According to the present disclosure, a passband filter is provided. The passband filter comprises a first connection, a second connection, and a third connection. One or more resonators of a first type are provided connected in series between the first connection and the second connection; and one or more resonators of a second type are provided connected from between the first connection and the second connection to the third connection. A radio-frequency front end module and wireless mobile device are also provided.

An acoustic resonator device includes a substrate having a surface and a single-crystal piezoelectric plate bonded to the substrate surface. A portion of the piezoelectric plate forms a diaphragm that spans a cavity. A conductor pattern including an interdigital transducer (IDT) formed on a surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. A dielectric cover is disposed over the IDT and the plate, and the dielectric cover forms an air gap above the IDT and the plate.

Acoustic resonators, filters, and methods. An acoustic resonator includes a substrate, a piezoelectric plate, and a diaphragm including a portion of the piezoelectric plate spanning a cavity in a substrate. An interdigital transducer (IDT) on a front surface of the piezoelectric plate includes first and second sets of interleaved interdigital transducer (IDT) fingers extending from first and second busbars respectively. The interleaved IDT fingers extend onto the diaphragm. Overlapping portions of the interleaved IDT fingers define an aperture of the acoustic resonator. First and second dielectric strips are on the front surface of the piezoelectric plate. Each dielectric strip has a first portion under the IDT fingers in a respective margin of the aperture and a second portion extending into a gap between the respective margin and the respective busbar.

An acoustic resonator device includes a portion of a piezoelectric plate is a diaphragm spanning a cavity in a substrate. A conductor pattern on a surface of the piezoelectric plate includes an interdigital transducer (IDT) with a first busbar, a second busbar, and a. plurality of interleaved fingers extending alternately from the first and second busbars, first and second reflector elementsproximate and parallel to a first finger of the interleaved fingers, and third and fourth reflector element proximate and parallel to a last finger of the interleaved fingers. Overlapping portions of the interleaved fingers and the first to fourth reflector elements are on the diaphragm. pr1 is a center-to-center distance of the first and second reflector elements and a center-to-center distance of the third and fourth reflector elements, p is a pitch of the interleaved fingers, and 1.1p≤pr1≤1.5p.

An elastic wave device in which a recess is provided on an upper side of a support, a piezoelectric thin film covers the recess, and an IDT electrode is provided on an upper surface of the piezoelectric thin film. A plate wave of an S0 mode or SH0 mode is used. A plurality of grooves are provided in the upper surface or lower surface of the piezoelectric thin film at a portion of the piezoelectric thin film that is positioned on a hollow section.

An elastic wave device includes a piezoelectric film laminated on a first main surface of a support substrate including a recessed portion open to a first main surface. A cavity portion including the recessed portion is defined by the support substrate and the piezoelectric film. An electrode is on the piezoelectric film. The electrode includes first and second bus bars, a first electrode finger connected to the first bus bar, and a second electrode finger connected to the second bus bar. The first and second bus bars include corner portions inside the cavity portion when viewed in plan view. A curved portion as a pressure relaxation portion to relax pressure on the piezoelectric film at at least one of the corner portions of the first and second bus bars is provided between the corner portion and an outer edge of the cavity portion.

A process for fabricating a transversely-excited film bulk acoustic resonator (XBAR) and that XBAR are described. A sacrificial pillar is formed on a surface of a piezoelectric wafer and a highly conforming dielectric layer is deposited on the piezoelectric wafer to bury the sacrificial pillar. The highly conforming dielectric layer is polished to form a planar surface and to leave a thickness of the highly conforming dielectric that covers the sacrificial pillar. The planar surface of the highly conforming dielectric layer is bonded to a surface of a substrate wafer. A conductor pattern is formed on a front surface of the piezoelectric plate and holes are formed through the piezoelectric wafer to the sacrificial pillar. The sacrificial pillar is removed using an etchant introduced through the holes in the piezoelectric wafer to form a cavity under a diaphragm of the piezoelectric wafer spanning the cavity.

A process for fabricating a transversely-excited film bulk acoustic resonator (XBAR) having a metal cavity, and the fabricated XBAR include forming a conductor pattern including interleaved interdigital transducer (IDT) fingers on a piezoelectric wafer. Thein forming a metal layer on a substrate, the metal layer having a cavity. Then, bonding the piezoelectric plate to the metal layer using a metal-to-metal bond such that the IDT fingers are disposed over the cavity. Then, thinning the piezoelectric wafer to form a piezoelectric plate having a portion of the piezoelectric plate forming a diaphragm that spans the cavity.

Acoustic resonator devices and methods are disclosed. An acoustic resonator device includes a substrate having a front surface and an intervening oxide layer on the front surface and having a cavity. A thickness of the intervening oxide layer defines a depth of the cavity, and the substrate has vertical etch-stop material for etching the intervening oxide layer. Lateral fences formed in the intervening oxide layer define a perimeter of the cavity. The lateral fences has a lateral etch-stop material for etching the intervening oxide layer. A single-crystal piezoelectric plate has a back surface attached to the front surface of the intervening oxide layer except for a portion of the piezoelectric plate forming a diaphragm that spans the cavity. An interdigital transducer is formed on the front surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm.

Acoustic resonator devices and methods are disclosed. An acoustic resonator device includes a substrate having a front surface and a cavity. A depth of the cavity is defined by a buried oxide layer comprising etch-stop material and a perimeter of the cavity is defined by lateral fences comprising etch-stop material. A back surface of a single-crystal piezoelectric plate is attached to the front surface of the substrate except for a portion of the piezoelectric plate that forms a diaphragm that spans the cavity. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm.