Izumi Takanaga

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.

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%).

Chemical composition dependences of the acoustical physical constants of LiNbO3 and LiTaO3 single crystals

We determined all the independent components of the acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of LiNbO3 and LiTaO3 crystals grown from the melts of three different starting materials with the Li2O contents set to 48.0, 48.5, and 49.0 mol %, and obtained the chemical composition dependences of the constants of each single crystal around the congruent composition. All the constants as well as the measured longitudinal, shear, and leaky surface acoustic wave (LSAW) velocities varied linearly with the composition ratios in the experimental range. The composition dependences of the LSAW velocities for the 128°YX-LiNbO3, X-112°Y-LiTaO3, and 36°YX-LiTaO3 substrates, previously obtained by line-focus-beam acoustic microscopy, were well matched with the calculated ones using the constants determined. Therefore the data of the composition dependences of the determined constants enable us to easily prepare the calibration lines for evaluating the cryst...

A method of determining acoustical physical constants for piezoelectric materials by line-focus-beam acoustic microscopy

We developed a new method of determining acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of piezoelectric materials with high accuracy. This method acquires velocities of leaky surface acoustic waves (LSAWs) excited on the water-loaded specimen surface, measured by line-focus-beam (LFB) acoustic microscopy, and bulk velocities of longitudinal and shear waves, measured with planewave transducers replacing the LFB device in the same system, together with the dielectric constants and density measured independently, for a small number of specimens. For LiNbO/sub 3/ and LiTaO/sub 3/ crystals, we demonstrated that we could accurately determine the constants by choosing proper propagation directions of LSAWs and bulk waves for three principal X-, Y-, and Z-cut specimens and one rotated Y-cut specimen [(104) plate for LiNbO/sub 3/ and (012) plate for LiTaO/sub 3/]. The accuracy is nearly the same as that for the constants determined only from the bulk wave velocities.

Elastic properties of single- and multi-domain crystals of LiTaO3

A basic study of the differences in elastic properties between single- and multi-domain crystals of LiTaO3 is conducted by measuring the longitudinal velocities for X-, Y-, and Z-cut specimens and the shear velocities for Z-cut specimens. Two sets of X-, Y-, and Z-cut specimens are prepared: one is for normal (single-domain) specimens and the other is for perfectly depoled (multi-domain) specimens. For the longitudinal wave propagation directions along the Y and Z axes, the velocities for the single-domain specimens, due to piezoelectricity, are 91.5 m/s (1.59%) and 92.7 m/s (1.50%) larger than those for the multi-domain specimens, respectively. On the other hand, for the X-axis longitudinal and Z-axis shear wave propagation directions, piezoelectricity is uncoupled, but the very interesting velocity changes are that the longitudinal and shear velocities for the single-domain specimens are 48.4 m/s (0.87%) and 135.6 m/s (3.79%) smaller than those for the multi-domain specimens, respectively. These differe...

Comparison of acoustic properties between natural and synthetic α-quartz crystals

Accurate measurements of bulk and leaky surface acoustic wave (LSAW) velocities of natural α-quartz crystal were carried out using the line-focus-beam and plane-wave ultrasonic material characterization systems and then these measured velocities were compared with the velocities of synthetic α-quartz crystals. Longitudinal velocities of principal X-, Y-, and Z-cut specimens; shear velocities with X-axis polarized particle displacements of the Y- and Z-cut specimens; and LSAW velocities for these three specimens were precisely measured. We found all the velocities for the bulk waves and the LSAWs of natural quartz to be slightly smaller (within 1.00 m/s) than the velocities of synthetic quartz. Therefore, the acoustical physical constants of the natural quartz are very similar to those of synthetic quartz we reported recently.

Elastic constants of multidomain LiTaO3 crystal

All the independent components of the elastic constant tensor of multidomain LiTaO3 crystal were determined by measuring bulk acoustic wave velocities and density for five multidomain LiTaO3 substrates perfectly depoled by heat treatment. Comparing these determined constants with the elastic constants of single-domain LiTaO3 crystal revealed that the elastic constants of multidomain crystal cij differ from both the elastic constants at constant electric field cijE and those at constant electric displacement cijD for single-domain crystal. The angular dependences of leaky surface acoustic wave velocity were measured on single and multidomain 36°Y-cut LiTaO3 substrates by line-focus-beam acoustic microscopy and compared with the calculated results using the determined constants. The measured results agreed well with the calculated results. The constants will be used to enhance theoretical understanding of the elastic properties of residual multidomains.

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.

Elastic properties of single‐ and multidomain crystals of LiTaO3

Ferroelectric single crystals of LiNbO3 and LiTaO3 are widely used as substrates for ultrasonic and optoelectronic devices. Obtaining homogeneity in elastic and optical properties of the crystals is one of the most important problems for wafer production. Recently, inhomogeneities of commercial wafers/crystals have been investigated with data of velocity changes obtained by line‐focus‐beam acoustic microscopy. The variations of the elastic properties are considered to be due primarily to chemical composition changes and secondarily to residual multidomains. In this paper, a fundamental study of the differences in elastic properties between single‐ and multidomain crystals of LiTaO3 is conducted by measuring the longitudinal velocities forX ‐, Y‐, and Z‐cut specimens and the shear velocities for Z‐cut specimens. Two sets of X‐, Y‐, and Z‐cut specimens are prepared: One is for normal (single‐domain) specimens and the other is for perfectly depoled (multidomain) specimens. For the longitudinal wave propagati...