Ceramic materials for Capacitors with a high dielectric constant and a low capacitance change with temperature

• US 20030100438A1
• Filed: 10/09/2001
• Published: 05/29/2003
• Est. Priority Date: 10/09/2001
• Status: Active Grant

• Current Assignee: Chih-Hung Wang, Dong-Hau Kuo
• Original Assignee: Chih-Hung Wang, Dong-Hau Kuo
• Inventors: Kuo, Dong-Hau, Wang, Chih-Hung
• Granted Patent: US 6,734,127 B2
• Time in Patent Office: Days
• US Class Current: 501/137
• CPC Class Codes: C04B 2235/3206 Magnesium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3213 Strontium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3227 Lanthanum oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3251 Niobium oxides, niobates, tantalum oxides, tantalates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/36 Glass starting materials for making ceramics, e.g. silica glass
• CPC Class Codes: C04B 2235/663 Oxidative annealing
• CPC Class Codes: C04B 2235/785 Submicron sized grains, i.e. from 0,1 to 1 micron
• CPC Class Codes: C04B 2235/786 Micrometer sized grains, i.e. from 1 to 100 micron
• CPC Class Codes: C04B 2235/96 Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• CPC Class Codes: C04B 35/4682 based on BaTiO3 perovskite phase
• CPC Class Codes: C04B 35/4684 containing lead compounds C04B35/472 takes precedence
• CPC Class Codes: C04B 35/64 Burning or sintering processes C04B33/32 takes precedence ; powder metallurgy B22F
• CPC Class Codes: C04B 35/645 Pressure sintering
• CPC Class Codes: H01G 4/1227 based on alkaline earth titanates

Abstract

The present invention discloses low-cost ceramic powders prepared by the conventional ceramic processing with ceramic raw materials comprising carbonates, oxides and/or hydroxides of barium (Ba), titanium (Ti), magnesium (Mg) and optionally strontium (Sr), lanthanum (La) and niobium (Nb), and lead titanate (PbTiO₃) and/or lead oxide (PbO). The present invention also discloses a ceramic material obtained by the ceramic powder through densification and reduction-reoxidation, which has a dielectric constant of about 20,000 to about 55,000, a dielectric loss tangent (tan δ) of about 0.05 to about 0.25, a low capacitance change with temperature (low TCC) of about −15% to about 10% at a temperature range of −55° C. to 150° C., a resistivity of about 10⁶ Ω·cm to about 10⁹ Ω·cm, and a small grain size of about 0.5 to about 3.5 μm. The ceramic materials are useful in the production of capacitors or modules having high performance such as high dielectric constants and low TCC values with low cost. The ceramic powder also can mix with a glass component of low melting temperature to form a low temperature co-fired capacitor.

Claims

1. A ceramic material, which has a dielectric constant of about 20,000 to about 55,000, a dielectric loss tangent (tan δ

) of about 0.05 to about 0.25, a low capacitance change with temperature (TCC) of about −

15% to about 10% at a temperature of −

55°

C. to 150°

C., a resistivity of about 10⁶ Ω

·

cm to about 10⁹ Ω

·

cm, and a grain size of about 0.5 to about 3.5 μ

m.

2. The ceramic material of claim 1, which has a grain size of about 0.8 to about 2.0 μ

m and a low capacitance change with temperature (TCC) of about −

10% to about 0% at a temperature of −

55°

C. to 150°

C.

3. The ceramic material of claim 1, wherein its composition has the following general formula (I):

(1−

w)[(Ba_aSr_bPb_m)La_x](Ti_yMg_z)O₃+wNb₂O₅ 

 

(I)

wherein a is 0.5 to 0.98, b is 0 to 0.3, m is more than 0 to 0.3, x is 0 to 0.05, y is 0.90 to 0.995, z is 0.005 to 0.1, and w is 0 to 0.05 in weight ratio.

4. The ceramic material of claim 3, wherein m is 0.05 to 0.2.

5. The ceramic material of claim 1 for use in the production of capacitors and modulus.

16. A ceramic composition of claims 3 and 6, which is prepared from raw materials of carbonates, oxides and/or hydroxides of barium (Ba), titanium (Ti), magnesium (Mg) and optionally strontium (Sr), lanthanum (La) and niobium (Nb), and lead titanate (PbTiO₃) and/or lead oxide (PbO), wherein the atomic percentage of lead, based on the total amount of Ba, Ti, Mg, Pb, and optionally Sr, La and Nb, is more than 0 to 0.158.

17. The ceramic composition of claim 16, wherein the atomic ratio of Ba:

Sr;

Pb;

La;

Ti;

Mg is (0.475-0.98);

(0-0.03);

(more than 0 to 0.3);

(0-0.05);

(0.90-0.995);

(0.005-0.1).

18. The ceramic composition of claim 16, wherein the weight ratio of [(Ba_a,Sr_bPb_m)La_x](Ti_yMg_z)O₃:

Nb₂O₅ is (0.95-1);

(0-0.05).

19. The ceramic composition of claim 16 for use in the production of capacitors and modulus.

20. The ceramic composition of claim 16 for use in the production of a capacitor having a dielectric constant of about 20,000 to about 55,000, a low dielectric loss tangent (tan δ

) of about 0.05 to about 0.25, a low TCC of about −

15% to about 10% at a temperature range of −

55°

C. to 150°

C., a resistivity of about 10⁶ Ω

≠

cm to about 10⁹ Ω

·

cm, and a fine grain size of about 0.5 to about 3.5 μ

m.

21. The ceramic composition of claim 20, wherein the capacitors have a grain size of about 0.8 to about 2.0 μ

m and a TCC value of about −

10% to about 0%.

6. A ceramic powder, which has its composition with the following general formula (I):

(1−

w)[(Ba_aSr_bPb_m)La_x](Ti_yMg_z)O₃+wNb₂O₅ 

 

(I)

wherein a is 0.5 to 0.98, b is 0 to 0.3, m is more than 0 to 0.3, a+b+m=1.0, x is 0 to 0.05, y is 0.90 to 0.995, z is 0.005 to 0.1, and w is 0 to 0.05 in weight ratio.

7. The ceramic powder of claim 6, wherein m is 0.05 to 0.2.

8. The ceramic powder of claim 6 for use in the production of capacitors and modules.

9. The ceramic powder of claim 6 for use in the production of a capacitor having a dielectric constant of about 20,000 to about 55,000, a dielectric loss tangent (tan δ

) of about 0.05 to about 0.25, a low TCC of about −

15% to about 10% at a temperature of −

55°

C. to 150°

C., a resistivity of about 10⁶ Ω

·

cm to about 10⁹ Ω

·

cm, and a grain size of about 0.5 to about 3.5 μ

m.

10. The ceramic powder of claim 9, wherein the capacitor has a grain size of about 0.8 to about 2.0 t m and a low capacitance change with temperature (TCC) of about −

10% to about 0% at a temperature of −

55°

C. to 150°

C.

11. The ceramic powder of claim 6, which further comprises a glass component selected from the group consisting of a low-firing-temperature glass, lead glass or a combination thereof.

12. The ceramic powder of claim 11, wherein the glass component is present from 10% to 35% by weight, based on the total amount of the ceramic powder and the glass component.

13. The ceramic powder of claim 11 for use in the production of low temperature co-fired capacitors.

14. The ceramic powder of claim 13, wherein the low temperature co-fired capacitors have dielectric constants of about 360 to about 2,500.

15. The ceramic powder of claim 14, wherein the low temperature co-fired capacitors have a dielectric loss tangent (tan δ

) of about 0.065 to about 0.27.