Leaky Surface Acoustic Wave Velocity Research Articles

Homogeneity Evaluation of LiNbO3 and LiTaO3 Single Crystals for Determining Acoustical Physical Constants

The homogeneity of surface acoustic wave (SAW) grade LiNbO3 and LiTaO3 single crystals, which are used to accurately measure acoustical physical constants, is evaluated using several specimens, by measuring the leaky surface acoustic wave (LSAW) velocity, longitudinal velocity, density, lattice constant, and Curie temperature. The specimens are taken perpendicular to the pulling-axis direction of each crystal. The variations of LSAW and longitudinal velocities along the pulling-axis direction are at most 1 m/s, and the corresponding changes of chemical composition ratio are estimated to be about 0.02 Li2O-mol% for both LiNbO3 and LiTaO3 crystals. The evaluation proves that the crystals employed can be regarded as homogeneous within the measurement accuracy, when the effect of the variations in the crystals on the constant determination is investigated.

Application of Measurements of Leaky Surface Acoustic Wave Velocity to Rolling Contact Fatigue Analysis.

We measured the depth distribution of Leaky surface acoustic wave (LSAW) velocity using a scanning acoustic microscope (SAM), for several inner rings of bearings tested for various revolution times, in order to evaluate rolling contact fatigue of rolling bearing. Both residual stress and half-value width of their inner rings were measured by the X-ray diffraction method, for comparison with the behavior of LSAW velocity. Although the dependence of rolling contact fatigue on revolution time was not recognized in the distributions of both X-ray parameters under this test condition, it was observed in the distribution of LSAW velocity. We confirmed that the SAM is an effective tool to evaluate the degree of rolling contact fatigue of bearings.

Determination of Elastic Constants of Anisotropic Materials by Multiple Mode Surface Waves.

An efficient inversion technique to determine elstic constants of anisotropic solids from the leaky surface acoustic wave (LSAW) is presented. In the present inversion two types of LSAW velocities, the leaky Rayleigh mode and the pseudo-leaky Rayleigh mode, have been used as knewn parameters, Both the velocities in specified directions on the solid surface can be obtained from either the phase change or the amplitude change of the ultrasonic reflection coefficient of the surface. The elastic constants are determined from the directional variations of both the LSAW velocities using an optimization procedure. Based on the investigations of the stability and accuracy of the solution in inverse problems defined on a cubic crystal, it has been shown that the use of dual mode LSAWs enables us to make better elastic constants determination with a high precision than the use of a single mode LSAW. In addition, it has been confirmed that, by performing a series of numerical simulations using a synthetic data and an experiment, all the elastic constants of the crystal can be determined accurately by the present inversion with the knowledge of the crystallographic orientation and the density.

Line-focus acoustic microscopy measurements of acoustic properties of LiTaO3 crystal plates with an inversion layer

Inversion layers of 2 μm and 30 μm thickness were formed at the negative dipole-end (−c) face of a Z-cut LiTaO3 crystal plate by proton exchange followed by heat treatment. The phase velocities of leaky surface acoustic waves (LSAWs) on both the positive (+c) and negative (−c) faces of the plate were measured by line-focus acoustic microscopy versus the angle of propagation, at a frequency of 225 MHz, and the results were compared with theoretical predictions. It is shown that for an inversion layer of 30 μm thickness the phase velocities of LSAWs on the +c and −c faces are the same, and almost equal to the velocities of the virgin plate. This suggests that the material constants, which are decreased due to the proton exchange, are restored to the original values by the heat treatment.

Quantitative characterization of proton-exchanged layers in LiTaO3 optoelectronic devices by line-focus-beam acoustic microscopy

Application of line-focus-beam (LFB) acoustic microscopy is extended to quantitative characterization of proton-exchanged/annealed layers employed in LiTaO/sub 3/ optical waveguides. Several specimens of Z-cut LiTaO/sub 3/ substrates, processed under the fabrication conditions for second-harmonic generation (SHG) optoelectronic devices, were prepared for measurements of the leaky surface acoustic wave (LSAW) velocities. Remarkable decreases in LSAW velocity due to the processes of proton exchange and annealing were observed, providing very useful information on the proton concentration and depth in diffusion layer, and on the process temperature distribution. It is found that measurement sensitivity is highest in the Y-axis wave propagation direction and the resolution to the optical waveguide parameters of diffusion depth and refractive index is much greater than the conventional techniques. It is suggested that this ultrasonic method should be adopted as a new analytical technique for development and evaluation of device fabrication processes and systems destined for future mass production.

Theoretical and experimental investigation for LFB acoustic microscopy characterization of proton-exchanged LiTaO3 optical waveguides

Line-focus-beam (LFB) acoustic microscopy has been recognized as a new analytical technique of quantitative material characterization, by measuring the phase velocities of leaky surface acoustic waves (LSAWs) excited on the water-loaded specimen surface. Recently, application of this ultrasonic technique has been demonstrated successfully for characterization of proton-exchanged layers for LiNbO3 and LiTaO3 optical waveguides and for evaluation of the device fabrication processes. It is necessary and important to calculate LSAW propagation characteristics, viz., velocity and attenuation, for interpretation of experimental results and for evaluation of physical properties, such as optical and elastic properties, in proton-exchanged layers. In this paper, LSAW propagation characteristics for the structural model of water/piezoelectric layer/piezoelectric substrate are analyzed. The propagation characteristics are interpreted with calculations of spatial distributions of mechanical displacements and electric potential. Specimens of Z-cut LiTaO3 substrates, with a layer thickness of 0.5 μm, were prepared. Experimental data of LSAW propagation characteristics, measured in the frequency range 100 to 300 MHz, are discussed in detail comparing with the calculated results.

Characterization of 36/spl deg/YX-LiTaO/sub 3/ wafers by line-focus-beam acoustic microscopy

Application of line-focus-beam (LFB) acoustic microscopy is extended to characterization of substrates for SH-type SAW devices. Theoretical and experimental studies on a wave mode for characterization are carried out on 36/spl deg/Y-cut LiTaO/sub 3/ wafers. A Rayleigh-type mode of leaky surface acoustic waves (LSAWs) must be employed instead of an SH-type mode of leaky pseudo-surface waves (LPSAWs). Experimental results show that the LSAW propagation should be directed along the X-axis because the LSAW velocities are more sensitive to chemical composition and elastic inhomogeneities. The relations among the LSAW velocities, densities, and Curie temperatures are determined. The LSAW velocity increases linearly at the rate of 0.52 m/s//spl deg/C with the Curie temperature. A chemical composition change of 0.03 Li/sub 2/O-mol%, corresponding to temperature resolution of better than 0.3/spl deg/C, is easily detected by the velocity measurements. Elastic inhomogeneities due to residual multi-domains, produced during the poling process during wafer fabrication, are interpreted quantitatively by this ultrasonic technology. >

An Analysis by Scanning Acoustic Microscopy of the Mechanical Stability of PSG and Si3N4 Passivation Films

ABSTRACTTwo types of mechanical tests associated with acoustic microscopy characterizations were performed to investigate the mechanical stability of PSG and Si3N4 passivation films. An in situ tensile test micro-device was installed under a scanning acoustic microscope to study the damage development in the passivation films deposited on A1,1%Si substrates. The analysis of the attenuation of the acoustic signature of the film/substrate systems and the variations of the leaky surface acoustic wave velocity permitted detection of the cracking and decohesion of the passivation films. The four-point bending test was used to submit passivated aluminum multilayers deposited on silicon substrates to cyclic compression. Then subsurface acoustic images revealed decohered zones in the passivation.

Measurement of leaky surface acoustic wave velocity using interdigital transducer in a layered structure composed of piezoelectric ceramic and fused quartz

AbstractAn ultrasonic system for measuring a leaky surface acoustic wave (SAW) velocity is described. A leaky SAW transducer consisting of a piezoelectric ceramic thin plate, an interdigital transducer (IDT), and a fused quartz plate is used in this system. A longitudinal wave which is reradiated from a test sample surface into a water layer is detected as electric signals having different delay times received at two different IDTs placed on a substrate surface. A phase difference between two delayed signals depends on the leaky SAW velocity. It is essential in this measurement method that an incident angle of an ultrasonic beam be nearly equal to the Rayleigh angle. The present method using a layered structure leaky SAW transducer has the advantage of a wider range of detecting SAW velocities, compared to a conventional single‐layer SAW one. Experimental results for a 128° rotated Y‐cut‐X propagation LiNbO3 plate and a glass plate are discussed. The layered structure leaky SAW transducer is useful for nondestructive evaluation of piezoelectric as well as nonpiezoelectric substrates.

Changes of surface-acoustic-wave velocity on z-cut LiTaO 3 substrate by proton exchange and post-exchange annealing

The velocity of leaky surface-acoustic-waves (LSAWs) on proton-exchanged and annealed proton-exchanged Z-cut LiTaO3 substrates was measured by line-focus-beam (LFB) acoustic microscopy. It is revealed that the LSAW velocity is decreased from 3220 to 3000 m/s by the proton exchange and that the post-exchange annealing gives some recovery to the decreased velocity.

Elastic properties of 5-mol % MgO doped LiNbO3 crystals measured by line focus beam acoustic microscopy

An ultrasonic method of line focus beam (LFB) acoustic microscopy is applied to quantitative characterization of LiNbO3 wafers destined for optical use. Commercial Z-cut wafers obtained from two optical grade LiNbO3 crystals, with and without 5-mol % MgO doping, are evaluated by measuring the leaky surface acoustic wave (LSAW) velocities. Doping of 5-mol % MgO to LiNbO3 results in an increase of about 1% in the LSAW velocities and in a decrease of about 0.1% in density. Fewer elastic inhomogeneities are observed in the undoped wafer than in the MgO doped wafer. The measured LSAW velocities are compared with the chemical and physical properties, chemical composition, density, lattice constant, refractive index, and Curie temperature. It is shown that the LFB system has a much greater sensitivity and resolution in the determination of these properties than do other analytical methods. It is suggested that this method should be adopted as a new analytical technique for establishment of the crystal growth conditions and for evaluation of optical grade LiNbO3 wafers.

Experimental and theoretical surface acoustic wave analysis of thin-film lipid multilayers

The leaky surface acoustic wave (LSAW) velocity of thin films of lipids on a glass substrate has been investigated, using a reflection acoustic microscope at a frequency of 1 GHz. Multilayers of ω-tricosenoic acid (28–220 nm in depth), collected with the Langmuir–Blodgett technique have been deposited on silanized glass. V(z) curves have been measured, and the LSAW velocity has been calculated from them. The results point out that the velocity decreases linearly as the lipid-layer thickness increases. A theory is also presented, which gives a linear dependence between the LSAW velocity and the layer thickness.

One GHz leaky SAW velocity of metal layers and bilayers evaporated onto fused quartz

An acoustic microscope operating at 1 GHz was used to determine the surface acoustic wave velocities v of thin film metal layers and metal bilayers deposited onto fused quartz. V(0)’s influence was reduced by gating. This produced a calibrated accuracy of 3%. A program was constructed from the explicitly solved 6×6 theoretical determinant. Single film thicknesses were decided upon by using this theory to produce a v equal to a standard. Since the single film v’s were linear with respect to their thickness, half the single film thicknesses were used for the bilayered films. The velocities for these bilayered films agreed with theory. This experimentally confirms the theoretical technique used here to examine bilayered systems, or a prototype composite interphase. No discrepancy was seen for gold films as others have reported. V(z) seemed insensitive to the formation of intermetallics or CuO. Some annealed and unannealed platinum films did not change the v from that of fused quartz. Two platinum films whose v’s were in agreement with theory peeled off with the tape test.

Characterization of LiNbO3 crystals by line-focus-beam acoustic microscopy

Line-focus-beam (LFB) acoustic microscopy is applied to quantitative characterization of piezoelectric LiNbO3 crystals to demonstrate the usefulness of this new analytical technique. Experimental relations between chemical composition ratios of Li/Nb and leaky surface acoustic wave (LSAW) velocities for 128°YX LiNbO3 wafers are determined. LSAW velocity measurements are carried out for commercial wafers obtained from a series of crystal growths. Small changes of 0.092% are detected due to the compositional variation. It is estimated that the ‘‘effective’’ congruent composition in the production line is 48.440 Li2O mol% with the density of 4647.4 kg/m3.

Characteristic features of leaky surface acoustic waves propagating on liquid/piezoelectric film glass structures

Particle displacement, electric potential distributions, velocity, and propagation loss for leaky surface acoustic waves (LSAWs) propagating on glycerine/ZnO or CdS film/Pyrex glass structures are studied theoretically and are compared with those of Rayleigh waves propagating on vacuum/ZnO or CdS/Pyrex glass structures. As a result it has been found, from the particle displacements, that the compressional waves are radiated into the liquid in the case of a LSAW. In particular, the power flow ratio in the liquid becomes nearly 100% when the ratio of the imaginary to the real part of the complex LSAW velocity becomes the same as that of the compressional wave. Such a phenomenon occurs for the glycerine/ZnO/Pyrex structure. On the other hand, a cut-off velocity exists for the glycerine/CdS/Pyrex structure, because the LSAW velocity lowers considerably with increasing CdS thickness, and approaches the compressional wave velocity of glycerine. The higher mode of LSAW is also found for the latter structure, and the difference between the higher and fundamental modes is discussed.

Quantitative evaluation of elastic properties of LiTaO3 crystals by line-focus-beam acoustic microscopy

The line-focus-beam acoustic microscope system is applied to investigate the elastic properties of LiTaO3. Elastic inhomogeneities are detected quantitatively as a significant variation of leaky surface acoustic wave (LSAW) velocities in X-112.2°Y LiTaO3 wafers. Large changes, about 2.5%, in LSAW velocities are observed in some wafers, which correspond to a difference between the velocities for single and multidomains. One of the causes is found to be in the poling process during wafer fabrication.

Ultrasonic imaging system using a leaky surface acoustic wave transducer composed of piezoelectric ceramic and fused quartz

An ultrasonic imaging system is described by using a leaky surface acoustic wave (SAW) transducer composed of a piezoelectric ceramic thin plate/interdigital transducer/fused quartz. It is shown, both numerically and experimentally, that three operation modes of the transducer at a water-solid interface are available. Each of the three modes has a different operation frequency range, corresponding to the leaky SAW velocity. The bulk wave in water as an acoustical coupler between the transducer and a tested object has a frequency-dependent angle relation; therefore, the acoustic beam steering is easily controlled and flexible in design. The reflection type of C-mode ultrasonic imaging results are demonstrated and are promising for nondestructive testing.

漏えいラム波用すだれ状トランスジューサの動作特性と漏えい表面波速度測定システム

漏えいラム波用すだれ状トランスジューサの動作特性と漏えい表面波速度測定システム

Precise Fabrication Technique of UHF SAW Al Electrodes and Leaky SAW Propagation Characteristics on 36° Y-X LiTaO3

Fabrication technique and leaky SAW (LSAW) propagation characteristics for GHz SAW filters are studied. Dyed photoresist and RIE are employed for fine dimension control of Al electrodes in these SAW filters and the deviation of the pattern width is remarkably decreased, for example, to a value of 110 nm (3σ) in a 0.6 µm line/space pattern. LSAW velocity dispersion and propagation loss on 36° Y-X LiTaO3 are also experimentally investigated. The results suggest requirement of some improvements in the substrates, the filter design and the fabrication technique.

Characterization of cladded glass fibers using acoustic microscopy

Spatial distribution profiles of leaky surface acoustic wave velocity (VLSAW ) and attenuation across the diameters of cladded glass fibers are presented. The profiles are obtained by using a novel V(x,z) analysis with a reflection scanning acoustic microscope operated at 775 MHz, and are compared with optical refractive index profiles. Optical fibers with different dopants and dopant concentrations have been investigated. The role of acoustic property profiles in the design of optical and acoustic fibers is outlined.