An IDT electrode includes first and second busbar electrodes opposed to each other, first and second electrode fingers extending respectively from the first and second busbar electrodes on a piezoelectric substrate. The first busbar electrode and a tip end of the second electrode finger are opposed to each other with a gap therebetween, and bottom surfaces of the first and second busbar electrodes are opposed to each other with a first gap therebetween. The first and second busbar electrodes respectively include portions opposed to each other with a second gap shorter than the first gap therebetween on the top surface side. In a first area located between a first side surface and a second side surface, a second area located between the piezoelectric substrate and the first busbar electrode or the second electrode finger includes a hollow portion.

A multiplexer includes a common terminal, first and second transmit filters, and a first receive filter connected to the common terminal and each including resonators, a relationship Tx1c < Rx1c < Tx2c is satisfied, where Tx1c, Tx2c, and Rx1c denote center frequencies of pass bands Tx1, Tx2, and Tx3 of the first and second transmit filters and the first receive filter, respectively, a resonator closest to the common terminal in the first receive filter is a series arm resonator, and a pitch ratio denoted by pS1(Rx1)/p(Tx2) is more than about 1 and less than or equal to about 1.035, where p(Tx2) denotes an electrode finger pitch of an IDT electrode in a resonator closest to the common terminal in the second transmit filter and pS1(Rx1) denotes an electrode finger pitch of an IDT electrode of the series arm resonator closest to the common terminal in the first receive filter.

The strength of a spurious signal is reduced while maintaining the uniformity of a resonant frequency in an identical elastic wave resonator. An elastic wave resonator (4) includes a piezoelectric body (6), and a plurality of electrode fingers (14, 22) located on the piezoelectric body and arranged in a propagation direction (TD) of an elastic wave. A region in which the plurality of electrode fingers are located includes a first region (24A) and a second region (24B) in a plan view. The plurality of electrode fingers include a first electrode finger group (14A) located in the first region and a second electrode finger group (14B) located in the second region, and a pitch (PA) of the first electrode finger group is different from a pitch (PB) of the second electrode finger group. The first region and the second region have frequency effective-characteristics acting in a direction to cancel out effects on a higher resonant or antiresonant frequency and a lower resonant or antiresonant frequency brought about by a magnitude correlation between the pitches of the first and second electrode finger groups.

The strength of a spurious signal is reduced while maintaining the uniformity of a resonant frequency in an identical elastic wave resonator. An elastic wave resonator (4) includes a piezoelectric body (6), and a plurality of electrode fingers (14, 22) located on the piezoelectric body and arranged in a propagation direction (TD) of an elastic wave. A region in which the plurality of electrode fingers are located includes a first region (24A) and a second region (24B) in a plan view. The plurality of electrode fingers include a first electrode finger group (14A) located in the first region and a second electrode finger group (14B) located in the second region, and a pitch (PA) of the first electrode finger group is different from a pitch (PB) of the second electrode finger group. The first region and the second region have frequency effective-characteristics acting in a direction to cancel out effects on a higher resonant or antiresonant frequency and a lower resonant or antiresonant frequency brought about by a magnitude correlation between the pitches of the first and second electrode finger groups.

A filter device includes a first series line, one or more first parallel lines extending from the first series line, two or more first series IDT electrodes on the first series line, and one or more first parallel IDT electrodes on the one or more first parallel lines. At least one of the two or more first series IDT electrodes is a first-type electrode. A dielectric layer is between the first-type electrode and a substrate. At least one of the two or more first series IDT electrodes except the first-type electrode and the one or more first parallel IDT electrodes is a second-type electrode directly contacting the substrate. A first series IDT electrode of the two or more first series IDT electrodes that has a largest pitch of electrode fingers is the first-type electrode.

A filter device includes a first series line, one or more first parallel lines extending from the first series line, two or more first series IDT electrodes on the first series line, and one or more first parallel IDT electrodes on the one or more first parallel lines. At least one of the two or more first series IDT electrodes is a first-type electrode. A dielectric layer is between the first-type electrode and a substrate. At least one of the two or more first series IDT electrodes except the first-type electrode and the one or more first parallel IDT electrodes is a second-type electrode directly contacting the substrate. A first series IDT electrode of the two or more first series IDT electrodes that has a largest pitch of electrode fingers is the first-type electrode.

A surface acoustic wave resonator comprises a multi-layer piezoelectric substrate including a carrier substrate, a layer of a first dielectric material disposed on the carrier substrate, and a layer of piezoelectric material disposed on the layer of the first dielectric material, interdigital transducer electrodes disposed on the layer of piezoelectric material and including interleaved electrode fingers, and a layer of a second dielectric material disposed on a central interleaved region of the interleaved electrode fingers, gap regions of the interdigital transducer electrodes being either free of the layer of the second dielectric material or having a thinner layer of the second dielectric material than the central interleaved region to reduce spurious signals in an admittance curve of the surface acoustic wave resonator.

A surface acoustic wave resonator comprises a multi-layer piezoelectric substrate including a carrier substrate, a layer of a first dielectric material disposed on the carrier substrate, and a layer of piezoelectric material disposed on the layer of the first dielectric material, interdigital transducer electrodes disposed on the layer of piezoelectric material and including interleaved electrode fingers, and a layer of a second dielectric material disposed on a central interleaved region of the interleaved electrode fingers, gap regions of the interdigital transducer electrodes being either free of the layer of the second dielectric material or having a thinner layer of the second dielectric material than the central interleaved region to reduce spurious signals in an admittance curve of the surface acoustic wave resonator.

An acoustic wave device, a method of manufacture of the same, and a radio frequency filter including the same. The acoustic wave device comprises a multilayer piezoelectric substrate (MPS) including a layer of piezoelectric material having a lower surface disposed on an upper surface of a layer of a dielectric material having a lower surface disposed on an upper surface of a carrier substrate. An interdigital transducer (IDT) is disposed on the multilayer piezoelectric substrate and includes an active region configured to generate an acoustic wave. First and second high impedance portions are included within the multilayer piezoelectric substrate, the first and second high impedance portions each positioned outside the active region of the interdigital transducer and extending in the direction of propagation of the acoustic wave to be generated by the interdigital transducer. The first and second high impedance portions reduce side leakage and suppress transverse modes.

An acoustic wave device, a method of manufacture of the same, and a radio frequency filter including the same. The acoustic wave device comprises a multilayer piezoelectric substrate (MPS) including a layer of piezoelectric material having a lower surface disposed on an upper surface of a layer of a dielectric material having a lower surface disposed on an upper surface of a carrier substrate. An interdigital transducer (IDT) is disposed on the multilayer piezoelectric substrate and includes an active region configured to generate an acoustic wave. First and second high impedance portions are included within the multilayer piezoelectric substrate, the first and second high impedance portions each positioned outside the active region of the interdigital transducer and extending in the direction of propagation of the acoustic wave to be generated by the interdigital transducer. The first and second high impedance portions reduce side leakage and suppress transverse modes.