Acoustic wave device, filter, multiplexer, and method of manufacturing acoustic wave device

An acoustic wave device comprising:

• a substrate;
• a lower electrode provided above the substrate;
• an upper electrode provided above the lower electrode;
• a piezoelectric layer provided above the substrate with at least a part of the piezoelectric layer interposed between the lower electrode and the upper electrode, the piezoelectric layer having a through hole along a resonance region where the lower electrode and the upper electrode overlap with each other with the at least a part of the piezoelectric layer interposed therebetween in planar view, the through hole exposing at least a part of the lower electrode;
• an insertion film provided either or both of between the lower electrode and the piezoelectric layer and between the upper electrode and the piezoelectric layer, the insertion film having a resistivity higher than resistivities of the lower electrode and the upper electrode;
• a first film in contact with, and extending upward from, a side surface of the lower electrode to a side of a side surface of the upper electrode, the first film containing a constituent element of the lower electrode;
• a second film in contact with, and extending upward from, a side surface of the piezoelectric layer to a region between the side surface of the upper electrode and the first film, the second film having a concentration of a constituent element of the piezoelectric layer higher than that of the first film;
• and
• a third film in contact with, and extending upward from, a side surface of the insertion film so as to extend to at least one of a region between the side surface of the upper electrode and the second film and a region between the first film and the second film, wherein a concentration of a first element of the third film, which is a constituent element of the insertion film and different from a constituent element of the piezoelectric layer, is higher than that of the second film, and a concentration of a second element of the third film, which is the constituent element of the piezoelectric layer and different from the constituent element of the insertion film, is lower than that of the second film.