A bulk acoustic wave (BAW) device comprises a layer stack including first and second electrodes, a first piezoelectric layer between the electrodes, and a second piezoelectric layer between the first piezoelectric layer and the second electrode. A polarization of a crystal structure of the second piezoelectric layer is opposite to a polarization of a crystal structure of the first piezoelectric layer to achieve higher order resonant frequencies in the BAW device by means other than merely thinning layers in the layer stack. In some examples, the BAW device is a two-terminal device and does not include a metal layer configured to be a third electrode. In some examples, the BAW device includes at least one intermediate layer between the first and second piezoelectric layers, and a total combined thickness of the at least one intermediate layer is less than 4% of a total thickness of the layer stack.

A frequency-tunable film bulk acoustic resonator and a preparation method therefor are provided. The resonator includes a substrate, an air gap, a sandwiched structure formed by electrodes and piezoelectric layers, and an electrode lead-out layer, wherein the substrate is connected to the sandwiched structure formed by the electrodes and the piezoelectric layers, and a connection face of the substrate and the sandwiched structure formed by the electrodes and the piezoelectric layers is recessed towards inside of the substrate to form the air gap; and the electrode lead-out layer is connected to the sandwiched structure formed by the electrodes and the piezoelectric layers. The sandwiched structure formed by the electrodes and the piezoelectric layers includes a bottom electrode, piezoelectric layers, intermediate electrodes, and a top electrode, wherein the electrodes and the piezoelectric layers are alternately arranged to form the sandwiched structure.

A resonator including a vibration structure, a first electrode, and a second electrode is provided. The vibration structure includes a vibration region, a protrusion portion, an opening, and a frame portion. The vibration region has a first surface and a second surface opposite to the first surface. The protrusion portion surrounds the vibration region. The opening is disposed at a side of the vibration region and between the vibration region and the protrusion portion. The opening has a first side adjacent to the vibration region and a second side far away from the vibration region. The second side is opposite to the first side. A length of the first side is greater than a length of the second side. The frame portion surrounds the protrusion portion. The first electrode is disposed on the first surface. The second electrode is disposed on the second surface.

A filter device includes a longitudinally coupled resonator elastic wave filter that includes IDT electrodes including low acoustic velocity regions in outer side portions of center regions of the IDT electrodes and high acoustic velocity regions in outer side portions of the low acoustic velocity regions in a direction orthogonal or substantially orthogonal to an elastic wave propagation direction, and defines and functions as a first bandpass filter, and elastic wave resonators that are electrically connected to the longitudinally coupled resonator elastic wave filter.

A crystal oscillator (101) includes: a piezoelectric resonator plate (2) on which a first excitation electrode and a second excitation electrode are formed; a first sealing member (3) covering the first excitation electrode of the piezoelectric resonator plate (2); a second sealing member (4) covering the second excitation electrode of the piezoelectric resonator plate (2); and an internal space (13) formed by bonding the first sealing member (3) to the piezoelectric resonator plate (2) and by bonding the second sealing member (4) to the piezoelectric resonator plate (2), so as to hermetically seal a vibrating part including the first excitation electrode and the second excitation electrode of the piezoelectric resonator plate (2). An electrode pattern (371) including a mounting pad for wire bonding is formed on an outer surface (first main surface (311)) of the first sealing member (3).

An elastic wave device includes a piezoelectric film and a high acoustic velocity member in which an acoustic velocity of a bulk wave propagating in the high acoustic velocity member is larger than an acoustic velocity of a main mode elastic wave propagating in the piezoelectric film, the piezoelectric film that is directly or indirectly laminated on the high acoustic velocity member, a first conductive film provided on the piezoelectric film, and a second conductive film that is provided on the piezoelectric film and on at least a portion of the first conductive film. A plurality of IDT electrodes including electrode fingers and busbars are provided on the piezoelectric film, at least electrode fingers of a plurality of IDT electrodes are defined by the first conductive film, and at least a portion of connection wiring with which the plurality of IDT electrodes are connected to each other is defined the second conductive film.

A micro-electro-mechanical system (MEMS) device includes a substrate having a cavity and a MEMS structure disposed over the cavity and attached to the substrate. The MEMS structure includes at least one first piezoelectric layer having a first piezoelectric coefficient and two second piezoelectric layers respectively disposed under and above the first piezoelectric layer, where each second piezoelectric layer has a second piezoelectric coefficient higher than the first piezoelectric coefficient. The MEMS structure further includes a first electrode layer and a second electrode layer sandwiching the two second piezoelectric layers.

A vibrator, a vibrating element and a method for producing the vibrating element may include vibrating piece having a central portion and a peripheral portion. The vibrator, the vibrating element and the method may further include a pair of excitation electrodes provided on a first side and a second side of a main surface of the central portion. The vibrator, the vibrating element and the method may further include a pair of connection electrodes provided on the peripheral portion and electrically connected to the pair of excitation electrodes. The vibrator, the vibrating element and the method may further include a substrate configured to be connected to the pair of connection electrodes via an electrically-conductive holding member interposed therebetween and configured to support the vibration element in an excitable manner.

A piezoelectric ceramic that contains an alkali niobate compound as its main ingredient. The alkali niobate compound has a perovskite crystal structure represented by A.sub.mBO.sub.3 and contains an alkali metal. There exists Sn in part of site A, and Zr in part of site B. A radial distribution function obtained from a K-edge X-ray absorption spectrum of Sn has a first peak intensity P1 at a first distance from a Sn atom and a second peak intensity P2 at a second distance from the Sn atom. The second distance is greater than the first distance, and the peak intensity ratio P1/P2 is 2.7 or less.

A piezoelectric thin film resonator includes: a substrate; lower and upper electrodes located on the substrate; a piezoelectric film that has a lower piezoelectric film mainly composed of aluminum nitride and an upper piezoelectric film mainly composed of aluminum nitride, the lower piezoelectric film and the upper piezoelectric film being in contact with each other in at least a part of a resonance region where the lower electrode and the upper electrode face each other across at least a part of the piezoelectric film, and a fluorine concentration at a boundary face with which the lower piezoelectric film and the upper piezoelectric film are in contact being 0.03 atomic % or less; and an insulating film that is located between the lower piezoelectric film and the upper piezoelectric film in a region other than the at least a part of the resonance region and contains silicon oxide.