Acoustic wave device

An acoustic wave device, comprising:

• a piezoelectric substrate;
• an interdigital transducer (IDT) electrode on the piezoelectric substrate and including a plurality of electrode fingers;
• and
• a first reflector and a second reflector on the piezoelectric substrate on both sides of the IDT electrode in an acoustic-wave propagation direction;
• wherein
• a portion of the IDT electrode at which each two of the plurality of electrode fingers adjacent to each other overlap in the acoustic-wave propagation direction defines an intersecting area, and the intersecting area includes a center area at or around a center portion in a direction in which the plurality of electrode fingers extend, and a pair of edge areas on both sides of the center area in the direction in which the plurality of electrode fingers extend;
• areas including the pair of edge areas and overlapping the pair of edge areas in the acoustic-wave propagation direction define a pair of expansion edge areas;
• a pair of acoustic-velocity adjusters are provided in the pair of expansion edge areas, and an acoustic velocity in the pair of acoustic-velocity adjusters is lower than an acoustic velocity in the center area;
• one acoustic-velocity adjuster of the pair of acoustic-velocity adjusters includes a first end portion located closer to the first reflector and a second end portion located closer to the second reflector, and another acoustic-velocity adjuster of the pair of acoustic-velocity adjusters includes a third end portion located closer to the first reflector and a fourth end portion located closer to the second reflector;
• the first end portion, the second end portion, the third end portion, and the fourth end portion are located at outer sides of the pair of edge areas in the acoustic-wave propagation direction;
• end portions in at least one of two pairs including a pair of the first end portion and the third end portion and a pair of the second end portion and the fourth end portion do not overlap each other in the direction in which the plurality of electrode fingers extend;
• the pair of acoustic-velocity adjusters extend to outer sides of the first reflector and the second reflector in the acoustic-wave propagation direction;
• a direction in which the pair of acoustic-velocity adjusters extend and the acoustic-wave propagation direction are parallel or substantially parallel to each other;
• and
• the pair of acoustic-velocity adjusters are each defined by a mass loading film.