Acoustic wave filter device and multiplexer

An acoustic wave filter device comprising:

• a piezoelectric layer;
• a high-acoustic-velocity member in which an acoustic velocity of bulk waves propagating therethrough is greater than an acoustic velocity of acoustic waves propagating through the piezoelectric layer;
• and
• a plurality of IDT electrodes on the piezoelectric layer and including a first IDT electrode and a second IDT electrode;
• wherein
• the high-acoustic-velocity member, the piezoelectric layer, and the plurality of IDT electrodes define a plurality of acoustic wave resonators;
• the plurality of acoustic wave resonators are provided in at least one series-arm resonator portion on a series arm connecting an antenna end and a signal end other than the antenna end, and in at least one parallel-arm resonator portion that is provided on a parallel arm connecting the series arm and a ground potential, and the series-arm resonator portion and the parallel arm resonator portion each include at least one acoustic wave resonator;
• at least one of the acoustic wave resonator of the series-arm resonator portion closest to the antenna end and the acoustic wave resonator of the parallel-arm resonator portion closest to the antenna end includes the first IDT electrode, and at least one acoustic wave resonator among one or more remaining acoustic wave resonators of the plurality of acoustic wave resonators includes the second IDT electrode;
• the first IDT electrode includes a first busbar and a second busbar facing each other, a plurality of first electrode fingers including first ends connected to the first busbar, and a plurality of second electrode fingers including first ends connected to the second busbar, the plurality of first electrode fingers and the plurality of second electrode fingers are interdigitated with each other, and a portion in which the first electrode fingers and the second electrode fingers overlap in an acoustic wave propagating direction is a crossing area;
• the crossing area includes a central area at a central portion in a direction orthogonal or substantially orthogonal to the acoustic wave propagating direction;
• a first low-acoustic-velocity area on a first busbar side of the central area and having an acoustic velocity less than an acoustic velocity in the central area, and a second low-acoustic-velocity area on a second busbar side of the central area and having an acoustic velocity less than the acoustic velocity in the central area are provided in the crossing area;
• in the first IDT electrode, a first high-acoustic-velocity area and a second high-acoustic-velocity area having an acoustic velocity greater than the acoustic velocity in the central area are provided, the first high-acoustic-velocity area is outside the first low-acoustic-velocity area in the direction orthogonal or substantially orthogonal to the acoustic wave propagating direction, and the second high-acoustic-velocity area is outside the second low-acoustic-velocity area in the direction orthogonal or substantially orthogonal to the acoustic wave propagating direction;
• the second IDT electrode includes a plurality of third electrode fingers and a plurality of fourth electrode fingers interdigitated with each other;
• and
• a first envelope which is a virtual line connecting tips of the plurality of third electrode fingers is inclined with respect to the acoustic wave propagating direction, and a second envelope which is a virtual line connecting tips of the plurality of fourth electrode fingers is inclined with respect to the acoustic wave propagating direction.