In a resonator is provided that suppresses a shift of a resonant frequency. The resonator includes a vibration portion that has a base with front and rear ends and multiple vibration arms with fixed ends connected to the front end of the base and that extend away from the front end. Moreover, the resonator includes a frame that at least partially surrounds the vibration portion and one or more holding arms provided between the vibration portion and the frame with first ends connected to the base and the second ends connected to a region of the frame at the front end side relative to the rear end of the base portion.

To improve the Q value of a piezoelectric thin-film element in a state in which unnecessary vibration is suppressed, an acoustic reflection film (104) is affixed to a first electrode (102), a piezoelectric single-crystal substrate (101) is thinned by polishing from the other surface (101b) of the piezoelectric single-crystal substrate (101), such that the first electrode (102) and piezoelectric thin film (105) are piled on the piezoelectric single-crystal substrate (101). In this polishing, a pressure (polishing pressure) to the surface (101b) during polishing in an electrode formation region where the first electrode (102) is formed differs from that in a non-electrode formation region around the electrode formation region. Consequently, the electrode formation region of the piezoelectric thin film (105), where the first electrode (102) is formed, is made thinner than the non-electrode formation region around the electrode formation region.

A piezoelectric vibration member that includes a substrate having a main surface on or in which a piezoelectric vibration member is mounted, a lid having a recess that is open so as to face the main surface and which includes a flange portion that projects outward from an opening edge of the recess, and a bonding layer that bonds the substrate and the lid together so as to hermetically seal the piezoelectric vibrator in a space between the recess and the main surface. The surface roughness of a side surface of the flange portion is greater than the surface roughness of the surface of the recess, and the bonding layer extends from the main surface of the substrate to the side surface of the flange portion.

In an array of single crystal acoustic resonators, the effective coupling coefficient of first and second strained single crystal filters are individually tailored in order to achieve desired frequency responses. In a duplexer embodiment, the effective coupling coefficient of a transmit band-pass filter is lower than the effective coupling coefficient of a receive band-pass filter of the same duplexer. The coefficients can be tailored by varying the ratio of the thickness of a piezoelectric layer to the total thickness of electrode layers or by forming a capacitor in parallel with an acoustic resonator within the filter for which the effective coupling coefficient is to be degraded. Further, a strained piezoelectric layer can be formed overlying a nucleation layer characterized by nucleation growth parameters, which can be configured to modulate a strain condition in the strained piezoelectric layer to adjust piezoelectric properties for improved performance in specific applications.

A resonator is provided that suppresses frequency variations with etching without decreasing the strength of vibration arms. The resonator includes a base portion, a first vibration portion extending from the base portion in a first direction and having a first width, and a second vibration portion extending from the base portion in the first direction with a first gap between the first and second vibration portions and having the first width. The first and second vibration portions perform out-of-plane bending vibration with opposite phases at a predetermined frequency. The predetermined frequency varies in accordance with the first width and the first gap. The ratio of the first gap to the first width is within a range that causes an absolute value of rates of variations in the predetermined frequency with respect to variations in the first width and in the first gap to be not more than about 100 ppm.

A bulk acoustic wave resonator includes a substrate protective layer disposed on a top surface of a substrate, a cavity defined by a membrane layer and the substrate, and a resonating part disposed on the membrane layer. The membrane layer includes a first layer and a second layer, the second layer having the same material as the first layer and having a density greater than that of the first layer.

A resonator includes a vibration portion with a vibration arm extending from a base and having an open end that performs bending vibration. The vibration portion includes upper and lower electrodes with a piezoelectric film disposed therebetween that causes bending vibration of the vibration arm when a voltage is applied between the upper and lower electrodes. A protective film faces the piezoelectric film with the upper electrode interposed therebetween and a conductive film faces the piezoelectric film with the protective film interposed therebetween. Moreover, the conductive film is exposed in a region at the open end and a via electrode is formed in the protective film to electrically connect the conductive film to one of the upper and lower electrodes. The via electrode is positioned closer to a first region than the open end in the second region of the vibration arm in a plan view of the piezoelectric film.

A resonator includes a vibration portion with upper and lower electrodes with a piezoelectric film disposed therebetween. Moreover, a protective film is provided to face the piezoelectric film with the upper electrode interposed therebetween and is exposed in a first region in the vibration portion. A conductive film is provided to face the piezoelectric film with the protective film interposed therebetween and is exposed in a second region that is adjacent to the first region in the vibration portion. A connection electrode is formed in the protective film to electrically connect the conductive film to the lower electrode. The upper electrode is formed such that an area of a region overlapping the conductive film is equal to or smaller than half of a total area of the conductive film and/or avoids the region overlapping the conductive film.

A bulk-acoustic resonator includes: a substrate; a first electrode disposed on the substrate; a piezoelectric layer at least partially covering the first electrode, and including a flat portion disposed in a central region, and an extension portion disposed outside the flat portion and having at least one step portion; an insertion layer disposed on the extension portion; and a second electrode disposed on upper portions of the insertion layer and the piezoelectric layer. The extension portion includes at least one first surface and at least one second surface disposed below an upper surface of the flat portion, and a connection surface connecting an upper surface of the flat portion to the at least one first surface or the at least one second surface, or connecting first surfaces among the at least one first surface to each other or second surfaces among the at least one second surface to each other.

An AT-cut crystal element is provided for reducing unnecessary vibration and for improving impedance of a resonator. Two side surfaces intersecting with a Z-axis of a crystallographic axis of crystal are constituted of three surfaces of a first surface as an m-surface of quartz crystal, a second surface that intersects with the first surface and is other than the m-surface, and a third surface that intersects with the second surface and is other than the m-surface. Moreover, the second surface is a surface corresponding to a surface obtained by rotating a principal surface of the AT-cut crystal element by 743 having an X-axis of crystal as a rotation axis, and the third surface is a surface corresponding to a surface obtained by rotating the principal surface by 563 having the X-axis of the crystal as the rotation axis.