Bulk acoustic wave (BAW) filter having a top portion that includes a protective acoustic mirror

• US 5,872,493 A
• Filed: 03/13/1997
• Issued: 02/16/1999
• Est. Priority Date: 03/13/1997
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Ella, Juha
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Summons, Barbara
• Application Number:
  US08/816,702
• Time in Patent Office: 705 Days
• Field of Search: 333/186-192, 310/311, 310/321, 310/322, 310/326, 310/327, 310/340, 310/342, 310/348, 310/334, 310/366, 310/335
• US Class Current: 333/191
• CPC Class Codes: H01L 2224/16225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H03H 3/02 for the manufacture of piezoelectric or electrostrictive resonators or networks H03H3/08 takes precedence
• CPC Class Codes: H03H 9/0514 consisting of mounting pads or bumps
• CPC Class Codes: H03H 9/0523 for flip-chip mounting
• CPC Class Codes: H03H 9/0528 consisting of clips
• CPC Class Codes: H03H 9/585 Stacked Crystal Filters [SCF]
• CPC Class Codes: H03H 9/589 Acoustic mirrors
• CPC Class Codes: H03H 9/605 consisting of a ladder configuration

Abstract

A Bulk Acoustic Wave (BAW) filter, comprising at least one resonator structure that is disposed over a substrate, and an acoustic mirror that is disposed over the resonator structure. The acoustic mirror includes a plurality of layers. The acoustic mirror substantially isolates acoustic vibrations produced by the resonator from reaching beyond an upper surface of the acoustic mirror. The acoustic mirror also prevents environmental contaminants from coming into contact with the resonator. Also disclosed are surface-mountable BAW components.

Claims

1. A Bulk Acoustic Wave (BAW) filter, said BAW filter comprising a plurality of adjacent resonator structures disposed over a substrate, and further comprising an acoustic mirror disposed over said plurality of adjacent resonator structures.

2. A BAW filter as set forth in claim 1, wherein said acoustic mirror comprises a plurality of layers.

3. A BAW filter as set forth in claim 2, wherein each of said plurality of layers has a thickness that is approximately equal to one-quarter wavelength.

4. A BAW filter as set forth in claim 1, wherein said acoustic mirror comprises a top layer that includes a material having a low acoustic impedance, a middle layer that includes a material having a high acoustic impedance, and a bottom layer that includes a material having a low acoustic impedance.

5. A BAW filter as set forth in claim 4, wherein said top and bottom layers comprise one of silicon, polysilicon, aluminum, and a polymer material, and wherein said middle layer comprises one of gold, molybdenum, and tungsten.

6. A BAW filter as set forth in claim 1, further comprising a protective passivation layer formed over said acoustic mirror.

7. A BAW filter as set forth in claim 6, wherein said protective passivation layer comprises one of epoxy, a glop top material, and silicon-dioxide, and has a thickness of at least 0.2 μ

m.

8. A BAW filter as set forth in claim 1, wherein at least one of said plurality of resonator structures includes at least one electrode having a portion which is exposed for providing a contact pad, said contact pad for coupling said at least one resonator structure to a wiring substrate via bonding wires.

9. A BAW filter as set forth in claim 1, wherein at least one of said plurality of resonator structures includes at least one electrode having a portion which is exposed for providing a contact pad, said contact pad for coupling said at least one resonator structure to a wiring substrate, using flip-chip technology.

10. A BAW filter as set forth in claim 1, wherein each of said plurality of resonator structures includes a plurality of electrodes, wherein a portion of a first one of said electrodes of a first one of said resonator structures is exposed for providing a first contact pad, and a portion of a first one of said electrodes of a second one of said resonator structures is exposed for providing a second contact pad, and wherein said BAW filter further comprises a third contact pad disposed over said substrate, said third contact pad being exposed and being electrically coupled to a first one of said electrodes of each of a third one and a fourth one of said resonator structures, and wherein said first, second, and third contact pads are for coupling respective ones of said first, second, and third resonator structures to a wiring substrate.

11. A BAW filter as set forth in claim 10, and further comprising a fourth contact pad disposed over said substrate, said fourth contact pad being exposed and being electrically coupled to said first one of said electrodes of each of said third and fourth resonator structures, said fourth contact pad for coupling said third and fourth resonator structures to a wiring substrate.

12. A BAW filter as set forth in claim 1, wherein each of said plurality of resonator structures includes at least two electrodes, said BAW filter further comprising a plurality of contacts disposed over an external surface of said BAW filter, individual ones of at least two of said contacts being electrically coupled to an electrode of a respective individual one of said resonator structures, said contacts for surface mounting said BAW filter to a wiring substrate.

13. A BAW filter as set forth in claim 1, wherein said acoustic mirror substantially isolates acoustic vibrations produced by said resonator structures from reaching beyond an upper surface of said acoustic mirror.

14. A BAW filter as set forth in claim 1, wherein said acoustic mirror protects said resonator structures by preventing environmental contaminants from coming into contact with said resonator structures.

15. A BAW filter as set forth in claim 1, wherein said acoustic mirror is an upper one of a pair of acoustic mirrors of said BAW filter, and wherein a lower one of said pair of acoustic mirrors is disposed between said substrate and said resonator structures.

16. A BAW filter as set forth in claim 15, wherein said lower acoustic mirror substantially prevents vibrations produced by said resonator structures from reaching said substrate, and wherein said upper acoustic mirror substantially prevents vibrations produced by said resonator structures from reaching an upper surface of said BAW filter.

17. A BAW filter as set forth in claim 1, wherein each of said resonator structures includes a plurality of electrodes, said BAW filter further comprising a plurality of contacts disposed over an external surface of said BAW filter, wherein a first one of said electrodes of a first one of said resonator structures is electrically coupled to a first one of said contacts, a first one of said electrodes of a second one of said resonator structures is electrically coupled to a second one of said contacts, a first one of said electrodes of a third one of said resonator structures is electrically coupled to a third one of said contacts, and a first one of said electrodes of a fourth one of said resonator structures is electrically coupled to said third contact.

18. A BAW filter as set forth in claim 17, wherein a second one of said electrodes of said first resonator structure is coupled to a second one of said electrodes of each of said second and third resonator structures, and wherein a second one of said electrodes of said fourth one of said resonator structures is coupled to said first electrode of said second resonator structure.

19. A BAW filter as set forth in claim 17, wherein said first electrodes of said third and fourth resonator structures are also electrically coupled to a fourth one of said contacts.

20. A Bulk Acoustic Wave (BAW) filter, comprising:

a substrate;

a first acoustic mirror disposed over said substrate;

a plurality of adjacent resonator structures disposed over at least a portion of said first acoustic mirror; and

a second acoustic mirror disposed over said plurality of adjacent resonator structures.

21. A BAW filter as set forth in claim 20, wherein at least one of said first and second acoustic mirrors comprises a top layer that includes a material having a low acoustic impedance, a middle layer that includes a material having a high acoustic impedance, and a bottom layer that includes a material having a low acoustic impedance.

22. A BAW filter as set forth in claim 21, wherein said top and bottom layers comprise one of silicon, poly-silicon, aluminum, and a polymer material, and wherein said middle layer comprises one of gold, molybdenum, and tungsten.

23. A BAW filter as set forth in claim 20, further comprising a protective passivation layer formed over said second acoustic mirror.

24. A BAW filter as set forth in claim 23, wherein said protective passivation layer comprises one of epoxy, a glop top material, and silicon-dioxide, and has a thickness of at least 0.2 μ

m.

25. A BAW filter as set forth in claim 20, wherein at least one of said resonator structures includes an electrode having a portion which is exposed for providing a contact pad, said contact pad for coupling said at least one resonator structure to a wiring substrate via bonding wires.

26. A BAW filter as set forth in claim 20, wherein at least one of said resonator structures includes an electrode having a portion which is exposed for providing a contact pad, said contact pad for coupling said at least one resonator structure to a wiring substrate, using flip-chip technology.

27. A BAW filter as set forth in claim 20, wherein each of said plurality of resonator structures includes a plurality of electrodes, wherein a portion of a first one of said electrodes of a first one of said resonator structures is exposed for providing a first contact pad, a portion of a first one of said electrodes of a second one of said resonator structures is exposed for providing a second contact pad, and wherein said BAW filter further comprises a third contact pad disposed over said substrate, said third contact pad being exposed and being electrically coupled to a first one of said electrodes of each of a third one and a fourth one of said resonator structures, and wherein said first, second, and third contact pads are for coupling respective ones of said first, second, and third resonator structures to a wiring substrate.

28. A BAW filter as set forth in claim 27, and further comprising a fourth exposed contact pad disposed over said substrate, said fourth contact pad being electrically coupled to said first one of said electrodes of each of said third and fourth resonator structures, said fourth contact pad for coupling said third and fourth resonator structures to a wiring substrate.

29. A BAW filter as set forth in claim 20, wherein each of said resonator structures includes at least two electrodes, said BAW filter further comprising a plurality of contacts disposed over an external surface of said BAW filter, individual ones of at least two of said contacts being electrically coupled to an electrode of respective individual ones of at least two of said resonator structures, said contacts for surface mounting said BAW filter to a wiring substrate.

30. A BAW filter as set forth in claim 20, wherein each of said resonator structures includes a plurality of electrodes, said BAW filter further comprising a plurality of contacts disposed over an external surface of said BAW filter, wherein a first one of said electrodes of a first one of said resonator structures is electrically coupled to a first one of said contacts, a first one of said electrodes of a second one of said resonator structures is electrically coupled to a second one of said contacts, a first one of said electrodes of a third one of said resonator structures is electrically coupled to a third one of said contacts, and a first one of said electrodes of a fourth one of said resonator structures is electrically coupled to said third contact.

31. A BAW filter as set forth in claim 30, wherein said first electrodes of said third and fourth resonator structures are also electrically coupled to a fourth one of said contacts.

32. A Bulk Acoustic Wave (BAW) filter, comprising:

a substrate;

a first acoustic mirror disposed over said substrate;

at least one resonator structure disposed over a portion of said first acoustic mirror; and

a second acoustic mirror disposed over said at least one resonator structure, wherein said at least one resonator structure includes a plurality of stacked resonators, thereby forming a stacked crystal filter structure.

33. A method of fabricating a BAW filter, comprising the steps of:

forming a first acoustic mirror over a substrate;

forming at least one resonator structure on the first acoustic mirror; and

forming a second acoustic mirror over at least a substantial portion of the at least one resonator structure, wherein the step of forming at least one resonator structure is performed by forming a plurality of adjacent resonators on the first acoustic mirror.

34. A method as set forth in claim 33, wherein the step of forming the second acoustic mirror includes the steps of:

forming a first layer over the plurality of adjacent resonators and over a portion of the first acoustic mirror, the first layer including a material having a low acoustic impedance;

forming a second layer over the first layer, the second layer including a material having a high acoustic impedance; and

forming a third layer over the second layer, the third layer including a material having a low acoustic impedance.

35. A method as set forth in claim 34, wherein the material having a low acoustic impedance includes one of silicon, poly-silicon, aluminum, and a polymer material, and wherein the material having a high acoustic impedance includes one of gold, molybdenum, and tungsten.

36. A method as set forth in claim 33, further comprising a step of forming a protective passivation layer over the second acoustic mirror.

37. A method as set forth in claim 33, wherein between the steps of forming the at least one resonator structure and forming the second acoustic mirror, a step is performed of forming contact pads on the first acoustic mirror.

38. A method as set forth in claim 37, and further comprising a step of coupling the BAW filter to a wiring substrate by coupling the contact pads to contacts of the wiring substrate.

39. A method as set forth in claim 33, further including a step of forming contacts over an external surface of the BAW filter.

40. A method as set forth in claim 39, and further comprising a step of surface mounting the BAW filter to a wiring substrate by coupling the contacts to contacts of the wiring substrate.

41. A surface mountable Bulk Acoustic Wave (BAW) device, comprising:

a substrate;

a plurality of adjacent BAW resonator structures;

a first acoustic isolator disposed between said substrate and said plurality of adjacent BAW resonator structures;

a second acoustic isolator disposed over said plurality of adjacent BAW resonator structures; and

a plurality of electrodes disposed over an external surface of said BAW device for surface mounting said device to a wiring substrate.

42. A surface mountable BAW device as set forth in claim 41, wherein said substrate comprises one of silicon (Si), silicon dioxide (SiO₂), gallium arsenide (GaAs), glass, or a ceramic material.

43. A surface mountable BAW device as set forth in claim 41, wherein said first acoustic isolator transforms an impedance of the substrate to a lower impedance level.

44. A Bulk Acoustic Wave (BAW) filter, said BAW filter comprising at least one resonator structure which is disposed over a substrate, and further comprising an acoustic mirror disposed over said at least one resonator structure, wherein said at least one resonator structure includes a plurality of stacked resonators.

45. A method of fabricating a BAW filter, comprising the steps of:

forming a first acoustic mirror over a substrate;

forming at least one resonator structure on the first acoustic mirror; and

forming a second acoustic mirror over at least a substantial portion of the at least one resonator structure, wherein the step of forming at least one resonator structure is performed by forming a stack of resonators to form a stacked crystal structure.

46. A surface mountable Bulk Acoustic Wave (BAW) device, comprising:

a substrate;

at least one BAW resonator structure;

a first acoustic isolator disposed between said substrate and said at least one BAW resonator structure;

a second acoustic isolator disposed over said at least one BAW resonator structure; and

a plurality of electrodes disposed over an external surface of said BAW device for surface mounting said device to a wiring substrate, wherein said resonator structure comprises a plurality of stacked resonators.