Jun-ichi Kushibiki

Accurate measurements of the acoustical physical constants of LiNbO/sub 3/ and LiTaO/sub 3/ single crystals

The acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of commercial surface acoustic wave (SAW)-grade LiNbO/sub 3/ and LiTaO/sub 3/ single crystals were determined by measuring the bulk acoustic wave velocities, dielectric constants, and densities of many plate specimens prepared from the ingots. The maximum probable error in each constant was examined by considering the dependence of each constant on the measured acoustic velocities. By comparing the measured values of longitudinal velocities that were not used to determine the constants with the calculated values using the previously mentioned constants, we found that the differences between the measured and calculated values were 1 m/s or less for both LiNbO/sub 3/ and LiTaO/sub 3/ crystals. These results suggest that the acoustical physical constants determined in this paper can give the values of bulk acoustic wave velocities with four significant digits.

Development of the line-focus-beam ultrasonic material characterization system

A line-focus-beam ultrasonic material characterization (LFB-UMC) system has been developed to evaluate large diameter crystals and wafers currently used in electronic devices. The system enables highly accurate detection of slight changes in the physical and chemical properties in and among specimens. Material characterization proceeds by measuring the propagation characteristics, viz., phase velocity and attenuation, of Rayleigh-type leaky surface acoustic waves (LSAWs) excited on the water-loaded specimen surface. The measurement accuracy depends mainly upon the translation accuracy of the mechanical stages used in the system and the stability of the temperature environment. New precision mechanical translation stages have been developed, and the mechanical system, including the ultrasonic device and the specimen, has been installed in a temperature-controlled chamber to reduce thermal convection and conduction at the specimen. A method for precisely measuring temperature and longitudinal velocity in the water couplant has been developed, and a measurement procedure for precisely measuring the LSAW velocities has been completed, achieving greater relative accuracy to better than /spl plusmn/0.002% at any single chosen point and /spl plusmn/0.004% for two-dimensional measurements over a scanning area of a 200-mm diameter silicon single-crystal substrate. The system was developed to address various problems arising in science and industry associated with the development of materials and device fabrication processes.

Cut‐off characteristics of leaky Sezawa and pseudo‐Sezawa wave modes for thin‐film characterization

A new method of determining the elastic constants, density, and thickness of thin‐film materials with the line‐focus‐beam acoustic microscope is developed using propagation characteristics of leaky Sezawa and pseudo‐Sezawa waves in the neighborhood of the cut‐off region. It is demonstrated for a sample of gold film on fused quartz that the values of the stiffness constant, C44, and density are, respectively, about 11% and 5.5% less than those for polycrystalline bulk gold, and the thickness is determined as 6370 A.

Piezoelectric Properties of Ca3NbGa3Si2O14 Single Crystal

Langasite-type single crystal Ca3NbGa3Si2O14 (CNGS) was grown by the Czochralski technique. Dielectric, elastic and piezoelectric constants of CNGS were measured by the resonance-antiresonance method. At room temperature, dielectric constants e11T/e0 and e33T/e0 were 17.8 and 27.9, respectively. Electromechanical coupling coefficients k12, k25 and k26 were also determined as 10.9, 17.3 and 11.9%, respectively. The measurements were carried out in a temperature range from -30 to 80°C. Temperature coefficients of the dielectric, elastic and piezoelectric constants were obtained. The line-focus-beam and plane-wave ultrasonic material characterization system was employed for measuring bulk acoustic velocities, and longitudinal and transverse wave velocities of 7408.4 m/s and 3136.2 m/s, respectively, in the c-direction uncoupled with piezoelectricity at 23°C were obtained. This was in good agreement with the results determined by the resonance-antiresonance method. The density of CNGS was 4125 kg/m3. All the parameters of the CNGS crystal for bulk and surface acoustic wave applications were determined in this research.

Diffraction effects on bulk-wave ultrasonic velocity and attenuation measurements

The loss and phase advance due to diffraction are experimentally observed by measuring the amplitude and phase of radio frequency (rf) tone burst signals in the VHF range, in an ultrasonic transmission line consisting of a buffer rod with an ultrasonic transducer on one end, a couplant of water, and a solid specimen of synthetic silica glass. The measured results agree well with the calculated results from the exact integral expression of diffraction. The diffraction effects on the velocity and attenuation measured in this frequency range and their corrections are investigated to realize more accurate measurements. It is shown that attenuation measurements are influenced by diffraction losses and can be corrected by numerical calculations, and that velocity measurements are affected by the phase advance caused by diffraction. This investigation demonstrates that, in complex-mode velocity measurements, in which the velocity is determined from the measured phase of the signals, the true velocity at each frequency can be obtained by correction using the numerical calculation of diffraction. Based on this result, a new correction method in amplitude-mode velocity measurements is also proposed. In this new method, the velocity is determined from the intervals of interference output obtained by sweeping the ultrasonic frequency for the superposed signals generated by the double-pulse method. Velocity may be measured accurately at frequencies in the Fresnel region, and diffraction correction is essential to obtain highly accurate values with five significant figures or more.

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.

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 non piezoelectric single crystals (viz., gadolinium gallium garnet [GGG], Si, and Ge) and an isotropic solid (synthetic silica [SiO/sub 2/] 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/spl deg/C, and bulk wave velocities were obtained with an accuracy of within /spl plusmn/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 SiO/sub 2/ substrates produced by different manufacturers.

Accurate measurements of the acoustical physical constants of synthetic /spl alpha/-quartz for SAW devices

Accurate measurements of the acoustical physical constants (elastic constants, piezoelectric constants, dielectric constants, and density) of commercially available and widely used surface acoustic wave (SAW)-grade synthetic /spl alpha/-quartz are reported. The propagation directions and modes of bulk waves optimal for accurately determining the constants were selected through numerical calculations, and three principal X-, Y-, and Z-cut specimens and several rotated Y-cut specimens were prepared from a single crystal ingot to determine the constants and to confirm their accuracy. All of the constants were determined through highly accurate measurements of the longitudinal velocities, shear velocities, dielectric constants, and density. The velocity values measured for the specimens that were not used to determine the constants agreed well with those calculated from the determined constants, within a difference of /spl plusmn/0.20 m/s (/spl plusmn/0.004%).

Acoustic properties of selected bovine tissues in the frequency range 20-200 MHz.

The acoustic properties of freshly excised bovine liver, heart muscle, and fat are characterized in the frequency range 20-200 MHz by the bioultrasonic spectroscopy system using an ultrasonic transmission comparison method. Significant differences are obtained in the attenuation coefficient, velocity, impedance, and density among these tissues. Measurements of aqueous solutions of bovine hemoglobin are also reported in order to compare the contribution of the protein content to the acoustic properties. The differences among the acoustic properties of liver and heart muscle can be described in terms of their protein contents and other molecular constituents.

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 con...