Acoustic wave device, acoustic wave device package, radio-frequency front-end circuit, and communication device
An acoustic wave device includes a silicon oxide film, a piezoelectric body, and an interdigital transducer electrode laminated on a support substrate made of silicon. Where a wave length that is determined by an electrode finger pitch of the interdigital transducer electrode is λ, a thickness of the support substrate is greater than or equal to about 3λ. An acoustic velocity of the first higher mode that propagates through the piezoelectric body is an acoustic velocity V si =(V 1 ) 1/2 of bulk waves that propagate in the support substrate, which is determined by V 1 out of solutions V 1 , V 2 , and V 3 of x derived from the mathematical expression Ax 3 +Bx 2 +Cx+D=0, or higher than V si .
1. An acoustic wave device comprising:
a support substrate made of silicon;
a silicon oxide film provided on or above the support substrate;
a piezoelectric body provided on or above the silicon oxide film; and
an interdigital transducer electrode provided on or above one of main surfaces of the piezoelectric body; wherein
where a wavelength that is determined by an electrode finger pitch of the interdigital transducer electrode is λ, a thickness of the support substrate is greater than or equal to about 3λ; and
an acoustic velocity of a first higher mode that propagates through the piezoelectric body is equal to an acoustic velocity V si of mathematical expression (1) below, which is an acoustic velocity of bulk waves that propagate in the support substrate, or higher than the acoustic velocity V si ,
V si =( V 1 ) 1/2 (m/s) mathematical expression (1)
where V 1 in the mathematical expression (1) is a solution to the following mathematical expression (2),
Ax 3 +Bx 2 +Cx+D= 0 mathematical expression (2)
where, in the mathematical expression (2), A, B, C, and D are respectively values expressed by the following mathematical expressions (2A) to (2D),
A=−ρ 3 mathematical expression (2A)
B=ρ 2 ( L 11 +L 22 +L 33 ) mathematical expression (2B)
C =ρ( L 21 2 +L 23 2 +L 31 2 −L 11 ·L 33 −L 22 ·L 33 −L 11 ·L 22 ) mathematical expression (2C)
D= 2· L 21 ·L 23 ·L 31 +L 11 ·L 22 ·L 33 −L 31 2 ·L 22 −L 11 ·L 23 2 −L 21 2 ·L 33 mathematical expression (2D)
where, in the mathematical expression (2A), the mathematical expression (2B), the mathematical expression (2C), or the mathematical expression (2D), ρ=2.331 (g/cm 3 ), and L 11 , L 22 , L 33 , L 21 , L 31 , and L 23 are values expressed by the following mathematical expressions (3A) to (3F),
L 11 =c 11 ·a 1 2 +c 44 ·a 2 2 +c 44 ·a 3 2 mathematical expression (3A)
L 22 =c 44 ·a 1 2 +c 11 ·a 2 2 +c 44 ·a 3 2 mathematical expression (3B)
L 33 =c 44 ·a 1 2 +c 44 ·a 2 2 +c 11 ·a 3 2 mathematical expression (3C)
L 21 =( c 12 +c 44 )· a 2 ·a 1 mathematical expression (3D)
L 31 =( c 12 +c 44 )· a 1 ·a 3 mathematical expression (3E)
L 23 =( c 44 +c 12 )· a 3 ·a 2 mathematical expression (3F)
where, in the mathematical expressions (3A) to (3F), c 11 is about 1.674E+11 (N/m 2 ), c 12 is about 6.523E+10 (N/m 2 ), and c 44 is about 7.957E+10 (N/m 2 ), and a 1 , a 2 , and a 3 are values expressed by the following mathematical expressions (4A) to (4C),
a 1 =cos(ϕ)·cos(ψ)−sin(ϕ)·cos(θ)·sin(ψ) mathematical expression (4A)
a 2 =sin(ϕ)·cos(ψ)+cos(ϕ)·cos(θ)·sin(ψ) mathematical expression (4B)
a 3 =sin(θ)·sin(ψ) mathematical expression (4C)
where ϕ, θ, and ψ in the mathematical expressions (4A) to (4C) are ϕ, θ, and ψ in a crystal orientation (ϕ, θ, ψ) of the support substrate.
2. The acoustic wave device according to claim 1 , wherein the thickness of the support substrate is greater than or equal to about 20λ.
3. The acoustic wave device according to claim 1 , wherein a film thickness of the silicon oxide film falls within any one of ranges shown in Table 1 below:
TABLE 1
SiO 2 Film Thickness Range
Silicon Acoustic Velocity V Si
0.00λ < SiO 2 ≤ 0.40λ
Lower Than or Equal to 5500 m/s
0.40λ < SiO 2 ≤ 0.64λ
Lower Than or Equal to 5300 m/s
0.64λ < SiO 2 ≤ 0.84λ
Lower Than or Equal to 5100 m/s
0.84λ < SiO 2 ≤ 1.04λ
Lower Than or Equal to 4900 m/s
1.04λ < SiO 2 ≤ 1.20λ
Lower Than or Equal to 4700 m/s.
4. The acoustic wave device according to claim 3 , further comprising a high acoustic velocity material layer between the silicon oxide film and the support substrate, an acoustic velocity of bulk waves that propagate through the high acoustic velocity material layer being higher than an acoustic velocity of acoustic waves that propagate through the piezoelectric body.
5. The acoustic wave device according to claim 1 , wherein a film thickness of the silicon oxide film falls within any one of ranges shown in Table 2 below:
TABLE 2
SiO 2 Film Thickness Range
Silicon Acoustic Velocity V Si
0.00λ < SiO 2 ≤ 0.12λ
Lower Than or Equal to 5300 m/s
0.12λ < SiO 2 ≤ 0.34λ
Lower Than or Equal to 5100 m/s
0.34λ < SiO 2 ≤ 0.44λ
Lower Than or Equal to 4900 m/s
0.44λ < SiO 2 ≤ 0.54λ
Lower Than or Equal to 4700 m/s.
6. The acoustic wave device according to claim 1 , wherein V 1 in the mathematical expression (1) is a minimum value among solutions V 1 , V 2 , and V 3 to the mathematical expression (2).
7. The acoustic wave device according to claim 1 , wherein the acoustic velocity V si of the support substrate is lower than or equal to about 4700 m/s.
8. The acoustic wave device according to claim 1 , wherein a thickness of the support substrate is less than or equal to about 180 μm.
9. The acoustic wave device according to claim 1 , wherein a film thickness of the piezoelectric body is less than or equal to about 3.5λ.
10. The acoustic wave device according to claim 1 , wherein the piezoelectric body is made of LiTaO 3 .
11. The acoustic wave device according to claim 1 , wherein an acoustic velocity of bulk waves that propagate through the silicon oxide film is lower than an acoustic velocity of acoustic waves that propagate through the piezoelectric body.
12. The acoustic wave device according to claim 1 , wherein the acoustic velocity of bulk waves that propagate through the support substrate is higher than an acoustic velocity of acoustic waves that propagate through the piezoelectric body.
13. The acoustic wave device according to claim 1 , further comprising a dielectric layer provided between the piezoelectric body and the interdigital transducer electrode.
14. The acoustic wave device according to claim 13 , wherein the dielectric layer is made of silicon oxide or tantalum pentoxide.
15. The acoustic wave device according to claim 1 , further comprising:
a support layer surrounding the interdigital transducer electrode;
a cover member covering the support layer and providing a hollow space surrounding the interdigital transducer electrode; and
a plurality of metal bumps provided on the cover member and electrically connected to the interdigital transducer electrode.
16. An acoustic wave device package comprising:
the acoustic wave device according to claim 15 ; and
a case substrate on one surface of which a plurality of electrode lands is provided; wherein
the acoustic wave device is mounted on the case substrate such that the plurality of metal bumps are joined with the plurality of electrode lands of the case substrate; and
the acoustic wave device package further includes a sealing resin layer provided so as to seal the acoustic wave device.
17. The acoustic wave device package according to claim 16 , wherein a gap is provided between the cover member and the case substrate.
18. The acoustic wave device according to claim 1 , further comprising:
a support layer surrounding the interdigital transducer electrode; and
a cover member covering the support layer and providing a hollow space surrounding the interdigital transducer electrode; wherein
in the support substrate, at least one through via extending through the support substrate and at least one terminal electrode electrically connected to the at least one through via and provided on a surface on an opposite side of the support substrate from a side on which the interdigital transducer electrode is provided, are provided; and
the at least one through via is electrically connected to the interdigital transducer electrode and the at least one terminal electrode.
19. An acoustic wave device package comprising:
a case substrate on one surface of which a plurality of electrode lands is provided; and
the acoustic wave device according to claim 1 ; wherein
at least one metal bump electrically connected to the interdigital transducer electrode is provided in the acoustic wave device;
the acoustic wave device is mounted on the case substrate such that the at least one metal bump of the acoustic wave device is joined with at least one of the electrode lands; and
the acoustic wave device package further includes a sealing resin layer provided on the case substrate so as to seal the acoustic wave device.