Acoustic wave device, radio-frequency front-end circuit, and communication apparatus

An acoustic wave device comprising:

• a high-acoustic-velocity material layer;
• a low-acoustic-velocity film provided on or above the high-acoustic-velocity material layer;
• a piezoelectric layer provided on or above the low-acoustic-velocity film;
• and
• an interdigital transducer (IDT) electrode provided on or above the piezoelectric layer;
• wherein
• an acoustic velocity of bulk waves propagating through the high-acoustic-velocity material layer is higher than an acoustic velocity of acoustic waves propagating through the piezoelectric layer;
• an acoustic velocity of bulk waves propagating through the low-acoustic-velocity film is lower than an acoustic velocity of bulk waves propagating through the piezoelectric layer;
• the low-acoustic-velocity film is made of a material including hydrogen atoms;
• and
• a hydrogen atom concentration of the low-acoustic-velocity film is greater than or equal to about 1.46×1021 atoms/cm3.