LITHIUM TANTALATE SINGLE CRYSTAL SUBSTRATE FOR SURFACE ACOUSTIC WAVE ELEMENTS, DEVICE USING SAME AND PRODUCTION METHOD AND INSPECTION METHOD THEREFOR

摘要

[Problem] To provide a lithium tantalate single crystal substrate for surface acoustic wave elements, said lithium tantalate single crystal substrate having a smaller temperature characteristic than conventional rotated Y-cut LiTaO3 substrates and allowing appropriate adjustment of the electromechanical coupling coefficient thereof so as to fit for the band of a cellular phone, and a method for producing the lithium tantalate single crystal substrate. [Solution] A lithium tantalate single crystal substrate having a concentration profile wherein Li is diffused inward from the surface of a rotated Y-cut LiTaO3 substrate with 36°-49° rotated Y-cut crystal orientation so that the Li concentration on the substrate surface differs from the Li concentration inside the substrate, characterized in that the acoustic velocity of a shear vertical-type acoustic wave comprising the vibrations in the thickness direction and propagation direction as main components, from among acoustic waves propagating in the X-axial direction on the surface of the LiTaO3 substrate, is 3140-3200 m/s inclusive. A method for producing the lithium tantalate single crystal substrate characterized by comprising adjusting the acoustic velocity of the shear vertical-type acoustic wave to 3140-3200 m/s inclusive by performing annealing at 800-1000°C.