JP5111426B2 - Barium titanate-based powder and manufacturing method thereof, dielectric ceramic and multilayer ceramic capacitor - Google Patents

Description

  The present invention relates to a barium titanate-based powder and a production method thereof, a dielectric ceramic formed by sintering the barium titanate-based powder, and a multilayer ceramic capacitor formed using the dielectric ceramic. The present invention relates to a technique for improving the reliability of a multilayer ceramic capacitor that is small in size and large in capacity.

  In a multilayer ceramic capacitor, as a means for increasing the capacitance per unit volume, a thin dielectric ceramic layer can be mentioned. Although the thinning of the dielectric ceramic layer is associated with the possibility of short-circuit failure and reliability deterioration, it is effective to improve the denseness and smoothness of the dielectric ceramic layer.

  In order to make the dielectric ceramic layer dense, first, the dielectric ceramic powder contained in the dielectric ceramic layer needs to be made fine. And it is necessary to reduce coarse grains larger than a certain average particle size as much as possible. In addition, particles smaller than the average particle size are in a very active state when fired and directly cause abnormal particle growth. Therefore, it is necessary to reduce the fine particles smaller than the average particle size.

  As a technique that can solve the above-described problems, for example, in Japanese Patent Application Laid-Open No. 2002-265277 (Patent Document 1), a plurality of fine particles are aggregated into one particle group. A method for producing ceramic powder is disclosed in which the variation in diameter is reduced. Patent Document 1 discloses that the particle size distribution of ceramic particles is 30% or less in terms of variation (σ / average particle size).

  However, the particle diameter of the ceramic particles disclosed in Patent Document 1 is about 100 nm, even if it is a fine particle, and the diameter of the particle group exceeds 500 nm. When the particle diameter is large in this way, short-circuit defects frequently occur due to the thinning of the dielectric ceramic layer, and the life reduction due to a decrease in insulation becomes remarkable.

  Further, in the method described in Patent Document 1 (a method of aggregating ceramic fine particles under a predetermined condition), it is difficult to obtain a powder having a small particle size variation in a region having a particle size of 100 nm or less.

JP 2002-265277 A

  Accordingly, an object of the present invention is to provide a dielectric ceramic powder and a manufacturing method thereof, particularly a barium titanate powder and a manufacturing method thereof, which can solve the above-described problems.

  Another object of the present invention is to provide a dielectric ceramic obtained by sintering the barium titanate powder.

  Still another object of the present invention is to provide a multilayer ceramic capacitor constructed using the dielectric ceramic.

The barium titanate-based powder according to the present invention is used for forming a dielectric ceramic layer of a multilayer ceramic capacitor, and in order to solve the above technical problem, the average particle diameter D1 is 10 to 200 nm. When the maximum particle size is D2 and the minimum particle size is D3, the relationship of 1.0 <D2 / D1 ≦ 2.0 and 0.5 ≦ D3 / D1 <1.0 is satisfied. It is characterized by.

  The barium titanate-based powder preferably has an average particle diameter D1 in the range of 12 to 107 nm.

The present invention is also directed to a method for producing the barium titanate-based powder according to the present invention. The method for producing a barium titanate-based powder according to the present invention includes a step of preparing a raw material powder before classification as a raw material of the barium titanate-based powder to be obtained, and a step of dispersing the raw material powder in a dispersion medium And a step of precipitating the raw material powder in the dispersion medium, and taking out only the raw material powder at a predetermined settling distance excluding both the upper and lower parts in the dispersion medium, thereby obtaining the target barium titanate-based powder. And a step of obtaining.

  The present invention is also directed to a dielectric ceramic obtained by sintering the barium titanate powder according to the present invention.

  The present invention is further directed to a multilayer ceramic capacitor comprising a plurality of laminated dielectric ceramic layers and a plurality of internal electrodes formed along a specific interface between the dielectric ceramic layers. The multilayer ceramic capacitor according to the present invention is characterized in that the dielectric ceramic layer is made of the dielectric ceramic according to the present invention.

  According to the barium titanate-based powder according to the present invention, the particle size distribution is very sharp. Therefore, when a ceramic slurry containing the powder is obtained, the dispersibility becomes extremely high. This leads to improvement in the density of the dielectric ceramic layer and smoothing of the surface in the multilayer ceramic capacitor formed by sintering the ceramic green sheet obtained from the ceramic slurry. Therefore, in the multilayer ceramic capacitor, since there are almost no short paths, insulation failure hardly occurs, and the failure life characteristics in the load test can be improved.

  In addition, according to the present invention, the integral width obtained by X-ray diffraction of the barium titanate-based powder is reduced, that is, the crystallinity is improved, and thus stable sinterability is expected.

  When the average particle diameter D1 of the barium titanate-based powder according to the present invention is in the range of 12 to 107 nm, the above-described effect becomes particularly remarkable when the thickness of the dielectric ceramic layer is 0.5 μm or less.

  According to the method for producing a barium titanate-based powder according to the present invention, a classification method is used in order to obtain a target powder. This indicates that the distance to settle in the dispersion medium is proportional to the particle size. Utilizing it and letting it settle for a certain period of time, so that only the powder at the settling distance calculated from the target particle size is taken out, so a barium titanate-based powder with a sharp particle size distribution can be easily obtained. .

  In general, when the average particle size is reduced, the particle size distribution tends to be broad, and it is difficult to sharpen it. On the other hand, according to the present invention, as described above, the particle size distribution is sharpened by classification, so that a barium titanate-based powder having a sharp particle size distribution can be obtained. In other words, according to the classification used in the present invention, each of the average particle size, the maximum particle size, and the minimum particle size of the barium titanate-based powder can be arbitrarily controlled. Therefore, it is possible to evaluate the reliability of a multilayer ceramic capacitor in which a dielectric ceramic layer is thinned using a barium titanate-based powder in which the average particle size, the maximum particle size, and the minimum particle size are variously changed. It becomes easy. As a result, according to the present invention, it is easy to find the relationship among the average grain size, the maximum grain size, and the minimum grain size that can improve the reliability in the multilayer ceramic capacitor in which the dielectric ceramic layer is thinned. become. Thus, the present invention provides a critical range for the relationship between the average grain size, the maximum grain size, and the minimum grain size, which can improve the reliability in a multilayer ceramic capacitor having a thin dielectric ceramic layer. It is important to find this.

1 is a cross-sectional view schematically showing a multilayer ceramic capacitor 1 according to an embodiment of the present invention. It is a SEM photograph of barium titanate-based powder concerning a specific sample produced in an experimental example.

  With reference to FIG. 1, a multilayer ceramic capacitor 1 constituted by using a dielectric ceramic obtained by sintering a barium titanate-based powder according to the present invention will be described first.

  A multilayer ceramic capacitor 1 includes a capacitor body 5 including a plurality of laminated dielectric ceramic layers 2 and a plurality of internal electrodes 3 and 4 formed along a specific interface between the dielectric ceramic layers 2. I have. The internal electrodes 3 and 4 are mainly composed of Ni, for example.

  First and second external electrodes 6 and 7 are formed at different positions on the outer surface of the capacitor body 5. The external electrodes 6 and 7 are mainly composed of Ag, Cu or Ag—Pd, for example. In the monolithic ceramic capacitor 1 shown in FIG. 1, the first and second external electrodes 6 and 7 are formed on the end surfaces of the capacitor body 5 facing each other. The internal electrodes 3 and 4 are a plurality of first internal electrodes 3 electrically connected to the first external electrode 6 and a plurality of second internal electrodes 4 electrically connected to the second external electrode 7. The first and second internal electrodes 3 and 4 are alternately arranged in the stacking direction.

In such a multilayer ceramic capacitor 1, the dielectric ceramic layer 2 includes ABO ₃ (A necessarily includes Ba and may further include at least one of Ca and Sr. B necessarily includes Ti and further includes Zr. And at least one of Hf.) And a barium titanate-based dielectric ceramic having a main component.

  The above dielectric ceramic is obtained by sintering a barium titanate-based powder. In the present invention, the barium titanate-based powder has an average particle diameter D1 in the range of 10 to 200 nm, and is the maximum. When the particle size is D2 and the minimum particle size is D3, the particle size distribution satisfies the relationship of 1.0 <D2 / D1 ≦ 2.0 and 0.5 ≦ D3 / D1 <1.0. It is characterized by the fact that it is very sharp. The basis for such numerical limitation can be derived from experimental examples described later.

  As described above, according to the barium titanate-based powder having a sharp particle size distribution, extremely high dispersibility can be realized in the ceramic slurry containing the powder. Therefore, when such a ceramic slurry is used, the density of the dielectric ceramic layer 2 can be improved and the smoothness of the surface can be improved. Accordingly, since there are almost no short paths in the multilayer ceramic capacitor 1, it is difficult for insulation failure to occur, and the failure life characteristics in the load test can be improved.

  In addition, according to the barium titanate-based powder as described above, since the integral width obtained by X-ray diffraction becomes small, that is, the crystallinity becomes good, stable sinterability can be expected.

  In particular, when the average particle diameter D1 of the barium titanate-based powder is in the range of 12 to 107 nm, the above-described effect becomes particularly remarkable when the thickness of the dielectric ceramic layer 2 is 0.5 μm or less.

  The barium titanate-based powder having the specific particle size distribution as described above can be manufactured, for example, as follows.

  First, raw material powder before classification, which is a raw material for the barium titanate-based powder to be obtained, is prepared. The average particle diameter of the raw material powder is in the range of 10 to 200 nm.

  Next, a step of dispersing the raw material powder in a dispersion medium is performed. Here, as the dispersion medium, pure water is typically used, but other liquids may be used. In the subsequent sedimentation step, it is preferable that the liquid is likely to have a difference in the sedimentation distance of the raw material powder depending on the particle size.

Next, a step of allowing the raw material powder to settle in the dispersion medium by allowing the dispersion medium to stand. And after leaving for a certain period of time, only the raw material powder at a predetermined settling distance excluding both the upper part and the lower part in the dispersion medium is taken out to obtain a target barium titanate-based powder having a specific particle size distribution. A process is performed.

  In the step of taking out the raw material powder, since the raw material powder is usually taken out together with the dispersion medium, a step of removing the dispersion medium from the taken out raw material powder is performed as necessary.

  According to the above-described method for producing a barium titanate-based powder, a classification method is used in order to obtain a target powder. This is based on the fact that the settling distance in the dispersion medium is proportional to the particle size. Since, after settling for a certain period of time, only the powder at the settling distance calculated from the target particle size is taken out, the barium titanate powder having a specific particle size distribution, that is, a sharp particle size distribution, is used. Can be easily obtained.

Below, the experiment example implemented in order to confirm the effect by this invention is demonstrated. In the following experimental examples, barium titanate (BaTiO ₃ ) powder was used as a sample as the barium titanate-based powder. However, the present invention is not limited to this, and ABO ₃ (A always contains Ba and further contains Ca and Sr). The same experimental results can be obtained for barium titanate-based powders whose main component is B, which must contain at least one of Zr and Hf. .

[Experiment 1]
(A) Preparation of barium titanate powder First, barium titanate (BaTiO ₃ ) powder as a main component was prepared. That is, each powder of BaCO ₃ and TiO ₂ was weighed and then mixed for 24 hours by a ball mill, heat treatment was performed, and BaTiO ₃ powder was obtained by solid phase reaction. The targeted particle size of the BaTiO ₃ powder was 6 levels of 10 nm, 30 nm, 70 nm, 100 nm, 150 nm and 200 nm.

(B) Classification treatment of barium titanate powder The BaTiO ₃ powder itself having a target particle size of 10 nm, 30 nm, 70 nm, 100 nm, 150 nm, and 200 nm, obtained in the step (A) above, Samples 101, 105, 107, 111, 114 and 116 shown in FIG.

In addition, BaTiO ₃ powder having a target particle size of 10 nm, 30 nm, 70 nm, 100 nm, 150 nm, and 200 nm obtained in the step (A) is placed in pure water as a dispersion medium in the flask. After being dispersed and allowed to stand for a certain period of time, BaTiO ₃ powder at a predetermined position was collected together with pure water.

  At this time, samples 102, 108, 112 and 118 shown in Table 1 were collected with the upper part of the pure water in the flask remaining. Samples 103, 109, and 117 shown in Table 1 were collected with the lower part of the pure water in the flask remaining. Samples 104, 106, 110, 113, 115 and 119 shown in Table 1 were collected with the upper and lower portions of pure water remaining in the flask.

(C) Preparation of dielectric ceramic raw material powder Each powder of MgO, MnO, Dy ₂ O ₃ , and SiO ₂ was added to the BaTiO ₃ powder obtained through the classification process of (B) above with 100BaTiO ₃ -1. It mix | blended so that it might become the molar ratio represented by 0Dy-1.0Mg-0.3Mn-1.0Si, and the compound was mixed for 5 hours with the ball mill. Thereafter, drying and dry pulverization were performed to obtain a barium titanate-based dielectric ceramic raw material powder.

(D) Manufacture of multilayer ceramic capacitor Add organic solvent such as polyvinyl butyral binder and ethanol to the barium titanate dielectric ceramic raw material powder obtained in step (C) above, and wet mix for a predetermined time with a ball mill A ceramic slurry was prepared. This ceramic slurry was formed into a sheet by a die coater to obtain a ceramic green sheet. In Experimental Example 1, the thickness of the ceramic green sheet was set to 1.0 μm after firing.

  Next, a conductive paste mainly composed of Ni was screen-printed on the ceramic green sheet to form a conductive paste film to be an internal electrode.

  Further, as a countermeasure against a level difference that may occur between a region where the internal electrode is present and a region where the internal electrode is not present in the surface direction, the conductive paste film is formed using the ceramic slurry described above in a region where the conductive paste film on the ceramic green sheet is not formed. A ceramic paste film having a thickness equivalent to the thickness of was formed.

  Then, the ceramic green sheets on which the conductive paste film and the ceramic paste film are formed are stacked so that the sides from which the conductive paste film is drawn are opposite to each other, and a raw capacitor body having one effective layer is formed. Obtained.

Next, the raw capacitor body is heated to a temperature of 300 ° C. in an N ₂ atmosphere to burn the binder, and then from an H ₂ —N ₂ —H ₂ O gas having an oxygen partial pressure of 10 ⁻¹⁰ MPa. The sintered capacitor body was obtained by firing at 1150 ° C. for 2 hours in a reducing atmosphere.

Next, a Cu paste containing B ₂ O ₃ —Li ₂ O—SiO ₂ —BaO glass frit is applied to both end faces of the capacitor body, and baked at a temperature of 800 ° C. in an N ₂ atmosphere. Electrically connected external electrodes were formed.

As for the external dimensions of the multilayer ceramic capacitor obtained as described above, the length was 1.6 mm, the width was 0.8 mm, and the facing area of the internal electrodes was 0.9 mm ² .

(E) Evaluation (E-1) Evaluation of barium titanate powder The particle size and integral width of the barium titanate powder obtained in the step (B) were evaluated.

  First, the particle size of the barium titanate powder is obtained by taking a photograph with a scanning electron microscope, processing the image of the outline of the powder projected in the photograph, and measuring the diameter of each particle as a circle. It was. About each sample, the diameter was measured about 500 particles or more, and the average particle diameter D1, the maximum particle diameter D2, and the minimum particle diameter D3 were calculated | required from the data.

  Further, the integral width of the barium titanate powder was analyzed by X-ray diffraction.

(E-2) Evaluation of ceramic green sheet The density and surface roughness of the ceramic green sheet obtained in the step (D) were evaluated.

  First, the density was evaluated as follows. The obtained ceramic green sheet was cut into a size of 10 cm × 10 cm and its weight was measured. Moreover, the thickness in a total of 25 places of 5 places x 5 places in the cut ceramic green sheet was measured, and the volume was calculated. Then, the density was calculated from the weight and volume thus determined. These operations were repeated 10 times for each sample, and the average value was obtained.

  Further, the surface roughness Ra of the ceramic green sheet was measured with an atomic force microscope. This operation was repeated three times for each sample, and the average value was obtained.

(E-3) Evaluation of Multilayer Ceramic Capacitor With respect to the dielectric ceramic constituting the dielectric ceramic layer provided in the multilayer ceramic capacitor obtained in the step (D), the average grain diameter and its variation are evaluated, and the multilayer ceramic A high temperature load test was performed on the capacitor.

  First, the grain diameter of the dielectric ceramic was measured as follows. The multilayer ceramic capacitor as a sample was broken and thermally etched at 1000 ° C., and the fracture surface was observed using a scanning microscope. Image analysis was performed from the observed image, and the equivalent circle diameter of each grain was defined as the grain diameter. The number of measured grains was 300, and the average grain diameter and its CV value were determined.

In the high temperature load life test, the change over time in the insulation resistance of the multilayer ceramic capacitor was measured at a temperature of 85 ° C. The applied voltage was changed according to the number of grains so that the electric field per grain boundary between grains was 0.5V. In particular,
(Thickness of dielectric ceramic layer / average grain diameter) -1
From this equation, the number of grain boundaries between grains arranged in the thickness direction in one dielectric ceramic layer was determined, and the voltage to be applied was determined by multiplying it by 0.5V. The high temperature load life test was performed on 50 samples, and by 2000 hours, a sample having an insulation resistance value of 100 kΩ or less was determined to be defective, and the number of defects was determined.

  The above evaluation results are shown in Table 1. In the evaluation of the above (E-1) barium titanate powder, among photographs taken with a scanning electron microscope, the sample 107 is shown in FIG. 2 (a), and the sample 110 is shown in FIG. 2 (b). Is shown in

  First, referring to FIG. 2, according to the sample 110 subjected to classification, the particle size distribution is sharper than that of the sample 107 not subjected to classification, and both the coarse particle side and the fine particle side are classified. I understand that.

Also, referring to Table 1, it can be seen that the sample subjected to classification has a sharper particle size distribution and a smaller integral width than the sample not subjected to classification. Therefore, according to the classified sample, the density of the ceramic green sheet is high and the surface roughness Ra is small, and in the multilayer ceramic capacitor after firing, the variation in grain diameter is small, and the life characteristics are improved. It has improved.
[Experiment 2]
In Experimental Example 2, the dielectric obtained through the steps of (A) preparation of barium titanate powder, (B) classification treatment of barium titanate powder, and (C) preparation of dielectric ceramic raw material powder in Experimental Example 1 The body ceramic raw material powder was used as it was. Therefore, the sample number in Experimental Example 2 is the same as the sample number in Experimental Example 1.

  In Experimental Example 2, the same procedure as in Experimental Example 1 was performed except that the thickness of the ceramic green sheet was set to 0.3 μm after firing in the production of the multilayer ceramic capacitor of (D) in Experimental Example 1. (D) A process for producing a multilayer ceramic capacitor was carried out.

  The evaluation results in Experimental Example 2 are shown in Table 2. In Table 2, the results of the evaluation of (E-1) barium titanate powder carried out in Experimental Example 1 are shown as they are.

  (E-2) Ceramic green sheets were evaluated in the same manner as in Experimental Example 1. In Experimental Example 2, the average grain diameter and its variation in the evaluation of the multilayer ceramic capacitor (E-3) carried out in Experimental Example 1 and the number of defects in the high temperature load test were not evaluated, and the short-circuit rate of the multilayer ceramic capacitor was determined. evaluated. That is, for each sample, 100 pieces were used as test items, and those having a resistance value of 10Ω or less were judged as short products, and the short rate was determined as a percentage.

  As can be seen from Table 2, in the multilayer ceramic capacitor having a dielectric ceramic layer thickness of 0.3 μm, when the average particle diameter D1 of the barium titanate powder is 150 nm or more, the short-circuit rate is almost 100%. This is considered to be because when the particles are large, the particles are difficult to arrange neatly in the ceramic green sheet. When the thickness of the dielectric ceramic layer is as thin as 0.3 μm, an average particle diameter D1 of 12 to 107 nm is necessary in order to sufficiently reduce the short circuit.

1 Multilayer Ceramic Capacitor 2 Dielectric Ceramic Layer 3, 4 Internal Electrode

Claims (5)

This is used to form a dielectric ceramic layer of a multilayer ceramic capacitor, wherein the average particle diameter D1 is in the range of 10 to 200 nm, the maximum particle diameter is D2, and the minimum particle diameter is D3. Barium titanate-based powder satisfying the relationship of 0.0 <D2 / D1 ≦ 2.0 and 0.5 ≦ D3 / D1 <1.0.   The barium titanate-based powder according to claim 1, wherein the average particle diameter D1 is in a range of 12 to 107 nm. A method for producing a barium titanate-based powder according to claim 1 or 2,
Preparing a raw material powder before classification to be a raw material of the barium titanate-based powder to be obtained;
Dispersing the raw material powder in a dispersion medium;
Precipitating the raw material powder in the dispersion medium;
Producing a target barium titanate powder by taking out only the raw material powder at a predetermined settling distance excluding both the upper part and the lower part in the dispersion medium. Method.   A dielectric ceramic obtained by sintering the barium titanate-based powder according to claim 1 or 2. A multilayer ceramic capacitor comprising a plurality of laminated dielectric ceramic layers and a plurality of internal electrodes formed along a specific interface between the dielectric ceramic layers,
The dielectric ceramic layer is made of the dielectric ceramic according to claim 4,
Multilayer ceramic capacitor.

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