Non-reducing dielectric ceramic, monolithic ceramic capacitor using the same, and method for making non-reducing dielectric ceramic

• US 6,730,624 B2
• Filed: 05/02/2003
• Issued: 05/04/2004
• Est. Priority Date: 04/07/2000
• Status: Expired due to Term

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Naito, Masahiro, Motoki, Tomoo, Sano, Harunobu
• Primary Examiner(s): BRUNSMAN, DAVID M
• Application Number:
  US10/427,978
• Publication Number:
  US 20030210512A1
• Time in Patent Office: 368 Days
• Field of Search: 501/136, 264/615, 361/305, 361/321.2, 361/32.4
• US Class Current: 501/136
• CPC Class Codes: C04B 35/465 based on alkaline earth metal titanates
• CPC Class Codes: H01G 4/1227 based on alkaline earth titanates
• CPC Class Codes: H01G 4/1236 based on zirconium oxides or zirconates H01G4/1263 takes precedence
• CPC Class Codes: H01G 4/1245 containing also titanates

Abstract

A non-reducing dielectric ceramic contains Ca, Zr and Ti as metallic elements and does not contain Pb. In a CuKα X-ray diffraction pattern, the ratio of the maximum peak intensity of secondary crystal phases to the maximum peak intensity at 2θ=25° to 35° of a perovskite primary crystal phase is about 12% or less, the secondary crystal phases including all the crystal phases other than the perovskite primary crystal phase. The non-reducing dielectric ceramic exhibits superior insulating resistance and dielectric loss after firing in a neutral or reducing atmosphere and high reliability in a high-temperature loading lifetime test and is useful for producing compact high-capacitance monolithic ceramic capacitors.

Claims

1. A monolithic ceramic capacitor comprising:

at least three dielectric ceramic layers;

at least one pair of internal electrodes each of which is disposed between a different pair of dielectric ceramic layers;

a pair of external electrodes, each of which is electrically connected to a different one of said pair of internal electrodes;

wherein the dielectric ceramic layers comprise a non-reducing dielectric ceramic comprising Ca, Zr and Ti as metallic elements, free of Pb, and having a perovskite primary crystal phase and other crystal phases;

wherein the ratio of the maximum peak intensity of secondary crystal phases to the maximum peak intensity at 2θ

=25°

to 35°

of the perovskite primary crystal phase in a CuKα

X-ray diffraction pattern is about 12% or less, wherein the secondary crystal phases include all the crystal phases other than the perovskite primary crystal phase; and

wherein the internal electrodes comprise a base metal.

2. A monolithic ceramic capacitor according to claim 1, wherein the base metal is at least one member selected from the group consisting of elemental nickel, a nickel alloy, elemental copper and a copper alloy.

3. A monolithic ceramic capacitor according to claim 2, wherein said ratio is about 5% or less.

4. A monolithic ceramic capacitor according to claim 2, wherein said ratio is about 3% or less.

5. A monolithic ceramic capacitor according to claim 1, wherein said ceramic is represented by the formula A_pBO₃ in which A comprises Ca, B comprises Zr and Ti, and p is about 0.98 to 1.02.

6. A monolithic ceramic capacitor according to claim 5, wherein said ratio is about 5% or less.

7. A monolithic ceramic capacitor according to claim 5, wherein p is about 0.99 to 1.01.

8. A method for making a non-reducing dielectric ceramic comprising Ca, Zr and Ti as metallic elements, free of Pb, and having a ratio of the maximum peak intensity of secondary crystal phases to the maximum peak intensity at 20=25°

to 35°

of a perovskite primary crystal phase in a CuKα

X-ray diffraction pattern of about 12% or less, wherein the secondary crystal phases include all the crystal phases other than the perovskite primary crystal phase, the method comprising the steps of;

(A) providing a calcined powder for providing the B-site component of a dielectric ceramic represented by the general formula A_pBO₃;

(B) providing powder for providing the A-site component;

(C) mixing the calcined B-site component powder and the A-site component powder to prepare an uncalcined primary material powder;

(D) calcining the uncalcined primary material powder to prepare a calcined primary material powder;

(E) adjusting the composition of the calcined primary material powder to realize the desired value of p by adding at least one of the A-site component powder and B-site component powder to the calcined primary material powder to prepare a secondary material powder; and

(F) molding and sintering the secondary material powder under a neutral or reducing atmosphere.

9. A method for making a non-reducing dielectric ceramic according to claim 8, further comprising calcining a B-site component powder.

10. A method for making a non-reducing dielectric ceramic according to claim 9, wherein the B-site component powder which is calcined has an average particle diameter of about 0.5 μ

m or less.

11. A method for making a non-reducing dielectric ceramic according to claim 9, wherein the uncalcined B-site component powder is calcined at a temperature of about 1,050°

C. to 1,200°

C. for 1 to 2 hours.

12. A method for making a non-reducing dielectric ceramic according to claim 11, wherein the calcined primary material powder has an average particle diameter of about 0.8 μ

m or less.

13. A method for making a non-reducing dielectric ceramic according to claim 11, wherein the provided powders are such that the calcined primary material powder is a ceramic powder having a composition represented by

14. A method for making a non-reducing dielectric ceramic according to claim 13, wherein the secondary material powder is a ceramic powder having a composition represented by (Ca_1-v-wSr_vBa_w)p(Zr_1-x-yTi_xHf_y)O₃, and wherein p is adjusted to a value of about 0.98 to 1.02.

15. A method for making a non-reducing dielectric ceramic according to claim 14, wherein p is adjusted to a value of about 0.98 to 1.02.

16. A method for making a non-reducing dielectric ceramic according to claim 15, wherein the B-site component powder which is calcined has an average particle diameter of about 0.5 μ

m or less.