An acoustic wave device includes a piezoelectric layer and first and second electrodes. The piezoelectric layer is made of lithium niobate or lithium tantalate. The first electrode and the second electrode oppose each other in a direction intersecting with a thickness direction of the piezoelectric layer. The first electrode and the second electrode are electrodes adjacent to each other. d/p is about 0.5 or smaller, where d is a thickness of the piezoelectric layer and p is a center-to-center distance between the first electrode and the second electrode. An intersecting width is about 4.6p or greater. The intersecting width is a dimension of a region where the first electrode and the second electrode oppose each other. The direction of the dimension is an extending direction of the first electrode and the second electrode.

A crystal element includes a vibration part, a holding part, an electrode part, and a recess that corresponds to a recess and/or protrusion. The vibration part has a pair of vibration-part main surfaces. The holding part is formed integrally with the vibration part to be connected to an outer edge of vibration part and has a pair of holding-part main surfaces and holding-part side surfaces. The electrode part is provided at the vibration-part main surfaces. The recess is located at the holding-part side surfaces.

Acoustic resonators are disclosed. An acoustic resonator includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces. The back surface is attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate. The IDT includes: a first busbar and a second busbar disposed on respective portions of the piezoelectric plate other than the diaphragm; a first set of elongate fingers extending from the first bus bar onto the diaphragm; and a second set of elongate fingers extending from the second bus bar onto the diaphragm, the second set of elongate fingers interleaved with the first set of elongate fingers.

Bulk acoustic wave (BAW) resonators and particularly top electrodes with step arrangements for BAW resonators are disclosed. Top electrodes on piezoelectric layers are disclosed that include a border (BO) region with a dual-step arrangement where an inner step and an outer step are formed with increasing heights toward peripheral edges of the top electrode. Dielectric spacer layers may be provided between the outer steps and the piezoelectric layer. Passivation layers are disclosed that extend over the top electrode either to peripheral edges of the piezoelectric layer or that are inset from peripheral edges of the piezoelectric layer. Piezoelectric layers may be arranged with reduced thickness portions in areas that are uncovered by top electrodes. BAW resonators as disclosed herein are provided with high quality factors and suppression of spurious modes while also providing weakened BO modes that are shifted farther away from passbands of such BAW resonators.

Acoustic resonator devices, filters, and methods are disclosed. An acoustic resonator includes a substrate and a piezoelectric plate having front and back surfaces, the back surface attached to a surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The IDT is configured to excite a primary acoustic mode in the diaphragm in response to a radio frequency signal applied to the IDT. At least one finger of the IDT is disposed in a groove in the diaphragm. A depth of the groove is less than a thickness of the at least one finger of the IDT.

A piezoelectric structure is disclosed which includes a single crystal having piezoelectric coefficients d.sub.31 and d.sub.32 of opposite magnitude, such that when an alternating electric field is applied in the Z direction, the piezoelectric structure expands in one of the X and Y directions and contracts in the other of the X and Y direction, a first electrode coupled to the single crystal, and a second electrode coupled to the single crystal, wherein the alternating electric field is input to the single crystal through the first and second electrodes.

Provided is an acoustic resonator in a transverse excitation shear mode. The acoustic resonator comprises: an acoustic mirror (120), which comprises at least one first acoustic reflecting layer (121, 123, 125) and at least one second acoustic reflecting layer (122, 124), wherein the acoustic impedance of each first acoustic reflecting layer is less than that of each second acoustic reflecting layer; a piezoelectric layer (130), which is arranged on the acoustic mirror, and which comprises lithium niobate of a single crystal material and/or lithium tantalate of a single crystal material; electrode units (142, 143, 144), which are arranged on the piezoelectric layer (130) and are used for forming an electric field; and transverse reflectors (152, 154), which are arranged on the piezoelectric layer, are used for transversely reflecting acoustic waves, and can have a high electromechanical coupling coefficient and a high Q value at a frequency greater than 3 GHz.

Filter devices are disclosed. A filter device includes a piezoelectric plate comprising a supported portion, a first diaphragm, and a second diaphragm. The supported portion is attached to a substrate and the first and second diaphragms spans respective cavities in the substrate. A first interdigital transducer (IDT) has interleaved fingers on the first diaphragm. A second interdigital transducer (IDT) has interleaved fingers on the second diaphragm. A first dielectric layer is between the interleaved fingers of the first IDT, and a second dielectric layer is between the interleaved fingers of the second IDT. A thickness of the first dielectric layer is greater than a thickness of the second dielectric layer. The piezoelectric plate and the first and second IDTs are configured such that radio frequency signals applied to first and second IDTs excite primary shear acoustic modes in the respective diaphragms.

Piston mode Lamb wave resonators are disclosed. A piston mode Lamb wave resonator can include a piezoelectric layer, such as an aluminum nitride layer, and an interdigital transducer on the piezoelectric layer. The piston mode Lamb wave resonator has an active region and a border region, in which the border region has a velocity with a lower magnitude than a velocity of the active region. The border region can suppress a transverse mode.

A crystal unit includes a crystal element, excitation electrodes, and a container. The crystal element vibrates in a thickness-shear mode. The excitation electrodes are disposed on front and back surfaces of the crystal element. The crystal element is mounted to the container. The excitation electrodes are disposed on the crystal element. When a thickness of the crystal element is expressed as T, and a total thickness of the excitation electrodes disposed on the front and back surfaces of the crystal element is expressed as t, a ratio t/T is from 0.026 to 0.030.