The present disclosure relates to a Bulk Acoustic Wave (BAW) device with a substantially symmetrical structure in a vertical direction. The disclosed BAW device includes a main device region having a top electrode, a bottom electrode, and a piezoelectric layer sandwiched between the top electrode and the bottom electrode, a bottom reflector section underneath the bottom electrode, a bottom substrate underneath the bottom reflector section, a top reflector section over the top electrode, and a top substrate over the bottom reflector section. Herein, the bottom reflector section, the bottom substrate, the top reflector section, and the top substrate are configured so that a neutral plane of the BAW device is positioned at a center of the piezoelectric layer.

A crystal resonator (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) that covers the first excitation electrode of the piezoelectric resonator plate (2); and a second sealing member (4) that covers the second excitation electrode of the piezoelectric resonator plate (2). The first sealing member (3) is bonded to the piezoelectric resonator plate (2) while the second sealing member (4) is bonded to the piezoelectric resonator plate (2) so that an internal space (13), which hermetically seals a vibrating part including the first excitation electrode and the second excitation electrode of the piezoelectric resonator plate (2), is formed. Plating films (51, 52) are formed respectively on both the first sealing member (3) and the second sealing member (4), on respective surfaces opposite to surfaces to be bonded to the piezoelectric resonator plate (2).

A resonator element includes a quartz crystal substrate including a first surface along an X axis which is an electrical axis, a second surface along the X axis, and a side surface, a first excitation electrode, a second excitation electrode, a first coupling electrode, a second coupling electrode, a first extraction electrode that couples the first excitation electrode and the first coupling electrode, and a second extraction electrode that couples the second excitation electrode and the second coupling electrode. In plan view, a virtual extension region is obtained by extending the first excitation electrode along the X axis.

A vibrator device includes a base, a relay substrate that is supported by the base, and a vibrator element that is supported by the relay substrate. In addition, the vibrator element includes a vibration substrate formed of a piezoelectric single-crystalline body and an excitation electrode disposed on the vibration substrate. In addition, the relay substrate includes a substrate formed of the piezoelectric single-crystalline body. A crystal axis of the substrate and a crystal axis of the vibration substrate are shifted from each other.

A vibration element includes: a quartz crystal substrate having a first vibration part and a second vibration part; a pair of first excitation electrodes formed at two main surfaces of the quartz crystal substrate, at the first vibration part; and a pair of second excitation electrodes formed in such a way as to sandwich the second vibration part in a direction of thickness of the quartz crystal substrate, at the second vibration part. At least one second excitation electrode of the pair of second excitation electrodes is formed at an inclined surface inclined to at least one of the two main surfaces.

A bulk-acoustic wave resonator includes: a first substrate formed of a first material; an insulating layer or a piezoelectric layer disposed on a first side of the first substrate; and a second substrate formed of a second material and disposed on a second side of the first substrate, wherein the second material has thermal conductivity that is higher than a thermal conductivity of the first material.

A vibration element includes: a quartz crystal substrate having a first vibration part and a second vibration part; a pair of first excitation electrodes formed at two main surfaces of the quartz crystal substrate, at the first vibration part; and a pair of second excitation electrodes formed in such a way as to sandwich the second vibration part in a direction of thickness of the quartz crystal substrate, at the second vibration part. At least one second excitation electrode of the pair of second excitation electrodes is formed at an inclined surface inclined to at least one of the two main surfaces.

A vibrator device includes a base, a first relay substrate mounted on the base, a second relay substrate mounted on the first relay substrate, and a vibrator element mounted on the second relay substrate, in which the second relay substrate is disposed between the first relay substrate and the vibrator, and the second relay substrate includes a terminal that is electrically coupled to the vibrator element and is positioned in a region overlapping with the first relay substrate and not overlapping the vibrator element in a plan view. The vibrator device being configured to reduce a mounting stress applied to a vibrator element and to reduce frequency variation of the vibrator element due to the mounting stress, in a case of mounting on a package after adjusting a frequency of the vibrator element.

A vibration element includes: a quartz crystal substrate having a first vibration part and a second vibration part; a pair of first excitation electrodes formed at two main surfaces of the quartz crystal substrate, at the first vibration part; and a pair of second excitation electrodes formed in such a way as to sandwich the second vibration part in a direction of thickness of the quartz crystal substrate, at the second vibration part. At least one second excitation electrode of the pair of second excitation electrodes is formed at an inclined surface inclined to at least one of the two main surfaces.

An electronic component includes a piezoelectric substrate, a functional electrode on the piezoelectric substrate, a support layer on the piezoelectric substrate, a cover layer on the support layer, the cover layer, the support layer, and the piezoelectric substrate defining a hollow space that the functional electrode faces, and connection terminals that are electrically connected to the functional electrode, that are each made from a metal particle aggregate, and that each have a porous structure. The connection terminals are each located at a position in which the connection terminals overlap at least a portion of the hollow space in plan view.