Acoustic wave device
An acoustic wave device includes a support substrate, a piezoelectric film on the support substrate, and an IDT electrode on the piezoelectric film. A film thickness of the piezoelectric film is equal to or less than about 1λ when λ is a wavelength of an acoustic wave determined by an electrode finger period of the IDT electrode. The piezoelectric film includes first and second regions in a thickness direction of the piezoelectric film. A first density that is a density in the first region and a second density that is a density in the second region are different from each other.
1 . An acoustic wave device, comprising:
a support substrate;
a piezoelectric film on the support substrate; and
an IDT electrode on the piezoelectric film; wherein
a film thickness of the piezoelectric film is, when A is a wavelength of an acoustic wave determined by an electrode finger period of the IDT electrode, equal to or less than about 1λ;
the piezoelectric film includes a first region and a second region in a thickness direction of the piezoelectric film; and
when a density in the first region is a first density and a density in the second region is a second density, the first density and the second density are different from each other.
2 . The acoustic wave device according to claim 1 , wherein
the second region is located closer to the IDT electrode than the first region; and
the first density is lower than the second density.
3 . The acoustic wave device according to claim 1 , wherein
the second region is located closer to the IDT electrode than the first region; and
the second density is lower than the first density.
4 . The acoustic wave device according to claim 1 , wherein the piezoelectric film is made of lithium tantalate.
5 . The acoustic wave device according to claim 1 , wherein one of the first density and the second density is lower than about 7.454×10 3 (kg/m 3 ).
6 . The acoustic wave device according to claim 1 , wherein one of the first density and the second density is higher than about 7.454×10 3 (kg/m 3 ).
7 . The acoustic wave device according to claim 1 , wherein the piezoelectric film is made of lithium niobate.
8 . The acoustic wave device according to claim 1 , further comprising:
a high acoustic velocity material layer stacked between the support substrate and the piezoelectric film and made of a high acoustic velocity material in which an acoustic velocity of a bulk wave that propagates through the high acoustic velocity material is higher than an acoustic velocity of an acoustic wave that propagates through the piezoelectric film; and
a low acoustic velocity material layer stacked between the high acoustic velocity material layer and the piezoelectric film and made of a low acoustic velocity material in which an acoustic velocity of a bulk wave that propagates through the low acoustic velocity material is lower than an acoustic velocity of a bulk wave that propagates through the piezoelectric film.
9 . The acoustic wave device according to claim 8 , wherein
the high acoustic velocity material includes at least one of aluminum nitride, aluminum oxide, silicon nitride, and DLC; and
the low acoustic velocity material is silicon oxide.
10 . The acoustic wave device according to claim 8 , wherein the support substrate and the high acoustic velocity material layer define an integrated high acoustic velocity support substrate made of the high acoustic velocity material.
11 . An acoustic wave device, comprising:
a support substrate;
a piezoelectric film on the support substrate; and
an IDT electrode on the piezoelectric film; wherein
a film thickness of the piezoelectric film is equal to or less than about 1λ when λ is a wavelength of an acoustic wave determined by an electrode finger period of the IDT electrode;
the piezoelectric film includes a first piezoelectric film and a second piezoelectric film stacked directly or indirectly on the first piezoelectric film;
the first piezoelectric film and the second piezoelectric film are made of piezoelectric materials of a same system; and
when a density of the first piezoelectric film is a first density and a density of the second piezoelectric film is a second density, the first density and the second density are different from each other.
12 . The acoustic wave device according to claim 11 , wherein
the second piezoelectric film is located closer to the IDT electrode than the first piezoelectric film; and
a film thickness of the first piezoelectric film is larger than a film thickness of the second piezoelectric film.
13 . The acoustic wave device according to claim 11 , wherein
the first piezoelectric film or the second piezoelectric film includes a high density region having a relatively high density and a low density region having a relatively low density; and
the high density region and the low density region are located along a thickness direction of the first piezoelectric film or the second piezoelectric film.
14 . The acoustic wave device according to claim 11 , wherein
the second piezoelectric film is located closer to the IDT electrode than the first piezoelectric film; and
the first density is lower than the second density.
15 . The acoustic wave device according to claim 11 , wherein
the second piezoelectric film is located closer to the IDT electrode than the first piezoelectric film; and
the second density is lower than the first density.
16 . The acoustic wave device according to claim 11 , wherein the piezoelectric film is made of lithium tantalate.
17 . The acoustic wave device according to claim 11 , wherein one of the first density and the second density is lower than about 7.454×10 3 (kg/m 3 ).
18 . The acoustic wave device according to claim 11 , wherein one of the first density and the second density is higher than about 7.454×10 3 (kg/m 3 ).
19 . The acoustic wave device according to claim 11 , wherein the piezoelectric film is made of lithium niobate.
20 . The acoustic wave device according to claim 11 , further comprising:
a high acoustic velocity material layer stacked between the support substrate and the piezoelectric film and made of a high acoustic velocity material in which an acoustic velocity of a bulk wave that propagates through the high acoustic velocity material is higher than an acoustic velocity of an acoustic wave that propagates through the piezoelectric film; and
a low acoustic velocity material layer stacked between the high acoustic velocity material layer and the piezoelectric film and made of a low acoustic velocity material in which an acoustic velocity of a bulk wave that propagates through the low acoustic velocity material is lower than an acoustic velocity of a bulk wave that propagates through the piezoelectric film.