Strain-relieved tunable dielectric thin films

• US 20030022030A1
• Filed: 04/13/2001
• Published: 01/30/2003
• Est. Priority Date: 04/13/2001
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Paratek Microwave Incorporated (Blackberry Limited)
• Inventors: Chang, Wontae
• Granted Patent: US 6,617,062 B2
• Time in Patent Office: Days
• US Class Current: 428/701
• CPC Class Codes: C23C 14/088 of the type ABO3 with A representing alkali, alkaline earth metal or Pb and B representing a refractory or rare earth metal
• CPC Class Codes: H01P 1/181 using ferroelectric devices
• CPC Class Codes: H01P 7/082 Microstripline resonators H01P7/088 takes precedence
• CPC Class Codes: H01P 7/084 Triplate line resonators H01P7/088 takes precedence
• CPC Class Codes: H01P 7/088 Tunable resonators

Abstract

Tunable dielectric thin films are provided which possess low dielectric losses at microwave frequencies relative to conventional dielectric thin films. The thin films include a low dielectric loss substrate, a buffer layer, and a crystalline dielectric film. Barium strontium titanate may be used as the buffer layer and the crystalline dielectric film. The buffer layer provides strain relief during annealing operations.

Claims

1. A tunable dielectric thin film comprising:

a low dielectric loss substrate;

a buffer layer on the low dielectric loss substrate; and

a crystalline dielectric film on the buffer layer.

2. The tunable dielectric thin film of claim 1, wherein the buffer layer comprises at least one material selected from barium strontium titanate, barium titanate, strontium titanate, barium calcium titanate, barium calcium zirconium titanate, lead titanate, lead zirconium titanate, lead lanthanum zirconium titanate, lead niobate, lead tantalate, potassium strontium niobate, sodium barium niobate/potassium phosphate, potassium niobate, lithium niobate, lithium tantalate, lanthanum tantalate, barium calcium zirconium titanate and sodium nitrate.

3. The tunable dielectric thin film of claim 1, wherein the buffer layer comprises barium strontium titanate.

4. The tunable dielectric thin film of claim 3, wherein the barium strontium titanate is of the formula Ba_xSr₁₋

xTiO₃, where x is from about 0.15 to about 0.6.

5. The tunable dielectric thin film of claim 4, wherein x is about 0.4.

6. The tunable dielectric thin film of claim 1, wherein the buffer layer comprises Ba_xCa₁₋

xTiO₃, where x is from about 0.2 to about 0.8.

7. The tunable dielectric thin film of claim 1, wherein the buffer layer comprises Pb_xZr₁₋

xSrTiO₃, where x is from about 0.05 to about 0.4.

8. The tunable dielectric thin film of claim 1, wherein the buffer layer comprises KTa_xNb₁₋

xO₃, where x is from 0 to 1.

9. The tunable dielectric thin film of claim 1, wherein the buffer layer comprises Pb_xZr₁₋

xTiO₃, where x is from 0 to 1.

10. The tunable dielectric thin film of claim 1, wherein the buffer layer has a thickness of from about 0.0005 to about 0.2 micron.

11. The tunable dielectric thin film of claim 1, wherein the buffer layer has a thickness of from about 0.01 to about 0.1 micron.

12. The tunable dielectric thin film of claim 1, wherein the buffer layer is vapor deposited.

13. The tunable dielectric thin film of claim 1, wherein the buffer layer is at least partially amorphous.

14. The tunable dielectric thin film of claim 1, wherein the buffer layer comprises a randomly oriented crystalline phase.

15. The tunable dielectric thin film of claim 1, wherein the buffer layer is porous.

16. The tunable dielectric thin film of claim 1, wherein the buffer layer is annealed.

17. The tunable dielectric thin film of claim 1, wherein the crystalline dielectric film comprises at least one material selected from barium strontium titanate, barium titanate, strontium titanate, barium calcium titanate, barium calcium zirconium titanate, lead titanate, lead zirconium titanate, lead lanthanum zirconium titanate, lead niobate, lead tantalate, potassium strontium niobate, sodium barium niobate/potassium phosphate, potassium niobate, lithium niobate, lithium tantalate, lanthanum tantalate, barium calcium zirconium titanate and sodium nitrate.

18. The tunable dielectric thin film of claim 1, wherein the crystalline dielectric film comprises barium strontium titanate.

19. The tunable dielectric thin film of claim 18, wherein the barium strontium titanate is of the formula Ba_xSr₁₋

xTiO₃, where x is from about 0.15 to about 0.6.

20. The tunable dielectric thin film of claim 19, wherein x is about 0.4.

21. The tunable dielectric thin film of claim 1, wherein the crystalline dielectric film has a thickness of from about 0.1 to about 5 micron.

22. The tunable dielectric thin film of claim 1, wherein the crystalline dielectric film has a thickness of from about 0.3 to about 1 micron.

23. The tunable dielectric thin film of claim 1, wherein the crystalline dielectric film is vapor deposited.

24. The tunable dielectric thin film of claim 1, wherein the crystalline dielectric film comprises a randomly oriented crystalline phase.

25. The tunable dielectric thin film of claim 1, wherein the crystalline dielectric film is annealed.

26. The tunable dielectric thin film of claim 1, wherein the buffer layer and the crystalline dielectric film comprise substantially the same composition.

27. The tunable dielectric thin film of claim 1, wherein the buffer layer and the crystalline dielectric film comprise barium strontium titanate.

28. The tunable dielectric thin film of claim 27, wherein the barium strontium titanate is of the formula Ba_xSr₁₋

xTiO₃, where x is from about 0.15 to about 0.6.

29. The tunable dielectric thin film of claim 28, wherein x is about 0.4.

30. The tunable dielectric thin film of claim 27, wherein the barium strontium titanate comprises a randomly oriented crystalline phase in each of the buffer layer and the crystalline dielectric film.

31. The tunable dielectric thin film of claim 30, wherein the crystalline phase is a cubic phase.

32. The tunable dielectric thin film of claim 27, wherein the barium strontium titanate is vapor deposited.

33. The tunable dielectric thin film of claim 32, wherein the barium strontium titanate of the buffer layer is deposited at a lower temperature than the barium strontium titanate of the crystalline dielectric film.

34. The tunable dielectric thin film of claim 1, wherein the buffer layer and the crystalline dielectric film are annealed.

35. The tunable dielectric thin film of claim 1, wherein the crystalline dielectric film is strain relieved.

36. The tunable dielectric thin film of claim 1, wherein the crystalline dielectric film is substantially strain free.

37. The tunable dielectric thin film of claim 1, wherein the low dielectric loss substrate comprises at least one crystalline material selected from magnesium oxide, aluminum oxide and lanthanum aluminum oxide.

38. The tunable dielectric thin film of claim 1, wherein the low dielectric loss substrate has a thickness of from about 250 to about 500 micron.

39. The tunable dielectric thin film of claim 1, wherein the dielectric thin film has a dielectric quality factor Q at 0 V_DC of greater than about 100 at a frequency of 2 GHz or 8 GHz.

40. The tunable dielectric thin film of claim 39, wherein the dielectric thin film has a dielectric tuning of at least about 20 percent at 50 V/micron at a frequency of 2 GHz or 8 GHz.

41. A method of making a thin film dielectric material, the method comprising:

depositing a dielectric buffer layer on a low dielectric loss substrate; and

depositing a layer of crystalline dielectric thin film on the dielectric buffer layer.

42. The method of claim 41, wherein in the depositing steps comprise at least one of RF sputtering, pulsed laser deposition, and metal-organic chemical vapor deposition.

43. The method of claim 41, wherein the dielectric buffer layer is deposited at a first temperature, and the layer of crystalline dielectric film is deposited at a second temperature different from the first temperature.

44. The method of claim 43, wherein the second temperature is higher than the first temperature.

45. The method of claim 44, wherein the second temperature is at least 100°

C. higher than the first temperature.

46. The method of claim 44, wherein the first temperature is between about room temperature and 300°

C.

47. The method of claim 44, wherein the first temperature is about room temperature.

48. The method of claim 44, wherein the second temperature is greater than 300°

C.

49. The method of claim 44, wherein the second temperature is greater than 500°

C.

50. The method of claim 41, wherein the dielectric buffer layer comprises a porous phase between a partially crystallized amorphous phase and a fully crystallized randomly oriented phase.

51. The method of claim 50, wherein the partially crystallized amorphous phase of the buffer layer is prepared by depositing at room temperature and then heating at a temperature up to about 750°

C. for less than about 5 minutes.

52. The method of claim 50, wherein the fully crystallized randomly oriented phase of the buffer layer is prepared by depositing at room temperature and then heating at a temperature higher than about 750°

C. for more than about 20 minutes.

53. The method of claim 41, wherein the as-deposited crystalline dielectric thin film has an average grain size of less than about 0.1 micron.

54. The method of claim 41, further comprising the step of annealing the crystalline dielectric thin film after it has been deposited.

55. The method of claim 54, wherein the crystalline dielectric thin film is annealed at a temperature higher than a temperature at which the crystalline dielectric thin film is deposited.

56. The method of claim 55, wherein the annealing temperature is at least 100°

C. higher than the crystalline dielectric thin film deposition temperature.

57. The method of claim 54, wherein the annealing temperature is higher than 1,000°

C.

58. The method of claim 57, wherein the annealing occurs for at least 3 hours in an oxygen atmosphere.

59. The method of claim 54, wherein the as-deposited crystalline dielectric thin film and the annealed crystalline dielectric thin film comprises a substantially fully crystallized randomly oriented phase.

60. The method of claim 54, wherein the as-deposited crystalline dielectric thin film and the annealed crystalline dielectric thin film comprises a cubic phase.

61. The method of claim 54, wherein the annealed crystalline dielectric thin film has an average grain size of from about 0.1 to about 0.5 micron.

62. The method of claim 54, wherein the annealed crystalline dielectric thin film has a dielectric quality factor Q at 0 V_DC of greater than about 100 at a frequency of 2 GHz or 8 GHz.

63. The method of claim 62, wherein the annealed crystalline dielectric thin film has a dielectric tuning of at least about 20 percent at 50V/μ

m at frequencies of 2 GHz and 8 GHz.

64. The method of claim 54, wherein the annealed crystalline dielectric thin film has a dielectric quality factor Q that is substantially equal or increases with DC bias voltages.

65. The method of claim 64, wherein the annealed crystalline dielectric film substantially maintains dielectric tuning at frequencies of 2 GHz and 8 GHz.