Transversely-excited film bulk acoustic resonator package and method
Methods of making acoustic resonator devices and filters are disclosed. A method of fabricating an acoustic resonator device includes fabricating an acoustic resonator chip including: attaching a back surface of a piezoelectric plate to a front surface of a substrate, such that portions of the piezoelectric plate form at least first and second diaphragms spanning at least first and second cavities, and forming a first conductor pattern as one or more conductor layers on the piezoelectric plate. The first conductor pattern includes at least first and second interdigitated transducers (IDTs) and a first plurality of contact pads. The method further includes fabricating an interposer having front and back surface and a second plurality of contact pads on the interposer back surface, forming conductive balls, and bonding each of the first plurality of contact pads to a respective pad of the second plurality of contact pads using the respective conductive ball.
1. A method of fabricating an acoustic resonator device comprising:
fabricating an acoustic resonator chip comprising:
attaching a back surface of at least one piezoelectric layer to a front surface of a substrate either directly or via one or more intermediate layers;
forming at least first and second cavities in the substrate or the one or more intermediate layers, such that portions of the at least one piezoelectric layer form at least first and second diaphragms over the at least first and second cavities, respectively; and
forming a first conductor pattern as one or more conductor layers at the at least one piezoelectric layer, the first conductor pattern including:
at least first and second interdigitated transducers (IDTs), interleaved fingers of the first and second IDTs on the first and second diaphragms, respectively, and
a first plurality of contact pads;
fabricating an interposer and a second plurality of contact pads on a surface of the interposer;
forming a plurality of conductive balls at either the first plurality of contact pads or the second plurality of contact pads; and
bonding each of the first plurality of contact pads to a respective pad of the second plurality of contact pads using a respective conductive ball of the plurality of conductive balls.
2. The method of claim 1 , wherein the fabricating of the interposer further comprises forming conductors and conductive vias that connect the second plurality of contact pads to a third plurality of contact pads on the front surface of the interposer.
3. The method of claim 2 , wherein the conductors form passive circuit components comprising at least one inductor.
4. The method of claim 1 , wherein the interposer comprises a low temperature co-fired ceramic circuit card.
5. The method of claim 1 , wherein the interposer comprises a printed circuit board.
6. The method of claim 1 , further comprising, after the bonding, forming a molded cover that forms a seal extending around and connecting an outer perimeter of the acoustic resonator chip to a perimeter of the interposer.
7. The method of claim 6 , wherein the molded cover is a polymer material, and wherein the forming of the molded cover comprises one of injection molding or casting a cover over the acoustic resonator chip and the interposer to seal side surfaces of the acoustic resonator chip to a perimeter of the front surface of the interposer.
8. The method of claim 6 , wherein
the at least first and second cavities extend through the substrate from the front surface to a back surface, and
the method further comprises bonding a cover over the back surface of the substrate to seal the cavities prior to forming the molded cover.
9. The method of claim 1 , wherein the bonding comprises flip-chip bonding the acoustic resonator chip to the interposer by one of soldering, thermo-compression bonding, or ultrasonic bonding the plurality of conductive balls to the first plurality and second plurality of contact pads.
10. The method of claim 1 , wherein the bonding includes physically attaching the acoustic resonator chip to the interposer and making electrical connections between the first plurality of contact pads and the second plurality of contact pads.
11. The method of claim 1 , wherein the at least one piezoelectric layer and the at least first and second IDTs are configured such that respective radio frequency signals applied to the IDTs excite primary shear acoustic waves in the respective diaphragms.
12. The method of claim 1 , wherein the forming of the interposer comprises forming recesses in the surface of the interposer facing the at least first and second diaphragms, such that a distance from a bottom of each recess to the respective diaphragm is greater than or equal to 15 microns and less than or equal to 100 microns.
13. The method of claim 1 , wherein:
a thickness between the front and back surfaces of the at least one piezoelectric layer is greater than or equal to 200 nm and less than or equal to 1000 nm;
a respective pitch of the interleaved fingers of each of the at least first and second IDTs is greater than or equal to 2 times the thickness of the at least one piezoelectric layer and less than or equal to 20 times the thickness of the at least one piezoelectric layer; and
the interleaved fingers of each of the at least first and second IDTs have a respective width, and the respective pitch is greater than or equal to 2 times the respective width and less than or equal to 20 times the respective width.
14. The method of claim 1 , further comprising depositing a first dielectric layer between the fingers of the first IDT that has a first thickness that is greater than a second thickness of a second dielectric layer deposited between the fingers of the second IDT.
15. A method of fabricating an acoustic resonator device comprising:
fabricating an acoustic resonator chip comprising:
a substrate having front and back surfaces;
at least one piezoelectric layer having front and back surfaces, the back surface attached to the front surface of the substrate either directly or via one or more intermediate layers, the at least one piezoelectric layer having portions that form at least two diaphragms over at least two cavities in the substrate or in the one or more intermediate layers; and
a first conductor pattern formed as one or more conductor layers at the at least one piezoelectric layer, the first conductor pattern comprising:
at least two interdigitated transducers (IDTs), interleaved fingers of each of the IDTs on one of the at least two diaphragms; and
a first plurality of contact pads;
fabricating an interposer having a second plurality of contact pads on a surface of the interposer; and
forming a plurality of conductive balls on either the first plurality of contact pads or the second plurality of contact pads, respectively; and
bonding each of the first plurality of contact pads to a respective pad of the second plurality of contact pads using a respective conductive ball of the plurality of conductive balls,
wherein the at least one piezoelectric layer and the at least two IDTs are configured such that a respective radio frequency signal applied to each IDT excites a bulk shear acoustic wave within the respective diaphragm of the at least two diaphragms.
16. The method of claim 15 , wherein the fabricating of the interposer further comprises forming conductors and conductive vias that connect the second plurality of contact pads to a third plurality of contact pads on a front surface of the interposer.
17. The method of claim 16 , wherein the conductors form passive circuit components comprising at least one inductor.
18. The method of claim 15 , wherein the interposer comprises a low temperature co-fired ceramic circuit card.
19. The method of claim 15 , wherein the interposer comprises a printed circuit board.
20. The method of claim 15 , further comprising, after the bonding, forming a molded cover forming a seal extending around and connecting an outer perimeter of the acoustic resonator chip to a perimeter of the interposer.
21. The method of claim 20 , wherein the molded cover is a polymer material, and wherein the forming of the molded cover comprises one of injection molding or casting a cover over the acoustic resonator chip and the interposer to seal side surfaces of the acoustic resonator chip to a perimeter of the front surface of the interposer.
22. The method of claim 20 , wherein
the at least first and second cavities extend through the substrate from the front surface to a back surface, and
the method further comprises bonding a cover over the back surface of the substrate to seal the cavities prior to forming the molded cover.
23. A method of fabricating a filter device, comprising:
fabricating an acoustic resonator chip comprising:
a substrate;
at least one piezoelectric layer having a back surface attached to the substrate either directly or via one or more intermediate layers; and
a conductor pattern at the at least one piezoelectric layer, the conductor pattern comprising:
a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators, interleaved fingers of each of the plurality of IDTs on respective portions of the at least one piezoelectric layer over one or more cavities formed in the substrate or the one or more intermediate layers;
conductors to connect the plurality of acoustic resonators in a ladder filter circuit; and
a first plurality of contact pads;
fabricating an interposer comprising a second plurality of contact pads on a surface of the interposer;
forming a plurality of conductive balls on either the first plurality of contact pads or the second plurality of contact pads, respectively; and
bonding each of the first plurality of contact pads to a respective pad of the second plurality of contact pads using a respective conductive ball of the plurality of conductive balls.
24. The method of claim 23 , wherein:
the plurality of resonators comprises one or more shunt resonators and one or more series resonator, and
the fabricating the acoustic resonator chip further comprises:
forming a first dielectric layer having a first thickness between the interleaved fingers of the IDTs of the one or more shunt resonators; and
forming a second dielectric layer having a second thickness, less than the first thickness, between the interleaved fingers of the IDTs of the one or more series resonators.
25. The method of claim 23 , wherein the plurality of IDTs and the at least one piezoelectric layer are configured such that respective radio frequency signals applied to the IDTs excite a primary shear acoustic modes within the respective diaphragms.