Thin film bulk acoustic resonator and method of producing the same

• US 20020190814A1
• Filed: 05/09/2002
• Published: 12/19/2002
• Est. Priority Date: 05/11/2001
• Status: Active Grant

• Current Assignee: MEMS Solution Co., Ltd.
• Original Assignee: UBE Industries Limited
• Inventors: Nagao, Keigo, Hashimoto, Chisen, Yamada, Tetsuo
• Granted Patent: US 6,842,088 B2
• Time in Patent Office: Days
• US Class Current: 333/187
• CPC Class Codes: B06B 1/0644 using a single piezoelectric element B06B1/0688 takes precedence
• CPC Class Codes: G10K 11/04 Acoustic filters ; Acoustic resonators
• CPC Class Codes: H03H 2003/021 the resonators or networks being of the air-gap type
• CPC Class Codes: H03H 2003/0428 of an electrode
• CPC Class Codes: H03H 3/02 for the manufacture of piezoelectric or electrostrictive resonators or networks H03H3/08 takes precedence
• CPC Class Codes: H03H 9/02094 of adherence
• CPC Class Codes: H03H 9/02102 of temperature influence cutting angles H03H9/02015
• CPC Class Codes: H03H 9/02149 of ageing changes of characteristics, e.g. electro-acousto-migration
• CPC Class Codes: H03H 9/173 Air-gaps
• CPC Class Codes: H03H 9/174 Membranes
• CPC Class Codes: H03H 9/562 comprising a ceramic piezoelectric layer
• CPC Class Codes: H03H 9/564 implemented with thin-film techniques
• CPC Class Codes: H03H 9/585 Stacked Crystal Filters [SCF]
• CPC Class Codes: H03H 9/587 Air-gaps
• CPC Class Codes: Y10S 977/888 Shaping or removal of materials, e.g. etching
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49155 Manufacturing circuit on or in base

Abstract

A pit (52) is formed in a substrate comprising a silicon wafer (51) on a surface of which a silicon oxide thin layer (53) is formed. A sandwich structure (60) comprising a piezoelectric layer (62) and lower and upper electrodes (61, 63) joined to both surfaces of the piezoelectric layer is disposed so as to stride over the pit (52). The upper surface of the lower electrode (61) and the lower surface of the piezoelectric layer (62) joined to the upper surface of the lower electrode are treated so that the RMS variation of the height thereof is equal to 25 nm or less. The thickness of the lower electrode (61) is set to 150 nm or less. According to such a structure, there is provided a high-performance thin film bulk acoustic resonator which are excellent in electromechanical coupling coefficient and acoustic quality factor.

Claims

1. A thin film bulk acoustic resonator, comprising:

a piezoelectric layer;

a first electrode joined to a first surface of said piezoelectric layer; and

a second electrode joined to a second surface of said piezoelectric layer, which is located at the opposite side to the first surface,

wherein RMS variation of the height of the first surface of said piezoelectric layer is equal to 25 nm or less.

2. The thin film bulk acoustic resonator as claimed in claim 1, wherein the RMS variation of the height of the first surface of said piezoelectric layer is equal to 20 nm or less.

3. The thin film bulk acoustic resonator as claimed in claim 1, wherein the RMS variation of the height of the second surface of said piezoelectric layer is set to not more than 5% of the thickness of said piezoelectric layer.

4. The thin film bulk acoustic resonator as claimed in claim 1, wherein a waviness height of a surface of said second electrode is set to not more than 25% of the thickness of said piezoelectric layer.

5. The thin film bulk acoustic resonator as claimed in claim 1, wherein said second electrode has a center portion and an outer peripheral portion having a larger thickness than said center portion.

6. The thin film bulk acoustic resonator as claimed in claim 5, wherein said outer peripheral portion is located in a frame shape so as to surround said center portion.

7. The thin film bulk acoustic resonator as claimed in claim 5, wherein said second electrode is designed so that thickness variation of said center portion is set to not more than 1% of the thickness of said center portion.

8. The thin film bulk acoustic resonator as claimed in claim 5, wherein the thickness of said outer peripheral portion is set to not less than 1.1 time as high as the height of said center portion.

9. The thin film bulk acoustic resonator as claimed in claim 5, wherein said outer peripheral portion is located within an area inwardly extending from an outer edge of said second electrode by a distance of 40 μ

m.

10. The thin film bulk acoustic resonator as claimed in claim 5, wherein the waviness height of a surface of said center portion is set to not more than 25% of the thickness of said piezoelectric layer.

11. The thin film bulk acoustic resonator as claimed in claim 1, wherein a sandwich structure comprising said piezoelectric layer, said first electrode and said second electrode is supported at an edge portion thereof by said substrate so as to stride over a pit formed on a surface of said substrate.

12. The thin film bulk acoustic resonator as claimed in claim 11, wherein an insulating layer is formed on the surface of said substrate so as to stride over said pit portion, and said sandwich structure is formed on the insulating layer.

14. The thin film bulk acoustic resonator as claimed in claim 13, wherein the surface of said first electrode facing said piezoelectric layer has the RMS variation of 20 nm or less.

15. The thin film bulk acoustic resonator as claimed in claim 13, wherein the RMS variation of the height of the second surface of said piezoelectric layer is set to not more than 5% of the thickness of said piezoelectric layer.

16. The thin film bulk acoustic resonator as claimed in claim 13, wherein a waviness height of a surface of said second electrode is set to not more than 25% of the thickness of said piezoelectric layer.

17. The thin film bulk acoustic resonator as claimed in claim 13, wherein said second electrode has a center portion and an outer peripheral portion having a larger thickness than said center portion.

18. The thin film bulk acoustic resonator as claimed in claim 17, wherein said outer peripheral portion is located in a frame shape so as to surround said center portion.

19. The thin film bulk acoustic resonator as claimed in claim 17, wherein said second electrode is designed so that thickness variation of said center portion is sct to not more than 1% of the thickness of said center portion.

20. The thin film bulk acoustic resonator as claimed in claim 17, wherein the thickness of said outer peripheral portion is set to not less than 1.1 time as high as the height of said center portion.

21. The thin film bulk acoustic resonator as claimed in claim 17, wherein said outer peripheral portion is located within an area inwardly extending from an outer edge of said second electrode by a distance of 40 μ

m.

22. The thin film bulk acoustic resonator as claimed in claim 17, wherein the waviness height of a surface of said center portion is set to not more than 25% of the thickness of said piezoelectric layer.

23. The thin film bulk acoustic resonator as claimed in claim 13, wherein a sandwich structure comprising said piezoelectric layer, said first electrode and said second electrode is supported at an edge portion thereof by said substrate so as to stride over a pit formed on a surface of said substrate.

24. The thin film bulk acoustic resonator as claimed in claim 23, wherein an insulating layer is formed on the surface of said substrate so as to stride over said pit portion, and said sandwich structure is formed on the insulating layer.

26. The method as claimed in claim 25, wherein the surface of the sacrificial layer is polished so that the RMS variation of the height of the surface of the sacrificial layer is equal to 20 nm or less.

27. The method as claimed in claim 25, wherein the first electrode is formed at a thickness of 150 nm or less, and RMS variation of the height of an upper surface of the first electrode is set to 25 nm or less.

28. The method as claimed in claim 27, wherein the RMS variation of the height of the upper surface of the first electrode is set to 20 nm or less.

29. The method as claimed in claim 25, wherein an insulating layer is formed before the first electrode is formed on the sacrificial layer.

13. A thin film bulk acoustic resonator, comprising:

a piezoelectric layer;

a first electrode joined to a first surface of said piezoelectric layer; and

a second electrode joined to a second surface of said piezoelectric layer, which is located at the opposite side to the first surface,

wherein a surface of said first electrode facing said piezoelectric layer has RMS variation of the height thereof that is equal to 25 nm or less.

25. A method of producing a thin film bulk acoustic resonator having a piezoelectric layer, a first electrode joined to a first surface of the piezoelectric layer, and a second electrode joined to a second surface of the piezoelectric layer, which is located at the opposite side to the first surface, comprising:

forming a pit on a surface of a substrate;

filling the pit with a sacrificial layer;

polishing a surface of the sacrificial layer so that RMS variation of the height of the surface of the sacrificial layer is equal to 25 nm or less;

forming the first electrode over a partial area of the surface of the sacrificial layer and a partial area of the surface of the substrate;

forming the piezoelectric layer on the first electrode;

forming the second electrode on the piezoelectric layer; and

removing the sacrificial layer from the inside of the pit by etching.

30. A thin film bulk acoustic resonator, comprising:

a substrate; and

a sandwich structure disposed on said substrate and having a piezoelectric thin film layer, a lower electrode layer at the substrate side and an upper electrode layer paired with said lower electrode layer, which are stacked so that said piezoelectric thin film layer is sandwiched between said lower electrode layer and said upper electrode layer,

wherein said sandwich structure has an adhesion electrode layer located between said lower electrode layer and said substrate and joined to said lower electrode layer, and said adhesion electrode layer is joined to said substrate around a pit which is formed on said substrate so as to permit vibration of said sandwich structure.

31. The thin film bulk acoustic resonator as claimed in claim 30, wherein said adhesion electrode layer is formed in an annular shape.

32. The thin film bulk acoustic resonator as claimed in claim 30, wherein when a plane area of a portion of said adhesion electrode layer which is brought into contact with said lower electrode layer is represented by S1 and a plane area of said lower electrode layer is represented by S2, the relationship:

0.01×

S2≦

S1≦

0.5×

S2 is satisfied.

33. The thin film bulk acoustic resonator as claimed in claim 30, wherein said upper electrode layer is located in an area corresponding to the inside of said adhesion electrode layer.

34. The thin film bulk acoustic resonator as claimed in claim 30, wherein said adhesion electrode layer comprises material containing at least one material selected from a group consisting of Ti, Cr, Ni and Ta.

35. The thin film bulk acoustic resonator as claimed in claim 30, wherein said lower electrode layer comprises material containing at least one material selected from a group consisting of Au, Pt, W and Mo.

36. The thin film bulk acoustic resonator as claimed in claim 30, wherein said piezoelectric thin film layer is formed of AlN or ZnO.

37. A method of producing a thin film bulk acoustic resonator of claim 30, comprising:

forming the adhesion electrode layer on the surface of the substrate having the pit so that the adhesion electrode layer is located around the pit;

forming a sacrificial layer on the surface of the substrate so that the sacrificial layer is located in an area corresponding to the pit located at the inside of the adhesion electrode layer;

polishing a surface of the sacrificial layer so that RMS variation of the height thereof is equal to 25 nm or less;

successively forming the lower electrode layer, the piezoelectric thin film layer and the upper electrode layer on the sacrificial layer and the adhesion electrode layer; and

then removing the sacrificial layer.

38. The method as claimed in claim 37, wherein the surface of the sacrificial layer is polished so that the RMS variation of the height thereof is equal to 20 nm or less.

39. The method as claimed in claim 37, wherein the sacrificial layer is formed by forming a layer of sacrificial layer material so that the substrate and the adhesion electrode layer are covered by the layer of the sacrificial layer material, and polishing the layer of the sacrificial layer material so that the surface of the adhesion electrode layer is exposed.

40. The method as claimed in claim 37, wherein the sacrificial layer is removed by etching.

41. The method as claimed in claim 37, wherein glass or plastic material is used for the sacrificial layer.

42. A piezoelectric thin film resonator, comprising:

a substrate; and

a piezoelectric stack structure formed on said substrate in which a vibrating portion is constructed to contain a part of the piezoelectric stack structure, the piezoelectric stack structure is formed by stacking a lower electrode, a piezoelectric film and an upper electrode in this order from the substrate side, and a cavity for permitting vibration of the vibrating portion is formed in the substrate in an area corresponding to the vibrating portion,

wherein said piezoelectric film is mainly formed of aluminum nitride, said lower electrode and said upper electrode are mainly formed of molybdenum, and said vibrating portion contains at least a part of at least one insulating layer mainly formed of silicon oxide or silicon nitride which is joined to said piezoelectric stack structure.

43. The piezoelectric thin film resonator as claimed in claim 42, wherein the thickness t of said piezoelectric film and the total thickness of at least one insulating layer satisfies the following inequality:

0.1≦

t′

/t≦

0.5.

44. The piezoelectric thin film resonator as claimed in claim 42, wherein the content of aluminum nitride in said piezoelectric film is set to 90 equivalent % or more.

45. The piezoelectric thin film resonator as claimed in claim 42, wherein the content of silicon oxide or silicon nitride in said insulating layer is set to 50 equivalent % or more.

46. The piezoelectric thin film resonator as claimed in claim 42, wherein the content of molybdenum in each of said lower electrode and said upper electrode is set to 80 atomic % or more.

47. The piezoelectric thin film resonator as claimed in claim 42, wherein one of said at least one insulating layer is formed on the surface of said substrate.

48. The piezoelectric thin film resonator as claimed in claim 42, wherein one of said at least one insulating layer is formed on a surface of said piezoelectric stack structure at the opposite side to said substrate.

49. The piezoelectric thin film resonator as claimed in claim 42, wherein said substrate is formed of single crystal silicon.

50. The piezoelectric thin film resonator as claimed in claim 42, wherein said upper electrode comprises a first electrode portion and a second electrode portion which are formed so as to be spaced from each other.

51. The piezoelectric thin film resonator as claimed in claim 42, wherein the electromechanical coupling coefficient determined on the basis of the measurement values of the resonance frequency and the antiresonance frequency in the neighborhood of 2.0 GHz is equal to 4.0 to 6.5%, and the acoustic quality factor thereof is equal to 750 to 2000, and the temperature coefficient of the resonance frequency is equal to −

20 to 20 ppm/°

C.