Solidly-mounted transversely-excited film bulk acoustic device and method
Methods of fabricating resonator and filter devices. A first conductor pattern formed on a front surface of a piezoelectric plate includes a first plurality of contact pads and an interdigital transducer (IDT). The IDT and the piezoelectric plate are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the piezoelectric plate. An acoustic Bragg reflector is between a substrate and a back surface of the piezoelectric plate, the acoustic Bragg reflector configured to reflect the shear primary acoustic mode. A second conductor pattern including a second plurality of contact pads is formed on a back surface of the interposer. The first plurality of contact pads is directly connected to respective contact pads of the second plurality of contact pads. A perimeter of the acoustic resonator chip is sealed to a perimeter of the interposer.
1. A method of fabricating an acoustic resonator device, the method comprising:
fabricating a bulk acoustic resonator chip comprising:
forming a first conductor pattern on a front surface of a piezoelectric layer, the first conductor pattern comprising a first plurality of contact pads and an interdigital transducer (IDT), the IDT and the piezoelectric layer configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the piezoelectric layer; and
forming an acoustic Bragg reflector between a surface of a substrate and a back surface of the piezoelectric layer, the acoustic Bragg reflector configured to reflect the shear primary acoustic mode;
fabricating an interposer comprising:
forming a second conductor pattern on a surface of the interposer that faces the bulk acoustic resonator chip, the second conductor pattern comprising a second plurality of contact pads;
forming gold bumps by thermocompression or ultrasonic bonding to connect each contact pad of the first plurality of contact pads to a respective contact pad of the second plurality of contact pads; and
forming a polymer cover that is cast over the bulk acoustic resonator chip to seal a space between the bulk acoustic resonator chip and the interposer.
2. The method of claim 1 , wherein the acoustic Bragg reflector is configured to reflect the primary shear acoustic mode over a frequency range comprising a resonance frequency and an anti-resonance frequency of the acoustic resonator device.
3. The method of claim 1 , wherein:
the first conductor pattern further comprises a first continuous conductor about the perimeter of the piezoelectric layer, and
the second conductor pattern further comprises a second continuous conductor about the perimeter of the interposer.
4. The method of claim 3 , further comprising applying and curing an adhesive material to seal the perimeter the bulk acoustic resonator chip to the perimeter of the interposer.
5. The acoustic resonator device of claim 1 , further comprising:
forming vias and conductors connecting the second plurality of contact pads to a third plurality of contact pads on a surface of the interposer that is opposite the surface of the interposer facing the bulk acoustic resonator chip.
6. The acoustic resonator device of claim 5 , wherein:
the interposer comprises a silicon base; and
the vias are through silicon vias.
7. The acoustic resonator device of claim 5 , wherein the interposer is a low temperature co-fired ceramic circuit card.
8. The acoustic resonator device of claim 5 , wherein the interposer is a printed circuit board.
9. The acoustic resonator device of claim 1 , further comprising forming a recess in the surface of the interposer to face the IDT.
10. A method of fabricating a filter device, the method comprising:
fabricating a bulk acoustic resonator chip comprising:
forming a first conductor pattern on a front surface of a piezoelectric layer, the first conductor pattern comprising a first plurality of contact pads and interdigital transducers (IDTs) of a plurality of acoustic resonators comprising a shunt resonator and a series resonator;
forming an acoustic Bragg reflector between a surface of a substrate and a back surface of the piezoelectric layer;
depositing a first dielectric layer on and between interleaved fingers of the IDT of the shunt resonator, the first dielectric layer having a first thickness between; and
depositing a second dielectric layer on and between the interleaved fingers of the IDT of the series resonator, the second dielectric layer having a second thickness less than the first thickness;
fabricating an interposer comprising:
forming a second conductor pattern on a surface of the interposer that faces the bulk acoustic resonator chip, the second conductor pattern comprising a second plurality of contact pads;
forming a polymer cover that is cast over the bulk acoustic resonator chip to seal a space between the bulk acoustic resonator chip and the interposer; and
forming gold bumps by thermocompression or ultrasonic bonding to connect each contact pad of the first plurality of contact pads to a respective contact pad of the second plurality of contact pads.
11. The method of claim 10 , wherein;
the piezoelectric layer and the IDTs of the plurality of resonators are configured such that radio frequency signals applied to the IDTs excite respective primary shear acoustic modes in the piezoelectric layer, and
the acoustic Bragg reflector is configured to reflect the respective primary shear acoustic modes excited by the IDTs.
12. The method of claim 11 , wherein the acoustic Bragg reflector is configured to reflect the primary shear acoustic modes excited by the IDTs over a frequency range comprising a resonance frequency and an anti-resonance frequency of all of the plurality of acoustic resonators.
13. The method of claim 10 , wherein:
the first conductor pattern further comprises a first continuous conductor about the perimeter of the piezoelectric layer, and
the second conductor pattern further comprises a second continuous conductor about the perimeter of the interposer.
14. The method of claim 13 , further comprising applying and curing an adhesive material to seal the perimeter the bulk acoustic resonator chip to the perimeter of the interposer.
15. The method of claim 10 , wherein the fabricating of the interposer further comprises forming conductor and vias connecting the second plurality of contact pads to a third plurality of contact pads on a surface of the interposer that is opposite the surface of the interposer facing the bulk acoustic resonator chip.
16. The method of claim 15 , wherein:
the interposer comprises a silicon base; and
the vias are through silicon vias.
17. The method of claim 15 , wherein the interposer is a low temperature co-fired ceramic circuit card.
18. The method of claim 15 wherein the interposer is a printed circuit board.
19. The method of claim 10 , further comprising:
forming a plurality of recesses in the surface of the interposer to face the IDTs of the plurality of acoustic resonators.
20. A method of fabricating a filter device, the method comprising:
fabricating an acoustic resonator chip comprising:
forming a first conductor pattern on a front surface of a piezoelectric layer, the first conductor pattern comprising a first plurality of contact pads and interdigital transducers (IDTs) of a plurality of acoustic resonators comprising a shunt resonator and a series resonator;
forming an acoustic Bragg reflector between a surface of a substrate and a back surface of the piezoelectric layer;
forming a first dielectric layer on and between interleaved fingers of the IDT of the shunt resonator, the first dielectric layer having a first thickness; and
forming a second dielectric layer on and between the interleaved fingers of the IDT of the series resonator, the second dielectric layer having a second thickness less than the first thickness;
fabricating an interposer comprising:
forming a second conductor pattern on a surface of the interposer that faces the acoustic resonator chip, the second conductor pattern comprising a second plurality of contact pads;
forming a plurality of recesses in the surface of the interposer to face the IDTs of the plurality of acoustic resonators;
sealing a perimeter of the piezoelectric layer to a perimeter of the interposer; and
directly bonding each contact pad of the first plurality of contact pads to a respective contact pad of the second plurality of contact pads,
wherein each of the plurality of recesses has a depth such that a distance from a bottom of each recess to the respective IDT is greater than or equal to 15 microns and less than or equal to 100 microns.