Disclosed herein are embodiments of a method of manufacturing film bulk acoustic wave resonators. The method comprises forming a sacrificial layer over a surface of a substrate to form a plurality of film bulk acoustic wave resonators on the surface of the substrate, forming a piezoelectric film on the surface of the substrate to cover the sacrificial layer, and removing the sacrificial layer to form an air gap between the surface of the substrate and the piezoelectric film that has covered the sacrificial layer, the air gap corresponding to each of the plurality of film bulk acoustic wave resonators. The step of forming the piezoelectric film includes controlling a concentration distribution of an additive added to the piezoelectric film across the surface of the substrate to suppress a variation of the acoustic velocity of the piezoelectric film depending on a position on the main surface of the substrate.

A method of manufacturing a piezoelectric resonator unit that includes preparing a piezoelectric resonator having a piezoelectric element, a pair of excitation electrodes respectively disposed on a first main surface and a second main surface of the piezoelectric element so as to face each other with the piezoelectric element therebetween, and a pair of connection electrodes that are respectively electrically connected to the pair of excitation electrodes; electrically connecting the pair of connection electrodes to a pair of electrode pads on a third main surface of a base member using an electroconductive holding member so as to excitably hold the piezoelectric resonator on the third main surface of the base member; and attaching an electroconductive material, which is scattered from an electroconductive member, to a surface of the electroconductive holding member.

A quartz crystal resonator unit that includes: a piezoelectric blank; a first excitation electrode on a first principal surface and within at least a part of a vibration portion of the piezoelectric blank; a second excitation electrode on a second principal surface and within at least a part of the vibration portion of the piezoelectric blank; a first extended electrode on the first principal surface and electrically connected to the first excitation electrode; and a second extended electrode on the second principal surface and electrically connected to the second excitation electrode; and an insulation layer including a hollow portion which defines a space with the second excitation electrode. A thickness of the first extended electrode is larger than a thickness of the second extended electrode. An end portion of the first extended electrode extends over the hollow portion in a plan view of the piezoelectric vibrator.

An elastic wave device includes a supporting substrate, an acoustic multilayer film on the supporting substrate, a piezoelectric substrate on the acoustic multilayer film, and an IDT electrode on the piezoelectric substrate. An absolute value of a thermal expansion coefficient of the piezoelectric substrate is larger than an absolute value of a thermal expansion coefficient of the supporting substrate. The acoustic multilayer film includes at least four acoustic impedance layers. The elastic wave device further includes a bonding layer provided at any position in a range of from inside the first acoustic impedance layer from the piezoelectric substrate side towards the supporting substrate side, to an interface between the third acoustic impedance layer and the fourth acoustic impedance layer.

An acoustic wave device includes a piezoelectric substrate that includes first and second main surfaces, an IDT electrode on the first main surface, a support having a rectangular or substantially rectangular frame shape and including a cavity, first and second sides, and a first corner portion connected to the first and second sides, and the support being provided on the first main surface such that the cavity surrounds the IDT electrode, and a cover on the support and covering the cavity. A straight or substantially straight grinding trace is provided on the second main surface. The grinding trace leads to the first corner portion as viewed in plan. One of an angle between the first side and the grinding trace and an angle between the second side and the grinding trace as viewed in plan is about 9.5° or less.

A method for manufacturing a ceramic substrate that includes forming a mother multilayer body by positioning a hole in at least one ceramic green sheet among a plurality of laminated ceramic green sheets in a location that does not overlap with a recess formation-planned region in which a recess is to be formed after firing of the mother multilayer body and that overlaps with a singulation-planned line for singulating the mother multilayer body into pieces after firing; and forming the recess in the mother multilayer body before firing by performing press working on the recess formation-planned region of the mother multilayer body.

Acoustic filters, resonators and methods are disclosed. An acoustic filter device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the 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 is formed on the front surface of the piezoelectric plate with interleaved fingers of the IDT disposed on the diaphragm. At least a portion of a perimeter of the cavity is curved, and the perimeter of the cavity is corner-less.

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.

A voltage sensor device includes an oscillator unit, the oscillator unit having a tunable bulk acoustic wave (BAW) resonator device and an oscillator core. The voltage sensor device also includes a frequency analyzer configured to obtain frequency measurements for the oscillator unit and to determine a voltage sense value based on a comparison of at least some of the obtained frequency measurements. The voltage sensor device also includes an output interface configured to store or output voltage sense values determined by the frequency analyzer.

An acoustic wave device includes a support including a support substrate, a piezoelectric layer extending in a first direction, which is a thickness direction of the support substrate, an IDT electrode provided in the first direction of the piezoelectric layer and including first and second busbars facing each other, first electrode fingers each including a base end connected to the first busbar, and second electrode fingers each including a base end connected to the second busbar, and a reinforcing film provided in the first direction of the piezoelectric layer. The support includes a cavity open to the piezoelectric layer side in the first direction, and the reinforcing film overlaps at least a portion of a boundary between a region where the piezoelectric layer and the cavity overlap and a region where the piezoelectric layer and the cavity do not overlap in a plan view in the first direction.