JP6034136B2 - Capacitor - Google Patents

Description

  The present invention relates to a capacitor using a dielectric ceramic whose main crystal particles are barium titanate crystal particles 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. (Hereinafter, expressed as a relative dielectric constant) that 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 includes first crystal particles mainly composed of barium titanate and second crystal particles of strontium zirconate, and at least one rare earth selected from the group of terbium, dysprosium, holmium, erbium, and gadolinium. A dielectric layer made of a dielectric ceramic containing an element (RE), wherein the first crystal particle has a rare earth element (RE) concentration of 0.3 at a depth of 20 nm from the grain boundary; The concentration of the rare earth element (RE) is lower than the crystal particles of the first crystal group, which is ~ 0.9 atomic% , and the crystal grains of the first crystal group, and the concentration is 0 to 0.5 atomic% together comprising a crystalline particles of the second crystal group, the density difference of the rare earth element (RE) between the first crystal group of crystal grains and the second crystal group of crystal grains 0.1 0.7 atom , And the crystal grains of the second crystal group, wherein the average particle diameter is smaller than the crystal grains of the first crystal 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 of the capacitor of this embodiment includes first crystal particles 9A mainly composed of barium titanate and second crystal particles 9B of strontium zirconate, and includes terbium, dysprosium, and holmium. , At least one rare earth element (RE) selected from the group of erbium and gadolinium. In this dielectric ceramic, the first crystal particles 9A mainly composed of barium titanate are main crystal particles. In this case, the main crystal particle means a particle having the highest diffraction intensity of the main peak of the X-ray diffraction pattern obtained by X-ray diffraction.

  Further, the first crystal particle 9A is composed of at least two types of crystal particles having a difference of a rare earth element (RE) concentration of 0.1 atomic% or more at a position 20 nm deep 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 a DC voltage is not applied at room temperature (25 ° C.) is used as a reference, the rate of change in capacitance when a DC voltage of about 25 V is applied at 125 ° C. ( Hereinafter, it is referred to as high temperature DC bias characteristics) within 64%. In the following description, when describing the characteristics, the relative permittivity may be used instead of the capacitance.

As described above, the dielectric ceramic according to the present embodiment has a configuration in which the first crystal particles 9A mainly composed of barium titanate and the second crystal particles 9B of strontium zirconate coexist. When the crystal particles (second crystal particles 9B) containing strontium as a main component coexist at the grain boundaries of the group of crystal particles (first crystal particles 9A) containing barium titanate as a main component, the first crystal particles 9A alone In comparison with the case, the insulation resistance in a temperature range higher than room temperature (25 ° C.) (the upper limit temperature of the temperature characteristic of the capacitance (for example, 85 to 150 ° C.)) can be increased.

  In addition, this dielectric ceramic is composed of first crystal particles 9A mainly composed of barium titanate among first crystal particles 9A mainly composed of barium titanate and second crystal particles 9B composed of strontium zirconate. Is composed of two kinds of crystal particles (here, the symbols are 9a and 9b) having different concentrations of one kind of rare earth element (RE) selected from the group of terbium, dysprosium, holmium, erbium and gadolinium It is supposed to be. Thereby, in addition to the high temperature, a dielectric ceramic with a small decrease in capacitance can be obtained even under a condition where a high voltage is applied to the dielectric ceramic. Hereinafter, the dielectric characteristics when a voltage is applied at a high temperature may be referred to as a high-temperature DC bias characteristic.

This of concentrations of different crystal grains of the rare earth elements composing the first crystal grains 9A, higher crystal particles (in this case, the crystal grains 9a of the first binding Akiragun) concentration of the rare earth element, its internal This is because it contains rare earth elements (RE) deeply, and therefore there are few defects such as oxygen vacancies throughout the crystal grains, thereby reducing the amount of carrier movement when a voltage is applied. .

The crystal grain 9b of the second binding Akiragun, since the concentration of the rare earth element contained in the crystal grains (RE) is low, center crystal phase control of small additive components tetragonal crystal grains 9b Therefore, a high dielectric constant can be maintained.

  However, it is difficult to reduce the rate of change of the dielectric constant when a DC voltage is applied to the crystal particle 9b alone, but the crystal particle 9a originally has the property that the voltage dependence of the dielectric constant can be reduced. Therefore, it is considered that the characteristics of the crystal particle 9a are reflected even when the crystal particle 9a is adjacent to the crystal particle 9b having a high relative dielectric constant.

Therefore, in the dielectric ceramic, (here, the crystal grains 9b of the second binding Akiragun) concentration low crystal grains of the rare earth element than the crystal grains 9a of the first binding Akiragun (RE) have a also, it is possible to maintain a high capacitance at the time of the amount corresponding voltage having a crystal grain 9a of the first binding Akiragun applied.

  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 25 V is applied is greater than 65%.

  In this dielectric ceramic, terbium, dysprosium, holmium, erbium and gadolinium are selected as the rare earth elements (RE) to be included, but these rare earth elements (RE) are rare earth elements (RE) in the periodic table. This is because it is easy to dissolve in the crystal particles 9 mainly composed of barium titanate.

In this dielectric ceramic, it is desirable that the second crystal particles 9B of strontium zirconate contain hafnium (Hf). Hafnium (Hf) to strontium zirconate
) Increases the melting point of strontium zirconate. As a result, the reaction between the crystal particles (first crystal particles 9A) mainly composed of barium titanate and the second crystal particles 9B of strontium zirconate can be suppressed, whereby the second crystal particles 9A and the second strontium zirconate of the second crystal particles. A mixed crystal structure with the crystal grains 9B can be formed.

The hafnium in the strontium zirconate crystal particles 9B was subjected to elemental analysis using EPMA (Electron Probe Micro Analysis) in the structure observation using a scanning electron microscope or a transmission electron microscope. In this case, the characteristic X-ray intensity of hafnium (Hf) is
This refers to a case where the noise level of the projected screen is 1.5 times or more of the noise level (value obtained by averaging the noise level on the screen), and the hafnium (Hf) characteristic X-ray intensity is 1.5 times the noise level. If it is smaller than twice, hafnium (Hf) is not contained in the crystal particles 9B of strontium zirconate. Further, in such an analysis, ten strontium zirconate crystal particles 9B are arbitrarily selected from dielectric ceramics, which are analysis samples for tissue observation, and seven or more strontium zirconate crystal particles 9B are selected. , In which hafnium (Hf) is included.

Next, vanadium, magnesium, manganese, and yttrium are included in this dielectric ceramic, and the content of each element is determined in terms of V ₂ O ₅ with respect to 100 moles of titanium constituting barium titanate. 0.05-0.20 mol, yttrium 0.5-2.0 mol in terms of Y ₂ O ₃ , magnesium 1.0-3.0 mol in terms of MgO, and manganese 0.22-0 in terms of MnO .50 moles and rare earth elements (RE) in the range of 0.65 to 2.80 moles in terms of RE ₂ O ₃ , and crystal grains 9 having different rare earth element (RE) concentrations are 20 nm deep from the grain boundaries. In the range, the concentration of the rare earth element (RE) is 0.02 to 0.42 atomic%, the first crystal group of crystal particles 9a, and the rare earth element (RE) concentration is 0.45 to 0.70 atomic%. A second crystal Of shall have a crystal grain 9b, these crystal grains 9a, among 9b, average particle diameter 0.2 ~ 0.5 [mu] m of the crystal grains 9a of the first binding Akiragun, crystals of the second binding Akiragun the average particle diameter of the particles 9b and 0.1 ~ 0.18 [mu] m, the crystal grain 9a and the component ratio of the crystal grains 9b of the second binding Akiragun first binding Akiragun unit area of the polishing surface of the dielectric ceramic The ratio of the crystal particle 9a as seen at the center is a, and the area of the crystal particle 9b is b, and a / (a + b) is 0.4 to 0.7. Further, in the X-ray diffraction chart, It is assumed that the diffraction intensity of the surface index (121,002) of strontium zirconate with respect to the diffraction intensity of the surface index (110) of barium titanate is 0.7 to 28.0%.

  When the dielectric ceramic is configured as described above, in addition to the high temperature DC bias characteristics, the dielectric constant is high, the dielectric loss and the temperature change rate of the dielectric constant are small, and the reliability of the high temperature load life is excellent. Can be obtained. For example, the relative dielectric constant at room temperature (25 ° C.) is 1708 or more, the dielectric loss is 1.7% or less, and the relative dielectric constant when the room temperature (25 ° C.) is the reference in the temperature range of −55 to 125 ° C. The rate of change (hereinafter referred to as the temperature characteristic of the dielectric constant) is ± 13.7% (the rate of change of the dielectric constant at 125 ° C. is the largest between −55 and 125 ° C. The ratio measured with a DC voltage applied at 125 ° C. relative to the relative dielectric constant measured with no DC voltage loaded (no load) at 25 ° C. The rate of change of dielectric constant can be within -43.9% (in the direction approaching NPO (± 0%)), and the high-temperature load life evaluated under the condition of applying a DC voltage of 170 ° C. and 170V for 30 hours. To do more Can do. Hereinafter, the term “high temperature load life” refers to the high temperature load life evaluated under the above conditions.

When a predetermined amount of magnesium, manganese, and yttrium in addition to rare earth elements (RE) are contained in the dielectric ceramic, these elements are solidified near the surfaces of the first crystal particles 9A and the second crystal particles 9B. A part of the first crystal particles 9A that dissolve and easily dissolve components such as rare earth elements can be made into crystal particles having a core-shell structure. As a result, the dielectric constant can be improved, the dielectric loss can be reduced, and a dielectric ceramic having a low relative dielectric constant temperature change rate can be obtained. In the core-shell structure, in the X-ray diffraction pattern, for example, a diffraction peak (index is an overlap of 200, 020, 002) due to a cubic system between a diffraction peak of 200 planes and a diffraction peak of 002 planes. The cubic diffraction peak has a diffraction intensity comparable to that of the 200-plane diffraction peak and the 002-plane diffraction peak due to the tetragonal system.

Further, the crystal grains 9a and 9b constituting the first crystal grains 9A of the dielectric ceramic have different rare earth element (RE) concentration gradients as shown in FIGS. 2 (a) and 2 (b), respectively. crystal grains 9a of 1 binding Akiragun 0.03 atomic% / nm or less, the crystal grain 9b of the second binding Akiragun is the good 0.05 to 0.20 atomic% / nm.

  In the dielectric ceramic according to the present embodiment, the average particle diameter of the crystal particles 9a having a high concentration of rare earth elements is larger than the average particle diameter of the crystal particles 9a having a low concentration of rare earth elements. Even if the rare earth element content is increased, the dielectric constant can be increased.

  As a result, the capacitor of this embodiment has a dielectric constant of not more than 1.7% and a high temperature DC bias characteristic within −43.9%, while the dielectric constant at room temperature (25 ° C.) is 1708 or more. Thus, the reliability of the high temperature load life can be improved.

  In this dielectric porcelain, yttrium (Y) 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. It is. For this reason, yttrium can be dissolved in the vicinity of the surface of the first crystal particle 9A mainly composed of barium titanate, and thus the dielectric constant, dielectric loss, no-load state and high-temperature load state of the dielectric ceramics. It is possible to control the temperature change rate of the dielectric constant and the reliability of the high temperature load life. In this case, the concentration gradient of yttrium is desirably 0.05 to 0.20 atomic% / nm for both the crystal particles 9a and 9b having different rare earth element contents.

  Here, the concentration and concentration distribution of the rare earth element (RE) in the first crystal particles 9A (crystal particles 9a and 9b) are reflected on the monitor attached to the transmission electron microscope after polishing the cross section of the dielectric ceramic. On the obtained image, a circle containing about 30 crystal particles is drawn, and the crystal particles in and around the circle are selected, and elemental analysis is performed using a transmission electron microscope provided with an elemental analysis instrument. 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. The crystal grain 9 is in the 60 range. The spot size of the electron beam at the time of analysis 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 grains.

  When the concentration of the rare earth element (RE) at a position 20 nm deep from the grain boundary of the crystal grain was obtained, it was obtained by irradiating an electron beam almost at the center in the range of 18 to 22 nm from the grain boundary of the crystal grain. The amount of main elements contained in crystal grains is determined from the output of X-rays as 100 atomic%, and the ratio of rare earth elements (RE) is determined from this amount. Here, examples of main elements include barium (Ba), titanium (Ti), vanadium (V), magnesium (Mg), manganese (Mn), and rare earth elements (RE). Thereafter, the crystal particle 9a of the first crystal group and the crystal particle 9b of the second crystal group are determined by determining the concentration of the rare earth element (RE) for each crystal particle.

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, 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). 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.

Dielectric ceramic constituting the capacitor of the present embodiment, as described above, as the first crystal grains 9A, and a crystal grain 9b that constitute the crystal grains 9a and the second binding Akiragun constituting the first binding Akiragun but those having, as its proportion, seen in per unit area, and a the area of the crystal grains 9a constituting the first binding Akiragun, the area of crystal grains 9b constituting the second binding Akiragun b when, a / (a + b) is 0.4 to 0.7, the average grain size of crystal grains 9b constituting the crystal grains 9a and the second binding Akiragun constituting the first binding Akiragun is It is desirable that they are 0.2 to 0.5 μm and 0.10 to 0.18 μm, respectively.

  In addition, since the second crystal particle 9B is paraelectric, it is smaller than the first crystal particle 9A because the advantages such as the high dielectric constant of the first crystal particle 9A having ferroelectricity cannot be suppressed. Desirably, the size is preferably 0.1 to 0.2 μm.

  The ratio of the diffraction intensity of the (110) plane of barium titanate and the diffraction intensity of the (121) plane and the (002) plane of strontium zirconate was measured using an X-ray diffractometer equipped with a Cukα tube. The angle is measured in the range of 2θ = 25 to 35 ° and obtained from the ratio of peak intensities.

  In addition, the average particle diameter of each of the first crystal particles 9A and the second crystal particles 9B is obtained by using an image projected by a transmission electron microscope on a polished surface obtained by polishing (ion milling) a cross section of the dielectric ceramic. The image is processed by processing the outline of the crystal particles present on the image, the area of each particle is obtained, the diameter when replaced with a circle having the same area is calculated, and the average value of the calculated 30 crystal particles is calculated. Ask more. When the average particle size of the crystal particles 9a and 9b having different rare earth element concentrations is determined for the first crystal particles 9A, the crystal based on the result of previously determining the rare earth element (RE) concentration from the crystal particles. The particles 9a and the crystal particles 9b are distinguished from each other, and an average value is obtained to obtain the average particle size of the crystal particles 9a and 9b.

The area ratio of the crystal grains 9a constituting the first crystal group to the total area of crystal grains 9b constituting the crystal grains 9a and the second binding Akiragun constituting the first binding Akiragun, said average particle size Calculate using the data used to determine

  In the capacitor of this embodiment, the composition of the dielectric ceramic is 25 ° C. when the manganese content is 0.30 to 0.50 mol in terms of MnO with respect to 100 mol of titanium constituting barium titanate. On the other hand, the change rate of the relative dielectric constant in the no-load state (voltage 0 V) at 125 ° C. can be made within −13.5%.

  Further, in the case of the capacitor according to the present embodiment, when the rare earth element (RE) contained in the dielectric ceramic is gadolinium (Gd), compared with the case where other rare earth elements (RE) are used, the no-load state and the high temperature are increased. While the temperature change rate of the relative permittivity in the loaded state can be reduced, the relative permittivity and the high temperature load life at room temperature (25 ° C.) can be improved.

Further, in the capacitor according to 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, a glass component as an auxiliary agent for enhancing sinterability. And other additive components can be contained 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, barium titanate powder (purity 99% by mass or more, hereinafter referred to as BT powder) and strontium zirconate powder (hereinafter referred to as SZ powder) are prepared as raw material powders. In this case, it is desirable to use the SZ powder containing hafnium (Hf) in an amount of 0.1 to 10 mol% as the substitution amount of Zr sites. Further, as additives, _Tb 4 _{O 7} powder, _Dy 2 _{O 3} powder, _Ho 2 _{O 3} powder, to prepare at least one selected from _Er 2 _{O 3} powder and _Gd 2 _{O 3} powder group.

The average particle diameter of the raw material powder is preferably 0.10 to 0.35 μm, particularly 0.15 to 0.30 μm. The additive Tb ₄ O ₇ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder and Gd ₂ O ₃ powder also have an average particle size equal to or less than that of the raw material powder. Is preferably used.

In addition, for the reason of further improving the dielectric characteristics, V ₂ O ₅ powder, MgO powder, MnCO ₃ powder and Y ₂ O ₃ powder are prepared as additives in some cases. Also in this case, the average particle diameter is preferably equal to or less than that of the raw material powder.

  Next, a slurry is prepared using these raw material powders. When the capacitor of the present embodiment is manufactured, the second crystal group after firing out of the total amount of the raw material powders used for forming the dielectric ceramic. The amount corresponding to the ratio of forming the crystal particles 9a is previously subdivided and the molar ratio corresponding to the ratio of the subdivided raw material powder among the rare earth element (RE) oxide powder added to the subdivided raw material 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 raw material powder and rare earth element (RE) oxide powder.

Next, a BT powder coated with a rare earth element (RE) oxide powder (hereinafter referred to as a coating powder), a remaining BT powder not coated with a rare earth element (RE) oxide powder, A rare earth element (RE) oxide powder and an SZ powder are mixed to prepare a dielectric powder. At this time, additive powders such as V ₂ O ₅ powder, MgO powder, MnCO ₃ powder, and Y ₂ O ₃ powder may be added in predetermined amounts.

  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 raw material powders, BT powder and SZ powder (Hf content was substituted by 0.5 mol% for Zr sites) were prepared. Further, as additives, 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, Er ₂ O ₃ powders and at least one rare earth element (RE) oxide powder selected from the group of Gd ₂ O ₃ powder (hereinafter referred to as rare earth element oxide powder) were prepared. Next, these various powders were mixed by the following procedure to prepare the dielectric powder so that the composition finally had the ratios shown in Tables 1 and 2. These raw material powders having a purity of 99.9% by mass were used. Both BT powder and SZ powder used had an average particle size of 0.2 μm. 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 BT powder and the Sr / Zr ratio of the SZ powder were both 1.

  In the case of preparing a powder (hereinafter referred to as a coating powder) in which a raw material powder is coated with a rare earth element oxide powder, the dielectric material is used out of the total amount of the BT powder and the rare earth element oxide powder to be used. The amount of the raw material powder corresponding to the proportion of the crystal particles of the first crystal group formed in the porcelain and the proportion of the rare earth element oxide powder corresponding to the proportion of the subdivided raw material powder are respectively 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 raw material powder, the remaining rare earth element oxide powder, and optionally 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. A dielectric powder was prepared by addition. In this case, the mixing ratio between the coating powder and the raw material powder not coated with the rare earth element (RE) oxide is such that the coating powder corresponds to the crystal particles of the first crystal group, and the BT powder has the second ratio. The a / (a + b) ratios in Tables 3 and 4 were set so as to correspond to the crystal grains of the crystal group.

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. 19-26 and sample no. Nos. 76 to 83 are prepared by mixing BT powder and coating powder having different average particle diameters in the range of 0.05 to 0.60 μm. Sample No. 36 and sample no. No. 88 was prepared by post-adding the total amount of rare earth oxide powder (no coating used). Sample No. 37 and Sample No. 89 is a coating powder prepared by mixing the total amount of rare earth element oxide powder and the total amount of raw material powder, to which V ₂ O ₅ powder, MgO powder, MnCO ₃ powder, and Y ₂ O ₃ powder are prepared. And a sintering aid. Sample No. 38 and Sample No. No. 90 is prepared by mixing a coating powder prepared using a raw material powder having an average particle size of 0.1 μm and a raw material powder having an average particle size of 0.45 μm. Sample No. 39 and sample no. 91 is an average particle diameter as a raw material powder for preparing a coating powder having an average particle diameter of 0.2 μm, and a post-added raw material powder (a crystal particle corresponding to the crystal particles of the first crystal group in Tables 1 and 2). The one with a diameter of 50 nm is used. Sample No. Nos. 40, 41, and 46 to 48 are obtained by changing the heating rate from 500 ° C. to the maximum temperature during the main firing. 40 is 1000 ° C./h, sample no. 41 is 1500 ° C./h. 46 is 1300 ° C./h. 47 is 150 ° C./h and sample no. 48 is 1900 ° C./h.

  Sample No. Nos. 92, 93 and 98 to 100 are also obtained by changing the heating rate from 500 ° C. to the maximum temperature during the main firing. 92 is 1000 ° C./h. 93 is 1500 ° C./h. 98 is 1300 ° C./h. 99 is 150 ° C./h and sample no. 100 is 1900 ° C./h.

  Sample No. Nos. 49 and 101 are raw material powders having an average particle size of 50 nm as raw material powders to be coated powders.

  Sample No. Nos. 50 to 53 are obtained by changing the calcining temperature when preparing the coating powder. 50 is 450 ° C., sample no. 51 is 650 ° C., sample No. 52 is 300 ° C. and sample no. 53 is 950 degreeC.

  Sample No. Nos. 102 to 105 are obtained by changing the calcining temperature when preparing the coating powder. 102 is 450 ° C., sample no. 103 is 650 ° C., sample no. 104 is 300 ° C. and sample no. 105 is 950 degreeC.

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, 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 referred to as high temperature load). This is called the temperature change rate of the relative permittivity in the state.
(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 (a / (a + b)) in crystal particles and average particle diameter of crystal particles About the concentration of rare earth element (RE) in crystal particles After polishing the cross section of the dielectric porcelain, draw a circle containing about 30 crystal particles on the image projected on the monitor attached to the transmission electron microscope, and select the crystal particles that fall within and around the circle. 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 a position in the range of 18 to 22 nm from the grain boundary of the crystal grain, and the obtained X-ray output includes the crystal grain. The amount of major elements (barium (Ba), titanium (Ti), vanadium (V), magnesium (Mg), manganese (Mn) and rare earth element (RE)) is determined as 100 atomic%, The ratio of (RE) was determined.

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, when the concentration difference of rare earth element (RE) is 0.1 atomic% or more in 90% of the number of measured crystal particles, the concentration of rare earth element (RE) is 0.1 atom. % Of crystal grains.

  The average particle size of each of the first crystal particles and the second crystal particles is calculated by taking an image projected by a transmission electron microscope on a polished surface obtained by polishing (ion milling) a cross section of a dielectric ceramic, The contours of the crystal grains present on the image were subjected to image processing, the area of each particle was determined, the diameter when replaced with a circle having the same area was calculated, and the average value of 30 calculated crystal grains was determined. For the first crystal particles, when determining the average particle diameter of each crystal particle having a different concentration of rare earth element, the concentration of the rare earth element is determined based on the result of previously determining the concentration of rare earth element (RE) from the crystal particle. Different crystal grains were distinguished, and an average value was obtained for each of the crystal grains (9a, 9b) having different rare earth element concentrations.

In the dielectric ceramic, the area ratio of crystal grains constituting the first binding Akiragun to the total area of crystal grains constituting the crystal particles and the second binding Akiragun constituting the first binding Akiragun, a / (a + b) (where, a denotes the area of the crystal grains 9a constituting the first binding Akiragun, b indicates the area of the crystal grain 9b that constitute the second binding Akiragun), said about 30 the crystal grains 9a, It calculated from the data which calculated | required the average particle diameter of 9b. The a / (a + b) ratio of the prepared sample was equivalent to the mixing ratio of the raw material powder and the coating powder.

As is apparent from the results of Tables 1 to 6, sample No. 1 to 35, 38 to 87, 90 to 110, a DC voltage of about 25 V is applied at 125 ° C. with reference to the capacitance measured under conditions where no DC voltage is applied at room temperature (25 ° C.). The change rate of the electrostatic capacity was 62% or less.

Sample No. 1-3, 6, 7, 10, 13, 14, 17, 19, 20, 23, 24, 27, 28, 31-35, 40, 43-47, 50, 51, 55-60, 63, 64, 67, 70, 71, 74, 76, 77, 80, 81, 84, 85, 92 , 95 to 99 , 102 , 103 and 107 to 110, the dielectric constant of the dielectric ceramic at room temperature (25 ° C.) is 1708. As described above, the dielectric loss is 1.7% or less, the temperature characteristic of the dielectric constant is −13.7% or less, and the relative dielectric constant is measured in a state where no DC voltage is loaded at 25 ° C. (no load state). The rate of change of relative permittivity measured with a DC voltage of 25 V applied to the dielectric layer at 125 ° C. can be made within −43.9% (in a direction approaching NPO (± 0%)) In addition, a DC voltage of 170 ° C and 170V was applied. The high temperature load life evaluated under the conditions was 30 hours or more.

Among them, the sample No. 1 in which the content of manganese contained in the dielectric ceramic was 0.30 to 0.50 mol in terms of MnO. 1-3, 6, 7, 10, 13, 14, 17, 19, 20, 23, 24, 27, 28, 31-35, 40, 43-47, 50, 51, 55-60, 63, 64, 67, 70, 71, 74, 76, 77, 80, 81, 84, 85, 92 , 95 to 99 , 102 , 103 and 107 to 110, measured at 125 ° C. with no DC voltage applied to the dielectric layer The relative dielectric constant change rate was within -13.5%.

In addition, samples (sample Nos. 34, 59, 60, 63, 64, 67, 70, 71, 74, 76, 77, 80, in which the rare earth element (RE) contained in the dielectric ceramic is gadolinium (Gd) are used. 81, 84, 85, 92 , 95 to 99 , 102 , 103 and 107 to 110) are samples (sample Nos. 1 to 1) having the same composition using other rare earth elements (Tb, Dy, Ho, Er, Yb). 3 , 6 , 7 , 10 , 13 , 14 , 17 , 19 , 20 , 23 , 24 , 27 , 28 , 31-33 , 35 , 40 , 43-47 , 50 , 51 , 55-58) The temperature change rate of the relative permittivity in the no-load state and the high-temperature load state was small, and the relative permittivity and the high-temperature load life at room temperature (25 ° C.) were high.

  In contrast, sample no. In 36, 37, 88 and 89, the measurement was performed with a DC voltage of 25 V applied to the dielectric layer at 125 ° C. with respect to the relative dielectric constant measured with no DC voltage loaded at 25 ° C. (no load state). The change rate of the relative dielectric constant was 65% or more (larger to the-side than -64%).

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)

Containing at least one rare earth element (RE) selected from the group of terbium, dysprosium, holmium, erbium and gadolinium, comprising first crystal particles mainly composed of barium titanate and second crystal particles of strontium zirconate The first crystal grains have a rare earth element (RE) concentration of 0.3 to 0.9 atomic% at a depth of 20 nm from the grain boundary. Crystal grains of the first crystal group, and crystals of the second crystal group having a concentration of the rare earth element (RE) lower than that of the crystal grains of the first crystal group and the concentration of 0 to 0.5 atomic% together comprising and a particle, with the density difference of the rare earth element (RE) is 0.1 to 0.7 atomic% between the said first crystal group of crystal grains second crystal group of crystal grains Yes, the second crystal Capacitor of the crystal grains, wherein the average particle diameter is smaller than the crystal grains of the first crystal group. The dielectric ceramic contains vanadium, magnesium, manganese, and yttrium, and 100 moles of titanium constituting the barium titanate,
The vanadium is 0.05 to 0.20 mol in terms of V ₂ O ₅ ,
The yttrium is 0.5 to 2.0 mol in terms of Y ₂ O ₃ ,
The magnesium is 1.0 to 3.0 mol in terms of MgO,
The manganese is 0.22 to 0.50 mol in terms of MnO,
The rare earth element (RE) is 0.65 to 2.80 mol 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 second crystal group is 0.02 to 0.42 atomic %,
Said first 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),
Average particle diameter of 0.2 ~ 0.5 [mu] m of the crystal grains forming the first sintered Akiragun, an average particle diameter of 0.1 ~ 0.18 [mu] m of the crystal grains forming the second sintered Akiragun As well as
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 , A / (a + b) is 0.4 to 0.7,
In the X-ray diffraction chart, the diffraction intensity of the surface index (121,002) of the strontium zirconate with respect to the diffraction intensity of the surface index (110) of barium titanate is 0.7 to 28.0%. The capacitor according to claim 1. The manganese is 0.30 to 0.50 mol in terms of MnO.
Capacitor described in.   The capacitor according to any one of claims 1 to 3, wherein the rare earth element (RE) is the gadolinium.