Film bulk acoustic resonator structure and fabricating method
A film bulk acoustic resonator (FBAR) structure includes a bottom cap wafer, a piezoelectric layer disposed on the bottom cap wafer, a bottom electrode disposed below the piezoelectric layer, and a top electrode disposed above the piezoelectric layer. Portions of the bottom electrode, the piezoelectric layer, and the top electrode that overlap with each other constitute a piezoelectric stack. The FBAR structure further includes a lower cavity disposed below the piezoelectric stack. A projection of the piezoelectric stack is located within the lower cavity.
1 . A bulk acoustic wave resonator structure, comprising:
a bottom cap wafer;
a piezoelectric layer disposed on the bottom cap wafer;
a bottom electrode disposed below the piezoelectric layer;
a top electrode disposed above the piezoelectric layer, wherein portions of the bottom electrode, the piezoelectric layer, and the top electrode that overlap with each other constitute a piezoelectric stack;
a sacrificial layer disposed between the bottom cap wafer and the piezoelectric layer;
a lower cavity disposed within the sacrificial layer and below the piezoelectric stack; and
a bottom bonding layer disposed between the sacrificial layer and the bottom cap wafer, the bottom bonding layer including a protruding structure integrally formed as a part of the bottom bonding layer and protruding towards the piezoelectric layer and surrounding the lower cavity, and an entire bottom surface of the bottom bonding layer facing the bottom cap wafer being planarized,
wherein a projection of the piezoelectric stack is located within the lower cavity,
the protruding structure of the bottom bonding layer includes a first side surface facing the lower cavity and a second side surface facing away from the lower cavity,
the bulk acoustic wave resonator structure further includes a boundary layer continuously disposed between the bottom bonding layer and the piezoelectric layer and overlaying the protruding structure of the bottom bonding layer, the boundary layer being disposed between the first side surface of the protruding structure and the lower cavity, and between the second side surface of the protruding structure and the sacrificial layer,
the continuous boundary layer is continuously overlaying an entire upper surface of the bottom bonding layer including the protruding structure, and
the boundary layer includes a first portion disposed between the protruding structure of the bottom bonding layer and the piezoelectric layer, and a second portion disposed between the protruding structure of the bottom bonding layer and the bottom electrode.
2 . The bulk acoustic wave resonator structure of claim 1 , further comprising a raised structure disposed along an edge of the bottom electrode, the raised structure protruding from the bottom electrode towards the lower cavity.
3 . The bulk acoustic wave resonator structure of claim 1 , wherein the bottom cap wafer is bonded to the bottom bonding layer.
4 . The bulk acoustic wave resonator structure of claim 1 , further comprising:
a top passivation layer disposed above the top electrode; and
a bottom passivation layer disposed below the bottom electrode.
5 . The bulk acoustic wave resonator structure of claim 4 , further comprising:
a bottom electrode contact layer disposed above the piezoelectric layer and electrically connected with the bottom electrode via a bottom electrode contact window formed in the piezoelectric layer; and
a top electrode contact layer disposed above the top passivation layer and electrically connected with the top electrode via a top electrode contact window formed in the top passivation layer.
6 . The bulk acoustic wave resonator structure of claim 5 , further comprising:
an upper cavity disposed above the piezoelectric stack;
a top bonding layer disposed on the piezoelectric layer, and surrounding the upper cavity; and
a top cap wafer bonded to the top bonding layer and covering the upper cavity.
7 . The bulk acoustic wave resonator structure of claim 6 , further comprising:
a bottom electrode through hole extending through the top bonding layer and the top cap wafer, and exposing a portion of the bottom electrode contact layer; and
a top electrode through hole extending through the top bonding layer and the top cap wafer, and exposing a portion of the top electrode contact layer.
8 . The bulk acoustic wave resonator structure of claim 7 , further comprising:
a conductive layer;
a first section of the conductive layer being disposed on sidewalls of the top electrode through hole and the exposed portion of the top electrode contact layer; and
a second section of the conductive layer being disposed on sidewalls of the bottom electrode through hole and the exposed portion of the bottom electrode contact layer.
9 . The bulk acoustic wave resonator structure of claim 8 , further comprising:
a first solder bump filled in the top electrode through hole and electrically connected with the first section of the conductive layer; and
a second solder bump filled in the bottom electrode through hole and electrically connected with the second section of the conductive layer.
10 . The bulk acoustic wave resonator structure of claim 8 , further comprising:
a first metal filling filled in the bottom electrode through hole;
a first solder bump disposed on the first metal filling;
a second metal filling filled in the top electrode through hole; and
a second solder bump disposed on the second metal filling.
11 . The bulk acoustic wave resonator structure of claim 8 , wherein the conductive layer is a redistribution layer, and
the bulk acoustic wave resonator structure further comprises:
a first passivation layer disposed above the conductive layer, the first passivation layer including a first contact window and a second contact window;
a first solder bump disposed on the first passivation layer and electrically connected with the first section of the conductive layer via the first contact window; and
a second solder bump disposed on the first passivation layer and electrically connected with the second section of the conductive layer via the second contact window.
12 . The bulk acoustic wave resonator structure of claim 11 , wherein the first contact window is not vertically aligned with the top electrode through hole, and the second contact window is not vertically aligned with the bottom electrode through hole.
13 . The bulk acoustic wave resonator structure of claim 1 , wherein the bottom cap wafer comprises glass or sapphire.
14 . The bulk acoustic wave resonator structure of claim 1 , wherein a projection of an edge of the top electrode is located within the lower cavity.
15 . The bulk acoustic wave resonator structure of claim 1 , wherein a projection of an edge of the bottom electrode is located within the lower cavity.
16 . The bulk acoustic wave resonator structure of claim 1 , further comprising a raised structure disposed along an edge of the top electrode, the raised structure protruding from the top electrode in a direction away from the bottom electrode.
17 . The bulk acoustic wave resonator structure 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.
18 . The bulk acoustic wave resonator structure of claim 1 , wherein the top electrode and the bottom electrode include molybdenum (Mo), aluminum (Al), copper (Cu), platinum (Pt), tantalum (Ta), tungsten (W), palladium (Pd), ruthenium (Ru), or a stacked combination of two or more of these materials.