Tunable planar capacitor

• US 6,970,055 B2
• Filed: 02/02/2004
• Issued: 11/29/2005
• Est. Priority Date: 04/11/2001
• Status: Expired due to Fees

• Current Assignee: Kyocera Corporation
• Original Assignee: Kyocera Wireless Corporation (Kyocera Corporation)
• Inventors: Toncich, Stan
• Primary Examiner(s): Takaoka, Dean
• Application Number:
  US10/770,089
• Publication Number:
  US 20050128032A1
• Time in Patent Office: 666 Days
• Field of Search: 333/24.C, 257/595, 361/306.3, 361/321.1, 361/434, 361/600, 361/601
• US Class Current: 333/24.00C
• CPC Class Codes: G01R 27/2694 Measuring dielectric loss, e.g. loss angle, loss factor or power factor
• CPC Class Codes: H01G 7/06 having a dielectric selected for the variation of its permittivity with applied voltage, i.e. ferroelectric capacitors electrets H01G7/02
• CPC Class Codes: H01L 27/0808 Varactor diodes
• CPC Class Codes: H01P 1/203 Strip line filters
• CPC Class Codes: H01P 1/20336 Comb or interdigital filters
• CPC Class Codes: H01P 1/20363 Linear resonators
• CPC Class Codes: H01P 1/20381 Special shape resonators
• CPC Class Codes: H01P 1/2039 Galvanic coupling between Input/Output
• CPC Class Codes: H01P 1/2056 Comb filters or interdigital filters with metallised resonator holes in a dielectric block
• CPC Class Codes: H01P 1/213 combining or separating two or more different frequencies H01P1/215 takes precedence
• CPC Class Codes: H01P 5/04 with variable factor of coupling
• CPC Class Codes: H03B 5/04 Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
• CPC Class Codes: H03B 5/124 the means comprising a voltage dependent capacitance
• CPC Class Codes: H03B 5/1262 the means comprising switched elements
• CPC Class Codes: H03B 5/1293 having means for achieving a desired tuning characteristic, e.g. linearising the frequency characteristic across the tuning voltage range
• CPC Class Codes: H03B 5/1841 the frequency-determining element being a strip line resonator H03B5/1805, H03B5/1817, H03B5/1864 and H03B5/1882 take precedence
• CPC Class Codes: H03B 5/362 the amplifier being a single transistor H03B5/364 - H03B5/368 take precedence
• CPC Class Codes: H03F 1/56 Modifications of input or output impedances, not otherwise provided for
• CPC Class Codes: H03F 2200/111 the amplifier being a dual or triple band amplifier, e.g. 900 and 1800 MHz, e.g. switched or not switched, simultaneously or not
• CPC Class Codes: H03F 2200/294 the amplifier being a low noise amplifier [LNA]
• CPC Class Codes: H03F 2200/372 : Noise reduction and elimination in amplifier
• CPC Class Codes: H03F 3/191 : Tuned amplifiers H03F3/193, H03F3/195 take precedence
• CPC Class Codes: H03H 7/0123 : comprising distributed impedance elements together with lumped impedance elements
• CPC Class Codes: H03H 7/12 : Bandpass or bandstop filters with adjustable bandwidth and fixed centre frequency H03H7/09 takes precedence; automatic control of bandwidth in amplifiers H03G5/16
• CPC Class Codes: H03H 7/20 : Two-port phase shifters providing an adjustable phase shift
• CPC Class Codes: H03J 5/246 : using electronic means H03J5/244 takes precedence
• CPC Class Codes: H03L 1/022 : by indirect stabilisation, i.e. by generating an electrical correction signal which is a function of the temperature H03L1/021 takes precedence
• CPC Class Codes: H03L 7/18 : using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence
• CPC Class Codes: H04B 1/0053 : with common antenna for more than one band
• CPC Class Codes: H04B 1/0458 : Arrangements for matching and coupling between power amplifier and antenna or between amplifying stages matching circuits in general H03H
• CPC Class Codes: H04B 1/30 : for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04B 1/40 : Circuits

Abstract

A tunable capacitor that introduces significantly less loss, if any, costs less and is smaller than previously available. A bias electrode is coupled to a FE material. The capacitor electrodes are electro-magnetically coupled to the FE material, such that the capacitor electrodes and the bias electrode are not touching. Only non-conductive material is in the gap defined by the capacitor electrodes. The bias electrode is used to apply a variable DC voltage to the FE material. A capacitor electrode serves as a DC ground for producing a variable DC field between the bias electrode and the capacitor electrodes.

Claims

1. A planar tunable capacitor comprising:

a substrate;

a bias electrode formed on the substrate;

a ferro-electric layer formed over the bias electrode;

wherein;

the bias electrode is more narrow than the ferro-electric layer;

a first capacitor electrode formed over the ferro-electric layer;

a second capacitor electrode formed over the ferro-electric layer and proximate the first capacitor electrode, the first and second capacitor electrodes forming a capacitor;

a gap defined by the capacitor electrodes, the gap consisting of non-conducting material;

wherein the bias electrode is not electrically connected to either of the capacitor electrodes.

2. The tunable capacitor of claim 1, further comprising a control signal generator coupled to a variable DC voltage source, the variable DC voltage source also coupled to the bias electrode for applying a variable DC voltage to the bias electrode.

3. The tunable capacitor of claim 1, wherein the second electrode is positioned within 3.0 microns of the first electrode.

4. The tunable capacitor of claim 1, wherein the capacitor comprises a gap capacitor.

5. The tunable capacitor of claim 1, wherein the capacitor comprises an interdigital capacitor.

6. The tunable capacitor of claim 1, wherein the capacitor is formed on a substrate.

7. The tunable capacitor of claim 6, wherein the substrate comprises a material chosen from the group consisting of:

sapphire, magnesium oxide, silicon dioxide, alumina, and FR4.

8. The tunable capacitor of claim 1, wherein the bias electrode comprises a material chosen from the group consisting of:

gold, silver, platinum, copper, and doped silicon.

9. The tunable capacitor of claim 1, wherein a thickness of the bias electrode is less than about 0.01 microns.

10. The tunable capacitor of claim 1, wherein an electrical thickness of the bias electrode is less than a fraction of about 0.1 times a skin depth of an RF signal.

11. The tunable capacitor of claim 10, wherein the RF signal comprises a 2.0 GHz signal.

12. The tunable capacitor of claim 1, wherein the ferro-electric layer is formed on the bias electrode.

13. The tunable capacitor of claim 1, wherein a thickness of the ferro-electric layer is equal to about one micron.

14. The tunable capacitor of claim 1, wherein a field attenuation caused by the bias electrode is about 0.28 percent.

15. The tunable capacitor of claim 14, wherein the field attenuation comprises field attenuation of a RF signal having a frequency equal to about 2.0 Ghz.

16. The tunable capacitor of claim 1, wherein the ferro-electric layer comprises barium strontium titanate.

17. The tunable capacitor of claim 1, wherein the bias electrode comprises two fingers.

18. The tunable capacitor of claim 1, wherein the bias electrode comprises two fingers that are not connected inside the gap.

19. The tunable capacitor of claim 1, wherein the bias electrode comprises two fingers connected at both ends.

20. A planar tunable capacitor comprising:

a first capacitor electrode;

a second capacitor electrode proximate the first capacitor electrode, the first and second capacitor electrodes forming a capacitor;

a gap defined by the capacitor electrodes, the gap consisting of non-conducting material;

a substrate proximate the gap;

a ferro-electric layer;

wherein the ferro-electric layer is a ferro-electric film deposited on the substrate;

a bias electrode proximate the ferro-electric layer;

wherein;

the bias electrode is not electrically connected to either of the capacitor electrodes.

21. The tunable capacitor of claim 20, further comprising a control signal generator coupled to a variable DC voltage source, the variable DC voltage source also coupled to the bias electrode for applying a variable DC voltage to the bias electrode.

22. The tunable capacitor of claim 20, wherein the second electrode is positioned within 3.0 microns of the first electrode.

23. The tunable capacitor of claim 20, wherein the capacitor comprises a gap capacitor.

24. The tunable capacitor of claim 20, wherein the capacitor comprises an interdigital capacitor.

25. The tunable capacitor of claim 20, wherein the capacitor is formed on a substrate.

26. The tunable capacitor of claim 25, wherein the substrate comprises a material chosen from the group consisting of:

sapphire, magnesium oxide, silicon dioxide, alumina, and FR4.

27. The tunable capacitor of claim 20, wherein the bias electrode comprises a material chosen form the group consisting of:

gold, silver, platinum, copper, and doped silicon.

28. The tunable capacitor of claim 20, wherein a thickness of the bias electrode is less than about 0.01 microns.

29. The tunable capacitor of claim 20, wherein an electrical thickness of the bias electrode is less than a fraction of about 0.1 times a skin depth of an RF signal.

30. The tunable capacitor of claim 29, wherein the RF signal comprises a 2.0 GHz signal.

31. The tunable capacitor of claim 20, wherein the ferro-electric material comprises a ferro-electric layer formed on the bias electrode.

32. The tunable capacitor of claim 20, wherein the ferro-electric material comprises a ferro-electric layer having a thickness of equal to about one micron.

33. The tunable capacitor of claim 20, wherein a field attenuation caused by the bias electrode is about 0.28 percent.

34. The tunable capacitor of claim 33, wherein the field attenuation comprises field attenuation of a RF signal having a frequency equal to about 2.0 Ghz.

35. The tunable capacitor of claim 20, wherein the ferro-electric material comprises barium strontium titanate.

36. The tunable capacitor of claim 20, wherein the bias electrode comprises two fingers.

37. The tunable capacitor of claim 20, wherein the bias electrode comprises two fingers that are not connected inside the gap.

38. The tunable capacitor of claim 20, wherein the bias electrode comprises two fingers connected at both ends.

39. A wireless communication device comprising:

a planar tunable capacitor comprising;

a substrate;

a bias electrode formed on the substrate;

a ferro-electric layer formed over the bias electrode;

wherein;

the bias electrode is more narrow than the ferro-electric layer;

a first capacitor electrode formed over the ferro-electric layer;

a second capacitor electrode formed over the ferro-electric layer and proximate the first capacitor electrode, the first and second capacitor electrodes forming a capacitor;

a gap defined by the capacitor electrodes, the gap consisting of non-conducting material;

wherein the bias electrode is not electrically connected to either of the capacitor electrodes; and

a transceiver comprising a band pass filter, the filter coupled to the capacitor.

40. The wireless communication device of claim 39, further comprising a control signal generator coupled to a variable DC voltage source, the variable DC voltage source also coupled to the bias electrode for applying a variable DC voltage to the bias electrode.

41. The wireless communication device of claim 39, wherein the second electrode is positioned within 3.0 microns of the first electrode.

42. The wireless communication device of claim 39, wherein the capacitor comprises a gap capacitor.

43. The wireless communication device of claim 39, wherein the capacitor comprises an interdigital capacitor.

44. The wireless communication device of claim 39, wherein the capacitor is formed on a substrate.

45. The wireless communication device of claim 44, wherein the substrate comprises a material chosen from the group consisting of:

sapphire, magnesium oxide, silicon dioxide, alumina, and FR4.

46. The wireless communication device of claim 39, wherein the bias electrode comprises a material chosen form the group consisting of:

gold, silver, platinum, copper, and doped silicon.

47. The wireless communication device of claim 39, wherein a thickness of the bias electrode is less than about 0.01 microns.

48. The wireless communication device of claim 39, wherein an electrical thickness of the bias electrode is less than a fraction of about 0.1 times a skin depth of an RF signal.

49. The wireless communication device of claim 48, wherein the RF signal comprises a 2.0 GHz signal.

50. The wireless communication device of claim 39, wherein the ferro-electric layer is formed on the bias electrode.

51. The wireless communication device of claim 39, wherein a thickness of the ferro-electric layer is equal to about one micron.

52. The wireless communication device of claim 39, wherein a field attenuation caused by the bias electrode is about 0.28 percent.

53. The wireless communication device of claim 52, wherein the field attenuation comprises field attenuation of a RF signal having a frequency equal to about 2.0 Ghz.

54. The wireless communication device of claim 39, wherein the ferro-electric layer comprises barium strontium titanate.

55. The wireless communication device of claim 39, wherein the bias electrode comprises two fingers.

56. The wireless communication device of claim 39, wherein the bias electrode comprises two fingers that are not connected inside the gap.

57. The wireless communication device of claim 39, wherein the bias electrode comprises two fingers connected at both ends.

58. A tunable planar capacitor comprising:

a substrate;

a bias electrode formed on the substrate;

a ferro-electric layer formed over the bias electrode; and

capacitor electrodes formed over the ferro-electric layer that are spaced to define a gap, wherein;

the bias electrode is more narrow than the ferro-electric layer in a direction substantially parallel to a capacitor electrode.

59. A tunable planar capacitor comprising:

a substrate;

a bias electrode formed on the substrate;

a ferro-electric layer formed over the bias electrode; and

capacitor electrodes formed over the ferro-electric layer that are spaced to define a gap, wherein;

the bias electrode is more narrow than the ferro-electric layer in a direction substantially perpendicular to a capacitor electrode.