Longitudinally coupled resonator acoustic wave filter and filter device

A longitudinally coupled resonator acoustic wave filter, comprising:

• a piezoelectric substrate;
• a plurality of IDT electrodes on the piezoelectric substrate and arranged along an acoustic wave propagation direction;
• and
• a pair of reflectors on the piezoelectric substrate on both sides of the plurality of IDT electrodes in the acoustic wave propagation direction;
• wherein
• each of the pair of reflectors includes a first reflector busbar and a second reflector busbar facing each other and a plurality of reflective electrode fingers connected to at least one of the first reflector busbar and the second reflector busbar;
• each of the pair of reflectors includes a first portion in which lengths of the plurality of reflective electrode fingers change in the acoustic wave propagation direction;
• each of the plurality of IDT electrodes includes a first busbar and a second busbar facing each other, a plurality of first electrode fingers each including one end connected to the first busbar, and a plurality of second electrode fingers each including one end connected to the second busbar and interdigitating with the plurality of first electrode fingers;
• a portion at which the first electrode finger and the second electrode finger overlap each other in the acoustic wave propagation direction is an intersecting region, and the intersecting region includes a center region in a central portion of the intersecting region in a direction orthogonal or substantially orthogonal to the acoustic wave propagation direction, a first edge region on a side of the center region toward the first busbar, and a second edge region on a side of the center region toward the second busbar;
• the plurality of IDT electrodes include a first gap region between the first edge region and the first busbar and a second gap region between the second edge region and the second busbar;
• a low acoustic velocity region having an acoustic velocity lower than an acoustic velocity in the center region is included in each of the first edge region and the second edge region;
• and
• the plurality of reflective electrode fingers in the first portion of each of the pair of reflectors overlap the center region of each of the plurality of IDT electrodes and do not overlap the first edge region or the second edge region when viewed in the acoustic wave propagation direction.

A longitudinally coupled resonator acoustic wave filter, comprising:

• a piezoelectric substrate;
• a plurality of IDT electrodes on the piezoelectric substrate and arranged along an acoustic wave propagation direction;
• and
• a pair of reflectors on the piezoelectric substrate on both sides of the plurality of IDT electrodes in the acoustic wave propagation direction;
• wherein
• each of the pair of reflectors includes a first reflector busbar and a second reflector busbar facing each other and a plurality of reflective electrode fingers connected to at least one of the first reflector busbar and the second reflector busbar;
• each of the pair of reflectors includes a first portion in which lengths of the plurality of reflective electrode fingers change in the acoustic wave propagation direction;
• each of the plurality of IDT electrodes includes a first busbar and a second busbar facing each other, a plurality of first electrode fingers each including one end connected to the first busbar, and a plurality of second electrode fingers each including one end connected to the second busbar and interdigitating with the plurality of first electrode fingers;
• a portion at which the first electrode finger and the second electrode finger overlap each other in the acoustic wave propagation direction is an intersecting region, and the intersecting region includes a center region in a central portion of the intersecting region in a direction orthogonal or substantially orthogonal to the acoustic wave propagation direction, a first edge region on a side of the center region toward the first busbar, and a second edge region on a side of the center region toward the second busbar;
• the plurality of IDT electrodes include a first gap region between the first edge region and the first busbar and a second gap region between the second edge region and the second busbar;
• a low acoustic velocity region having an acoustic velocity lower than an acoustic velocity in the center region is included in each of the first edge region and the second edge region;
• each of the first busbar and the second busbar of each of the plurality of IDT electrodes includes a cavity formation region in which a plurality of cavities are provided along the acoustic wave propagation direction;
• a high acoustic velocity region having an acoustic velocity higher than an acoustic velocity in the center region is included in each of the cavity formation regions;
• and
• the plurality of reflective electrode fingers in the first portion of each of the pair of reflectors overlap the center region of each of the plurality of IDT electrodes when viewed in the acoustic wave propagation direction, at least a reflective electrode finger of the plurality of reflective electrode fingers closest to a side of the plurality of IDT electrodes in the first portion extends so as to overlap both of the first gap region and the second gap region, and none of the plurality of reflective electrode fingers overlaps the cavity formation region when viewed in the acoustic wave propagation direction.