Makoto Kumatoriya

Properties of Leaky, Leaky Pseudo, and Rayleigh Surface Acoustic Waves on Various Rotated Y-cut Langasite Crystal Substrates

A leaky surface acoustic wave (LSAW) and a leaky pseudo SAW (LPSAW) of various rotated Y-cut langasite substrates grown by the Czochralski method were measured by an ultrasonic microscope. The measured results agreed well with the values calculated using Ilyaeves material constants of five kinds of material. Rayleigh SAW transversal filters, having various aluminum (Al) thicknesses of interdigital transducers (IDT), were constituted on (0°, 140–150°, 24–25°) and (12°, 150–153°, 36–37°) plates. A temperature coefficient of frequency (TCF) of the Rayleigh SAW filters was measured by measuring their center frequency. It was clarified that (0°, 142°, 24.5°) and (0°, 143°, 24°) plates at normalized Al-IDT thickness (HAl/λ) 0.0125, and (12°, 153°, 37°) plates at HAl/λ = 0.0625 showed turnover temperatures of 25°C, 30°C and 28°C and excellent TCFs (ΔF/F/°C = 1.83, 1.63, and 1.95 ppm/°C). Measured results of electromechanical coupling factor on their substrates showed similar values (ks2 = 0.41, 0.42 and 0.46%) to the theoretical ones. The (12°, 153°, 37°) plate having the largest coupling factor is the most suitable one for SAW devices. Furthermore, the velocity, the coupling factor, and the propagation loss of LSAW on air/various Y-X langasite plates (0°, θ, 0°) were also calculated.

Crystal growth and electromechanical properties of Al substituted langasite (La3Ga5−xAlxSiO14)

Al-substituted langasite (La 3 Ga 5-x Al x SiO 14 ) single crystals up to x = 0.9 have been grown by the Czochralski method. The effective segregation coefficient (k eff ) of Al in langasite was estimated to be between 1.03 and 1.07. X-ray structural analysis indicated that Al occupied the octahedral and the two kinds of tetrahedral sites in the crystal lattice. The piezoelectricity of Al-substituted langasite was also compared with that of langasite. By Al substitution, while the piezoelectric constant |d 11 | became slightly larger, d 14 was smaller. The electromechanical coupling factors (k 12 , k 25 and k 26 ) became larger. It was found that Al substitution of langasite created a material with preferred electromechanical properties applicable to the next generation of advanced digital communication systems.

Effect of aluminum substitution in La3Ga5SiO14 crystals on their structure and piezoelectricity

We report La3Ga5−xAlxSiO14 (0⩽x⩽1) crystals, with a Ca3Ga2Ge4O14-type structure, suitable for piezoelectric application. A single-crystal x-ray structure analysis reveals that Al atoms are distributed in all cation sites except for the decahedral one occupied by La, by rather favoring the smallest tetrahedral one. The piezoelectric modulus |d11| increased ∼1.3% and d14 decreased ∼7.7% with the increasing Al content, x, up to 1.0. We discuss the possible correlation between the atomic displacement and the observed compositional dependence of the piezoelectric modulus |d11| by referring to other isomorphs. The optimal solid-solution compositions and the use of Al substitution for obtaining the maximum electromechanical coupling factors (k12, k25, and k26) are advanced.

Czochralski growth of Sr3Ga2Ge4O14 single crystals for piezoelectric applications

Abstract Single crystals of strontium gallogemanate (Sr 3 Ga 2 Ge 4 O 14 ) with langasite structure were successfully grown by Czochralski technique for the piezoelectric applications. The largest crystal had 90 mm in length and 22 mm in diameter. The optimal growth conditions were investigated. The composition of crystal and the values of lattice parameters were measured. The superior piezoelectric properties of Sr 3 Ga 2 Ge 4 O 14 crystals were determined.

Surface acoustic wave properties on various rotated Y-cut langasite crystal substrates grown by Czochralski method

A langasite crystal has been paid to much attention as a substrate for surface acoustic wave (SAW) devices recently, because it has a larger electromechanical coupling factor (k/sub s/) than quartz and an excellent temperature coefficient of frequency (TCF) similar to quartz. A leaky SAW (LSAW) and a leaky pseudo SAW (LPSAW) of the various rotated Y cut langasite substrates grown by the Czochralski method were measured by an ultrasonic microscope. The measured results were compared with the theoretical values calculated by five kinds of material constants. The TCFs of Rayleigh SAW filters having various Al thickness of interdigital transducer (IDT) on various rotated Y plates were measured. It was clarified that (0/spl deg/, 142/spl deg/, 24.5/spl deg/) and (0/spl deg/, 143/spl deg/, 24/spl deg/) substrates showed turnover temperatures of 25/spl deg/C and 30/spl deg/C, and more excellent TCFs (1.83 and 1.63 ppm//spl deg/C) at normalized Al-IDT thickness 0.0125 compared with ones reported until now. Measured results of electromechanical coupling factor on their substrates showed almost equal values to theoretical ones.

Control of the facet plane formation on solid–liquid interface of LGS

Abstract The correlation of the facet plane that formed on the solid–liquid interface of Langasite (La 3 Ga 5 SiO 14 ) single crystals grown by the Czochralski method with its growth conditions was investigated. The crystal homogeneity was characterized by measuring leaky-surface acoustic wave velocity and X-ray topography. In [ 0 0 0 1 ] growth, ( 1 0 1 0 ) and ( 0 0 0 1 ) facets were formed at the solid–liquid interface. The former often causes an alteration growth in its conical part, and the latter generate a core dislocation that deteriorates the crystal homogeneity. We were able to reduce these crystal defects by controlling the growth conditions, such as the temperature gradient at the melt surface along the radial direction ( T g ) or the crystal-rotation rate ( R c ). When T g became higher, the alteration caused by nucleation in a super-cooling melt in contact with a ( 1 0 1 0 ) facet was reduced. Controlling R c enabled core dislocations to be reduced.

Characterization of Structures Induced in LiTaO3 by Femtosecond Laser Pulses

Optical waveguides were successfully fabricated by femtosecond laser direct writing inside a LiTaO3 crystal, and the optical properties of these waveguides were investigated. Optimum writing conditions such as pulse energy and duration were determined on the basis of the refractive index changes calculated using the near-field pattern of the light guided through the waveguides. μ-Raman spectroscopy results and birefringence observations around the formed waveguides suggested that the local increase in refractive index was caused by anisotropic compressive stress in the laser-irradiated region. The light guided through the formed waveguide showed strong polarization dependence.