ACOUSTIC WAVE DEVICE

An acoustic wave device includes a support substrate, a low-acoustic-velocity film on the support substrate, a piezoelectric layer on the low-acoustic-velocity film, an IDT electrode on the piezoelectric layer, and a high-acoustic-velocity film between the support substrate and the low-acoustic-velocity film. An acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film is lower than an acoustic velocity of a bulk wave propagating through the piezoelectric layer. An acoustic velocity of a bulk wave propagating though the high-acoustic-velocity film is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer. Adhesion between the low-acoustic-velocity film and the support substrate is higher than adhesion between the high-acoustic-velocity film and the support substrate. The high-acoustic-velocity film is between portions of the support substrate and the low-acoustic-velocity film, and a portion of the low-acoustic-velocity film and a portion of the support substrate contact each other.