Piezoelectric resonator, piezoelectric filter, duplexer, communication apparatus, and method for manufacturing piezoelectric resonator

• US 20030132683A1
• Filed: 12/27/2002
• Published: 07/17/2003
• Est. Priority Date: 01/08/2002
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Uesaka, Ken-Ichi, Nakamura, Daisuke, Hayashi, Takashi, Yamada, Hajime, Kawamura, Hideki, Fujino, Hiroyuki, Takeuchi, Masaki, Nomura, Tadashi, Ushimi, Yoshimitsu, Yoshino, Yukio
• Granted Patent: US 6,906,451 B2
• Time in Patent Office: Days
• US Class Current: 310/346
• CPC Class Codes: C23C 14/10 Glass or silica
• CPC Class Codes: C23C 14/35 by application of a magnetic field, e.g. magnetron sputtering C23C14/3457 takes precedence
• CPC Class Codes: H03H 3/02 for the manufacture of piezoelectric or electrostrictive resonators or networks H03H3/08 takes precedence
• CPC Class Codes: H03H 3/04 for obtaining desired frequency or temperature coefficient
• CPC Class Codes: H03H 9/02133 of stress
• 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 9/564 implemented with thin-film techniques
• CPC Class Codes: H03H 9/568 consisting of a ladder configuration
• CPC Class Codes: H04R 17/00 Piezoelectric transducers; Electrostrictive transducers piezoelectric or electrostrictive elements in general H10N30/00; details of piezoelectric or electrostrictive motors, generators or positioners H10N30/00
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49005 Acoustic transducer
• CPC Class Codes: Y10T 29/49126 Assembling bases
• CPC Class Codes: Y10T 29/49128 Assembling formed circuit to base
• CPC Class Codes: Y10T 29/4913 Assembling to base an electrical component, e.g., capacitor, etc.
• CPC Class Codes: Y10T 29/49155 Manufacturing circuit on or in base
• CPC Class Codes: Y10T 29/49156 with selective destruction of conductive paths

Abstract

A piezoelectric thin film resonator having a stabilized temperature characteristic of resonant frequency, a method for manufacturing the same, and a communication apparatus using the piezoelectric thin film resonator are provided. The piezoelectric thin film resonator is provided with a substrate having an opening, first and second insulation films which are provided on one surface of the substrate while covering the opening and which primarily include SiO₂ and Al₂O₃, respectively, Al₂O₃ having oxygen defect and being in an amorphous state, and a piezoelectric thin film which is provided on the second insulation film and is sandwiched between electrodes and which primarily includes ZnO.

Claims

1. A piezoelectric resonator comprising:

a substrate; and

a vibration portion provided on the substrate, the vibration portion including a thin film portion in which top and bottom surfaces of the thin film portion includes at least one layer of piezoelectric thin film sandwiched between at least a pair of upper and lower electrodes facing each other in a thickness direction of the thin film portion;

wherein

first and second insulation films arranged between the substrate and the vibration portion; and

a temperature coefficient of resonant frequency of one of the first insulation film, the second insulation film, and the piezoelectric thin film and temperature coefficients of resonant frequencies of the others of the first insulation film, the second insulation film, and the piezoelectric thin film have opposite signs.

2. The piezoelectric resonator according to claim 1, wherein one of the first and second insulation films primarily comprises Al₂O₃.

3. The piezoelectric resonator according to claim 1, wherein one of the first and second insulation films primarily comprises SiO₂.

4. The piezoelectric resonator according to claim 1, wherein the first insulation film primarily comprises Al₂O₃ and the second insulation film primarily comprises SiO₂.

5. The piezoelectric resonator according to claim 1, wherein the arithmetic average surface roughness of the lower electrode is about 2.5 nm or less.

6. The piezoelectric resonator according to claim 1, wherein an upper layer of the first and second insulation films primarily comprises Al₂O₃, and the arithmetic average surface roughness thereof is about 1.0 nm or less.

7. The piezoelectric resonator according to claim 1, wherein an upper layer of the first and second insulation films primarily comprises Al₂O₃, and the stress therein is in a range of about 250 MPa to about 400 MPa on a tensile stress basis.

8. The piezoelectric resonator according to claim 1, wherein an upper layer of the first and second insulation films primarily comprises SiO₂, and the arithmetic average surface roughness thereof is about 1.0 nm or less.

9. The piezoelectric resonator according to claim 1, wherein an upper layer of the first and second insulation films primarily comprises SiO₂, and the stress therein is about 250 MPa or less on a compressive stress basis.

10. The piezoelectric resonator according to claim 1, wherein:

the first insulation film is arranged as an upper layer;

the second insulation film is arranged as a lower layer;

the film thickness ratio of piezoelectric thin film/(the first insulation film and second insulation film) is a range of about 0.7 to about 1.2; and

the film thickness ratio of the second insulation film/the first insulation film is in a range of about 1 to about 3.

11. The piezoelectric resonator according to claim 1, wherein an anti-oxidation film is arranged on the lower electrode.

12. The piezoelectric resonator according to claim 11, wherein the anti-oxidation film comprises a metal primarily including any one selected from the group consisting of Au, Ru, Rh, Pd, Os, Ir, and Pt.

13. The piezoelectric resonator according to claim 1, wherein the lower electrode comprises a metal primarily including any one selected from the group consisting of Al, Ni, Fe, Mn, Cu, Ti, Mo, W, Ta, and Ag.

14. The piezoelectric resonator according to claim 11, wherein:

the anti-oxidation film comprises a metal primarily including Au;

the lower electrode comprises a metal primarily including Al; and

a diffusion prevention film is arranged between the anti-oxidation film and the lower electrode.

15. The piezoelectric resonator according to claim 14, wherein the diffusion prevention film comprises a metal primarily including any one selected from the group consisting of Ag, Ru, Rh, Pd, Os, Ir, Pt, Mo, and Ti.

16. The piezoelectric resonator according to claim 2, wherein Al₂O₃ in the first or second insulation film comprises an oxygen defect.

17. The piezoelectric resonator according to claim 2, wherein Al₂O₃ in the first or second insulation film comprises an oxygen defect, and the value of the oxygen defect is within the range of about 0.05≦

x≦

about 0.5 in terms of Al₂O<sub>3−

x</sub>.

18. The piezoelectric resonator according to claim 2, wherein Al₂O₃ in the first or second insulation film is in an amorphous state.

19. The piezoelectric resonator according to of claim 1, wherein the substrate comprises an opening or a concavity and the vibration portion is arranged on the opening or concavity.

20. The piezoelectric resonator according to claim 1, wherein the piezoelectric thin film primarily comprises ZnO or AlN.

21. A piezoelectric filter comprising the piezoelectric resonator according to claim 1.

22. A piezoelectric filter having a ladder configuration and including the piezoelectric resonator according to claim 1.

23. A duplexer comprising the piezoelectric resonator according to claim 1.

24. A communication apparatus comprising the piezoelectric resonator according to claim 1.

25. A method for manufacturing a piezoelectric resonator comprising a substrate, first and second insulation films provided on the substrate, wherein the first and second insulation films and top and bottom surfaces of a thin film portion including at least one layer of piezoelectric thin film are sandwiched between at least a pair of upper and lower electrodes which face each other in the thickness direction of the thin film, the method comprising the step of:

forming an insulation film primarily including Al₂O₃ by a vacuum evaporation method while the pressure in a film formation apparatus before starting the film formation is less than about 3.0×

10<sup>−

4</sup> Pa, wherein the insulation film primarily including Al₂O₃ is an upper layer of the first and second insulation films.

26. A method for manufacturing a piezoelectric resonator comprising a substrate, first and second insulation films provided on the substrate, wherein the first and second insulation films and top and bottom surfaces of a thin film portion including at least one layer of piezoelectric thin film are sandwiched between at least a pair of upper and lower electrodes which face each other in the thickness direction of the thin film, the method comprising the step of:

forming an insulation film primarily including Al₂O₃ by an electron beam evaporation method at a film thickness growth rate of about 0.6 nm/sec to about 1.0 nm/sec, wherein the insulation film primarily including Al₂O₃ is an upper layer of the first and second insulation films.

27. A method for manufacturing a piezoelectric resonator comprising a substrate, first and second insulation films provided on the substrate, wherein the first and second insulation films and top and bottom surfaces of a thin film portion including at least one layer of piezoelectric thin film are sandwiched between at least a pair of upper and lower electrodes which face each other in the thickness direction of the thin film, the method comprising the step of:

forming an insulation film primarily including SiO₂ by an RF magnetron sputtering method while the power density is set to about 2.0 W/cm² to about 8.5 W/cm², wherein the insulation film primarily including SiO₂ is an upper layer of the first and second insulation films.

28. The method for manufacturing a piezoelectric resonator according to claim 27, wherein the gas pressure during film formation by the RF magnetron sputtering method is about 0.6 Pa or less.

29. A piezoelectric resonator, comprising:

a substrate;

an insulation film provided on the substrate; and

a vibration portion provided on the insulation film, the vibration portion including a thin film portion including at least one layer of piezoelectric thin film which is sandwiched between at least a pair of upper and lower electrodes which face each other in the thickness direction of the thin film;

wherein an arithmetic average surface roughness of the lower electrode is about 2.5 nm or less.

30. The piezoelectric resonator according to claim 29, wherein the surface of the insulation film has an arithmetic average surface roughness of about 1.0 nm or less and the stress in the insulation film is about 250 MPa or less on a compressive stress basis and about 400 MPa or less on a tensile stress basis.

31. The piezoelectric resonator according to claim 29, wherein the insulation film primarily comprises Al₂O₃, and the arithmetic average surface roughness thereof is about 1.0 nm or less.

32. The piezoelectric resonator according to claim 29, wherein the insulation film primarily comprises SiO₂, and the arithmetic average surface roughness thereof is about 1.0 nm or less.

33. The piezoelectric resonator according to claim 29, wherein the insulation film primarily comprises SiO₂, and the stress therein is about 250 MPa or less on a compressive stress basis.

34. The piezoelectric resonator according to claim 29, wherein an anti-oxidation film is arranged on the lower electrode.

35. The piezoelectric resonator according to claim 34, wherein the anti-oxidation film comprises a metal primarily including any one selected from the group consisting of Au, Ru, Rh, Pd, Os, Ir, and Pt.

36. The piezoelectric resonator according to claim 29, wherein the lower electrode comprises a metal primarily including any one selected from the group consisting of Al, Ni, Fe, Mn, Cu, Ti, Mo, W, Ta, and Ag.

37. The piezoelectric resonator according to claim 34, wherein the anti-oxidation film comprises a metal primarily including Au, the lower electrode comprises a metal primarily including Al, and a diffusion prevention film is arranged between the anti-oxidation film and the lower electrode.

38. The piezoelectric resonator according to claim 37, wherein the diffusion prevention film comprises a metal primarily including any one selected from the group consisting of Ag, Ru, Rh, Pd, Os, Ir, Pt, Mo, and Ti.

39. The piezoelectric resonator according to claim 29, wherein the substrate comprises an opening or a concavity, and the vibration portion is arranged on the opening or concavity.

40. A piezoelectric filter comprising the piezoelectric resonator according to claim 29.

41. A piezoelectric filter comprising a plurality of piezoelectric resonators according to claim 29, the plurality of piezoelectric resonators defining filter elements, wherein the filter elements are connected so as to define a ladder type configuration.

42. A duplexer comprising the piezoelectric resonator according to claim 29.

43. A duplexer comprising the piezoelectric filter according to claim 40.

44. A duplexer comprising the piezoelectric filter according to claim 41.

45. A method for manufacturing a piezoelectric resonator comprising a substrate, an insulation film provided on the substrate, and a vibration portion provided on the insulation film, the vibration portion including a thin film portion having top and bottom surfaces including at least one layer of piezoelectric thin film sandwiched between at least a pair of upper lower electrodes which face each other in the thickness direction of the thin film, the method comprising:

a first step of forming the insulation film from silicon oxide as a primary component by an RF magnetron sputtering method while the power density is within a range of about 2.0 W/cm² to about 8.5 W/cm²; and

a second step of forming the piezoelectric thin film from zinc oxide as a primary component.

46. The method for manufacturing a piezoelectric resonator according to claim 45, wherein the gas pressure during film formation by the RF magnetron sputtering method is about 0.6 Pa or less.

47. A method for manufacturing a piezoelectric resonator comprising a substrate, first and second insulation films provided on the substrate, and a vibration portion provided on the first and second insulation films, the vibration portion including a thin film portion having top and bottom surfaces including at least one layer of piezoelectric thin film sandwiched between at least a pair of upper and lower electrode which face each other in the thickness direction of the thin film, the method comprising the step of:

forming an insulation film primarily including Al₂O₃ by a vacuum evaporation method while the pressure in a film formation apparatus before start of film formation is less than about 3.0×

10<sup>−

4</sup> Pa, wherein the insulation film primarily including Al₂O₃ is an upper layer of the first and second insulation films.

48. A method for manufacturing a piezoelectric resonator comprising a substrate, an insulation film provided on the substrate, and a vibration portion provided on the insulation film, the vibration portion including a thin film portion having top and bottom surfaces of including at least one layer of piezoelectric thin film sandwiched between at least a pair of upper and lower electrodes facing each other in the thickness direction, the method comprising:

a first step of forming the insulation film from aluminum oxide as a primary component by an electron beam evaporation method at a film thickness growth rate within the range of about 0.6 nm/sec to about 1.0 nm/sec; and

a second step of forming the piezoelectric thin film from zinc oxide as a primary component.