Composite substrate, elastic wave device using the same, and method for manufacturing composite substrate

A composite substrate comprising:

• a piezoelectric substrate which has an anisotropy and which is capable of transmitting an elastic wave;
• and a support substrate which has an anisotropy and a smaller thermal expansion coefficient than that of the piezoelectric substrate and which is bonded thereto,
• wherein an in-plane maximum thermal strain amount which is the largest thermal strain amount in the plane of the composite substrate has a minimum value and a maximum value when the piezoelectric substrate and the support substrate are relatively rotated 0° to 360°, and the piezoelectric substrate and the support substrate are bonded to each other so that the in-plane maximum thermal strain amount is in the range of from the minimum value to a value obtained by reducing the maximum value by 10%.

A manufacturing method of a composite substrate comprising the step of bonding a piezoelectric substrate which has an anisotropy and which is capable of transmitting an elastic wave to a support substrate which has an anisotropy and a smaller thermal expansion coefficient than that of the piezoelectric substrate,

• wherein an in-plane maximum thermal strain amount which is the largest thermal strain amount in the plane of the composite substrate has a minimum value and a maximum value when the piezoelectric substrate and the support substrate are relatively rotated 0° to 360°, and the method bonds the piezoelectric substrate and the support substrate to each other so that the in-plane maximum thermal strain amount has the minimum value or a value in the vicinity thereof.