Transversely-excited film bulk acoustic resonator with etched conductor patterns
An acoustic resonator is fabricated by forming a patterned first photoresist mask on a piezoelectric plate at locations of a desired interdigital transducer (IDT) pattern. An etch-stop layer is then deposited on the plate and first photoresist mask. The first photoresist mask is removed to remove parts of the etch-stop and expose the plate. An IDT conductor material is deposited on the etch stop and the exposed plate. A patterned second photoresist mask is then formed on the conductor material at locations of the IDT pattern. The conductor material is then etched over and to the etch-stop to form the IDT pattern which has interleaved fingers on a diaphragm to span a substrate cavity. A portion of the plate and the etch-stop form the diaphragm. The etch-stop and photoresist mask are impervious to this etch. The second photoresist mask is removed to leave the IDT pattern.
1. An acoustic resonator device comprising:
a substrate having a front surface;
a single-crystal piezoelectric plate having front and back surfaces, the back surface of the piezoelectric plate bonded to the front surface of the substrate;
an interdigital transducer (IDT) formed on the front surface of the single-crystal piezoelectric plate, the IDT having interleaved fingers disposed on a diaphragm spanning a cavity in the substrate; and
an etch-stop layer formed on the front surface of the piezoelectric plate between the interleaved fingers, a portion of the piezoelectric plate and the etch-stop layer forming the diaphragm, wherein
the etch-stop layer is impervious to an etch process used to form the interleaved fingers.
2. The acoustic resonator device of claim 1 , wherein the etch-stop layer is formed on the front surface of the single-crystal piezoelectric plate between but not under the interleaved fingers.
3. The acoustic resonator device of claim 1 , wherein the etch-stop layer is formed on the front surface of the single-crystal piezoelectric plate between and under the interleaved fingers.
4. The acoustic resonator device of claim 1 , wherein the single-crystal piezoelectric plate is one of lithium niobate and lithium tantalate; and wherein the etch-stop layer is one of an oxide, sapphire, a nitride, silicon carbide, and diamond.
5. The acoustic resonator device of claim 4 , wherein the etch-stop layer is aluminum oxide.
6. The acoustic resonator device of claim 4 , wherein the etch-stop layer is a high thermal conductivity material selected from aluminum nitride, boron nitride, and the diamond.
7. The acoustic resonator device of claim 1 , further comprising:
a front-side dielectric layer on the etch stop layer and on the interleaved fingers, wherein the diaphragm includes the single-crystal piezoelectric plate, the front-side dielectric layer, and the etch-stop layer.
8. The acoustic resonator device of claim 7 , wherein the front-side dielectric layer is SiO 2 , Si 3 N 4 , or Al 2 O 3 .
9. The acoustic resonator device of claim 7 , further comprising:
a passivation layer over the front-side dielectric layer.
10. The acoustic resonator device of claim 1 , wherein the IDT and single-crystal piezoelectric plate are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the single-crystal piezoelectric plate, and wherein a direction of acoustic energy flow of the shear primary acoustic mode is substantially orthogonal to the front and back surfaces of the single-crystal piezoelectric plate.
11. A filter device, comprising:
a substrate having a front surface;
a single-crystal piezoelectric plate having front and back surfaces, the back surface of the piezoelectric plate bonded to the front surface of the substrate;
a conductor pattern formed on the front surface of the piezoelectric plate, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators including a shunt resonator and a series resonator, interleaved fingers of each of the plurality of IDTs disposed on a respective diaphragm of one or more diaphragms spanning respective cavities in the substrate; and
an etch-stop layer formed on the front surface of the piezoelectric plate between interleaved fingers of the IDTs, portions of the single-crystal piezoelectric plate and the etch-stop layer forming the one or more diaphragms, wherein
the etch-stop layer is impervious to an etch process used to form the interleaved fingers.
12. The filter device of claim 11 , further comprising:
a frequency setting dielectric layer disposed on a front surface of the etch-stop layer between the interleaved fingers of the IDT of the shunt resonator.
13. The filter device of claim 12 , wherein
the frequency setting dielectric layer is a first dielectric layer that has a first thickness that is greater than a second thickness of a second dielectric layer deposited between the fingers of the IDT of the series resonator,
a resonance frequency of the shunt resonator is set, at least in part, by the first thickness, and
a resonance frequency of the series resonator is set, at least in part, by the second thickness.
14. The filter device of claim 11 , wherein the etch-stop layer is formed on the front surface of the single-crystal piezoelectric plate between but not under the interleaved fingers.
15. The filter device of claim 11 , wherein the etch-stop layer is formed on the front surface of the single-crystal piezoelectric plate between and under the interleaved fingers.
16. A filter device, comprising:
a substrate having a front surface;
a piezoelectric plate having front and back surfaces, the back surface of the piezoelectric plate coupled to the front surface of the substrate;
a conductor pattern of a conductor material formed over the front surface of the piezoelectric plate, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators including at least one shunt resonator and at least series resonator, interleaved fingers of each of the plurality of IDTs disposed on a respective diaphragm of one or more diaphragms spanning respective cavities in the substrate; and
an etch-stop layer formed on the front surface of each IDT between interleaved fingers of the IDTs, the one or more diaphragms including portions of the single-crystal piezoelectric plate and the etch-stop layer, wherein the etch-stop layer is a material selected to be impervious to at least one etch process capable of etching the conductor material.
17. The filter device of claim 16 , wherein the at least one etch process is a highly anisotropic, high-energy chemical etch process or physical sputtering etch process.