Acoustic wave device
An acoustic wave device includes an energy confinement layer, a piezoelectric film, and an IDT electrode laminated on a support substrate. Acoustic velocity adjustment films are at least partially provided between the piezoelectric film and the support substrate and are made of a material different from that of the piezoelectric film.
1. An acoustic wave device comprising:
a support substrate;
a piezoelectric film;
an IDT electrode on the piezoelectric film;
an energy confinement layer between the piezoelectric film and the support substrate to confine energy in the piezoelectric film; and
an acoustic velocity adjustment film at least partially between the piezoelectric film and the support substrate and made of a material different from a material of the piezoelectric film; wherein
the IDT electrode includes first and second electrode fingers interdigitating with each other;
when a region where the first electrode finger and the second electrode finger overlap with each other when viewed in an acoustic wave propagation direction is defined as an overlap region, the overlap region includes a central region at a center in a direction in which the first and second electrode fingers extend and an edge region on each side of the central region; and
the acoustic velocity adjustment film is below only the edge region to extend in the acoustic wave propagation direction, and/or the acoustic velocity adjustment film does not overlap with the overlap region in a plan view.
2. The acoustic wave device according to claim 1 , wherein the energy confinement layer includes, on a side of the piezoelectric film, a cavity positioned below a portion where the IDT electrode is provided.
3. The acoustic wave device according to claim 2 , wherein the piezoelectric film is made of LiNbO 3 or LiTaO 3 , and d/p is about 0.5 or less where d is a thickness of the piezoelectric film and p is a center-to-center distance between electrode fingers of the IDT electrode that are adjacent to each other.
4. The acoustic wave device according to claim 3 , wherein Euler angles (ϕ, θ, ψ) of the LiNbO 3 or the LiTaO 3 fall within the range of any of the following formula 1), 2) and 3):
(0°±10°,0°˜20°,ψ) formula 1);
(0°±10°,20°˜80°,0°˜60°(1−(θ−50) 2 /900) 1/2 )) or (0°±10°,20°˜80°,[180°−60°(1−(θ−50) 2 /900) 1/2 )])˜180° formula 2); and
(0°±10°,[180°−30°(1−(ψ−90) 2 /8100) 1/2 )]˜180°,ψ) formula 3).
5. The acoustic wave device according to claim 4 , wherein Euler angles (ϕ, θ, ψ) of the LiNbO 3 or the LiTaO 3 are positioned within at least one of the regions shown in FIG. 8 .
6. The acoustic wave device according to claim 3 , wherein d/p is 0.24 or less.
7. The acoustic wave device according to claim 3 , wherein
a metallization ratio MR satisfies MR≤1.75 (d/p)+0.075, MR being a ratio of B) to A), where A) is an excitation region where the first electrode finger and the second electrode finger are overlapped when viewed in a direction in which the first electrode finger and the second electrode finger are opposed to each other, and B) is a total area of the first electrode finger and the second electrode finger within the excitation region.
8. The acoustic wave device according to claim 2 , wherein a recess including the cavity is provided in the energy confinement layer.
9. The acoustic wave device according to claim 1 , wherein the energy confinement layer includes a low acoustic impedance layer having relatively low acoustic impedance, and a high acoustic impedance layer having relatively high acoustic impedance and positioned closer to a side of the support substrate than the low acoustic impedance layer.
10. The acoustic wave device according to claim 9 , wherein a plurality of the low acoustic impedance layers and a plurality of the high acoustic impedance layers are alternately laminated.
11. The acoustic wave device according to claim 9 , wherein the low acoustic impedance layer includes at least one of silicon oxide or silicon oxynitride.
12. The acoustic wave device according to claim 9 , wherein the high acoustic impedance layer includes Al 2 O 3 .
13. The acoustic wave device according to claim 1 , wherein the energy confinement layer includes a high acoustic velocity material layer in which an acoustic velocity of a bulk wave propagating through the high acoustic velocity material layer is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric film, and a low acoustic velocity material layer in which an acoustic velocity of a bulk wave propagating through the low acoustic velocity material layer is lower than an acoustic velocity of a bulk wave propagating through the piezoelectric film.
14. The acoustic wave device according to claim 13 , wherein the support substrate is made of a high acoustic velocity material, and the high acoustic velocity material layer and the support substrate are integrally made of a same or substantially a same material.
15. The acoustic wave device according to claim 1 , wherein the acoustic velocity adjustment film is in contact with the piezoelectric film.
16. The acoustic wave device according to claim 1 , wherein the IDT electrode is a normal IDT electrode.
17. The acoustic wave device according to claim 1 , wherein the support substrate at least one of Si or Al 2 O 3 .
18. The acoustic wave device according to claim 1 , wherein the piezoelectric film includes LiNbO 3 or LiTaO 3 .
19. The acoustic wave device according to claim 1 , wherein the IDT electrode includes at least one of Al, Cu, W, or Mo, or an alloy including any of Al, Cu, W, or Mo as a main component.