Bulk acoustic wave filter having release hole and fabricating method of the same
A bulk acoustic wave filter includes: a first bulk acoustic wave resonator including, in an order from bottom to top, a first cavity, a first bottom electrode, a first segment of a piezoelectric layer, and a first top electrode; a second bulk acoustic wave resonator disposed adjacent to the first bulk acoustic wave resonator, and including, in the order from bottom to top, a second cavity, a second bottom electrode, a second segment of the piezoelectric layer, and a second top electrode; a boundary structure surrounding the first cavity and the second cavity, the boundary structure including a boundary portion extending between and separating the first cavity and the second cavity, and the boundary portion being disconnected at a disconnection region; and a first release hole formed in the piezoelectric layer, and overlapping the disconnection region.
1. A bulk acoustic wave filter, comprising:
a first bulk acoustic wave resonator including, in an order from bottom to top, a first cavity, a first bottom electrode, a first segment of a piezoelectric layer, and a first top electrode;
a second bulk acoustic wave resonator disposed adjacent to the first bulk acoustic wave resonator, and including, in the order from bottom to top, a second cavity, a second bottom electrode, a second segment of the piezoelectric layer, and a second top electrode;
a boundary structure surrounding the first cavity and the second cavity, the boundary structure including a boundary portion extending between and separating the first cavity and the second cavity, and the boundary portion being disconnected at a disconnection region; and
a first release hole formed in the piezoelectric layer, and overlapping the disconnection region.
2. The bulk acoustic wave filter of claim 1 , wherein a length of the disconnection region along an extending direction of the boundary portion is greater than a diameter of the first release hole.
3. The bulk acoustic wave filter of claim 1 , wherein:
each of the first cavity and the second cavity has a polygon shape,
the first cavity and the second cavity share a side, and
the boundary portion extending between the first cavity and the second cavity extends along the side shared by the first cavity and the second cavity.
4. The bulk acoustic wave filter of claim 1 , wherein:
the first bottom electrode is separated from the second bottom electrode, and
the first top electrode is separated from the second top electrode.
5. The bulk acoustic wave filter of claim 4 , further comprising:
a first gap between the first bottom electrode and the second bottom electrode; and
a second gap between the first top electrode and the second top electrode,
wherein the first release hole overlaps with the first gap and the second gap.
6. The bulk acoustic wave filter of claim 5 , wherein each of a width of the first gap and a width of the second gap is greater than a diameter of the first release hole.
7. The bulk acoustic wave filter of claim 1 , wherein:
the first bottom electrode is separated from the second bottom electrode, and
the first top electrode is integrally formed with the second top electrode to constitute a top electrode.
8. The bulk acoustic wave filter of claim 7 , further comprising:
a top opening formed in the top electrode and overlapping the first release hole.
9. The bulk acoustic wave filter of claim 8 , wherein a size of the top opening is greater than a diameter of the first release hole.
10. The bulk acoustic wave filter of claim 1 , wherein
the first bottom electrode is integrally formed with the second bottom electrode to constitute a bottom electrode,
the first top electrode is separated from the second top electrode.
11. The bulk acoustic wave filter of claim 10 , further comprising:
a bottom opening formed in the bottom electrode and overlapping the first release hole.
12. The bulk acoustic wave filter of claim 11 , wherein a size of the bottom opening is greater than a diameter of the first release hole.
13. The bulk acoustic wave filter of claim 1 , further comprising:
a second release hole adjacent to a side of the first cavity or the second cavity.
14. The bulk acoustic wave filter of claim 13 , wherein the boundary structure includes a protrusion protruding away from the first and second bottom electrodes and the first and second top electrodes, and
the second release hole is located adjacent to the protrusion.
15. The bulk acoustic wave filter of claim 1 , further comprising:
a substrate;
a support layer disposed on the substrate and including the first cavity and the second cavity;
a bonding layer disposed between the substrate and the support layer and including a protruding structure; and
a boundary layer overlying the bonding layer,
wherein the boundary layer and the protruding structure of the bonding layer constitute the boundary structure surrounding the first cavity and the second cavity.
16. The bulk acoustic wave filter of claim 15 , wherein the bonding layer is formed of SiO 2 for bonding the substrate and the boundary layer.
17. The bulk acoustic wave filter of claim 15 , wherein the boundary layer is formed of SiN, AlN, polysilicon, amorphous silicon or a stacked combination of two or more of those materials.
18. The bulk acoustic wave filter of claim 15 , wherein the support layer is formed of SiO 2 .
19. The bulk acoustic wave filter of claim 15 , wherein the substrate is formed of Si, glass, SiC, sapphire (Al 2 O 3 ), or GaN.
20. The bulk acoustic wave filter of claim 1 , wherein the piezoelectric layer includes aluminum nitride (AlN), zinc oxide (ZnO), lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), lead zirconate titanate (PZT), barium strontium titanate (BST), or a stacked combination of two or more of these materials.