Thin film acoustic resonator and method of producing the same

• US 6,842,088 B2
• Filed: 05/09/2002
• Issued: 01/11/2005
• Est. Priority Date: 05/11/2001
• Status: Expired due to Term

• Current Assignee: MEMS Solution Co., Ltd.
• Original Assignee: UBE Industries Limited (UBE Corporation)
• Inventors: Nagao, Keigo, Hashimoto, Chisen, Yamada, Tetsuo
• Primary Examiner(s): Summons, Barbara
• Application Number:
  US10/142,233
• Publication Number:
  US 20020190814A1
• Time in Patent Office: 978 Days
• Field of Search: 333186-192, 310/322, 310/324, 310/335
• 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, and 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.

2. 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, and 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.

3. 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, and wherein said second electrode has a center portion and an outer peripheral portion having a larger thickness than said center portion.

4. The thin film bulk acoustic resonator as claimed in any one of claims 1, 2 or 3, wherein the RMS variation of the height of the first surface of said piezoelectric layer is equal to 20 nm or less.

5. The thin film bulk acoustic resonator as claimed in claim 3, 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.

6. The thin film bulk acoustic resonator as claimed in claim 3, 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 3, 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 3, 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 3, 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. A thin film bulk acoustic resonator, comprising:

a piezoelectric layer;

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

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

an insulating layer formed on a surface of a substrate so as to stride over a pit portion formed on the surface of said substrate,

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 said pit portion, said sandwich structure is formed on the insulating layer, and RMS variation of the height of the first surface of said piezoelectric layer is equal to 25 nm or less.

11. 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, wherein a sandwich structure comprising said piezoelectric layer, said first electrode and said second electrode are supported at an edge portion thereof by a substrate so as to stride over a pit portion formed on a surface of said substrate, and 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.

12. 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, and 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.

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, and 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.

14. 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, and wherein said second electrode has a center portion and an outer peripheral portion having a larger thickness than said center portion.

15. The thin film bulk acoustic resonator as claimed in any one of claims 12, 13 or 14, wherein the surface of said first electrode facing said piezoelectric layer has the RMS variation of 20 nm or less.

16. The thin film bulk acoustic resonator as claimed in claim 14, 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.

17. The thin film bulk acoustic resonator as claimed in claim 14, 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.

18. The thin film bulk acoustic resonator as claimed in claim 14, 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 14, 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.

20. The thin film bulk acoustic resonator as claimed in claim 14, 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. A thin film bulk acoustic resonator, comprising:

a piezoelectric layer formed of AlN or ZnO;

a first electrode joined to a first surface of said piezoelectric layer and formed of material containing at least one material selected from a group consisting of Au, Pt, W and Mo; 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, and a full width at half maximum of XRD rocking curve of said piezoelectric layer is 2.2 to 2.8 degrees.

22. A thin film bulk acoustic resonator, comprising:

a piezoelectric layer formed of AlN or ZnO;

a first electrode joined to a first surface of said piezoelectric layer and formed of material containing at least one material selected from the group consisting of Au, Pt, W and Mo; 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, and an electromechanical coupling coefficient determined on the basis of measured values of resonance frequency and antiresonance frequency of approximately 2.0 GHz is equal to 4.5 to 7.5%.

23. A thin film bulk acoustic resonator, comprising:

a piezoelectric layer formed of AlN or ZnO;

a first electrode joined to a first surface of said piezoelectric layer and formed of material containing at least one material selected from the group consisting of Au, Pt, W and Mo; 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, and an acoustic quality factor determined on the basis of measured values of resonance frequency and antiresonance frequency of approximately 2.0 GHz is equal to 650 to 980.

24. A thin film bulk acoustic resonator, comprising:

a piezoelectric layer formed of AlN or ZnO;

a first electrode joined to a first surface of said piezoelectric layer and formed of material containing at least one material selected from the group consisting of Au, Pt, W and Mo; 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, and a full width at half maximum of XRD rocking curve of said piezoelectric layer is 2.2 to 2.8 degrees.

25. A thin film bulk acoustic resonator, comprising:

a piezoelectric layer formed of AlN or ZnO;

a first electrode joined to a first surface of said piezoelectric layer and formed of material containing at least one material selected from the group consisting of Au, Pt, W and Mo; 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, and an electromechanical coupling coefficient determined on the basis of measured values of resonance frequency and antiresonance frequency of approximately 2.0 GHz is equal to 4.5 to 7.5%.

26. A thin film bulk acoustic resonator, comprising:

a piezoelectric layer formed of AlN or ZnO;

a first electrode joined to a first surface of said piezoelectric layer and formed of material containing at least one material selected from the group consisting of Au, Pt, W and Mo; 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, and an acoustic quality factor determined on the basis of measured values of resonance frequency and antiresonance frequency of approximately 2.0 GHz is equal to 650 to 980.

27. The thin film bulk acoustic resonator as claimed in any one of claims 21, 22, 23, 24, 25, or 26, wherein a sandwich structure comprising said piezoelectric layer, said first electrode and said second electrode is supported at an edge portion thereof by a substrate so as to stride over a pit portion formed on a surface of said substrate.

28. The thin film bulk acoustic resonator as claimed in claim 27, 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.