Single-crystal bulk acoustic wave resonator and method of making thereof
A single-crystal bulk acoustic wave resonators with better performance and better manufacturability and a process for fabricating the same are described. A low-acoustic-loss layer of one or more single-crystal and/or poly-crystal piezoelectric materials is epitaxially grown and/or physically deposited on a surrogate substrate, followed with the formation of a bottom electrode and then a support structure on a first side of the piezoelectric layer. The surrogate substrate is subsequently removed to expose a second side of the piezoelectric layer that is opposite to the first side. A top electrode is then formed on the second side of the piezoelectric layer, followed by further processes to complete the BAW resonator and filter fabrication using standard wafer processing steps. In some embodiments, the support structure has a cavity or an acoustic mirror adjacent the first electrode layer to minimize leakage of acoustic wave energy.
1. A bulk acoustic resonator, comprising:
a piezoelectric layer having a first side and a second side opposite to the first side, the piezoelectric layer including one or more sublayers of one or more piezoelectric materials epitaxially grown on a surrogate substrate that has been removed, wherein the second side of the piezoelectric layer is in contact with the surrogate substrate prior to removal of the surrogate substrate;
a first electrode layer formed on the first side of the piezoelectric layer;
a support structure on the first side of the piezoelectric layer, the support structure including a cavity adjacent the first electrode layer; and
a second electrode layer formed on the second side of the piezoelectric layer;
wherein the support structure includes a cavity frame and a support substrate, the cavity frame including:
a first metal frame formed on the first electrode layer; and
a second metal frame formed on the support substrate and bonded with the first metal frame via metal-to-metal bonding, the second metal frame having a pattern at least partially matching that of the first metal frame.
2. The bulk acoustic resonator of claim 1 , wherein the piezoelectric layer includes one or more single-crystalline piezoelectric materials epitaxially grown from the second side to the first side on the surrogate substrate that has been removed.
3. The bulk acoustic resonator of claim 2 , wherein the piezoelectric layer includes a multilayer structure of piezoelectric materials, the multilayer structure including a first sublayer of a first piezoelectric material at the second side and a second sublayer of a second piezoelectric material at the first side, the first sublayer being epitaxially grown on the surrogate substrate that has been removed, and the second sublayer being epitaxially grown over the first sublayer.
4. The bulk acoustic resonator of claim 1 , wherein the first electrode layer is deposited on the first side of the piezoelectric layer, and wherein the second electrode layer is deposited on the second side of the piezoelectric layer.
5. The bulk acoustic resonator of claim 1 , wherein the support substrate includes one or more layers of one or more high resistivity materials.
6. The bulk acoustic resonator of claim 5 , wherein the one or more high resistivity materials include one or more ceramic materials.
7. The bulk acoustic resonator of claim 5 , wherein the one or more high resistivity materials include one or more materials selected from the group consisting of aluminum oxide (Al 2 O 3 ), polysilicon, benzocyclobutene (BCB), and glass.
8. The bulk acoustic resonator of claim 5 , wherein the support structure further includes a frame layer surrounding the cavity, and the support substrate is adjacent the frame layer and the cavity, the frame layer including one or more layers of one or more high resistivity materials selected from the group consisting of: aluminum oxide or alumina (Al 2 O 3 ), polysilicon, and/or benzocyclobutene (BCB), the support substrate including one or more layers of one or more high resistivity materials selected from the group consisting of alumina (Al 2 O 3 ), gallium arsenide (GaAs), silicon (Si), silicon carbide (SiC), sapphire, and glass.
9. The bulk acoustic resonator of claim 8 , wherein the support substrate is attached to the frame layer by a glue material.
10. The bulk acoustic resonator of claim 1 , wherein the support substrate is attached to the first electrode layer, the support substrate including one or more materials selected from the group consisting of high-resistivity aluminum oxide (Al 2 O 3 ), silicon (Si), gallium arsenide (GaAs), silicon carbide (SiC), sapphire, and glass, and wherein the support substrate has a cavity etched therein before the support substrate is attached to the first electrode layer.
11. A bulk acoustic resonator, comprising:
a piezoelectric layer having a first side and a second side opposite to the first side, the piezoelectric layer including one or more sublayers of one or more single-crystalline piezoelectric materials;
a first electrode layer formed on the first side of the piezoelectric layer;
a support structure on the first side of the piezoelectric layer, the support structure including:
a support substrate;
a cavity adjacent the first electrode layer that extends from the support substrate to the first electrode;
a frame surrounding the cavity, wherein the support substrate is adjacent the frame and the cavity and the frame extends from the support substrate to the first electrode; and
a second electrode layer formed on the second side of the piezoelectric layer;
wherein the frame includes:
a first metal frame formed on the first electrode layer, and
a second metal frame formed on the support structure and bonded with the first metal frame via metal-to-metal bonding, the second metal frame having a pattern at least partially matching that of the first metal frame.
12. The bulk acoustic resonator of claim 11 , wherein the support substrate includes one or more layers of one or more high resistivity materials.