Elastic wave device, high-frequency front-end circuit, and communication apparatus
An elastic wave device includes a piezoelectric substrate and an interdigital transducer electrode on the piezoelectric substrate, the piezoelectric substrate including a piezoelectric layer and a high-acoustic-velocity member layer, the piezoelectric layer being stacked on the high-acoustic-velocity member layer. The piezoelectric layer is made of lithium tantalate. Denoting an elastic wave propagation direction as a first direction, and a direction perpendicular or substantially perpendicular to the first direction as a second direction, a central region, low-acoustic-velocity regions, and high-acoustic-velocity regions are provided in the interdigital transducer electrode in the second direction. The low-acoustic-velocity regions include mass-adding films on electrode fingers. Denoting a film thickness normalized to a wavelength determined by the electrode finger pitch of the interdigital transducer electrode as a wavelength-normalized film thickness (%), a product of the wavelength-normalized film thickness of the mass-adding films and the density (g/cm 3 ) of the mass-adding films is about 13.4631 or less.
1. An elastic wave device comprising:
a piezoelectric substrate; and
an interdigital transducer electrode on the piezoelectric substrate; wherein
the piezoelectric substrate includes:
a piezoelectric layer; and
a high-acoustic-velocity member layer in which an acoustic velocity of a bulk wave that propagates through the high-acoustic-velocity member layer is higher than an acoustic velocity of an elastic wave that propagates through the piezoelectric layer, the piezoelectric layer being stacked directly or indirectly on the high-acoustic-velocity member layer;
the piezoelectric layer includes lithium tantalate;
the interdigital transducer electrode includes:
a first busbar;
a second busbar facing the first busbar;
first electrode fingers each including an end portion connected to the first busbar; and
second electrode fingers each including an end portion connected to the second busbar, the first electrode fingers being interdigitated with the second electrode fingers; wherein
denoting an elastic wave propagation direction as a first direction, and denoting a direction perpendicular or substantially perpendicular to the first direction as a second direction, a portion in which the first electrode fingers overlap the second electrode fingers in the first direction is defined as an intersecting region;
the intersecting region includes:
a central region located in a middle of the intersecting region in the second direction;
a first low-acoustic-velocity region located on a side of the central region adjacent to the first busbar, an acoustic velocity in the first low-acoustic-velocity region being lower than an acoustic velocity in the central region; and
a second low-acoustic-velocity region located on a side of the central region adjacent to the second busbar, an acoustic velocity in the second low-acoustic-velocity region being lower than an acoustic velocity in the central region;
the first low-acoustic-velocity region and the second low-acoustic-velocity region include mass-adding films disposed on the first electrode fingers and the second electrode fingers;
the interdigital transducer electrode includes:
a first high-acoustic-velocity region; and
a second high-acoustic-velocity region, an acoustic velocity in the first high-acoustic-velocity region and the second high-acoustic-velocity region being higher than an acoustic velocity in the central region;
the first low-acoustic-velocity region is located between the central region and the first high-acoustic-velocity region;
the second low-acoustic-velocity region is located between the central region and the second high-acoustic-velocity region; and
denoting a film thickness normalized to a wavelength determined by an electrode finger pitch of the interdigital transducer electrode as a wavelength-normalized film thickness (%), a product of the wavelength-normalized film thickness of the mass-adding films and a density (g/cm 3 ) of the mass-adding films is about 13.4631 (% ·g/cm 3 ) or less.
2. The elastic wave device according to claim 1 , wherein a combination of a material of the mass-adding films and an upper limit of the wavelength-normalized film thickness of the mass-adding films is selected from combinations in Table 1:
TABLE 1
Upper limit of
wavelength-normalized
Density (g/cm 3 )
film thickness (%)
Al
about 2.69
about 5
Ti
about 4.54
about 2.97
Cu
about 8.93
about 1.51
Ta
about 16.67
about 0.81
Au
about 19.3
about 0.7
Pt
about 21.37
about 0.63
Aluminum oxide
about 3.98
about 3.38
Silicon oxide
about 2.21
about 6.09
Germanium oxide
about 6.2
about 2.17
Tantalum oxide
about 8.47
about 1.59.
3. The elastic wave device according to claim 1 , wherein the mass-adding films are made of a metal.
4. The elastic wave device according to claim 3 , wherein the mass-adding films are made of Pt and have a wavelength-normalized film thickness of about 0.55% or less.
5. The elastic wave device according to claim 1 , wherein the mass-adding films are made of an oxide.
6. The elastic wave device according to claim 1 , wherein a low-acoustic-velocity film in which an acoustic velocity of an elastic wave that propagates through the low-acoustic-velocity film is lower than an acoustic velocity of an elastic wave that propagates through the piezoelectric layer is disposed between the high-acoustic-velocity member layer and the piezoelectric layer.
7. The elastic wave device according to claim 6 , further comprising:
a supporting substrate; wherein
the high-acoustic-velocity member layer is a high-acoustic-velocity film disposed between the supporting substrate and the low-acoustic-velocity film.
8. The elastic wave device according to claim 1 , wherein the high-acoustic-velocity member layer is a supporting substrate.
9. The elastic wave device according to claim 1 , wherein the piezoelectric layer has a wavelength-normalized film thickness of about 350% or less.
10. A high-frequency front-end circuit comprising:
the elastic wave device according to claim 1 ; and
a power amplifier.
11. The high-frequency front-end circuit according to claim 10 , wherein a combination of a material of the mass-adding films and an upper limit of the wavelength-normalized film thickness of the mass-adding films is selected from combinations in Table 1:
TABLE 1
Upper limit of
wavelength-normalized
Density (g/cm 3 )
film thickness (%)
Al
about 2.69
about 5
Ti
about 4.54
about 2.97
Cu
about 8.93
about 1.51
Ta
about 16.67
about 0.81
Au
about 19.3
about 0.7
Pt
about 21.37
about 0.63
Aluminum oxide
about 3.98
about 3.38
Silicon oxide
about 2.21
about 6.09
Germanium oxide
about 6.2
about 2.17
Tantalum oxide
about 8.47
about 1.59.
12. The high-frequency front-end circuit according to claim 10 , wherein the mass-adding films are made of a metal.
13. The high-frequency front-end circuit according to claim 12 , wherein the mass-adding films are made of Pt and have a wavelength-normalized film thickness of about 0.55% or less.
14. The high-frequency front-end circuit according to claim 10 , wherein the mass-adding films are made of an oxide.
15. The high-frequency front-end circuit according to claim 10 , wherein a low-acoustic-velocity film in which an acoustic velocity of an elastic wave that propagates through the low-acoustic-velocity film is lower than an acoustic velocity of an elastic wave that propagates through the piezoelectric layer is disposed between the high-acoustic-velocity member layer and the piezoelectric layer.
16. The high-frequency front-end circuit according to claim 15 , further comprising:
a supporting substrate; wherein
the high-acoustic-velocity member layer is a high-acoustic-velocity film disposed between the supporting substrate and the low-acoustic-velocity film.
17. The high-frequency front-end circuit according to claim 10 , wherein the high-acoustic-velocity member layer is a supporting substrate.
18. The high-frequency front-end circuit according to claim 10 , wherein the piezoelectric layer has a wavelength-normalized film thickness of about 350% or less.
19. A communication apparatus comprising:
the high-frequency front-end circuit according to claim 10 ; and
an RF signal processing circuit.
20. The communication apparatus according to claim 19 , wherein a combination of a material of the mass-adding films and an upper limit of the wavelength-normalized film thickness of the mass-adding films is selected from combinations in Table 1:
TABLE 1
Upper limit of
wavelength-normalized
Density (g/cm 3 )
film thickness (%)
Al
about 2.69
about 5
Ti
about 4.54
about 2.97
Cu
about 8.93
about 1.51
Ta
about 16.67
about 0.81
Au
about 19.3
about 0.7
Pt
about 21.37
about 0.63
Aluminum oxide
about 3.98
about 3.38
Silicon oxide
about 2.21
about 6.09
Germanium oxide
about 6.2
about 2.17
Tantalum oxide
about 8.47
about 1.59.