JP2005243890A - Laminated ceramic capacitor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated ceramic capacitor large in an electrostatic capacity and excellent in dielectric property and DC bias characteristics. <P>SOLUTION: The average grain size of particles constituting the dielectric layer of the laminated ceramic capacitor is formed of first crystalline particles having large grain sizes, and second crystalline particles having small grain sizes. When the average grain size of the first crystalline particles is shown by R<SB>1</SB>and the average grain size of the second crystalline grains is shown by R<SB>2</SB>, it is specified that 0.10 μm≤R<SB>1</SB>≤0.30 μm and the ratio of R<SB>1</SB>to R<SB>2</SB>or R<SB>1</SB>/R<SB>2</SB>≥5 while the ratio of S<SB>2</SB>to S<SB>1</SB>or S<SB>2</SB>/S<SB>1</SB>is specified so as to be 0.10≤S<SB>2</SB>/S<SB>1</SB>≤0.40, when an area occupied by the first crystalline particles existing in a unit area on the observed surface of the dielectric body layer is shown by S<SB>1</SB>, and an area occupied by the second crystalline particles on the same surface is shown by S<SB>2</SB>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a multilayer ceramic capacitor.

  A conventional multilayer ceramic capacitor will be described.

  First, barium titanate powder as a main component and metal oxide powder as a subcomponent are mixed, and organic substances such as a binder and a plasticizer are mixed to prepare a slurry, and a ceramic sheet is prepared using the slurry.

  Then, the laminated body which laminated | stacked the ceramic sheet and the internal electrode alternately is baked, and a multilayer ceramic capacitor is obtained by forming an external electrode.

  Here, when the thickness of the dielectric layer is reduced, the electrical performance (CR product and electric field strength dependency) is lowered. In order to prevent this, a method of controlling the crystal grain size in the dielectric layer has been proposed.

For example, Patent Document 1 is known as prior art document information related to the above-described conventional technology.
JP 2001-338828 A

  In recent years, small and large-capacity monolithic ceramic capacitors have been desired to have excellent voltage resistance and excellent capacitance reduction (hereinafter referred to as DC bias characteristics) when a DC voltage is applied.

  In order to obtain a small-sized and large-capacity monolithic ceramic capacitor, it is necessary to reduce the dielectric layer and increase the dielectric constant of the dielectric. In reducing the thickness of the dielectric layer, it is important not to lower the withstand voltage. Therefore, it is necessary to use barium titanate particles having a small particle size as the main component constituting the dielectric layer. However, in general, in a dielectric layer of 2 μm or less, there is a close relationship between the size of the barium titanate particles constituting the dielectric layer and the relative dielectric constant and DC bias characteristics of the dielectric ( If the relative dielectric constant is increased, there is a contradictory negative correlation that the DC bias characteristic is reduced), and it is very important to increase the dielectric constant of the dielectric layer without reducing the DC bias characteristic when the layer is thinned. difficult.

  In the invention described in Patent Document 1, it is shown that the barium titanate particles have large particles having a particle size of 0.4 μm or more and small particles having a particle size of 0.25 μm or less at a certain ratio.

  However, in the barium titanate particles having the above-described structure, if the dielectric layer has a thickness of 1.5 μm or less, particularly about 1.0 μm, the crystal particles existing between the internal electrodes in the dielectric layer are reduced. Therefore, the withstand voltage is reduced.

  Further, when the particle size of barium titanate constituting the dielectric layer is reduced with respect to the voltage resistance, it is difficult to increase the dielectric constant of the dielectric material.

  Further, since the crystal grain size is as large as 0.4 μm or more, when the dielectric layer is thinned to 1.5 μm or less (especially around 1.0 μm), static electricity is applied by applying a DC voltage. There is a problem that the decrease in electric capacity becomes large.

  Accordingly, an object of the present invention is to provide a monolithic ceramic capacitor having a large capacitance, excellent voltage resistance and DC bias characteristics.

  In order to achieve the above object, the present invention has the following configuration.

The invention according to claim 1 of the present invention is a particle comprising a laminate in which dielectric layers and internal electrodes are alternately laminated, and an external electrode formed on the surface of the laminate, and constituting the dielectric layer Has a first crystal particle having a large particle size and a second crystal particle having a small particle size, the average particle size of the first crystal particle is R ₁ , and the average particle size of the second crystal particle is R when a _2, a 0.10 .mu.m ≦ R ₁ ≦ 0.30 .mu.m, and by R ₁ and the ratio R ₁ / R ₂ ≧ 5 of R _2, the capacitance is large, the voltage resistance and the DC bias A multilayer ceramic capacitor having excellent characteristics can be provided.

The invention according to claim 2 of the present invention, in particular, the S ₁ a first area of crystal grains account present per unit area in one observation plane of the dielectric layer S _1, the area of the entire viewing surface When the excluded area is S ₂ , the ratio S ₂ / S ₁ of S ₁ and S ₂ is 0.10 ≦ S ₂ / S ₁ ≦ 0.40. A multilayer ceramic capacitor excellent in DC bias characteristics can be provided.

  According to the third aspect of the present invention, in particular, the particles constituting the dielectric layer are mainly composed of barium titanate, and a multilayer ceramic capacitor having a large capacitance can be provided.

The invention according to claim 4 of the present invention is the first barium titanate in the raw material that mainly becomes the first crystal particles by sintering, in the X-ray diffraction chart of the diffraction line of (002) plane. Ratio [I (200)] of the peak intensity [I (200)] of the (200) plane diffraction line to the intensity (Ib) at the midpoint between the peak point angle and the peak point angle of the (200) plane diffraction line / Ib] is 2 to 6, and the numerical value when the average particle diameter is expressed in μm is r, and the numerical value when the specific surface area is expressed in m ² / g is Sa, 1 ≦ Sa · r ≦ 2 A dielectric layer is formed using satisfactory barium titanate, and a multilayer ceramic capacitor having a large capacitance and excellent withstand voltage can be provided.

The invention according to claim 5 of the present invention, in particular, in the second barium titanate in the raw material that mainly becomes the second crystal particles by sintering, the diffraction line of the (002) plane in the X-ray diffraction chart thereof. Ratio [I (200)] of the peak intensity [I (200)] of the (200) plane diffraction line to the intensity (Ib) at the midpoint between the peak point angle and the peak point angle of the (200) plane diffraction line / Ib] is 2 or less, the numerical value when the average particle diameter is expressed in μm is r, and the numerical value when the specific surface area is expressed in m ² / g is Sa, 1 ≦ Sa · r ≦ 2 is satisfied The dielectric layer is formed using barium titanate, and a multilayer ceramic capacitor having a large capacitance, excellent voltage resistance and DC bias characteristics can be provided.

  In the invention according to claim 7 of the present invention, in particular, the second crystal particle is a particle in which a core-shell structure having a shell phase in which a trace amount of Mg-based compound or rare earth oxide is diffused is formed around the second crystal particle. In order to prevent trace additives that diffuse during sintering from entering the glass phase at the grain boundary, it suppresses the decrease in insulation resistance, increases the capacitance, and withstand voltage. It is possible to provide a monolithic ceramic capacitor having excellent characteristics and DC bias characteristics.

  The invention according to claim 8 of the present invention, in particular, contains at least Mg compound or Mg compound and rare earth compound as subcomponents forming the dielectric layer, and the total amount of Mg compound or Mg compound and rare earth compound is Provided is a multilayer ceramic capacitor having a total voltage of 3.0 mol% or more with respect to barium titanate and a content of the Mg compound of 3.0 mol% or more and having excellent voltage resistance and DC bias characteristics. be able to.

  The invention according to claim 9 of the present invention particularly includes at least an Mg compound or an Mg compound and a rare earth compound as subcomponents forming the dielectric layer, and the total amount of the Mg compound or Mg compound and the rare earth compound is titanium. To provide a multilayer ceramic capacitor having a total voltage of 3.0 mol% or more with respect to barium acid and a content of the Mg compound of 3.0 mol% or more and having excellent voltage resistance and DC bias characteristics. Can do.

  The invention according to claim 10 of the present invention can provide a multilayer ceramic capacitor in which the thickness of the dielectric layer is 1.5 μm or less and the capacitance is large.

In the eleventh aspect of the present invention, particularly as the ceramic raw material powder, at least the angle of the peak point of the (002) plane diffraction line and the peak point of the (200) plane diffraction line in the X-ray diffraction chart thereof. The ratio [I (200) / Ib] of the peak intensity [I (200)] of the diffraction line of the (200) plane to the intensity (Ib) at the midpoint with respect to the angle is 2 to 6, and the average particle diameter is expressed in μm. In the X-ray diffraction chart of the first barium titanate satisfying 1 ≦ Sa · r ≦ 2, where r is the numerical value when expressed, and Sa is the numerical value when the specific surface area is expressed in m ² / g The peak intensity of the (200) plane diffraction line relative to the intensity (Ib) at the midpoint between the (002) plane diffraction line peak angle and the (200) plane diffraction line peak angle [I (200) ] Ratio [I (200) / Ib] is 2 or less And a numerical value when expressed an average particle diameter in [mu] m r, when a numerical value when the specific surface area expressed in m ² / g was Sa, a second titanate satisfying the 1 ≦ Sa · r ≦ 2 A first step of mixing the ceramic raw material powder containing barium and subcomponents, and a second step of preparing a ceramic slurry by mixing the ceramic powder and organic matter after calcination and pulverization of the ceramic raw material powder And a third step of producing a ceramic sheet using the ceramic slurry, a fourth step of producing a laminate by alternately laminating the ceramic sheets and the conductor layers, and a fifth step of firing the laminate. The method of manufacturing a multilayer ceramic capacitor comprising the steps of: wherein the particles constituting the fired dielectric layer include first crystal particles having a large particle size and second crystal particles having a small particle size The average grain of the first crystal grain The R _1, when the average particle diameter of the second crystal grains was R _2, is 0.10 .mu.m ≦ R ₁ ≦ 0.30 .mu.m, and satisfying the ratio R ₁ / R ₂ ≧ 5 of R ₁ and R ₂ In addition, it is possible to provide a manufacturing method for manufacturing a multilayer ceramic capacitor having a large capacitance and excellent voltage resistance and DC bias characteristics.

In the invention according to claim 12 of the present invention, in particular, as the ceramic raw material powder, at least the angle of the peak point of the (002) plane diffraction line and the peak point of the (200) plane diffraction line in the X-ray diffraction chart thereof. The ratio [I (200) / Ib] of the peak intensity [I (200)] of the diffraction line of the (200) plane to the intensity (Ib) at the midpoint with respect to the angle is 2 to 6, and the average particle diameter is expressed in μm. Ceramic raw material powder containing the first barium titanate and subcomponents satisfying 1 ≦ Sa · r ≦ 2, where r is the numerical value when expressed and r is the specific surface area expressed as m ² / g The intensity at the intermediate point between the first step of mixing and calcining, and at least the peak point angle of the (002) plane diffraction line and the peak point angle of the (200) plane diffraction line in the X-ray diffraction chart Of (200) plane against (Ib) The ratio of the peak intensity of the polygonal line [I (200)] [I (200) / Ib] is 2 or less, and showing the numerical value when expressed an average particle diameter in [mu] m r, the specific surface area m ² / g When the time value is Sa, the second step of mixing and calcining the second barium titanate satisfying 1 ≦ Sa · r ≦ 2 and the ceramic raw material powder containing subcomponents; A third step of producing a ceramic slurry by mixing ceramic powder after firing and an organic material, a fourth step of producing a ceramic sheet using the ceramic slurry, and the ceramic sheet and the conductor layer alternately A multilayer ceramic capacitor manufacturing method comprising a fifth step of producing a laminated body by laminating and a sixth step of firing the laminated body, and particles constituting the dielectric layer after firing are: 1st crystal particle with large particle size and small particle size There second and a crystal grain, when the average particle diameter of the first crystal grains and R _1, an average particle diameter of the second crystal grains and _{R 2, 0.10μm ≦ R 1 ≦} 0.30μm And a manufacturing method for more reliably producing a multilayer ceramic capacitor satisfying the ratio R ₁ / R ₂ ≧ 5 of R ₁ and R ₂ , having a large capacitance, and having excellent voltage resistance and DC bias characteristics. Can be provided.

As described above, according to the present invention, the particles constituting the dielectric layer include the first crystal particles having a large particle size and the second crystal particles having a small particle size, and the particle size R ₁ of the first crystal particle. There meet 0.10μm ≦ R ₁ ≦ 0.30μm, the first and the crystal grain size R ₁ second ratio R ₁ / R ₂ of the crystal grain size R ₂ is R ₁ / R ₂ ≧ 5, further when S ₁ a first area of crystal grains account present per unit area in one observation plane of the dielectric layer, an area in which the second crystal grains account was S _2, the ratio of S ₁ and S ₂ S _{When 2} / S ₁ satisfies 0.10 ≦ S ₂ / S ₁ ≦ 0.40, it is possible to provide a multilayer ceramic capacitor having a large electrostatic capacity and excellent voltage resistance and DC bias characteristics.

(Embodiment 1)
The first to eleventh aspects of the present invention will be described below with reference to the first embodiment.

  FIG. 1 is a partially enlarged cross-sectional view of a multilayer ceramic capacitor in the present embodiment, FIG. 2 is an X-ray diffraction chart of barium titanate in the present embodiment, and FIG. 3 is a diagram for explaining a mixing process in the present embodiment. It is sectional drawing.

  In FIG. 1, 10 is a dielectric layer mainly composed of barium titanate, 11 is an internal electrode mainly composed of Ni, 12 is a particle phase having a first crystal grain size, and 13 is a second crystal. A particle phase having a particle size.

  In FIG. 3, 20 is a mixing tank, 21 is a zirconia ball as a medium, 22 is a stirring bar, 23 is an inlet, and 24 is an outlet.

First, 100 mol% of barium titanate as a starting material for the dielectric layer 10, 1.0 mol% of MgO, 3.0 mol% of Dy ₂ O ₃ , 1.0 mol% of SiO ₂ , and 0 of MnO ₂ as subcomponents are used. Each powder is weighed so as to be 2 mol%.

  The barium titanate used here is a first barium titanate for forming first crystal grains having a large particle size after sintering and a second crystal particle for forming second crystal particles having a small particle size. It has two types of average particle sizes, barium titanate. Usually, barium titanate is tetragonal near room temperature. At this time, for example, in the X-ray diffraction chart shown in FIG. 2, the (002) plane diffraction line is observed near 2θ = 44.9 °, and the (200) plane diffraction line is observed near 2θ = 45.4 °. The The angle and intensity of the peak point of the (002) plane diffraction line are 2θ (002) and Ic, and the angle and intensity of the peak point of the (200) plane diffraction line are 2θ (200) and I (200), respectively. In this case, in the present invention, the first raw material powder of barium titanate to be the first crystal particles having a large particle size after sintering has I (200) / Ib of 2 to 6, and after sintering, In the second raw material powder of barium titanate to be the second crystal particles having a small particle diameter, I (200) / Ib is 2 or less.

  I (200) / Ib is defined as follows. That is, an intermediate angle between the peak point angle of the (002) plane diffraction line and the peak point of the (200) plane diffraction line is 2θb, that is, 2θb = (2θ (002) + 2θ (200)) / 2. The ratio of the peak intensity I (200) of the diffraction line on the (200) plane is defined as I (200) / Ib, with the intensity Ib at the intermediate degree 2θb as a reference. When I (200) / Ib exceeds 6, production of barium titanate becomes difficult, which is not preferable.

  As for the particle size of the barium titanate raw material powder, the average particle size of the first barium titanate is 0.15 to 0.30 μm, and the average particle size of the second barium titanate is the first titanate. It is 1/5 or less of the average particle diameter of barium. In particular, the average particle diameter of the first barium titanate is preferably 0.15 to 0.20 μm. The average particle size of the second barium titanate is preferably 1/5 or less, more preferably 1/8 or less, of the average particle size of the first barium titanate.

  Further, the ratio of the added amount of the second barium titanate to the total added amount of barium titanate is preferably 5 to 30%, more preferably 5 to 10%.

  Next, the raw material powder and pure water are mixed to prepare a slurry.

  If the amount of pure water to be added is too small, the dispersibility of the raw material powder is lowered, and if it is too much, agglomerated powder is easily generated in the drying step. Therefore, the amount of pure water is desirably 1 to 3 times the weight of the raw material powder in weight ratio.

  Moreover, you may add the dispersing agent which improves the dispersibility of raw material powder with a pure water.

  The stirrer shown in FIG. 3 is provided with a rotatable stirring rod 22 inside a mixing tank 20 and close-packed with zirconia balls 21 having an average particle diameter of 0.10 mm or less, preferably 0.05 mm or less. The zirconia balls 21 occupy about 70% of the internal volume of the mixing tank 20 excluding the volume of the stirring rod 22.

  The stirring rod 22 is rotated at a predetermined speed, a mixture of pure water and raw material powder is introduced from the inlet 23 of the mixing tank 20 at a predetermined speed, and the mixture is passed through the gap between the zirconia balls 21 and flows out from the outlet 24. Thus, a slurry having excellent dispersibility is obtained. Filters are installed at the inflow and the outlets 23 and 24 of the mixing tank 20 to prevent intrusion of foreign matters, and only homogeneous slurry comes out from the outlet 24.

  At this time, the raw material powder collides with the zirconia balls 21 and is pulverized. However, the zirconia balls 21 have an average particle diameter of 0.20 mm or less, and conventionally used balls having an average particle diameter of 1 mm to 2 mm. Since the mass is much smaller than that, it is possible to suppress excessive pulverization due to excessive impact.

  In order to obtain a slurry with high productivity, it is desirable that the spherical zirconia balls 21 are packed in the mixing tank 20 in a close-packed manner. At this time, the zirconia balls 21 theoretically occupy 74% of the internal volume of the mixing tank 20. Further, when the zirconia balls 21 are less than 60% of the internal volume of the mixing tank 20, the mixing cannot be performed sufficiently and the dispersibility is deteriorated.

  Therefore, it is preferable that the zirconia balls 21 occupy 60% or more of the internal volume of the mixing tank 20.

  The rotational speed of the stirring rod 22 and the inflow speed of the mixture are controlled so that an excessive force is not applied to the barium titanate.

  Next, the slurry is filtered and dehydrated, and dried in a drying room at a room temperature of 120 ° C.

  By dehydrating before drying, aggregation during drying can be suppressed.

  Further, by performing drying in a drying room at a room temperature of 120 ° C. or less, it is possible to suppress moisture from rapidly evaporating and aggregating. Although aggregation can be suppressed at 120 ° C. or lower, the lower the temperature, the longer it takes. Therefore, it is preferably performed at 100 to 120 ° C.

  Thereafter, the dry powder is put into a high-purity alumina crucible and calcined at 700 to 1100 ° C. in air. The calcination temperature and time are determined by the raw material powder composition.

  When the calcined powder is analyzed by X-ray diffraction, it is considered that the barium titanates or the subcomponents and the barium titanate react to form a slightly solid solution.

  Next, using the stirrer shown in FIG. 3, the calcined powder lightly pulverized and pure water are mixed to produce a slurry, dehydrated and dried.

  The steps of slurry preparation, dehydration, and drying are performed in the same manner as when slurry is prepared, dehydrated, and dried using raw material powder and pure water. Note that the calcined powder is obtained by a solid phase reaction of the ceramic powder to some extent, but it is mainly the second barium titanate that reacts.

  Although the first barium titanate is not particularly in a temperature range where grain growth starts, the first barium titanate is likely to be larger than the raw material powder because it is solidified in a state where the powders are aggregated. Therefore, in order to appropriately pulverize the calcined powder, it is desirable that the zirconia balls 21 have a size that is equal to or larger than that used when mixing the raw material powder, and preferably larger.

  The specific surface area Sb of the pulverized powder after drying is desirably Sb ≦ 1.2Sa (where 0 <Sb ≦ 6.0, Sa being the specific surface area of the barium titanate raw material powder>. By doing so, the desired dielectric layer 10 can be obtained effectively.

  Next, alcohol such as ethanol is mixed with the pulverized powder so that the surface of the powder particles is coated with alcohol.

  Next, a slurry is obtained by mixing a mixture of pulverized powder and an organic binder made of polyvinyl butyral resin, a solvent made of n-butyl acetate, and a plasticizer such as phthalates.

  Thus, by first coating the surface of the pulverized powder particles with alcohol and then mixing with the binder, solvent, and plasticizer, aggregation of the particles can be suppressed.

  However, if the amount of alcohol added is too large, a desired ceramic sheet cannot be obtained. Therefore, the amount of alcohol added is an amount capable of suppressing the aggregation of particles and covering the surface thereof, and is less than the total amount of binder, solvent and plasticizer.

  Thereafter, the slurry is formed into a ceramic sheet to be the dielectric layer 10 by a doctor blade method.

  Next, screen printing is performed on the ceramic sheet using an internal electrode paste made of Ni powder having an average particle diameter of about 0.40 μm so as to obtain a desired pattern.

  Next, three ceramic sheets on which the internal electrode patterns have been formed are stacked so that the internal electrode patterns face each other through the ceramic sheet, and are integrated by heating and pressurizing, and then cut to prepare an unsintered laminate. .

Then, the unsintered laminate is put into a zirconia sheath with zirconia powder and heated in nitrogen to burn the organic binder, and then fired at 1250 ° C. in N ₂ + H ₂ to obtain a sintered body. obtain. The firing temperature is desirably 1100 to 1250 ° C.

  Next, a copper paste for firing in a nitrogen atmosphere is applied to the exposed end face of the internal electrode 11 of the sintered body, and a fired external electrode is formed by a mesh type continuous belt furnace to obtain a multilayer ceramic capacitor as shown in FIG.

  The thickness of the internal electrode 11 of this multilayer ceramic capacitor is 1.5 μm or less, and the dielectric layer 10 is 1.5 μm or less in thickness, and the desired effect is obtained. In particular, the preferred thickness of the dielectric layer is about 1.2 μm or 1.0 μm. Thus, a more effective effect is obtained.

The dielectric layer 11 has core-shell particles in which the core part is barium titanate and the shell part is diffused around the barium titanate with the above-mentioned accessory components (MgO, Dy ₂ O _3, etc.). Also in the core-shell structure particles, the entire core portion surface is not covered with the shell portion, and there are particles in which the core portion is exposed. Further, in the dielectric layer 10, there are also particles of only the core portion, that is, only barium titanate.

  Further, since the second crystal particles having a small particle size absorb the additive diffused during the sintering, the shell portion forming additive is prevented from entering the grain boundary portion, and an effect of suppressing a decrease in insulation resistance is obtained. .

  Next, the obtained multilayer ceramic capacitor sample was heat-treated at a temperature of 150 ° C. for 1 hour, left at room temperature for 48 hours, and then electrostatically set at a frequency of 1 kHz and an input signal level of 1.0 Vrms in a constant temperature bath at 20 ° C. The capacitance and dielectric loss were measured, and the relative dielectric constant was calculated from the capacitance.

  Here, it was judged that a dielectric constant of 2000 or more is excellent.

  The DC bias characteristic is measured by measuring the capacitance, applying 3.15 V DC voltage, measuring the capacitance value after 20 seconds, and determining the rate of change from the difference from the capacitance value before application. Calculated.

  In this case, it was judged that the DC bias characteristics were excellent within -10%.

  Furthermore, a voltage was applied to the sample at a boosting rate of 100 V / sec, and the voltage when the sample was destroyed was defined as the withstand voltage of the sample. In this withstand voltage measurement, 20 samples were evaluated for each sample, and the average value was taken as the withstand voltage. In this measurement, the charge / discharge current is 25 mA or less.

  Here, a voltage of 150 V or higher was determined to have excellent voltage resistance.

Table 1 shows the particle diameter R ₁ of the first crystal particle having a large particle diameter in the dielectric layer and the particle diameter R of the second crystal particle having a small particle diameter when the thickness of the dielectric layer is 1.5 μm. _When the particle size ratio of ₂ is R ₁ / R ₂ , the area occupied by the first crystal grains per unit area on the observation surface is S ₁ , and the area occupied by the second crystal grains is S ₂ , S The ratio S ₂ / S _{1 of 1} and S ₂ is shown together with the relative dielectric constant, DC bias characteristics, and withstand voltage obtained by the above measurement.

From Table 1, dielectric sample numbers 1, 2, and 3 are dielectric materials having different crystal grain size ratios R ₁ / R ₂ and S ₂ / S ₁ when the grain size of barium titanate used as a raw material is changed. A sample with material.

Sample in which R ₁ is in the range of 0.10 to 0.30 μm, the crystal grain size ratio R ₁ / R ₂ is 5 or more, and S ₂ / S ₁ is in the range of 0.10 to 0.40. In No. 3, the dielectric constant, the DC bias characteristic, and the withstand voltage are all excellent values.

In contrast, Sample No. 1 with R ₁ of less than 0.10 μm and Sample No. 2 with a crystal grain size ratio R ₁ / R ₂ of less than 5 had a low relative dielectric constant and a low withstand voltage value. .

  Sample Nos. 4A to 4D are the results when a laminate was prepared using barium titanate having the same particle size and only the firing temperature was changed.

Sample number in which R ₁ is in the range of 0.10 to 0.30 μm, the crystal grain size ratio R ₁ / R ₂ is 5 or more, and S ₂ / S ₁ is in the range of 0.10 to 0.40. In 4B and 4C, the dielectric constant, the DC bias characteristic, and the withstand voltage are all excellent values.

In contrast, sample No. 4A has a S ₂ / S ₁ range of 0.4 or more and good DC bias characteristics, but has a low relative dielectric constant and withstand voltage.

In Sample No. 4D where S ₂ / S ₁ is 0.05, a high relative dielectric constant was obtained, but it was confirmed that the DC bias characteristics and the withstand voltage characteristics were deteriorated.

  According to electron microscopic observation of the sample cross section, sample No. 4D shows grain growth of barium titanate, and the firing temperature is not an appropriate temperature, so that barium titanate grows and this is the cause of the deterioration of DC bias characteristics. It is thought that it became.

Sample Nos. 5A to 5D are the results when a laminate was prepared using barium titanate having the same particle size as in Sample Nos. 4A to 4D, and only the firing temperature was changed. When the firing temperature was increased, R ₁ exceeded the range of 0.10 to 0.30 μm, and it was confirmed that the DC bias characteristics and the withstand voltage were deteriorated.

  This is the same as 4D, and it is considered that the firing temperature was not an appropriate temperature, and barium titanate caused grain growth.

Therefore, in order to increase the relative dielectric constant, the value of R ₁ / R ₂ may be increased. However, if the firing temperature is not appropriate, barium titanate tends to cause grain growth, and R ₁ has an appropriate particle size. It is considered that the DC bias characteristics are deteriorated beyond the range.

(Embodiment 2)
Hereinafter, a twelfth aspect of the present invention will be described using the second embodiment.

First, as a starting material for the dielectric layer 10, the subcomponent and MgO are 1.0 mol%, Dy ₂ O ₃ is 3.0 mol%, SiO _{2 is} SiO ₂ with respect to the total of 100 mol% of the two types of barium titanate as in the first embodiment. Each powder is weighed so that ₂ is 1.0 mol% and MnO ₂ is 0.2 mol%.

First, the second barium titanate having a small average particle size and relatively low crystallinity, a part of the subcomponent and pure water are mixed, and the treatment is performed in the order of dehydration, drying, and calcination. At this time, at least a material for forming a shell portion such as MgO or Dy ₂ O ₃ is added as a subcomponent to be mixed. The apparatus and conditions used for mixing are the same as those in the first embodiment.

  Next, the first barium titanate having a large average particle size and high crystallinity, the remaining auxiliary components and pure water are mixed, and the treatment is performed in the order of dehydration, drying, and calcination. About the calcination temperature, since the material which forms a shell part does not exist, 600 degreeC-900 degreeC and below the calcination temperature of 2nd barium titanate are set. More preferably, it is 600 to 700 ° C., and excessive aggregation is suppressed here.

  Next, the calcined second barium titanate powder and the first barium titanate powder are mixed. The apparatus used for mixing is the same as that of the first embodiment, and the zirconia balls 21 used for the mixing are desirably the same size or smaller, preferably smaller, than those used when mixing the raw material powder.

  A multilayer ceramic capacitor is obtained by the same method as in the first embodiment.

  Next, the obtained multilayer ceramic capacitor sample was heat-treated at a temperature of 150 ° C. for 1 hour, left at room temperature for 48 hours, and then electrostatically set at a frequency of 1 kHz and an input signal level of 1.0 Vrms in a constant temperature bath at 20 ° C. The capacitance and dielectric loss were measured, and the relative dielectric constant was calculated from the capacitance.

  Here, it was judged that a dielectric constant of 2000 or more is excellent.

  The DC bias characteristic is measured by measuring the capacitance, applying 3.15 V DC voltage, measuring the capacitance value after 20 seconds, and determining the rate of change from the difference from the capacitance value before application. Calculated.

  In this case, it was judged that the DC bias characteristics were excellent within -10%.

  A voltage was applied to the sample at a boosting rate of 100 V / sec, and the voltage when the sample was destroyed was defined as the withstand voltage of the sample. In this withstand voltage measurement, 20 samples were evaluated for each sample, and the average value was taken as the withstand voltage. In this measurement, the charge / discharge current is 25 mA or less.

  Here, a voltage of 150 V or higher was determined to have excellent voltage resistance.

  Table 2 shows the results of the second embodiment by using sample numbers 6A to 6D.

  The particle size of barium titanate used here is the same as that used for sample numbers 4A to 4D.

  Sample numbers 4A to 4D in (Table 2) are the same as those in (Table 1).

  From Table 2, it was confirmed that the deterioration of DC bias characteristics was confirmed by increasing the firing temperature in Sample No. 4D, but it was confirmed that Sample No. 6D exhibited good DC bias characteristics.

Further, it is confirmed that the width of the increase rate of the particle size ratio R ₁ / R ₂ and the width of the decrease rate of S ₂ / S ₁ are smaller in 6A to 6D than the sample numbers 4A to 4D as the firing temperature becomes higher. did it.

In Sample Nos. 6A to 6D, the material forming the shell portion such as MgO and Dy ₂ O ₃ sufficiently reacts with the second crystal particles of barium titanate, and the reaction to the first crystal particles decreases. This is considered to be due to high dielectric constant and high dispersibility.

In the above embodiment, the raw material powder using the dielectric layer 10 as a main component of barium titanate and MgO, Dy ₂ O ₃ , SiO ₂ or the like as a subcomponent is used. In the case of powder, the above-described effects can be obtained even when other subcomponents are used.

  Furthermore, when the slurry is produced in the mixing tank 20 as shown in FIG. 3, the temperature of the pure water rises. However, if the temperature is too high, the energy of the raw material powder increases, and it is difficult to obtain a desired slurry. It becomes. Therefore, the temperature of the mixture of pure water and raw material powder is kept at 50 ° C. or lower. In addition, you may mix using the container which can mix media, such as the zirconia ball | bowl 21, and raw material powder other than the mixing tank 20 which has the stirring rod 22 as shown in FIG.

  The method for measuring the crystal particle diameter in the first and second embodiments will be described below.

  The free surface after sintering of each sample was observed using a scanning electron microscope, and a straight line was randomly drawn on the portion of the observation surface where the first crystal particles and the second crystal particles existed side by side. The length of each straight line and the number of particles contained therein are measured, and the average particle diameter in a straight line is calculated. An average value is calculated after measuring by drawing a straight line on 200 or more of each particle, and this is taken as the average particle diameter.

  Furthermore, the specific surface area measurement method in the first and second embodiments will be described.

  First, the monomolecular layer adsorption amount Vm is obtained by (Equation 1).

  When three points (x, V) in the low-pressure body pressure region of the actual adsorption adsorption isotherm of He are taken out, the horizontal axis is x, the vertical axis is x / V (1-x), and when the plot is made, the slope becomes (C -1) A straight line with / VmC and an intercept of 1 / VmC is obtained. From this slope and intercept, the adsorption amount Vm of the monomolecular layer of He is obtained.

  Subsequently, the specific surface area is obtained by (Equation 2) using the monomolecular layer adsorption amount Vm obtained by (Equation 1).

  The multilayer ceramic capacitor according to the present invention uses, as a starting material, barium titanate having a different average particle diameter and crystallinity, and crystal particles that form a sintered dielectric layer by performing an optimum treatment on the barium titanate. Since the diameter is controlled, it is possible to obtain a monolithic ceramic capacitor having a large capacitance, excellent voltage resistance and DC bias characteristics, and is useful as a monolithic ceramic capacitor having a large capacity.

Partially enlarged sectional view of the multilayer ceramic capacitor in the first and second embodiments of the present invention X-ray diffraction chart of barium titanate in the same embodiment Sectional drawing for demonstrating the mixing process in the embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Dielectric layer 11 Internal electrode 12 Particle phase of 1st crystal particle 13 Particle phase of 2nd crystal particle 20 Mixing tank 21 Zirconia ball 22 Stirring rod 23 Inlet port 24 Outlet port

Claims (12)

The laminated body which laminated | stacked the dielectric material layer and the internal electrode alternately, and the external electrode formed in the surface of the said laminated body, The particle | grains which comprise the said dielectric material layer are 1st crystal particle with a large particle size, Second crystal particles having a small particle size, where the average particle size of the first crystal particles is R ₁ and the average particle size of the second crystal particles is R ₂ , 0.10 μm ≦ R ₁ ≦ is 0.30 .mu.m, and R ₁ and the ratio R ₁ / R ₂ ≧ 5 a is a multilayer ceramic capacitor of R _2. When S ₁ a first area of crystal grains account present per unit area in one observation plane of the dielectric layer, the area excluding the S ₁ from the area of the entire observation surface was S _2, S ₁ and S _2. The multilayer ceramic capacitor according to claim 1, wherein a ratio S ₂ / S _{1 of 2} is 0.10 ≦ S ₂ / S ₁ ≦ 0.40. The multilayer ceramic capacitor according to claim 1, wherein the particles constituting the dielectric layer are mainly composed of barium titanate. The first barium titanate in the raw material, which mainly becomes the first crystal particles by sintering, is the angle of the peak point of the (002) plane diffraction line and the peak of the (200) plane diffraction line in the X-ray diffraction chart. The ratio [I (200) / Ib] of the peak intensity [I (200)] of the diffraction line on the (200) plane to the intensity (Ib) at the midpoint of the point angle is 2-6, and the average particle diameter is μm The multilayer ceramic capacitor according to claim 1, wherein r is a numerical value when expressed as s, and Sa is a numerical value when the specific surface area is expressed as m ² / g. . The second barium titanate in the raw material, which mainly becomes the second crystal particles by sintering, is the angle of the peak point of the (002) plane diffraction line and the peak of the (200) plane diffraction line in the X-ray diffraction chart. The ratio [I (200) / Ib] of the peak intensity [I (200)] of the (200) plane diffraction line to the intensity (Ib) at the midpoint of the point angle is 2 or less, and the average particle diameter is μm 2. The multilayer ceramic capacitor according to claim 1, wherein 1 ≦ Sa · r ≦ 2 is satisfied, where r is a numerical value when expressed, and Sa is a numerical value when a specific surface area is expressed in m ² / g. The second crystal particle is a particle having a core-shell structure in which a shell phase, which is a phase in which a Mg-based compound or a rare earth oxide as a trace additive is diffused, is present around the second crystal particle. Multilayer ceramic capacitor. The multilayer ceramic capacitor according to claim 4, wherein some of the first crystal particles are particles forming a core-shell structure. As a part of subcomponents forming the dielectric layer, at least Mg compound or Mg compound and rare earth compound are included, and the total amount of Mg compound or Mg compound and rare earth compound is 3.0 mol in total with respect to barium titanate. The multilayer ceramic capacitor according to claim 6, wherein the content of the Mg compound is 3.0 mol% or more. As an auxiliary component forming the dielectric layer, at least Mg compound or Mg compound and rare earth compound are included, and the total amount of Mg compound or Mg compound and rare earth compound is 3.0 mol% or more in total with respect to barium titanate. The multilayer ceramic capacitor according to claim 7, wherein the content of the Mg compound is 3.0 mol% or more. The multilayer ceramic capacitor according to claim 1, wherein the dielectric layer has a thickness of 1.5 μm or less. As a ceramic raw material powder, at least in the X-ray diffraction chart (200) with respect to the intensity (Ib) at the midpoint between the angle of the (002) plane diffraction line and the angle of the (200) plane diffraction line When the ratio [I (200) / Ib] of the peak intensity [I (200)] of the surface diffraction line is 2 to 6 and the average particle diameter is expressed in μm, the numerical value is r, and the specific surface area is m ² / g. When Sa is a numerical value when expressed by the following formula, the first barium titanate satisfying 1 ≦ Sa · r ≦ 2, and the angle of the peak point of the (002) plane diffraction line in the X-ray diffraction chart ( The ratio [I (200) / Ib] of the peak intensity [I (200)] of the (200) plane diffraction line to the intensity (Ib) at the midpoint of the peak point of the 200) plane diffraction line is 2 or less. And when the average particle diameter is expressed in μm r, when the numerical value when the specific surface area is expressed in m ² / g is Sa, a first barium titanate satisfying 1 ≦ Sa · r ≦ 2 and a ceramic raw material powder containing subcomponents are mixed. A second step of preparing a ceramic slurry by preliminarily firing and pulverizing the ceramic raw material powder, and then mixing the pulverized ceramic powder and an organic substance, and preparing a ceramic sheet using the ceramic slurry. 3 is a method of manufacturing a multilayer ceramic capacitor, comprising: a fourth step of alternately stacking the ceramic sheet and the conductor layer to produce a laminate; and a fifth step of firing the laminate. . As a ceramic raw material powder, at least in the X-ray diffraction chart (200) with respect to the intensity (Ib) at the midpoint between the angle of the (002) plane diffraction line and the angle of the (200) plane diffraction line When the ratio [I (200) / Ib] of the peak intensity [I (200)] of the surface diffraction line is 2 to 6 and the average particle diameter is expressed in μm, the numerical value is r, and the specific surface area is m ² / g. The first step of mixing and calcining the first barium titanate satisfying 1 ≦ Sa · r ≦ 2 and the ceramic raw material powder containing subcomponents, where Sa is the numerical value when In the X-ray diffraction chart, the peak intensity of the (200) plane diffraction line relative to the intensity (Ib) at the midpoint between the (002) plane diffraction line peak angle and the (200) plane diffraction line peak angle. Ratio of [I (200)] [ (200) / Ib] is 2 or less, and when the numerical value when expressed an average particle diameter in [mu] m r, the value of when the specific surface area expressed in m ² / g was Sa, 1 ≦ Sa · r The second step of mixing and calcining the second barium titanate satisfying ≦ 2 and the ceramic raw material powder containing subcomponents, and mixing the two kinds of the calcined ceramic powder and the organic substance to produce a ceramic slurry A third step of manufacturing a ceramic sheet, a fourth step of manufacturing a ceramic sheet using the ceramic slurry, and a fifth step of stacking the ceramic sheet and a conductor layer alternately to form a laminate. And a sixth step of firing the multilayer body.

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