Piezoelectric acoustic resonator manufactured with piezoelectric thin film transfer process
A method and structure for a transfer process for an acoustic resonator device. In an example, a bulk acoustic wave resonator (BAWR) with an air reflection cavity is formed. A piezoelectric thin film is grown on a crystalline substrate. A first patterned electrode is deposited on the surface of the piezoelectric film. An etched sacrificial layer is deposited over the first electrode and a planarized support layer is deposited over the sacrificial layer, which is then bonded to a substrate wafer. The crystalline substrate is removed and a second patterned electrode is deposited over a second surface of the film. The sacrificial layer is etched to release the air reflection cavity. Also, a cavity can instead be etched into the support layer prior to bonding with the substrate wafer. Alternatively, a reflector structure can be deposited on the first electrode, replacing the cavity.
1. A method for fabricating an acoustic resonator device, the method comprising:
forming a piezoelectric film overlying a growth substrate;
forming a first electrode overlying the piezoelectric film;
forming a first passivation layer overlying the first electrode and the piezoelectric film;
forming a sacrificial layer overlying the first passivation layer, the first electrode, and the piezoelectric film;
forming a support layer overlying the sacrificial layer, the first passivation layer, the first electrode, and the piezoelectric film thereby forming a device on the growth substrate;
polishing the support layer;
forming a bonding support layer overlying a bond substrate;
flipping the device on the growth substrate and bonding the polished support layer to the bonding support layer thereby forming a bonded device;
removing the growth substrate from the bonded device;
forming an electrode contact via within the piezoelectric film overlying the first electrode on the bonded device;
forming one or more release holes within the piezoelectric film and the first passivation layer overlying the sacrificial layer on the bonded device;
forming a second electrode layer overlying the piezoelectric film and within the contact via;
etching the second electrode layer to form a top metal separated from a second electrode, wherein the top metal is physically coupled to the first electrode through the electrode contact via and the second electrode is overlying the piezoelectric film;
forming a first contact metal overlying the second electrode and the piezoelectric film;
forming a second contact metal overlying the top metal and the piezoelectric film;
forming a second passivation layer overlying the piezoelectric film, the second electrode, and the top metal; and
removing the sacrificial layer by way of the one or more release holes to form an air cavity within the bonded device.
2. The method of claim 1 wherein the growth substrate and bond substrate includes silicon (S), silicon carbide (SiC), sapphire (Al 2 O 3 ), silicon dioxide (SiO 2 ), or other silicon materials.
3. The method of claim 1 wherein the piezoelectric film is a single crystal or polycrystalline piezoelectric film that includes aluminum nitride (AlN), gallium nitride (GaN), Al x Ga 1-x N alloys, or other epitaxial materials.
4. The method of claim 1 wherein the piezoelectric film is an upper portion of a polycrystalline piezoelectric film that includes aluminum nitride (AlN), gallium nitride (GaN), Al x Ga 1-x N alloys, or other polycrystalline epitaxial materials.
5. The method of claim 1 wherein the first electrode, second electrode, and top metal can include molybdenum (Mo), ruthenium (Ru), tungsten (W), or other conductive materials, wherein the first and second passivation layers and the sacrificial layer can include silicon nitride (SiN), silicon oxide (SiOx), silicon dioxide (SiO 2 ), or other silicon materials.
6. The method of claim 1 wherein the first and second contact metals can include gold (Au), aluminum (Al), copper (Cu), nickel (Ni), aluminum bronze (AlCu), or other metal materials.
7. The method of claim 1 wherein polishing the support layer includes a chemical-mechanical planarization (CMP) process; wherein the support layer and the bonding support layer include silicon dioxide (SiO 2 ) or other silicon materials; and wherein removing the growth substrate includes a grinding process, a blanket etching process, a film transfer process, an ion implantation transfer process, or a laser crack transfer process; and wherein the removal of the sacrificial layer includes a poly-Si etch or an a-Si etch or other etching process.
8. The method of claim 1 further comprising processing the second electrode and the top metal to form a processed second electrode and a processed top metal, wherein the processed second electrode includes an energy confinement structure.
9. The method of claim 1 further comprising processing the first electrode to form a processed first electrode, wherein the processed first electrode includes an energy confinement structure.
10. The method of claim 1 further comprising processing the second electrode and the top metal to form a processed second electrode and a processed top metal, wherein the processed second electrode includes an energy confinement structure; and further comprising processing the first electrode to form a processed first electrode, wherein the processed first electrode includes an energy confinement structure.