JP4728051B2 - Dielectric ceramic and multilayer ceramic capacitor - Google Patents

Description

  The present invention relates to a dielectric ceramic, a multilayer ceramic capacitor using the dielectric ceramic and a base metal such as Ni as an internal electrode, and a method for manufacturing the multilayer ceramic capacitor.

In a multilayer ceramic capacitor having a base metal as an internal electrode, the material must be fired in a reducing atmosphere. Therefore, in order to ensure high reliability, it is necessary to provide reduction resistance and reoxidation property. V has been found to give reduction resistance and reoxidation as an additive, and is effective in improving the life characteristics, and also has the effect of improving the change in capacitance with time (Patent Documents 1 and 2). reference).
Japanese Patent Laid-Open No. 2000-210613 JP-A-8-124785

As described above, V has an effect. However, when a multilayer ceramic capacitor whose internal electrode is a base metal is manufactured using a ceramic dielectric added with V, there are many variations in the insulation characteristics and life characteristics of the product. There is a problem that it is difficult to stably obtain desired characteristics. Further, there is a problem that the variation rate of the temperature of the electrostatic capacitance also varies, and there is a problem that a deviation from desired temperature characteristics, for example, X7R characteristics occurs.
As a result of earnest research on such a phenomenon, it has been found that V exists in a wide range of valences ranging from 3 to 5 in a reducing firing atmosphere. Therefore, it has been found that hopping conduction is caused by the exchange of electrons and the insulation resistance is lowered. Trivalent V is highly diffusible in BaTiO ₃ and the substitution reaction with Ti ⁴⁺ proceeds. For this reason, it has been found that when the trivalent V is large, the core-shell structure is easily broken, and the relative permittivity is lowered and the temperature characteristics are deteriorated. On the other hand, pentavalent V hardly diffuses into BaTiO ₃ , forms a secondary phase with Ba, and precipitates as barium vanadate. For this reason, it has been found that when pentavalent V is large, the dielectric constant is lowered and the life characteristics are deteriorated due to the reduction in resistance to reduction and reoxidation.

  The present invention is intended to solve the above-described problems, and provides a multilayer ceramic capacitor having small variations in insulation resistance, life characteristics, and capacitance temperature characteristics, and a method of manufacturing the multilayer ceramic capacitor. Let it be an issue.

The present invention employs the following means in order to solve the above problems.
(1) In a dielectric ceramic mainly containing BaTiO ₃ and containing V,
The dielectric ceramic comprises a main component BaTiO ₃ and
As a minor component
For 100 mol of BaTiO ₃ ,
V to 0.05 to 5.0 mol,
0 to 5.0 mol of rare earth oxide,
Containing 0.1 to 5.0 mol of one or more alkaline earth oxides selected from MgO, CaO and SrO;
The dielectric ceramic has a core-shell structure, V is present as V ³⁺ , V ⁴⁺ , V ⁵⁺ in the core-shell structure, and an average valence of V present in the core-shell structure is 3.8. The dielectric ceramic is characterized in that it is ^{˜4.1 and} the abundance of V ⁴⁺ is 30% or more with ^{respect to} the abundance of (V ³⁺ , V ⁴⁺ , V ⁵⁺ ) .
(2) The dielectric ceramic of (1) is used for a ceramic dielectric layer,
The multilayer ceramic capacitor includes an external electrode on a surface of a multilayer chip in which the ceramic dielectric layers and internal electrode layers are alternately stacked.
(3) The multilayer ceramic capacitor according to (2) , wherein the internal electrode is a base metal.

  By suppressing the hopping conduction mechanism, the amount of leakage current can be reduced and the variation in insulation resistance can be reduced. Moreover, the variation in the temperature characteristic of the capacitance can be reduced by the shell phase having an appropriate concentration gradient. Furthermore, the effects of reduction resistance and reoxidation by V addition are exhibited without being impaired, and the introduction of oxygen defects that deteriorate the life characteristics is suppressed, so that variations in the life characteristics can be reduced.

According to the present invention, in a dielectric ceramic containing BaTiO ₃ as a main component and containing V, the valence of V is present in the dielectric ceramic between 3.8 and 4.1. Also, the proportion of V ⁴⁺ is made 30% or more.
For the calculation method of the valence and the existence ratio of V, spectrum separation is used from the V2p spectrum observation result by XPS.

By causing the valence distribution of V to exist within a narrow range, generation of a hopping conduction mechanism is suppressed.
Moreover, by setting it to a state close to tetravalent, excessive diffusion to BaTiO ₃ or precipitation of the barium vanadate phase is suppressed, and a core-shell structure having a shell phase with an appropriate concentration gradient can be formed.
The amount of V added is preferably 0.05 to 5.0 mol with respect to 100 mol of BaTiO ₃ .

The dielectric ceramic of the present invention can contain rare earth oxides in addition to BaTiO ₃ and V. The addition range of the rare earth oxide is preferably 0 to 5.0 mol with respect to 100 mol of BaTiO ₃ . By adding the rare earth oxide, the DC bias characteristics are improved. However, if it exceeds 5.0 mol, the relative dielectric constant and the sinterability are lowered, which is not preferable. In the following examples, Ho ₂ O ₃ is contained, but Ho ₂ O ₃ is another rare earth oxide listed below: Sm ₂ O ₃ , Eu ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , Y ₂ O ₃ , even if part or all of the amount is substituted, a fine structure is obtained and desired electrical characteristics are obtained as in the case of the examples. be able to.

Furthermore, the dielectric ceramic of the present invention may contain an alkaline earth oxide other than Ba. The addition range of the alkaline earth oxide is preferably 0.1 to 5.0 mol with respect to 100 mol of BaTiO ₃ . If the amount is less than 0.1 mol, it is difficult to suppress grain growth. If the amount is more than 5.0 mol, the relative permittivity and the sinterability decrease, which is not preferable. In the following examples, MgO is contained. However, even when MgO is partially or entirely replaced with CaO or SrO, a fine structure can be obtained and desired electrical characteristics can be obtained as in the case of the examples. Can do.

The dielectric ceramic of the present invention may contain other metal oxides such as Mn ₂ O ₃ and BaSiO ₃ , composite oxides, and the like. The addition range of these metal oxides and composite oxides is preferably 0.1 to 2.0 mol with respect to 100 mol of BaTiO ₃ . Within this range, the sinterability is improved.

The multilayer ceramic capacitor of the present invention has an external electrode on the surface of a multilayer chip in which the above-mentioned BaTiO ₃ as a main component and ceramic dielectric layers made of a dielectric ceramic containing V and internal electrode layers are alternately laminated. Through the same process as the manufacturing process of the conventional multilayer ceramic capacitor in which the green ceramic layer, the internal electrode layer and the external electrode are simultaneously fired as shown in the following (a) to (i) Manufactured.

(A) Calcination process of material powder A ceramic material powder obtained by mixing and pulverizing a powder that becomes BaTiO ₃ as a main component and a powder that becomes V oxide as a subcomponent with a ball mill or the like is calcined, and BaTiO ₃ and V oxide, etc. A calcined product made of The calcining temperature is preferably about 800 ° C.
Note that as the V oxide, in addition to V ₂ O _5, a mixture of different V ₂ O ₄ equivalent numbers may be used as appropriate.

(B) Green sheet forming step A binder and a solvent are added to the obtained calcined product, and this is stirred and mixed with a ball mill or the like for several hours to prepare a slurry having an appropriate viscosity. Next, a ceramic green sheet is produced from the slurry by a doctor blade method or the like. In this doctor blade method, slurry is flowed on a base film such as PET, and the thickness thereof is adjusted by a gap with the doctor blade. Thereafter, this is dried to obtain a ceramic green sheet having a predetermined thickness.

(C) Internal electrode layer forming step A conductor paste prepared in advance is printed on the surface of the green sheet with a predetermined pattern and a predetermined thickness by a printing method such as a screen printing method to form an internal electrode layer. The internal electrode is preferably a base metal such as Ni.

(D) Lamination process The green sheet after printing is cut by a predetermined unit size, taken out from the base film, and the required number of the taken green sheets is stacked.
The green sheets that have been stacked are temporarily pressed and further pressed.

(E) Cutting step The laminated green sheet after the main press-bonding is cut into individual laminated chips with a blade such as a rotating blade or a lifting blade.

(F) Debinding process The cut multilayer chip is put into a binder removal furnace, and the binder contained in the multilayer chip body (green ceramic layer) is removed under conditions such as a predetermined temperature and time. The atmosphere is preferably an N ₂ atmosphere.

(G) Firing step The laminated chip is put into a firing furnace and fired under conditions such as a predetermined temperature and time. The firing temperature is preferably 1150 ° C to 1350 ° C.
The atmosphere during firing is generally an oxygen partial pressure of 10 ⁻⁹ atm (10 ⁻⁴ Pa) to 10 ⁻¹² atm (10 ⁻⁷ Pa). In order to control the valence of V, Ni— An atmosphere up to about 10 ⁻⁸ atm (10 ⁻³ Pa) corresponding to the equilibrium oxygen partial pressure of NiO is applicable. The valence control of V can also be performed by the rate of temperature increase or decrease of the firing temperature and the conditions of the reoxidation process described later.

(H) External electrode forming step A conductor paste prepared in advance is applied to both ends of the fired laminated chip in a predetermined thickness and shape by a coating method such as a roller coating method or a dip method, and baked to form an external electrode. To do. Ni, Cu, Ag or the like is preferable as the external electrode.
The external electrode paste may be applied at the stage of the laminated chip before firing, and the green ceramic layer, the internal electrode layer, and the external electrode may be fired simultaneously.

(I) Reoxidation treatment step After the firing step, reoxidation treatment is performed in an oxidizing atmosphere at a temperature lower than the firing temperature. The reoxidation temperature is preferably 600 to 800 ° C.
The oxidizing atmosphere is not limited to the air atmosphere, and for example, an atmosphere having a low oxygen concentration such as N ₂ or a mixture of N ₂ with several ppm of O ₂ can also be used.
It is necessary to make various changes in consideration of the oxidation of the internal electrode (base metal such as Ni) or the control of the valence of V, etc.

BaTiO ₃ ; 100 mol, V ₂ O ₅ ; 0.1 mol, Ho ₂ O ₃ ; 0.5 mol, MgO; 1.0 mol, Mn ₂ O ₃ ; 0.1 mol, BaSiO ₃ ; The mixture was weighed and sufficiently wet-mixed and pulverized with a ball mill to obtain a mixture.
Next, this mixture was dehydrated and dried, and calcined in air at 800 ° C. to obtain a calcined product. This calcined product was wet crushed with ethanol and dried. An organic binder and a solvent were added thereto to form a sheet with a thickness of about 4 μm by the doctor blade method.
Next, Ni internal electrodes were formed on the sheet by a printing method. This sheet was laminated into 10 layers, and thermocompression bonded to obtain a laminate, which was cut into a 3216 shape having a length of 3.2 mm and a width of 1.6 mm.
Then, after the obtained laminate was treated to remove the binder in an N ₂ atmosphere, the oxygen partial pressure was 2.5 × 10 ⁻⁹ atm (= 2.5 × 10 ⁻⁴ Pa) to 2.0 × 10 ^−8. Heat treatment was performed at 1200 ° C. in the range of atm (= 2.0 × 10 ⁻³ Pa) to obtain a chip sintered body.
The Ag external electrodes were formed by dipping the obtained sintered body, then subjected to reoxidation tip sintered under conditions of N _2/600 to 800 ° C., to obtain a laminated ceramic capacitor.

The valence evaluation of V was performed about the obtained sample (multilayer ceramic capacitor). XPS was used for the valence evaluation of V. The V2p spectrum was observed, and the abundances of V ³⁺ , V ⁴⁺ and V ⁵⁺ were calculated from peak separation by curve fitting. The results are shown in Table 1. An example of peak separation is shown in FIG.

As shown in Table 1, the oxygen partial pressure is 4.0 × 10 ⁻⁹ atm (= 4.1 × 10 ⁻⁴ Pa) to 9.9 × 10 ⁻⁹ atm (= 1.0 × 10 ⁻³ Pa). It was confirmed that a microstructure having an average valence of V of 3.83 to 4.04 and a V ⁴⁺ of 30% or more was obtained.

  The electrical characteristics of the obtained sample were evaluated. As electrical characteristics, a room temperature dielectric constant measurement, a capacitance temperature change rate measurement, a room temperature resistivity measurement, and a high temperature accelerated life test at 150 ° C./100 V load were performed. The results are shown in Table 2.

As shown in Table 2, when the oxygen partial pressure was 4.0 × 10 ⁻⁹ atm (= 4.1 × 10 ⁻⁴ Pa) or more, improvement in dielectric constant, resistivity, and life characteristics was confirmed.

Further, as shown in FIG. 2, it was confirmed that the X7R characteristic was satisfied when the oxygen partial pressure was 9.9 × 10 ⁻⁹ atm (= 1.0 × 10 ⁻³ Pa) or less.

As described above, in the multilayer capacitor manufactured so that the average valence of V is 3.8 to 4.1 and V ⁴⁺ is 30% or more, the X7R characteristic is satisfied, the dielectric constant is high, the life is long, and the high insulation resistance is satisfied. It was confirmed that

It is a figure which shows an example which performs the valence evaluation of V of a multilayer ceramic capacitor from the peak separation by a V2p spectrum. It is a figure which shows the temperature change rate (25 degreeC reference | standard) of the electrostatic capacitance of a multilayer ceramic capacitor.

Claims (3)

1. In a dielectric ceramic mainly containing BaTiO ₃ and containing V,
   The dielectric ceramic comprises a main component BaTiO ₃ and
   As a minor component
   For 100 mol of BaTiO ₃ ,
   V to 0.05 to 5.0 mol,
   0 to 5.0 mol of rare earth oxide,
   Containing 0.1 to 5.0 mol of one or more alkaline earth oxides selected from MgO, CaO and SrO;
   The dielectric ceramic has a core-shell structure, V is present as V ³⁺ , V ⁴⁺ , V ⁵⁺ in the core-shell structure, and an average valence of V present in the core-shell structure is 3.8. A dielectric ceramic characterized in that the abundance of V ⁴⁺ is 30% or more with ^{respect to} the abundance of (V ³⁺ , V ⁴⁺ , V ⁵⁺ ) .
2. The dielectric ceramic according to claim 1 is used for a ceramic dielectric layer,
   The ceramic dielectric layers and the multilayer ceramic capacitor having an external electrode and an internal electrode layer on the surface of the laminated chip laminated alternately.
3. The multilayer ceramic capacitor according to claim 2 , wherein the internal electrode is a base metal.

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