NANO COMPLEX OXIDE DOPED DIELECTRIC CERAMIC MATERIAL, PREPARATION METHOD THEREOF AND MULTILAYER CERAMIC CAPACITORS MADE FROM THE SAME

• US 20090135546A1
• Filed: 11/25/2008
• Published: 05/28/2009
• Est. Priority Date: 11/27/2007
• Status: Abandoned Application

• Current Assignee: Tsinghua University
• Original Assignee: Tsinghua University
• Inventors: Wang, Xiaohui, Wang, Tian, Li, Longtu, Tian, Zhibin
• Application Number:
  US12/277,994
• Publication Number:
  US 20090135546A1
• Time in Patent Office: Days
• US Class Current: 361/321.200
• CPC Class Codes: B32B 18/00 Layered products essentially comprising ceramics, e.g. refractory products
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01G 23/006 Alkaline earth titanates
• CPC Class Codes: C01P 2002/52 containing elements as dopants
• CPC Class Codes: C01P 2004/04 obtained by TEM, STEM, STM or AFM
• CPC Class Codes: C01P 2004/62 Submicrometer sized, i.e. from 0.1-1 micrometer
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2006/32 Thermal properties
• CPC Class Codes: C01P 2006/40 Electric properties
• CPC Class Codes: C04B 2235/3206 Magnesium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3208 Calcium oxide or oxide-forming salts thereof, e.g. lime
• CPC Class Codes: C04B 2235/3225 Yttrium oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3229 Cerium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3236 Alkaline earth titanates
• CPC Class Codes: C04B 2235/3262 Manganese oxides, manganates, rhenium oxides or oxide-forming salts thereof, e.g. MnO
• CPC Class Codes: C04B 2235/3418 Silicon oxide, silicic acids, or oxide forming salts thereof, e.g. silica sol, fused silica, silica fume, cristobalite, quartz or flint glass constituents C04B2235/36
• CPC Class Codes: C04B 2235/441 Alkoxides, e.g. methoxide, tert-butoxide
• CPC Class Codes: C04B 2235/443 Nitrates or nitrites
• CPC Class Codes: C04B 2235/449 Organic acids, e.g. EDTA, citrate, acetate, oxalate
• CPC Class Codes: C04B 2235/5445 submicron sized, i.e. from 0,1 to 1 micron
• CPC Class Codes: C04B 2235/5454 : nanometer sized, i.e. below 100 nm
• CPC Class Codes: C04B 2235/6025 : Tape casting, e.g. with a doctor blade
• CPC Class Codes: C04B 2235/656 : characterised by specific heating conditions during heat treatment
• CPC Class Codes: C04B 2235/6567 : Treatment time
• CPC Class Codes: C04B 2235/6582 : Hydrogen containing atmosphere
• CPC Class Codes: C04B 2235/6584 : at an oxygen percentage below that of air
• 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 2237/346 : Titania or titanates
• CPC Class Codes: C04B 35/46 : based on titanium oxides or titanates containing also zirconium or hafnium oxides, zirconates or hafnates C04B35/49
• CPC Class Codes: C04B 35/462 : based on titanates
• CPC Class Codes: C04B 35/468 : based on barium titanates
• CPC Class Codes: C04B 35/4682 : based on BaTiO3 perovskite phase
• CPC Class Codes: C04B 35/624 : Sol-gel processing
• CPC Class Codes: C04B 35/6261 : Milling
• CPC Class Codes: C04B 35/62625 : Wet mixtures
• CPC Class Codes: C04B 35/62635 : Mixing details
• CPC Class Codes: C04B 35/628 : Coating the powders or the macroscopic reinforcing agents
• CPC Class Codes: C04B 35/62805 : Oxide ceramics
• CPC Class Codes: C04B 35/62807 : Silica or silicates
• CPC Class Codes: C04B 35/6281 : Alkaline earth metal oxides
• CPC Class Codes: C04B 35/62815 : Rare earth metal oxides
• CPC Class Codes: C04B 35/62886 : by wet chemical techniques
• CPC Class Codes: C04B 35/62897 : Coatings characterised by their thickness
• CPC Class Codes: C04B 35/632 : Organic additives
• CPC Class Codes: C04B 35/638 : Removal thereof
• CPC Class Codes: C04B 37/001 : directly with other burned ceramic articles
• CPC Class Codes: C04B 37/006 : consisting of metals or metal salts
• CPC Class Codes: H01G 4/1218 : based on titanium oxides or titanates H01G4/1245 takes precedence
• CPC Class Codes: H01G 4/1227 : based on alkaline earth titanates
• CPC Class Codes: H01G 4/30 : Stacked capacitors H01G4/33 takes precedence
• CPC Class Codes: H01G 4/33 : Thin- or thick-film capacitors thin- or thick-film circuits H01L27/00; capacitors without a potential-jump or surface barrier specially adapted for integrated circuits, details thereof, multistep manufacturing processes therefor H01L28/40

Abstract

The present invention provides a nano complex oxide doped dielectric ceramic material used for a multilayer ceramic capacitor using a base metal as a material of internal electrodes. The doped dielectric ceramic material comprises barium titanate and a nano complex oxide dopant, wherein the molar ratio of the barium titanate to the nano complex oxide dopant is in the range of (90˜98):(2˜10), the average particle size of the barium titanate is 50˜300 nm and the nano complex oxide dopant has the following formula (1): w A+x B+y C+z D. The present invention also provides processes for preparing the nano complex oxide doped dielectric ceramic material and ultrafine-grained and temperature-stable multilayer ceramic capacitors using the nano complex oxide doped dielectric ceramic material as the material of dielectric layers.

Claims

1. A nano complex oxide doped dielectric ceramic material used for a multilayer ceramic capacitor, comprising barium titanate and a nano complex oxide dopant, wherein the molar ratio of the barium titanate to the nano complex oxide dopant is in the range of (90˜

98);

(2˜

10), the average particle size of the barium titanate is in the range of 50˜

300 nm and the nano complex oxide dopant has the following formula (1);

w A+x B+y C+z D  

 

(1)

wherein,

A represents one or more selected from the group consisting of CaTiO₃, CaO, BaO, SrO and MgO;

B represents one or more selected from the group consisting of MnO₂, Co₂O₃, Co₃O₄, Fe₂O₃ and Y₂O₃;

C represents one or more selected from the group consisting of SiO₂, B₂O₃ and Li₂O;

D represents an oxide of Re, wherein Re is one or more rare-earth elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; and

w, x, y and z are molar percentages of the oxides with respect to the BaTiO₃, wherein w is 0.01 to 2%, x is 0.01 to 3%, y is 0.1 to 6%, and z is 0 to 4%.

2. The nano complex oxide doped dielectric ceramic material according to claim 1, wherein the molar ratio of the barium titanate to the nano complex oxide dopant is in the range of (90˜

97);

(3˜

10) and the average particle size of the barium titanate is 100˜

200 nm.

3. The nano complex oxide doped dielectric ceramic material according to claim 1, wherein said doped dielectric ceramic material is prepared by a chemical coating process comprising the following steps:

(1). Adding barium titanate powders into a solvent selected from de-ionized water, ethanol, propanol, isopropanol or the like and milling to obtain a well dispersed suspension of barium titanate, wherein the average particle size of the barium titanate powders is in the range of 50˜

300 nm;

(2). Dissolving acetates or nitrates of metal elements corresponding to the oxides in the nano complex oxide “

w A+x B+y C+z D”

according to the molar ratios of that w is 0.01 to 2%, x is 0.01 to 3%, y is 0.1 to 6%, and z is 0 to 4% in de-ionized water to obtain a transparent solution S1;

(3). Mixing alkoxide of silicon, ethanol, acetic acid and de-ionized water with continuous stirring to get a transparent and stable solution S2;

(4). Adding solution S1 and solution S2 into the suspension of barium titanate with stirring to obtain an even slurry, wherein the volume ratios of the solutions and the suspension are set as S1;

S2;

BaTiO₃ suspension=(1˜

8);

(1˜

4);

(10˜

50);

(5). Adding ammonia water into the slurry obtained in step (4) to adjust the pH value to 6˜

11 so that the doping elements are uniformly coated onto the barium titanate particles through a co-precipitation process;

(6). Drying the slurry obtained in step (5) at 80°

C.˜

120°

C. to get dried powders;

(7). Calcining the dried powders obtained in step (6) at 300˜

600°

C. for 1˜

6 hours, followed by crushing and sieving;

wherein the nano complex oxide doped dielectric ceramic material thus obtained has a coating layer formed by the doping elements on the barium titanate particle, and the thickness of the coating layer is 1˜

20 nm.

4. The nano complex oxide doped dielectric ceramic material according to claim 3, wherein in step (1) of the chemical coating process, the average particle size of the barium titanate is 100˜

200 nm, and in step (3) the volume ratios of the liquids are set as alkoxide of silicon;

ethanol;

acetic acid;

de-ionized water=1;

(1˜

15);

(1˜

8);

(5˜

40) and the alkoxide of silicon is ethyl orthosilicate or butyl orthosilicate.

5. The nano complex oxide doped dielectric ceramic material according to claim 1, wherein said doped dielectric ceramic material is prepared by a process, wherein a nano complex oxide dopant is prepared by a sol-gel method firstly and then the nano complex oxide dopant is mixed with powders of BaTiO₃ having an average particle size in the range of 50˜

300 nm by a molar ratio of BaTiO₃ to the complex oxide as (90˜

98);

(2˜

10), milled and then dried to obtain the nano complex oxide doped dielectric ceramic material,

said sol-gel method comprises the following steps;

(1). Dissolving acetates or nitrates of metal elements corresponding to the oxides in the complex oxide “

w A+x B+y C+z D”

according to the mole ratios of that w is 0.01 to 2%, x is 0.01 to 3%, y is 0.1 to 6%, and z is 0 to 4% in de-ionized water, and then adding polyethylene glycol (PEG) into the solution with continuous stirring till a transparent solution S1 is obtained, wherein the weight ratio of PEG and the metal acetates or nitrates is set as PEG;

acetates or nitrates=(0.1˜

3);

1;

(2). Mixing alkoxide of silicon, ethanol, acetic acid and de-ionized water with continuous stirring to get a transparent and stable solution S2;

(3). Adding solution S1 into solution S2 with continuous stirring to obtain a transparent precursor solution (sol), wherein the volume ratio of solution S1 to solution S2 is set as S1;

S2=(0.5˜

20);

1;

(4). Drying the sol obtained in step (3) at 80˜

160°

C. for 6˜

48 hours to get a xerogel;

(5). Calcining the xerogel at 400˜

1000°

C. for 1˜

10 hours in air, followed by crushing and sieving to obtain a nano complex oxide dopant with an average particle size of 5˜

100 nm.

6. The nano complex oxide doped dielectric ceramic material according to claim 5, wherein the average particle size of the barium titanate is 100˜

200 nm, in step (2) of the sol-gel method, the volume ratios of the liquids are set as alkoxide of silicon;

ethanol;

acetic acid;

de-ionized water=1;

(1˜

15);

(1˜

8);

(5˜

40) and the alkoxide of silicon is ethyl orthosilicate or butyl orthosilicate, and the obtained nano complex oxide dopant has an average particle size of 10˜

80 nm.

11. A multilayer ceramic capacitor using a base metal as a material of internal electrodes, comprising the nano complex oxide doped dielectric ceramic material according to claim 1 as the material of dielectric layers, wherein the capacitor is an ultrafine grained and temperature-stable capacitor satisfying X5R or X7R standards, and the average grain size of the dielectric layers is less than 300 nm.

12. A Process for manufacturing an ultrafine grained and temperature-stable multilayer ceramic capacitor, comprising the following steps:

the nano complex oxide doped dielectric ceramic material according to claim 1 is mixed with suitable organic solvent, binder, dispersant and plasticizer to provide a ceramic slurry;

a dielectric layer is formed by a tape-casting method using the slurry with the thickness of the dielectric layer of below 10 μ

m;

multiple of the dielectric layers and base-metal internal electrode layers are alternately stacked to prepare a stack body;

the binder is removed after the stacked body is formed;

the binder-removed stack body is then sintered under a reducing atmosphere at a temperature of from 950°

C. to 1250°

C.;

the sintered stack body is reoxidized in a weak oxidation atmosphere at 800°

C˜

1100°

C. to enhance insulation resistance of the dielectric;

the sintered stack body is cooled down to room temperature; and

Cu or Ag terminal electrode is mounted to obtain an ultrafine-grained and temperature-stable multilayer ceramic capacitor having base-metal internal electrodes, wherein the capacitor satisfies X5R or X7R standards, and the average grain size of the dielectric layers is less than 200 nm.

13. The process for manufacturing an ultrafine grained and temperature-stable multilayer ceramic capacitor according to claim 12, wherein the sintering process is carried out by two ways:

(a) two-step sintering, the stack body is held at a relative high temperature T₁ for 0˜

30 min, then the temperature is decreased quickly to a relative low temperature T₂ and held for 2˜

10 h, wherein 950°

C.≦

T₂≦

T₁≦

1250°

C.;

(b) normal sintering, the stack body is held at 1050°

C.˜

1250°

C. for 2˜

10 h.

14. The process for manufacturing an ultrafine grained and temperature-stable multilayer ceramic capacitor according to claim 12, comprising the following steps:

(1). The nano complex oxide doped dielectric ceramic material is mixed with an organic solvent, a binder, a dispersant and a plasticizer to provide a ceramic slurry, wherein the weight ratios of the above materials are set as ceramic powder;

organic solvent;

binder;

dispersant;

plasticizer=(10˜

60);

(3˜

15);

(1˜

5);

(1˜

10);

(1˜

3);

(2). A dielectric layer is formed by tape-casting method from the slurry with the thickness of the dielectric layer of below 10 μ

m;

(3). Multiple of the dielectric layers and base-metal internal electrode layers are alternately stacked to prepare a stack body;

(4). The stack body fabricated in step (3) is subjected to a binder removing process at a temperature in the range of from 280˜

350°

C. for 10˜

20 hours in air or under nitrogen atmosphere;

(5). The binder-removed stack body is sintered under a reducing atmosphere having oxygen partial pressure in the order of 10<sup>−

6</sup>˜

10<sup>−

12</sup> atm and a volume ratio of N₂ to H₂ in the range of 40;

1 to 15;

1 through a two-step sintering or a normal sintering at 950˜

1250°

C.;

(6). The sintered stack body is reoxidized in a weak oxidation atmosphere with oxygen partial pressure of 10<sup>−

5</sup>˜

10<sup>−

2</sup> atm at 800°

C.˜

1100°

C. for 2˜

10 hours;

(7). The sintered stack body is cooled down to room temperature;

(8). Cu or Ag terminal electrode is mounted and heated at 600°

C.˜

800°

C. under N₂ atmosphere to obtain an ultrafine-grained and temperature-stable multilayer ceramic capacitor having base-metal internal electrodes.

15. The process for manufacturing an ultrafine grained and temperature-stable multilayer ceramic capacitor according to claim 14, wherein in step (1) the organic solvent is toluene or ethanol, the binder is polyvinyl-butyral, the dispersant is a phosphate and the plasticizer is di-n-butyl phthalate or di-sec-octyl phthalate.

7. A preparation process of a nano complex oxide doped dielectric ceramic material used for a multilayer ceramic capacitor, wherein said doped dielectric ceramic material comprises barium titanate and a nano complex oxide dopant, the molar ratio of the barium titanate to the nano complex oxide dopant is in the range of (90˜

98);

(2˜

10), the average particle size of the barium titanate is in the range of 50˜

300 nm and the nano complex oxide dopant has the following formula (1);

w A+x B+y C+z D  

 

(1)

wherein,

A represents one or more selected from the group consisting of CaTiO₃, CaO, BaO, SrO and MgO;

B represents one or more selected from the group consisting of MnO₂, Co₂O₃, Co₃O₄, Fe₂O₃ and Y₂O₃;

C represents one or more selected from the group consisting of SiO₂, B₂O₃ and Li₂O;

D represents an oxide of Re, wherein Re is one or more rare-earth elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; and

w, x, y and z are molar percentages of the oxides with respect to the BaTiO₃, wherein w is 0.01 to 2%, x is 0.01 to 3%, y is 0.1 to 6%, and z is 0 to 4%, and

said preparation process is a chemical coating process comprising the following steps;

(1). Adding barium titanate powders into a solvent selected from de-ionized water, ethanol, propanol, isopropanol or the like and milling to obtain a well dispersed suspension of barium titanate, wherein the average particle size of the barium titanate powders is in the range of 50˜

300 nm;

(2). Dissolving acetates or nitrates of metal elements corresponding to the oxides in the nano complex oxide “

w A+x B+y C+z D”

according to the molar ratios of that w is 0.01 to 2%, x is 0.01 to 3%, y is 0.1 to 6%, and z is 0 to 4% in de-ionized water to obtain a transparent solution S1;

(3). Mixing alkoxide of silicon, ethanol, acetic acid and de-ionized water with continuous stirring to get a transparent and stable solution S2;

(4). Adding solution S1 and solution S2 into the suspension of barium titanate with stirring to obtain an even slurry, wherein the volume ratios of the solutions and the suspension are set as S1;

S2;

BaTiO₃ suspension=(1˜

8);

(1˜

4);

(10˜

50);

(5). Adding ammonia water into the slurry obtained in step (4) to adjust the pH value to 6˜

11 so that the doping elements are uniformly coated onto the barium titanate particles through a co-precipitation process;

(6). Drying the slurry obtained in step (5) at 80°

C.˜

120°

C. to get dried powders;

(7). Calcining the dried powders obtained in step (6) at 300˜

600°

C. for 1˜

6 hours, followed by crushing and sieving;

wherein the nano complex oxide doped dielectric ceramic material thus obtained has a coating layer formed by the doping elements on the barium titanate particle, and the thickness of the coating layer is 1˜

20 nm.

8. The preparation process according to claim 7, wherein in step (1) of the chemical coating process the average particle size of the barium titanate is 100˜

200 nm, and in step (3) the volume ratios of the liquids are set as alkoxide of silicon;

ethanol;

acetic acid;

de-ionized watery=1;

(1˜

15);

(1˜

8);

(5˜

40) and the alkoxide of silicon is ethyl orthosilicate or butyl orthosilicate.

9. A preparation process of a nano complex oxide doped dielectric ceramic material used for a multilayer ceramic capacitor, wherein said doped dielectric ceramic material comprises barium titanate and a nano complex oxide dopant, the molar ratio of the barium titanate to the nano complex oxide dopant is in the range of (90˜

98);

(2˜

10), the average particle size of the barium titanate is in the range of 50˜

300 nm and the nano complex oxide dopant has the following formula (1);

w A+x B+y C+z D  

 

(1)

wherein,

A represents one or more selected from the group consisting of CaTiO₃, CaO, BaO, SrO and MgO;

B represents one or more selected from the group consisting of MnO₂, Co₂O₃, Co₃O₄, Fe₂O₃ and Y₂O₃;

C represents one or more selected from the group consisting of SiO₂, B₂O₃ and Li₂O;

D represents an oxide of Re, wherein Re is one or more rare-earth elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu;

w, x, y and z are molar percentages of the oxides with respect to the BaTiO₃, wherein w is 0.01 to 2%, x is 0.01 to 3%, y is 0.1 to 6%, and z is 0 to 4%, and

in said preparation process, a nano complex oxide dopant is prepared by a sol-gel method firstly and then the nano complex oxide dopant is mixed with powders of BaTiO₃ having an average particle size in the range of 50˜

300 nm by a molar ratio of BaTiO₃ to the complex oxide as (90˜

98);

(2˜

10), milled and then dried to obtain the nano complex oxide doped dielectric ceramic material,

said sol-gel method comprises the following steps;

(1). Dissolving acetates or nitrates of metal elements corresponding to the oxides in the complex oxide “

w A+x B+y C+z D”

according to the mole ratios of that w is 0.01 to 2%, x is 0.01 to 3%, y is 0.1 to 6%, and z is 0 to 4% in de-ionized water, and then adding polyethylene glycol (PEG) into the solution with continuous stirring till a transparent solution S1 is obtained, wherein the weight ratio of PEG and the metal acetates or nitrates is set as PEG;

acetates or nitrates=(0.1˜

3);

1;

(2). Mixing alkoxide of silicon, ethanol, acetic acid and de-ionized water with continuous stirring to get a transparent and stable solution S2;

(3). Adding solution S1 into solution S2 with continuous stirring to obtain a transparent precursor solution (sol), wherein the volume ratio of solution S1 to solution S2 is set as S1;

S2=(0.5˜

20);

1;

(4). Drying the sol obtained in step (3) at 80˜

160°

C. for 6˜

48 hours to get a xerogel;

(5). Calcining the xerogel at 400˜

1000°

C. for 1˜

10 hours in air, followed by crushing and sieving to obtain a nano complex oxide dopant with an average particle size of 5˜

100 nm.

10. The preparation process according to claim 9, wherein the average particle size of the barium titanate is 100˜

200 nm, in step (2) of the sol-gel method, the volume ratios of the liquids are set as alkoxide of silicon;

ethanol;

acetic acid;

de-ionized water−

1;

(1˜

15);

(1˜

8);

(5˜

40) and the alkoxide of silicon is ethyl orthosilicate or butyl orthosilicate, and the obtained nano complex oxide dopant has an average particle size of 10˜

80 nm.