Acoustic wave device
An acoustic wave device includes a support substrate, an intermediate layer on the support substrate, a piezoelectric layer on the intermediate layer, a bonding layer between the support substrate and the piezoelectric layer, a low-resistivity layer between the support substrate and the piezoelectric layer, and an IDT electrode on the piezoelectric layer and including a pair of busbars and first and second electrode fingers. The low-resistivity layer closer to the piezoelectric layer than the bonding layer and includes Al as a main component.
1 . An acoustic wave device comprising:
a support substrate;
an intermediate layer on the support substrate;
a piezoelectric layer on the intermediate layer;
a bonding layer between the support substrate and the piezoelectric layer;
a low-resistivity layer between the support substrate and the piezoelectric layer; and
an IDT electrode on the piezoelectric layer and including a pair of busbars and a plurality of electrode fingers; wherein
the low-resistivity layer is closer to the piezoelectric layer than the bonding layer and the low-resistivity layer includes Al as a main component;
the intermediate layer is a multilayer body; and
the bonding layer is between two layers of the multilayer body.
2 . The acoustic wave device according to claim 1 , wherein the bonding layer and the low-resistivity layer are provided within the intermediate layer.
3 . The acoustic wave device according to claim 2 , wherein
the multilayer body includes a high-acoustic-velocity film and a low-acoustic-velocity film, the bonding layer and the low-resistivity layer being provided within the low-acoustic-velocity film;
an acoustic velocity of a bulk wave propagating though the high-acoustic-velocity film is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer; and
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 piezoelectric layer.
4 . The acoustic wave device according to claim 1 , wherein a sheet resistance of the low-resistivity layer is less than or equal to about 1 Ω□.
5 . The acoustic wave device according to claim 1 , wherein when a resistivity of the low-resistivity layer is denoted by ρ[Ω·m] and a thickness of the low-resistivity layer is denoted by tL [nm], a relationship between the thickness tL and Y [nm] in Formula 1 is tL≥ Y:
Y=10 9 ×ρ+1.21×10 -13 Formula 1.
6 . The acoustic wave device according to claim 1 , wherein a thickness of the low-resistivity layer is larger than a thickness of the bonding layer.
7 . The acoustic wave device according to claim 1 , wherein adhesive layers are provided on one main surface and another main surface of the low-resistivity layer, and a thickness of both adhesive layers is smaller than a thickness of the low-resistivity layer.
8 . The acoustic wave device according to claim 1 , wherein the intermediate layer includes a silicon oxide film and the silicon oxide film and the bonding layer contact each other.
9 . The acoustic wave device according to claim 1 , wherein
one of the pair of busbars of the IDT electrode is connected to a ground potential; and
the low-resistivity layer is electrically connected to the busbar connected to the ground potential.
10 . An acoustic wave device comprising:
a support substrate;
an intermediate layer on the support substrate;
a piezoelectric layer on the intermediate layer;
a bonding layer between the support substrate and the piezoelectric layer;
a low-resistivity layer between the support substrate and the piezoelectric layer; and
an IDT electrode on the piezoelectric layer and including a pair of busbars and a plurality of electrode fingers; wherein
a resistivity of the low-resistivity layer is lower than a resistivity of the bonding layer; and
the low-resistivity layer is closer to the piezoelectric layer than the bonding layer, and the low-resistivity layer is provided only in a region overlapping at least one of the pair of busbars in plan view.
11 . The acoustic wave device according to claim 10 , wherein when a thickness of the low-resistivity layer is denoted by tL [nm], a material of the low-resistivity layer and a range of the thickness tL are any of the combinations listed in Table 1:
TABLE 1
Material
Thickness tL [nm]
Ag
tL ≥ 15.9
Au
tL ≥ 24.4
Al
tL ≥ 26.5
Cu
tL ≥ 16.8.
12 . The acoustic wave device according to claim 10 , wherein the bonding layer and the low-resistivity layer are provided within the intermediate layer.
13 . The acoustic wave device according to claim 12 , wherein
the intermediate layer is a multilayer body including a high-acoustic-velocity film and a low-acoustic-velocity film, the bonding layer and the low-resistivity layer being provided within the low-acoustic-velocity film;
an acoustic velocity of a bulk wave propagating though the high-acoustic-velocity film is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer; and
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 piezoelectric layer.
14 . The acoustic wave device according to claim 10 , wherein a sheet resistance of the low-resistivity layer is less than or equal to about 1 Ω□.
15 . The acoustic wave device according to claim 10 , wherein when a resistivity of the low-resistivity layer is denoted by ρ[Ω·m] and a thickness of the low-resistivity layer is denoted by tL [nm], a relationship between the thickness tL and Y [nm] in Formula 1 is tL≥Y:
Y=10 9 ×ρ+1.21×10 -13 Formula 1.
16 . The acoustic wave device according to claim 10 , wherein a thickness of the low-resistivity layer is larger than a thickness of the bonding layer.
17 . The acoustic wave device according to claim 10 , wherein adhesive layers are provided on one main surface and another main surface of the low-resistivity layer, and a thickness of both adhesive layers is smaller than a thickness of the low-resistivity layer.
18 . The acoustic wave device according to claim 10 , wherein the intermediate layer includes a silicon oxide film and the silicon oxide film and the bonding layer contact each other.
19 . The acoustic wave device according to claim 10 , wherein
one of the pair of busbars of the IDT electrode is connected to a ground potential; and
the low-resistivity layer is electrically connected to the busbar connected to the ground potential.