JP6034145B2 - Capacitor - Google Patents

Description

  The present invention relates to a capacitor using a dielectric ceramic composed of crystal particles mainly composed of barium titanate as a dielectric layer.

  In recent years, with the development of high-luminance blue light-emitting diodes (LEDs), the development of lighting equipment that uses LEDs as light sources has rapidly progressed along with full-color LED display devices that can achieve high visibility. It's getting on.

  In such an electronic device using an LED, a method of generating a DC voltage for driving the LED from a commercial power source using an AC-DC converter is adopted. However, the AC-DC converter uses a commercial power source (100V). ) Is a circuit that drives a LED by generating a desired DC output voltage from the AC voltage, and a rectifier circuit used in such a circuit is equipped with a capacitor together with a field effect transistor (MOSFET) as a control circuit element (For example, refer to Patent Document 1).

  However, in an electronic device using such an LED, since the applied voltage is high and the temperature change due to heat generation during light emission is large, the capacitance is high even when a voltage is applied as a capacitor. What can be maintained is required.

JP 2011-35112 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a capacitor capable of maintaining a high capacitance even when a voltage is applied at a high temperature.

The capacitor of the present invention comprises a dielectric ceramic containing barium titanate crystal grains containing calcium and containing at least one rare earth element (RE) selected from the group of terbium, dysprosium, holmium, erbium and gadolinium. A crystal layer comprising: a dielectric layer, wherein the crystal grain is a crystal grain of a first crystal group having a rare earth element (RE) concentration of 0 to 0.5 atomic% at a depth of 20 nm from a grain boundary ; , the concentration of the said rare earth element than the crystal grains of the first crystal group (RE) is high, with the concentration becomes and a crystal grain of the second crystal group is 0.3 to 0.9 atomic% The concentration difference of the rare earth element (RE) between the crystal grains of the first crystal group and the crystal grains of the second crystal group is 0.1 to 0.7 atomic%, The crystal particles are Wherein the average particle diameter is larger than the crystal grains of the group.

  According to the present invention, it is possible to obtain a capacitor capable of maintaining a high capacitance even when a voltage is applied at a high temperature.

(A) is a schematic sectional drawing which shows an example of the capacitor | condenser of this invention, (b) is an enlarged view of the dielectric material layer which comprises the capacitor | condenser of FIG. 1, and is the schematic diagram which shows a crystal grain and a grain boundary phase It is. (A) is a schematic diagram showing the concentration gradient of the crystal grains constituting the first crystal group and the rare earth element (RE) therein, and (b) is the crystal grains constituting the second crystal group. It is a schematic diagram showing the concentration gradient of the rare earth element (RE) inside.

  The capacitor of this embodiment will be described in detail based on the schematic cross-sectional view of FIG. FIG. 1A is a schematic cross-sectional view showing an example of the capacitor of the present invention, and FIG. 1B is an enlarged view of a dielectric layer constituting the capacitor of FIG. 1, showing crystal grains and grain boundary phases. It is a schematic diagram. FIG. 2A is a schematic diagram showing the concentration gradient of the crystal grains constituting the first crystal group and the rare earth element (RE) therein, and FIG. 2B is the crystal constituting the second crystal group. It is a schematic diagram showing the density | concentration gradient of particle | grains and the rare earth element (RE) inside it.

  In the capacitor of this embodiment, external electrodes 3 are formed at both ends of the capacitor body 1. The external electrode 3 is formed, for example, by baking Cu or an alloy paste of Cu and Ni.

  The capacitor body 1 is configured by alternately laminating dielectric layers 5 made of dielectric ceramics and internal electrode layers 7. In FIG. 1, the laminated state of the dielectric layer 5 and the internal electrode layer 7 is shown in a simplified manner. However, the capacitor of the present invention includes a laminated body having several hundreds of dielectric layers 5 and internal electrode layers 7. It has become.

  The dielectric layer 5 made of a dielectric ceramic is composed of crystal grains 9 and a grain boundary phase 11, and the average thickness is preferably 5 μm or less, particularly 3 μm or less. Can be realized. The average thickness of the dielectric layer 5 is preferably 1 μm or more from the viewpoint of reducing variation in capacitance, stabilizing capacitance-temperature characteristics, and improving high-temperature load life.

  The internal electrode layer 7 is preferably a base metal such as nickel (Ni) or copper (Cu) in that the manufacturing cost can be suppressed even when the number of layers is increased, and in particular, the dielectric layer 5 constituting the capacitor of the present embodiment Of these, nickel (Ni) is more desirable in that it can be fired simultaneously.

The dielectric ceramic constituting the dielectric layer 5 in the capacitor of this embodiment is
It has crystal grains 9 of barium titanate containing calcium and contains at least one rare earth element (RE) selected from the group of terbium, dysprosium, holmium, erbium and gadolinium. Here, the dielectric ceramic constituting the capacitor of the present embodiment has crystal grains 9 mainly composed of barium titanate containing calcium as main crystal grains, and X obtained by performing X-ray diffraction. On the line diffraction pattern, the diffraction intensity of the main peak derived from barium titanate is higher than the diffraction intensity of the main peak of the crystal phase other than barium titanate.

  The crystal grain 9 is composed of at least two kinds of crystal grains having a difference of not less than 0.1 atomic% in the rare earth element (RE) concentration at a depth of 20 nm from the grain boundary.

  Thereby, even if the capacitor is exposed to a high temperature and a DC voltage is applied, a capacitor with a small decrease in capacitance can be obtained. For example, when the capacitance measured under the condition that no DC voltage is applied at room temperature (25 ° C.) is used as a reference, the rate of change in capacitance when a DC voltage of about 50 V is applied at 125 ° C. ( Hereinafter, it is referred to as high temperature DC bias characteristics) within 77%. In the following description, when describing the characteristics, the relative permittivity may be used instead of the capacitance.

On the other hand, there is no difference in the concentration of the rare earth element (RE) contained in the crystal grains 9 constituting the dielectric ceramic, and the concentration of the rare earth element (RE) at a depth of 20 nm from the grain boundary is 0. When it is composed of a group of crystal grains that cannot find a difference of 1 atomic% or more, when the capacitance measured under the condition that a DC voltage is not applied at room temperature (25 ° C.) is used as a reference, At 125 ° C., the rate of change in capacitance when a DC voltage of about 50 V is applied is greater than 77%.

The dielectric ceramic further includes vanadium, magnesium, manganese, and yttrium. As a ratio of these additional components, vanadium is V ₂ O _{5 with} respect to 100 mol of titanium constituting barium titanate. 0.05 to 0.20 mol in terms of conversion, yttrium 0.5 to 2.0 mol in terms of Y ₂ O ₃ , magnesium 1.0 to 3.0 mol in terms of MgO, and manganese 0.22 in terms of MnO ˜0.50 mol, the rare earth element (RE) is 0.65 to 2.80 mol in terms of RE ₂ O ₃ , and the crystal grains 9 are rare earth elements (at a depth of 20 nm from the grain boundary). (RE) in the first crystal group having a concentration of 0.02 to 0.42 atomic%, and in the second crystal group having a rare earth element (RE) concentration of 0.45 to 0.70 atomic%. With crystal grains 9b The average particle size of the crystal particles 9a is 0.10 to 0.18 μm, the average particle size of the crystal particles 9b is 0.2 to 0.5 μm, and further, per unit area of the polished surface of the dielectric ceramic. It is desirable that b / (a + b) is 0.4 to 0.7, where a is the crystal grain 9a area and b is the crystal grain 9b area.

  Thereby, it is possible to obtain a capacitor having a high relative dielectric constant, a small temperature change rate of the relative dielectric constant, and excellent reliability in high temperature load life. For example, the relative dielectric constant at room temperature (25 ° C.) is 2100 or more, and the rate of change of the relative dielectric constant when the room temperature (25 ° C.) is the reference in the temperature range of −55 to 125 ° C. Temperature characteristic) is within ± 13.5% (the rate of change in the relative permittivity at 125 ° C. is the largest between −55 and 125 ° C., and hence the rate of change at 125 ° C. is shown below). In addition, a voltage per unit thickness of the dielectric layer (DC voltage) of 5 to 10 V is applied at 125 ° C. relative to the relative dielectric constant measured at 25 ° C. with no DC voltage applied (no load condition). The rate of change of the relative dielectric constant measured in the above condition can be made within −53.6% (in the direction approaching NPO (± 0%)), and further, a DC voltage of 170 ° C. and 170 V is evaluated under the application conditions. 4 high temperature load life It can be 0 hours or more. Hereinafter, the term “high temperature load life” refers to the high temperature load life evaluated under the above conditions.

The dielectric ceramic in the present embodiment includes two types of at least one rare earth element (RE) selected from the group of terbium, dysprosium, holmium, erbium, and gadolinium in different amounts in the crystal grains 9a and 9b. crystal grains 9a, are constituted by 9b, these crystal grains 9a, among 9b, the crystal grains 9a of the first binding Akiragun is the concentration of the rare earth element contained in the crystal grains 9 (RE) is less Therefore, since rare earth elements (RE) are hardly dissolved in the central portion of the crystal particle 9a, the central portion is dominated by a tetragonal crystal phase with few additive components. A high dielectric ceramic can be obtained. Crystal grains 9a of the first imaging Akiragun is additive component in the vicinity of the surface of the solid solution has a cubic crystal structure, whereas, since the center portion is tetragonal, the crystal grains 9a is Basically, it has a core-shell structure. Therefore, the crystal structure is a core-shell structure (in the X-ray diffraction pattern, for example, a diffraction peak caused by a cubic system between the diffraction peak of the 200 plane and the diffraction peak of the 002 plane (index is overlapped with 200, 020, 002). state) appears. the cubic diffraction peak of crystal system has a diffraction intensity comparable to the diffraction peaks of the diffraction peak and 002 plane 200 plane due to tetragonal. hereinafter, the first crystal group first In some cases, the first crystal group is referred to as the first crystal group, and the second crystal group is referred to as the second crystal group.

On the other hand, since the concentration of the rare earth element (RE) contained in the crystal particles 9 is high in the crystal particles 9b of the second crystal group, the rare earth elements (RE) are dissolved in the deep portion inside the crystal particles 9b. Therefore, the crystal grains 9b have a smaller proportion of the tetragonal crystal phase that does not contain the additive component, and the crystal phase in which the additive component is dissolved (in the X-ray diffraction pattern, the 200 and 002 planes). A tetragonal crystal phase in which a diffraction peak appears remarkably) appears. As a result, the crystal particles 9b have fewer defects such as oxygen vacancies than the crystal particles 9a, and the voltage dependency of the relative permittivity can be reduced while maintaining a high relative permittivity. Also, the high temperature load life can be increased.

  That is, in this dielectric ceramic, a diffraction peak due to the first crystal particles having a core-shell structure and a diffraction peak due to the second crystal particles having a large amount of added components appear simultaneously. Here, the diffraction peak attributed to the first crystal particle and the diffraction peak attributed to the second crystal particle have different lattice constants due to the different solubility of the additive component.

  Further, as shown in FIGS. 2 (a) and 2 (b), the crystal particles 9a and 9b constituting the dielectric ceramic have different rare earth element (RE) concentration gradients, and crystals of the first crystal group. It is preferable that the particle 9a is 0.05 to 0.20 atomic% / nm and the crystal particle 9b of the second crystal group is 0.03 atomic% / nm or less.

  Although it is difficult for the crystal particles 9a alone to reduce the temperature change rate of the dielectric constant when a DC voltage is applied, if the crystal particles 9b coexist with the crystal particles 9a, the crystal particles 9b originally have a specific ratio. Due to the property that the voltage dependence of the dielectric constant can be reduced, the temperature change rate of the relative dielectric constant when a DC voltage is applied becomes small.

  In addition, the dielectric ceramic according to the present embodiment can increase the dielectric constant because the average particle diameter of the crystal particles 9b is larger than the average particle diameter of the crystal particles 9a.

  As a result, the capacitor according to the present embodiment has a relative dielectric constant measured at a room temperature (25 ° C.) of 2100 or more, particularly at 25 ° C. in a state where no DC voltage is applied (no load state). On the other hand, at 125 ° C., the change rate of the relative dielectric constant within 53.6% when the voltage (DC voltage) per unit thickness of the dielectric layer 5 is applied from 5 to 10 V (hereinafter referred to as high temperature load state). In addition, the reliability of the high-temperature load life is excellent.

  In the dielectric ceramic according to the present embodiment, terbium, dysprosium, holmium, erbium, and gadolinium are selected as the rare earth elements (RE) contained therein. These rare earth elements (RE) are rare earth elements in the periodic table. This is because, among the elements, the solid particles are easily dissolved in the crystal particles 9 mainly composed of barium titanate. Then, by dissolving these rare earth elements (RE) in the crystal particles 9 to form two kinds of crystal particles 9a and 9b having different concentrations of the rare earth elements (RE) in the dielectric ceramic, The relative permittivity of the porcelain, the temperature change rate of the relative permittivity, and the withstand voltage characteristics can be changed.

  Yttrium (Y), which is contained separately from the rare earth element (RE), is an element that is less soluble in barium titanate than elements such as terbium, dysprosium, holmium, erbium, and gadolinium. Yttrium can be dissolved in the vicinity of the surface of the barium titanate crystal particles 9, and thus the relative permittivity of the dielectric ceramic, the temperature change rate of the relative permittivity in the no-load state and the high-temperature load state, In addition, the reliability of the high temperature load life can be controlled. In this case, the concentration gradient of yttrium is preferably 0.05 to 0.20 atomic% / nm for both the crystal particles 9a and 9b.

Here, regarding the concentration and concentration distribution of the rare earth element (RE) in the crystal particles 9, after the cross section of the dielectric ceramic is polished, the crystal particles are approximately on the image displayed on the monitor attached to the transmission electron microscope. Draw 30 circles, select crystal particles in and around the circle, and perform elemental analysis using a transmission electron microscope equipped with elemental analysis equipment. The crystal particles 9 to be selected at this time are obtained by calculating the area of each particle by image processing from the outline, and calculating the diameter when replaced with a circle having the same area. The diameter of the obtained crystal particle 9 is approximately 0.08. The crystal grain 9 is in the range of ˜0.60. The spot size of the electron beam when the analysis is performed is 0.5 to 2 nm, and the location to be analyzed is a position 20 nm (± 1 nm) deep from the grain boundary of the crystal grain 9.

  When the concentration of rare earth element (RE) in the crystal particle 9 is obtained, an electron beam is applied to the center of the crystal particle 9 and the amount of main elements contained in the crystal particle 9 is determined from the output of the obtained X-ray. It is determined as 100 atomic%, and the ratio of rare earth elements (RE) is determined from this. Here, examples of main elements include barium (Ba), titanium (Ti), vanadium (V), magnesium (Mg), manganese (Mn), and rare earth elements (RE).

Next, when determining the concentration gradient of the rare earth element (RE), the points are located at substantially equal intervals on a straight line drawn toward the center in the range from the vicinity of the grain boundary to the center position of the central part, and near the grain boundary is obtained from the values analyzed in approximately 20nm and 200nm in depth from the grain boundary (referred to as _{d G} in FIG. 2 (a) (b)) . In this case, a value obtained by subtracting the rare earth element (RE) concentration at a depth of 19 to 21 nm and 195 to 205 nm from the concentration of the rare earth element (RE) at the grain boundary (0 to 1 nm) of the crystal grain 9 (concentration of the rare earth element). ) Is divided by the distance of the analyzed range (for example, 20 nm-0 nm = 20 nm, 200 nm-0 nm = 200 nm) to obtain a concentration gradient.

  Thereafter, the crystal grain 9a of the first crystal group and the crystal grain 9b of the second crystal group are determined by determining the concentration gradient of the rare earth element (RE) for each crystal particle 9.

  Here, the average particle diameter of each of the crystal grains 9a constituting the first crystal group and the crystal grains 9b constituting the second crystal group is determined on the polished surface obtained by polishing (ion milling) the cross section of the dielectric ceramic. The diameter when the image displayed by the transmission electron microscope is taken into a computer, the contours of the crystal particles present on the image are processed, the area of each particle is obtained, and replaced with a circle with the same area. Is calculated from the average value of the calculated 30 crystal grains. In this case, the crystal particles 9a and 9b are distinguished from each other based on the result of previously determining the concentration gradient of the rare earth element (RE) from the crystal particles 9, and the average values of the crystal particles 9a and 9b are obtained by respectively determining the average values. Obtain the particle size.

  Further, the area ratio of the crystal grains 9b constituting the second crystal group to the total area of the crystal grains 9a constituting the first crystal group constituting the dielectric ceramic and the crystal grains 9b constituting the second crystal group. Is calculated using the data used to determine the average particle size.

  In the capacitor according to the present embodiment, the dielectric porcelain is 0.30 to 0.50 mol of manganese in terms of MnO with respect to 100 mol of titanium constituting barium titanate, and b / (a + b) is It is desirable that it is 0.4 to 0.6, and thereby, the temperature change rate of the relative permittivity in a high temperature load state can be made −53.1% or less.

  Furthermore, it is desirable that the concentration of the calcium contained in the crystal particles 9a and 9b is 1 to 5 mol%, thereby making it possible to make the temperature characteristic of the relative dielectric constant in an unloaded state to -13.0% or less. The dielectric loss (tan δ) can be made 4.1 or less.

Regarding the concentration of calcium in the crystal particles 9a and 9b, elemental analysis is performed on the crystal particles present on the polished surface obtained by polishing the cross section of the dielectric ceramic using a transmission electron microscope provided with an elemental analysis device. At this time, the spot size of the electron beam is 5 nm or less, and the analysis site is the central part of the crystal particles 9a and 9b, and Ba, Ti, Ca, V, Mg, Y detected by the analysis.
, And the ratio of calcium when the total amount of RE (rare earth element) and Mn is 100%. The crystal particles 9a and 9b to be analyzed are selected by drawing a circle containing about 10 crystal particles in the substantially central portion shown on the monitor (photograph) for microscopic observation. The center part of the crystal grains 9a and 9b is the center of a circle drawn along the outline of each crystal grain. )
Further, in the multilayer ceramic capacitor of the present embodiment, other components may be included in addition to the above-described components as long as desired dielectric characteristics can be maintained. For example, as an auxiliary agent for improving sinterability. It is possible to contain a glass component and other additive components in the dielectric ceramic in a proportion of 0.5 to 2% by mass.

Next, a method for manufacturing the capacitor of the present embodiment will be described. However, the manufacturing method described below is an example, and the method is not limited to this method. First, as raw material powder, barium calcium titanate powder in which calcium is dissolved in barium titanate (purity is 99 mass% or more, hereinafter referred to as BCT powder), V ₂ O ₅ powder, MgO powder, and MnCO ₃ powder, Y ₂ O ₃ powder, and Tb ₄ O ₇ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder and at least one selected from the group of Gd ₂ O ₃ powder prepare.

The BCT powder is a perovskite-type barium titanate in which part of the Ba site of barium titanate is substituted with Ca, and is represented by the chemical formula (Ba _1-x Ca _x ) TiO ₃ . In the present invention, the Ca substitution amount in the Ba site is preferably X = 0.01 to 0.05.

Here, the average particle diameter of the BCT powder is preferably 0.10 to 0.35 μm, particularly preferably 0.15 to 0.30 μm. _V 2 _{O 5} powder is an additive, MgO powder, MnCO _{3 powder,} Y 2 _{O 3} powder or, _Tb 4 _{O 7} powder, _Dy 2 _{O 3} powder, _Ho 2 _{O 3} powder, _Er 2 _{O 3} powder and Gd ₂ Also for the O ₃ powder, it is preferable to use an average particle diameter equal to or less than that of the BCT powder.

  Next, a slurry is prepared using these raw material powders. When the capacitor of this embodiment is manufactured, the second crystal group after firing out of the total amount of the BCT powder used for forming the dielectric ceramic. The amount corresponding to the ratio of forming the crystal particles 9b is divided in advance and the molar ratio corresponding to the ratio of the subdivided BCT powder among the rare earth element (RE) oxide powder added to the subdivided BCT powder. The rare earth element (RE) is added and coating is performed. The coating process is performed by calcining at a temperature of 450 to 800 ° C. after mixing a predetermined amount of BCT powder and rare earth element (RE) oxide powder.

Next, a BCT powder coated with a rare earth element (RE) oxide powder (hereinafter referred to as a coating powder), a remaining BCT powder not coated with a rare earth element (RE) oxide powder, and the remaining A dielectric powder is prepared by adding a predetermined amount of each of rare earth element (RE) oxide powder and additive powders such as V ₂ O ₅ powder, MgO powder, MnCO ₃ powder, and Y ₂ O ₃ powder.

  Next, a ceramic slurry is prepared by adding a special organic vehicle to the dielectric powder prepared as described above, and then a ceramic green sheet is formed using a sheet forming method such as a doctor blade method or a die coater method. To do. In this case, the thickness of the ceramic green sheet is preferably 1 to 6 μm from the viewpoint of reducing the thickness of the dielectric layer 5 to increase the capacity and maintaining high insulation.

  Next, a rectangular internal electrode pattern is printed and formed on the main surface of the obtained ceramic green sheet. Ni, Cu, or an alloy powder thereof is suitable for the conductor paste that forms the internal electrode pattern.

  Next, stack the desired number of ceramic green sheets with internal electrode patterns, and stack multiple ceramic green sheets without internal electrode patterns on the top and bottom so that the upper and lower layers are the same number. Form the body. In this case, the internal electrode pattern in the sheet laminate is shifted by a half pattern in the longitudinal direction.

  Next, the sheet laminate is cut into a lattice shape to form a capacitor body molded body so that the end of the internal electrode pattern is exposed. By such a laminating method, the internal electrode pattern can be formed so as to be alternately exposed on the end surface of the cut capacitor body molded body.

  Next, the capacitor body molded body is degreased and fired. The firing temperature is preferably 1200 to 1300 ° C. because the solid solution of the additive in the BCT powder and the coating powder and the grain growth of the crystal particles are suppressed in this embodiment.

  Moreover, after baking, it heat-processes in a weak reducing atmosphere again. This heat treatment is performed to reoxidize the dielectric ceramic reduced in firing in a reducing atmosphere and recover the insulation resistance reduced and reduced during firing. The temperature is preferably 900 to 1100 ° C. for the purpose of increasing the amount of reoxidation while suppressing the grain growth of the crystal grains 9. In this way, a dielectric ceramic having a small relative dielectric constant temperature change rate can be obtained even in a high temperature load state.

  Next, an external electrode paste is applied to the opposing ends of the capacitor body 1 and baked to form the external electrodes 3. Further, a plating film may be formed on the surface of the external electrode 3 in order to improve mountability.

  Hereinafter, although an example is given and a capacitor of the present invention is explained in detail, the present invention is not limited to the following examples.

First, as a raw material powder, BCT powder, V ₂ O ₅ powder, MgO powder, MnCO ₃ powder, Y ₂ O ₃ powder, Tb ₄ O ₇ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder And at least one rare earth element (RE) oxide powder selected from the group consisting of Er ₂ O ₃ powder and Gd ₂ O ₃ powder (hereinafter referred to as rare earth element oxide powder). Were mixed by the following procedure, so that the composition of the dielectric powder was finally adjusted to the ratio shown in Tables 1 and 3. These raw material powders having a purity of 99.9% by mass were used. BCT powder having an average particle size of 0.2 μm was used. V ₂ O ₅ powder, MgO powder, MnCO ₃ powder, Y ₂ O ₃ powder, and rare earth element oxide powder having an average particle diameter of about 0.1 μm were used. The Ba / Ti ratio of the BCT powder was set to 1.

  In the case of preparing a powder (hereinafter referred to as a coating powder) in which a BCT powder is coated with a rare earth element oxide powder and adhered, a dielectric material is used out of the total amount of the BCT powder and the rare earth element oxide powder to be used. The amount of the BCT powder corresponding to the ratio of the crystal particles of the second crystal group formed in the porcelain and the ratio of the rare earth element oxide powder corresponding to the ratio of the subdivided BCT powder were weighed, and these powders Were mixed using a ball mill, and then placed in a ceramic container and subjected to heat treatment at 500 ° C. for 1 hour. A coated powder was thus prepared.

Next, the remaining BCT powder, the remaining rare earth element oxide powder, the V ₂ O ₅ powder, the MgO powder, the MnCO ₃ powder, and the Y ₂ O ₃ powder are added to the coating powder to form a dielectric. Body powder was prepared. In this case, the mixing ratio of the coating powder and the BCT powder is as shown in Table 1 so that the coating powder corresponds to the crystal particles of the second crystal group, and the BCT powder corresponds to the crystal particles of the first crystal group. B / (a + b) ratio of 3.

As the sintering aid, glass powder having a composition of SiO ₂ = 55, BaO = 20, CaO = 15, and Li ₂ O = 10 (mol%) was used. The addition amount of the glass powder was 1 part by mass with respect to 100 parts by mass of the BCT powder.

  Next, these raw material powders were wet mixed by adding a mixed solvent of toluene and alcohol as a solvent using zirconia balls having a diameter of 5 mm. A polyvinyl butyral resin and a mixed solvent of toluene and alcohol were added to the wet-mixed powder, and wet-mixed using a zirconia ball having a diameter of 5 mm to prepare a ceramic slurry. A ceramic green sheet having a thickness of 2 μm was prepared by a doctor blade method. .

  A plurality of rectangular internal electrode patterns mainly containing Ni were formed on the upper surface of the ceramic green sheet. The conductor paste used for the internal electrode pattern was Ni powder having an average particle size of 0.3 μm, and 30 parts by mass of BCT powder used for a green sheet as a co-material with respect to 100 parts by mass of Ni powder.

Next, 300 ceramic green sheets on which internal electrode patterns were printed were laminated, and 20 ceramic green sheets on which the internal electrode patterns were not printed were laminated on the upper and lower surfaces, respectively, using a press machine at a temperature of 60 ° C. and pressure Lamination was performed under the conditions of 10 ⁷ Pa and time 10 minutes, and cut into predetermined dimensions to form a laminated molded body.

The obtained laminated molded body was subjected to binder removal treatment at 300 ° C. in the atmosphere at a temperature rising rate of 10 ° C./h, heated at the same temperature rising rate, and then heated from 500 ° C. to 300 ° C./h. Then, after baking at 1250 ° C. for 2 hours in hydrogen-nitrogen, and then cooling to 1000 ° C. at a temperature drop rate of 300 ° C./h, heat treatment (reoxidation treatment) is performed at 1000 ° C. for 4 hours in a nitrogen atmosphere. The capacitor body was manufactured by cooling at a temperature decrease rate of 300 ° C./h. The size of the capacitor body is a size of a multilayer ceramic capacitor that is compatible with the 3216 type. The average thickness of the dielectric layer was 3.6 μm, and the effective area of one internal electrode layer was 3.54 mm ² . Here, the effective area is an area where internal electrode layers formed so as to be exposed at end faces in different directions of the capacitor body overlap.

Sample No. I-36 and II-30 were prepared by post-adding the whole amount of rare earth element (Tb ₄ O ₇ ) oxide powder (nothing used for coating treatment). Sample No. I-37 and II-31 were prepared by mixing a total amount of rare earth element (Tb ₄ O ₇ ) oxide powder and a total amount of BCT powder to prepare a coated powder, to which V ₂ O ₅ powder and MgO powder were mixed. And MnCO ₃ powder, Y ₂ O ₃ powder, and a sintering aid. Sample No. I-38 and II-32 are prepared by mixing a coating powder prepared using a BCT powder having an average particle diameter of 0.1 μm and a BCT powder having an average particle diameter of 0.45 μm. Sample No. I-39 and II-33 are BCT powders having an average particle diameter of 0.2 μm used as BCT powders for preparing coating powders, and correspond to crystal grains of the first crystal group in Tables 1 and 3 to be added later. Crystal grains) having an average particle diameter of 50 nm are used. Sample No. I-40, I-41, I-46 to 48, II-34, II-35 and II-40 to 42 are obtained by changing the heating rate from 500 ° C. to the maximum temperature during the main firing. Sample No. I-40 and II-34 are 1000 ° C./h. I-41 and II-35 are 1500 ° C./h. I-46 and II-40 are 1300 ° C./h. I-47 and II-41 are 150 ° C./h. I-48 and II-42 are 1900 ° C / h.

  Sample No. In I-49 and II-43, BCT powder having an average particle diameter of 50 nm is used as BCT powder to be a coating powder.

  Sample No. Nos. I-50 to 53 and II-44 to 47 are obtained by changing the calcining temperature when preparing the coating powder. I-50 and II-44 are 450 ° C., Sample No. I-51 and II-45 are 650 ° C., sample No. I-52 and II-46 are 300 ° C. and sample no. I-53 and II-47 are 950 ° C.

Next, the fired capacitor body was barrel-polished, and then an external electrode paste containing Cu powder and glass was applied to both ends of the capacitor body and baked at 850 ° C. to form external electrodes. Thereafter, using an electrolytic barrel machine, Ni plating and Sn plating were sequentially performed on the surface of the external electrode to produce a multilayer capacitor.
<Evaluation>
The obtained multilayer ceramic capacitor was evaluated as follows. Here, the evaluation of the temperature characteristics of the relative permittivity, dielectric loss, and capacitance was all 10 samples, and the average value was obtained.
(1) Relative permittivity The capacitance is measured under the measurement conditions of a temperature of 25 ° C., a frequency of 1.0 kHz, and a measurement voltage of 1 Vrms. From the obtained capacitance, the thickness of the dielectric layer and the effectiveness of all layers of the internal electrode layer are measured. It was calculated based on the sum of areas and the dielectric constant of vacuum.
(2) Dielectric loss It measured on the same conditions as an electrostatic capacitance.
(3) Temperature characteristics of relative permittivity The capacitance was measured at a temperature of 125 ° C., and the rate of change relative to the capacitance at 25 ° C. was determined. In addition, by applying a DC voltage of 25 V and 50 V, the capacitance at 125 ° C. was measured, and the rate of change with respect to the capacitance at 25 ° C. in a no-load (DC = 0 V) state was obtained (hereinafter, This is called the temperature change rate of the dielectric constant under high temperature load conditions.)
(4) High-temperature load test The test was performed at a temperature of 170 ° C. under an applied voltage of 170V. The number of samples in the high-temperature load test was 30 samples, and the average failure time, which was the time when the failure probability reached 50%, was examined. (5) Measurement of rare earth element (RE) concentration, concentration gradient and crystal particle ratio (b / (a + b)) in crystal grains and average particle diameter of crystal grains Concentration distribution of rare earth elements (RE) in crystal grains After polishing the dielectric ceramic cross section, draw a circle containing about 30 crystal grains on the image displayed on the monitor attached to the transmission electron microscope, and select the crystal grains that fall within and around the circle. Then, elemental analysis was performed using a transmission electron microscope equipped with elemental analysis equipment. In this embodiment, a unit area is a circle containing about 30 crystal grains. The crystal particles to be selected at this time are obtained by calculating the area of each particle by image processing from the outline, and calculating the diameter when replaced with a circle having the same area, and the calculated crystal particle diameter is approximately 0.08 to 0. Crystal grains in the range of .60. The spot size of the electron beam at the time of analysis was 0.5 to 2 nm, and the location to be analyzed was a position 20 nm (± 1 nm) deep from the grain boundary of the crystal grains. Specifically, when the concentration of the rare earth element (RE) in the crystal grain is obtained, an electron beam is applied to the center of the crystal grain, and the main element contained in the crystal grain (barium (Ba) (Ba) ), Titanium (Ti), vanadium (V), magnesium (Mg), manganese (Mn) and rare earth element (RE)) were determined as 100 atomic%, and the ratio of rare earth element (RE) was determined from this amount. .

Next, when determining the concentration gradient of the rare earth element (RE), the location to be analyzed is in the range from the vicinity of the grain boundary of the crystal grains to the center position of the central portion, and is almost equal on the straight line drawn toward the center. The points were located at intervals, and were determined from values analyzed in the vicinity of the grain boundary and at a depth of approximately 20 nm and 200 nm from the grain boundary. In this case, the value obtained by subtracting the rare earth element (RE) concentration at a depth of 19 to 21 nm and 195 to 205 nm from the concentration of the rare earth element (RE) at the grain boundary (0 to 1 nm) of the crystal grain (concentration of the rare earth element). Was divided by the distance of the analyzed range (for example, 20 nm-0 nm = 20 nm, 200 nm-0 nm = 200 nm) to obtain a concentration gradient. Thereafter, the crystal grain 9a of the first crystal group and the crystal grain 9b of the second crystal group were determined by determining the concentration gradient of the rare earth element (RE) for each crystal particle. This analysis was performed at five locations for each sample to determine the average value.

  In such an analysis, a crystal particle having a rare earth element (RE) concentration gradient of 0.05 to 0.20 atomic% is referred to as “crystal particle constituting the first crystal group”, and the rare earth element (RE) A crystal grain having a concentration gradient of 0.03 atomic% or less was designated as “crystal grain constituting the second crystal group”.

  Regarding the concentration of calcium in the crystal particles, elemental analysis was performed on the crystal particles present on the polished surface obtained by polishing the cross section of the dielectric ceramic using a transmission electron microscope provided with an elemental analysis device. At this time, the spot size of the electron beam is 3 nm or less, the center part of the crystal particles is analyzed, and the total amount of Ba, Ti, Ca, V, Mg, Y, RE (rare earth element) and Mn detected by the analysis is 100%. The ratio of calcium was determined. As a result, it was confirmed that calcium was contained at a ratio shown in Table 1. The crystal particles to be analyzed were selected by drawing a circle with about 10 crystal particles in the approximate center shown in the microscope observation monitor (photo). The center part of the crystal grains was the center of a circle drawn along the outline of each crystal grain.

  The average particle diameter of each of the crystal grains constituting the first crystal group and the crystal grains constituting the second crystal group is measured with a transmission electron microscope on the polished surface obtained by polishing (ion milling) the cross section of the dielectric ceramic. The projected image is taken into a computer, the contours of the crystal particles present on the image are processed, the area of each particle is obtained, and the diameter when replaced with a circle with the same area is calculated and calculated. It calculated | required from the average value of 30 crystal grains. In this case, the crystal particle 9a and the crystal particle 9b are distinguished from each other based on the result of the concentration gradient of the rare earth element (RE) previously obtained from the crystal particles, and the average value is obtained for each to obtain the average particle size of the crystal particles. It was.

In the dielectric ceramic, the area ratio of the crystal grains constituting the second crystal group to the total area of the crystal grains constituting the first crystal group and the crystal grains constituting the second crystal group, b / (a + b) (Where a represents the area of the crystal grains 9a constituting the first crystal group, and b represents the area of the crystal grains 9b constituting the second crystal group). It calculated from the data which calculated | required the average particle diameter of 9b. The b / (a + b) ratio of the prepared sample was equivalent to the mixing ratio of the BCT powder and the coating powder.
(6) Composition analysis of sample The composition analysis of the sample which is the obtained sintered compact was performed by ICP analysis and atomic absorption analysis. In this case, the obtained dielectric porcelain mixed with boric acid and sodium carbonate and dissolved in hydrochloric acid is first subjected to qualitative analysis of the elements contained in the dielectric porcelain by atomic absorption spectrometry, and then specified. The diluted standard solution for each element was used as a standard sample and quantified by ICP emission spectroscopic analysis. Further, the amount of oxygen was determined using the valence of each element as the valence shown in the periodic table. Manganese was determined in terms of MnO. As a result of the analysis, the composition of the dielectric layer was consistent with the prepared composition for all the samples. The results of the composition and properties are shown in Tables 1-4. Sample No. I-36, I-37, I-39, II-30, II-31 and II-33 are reference samples.

  As is clear from the results in Tables 1 to 4, the sample No. In I-1 to 35, I-38 to 56, II-1 to 29, and II-32 to 50, when the capacitance measured under the condition that no DC voltage is applied at room temperature (25 ° C.) is used as a reference At 125 ° C., the change rate of the capacitance when a DC voltage of about 50 V was applied was within −77%.

  Sample No. I-1 to 3, I-6, I-7, I-10, I-13, I-14, I-17, I-19, I-20, I-23, I-24, I-27, In I-28, I-31 to 35, I-40, I-42 to 47, I-50, I-51 and I-54 to 56, the dielectric constant of the dielectric ceramic at room temperature (25 ° C.) is 2100. As described above, the temperature characteristic of the dielectric constant satisfies −13.5% or less, and the dielectric constant at 125 ° C. is measured with respect to the relative dielectric constant measured at 25 ° C. with no DC voltage loaded (no load state) The rate of change of relative permittivity measured with a DC voltage of 25 V applied to the body layer can be within -53.5% (in the direction approaching NPO (± 0%)), and the DC voltage of 170 ° C. and 170 V The high temperature load life evaluated under the condition of applying was 40 hours or more.

  Sample No. II-1, II-2, II-5, II-6, II-9, II-12, II-13, II-16, II-18, II-19, II-22, II-23, II- 26, II-27, II-34, II-37-41, II-44, II-45 and II-48-50, the dielectric constant of the dielectric ceramic at room temperature (25 ° C.) is 2100 or more, The temperature characteristics of the dielectric constant satisfy −13.4% or less, and the dielectric layer measured at 25 ° C. with no DC voltage loaded (no load state) has a dielectric layer of 25 V at 125 ° C. The rate of change of the relative dielectric constant measured with the DC voltage applied can be within -53.6% (in the direction approaching NPO (± 0%)), and the DC voltage of 170 ° C. and 170 V is applied. The high temperature load life evaluated by Was Tsu.

  Among them, the content of manganese contained in the dielectric ceramic is 0.30 to 0.50 mol in terms of MnO, and the ratio of the second crystal particles to the first and second crystal particles (b / Sample No. (a + b)) of 0.4 to 0.6. Sample No. I-1 to 3, I-6, I-7, I-10, I-13, I-14, I-17, I-19, I-20, I-23, I-24, I-28, I-31 to 35, I-40, I-42, I-43, I-45 to 47, I-50, I-51, I-54 to 56, II-1, II-2, II-5, II-6, II-9, II-12, II-13, II-16, II-18, II-19, II-22, II-23, II-27, II-34, II-37, II- In 39-41, II-44, II-45, and II-48-50, the change rate of the relative dielectric constant measured with a DC voltage of 25 V applied to the dielectric layer at 125 ° C. is within −53.1%. Met.

  Furthermore, sample No. 1 in which the concentration of calcium contained in the crystal particles was 1 to 5 mol%. I-1 to 3, I-6, I-7, I-10, I-13, I-14, I-17, I-19, I-20, I-23, I-24, I-28, I-31 to 35, I-40, I-42, I-43, I-45 to 47, I-50, I-51, I-55, II-1, II-2, II-5, II- 6, II-9, II-12, II-13, II-16, II-18, II-19, II-22, II-23, II-27, II-34, II-37, II-39 to In 41, II-44, II-45 and II-49, the temperature characteristics of the relative dielectric constant were -13.0% or less, and the dielectric loss was 4.1% or less.

  In contrast, sample no. In I-36, I-37, II-30, and II-31, 50 V is applied to the dielectric layer at 125 ° C. relative to the relative dielectric constant measured at 25 ° C. with no DC voltage applied (no load state). The change rate of the relative dielectric constant measured with the DC voltage applied was 77.2% or more (larger to the-side than -77.2%).

DESCRIPTION OF SYMBOLS 1 ...... Capacitor body 3 ... External electrode 5 ... Dielectric layer 7 ... Internal electrode layer 11 ... Grain boundary phase 9 ... Crystal grain 9a ... 1st The crystal particles 9b constituting the crystal group of the crystal grains constituting the second crystal group

Claims (4)

A dielectric layer comprising a dielectric porcelain having crystal grains of barium titanate containing calcium and containing at least one rare earth element (RE) selected from the group of terbium, dysprosium, holmium, erbium and gadolinium. cage, wherein the crystal grains, at the position of depth 20nm from the grain boundary, and crystal particle concentration of the first crystal group which is 0 to 0.5 atomic% of the rare earth element (RE), the first crystal group A concentration of the rare earth element (RE) is higher than that of the crystal grains of the second crystal group having a concentration of 0.3 to 0.9 atomic%, and the first crystal group The concentration difference of the rare earth element (RE) between the crystal particles of the second crystal group and the crystal particles of the second crystal group is 0.1 to 0.7 atomic%, and the crystal particles of the second crystal group are the first Flatter than the crystal grains of the crystal group Capacitor, wherein the particle diameter is large. The dielectric ceramic further includes vanadium, magnesium, manganese, and yttrium, and 100 moles of titanium constituting the barium titanate,
0.05 to 0.20 mol of the vanadium in terms of V ₂ O ₅ ,
0.5 to 2.0 mol of the yttrium in terms of Y ₂ O ₃ ,
1.0 to 3.0 mol of the magnesium in terms of MgO,
0.22 to 0.50 mol of manganese in terms of MnO,
Containing 0.65 to 2.80 mol of the rare earth element (RE) in terms of RE ₂ O ₃ ;
The concentration of the rare earth element (RE) at a position 20 nm deep from the grain boundary of the crystal grains of the first crystal group is 0.02 to 0.42 atomic %,
Said second crystal group of crystal grains, at the position of depth 20nm from the grain boundary, Ri concentration 0.45 to 0.70 atomic% der of the rare earth element (RE),
The average particle diameter of the crystal particles constituting the first binding Akiragun is 0.10～0.18Myuemu, with an average grain size of crystal grains constituting the second binding Akiragun is 0.2~0.5μm ,
Found per unit area of the polishing surface of the dielectric ceramic, the surface area of the crystal grains forming the first sintered Akiragun a, the area of the crystal grains forming the second binding Akiragun when the b , B / (a + b) is 0.4 to 0.7.   The capacitor according to claim 2, wherein the manganese is 0.30 to 0.50 mol in terms of MnO, and the b / (a + b) is 0.4 to 0.6.   The capacitor according to claim 1, wherein the concentration of the calcium contained in the crystal particles is 1 to 5 mol%.