Lithium tantalate single crystal substrate for a surface acoustic wave device and a device using the same, and a manufacturing method thereof and an inspection method thereof

A method for manufacturing a lithium tantalate single crystal substrate that is a rotated Y-cut LiTaO3 substrate whose crystal orientation has a Y-cut angle of not smaller than 36° and not larger than 49° and which has such a Li concentration profile after diffusion of Li into the LiTaO3 substrate from a surface thereof that the Li concentration at the surface of the LiTaO3 substrate differs from that inside the LiTaO3 substrate, the method comprising:

• applying an annealing treatment at 800-1000° C. to the LiTaO3 substrate after said Li diffusion treatment to thereby adjust a shear vertical type elastic wave whose main components are vibrations in the thickness direction and in the propagation direction and which is among those elastic waves which propagate in an X axis direction in a manner such that said shear vertical type elastic wave has an acoustic velocity of not lower than 3140 m/s and not higher than 3200 m/s.

A method for inspecting a lithium tantalate single crystal substrate that is a rotated Y-cut LiTaO3 substrate whose crystal orientation has a Y-cut angle of not smaller than 36° and not larger than 49° and which has such a Li concentration profile after diffusion of Li into the LiTaO3 substrate from a surface thereof that the Li concentration at the surface of the LiTaO3 substrate differs from that inside the LiTaO3 substrate, the method comprising:

• measuring an acoustic velocity of a shear vertical type elastic wave whose main components are vibrations in the thickness direction and in the propagation direction and which is among those elastic waves that propagate in an X axis direction within the surface of said rotated Y-cut LiTaO3 substrate, and
• determining whether or not the LiTaO3 substrate can be used as a surface acoustic wave device based on a result of said measurement.