Lithium niobate or lithium tantalate FBAR structure and fabricating method thereof
A film bulk acoustic resonator (FBAR) structure includes, a bottom cap wafer, a piezoelectric layer disposed on the bottom cap wafer, the piezoelectric layer including lithium niobate or lithium tantalate, 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 also includes a cavity disposed below the piezoelectric stack. A projection of the piezoelectric stack is located within the cavity.
1 . A film bulk acoustic resonator (FBAR) structure, comprising:
a bottom cap wafer;
a piezoelectric layer disposed on the bottom cap wafer, the piezoelectric layer including lithium niobate or lithium tantalate;
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; and
a cavity disposed below the piezoelectric stack;
wherein a projection of the piezoelectric stack is located within the cavity,
the cavity includes a top surface, a bottom surface between the top surface and the bottom cap wafer, and a side surface surrounding the cavity,
an interior angle of the cavity between the bottom surface and the side surface of the cavity is great than 90 degree,
the bottom electrode includes a top surface facing the piezoelectric layer, a bottom surface facing the bottom cap wafer, and a side surface connecting the top surface and the bottom surface,
at least a portion of the side surface of the bottom electrode is disposed within the cavity, and
both a top surface and a bottom surface of the whole piece of the piezoelectric layer are entirely flat.
2 . The FBAR 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, or
a raised structure disposed along an edge of the bottom electrode, the raised structure protruding from the bottom electrode towards the cavity.
3 . The FBAR structure of claim 2 , wherein the raised structure includes a conductive material.
4 . The FBAR structure of claim 1 , further comprising:
a boundary layer disposed below the piezoelectric layer, and surrounding the cavity.
5 . The FBAR structure of claim 4 , wherein the boundary layer includes a non-conductive material.
6 . The FBAR structure of claim 1 , further comprising:
a bonding layer disposed below the bottom electrode,
wherein the bottom cap wafer is bonded to the bonding layer.
7 . The FBAR structure of claim 6 , wherein the bonding layer includes at least one of silicon oxide, silicon nitride, or ethyl silicate.
8 . The FBAR structure of claim 1 , further comprising:
a top passivation layer disposed above the top electrode.
9 . The FBAR structure of claim 8 , wherein the top passivation layer includes an electrically insulating material.
10 . The FBAR structure of claim 8 , further comprising:
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.
11 . The FBAR structure of claim 10 , wherein the top electrode contact layer includes a metal material.
12 . The FBAR structure of claim 1 , further comprising:
a bottom passivation layer disposed below the bottom electrode.
13 . The FBAR structure of claim 12 , wherein the bottom passivation layer includes an electrically insulating material.
14 . The FBAR structure of claim 12 , 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.
15 . The FBAR structure of claim 14 , wherein the bottom electrode contact layer includes a metal material.
16 . The FBAR structure of claim 1 , wherein the bottom cap wafer comprises silicon, glass, or sapphire.
17 . The FBAR structure of claim 1 , wherein a vertical projection of an edge of the top electrode is located within the cavity.
18 . The FBAR structure of claim 1 , wherein a vertical projection of an edge of the bottom electrode is located within the cavity.
19 . The FBAR 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 those materials.
20 . The FBAR structure of claim 1 , wherein the cavity is formed by etching a sacrificial island formed below the piezoelectric stack.