical composition was obtained. Simulations on the variation of the melt and crystal compositions in a mass production of 100 crystals were conducted as a function of the composition of the starting material around the congruent composition. The result showed that the distributions of the melt and crystal compositions within and among the crystals varied largely with the material composition, providing the relationship of the material composition with the maximum composition variation for the 100 crystals. Based on these results, we verified the relationships between the tolerance of the material composition variation and the tolerances for the SH-type SAW velocity, LSAW velocity, and Curie temperature. The material composition needs to be constrained to within +/- 0.007 Li2O-mol% around the congruent composition to mass-produce the crystals with reliable homogeneity, satisfying the tolerance of +/- 0.01% in the SAW velocity. Furthermore, a guideline for the specification of reliable piezoelectric SAW-device wafer substrates was presented with the accurate interrelationships among the chemical composition ratio, LSAW velocity, and Curie temperature.