Acoustic wave device

An acoustic wave device comprising:

• a piezoelectric substrate with a reverse velocity surface having an elliptic shape;
• an interdigital transducer electrode disposed on or above the piezoelectric substrate;
• and
• a dielectric film disposed on the piezoelectric substrate to cover the interdigital transducer electrode, the acoustic wave device utilizing a Rayleigh wave;
• wherein
• the interdigital transducer electrode includes first electrode fingers and second electrode fingers interdigitated with the first electrode fingers, and where a direction perpendicular or substantially perpendicular to an extension direction of the first electrode fingers and the second electrode fingers is a propagation direction of an acoustic wave, a region in which the first electrode fingers and the second electrode fingers overlap with each other when viewed from the propagation direction of the acoustic wave is an intersecting region, the extension direction of the first and second electrode fingers is an intersecting width direction, and an electrode density (%) of the interdigital transducer electrode is denoted by y (%) and a wavelength-normalized film thickness 100 h/λ (%) of the interdigital transducer electrode, where h denotes a thickness and λ denotes a wavelength determined by an electrode finger pitch of the interdigital transducer electrode, is denoted by x (%), the wavelength-normalized film thickness x of the interdigital transducer electrode has a value not less than x satisfying y=0.3452x2−6.0964x+36.262 depending on the electrode density y of the interdigital transducer electrode;
• the intersecting region of the interdigital transducer electrode includes a central region positioned at a center portion in the intersecting width direction and a first edge region and a second edge region positioned respectively on one outer side and another outer side of the central region in the intersecting width direction;
• and
• a film thickness of the dielectric film in each of the first edge region and the second edge region is thinner than a film thickness of the dielectric film in the central region.