[PROBLEM TO BE SOLVED] To provide a bulk wave resonator having a high frequency passband.

[SOLUTION] A bulk wave resonator using a bulk wave, includes a support substrate, an acoustic multilayer film that includes, stacked on the support substrate, a plurality of types of dielectrics having different acoustic impedances, a piezoelectric layer that is stacked on the acoustic multilayer film, a first electrode, and a second electrode. The first and second electrodes are disposed to face each other with a gap therebetween on a first surface of the piezoelectric layer opposite to the acoustic multilayer film, and are applied with a voltage for allowing the piezoelectric layer to generate the bulk wave. A direction that is parallel to the surface of the piezoelectric layer and in which the first electrode and the second electrode face each other is defined as a first direction. The bulk wave resonator uses, as a main mode, a bulk wave in the first direction that is generated by a thickness shear vibration in the first direction, which is excited by a parallel electric field formed in the piezoelectric layer when a voltage applied to the first electrode and the second electrode.

Acoustic resonators, acoustic filter devices and methods of making the same. An acoustic resonator device includes a piezoelectric plate having front and back surfaces, an interdigital transducer (IDT) on the front surface including interleaved fingers, an overlapping distance of the interleaved fingers defining an aperture of the acoustic resonator device, and a modified acoustic velocity region proximate an edge of the aperture.

Filters and methods of making filters are disclosed. A filter device includes a substrate, a piezoelectric plate, and an acoustic Bragg reflector between a surface of the substrate and a back surface of the piezoelectric plate. A conductor pattern on a front surface of the piezoelectric plate includes interdigital transducers (IDTs) of a plurality of resonators and a plurality of conductors to connect the plurality of resonators in a ladder filter circuit, the plurality of conductors including adjacent first and second conductors. A portion of the piezoelectric plate between the first and second conductors is removed.

A quartz crystal resonator unit includes a quartz crystal resonator that includes a quartz crystal blank. A pair of excitation electrodes are disposed on opposed main surfaces of the quartz crystal blank so as to face each other. A pair of connection electrodes are electrically connected to respective ones of the pair of excitation electrodes. A base member has a surface on which the quartz crystal resonator is mounted. A lid member is joined to the surface of the base member via a joining member. The quartz crystal resonator is accommodated in an inner space defined by the lid member and the base member on the surface of the base member. Parts of the joining member that cover protruding portions are in contact with a side wall of the lid member so as to restrain movement of the lid member when seen in a plan view in a direction normal to the surface of the base member.

An acoustic wave device includes a support substrate, a dielectric film, a piezoelectric layer, and an excitation electrode. The piezoelectric layer includes first and second main surfaces. The second main surface is on a side including the dielectric film. A cavity portion is provided in the dielectric film and overlaps at least a portion of the excitation electrode in plan view. The dielectric film includes a side wall surface facing the cavity portion and including an inclined portion inclined so that a width of the cavity portion decreases with increasing distance away from the piezoelectric layer. The inclined portion includes at least an end portion on a side including the piezoelectric layer, in the side wall surface. When an angle between the inclined portion and the second main surface of the piezoelectric layer is defined as an inclination angle α, the inclination angle α is from about 40° to about 80° inclusive.

Disclosed is a Bulk Acoustic Wave (BAW) filter structure with a conductive bridge forming an electrical loop with an electrode for reduced electrical losses. In exemplary aspects disclosed herein, the BAW filter structure includes a transducer with electrodes, a piezoelectric layer between the electrodes, and at least one conductive bridge offset from at least a portion of one of the electrodes by an insulating volume. The conductive bridge forms a first electrical loop between a medial end and a distal end of the electrode. Such a configuration reduces electrical resistance, heat resistance, and/or ohmic losses for improved electrical loss of the BAW filter structure.

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.

An acoustic wave device includes a high-acoustic-velocity layer, a piezoelectric layer made of lithium tantalate, and an interdigital transducer electrode that are successively laminated. An acoustic velocity of a bulk wave propagating in the high-acoustic-velocity layer is higher than an acoustic velocity of an acoustic wave propagating in the piezoelectric layer, and an acoustic velocity Vsub of a fast transversal bulk wave propagating in the high-acoustic-velocity layer satisfies Vsh0≤Vsub≤Vsp with respect to an acoustic velocity Vsh0 of an SH0 mode and an acoustic velocity Vsp of a mode becoming a spurious of which acoustic velocity is not lower than the acoustic velocity of the SH0 mode, wherein the acoustic velocity Vsh0 and the acoustic velocity Vsp is obtained from Eq. (1).

A filter device having a pass band and a stop band on a lower frequency side than the pass band includes a filter having a pass band including the pass band, a series arm resonator connected in series to the filter, a first inductor directly connected in series to the series arm resonator, and a parallel arm resonator connected between a node on a path connecting the filter and the series arm resonator and the ground. The parallel arm resonator constitutes a resonance circuit having a resonant frequency at which an attenuation pole corresponding to a high frequency end of the first stop band, and the series arm resonator and the inductor constitute a resonance circuit having an anti-resonant frequency on a lower frequency side than the pass band and having a sub-resonant frequency higher than a resonant frequency of the resonance circuit.

Methods of designing a BAW resonator and filter and the resulting devices are provided. Embodiments include patterning a bottom electrode of a resonator; patterning a top electrode of the resonator; and intersecting areas of the top and bottom electrodes to provide an effective area of the resonator, wherein the effective area includes a closed-loop contour line including a pulse function pattern with pre-defined amplitude, period and a number of repetitions of pulses along the closed-loop contour line.