Acoustic wave device
An acoustic wave device includes a high-acoustic-velocity layer, a piezoelectric layer made of lithium tantalate, and an interdigital transducer electrode that are successively laminated. An acoustic velocity of a bulk wave propagating in the high-acoustic-velocity layer is higher than an acoustic velocity of an acoustic wave propagating in the piezoelectric layer, and an acoustic velocity Vsub of a fast transversal bulk wave propagating in the high-acoustic-velocity layer satisfies Vsh0≤Vsub≤Vsp with respect to an acoustic velocity Vsh0 of an SH0 mode and an acoustic velocity Vsp of a mode becoming a spurious of which acoustic velocity is not lower than the acoustic velocity of the SH0 mode, wherein the acoustic velocity Vsh0 and the acoustic velocity Vsp is obtained from Eq. (1).
1. An acoustic wave device comprising:
a high-acoustic-velocity layer;
a piezoelectric layer laminated on the high-acoustic-velocity layer, the piezoelectric layer being made of lithium tantalate; and
an interdigital transducer electrode provided on the piezoelectric layer; wherein
an acoustic velocity of a bulk wave propagating in the high-acoustic-velocity layer is higher than an acoustic velocity of an acoustic wave propagating in the piezoelectric layer; and
an acoustic velocity Vsub of a fast transversal bulk wave propagating in the high-acoustic-velocity layer satisfies Vsh0≤Vsub≤Vsp with respect to an acoustic velocity Vsh0 of an SH0 mode and an acoustic velocity Vsp of a mode becoming a spurious response of which acoustic velocity is not lower than the acoustic velocity of the SH0 mode, the acoustic velocity Vsh0 and the acoustic velocity Vsp being obtained from Eq. (1) below;
Eq
.
(
1
)
V
mode
=
a
T
piezo
(
2
)
(
(
T
piezo
-
c
T
piezo
)
2
+
b
T
piezo
(
2
)
)
+
a
T
piezo
(
1
)
(
T
piezo
-
c
T
piezo
)
+
a
T
e
(
2
)
(
(
T
e
-
c
T
e
)
2
+
b
T
e
(
2
)
)
+
a
T
e
(
1
)
(
T
e
-
c
T
e
)
+
a
θ
(
2
)
(
(
θ
-
c
θ
)
2
+
b
θ
(
2
)
)
+
a
θ
(
1
)
(
θ
-
c
θ
)
+
a
Y
(
2
)
(
(
Y
-
c
Y
)
2
+
b
Y
(
2
)
)
+
a
γ
(
1
)
(
Y
-
c
γ
)
+
a
ρ
(
2
)
(
(
ρ
-
c
ρ
)
2
+
b
ρ
(
2
)
)
+
a
ρ
(
1
)
(
Y
-
c
ρ
)
+
d
T
piezoTe
(
T
piezo
-
c
T
piezo
)
(
T
e
-
c
T
e
)
+
d
T
piezo
θ
(
T
piezo
-
c
T
piezo
)
(
θ
-
c
θ
)
+
d
T
piezo
Y
(
T
piezo
-
c
T
piezo
)
(
Y
-
c
Y
)
+
d
T
piezo
ρ
(
T
piezo
-
c
T
piezo
)
(
Y
-
c
ρ
)
+
d
T
e
θ
(
T
e
-
c
T
e
)
(
θ
-
c
θ
)
+
d
T
e
Y
(
T
e
-
c
T
e
)
(
Y
-
c
Y
)
+
d
T
e
ρ
(
T
e
-
c
T
e
)
(
ρ
-
c
ρ
)
+
d
θ
Y
(
θ
-
c
θ
)
(
Y
-
c
Y
)
+
d
θ
ρ
(
T
θ
-
c
θ
)
(
ρ
-
c
p
)
+
d
Y
ρ
(
Y
-
c
Y
)
(
ρ
-
c
ρ
)
+
e
in Eq. (1), V mode is Vsh0 or Vsp, coefficients for Vsh0 and Vsp are as listed in Table 1 below, λ is a wavelength determined by a pitch of electrode fingers of the interdigital transducer electrode, T piezo is a film thickness (λ) of the piezoelectric layer, T e is a film thickness (λ) of the interdigital transducer electrode, θ is a second Euler angle (°) of the piezoelectric layer, Y is the Young's modulus (GPa) of the interdigital transducer electrode, and ρ is the density (g/cm 3 ) of the interdigital transducer electrode:
TABLE 1
MODE ACOUSTIC
VELOCITY
V_SH0
V_SP
aTpiezo(2)
7.048E+00
4.060E+01
aTpiezo(1)
−1.560E+00
−3.466E+00
bTpiezo(2)
−1.250E−02
−1.250E−02
cTpiezo
3.500E−01
3.500E−01
aTe(2)
5.482E+01
7.950E+01
aTe(1)
−7.154E+00
−7.636E+00
bTe(2)
−3.200E−03
−3.200E−03
cTe
1.200E−01
1.200E−01
a θ (2)
0.000E+00
0.000E+00
a θ (1)
8.215E−03
1.271E−02
b θ (2)
0.000E+00
0.000E+00
c θ
1.395E+02
1.395E+02
aY(2)
0.000E+00
3.371E−06
aY(1)
1.347E−04
−6.086E−04
bY(2)
0.000E+00
−3.954E+04
cY
3.515E+02
3.515E+02
a ρ (2)
3.156E−03
3.849E−03
a ρ (1)
−7.670E−02
−8.435E−02
b ρ (2)
−5.832E+01
−5.832E+01
c ρ
1.350E+01
1.350E+01
dTpiezoTe
0.000E+00
0.000E+00
dTpiezo θ
0.000E+00
0.000E+00
dTpiezoY
0.000E+00
0.000E+00
dTpiezo ρ
9.988E−02
9.090E−02
dTe θ
0.000E+00
0.000E+00
dTeY
−7.413E−03
−1.586E−02
dTe ρ
0.000E+00
0.000E+00
d θ Y
0.000E+00
0.000E+00
d θ ρ
0.000E+00
0.000E+00
dY ρ
−4.456E−05
−9.875E−05
e
3.248E+00
4.270E+00.
2. An acoustic wave device comprising:
a high-acoustic-velocity layer;
an intermediate layer laminated on the high-acoustic-velocity layer, the intermediate layer being made of silicon oxide;
a piezoelectric layer laminated on the intermediate layer and being made of lithium tantalate; and
an interdigital transducer electrode provided on the piezoelectric layer; wherein
an acoustic velocity of a bulk wave propagating in the high-acoustic-velocity layer is higher than an acoustic velocity of an acoustic wave propagating in the piezoelectric layer; and
an acoustic velocity Vsub of a fast transversal bulk wave propagating in the high-acoustic-velocity layer satisfies Vsh0≤Vsub≤Vsp with respect to an acoustic velocity Vsh0 of an SH0 mode and an acoustic velocity Vsp of a mode becoming a spurious of which acoustic velocity is not lower than the acoustic velocity of the SH0 mode, the acoustic velocity Vsh0 and the acoustic velocity Vsp being obtained from Eq. (2) below;
Eq
.
(
2
)
V
mode
=
a
T
piezo
(
2
)
(
(
T
piezo
-
c
T
piezo
)
2
+
b
T
piezo
(
2
)
)
+
a
T
piezo
(
1
)
(
T
piezo
-
c
T
piezo
)
+
a
T
int
(
2
)
(
(
T
int
-
c
T
int
)
2
+
b
T
int
(
2
)
)
+
a
T
int
(
1
)
(
T
int
-
c
T
int
)
+
a
T
e
(
2
)
(
(
T
e
-
c
T
e
)
2
+
b
T
e
(
2
)
)
+
a
T
e
(
1
)
(
T
e
-
c
T
e
)
+
a
θ
(
2
)
(
(
θ
-
c
θ
)
2
+
b
θ
(
2
)
)
+
a
θ
(
1
)
(
θ
-
c
θ
)
+
a
Y
(
2
)
(
(
Y
-
c
Y
)
2
+
b
Y
(
2
)
)
+
a
Y
(
1
)
(
Y
-
c
Y
)
+
a
ρ
(
2
)
(
(
ρ
-
c
ρ
)
2
+
b
ρ
(
2
)
)
+
a
ρ
(
1
)
(
Y
-
c
ρ
)
+
d
T
piezo
T
int
(
T
piezo
-
c
T
piezo
)
(
T
int
-
c
int
)
+
d
T
piezo
Te
(
T
piezo
-
c
T
piezo
)
(
T
e
-
c
T
e
)
+
d
T
piezo
θ
(
T
piezo
-
c
T
piezo
)
(
θ
-
c
θ
)
+
d
T
piezo
Y
(
T
piezo
-
c
T
piezo
)
(
Y
-
c
Y
)
+
d
T
piezo
ρ
(
T
piezo
-
c
T
piezo
)
(
Y
-
c
ρ
)
+
d
T
int
T
e
(
T
int
-
c
T
int
)
(
T
e
-
c
T
e
)
+
d
T
int
θ
(
T
int
-
c
T
e
)
(
θ
-
c
θ
)
+
d
T
int
Y
(
T
int
-
c
T
int
)
(
Y
-
c
Y
)
+
d
T
int
ρ
(
T
int
-
c
T
int
)
(
ρ
-
c
ρ
)
+
d
T
e
θ
(
T
e
-
c
T
e
)
(
θ
-
c
θ
)
+
d
T
e
Y
(
T
e
-
c
T
e
)
(
Y
-
c
Y
)
+
d
T
e
ρ
(
T
e
-
c
T
e
)
(
ρ
-
c
ρ
)
+
d
θ
Y
(
θ
-
c
θ
)
(
Y
-
c
Y
)
+
d
θ
ρ
(
T
θ
-
c
θ
)
(
ρ
-
c
ρ
)
+
d
Y
ρ
(
Y
-
c
Y
)
(
ρ
-
c
ρ
)
+
e
in Eq. (2), V mode is Vsh0 or Vsp, coefficients for Vsh0 and Vsp are as listed in Table 2 below, λ is a wavelength determined by a pitch of electrode fingers of the interdigital transducer electrode, T piezo is a film thickness (λ) of the piezoelectric layer, T e is a film thickness (λ) of the interdigital transducer electrode, θ is a second Euler angle (°) of the piezoelectric layer, Y is the Young's modulus (GPa) of the interdigital transducer electrode, and ρ is the density (g/cm 3 ) of the interdigital transducer electrode:
TABLE 2
MODE ACOUSTIC
VELOCITY
V_SH0
V_SP
aTpiezo(2)
0.000E+00
−1.163E+01
aTpiezo(1)
8.939E−01
−1.176E+00
bTpiezo(2)
0.000E+00
1.250E−02
cTpiezo
2.500E−01
2.500E−01
aTint(2)
0.000E+00
−2.248E+01
aTint(1)
−5.610E−01
1.908E+00
bTint(2)
0.000E+00
1.250E−02
cTint
2.500E−01
2.500E−01
aTe(2)
4.789E+01
0.000E+00
aTe(1)
−6.682E+00
−6.371E+00
bTe(2)
2.000E−03
0.000E+00
cTe
1.000E−01
1.000E−01
a θ (2)
−2.255E−04
0.000E+00
a θ (1)
2.552E−04
0.000E+00
b θ (2)
1.667E+02
0.000E+00
c θ
1.400E+02
1.400E+02
aY(2)
0.000E+00
0.000E+00
aY(1)
−2.030E−05
6.691E−04
bY(2)
0.000E+00
0.000E+00
cY
4.218E+02
4.218E+02
a ρ (2)
2.215E−03
0.000E+00
a ρ (1)
−5.835E−02
−4.208E−02
b ρ (2)
5.832E+01
0.000E+00
c ρ
1.350E+01
1.350E+01
dTpiezoTin
2.593E+00
−2.616E+01
dTpiezoTe
1.069E+01
0.000E+00
dTpiezo θ
0.000E+00
0.000E+00
dTpiezoY
−2.009E−03
−2.664E−03
dTpiezo ρ
7.747E−02
0.000E+00
dTintTe
0.000E+00
2.905E+01
dTint θ
0.000E+00
−4.267E−02
dTintY
5.308E−04
0.000E+00
dTint ρ
0.000E+00
1.901E−01
dTe θ
0.000E+00
1.520E−01
dTeY
−5.003E−03
7.229E−03
dTe ρ
−1.701E−01
−5.170E−01
d θ Y
0.000E+00
0.000E+00
d θ ρ
0.000E+00
9.593E−04
dY ρ
−3.071E−05
0.000E+00
e
3.120E+00
5.104E+00.
3. The acoustic wave device according to claim 1 , wherein a cut-angle of the lithium tantalate is in a range of about −10° to about +65° in Y cut X SAW propagation.
4. The acoustic wave device according to claim 1 , wherein at least one dielectric selected from a group of Al 2 O 3 , MgO, BeO, HfO 2 , AlN, SiN, TiN, ZrN, SiC, TiC, DLC, B 4 C, TiB 2 , ZrB 2 , and NbB 2 is provided between the interdigital transducer electrode and the piezoelectric layer.
5. The acoustic wave device according to claim 1 , wherein the piezoelectric layer is a LiTaO 3 layer.
6. The acoustic wave device according to claim 1 , wherein the high-acoustic-velocity layer includes Si.
7. The acoustic wave device according to claim 1 , wherein at least one reflector is provided on the piezoelectric layer.
8. The acoustic wave device according to claim 1 , wherein the acoustic wave device defines an acoustic wave resonator.
9. The acoustic wave device according to claim 1 , wherein the interdigital transducer electrode is a multilayer metal film that includes Ti, Mo, and Ti laminated in order.
10. The acoustic wave device according to claim 1 , wherein the second Euler angle θ (°) of the piezoelectric layer is between about 120° and about 160°.
11. The acoustic wave device according to claim 2 , wherein a cut-angle of the lithium tantalate is in a range of about −10° to about +65° in Y cut X SAW propagation.
12. The acoustic wave device according to claim 2 , wherein at least one dielectric selected from a group of Al 2 O 3 , MgO, BeO, HfO 2 , AlN, SiN, TiN, ZrN, SiC, TiC, DLC, B 4 C, TiB 2 , ZrB 2 , and NbB 2 is provided between the interdigital transducer electrode and the piezoelectric layer.
13. The acoustic wave device according to claim 2 , wherein the piezoelectric layer is a LiTaO 3 layer.
14. The acoustic wave device according to claim 2 , wherein the high-acoustic-velocity layer includes Si.
15. The acoustic wave device according to claim 2 , wherein at least one reflector is provided on the piezoelectric layer.
16. The acoustic wave device according to claim 2 , wherein the acoustic wave device defines an acoustic wave resonator.
17. The acoustic wave device according to claim 2 , wherein the interdigital transducer electrode is a multilayer metal film that includes Ti, Mo, and Ti laminated in order.
18. The acoustic wave device according to claim 2 , wherein the second Euler angle θ (°) of the piezoelectric layer is between about 120° and about 160°.