Acoustic wave device
An acoustic wave device includes a support substrate, first and second piezoelectric layers, and an IDT electrode. The first and second piezoelectric layers are on the support substrate. The IDT electrode is on the first piezoelectric layer and includes electrode fingers. The second piezoelectric layer is between the first piezoelectric layer and the support substrate. The first and second piezoelectric layers are made of lithium tantalate or lithium niobate. Euler angles of the second piezoelectric layer are different from Euler angles of the first piezoelectric layer.
1. An acoustic wave device comprising:
a support substrate;
a first piezoelectric layer and a second piezoelectric layer on the support substrate; and
an IDT electrode on the first piezoelectric layer and including a plurality of electrode fingers; wherein
the second piezoelectric layer is between the first piezoelectric layer and the support substrate;
Euler angles of the second piezoelectric layer are different from Euler angles of the first piezoelectric layer;
the first piezoelectric layer and the second piezoelectric layer are made of lithium tantalate;
when a thickness of the first piezoelectric layer is denoted by LT1, a thickness of the second piezoelectric layer is denoted by LT2, a second Euler angle of the first piezoelectric layer is denoted by θ 1 , and a second Euler angle of the second piezoelectric layer is denoted by θ 2 , an electromechanical coupling coefficient satisfies Expression 1;
each of the second Euler angle θ 1 and the second Euler angle θ 2 is greater than or equal to about −180° and less than or equal to about 180°; and
the second Euler angle θ 1 and the second Euler angle θ 2 are values such that the electromechanical coupling coefficient is equal to or more than about 4.0%:
the electromechanical coupling coefficient=
3.00330520967856
+
0.346620517082123
×
(
L
T
1
LT
2
-
1.44444444433334
)
+
0.0570057523277407
×
(
θ
1
-
85.5
)
+
0.0124323016193303
×
(
θ
2
-
0
)
+
(
-
0.00066220403802972
)
×
{
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
-
3234.75
}
+
(
-
0.0000074522275643441
)
×
{
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
-
7310.25
}
+
5.27344575735
×
10
-
8
×
{
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
-
1.83516523125
×
10
7
}
+
0.000224701682752685
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
11400
}
+
9.558742707317
×
10
-
7
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
0
}
+
(
-
5.9893558361
×
10
-
9
)
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
233700000
}
+
(
-
4.32597449093616
×
10
-
11
)
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
0
}
.
Expression
1
2. The acoustic wave device according to claim 1 , wherein at least one of the first piezoelectric layer and the second piezoelectric layer is of a rotated Y-cut.
3. The acoustic wave device according to claim 2 , wherein both of the first piezoelectric layer and the second piezoelectric layer are of a rotated Y-cut.
4. The acoustic wave device according to claim 1 , wherein a ratio of a thickness of the second piezoelectric layer to a thickness of the first piezoelectric layer is equal to or more than about 1/10 and equal to or less than about 10.
5. The acoustic wave device according to claim 1 , further comprising:
a low acoustic velocity film in which an acoustic velocity of a bulk wave propagating through the low acoustic velocity film is lower than an acoustic velocity of a bulk wave propagating through the first piezoelectric layer and the second piezoelectric layer; wherein
the low acoustic velocity film is between the support substrate and the second piezoelectric layer.
6. The acoustic wave device according to claim 5 , further comprising:
a high acoustic velocity film in which an acoustic velocity of a bulk wave propagating through the high acoustic velocity film is higher than an acoustic velocity of an acoustic wave propagating through the first piezoelectric layer and the second piezoelectric layer; wherein
the high acoustic velocity film is between the support substrate and the low acoustic velocity film.
7. The acoustic wave device according to claim 6 , wherein a material of the high acoustic velocity film is silicon nitride.
8. The acoustic wave device according to claim 5 , wherein the support substrate is a high acoustic velocity support substrate in which an acoustic velocity of a bulk wave propagating through the high acoustic velocity support substrate is higher than an acoustic velocity of an acoustic wave propagating through the first piezoelectric layer and the second piezoelectric layer.
9. The acoustic wave device according to claim 5 , wherein a material of the low acoustic velocity film is silicon oxide.
10. The acoustic wave device according to claim 1 , wherein a material of the support substrate is silicon.
11. The acoustic wave device according to claim 1 , further comprising a silicon oxide layer between the first piezoelectric layer and the second piezoelectric layer.
12. An acoustic wave device comprising:
a support substrate;
a first piezoelectric layer and a second piezoelectric layer on the support substrate; and
an IDT electrode on the first piezoelectric layer and including a plurality of electrode fingers; wherein
the second piezoelectric layer is between the first piezoelectric layer and the support substrate;
Euler angles of the second piezoelectric layer are different from Euler angles of the first piezoelectric layer;
the first piezoelectric layer and the second piezoelectric layer are made of lithium tantalate;
when a thickness of the first piezoelectric layer is denoted by LT1, a thickness of the second piezoelectric layer is denoted by LT2, a second Euler angle of the first piezoelectric layer is denoted by θ 1 , and a second Euler angle of the second piezoelectric layer is denoted by θ 2 , a TCF satisfies Expression 2;
each of the second Euler angle θ 1 and the second Euler angle θ 2 is greater than or equal to about −180° and less than or equal to about 180°; and
the second Euler angle θ 1 and the second Euler angle θ 2 are values such that an absolute value of the TCF is in a range of equal to or less than about 10 ppm/° C.:
the TCF=
-
3.29013891692386
+
0.829996307633191
×
(
LT
1
LT
2
-
1.44444444433334
)
+
0.483995654864519
×
(
θ1
-
85.5
)
+
(
-
0.194567821179747
)
×
(
θ
2
-
0
)
+
0.000179452385587509
×
{
(
θ1
-
85.5
)
×
(
θ
1
-
85.5
)
-
3234.75
}
+
(
-
0.0000974537560393475
)
×
{
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
-
7310.25
}
+
(
-
1.92594958352
×
10
-
8
)
×
{
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
-
1.83516523125
×
10
7
}
+
4.6470081457
×
10
-
9
×
{
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
×
(
θ
1
-
85.5
)
-
1.19136362625
×
10
8
}
+
(
-
0.000422585955937192
)
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
11400
}
+
0.0000232656788288669
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
0
}
+
1.32633840535
×
10
-
8
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
233700000
}
+
(
-
5.476321966
×
10
-
10
)
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
0
}
+
0.0224071239542036
×
(
LT
1
LT
2
-
1.44444444433334
)
×
(
θ
1
-
85.5
)
+
(
-
0.000253262537154296
)
×
(
θ
1
-
85.5
)
×
(
θ
2
-
0
)
.
Expression
2
13. An acoustic wave device comprising:
a support substrate;
a first piezoelectric layer and a second piezoelectric layer on the support substrate; and
an IDT electrode on the first piezoelectric layer and including a plurality of electrode fingers; wherein
the second piezoelectric layer is between the first piezoelectric layer and the support substrate;
Euler angles of the second piezoelectric layer are different from Euler angles of the first piezoelectric layer;
the first piezoelectric layer and the second piezoelectric layer are made of lithium niobate;
when a thickness of the first piezoelectric layer is denoted by LN1, a thickness of the second piezoelectric layer is denoted by LN2, a second Euler angle of the first piezoelectric layer is denoted by θ 1 , and a second Euler angle of the second piezoelectric layer is denoted by θ 2 , an electromechanical coupling coefficient satisfies Expression 3;
each of the second Euler angle θ 1 and the second Euler angle θ 2 is greater than or equal to about −180° and less than or equal to about 180°; and
the second Euler angle θ 1 and the second Euler angle θ 2 are values such that the electromechanical coupling coefficient is equal to or more than about 4.0%:
the electromechanical coupling coefficient=
7.30749421642302
+
0.126467527077711
×
(
θ
1
-
90
)
+
1.02330895196759
×
(
L
N
1
L
N
2
-
1.44444444433335
)
+
0.0366048938272421
×
(
θ
2
-
0
)
+
(
-
0.00227170614085879
)
×
{
(
θ
1
-
90
)
×
(
θ
1
-
90
)
-
3000
}
+
(
-
0.0000164151797189738
)
×
{
(
θ
1
-
90
)
×
(
θ
1
-
90
)
×
(
θ
1
-
90
)
-
0
}
+
1.767839846311
×
10
-
7
×
{
(
θ
1
-
90
)
×
(
θ
1
-
90
)
×
(
θ
1
-
90
)
×
(
θ
1
-
90
)
-
16140000
}
+
0.00527616891343059
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
11400
}
+
0.0000016737181647348
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
0
}
+
(
-
1.24001733652
×
10
-
8
)
×
{
(
θ
2
-
0
)
×
(
θ2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
233700000
}
+
(
-
9.10141229661622
×
10
-
11
)
×
{
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
×
(
θ
2
-
0
)
-
0
}
+
0.0159877881713206
×
(
θ
1
-
90
)
×
(
L
N
1
L
N
2
-
1.44444444433335
)
+
0.00022852665674879
×
(
θ
1
-
90
)
×
(
θ
2
-
0
)
+
(
-
0.00673513735675292
)
×
(
L
N
1
L
N
2
-
1.44444444433335
)
×
(
θ
2
-
0
)
.
Expression
3