A ladder-type filter includes a support substrate, a piezoelectric layer provided on the support substrate, a parallel resonator including first electrode fingers provided on the piezoelectric layer and having a first average pitch and a first average duty ratio, a largest first average pitch being equal to or greater than two times a thickness of the piezoelectric layer, a first end of the parallel resonator being coupled to a path between input and output terminals, a second end of the parallel resonator being coupled to a ground, and a series resonator connected in series between the input and output terminals, the series resonator including second electrode fingers provided on the piezoelectric layer and having a second average pitch and a second average duty ratio, a second average duty ratio in at least one series resonator being less than a smallest first average duty ratio.

A piezoelectric device includes a support substrate, an intermediate layer on the support substrate in a first region, a piezoelectric layer on the intermediate layer, a functional element on the piezoelectric layer, and an insulating layer. The insulating layer is located on the support substrate in a second region adjacent to the first region. A surface roughness of the support substrate in the second region is greater than a surface roughness of the support substrate in the first region.

Aspects of this disclosure relate to acoustic wave devices on stacked die. A first die can include first acoustic wave device configured to generate a boundary acoustic wave. A second die can include a second acoustic wave device configured to generate a second boundary acoustic wave, in which the second die is stacked with the first die. The first acoustic wave resonator can include a piezoelectric layer, an interdigital transducer electrode on the piezoelectric layer, and high acoustic velocity layers on opposing sides of the piezoelectric layer. The high acoustic velocity layers can each have an acoustic velocity that is greater than a velocity of the boundary acoustic wave.

An acoustic wave device includes a support substrate, a piezoelectric body layer, an interdigital transducer electrode, and an external connection electrode. The piezoelectric body layer is on the support substrate. The interdigital transducer electrode is on the piezoelectric body layer. The external connection electrode is electrically connected to the interdigital transducer electrode. The external connection electrode does not overlap the piezoelectric body layer in a plan view from a thickness direction of the support substrate. The support substrate includes a hollow portion. The hollow portion is at least on an end portion of the support substrate in a plan view from the thickness direction.

An acoustic wave device includes a material layer which has Euler angles and an elastic constant at the Euler angles, a piezoelectric body which includes first and second principal surfaces opposing each other, is laminated directly or indirectly on the material layer so that the second principal surface is on the material layer side and has Euler angles, and whose elastic constant at the Euler angles, and an IDT electrode which is disposed on at least one of the first principal surface and the second principal surface of the piezoelectric body. At least one elastic constant among elastic constants C.sub.11 to C.sub.66 of the material layer not equal to 0 and at least one elastic constant among elastic constants C.sub.11 to C.sub.66 of the piezoelectric body not equal to 0 have opposite signs to each other.

An acoustic wave device includes an interdigital transducer electrode connected to first and second terminals, and a reflector connected to the second terminal. In a group of electrode fingers of the interdigital transducer electrode, the electrode fingers at one end and another end in a second direction are respectively first and second end electrode fingers, the first end electrode finger includes a wide portion at a distal end portion. The first end electrode finger is located between the reflector and the second end electrode finger in the second direction. An inner busbar portion of one of first and second busbars not connected to the first end electrode finger, is located on an inner side in the second direction relative to the wide portion of the first end electrode finger so as not to overlap the wide portion of the first end electrode finger in a first direction.

A layered structure (100) for transmission of an acoustic wave, the layered structure (100) comprising: a substrate layer (102); and a second layer (104) over the substrate layer (102), wherein the second layer (104) comprises a plurality of discrete portions (105) adjacent to each other, each discrete portion (105) of the plurality of discrete portions (105) comprising a first subregion (104A) and a second subregion (104B). Also an epitaxial layer (108), grown over the second layer (104), for transmission of the acoustic wave in a major plane of the epitaxial layer (108), wherein a periodicity (λ) of a wavelength of the acoustic wave to be transmitted through the epitaxial layer (108) is approximately equal to a sum of a width (d.sub.A) of the first subregion (104A) and a width (d.sub.B) of the second subregion (104B).

An elastic wave device includes a support substrate made of silicon, a piezoelectric film disposed directly or indirectly on the support substrate, and an interdigital transducer electrode disposed on one surface of the piezoelectric film. A higher-order mode acoustic velocity of propagation through the piezoelectric film is equal or substantially equal to an acoustic velocity V.sub.si=(V.sub.1).sup.1/2 of propagation through silicon or higher than the acoustic velocity V.sub.si, where V.sub.si is specified by V.sub.1 among solutions V.sub.1, V.sub.2, and V.sub.3 with respect to x derived from Ax.sup.3+Bx.sup.2+Cx+D=0.

An apparatus is disclosed for a surface-acoustic-wave filter with a compensation layer having multiple densities. In an example aspect, the apparatus includes at least one surface-acoustic-wave filter with a piezoelectric layer, a substrate layer, and a compensation layer positioned between the piezoelectric layer and the substrate layer. The compensation layer includes a first portion having a first density and a second portion having a second density. The second density is greater than the first density. The first portion is positioned closer to the piezoelectric layer as compared to the second portion. The second portion is positioned closer to the substrate layer as compared to the first portion.

A substrate for a surface acoustic wave device is constituted of a piezoelectric material and includes a first surface on which a surface acoustic wave propagates, and a second surface located opposite to the first surface. The second surface has an arithmetic mean roughness (Ra) of 0.2 μm to 0.4 μm, and there is satisfied either of the relationship between the arithmetic mean roughness (Ra) and mean spacing (S) of local peaks of Ra/S≥11, and the relationship between the arithmetic mean roughness (Ra) and mean spacing (Sm) of irregularities of Ra/Sm≥6.7. Further, the second surface has a maximum height (Rmax) of 2.5 μm to 4.5 μm, and there is satisfied either of the relationship between the maximum height (Rmax) and mean spacing (S) of local peaks of Rmax/S≥130, and the relationship between the maximum height (Rmax) and mean spacing (Sm) of irregularities of Rmax/Sm≥80.