Acoustic wave device
An acoustic wave device includes a piezoelectric layer and first and second electrodes facing each other in a direction intersecting a thickness direction of the piezoelectric layer. The acoustic wave device utilizes a bulk wave in a thickness-shear primary mode. A material of the piezoelectric layer is lithium niobate or lithium tantalate. At least a portion of each of the first and second electrodes is embedded in the piezoelectric layer.
1 . An acoustic wave device, comprising:
a piezoelectric layer; and
a first electrode and a second electrode facing each other in a direction intersecting a thickness direction of the piezoelectric layer; wherein
the acoustic wave device utilizes a bulk wave in a thickness-shear primary mode;
a material of the piezoelectric layer is lithium niobate or lithium tantalate;
at least a portion of each of the first electrode and the second electrode is embedded in the piezoelectric layer;
about 0.048≤d/p≤about 0.072, where in a cross-section along the thickness direction of the piezoelectric layer, an inter-centerline distance between the first electrode and the second electrode is denoted as p, and a thickness of the piezoelectric layer is denoted as d;
the first electrode and the second electrode are adjacent to each other;
the first electrode includes a first electrode main portion intersecting the second electrode in the direction in which the first electrode and the second electrode face each other;
the second electrode includes a second electrode main portion intersecting the first electrode in the direction in which the first electrode and the second electrode face each other;
the piezoelectric layer includes a defined region in the piezoelectric layer which intersects both the first electrode and the second electrode in the direction in which the first electrode and the second electrode face each other and is between the first electrode and the second electrode in a plan view from the thickness direction of the piezoelectric layer; and
in a plan view from the thickness direction of the piezoelectric layer, when an area of the first electrode main portion is denoted as S1, an area of the second electrode main portion is denoted as S2, an area of the defined region is denotes as S0, and a structural parameter defined by (S1+S2)/(S1+S2+S0) is denoted as MR, the acoustic wave device satisfies a condition of MR≤1.75×(d/p)+0.075.
2 . The acoustic wave device according to claim 1 , further comprising:
a support substrate including a first main surface and a second main surface facing each other; and
an acoustic reflection layer on the first main surface of the support substrate; wherein
the piezoelectric layer is on the acoustic reflection layer; and
the acoustic reflection layer includes:
at least one high acoustic impedance layer; and
at least one low acoustic impedance layer with an acoustic impedance lower than an acoustic impedance of the at least one high acoustic impedance layer.
3 . The acoustic wave device according to claim 1 , further comprising:
a support substrate including a first main surface and a second main surface facing each other; wherein
the piezoelectric layer is on the support substrate;
the acoustic wave device further includes a cavity;
the cavity overlaps an acoustic wave resonator including the first electrode, the second electrode, and a portion between the first electrode and the second electrode in the piezoelectric layer in a plan view from the thickness direction of the piezoelectric layer; and
the cavity is on a side of the support substrate with respect to the piezoelectric layer.
4 . The acoustic wave device according to claim 1 , wherein the first electrode penetrates the piezoelectric layer.
5 . The acoustic wave device according to claim 1 , wherein the first electrode includes a portion protruding from the piezoelectric layer.
6 . The acoustic wave device according to claim 1 , wherein
the piezoelectric layer includes a first main surface and a second main surface facing each other in the thickness direction; and
the first electrode includes:
a penetrating portion penetrating the piezoelectric layer;
a first protruding portion connected to the penetrating portion and protruding from the first main surface of the piezoelectric layer; and
a second protruding portion connected to the penetrating portion and protruding from the second main surface of the piezoelectric layer.
7 . The acoustic wave device according to claim 6 , wherein a protruding dimension of the first protruding portion is greater than a protruding dimension of the second protruding portion.
8 . The acoustic wave device according to claim 1 , wherein the first electrode includes conductor portions in the thickness direction of the piezoelectric layer.
9 . The acoustic wave device according to claim 1 , wherein the first electrode and the second electrode have respective cross-sectional shapes different from each other.
10 . The acoustic wave device according to claim 1 , wherein
a plurality of the first electrodes and a plurality of the second electrodes are provided;
the plurality of first electrodes and the plurality of second electrodes are alternately provided one by one; and
the acoustic wave device further includes:
a first wiring portion connected to the plurality of first electrodes; and
a second wiring portion connected to the plurality of second electrodes.
11 . The acoustic wave device according to claim 1 , wherein
the acoustic wave device is an acoustic wave filter including a plurality of acoustic wave resonators;
each of the plurality of acoustic wave resonators includes the first electrode and the second electrode; and
the piezoelectric layer is shared by the plurality of acoustic wave resonators.
12 . An acoustic wave device, comprising:
a piezoelectric layer; and
a first electrode and a second electrode facing each other in a direction intersecting a thickness direction of the piezoelectric layer; wherein
the first electrode and the second electrode are adjacent to each other;
about 0.048≤d/p≤about 0.072, where in a cross-section along the thickness direction of the piezoelectric layer, an inter-centerline distance between the first electrode and the second electrode is denoted as p, and a thickness of the piezoelectric layer is denoted as d;
a material of the piezoelectric layer is lithium niobate or lithium tantalate;
at least a portion of each of the first electrode and the second electrode is embedded in the piezoelectric layer;
the first electrode includes a first electrode main portion intersecting the second electrode in the direction in which the first electrode and the second electrode face each other;
the second electrode includes a second electrode main portion intersecting the first electrode in the direction in which the first electrode and the second electrode face each other;
the piezoelectric layer includes a defined region in the piezoelectric layer which intersects both the first electrode and the second electrode in the direction in which the first electrode and the second electrode face each other and is between the first electrode and the second electrode in a plan view from the thickness direction of the piezoelectric layer; and
in a plan view from the thickness direction of the piezoelectric layer, when an area of the first electrode main portion is denoted as S1, an area of the second electrode main portion is denoted as S2, an area of the defined region is denotes as S0, and a structural parameter defined by (S1+S2)/(S1+S2+S0) is denoted as MR, the acoustic wave device satisfies a condition of MR≤1.75×(d/p)+0.075.
13 . The acoustic wave device according to claim 12 , further comprising:
a support substrate including a first main surface and a second main surface facing each other; and
an acoustic reflection layer on the first main surface of the support substrate; wherein
the piezoelectric layer is on the acoustic reflection layer; and
the acoustic reflection layer includes:
at least one high acoustic impedance layer; and
at least one low acoustic impedance layer with an acoustic impedance lower than an acoustic impedance of the at least one high acoustic impedance layer.
14 . The acoustic wave device according to claim 12 , further comprising:
a support substrate including a first main surface and a second main surface facing each other; wherein
the piezoelectric layer is on the support substrate;
the acoustic wave device further includes a cavity;
the cavity overlaps an acoustic wave resonator including the first electrode, the second electrode, and a portion between the first electrode and the second electrode in the piezoelectric layer in a plan view from the thickness direction of the piezoelectric layer; and
the cavity is on a side of the support substrate with respect to the piezoelectric layer.