Acoustic wave device

An acoustic wave device comprising:

• a support substrate;
• a piezoelectric layer including first and second major surfaces that oppose each other, with the second major surface extending in a first direction with respect to the first major surface;
• at least one pair of functional electrodes that face each other in a second direction that intersects the first direction and that are adjacent to each other on one of the first and second major surfaces;
• and
• a space defining either a cavity in the support substrate or an air gap between the support substrate and the piezoelectric layer,
• wherein the space overlaps with at least a portion of the at least one pair of functional electrodes in a planar view in the first direction, and
• wherein a value of half a difference between a maximum length of a bottom surface of one of the at least one pair of functional electrodes in the second direction and a maximum length of a top surface of the one of the at least one pair of functional electrodes in the second direction is equal to or more than about 0.2% of a thickness of the piezoelectric layer from the first major surface to the space, and is equal to or less than a thickness of the one of the at least one pair of functional electrodes in the first direction.