JP5496331B2 - Capacitor - Google Patents

Description

  The present invention relates to a capacitor which is made of crystal particles mainly composed of barium titanate and can be thinned.

  Conventionally, barium titanate has been used as a dielectric material for multilayer ceramic capacitors because of its high relative dielectric constant, and inexpensive base metals (such as Ni) have been used for the internal electrode layers of multilayer ceramic capacitors. It is used. When the dielectric layer mainly composed of barium titanate and the internal electrode layer are fired at the same time, it is necessary to reduce the oxygen partial pressure (for example, 0.03 Pa or less at 1300 ° C.) in order not to oxidize Ni. In this case, there is a problem that the dielectric layer is reduced and the insulating property is lowered, so that practical characteristics cannot be obtained.

Therefore, for example, in the case of a multilayer ceramic capacitor satisfying the X5R characteristic (or JIS standard B characteristic) of the EIA standard, as a dielectric material, for example, barium titanate as a main component, rare earth element oxide, Mn , V, Cr, Mo, Fe, Ni, Cu, Co and the like, reduction-resistant dielectric ceramics to which compounds of acceptor type and donor type elements are added are used (see, for example, Patent Document 1). A crystal particle in which a plurality of such additive components are dissolved in barium titanate has a tetragonal core part (usually pure BaTiO ₃ ) and a core part surrounding the core part. It has the core-shell structure comprised from the shell part.

  In addition, rare earth elements such as vanadium, magnesium, yttrium and manganese are added to barium titanate as dielectric ceramics that have a core-shell structure in the crystal grains mainly composed of barium titanate and satisfy the X5R characteristics of the EIA standard. Have also been proposed (see, for example, Patent Document 2).

JP 2001-230150 A JP 2008-239407 A

  In recent years, electronic devices such as mobile phones have been reduced in size and increased in mounting density. However, multilayer ceramic capacitors used in such small electronic devices also satisfy the X5R characteristics of the EIA standard. However, further increase in capacity is required.

  Accordingly, an object of the present invention is to provide a capacitor having a high dielectric constant while satisfying the X5R characteristic of the EIA standard.

The capacitor of the present invention is a crystal particle in which the dielectric layer has a barium titanate as a main component, a core part having a tetragonal crystal structure , and a shell part having a cubic crystal structure and vanadium solid solution. The thickness of the shell portion is 11.8 to 2 4 . The dielectric ceramic is characterized in that it is 5 nm and the average grain size of the crystal grains is 0.15 to 0.35 μm.

In the capacitor of the present invention, the dielectric ceramic contains vanadium, magnesium, at least one rare earth element (RE) selected from yttrium, dysprosium, holmium, terbium and ytterbium, and manganese, and titanate. With respect to 100 mol of barium, the vanadium is 0.04 to 0.10 mol in terms of V ₂ O ₅ , the magnesium is 0.4 to 1.2 mol in terms of MgO, and the rare earth element (RE) is RE ₂ O. It is desirable to be made of a dielectric ceramic containing 0.12 to 0.48 mol in terms of ₃ and 0.05 to 0.35 mol in terms of manganese in terms of MnO.

In the capacitor of the present invention, the dielectric ceramic contains vanadium, magnesium, at least one rare earth element (RE) selected from yttrium, dysprosium, holmium, terbium and ytterbium, and manganese, and titanate. The vanadium is 0.04 to 0.10 mol in terms of V ₂ O ₅ , the magnesium is 0.4 to 1.2 mol in terms of MgO, and the rare earth element (RE) is RE ₂ O with respect to 100 mol of barium. It is desirable to contain 0.30 to 0.48 mol in terms of ₃ and 0.05 to 0.35 mol of manganese in terms of MnO.

  Further, in the capacitor of the present invention, the dielectric ceramic has a grain boundary phase between the crystal grains, and the grain boundary phase is formed by a plurality of crystal grains and an interfacial grain boundary phase and a triple point grain boundary. The rare earth element, magnesium and silicon, and the concentration of the rare earth element, magnesium and silicon in the interfacial grain boundary phase is C1, and the triple point grain boundary phase. It is desirable that the concentration ratio C2 / C1 of the two elements among the respective elements when the respective concentrations of the rare earth element, magnesium and silicon in C are C2 is 0.8 to 1.2.

  Further, in the capacitor of the present invention, the dielectric ceramic has a grain boundary phase between the crystal grains, and the grain boundary phase is formed by a plurality of the crystal grains and the interfacial grain boundary phase and the triple point grain boundary. The rare earth element, magnesium and silicon, and the concentration of the rare earth element, magnesium and silicon in the interfacial grain boundary phase is C1, and the triple point grain boundary phase. It is desirable that the concentration ratio C2 / C1 of each element is 0.8 to 1.2 when the concentration of each of the rare earth element, magnesium and silicon is C2.

  According to the present invention, a capacitor having a high dielectric constant can be obtained while satisfying the X5R characteristic of the EIA standard.

(A) is a schematic sectional drawing which shows an example of the capacitor | condenser of this invention, (b) is an internal enlarged view. It is a cross-sectional schematic diagram which shows the internal structure of the crystal grain which has a barium titanate as a main component in the dielectric material ceramic which is a dielectric material layer which comprises the capacitor | condenser of this embodiment. In a dielectric ceramic that is a dielectric layer constituting the capacitor of the present embodiment, a grain boundary phase between two faces and a triple point formed by a plurality of crystal grains for measuring the concentration ratio of rare earth elements, magnesium and silicon It is a cross-sectional schematic diagram which shows the measurement position of a grain boundary phase.

  The capacitor of this embodiment will be described in detail based on the schematic cross-sectional view of the multilayer ceramic capacitor shown in 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 the inside. FIG. 2 is a schematic cross-sectional view showing the internal structure of crystal grains mainly composed of barium titanate in a dielectric ceramic that is a dielectric layer constituting the capacitor of this embodiment.

  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, but the capacitor of this embodiment is a laminated body in which the dielectric layer 5 and the internal electrode layer 7 are several hundred layers. It has become.

  The dielectric layer 5 made of dielectric porcelain is composed of crystal grains 9 and grain boundary phases 11, and the thickness is preferably 3 μm or less, particularly 2 μm or less, thereby reducing the size and increasing the capacity of the multilayer ceramic capacitor. It becomes possible to do. If the thickness of the dielectric layer 5 is 0.5 μm or more, it becomes possible to stabilize the temperature characteristics of the capacitance.

  The internal electrode layer 7 is preferably made of nickel (Ni) in that the manufacturing cost can be suppressed even when the internal electrode layer 7 is made highly laminated, and simultaneous firing with the dielectric layer 5 can be achieved.

In the capacitor according to this embodiment, the dielectric layer is composed of a barium titanate as a main component, a crystal structure having a tetragonal core part, and a crystal part having a cubic crystal structure and a shell part in which vanadium is dissolved. is constituted by particles, the thickness of the shell portion is from 11.8 to 2 4. The dielectric ceramic is 5 nm and the average grain size of the crystal grains is 0.15 to 0.35 μm.

  The dielectric layer 5 constituting the multilayer ceramic capacitor has crystal grains in the above average particle diameter range, and the crystal structure of the crystal grains 9 is a tetragonal core portion 9a and a cubic shell portion 9b. When the thickness t of the shell portion 9b is in the above range, the dielectric layer 5 constituting the capacitor has a relative dielectric constant of 3950 or more at room temperature (25 ° C.) and the temperature characteristics of the capacitance. A multilayer ceramic capacitor satisfying the EIA standard X5R characteristics (in the temperature range of −55 to 85 ° C., the change rate of the capacitance is within ± 15% with respect to 25 ° C.) it can.

  Note that the X5R characteristic of the EIA standard means that the change rate of the capacitance when the temperature is in the range of −55 to 85 ° C. with 25 ° C. as a reference is within ± 15%.

  In the capacitor of this embodiment, the thickness of the shell portion 9b of the crystal particle 9 having the core-shell structure is 11.8 to 26.5 nm. When the thickness of the shell portion 9b is less than 11.8 nm, the temperature characteristic of the capacitance becomes difficult to satisfy the X5R characteristic. On the other hand, when the thickness of the shell portion 9b is greater than 26.5 nm, the relative dielectric constant is from 3950. Also lower.

  In the capacitor of this embodiment, the average particle diameter of the crystal particles 9 constituting the dielectric ceramic that is the dielectric layer 5 is 0.15 to 0.35 μm. When the average particle diameter of the crystal particles 9 is smaller than 0.15 μm, it becomes difficult to form a core-shell structure in the crystal particles 9, and the structure is changed to a structure in which the additive component is dissolved in the center of the crystal particles 9. For this reason, the temperature change rate of the capacitance is larger than ± 15%, and the X5R characteristic of the EIA standard is not satisfied. On the other hand, if the average grain size of the crystal grains 9 is larger than 0.35 μm, the temperature change rate of the capacitance is larger than ± 15%, which does not satisfy the EIA standard X5R characteristics.

In the capacitor of the present embodiment, the dielectric ceramic constituting the dielectric layer 5 includes vanadium, magnesium, at least one rare earth element (RE) selected from yttrium, dysprosium, holmium, terbium and ytterbium, Manganese, with respect to 100 mol of barium titanate, vanadium is 0.04 to 0.10 mol in terms of V ₂ O ₅ , magnesium is 0.4 to 1.2 mol in terms of MgO, yttrium, dysprosium, holmium , Terbium and ytterbium containing at least one rare earth element (RE) in the range of 0.12 to 0.48 mol in terms of RE ₂ O ₃ and manganese in the range of 0.05 to 0.35 mol in terms of MnO It is desirable to consist of.

  When the composition of the dielectric ceramic constituting the dielectric layer 5 is in the above range, the relative permittivity can be increased to 4500 or more while the temperature characteristic of the capacitance satisfies the X5R characteristic, and the AC bias characteristic is 30% or less. In addition, a multilayer ceramic capacitor having a dielectric loss of 5% or less can be obtained. Here, the AC bias characteristic is a ratio of a change amount of a dielectric constant when an alternating current of 1 V / um is applied to a dielectric constant when an alternating current of 0.01 V / um is applied.

In the capacitor according to the present embodiment, the dielectric ceramic constituting the dielectric layer 5 is composed of 0.04 to 0.10 mol of vanadium in terms of V ₂ O ₅ and Mg of MgO with respect to 100 mol of barium titanate. Dielectric porcelain containing 0.5 to 1.2 mol in terms of conversion, rare earth element (RE) in an amount of 0.30 to 0.48 mol in terms of RE ₂ O ₃ and manganese in an amount of 0.05 to 0.35 mol in terms of MnO It is desirable to consist of. When the dielectric ceramic constituting the dielectric layer 5 has the above composition, the AC bias characteristic can be further reduced.

  In the capacitor of this embodiment, a glass component and other additive components are contained in the dielectric ceramic in an amount of 4% by mass or less as an aid for enhancing the sinterability as long as desired dielectric characteristics can be maintained. May be.

  In the capacitor according to this embodiment, the shell portion 9b surrounds the core portion 9a. However, the crystal particle 9 surrounding the core portion 9a by the shell portion 9b has a transmission electron microscope provided with an element analyzer (EDS). Confirm by analysis using. As a sample to be analyzed, 10 to 20 crystal particles 9 in the range of ± 30% of the average particle diameter are extracted from a sample produced by processing a multilayer ceramic capacitor. The spot size of the electron beam at the time of performing the elemental analysis is 1 to 3 nm, and the site to be analyzed is a region from the grain boundary to the center of the crystal grain 9. In this case, the concentration of the element (magnesium or rare earth element) is obtained every 5 to 10 nm from the grain boundary which is the surface of the crystal grain 9 to the center, and a graph is created with the horizontal axis representing the distance and the vertical axis representing the element concentration. . Here, in the graph, three points are taken in order from the measurement point closest to the grain boundary side, an approximate straight line is drawn using these three points, the slope of the straight line is taken as the concentration gradient of the element on the surface layer side, and the crystal From the measurement points within the range of 30 to 100 nm from the grain boundary of the particle 9, three points are taken in order from the measurement point closest to the center of the crystal particle 9, and an approximate straight line is drawn from these three points, and the inclination of the straight line is obtained. The concentration gradient of the element on the center side is used. When the concentration gradient of the element on the surface layer side is 0.15 atomic% / nm or more and the concentration gradient of the element on the center side is 0.5 atomic% / nm or less, the core-shell structure is formed. Shall.

  Next, the crystal structures of the core portion 9a and the shell portion 9b constituting the crystal particle 9 are obtained by an X-ray diffraction method. First, from the X-ray diffraction pattern of the dielectric layer 5, the (004) plane showing the cubic system of barium titanate appearing between the (004) plane showing the tetragonal system of barium titanate and the (400) plane (( (040) plane and (400) plane overlap)) or the diffraction intensity of any one of the (400) plane and (004) plane showing the tetragonal system of barium titanate, or It is assumed that the crystal grains 9 have tetragonal and cubic crystal structures when larger than that.

  And the analysis result by the transmission electron microscope which confirmed that the crystal grain 9 had the core part 9a and the shell part 9b surrounding the core part 9a, and the crystal grain 9 have a tetragonal crystal system and a cubic crystal structure Based on the result, the crystal particle 9 is determined to have a tetragonal core portion 9a and a cubic shell portion 9b surrounding the core portion 9a.

  Next, the thickness of the shell portion of the crystal particle 9 is determined for the crystal particle 9 determined to be composed of a tetragonal core portion 9a and a cubic shell portion 9b surrounding the core portion 9a. The thickness of the shell portion 9b of the crystal grain 9 was determined using the X-ray diffraction method disclosed in Japanese Patent Application Laid-Open No. 2006-137647 and J. Am. Ceram. Soc., 90 [4] 1107-1111 (2007). Based on the evaluation method, the following formula is used.

  The crystal structure of the target crystal grain 9 is compared with the reflection of a pure tetragonal crystal (h k l) or cubic crystal (h ′ k ′ l ′) in the measured X-ray diffraction pattern. It is assumed that the reflection of the tetragonal crystal (h k l) and the cubic crystal (h ′ k ′ l ′) is included from the identification of the peak position.

  The target diffraction data are reflections of tetragonal crystals (h k l) and cubic crystals (h ′ k ′ l ′). From the diffraction peak, the peak intensity (= integrated intensity), the 2θ position of the peak top, Parameters such as half width and peak shape function are obtained. At that time, peak separation is performed as necessary. In this case, the conditions for peak separation are as follows: background function: 0th order polynomial, synchrotron radiation: Kα1, profile function: the psedo-Voigt function, half width: different half width for all reflections, object of profile: object, Data resolution: Sharp (minimum half-value width: about 0.1 °). Note that commercially available software (for example, PROFIT) can be used for peak separation, and the tool for peak separation is not particularly limited.

  The average particle size of the crystal particles 9 is measured by the following procedure. First, the fracture surface of the sample which is the capacitor body 1 after firing is polished. Thereafter, a photograph of the internal structure is taken of the polished sample using a scanning electron microscope, a circle containing 50 to 100 crystal particles is drawn on the photograph, and crystal particles that fall within and around the circle are selected. . Next, image processing is performed on the outline of each crystal particle to determine the area of each crystal particle, and the diameter when the crystal particle is replaced with a circle having the same area is calculated and obtained from the average value.

  The composition of the dielectric ceramic is determined by using a solution in which the multilayer ceramic capacitor is dissolved in an acid, using ICP (Inductively Coupled Plasma) analysis and atomic absorption analysis. In this case, the amount of oxygen is determined using the valence of each element as the valence shown in the periodic table.

  Further, in the capacitor of this embodiment, the grain boundary phase 11 forming the dielectric ceramic that is the dielectric layer 5 is formed by a plurality of crystal grains 9 between the two-sided grain boundary phase and the triple point grain boundary phase. The rare earth elements, magnesium and silicon contained in the dielectric ceramic are between the interfacial grain boundary phase and the triple point intergranular phase, and the rare earth elements, magnesium and silicon in the interfacial grain boundary phase. When the respective concentrations are C1, and the respective concentrations of rare earth elements, magnesium and silicon in the triple-point grain boundary phase are C2, C2 / C1 of two kinds of rare earth elements, magnesium and silicon are 0.8 to 1 .2 is desirable. When C2 / C1 of two elements of rare earth elements, magnesium and silicon is 0.8 to 1.2, at a temperature higher than room temperature (25 ° C.) (for example, 85 ° C.), the capacitance of the capacitor The variation (CV) can be reduced. Further, when C2 / C1 of all elements of rare earth elements, magnesium and silicon is 0.8 to 1.2, the electrostatic capacity of the capacitor at a temperature higher than room temperature (25 ° C.) (for example, 85 ° C.). Capacitance variation (CV) can be further reduced.

  FIG. 3 shows a two-sided surface formed by a plurality of crystal grains 9 for measuring a concentration ratio of rare earth elements, magnesium and silicon in a dielectric ceramic that is the dielectric layer 5 constituting the capacitor of the present embodiment. It is a cross-sectional schematic diagram which shows the measurement position of the grain boundary phase 11a and the triple point grain boundary phase 11b.

  The concentrations of rare earth elements, magnesium and silicon in the interfacial grain boundary phase 11a and the triple point grain boundary phase 11b are determined by an X-ray microanalyzer (XMA) attached to the transmission electron microscope. In this case, a sample used for analysis is a thin plate-shaped dielectric ceramic cut out from the dielectric layer 5 of the capacitor and subjected to ion milling. The region to be analyzed is that when the two-sided grain boundary phase 11a and the triple point grain boundary phase 11b formed from the plurality of crystal grains 9 are viewed in cross section, the maximum diameter of at least three crystal grains 9 is the average grain diameter. Of crystal grains in a range within ± 20%. Then, using an X-ray microanalyzer (XMA), as shown in FIG. 3, each of the rare earth elements, magnesium and silicon at the position S1 of the intergranular grain boundary phase 11a and the position S2 of the triple point grain boundary phase 11b, respectively. The concentration is obtained, and the ratio C2 / C1 between the concentration C1 of each element in the interfacial grain boundary phase 11a and the concentration C2 of each element in the triple point grain boundary phase 11b is obtained. At this time, the position S1 of the interfacial grain boundary phase 11a to be analyzed is substantially the center of the width of the grain boundary phase 11, and the position S2 of the triple point grain boundary phase 11b is the center of the triple point grain boundary phase 11b. In addition, the position S1 of the interfacial grain boundary phase 11a is a position separated by 50 nm or more from the position where the position S2 of the triple point grain boundary phase 11b is determined.

  Next, a method for manufacturing the capacitor of this embodiment will be described.

  First, a ceramic slurry is prepared by using a ball mill or the like together with a dielectric powder, an organic resin such as polyvinyl butyral resin, a solvent such as toluene and alcohol, and then the ceramic slurry is subjected to a sheet molding method such as a doctor blade method or a die coater method. A ceramic green sheet is formed on the substrate. The thickness of the ceramic green sheet is preferably 1 to 5 μm from the viewpoint of reducing the thickness of the dielectric layer 5 to increase the capacity and maintaining high insulation.

  The dielectric powder used in the manufacturing method of the multilayer ceramic capacitor of the present embodiment is a barium titanate powder (hereinafter referred to as BT powder; Ba / Ti molar ratio is 1.001 to 1.009). The average particle size of the BT powder is preferably 0.21 to 0.30 μm. In the method for manufacturing the multilayer ceramic capacitor of the present embodiment, the average particle size is 0.21 to 0.30 μm as BT powder for forming the crystal particles 9 constituting the dielectric ceramic serving as the dielectric layer 5. By using the material in the range, it is possible to suppress the solid solution of the additive component including the rare earth element (RE) in the BT powder and to form a shell portion having a thickness described later. This facilitates the thinning of the dielectric layer 5, and the BT powder can be made into crystal particles 9 having a high dielectric constant under the firing conditions described later and satisfying the X5R characteristics of the EIA standard.

  The dielectric powder used in manufacturing the capacitor of this embodiment is mainly composed of barium titanate, which will be described later, and, for example, vanadium, magnesium, rare earth elements, manganese, and a predetermined amount of all components of the sintering aid. It is good to use what was coat | covered.

  In this case, the dielectric powder to be used is prepared as follows, for example. First, a suspension of barium titanate powder (BT powder) having a purity of 99.9% or more, a Ba / Ti molar ratio of 1.001 to 1.009, and an average particle diameter of 0.21 to 0.30 μm. Ammonia water is used as a pH adjusting agent in the turbid liquid to adjust the pH to a range of 6 to 8, and this includes a lithium aqueous solution, silica sol, barium carbonate aqueous solution, magnesium hydroxide aqueous solution, calcium hydroxide aqueous solution, ammonium vanadate aqueous solution, An aqueous solution of manganese acetate and an aqueous solution of at least one rare earth element selected from yttrium, dysprosium, holmium, terbium and ytterbium are added and mixed in this order to prepare a ceramic slurry. Note that the purity of these raw material reagents is preferably 99.5% or more for the purpose of suppressing the mixing of impurities into the obtained dielectric ceramic and obtaining high dielectric properties.

  Next, the ceramic slurry is put into a spray dryer equipped with a four-fluid nozzle, droplets having a diameter of 10 μm or less are generated from the four-fluid nozzle, and dried at a temperature of about 200 ° C. A precursor is prepared, and then the dielectric powder precursor is prepared by heat treatment at a temperature higher than the temperature of the drying treatment.

As the composition of the dielectric powder, when the BT powder is 100 mol, the ammonium vanadate aqueous solution is 0.04 to 0.10 mol in terms of V ₂ O ₅ , and the magnesium hydroxide aqueous solution is 0.5 to 0.5 in terms of MgO. 1.2 mol, 0.05 to 0.35 mol of manganese acetate aqueous solution in terms of MnO, and an aqueous solution of at least one rare earth element (RE) selected from yttrium, dysprosium, holmium, terbium and ytterbium in terms of RE ₂ O ₃ It is desirable that the composition be 0.12 to 0.48 mol, thereby obtaining a multilayer ceramic capacitor having a high dielectric constant, a capacitance temperature characteristic satisfying the X5R characteristic, and a low AC bias characteristic and dielectric loss. It becomes possible.

Moreover, the addition amount of a sintering auxiliary agent is prepared so that it may become 0.5-2.0 mass parts with respect to 100 mass parts of BT powder. Thereby, the sinterability of the dielectric ceramic can be further enhanced. The composition is preferably Li ₂ O = 1-15 mol%, SiO ₂ = 40-60 mol%, BaO = 15-35 mol%, and CaO = 5-25 mol%.

  Next, a rectangular internal electrode pattern is printed and formed on the main surface of the obtained ceramic green sheet. The conductor paste used as the internal electrode pattern is prepared by mixing Ni or an alloy powder thereof as a main component metal, mixing ceramic powder as a co-material with this, and adding an organic binder, a solvent and a dispersant. Further, in order to eliminate the step due to the internal electrode pattern on the ceramic green sheet, it is preferable to form the ceramic pattern with substantially the same thickness as the internal electrode pattern around the internal electrode pattern. In this case, it is preferable to use the dielectric powder used for the ceramic green sheet as the ceramic component constituting the ceramic pattern in that the firing shrinkage in the simultaneous firing is the same.

  Next, a desired number of ceramic green sheets with internal electrode patterns are stacked, and a plurality of ceramic green sheets without internal electrode patterns are stacked on top and bottom of the ceramic green sheets so that the upper and lower layers have the same number. Form the body. The internal electrode patterns in the temporary laminate are shifted by half patterns in the longitudinal direction. By such a laminating method, the internal electrode pattern can be formed so as to be alternately exposed on the end face of the cut laminate.

  In addition to the method of laminating after the internal electrode pattern is formed in advance on the main surface of the ceramic green sheet, the capacitor according to the present embodiment has the internal electrode pattern formed after the ceramic green sheet is once brought into close contact with the underlying equipment. Printed, dried, printed and dried internal electrode patterns are stacked with a ceramic green sheet that is not printed with an internal electrode pattern, temporarily adhered, and the ceramic green sheet is adhered and the internal electrode pattern is printed sequentially. Can also be formed.

  Next, the temporary laminate is pressed under conditions of higher temperature and higher pressure than the temperature and pressure at the time of temporary lamination to form a laminate in which the ceramic green sheet and the internal electrode pattern are firmly adhered.

  Next, the capacitor body molded body in which the end portions of the internal electrode patterns are exposed is formed by cutting the laminate into a lattice shape.

  Next, the obtained capacitor body molded body is degreased and fired. The firing is desirably performed in a hydrogen-nitrogen atmosphere at a maximum temperature of 1150 to 1230 ° C. and a holding time of 0.1 to 4 hours. Then, the capacitor body 1 is obtained by performing reoxidation treatment in the temperature range of 900 to 1100 ° C. Thereafter, if necessary, the ridge line portion of the capacitor body 1 may be chamfered and barrel polishing may be performed to expose the internal electrode layer 7 exposed from the opposing end surface of the capacitor body 1. By performing the firing under such conditions, the average particle diameter of the crystal particles 9 constituting the dielectric layer 5 is in the range of 0.15 to 0.35 μm, and the crystal structure of the crystal particles 9 is a tetragonal core part. 9a and a cubic shell portion 9b that surrounds the core portion and in which at least one additive component of vanadium, magnesium, rare earth element (RE), and manganese is in solid solution, and the thickness of the shell portion 9b is 10 to 10. A capacitor body 1 having a thickness of 20 nm can be obtained.

  Moreover, when manufacturing the capacitor | condenser of this embodiment, after degreasing the obtained capacitor main body molded object, before reaching maximum temperature in hydrogen-nitrogen atmosphere, it is once at the temperature of 900-1000 degreeC. It is desirable to provide a heat treatment step for holding for about 5 to 3 hours. By providing such a heat treatment step, the difference in the composition of rare earth elements, magnesium and glass components in the interfacial grain boundary phase 11a and the triple-point grain boundary phase 11b of the crystal grain 9 can be reduced, and thus the capacitor Capacitance variation (CV) at a temperature (about 85 ° C.) higher than room temperature (25 ° C.) can be reduced. Here, the variation in capacitance (CV) is expressed by a ratio (σ / x) of an average value (x) and a standard deviation (σ) obtained by using a measured value of the capacitance of a plurality of samples as a parameter. Is the value to be

  As described above, the capacitor according to the present embodiment is mainly composed of barium titanate to produce the dielectric layer 5, and vanadium, magnesium, rare earth element (RE), manganese, and a sintering aid. Crystal grains 9 having a small average thickness of the shell portion 9b can be obtained by firing the obtained raw capacitor body molded body with a predetermined amount of all components and firing the obtained raw capacitor body under firing conditions with a high heating rate. .

  Next, an external electrode paste is applied to the opposing ends of the capacitor body 1 and baked to form the external electrodes 3. In some cases, a plating film is formed on the surface of the external electrode 3 in order to improve mountability. Thus, the capacitor of the present invention can be obtained.

  First, barium titanate powder (hereinafter referred to as BT powder) having a purity of 99.9% and a Ba / Ti molar ratio of 1.005 was prepared as a raw material powder.

  Next, ammonia water was used as a pH adjuster in the suspension of BT powder so that the pH was in the range of 6-8. Next, to this, at least one selected from lithium aqueous solution, silica sol, barium carbonate aqueous solution, magnesium hydroxide aqueous solution, calcium hydroxide aqueous solution, ammonium vanadate aqueous solution, manganese acetate aqueous solution and yttrium, dysprosium, holmium, terbium and ytterbium An aqueous solution of rare earth elements was added and mixed in this order to prepare a ceramic slurry.

Next, the ceramic slurry is put into a spray dryer equipped with a four-fluid nozzle, droplets having a diameter of 10 μm or less are generated from the four-fluid nozzle, and dried at a temperature of about 200 ° C. A precursor is prepared, and then the dielectric powder precursor is heat-treated at 400 ° C. to cover the surface of the BT powder with a predetermined amount of all components of vanadium, magnesium, rare earth element, manganese and sintering aid. A dielectric powder was prepared. The sintering aid was adjusted to have a composition of SiO ₂ = 55, BaO = 20, CaO = 15, Li ₂ O = 10 (mol%), and the amount of the sintering aid added was BT. It adjusted so that it might become 1 mass part with respect to 100 mass parts of powder. A sample was prepared by adding glass powder as a sintering aid to BT powder coated with a predetermined amount of vanadium, magnesium, rare earth element and manganese (sample No. 33).

  Next, the obtained dielectric powder is put into a mixed solvent of polyvinyl butyral resin, toluene and alcohol, and wet-mixed using a zirconia ball having a diameter of 1 mm to prepare a ceramic slurry. A 2 μm ceramic green sheet was prepared.

  Next, a plurality of conductive pastes containing Ni as a main component were formed on the upper surface of the ceramic green sheet so as to form a rectangular internal electrode pattern. The conductor paste for forming the internal electrode pattern was obtained by adding BT powder to 100 parts by mass of Ni powder having an average particle size of 0.3 μm.

Next, 200 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 A laminated body was prepared by closely adhering under conditions of 10 ⁷ Pa and time 10 minutes, and then the laminated body was cut into a predetermined size to form a capacitor body molded body.

  Next, the capacitor body molded body was treated to remove the binder in the air, and then fired at a temperature rising rate of 2000 ° C./h in hydrogen-nitrogen at a temperature shown in Table 1 to produce a capacitor body. This firing was performed using a roller hearth kiln. Moreover, the sample which made the temperature increase rate 500 degreeC / h was produced (sample No. 34).

The produced capacitor body was subsequently reoxidized at 1000 ° C. for 4 hours in a nitrogen atmosphere. The size of the capacitor body was 2.05 × 1.28 × 1.28 mm ³ , the thickness of the dielectric layer was 2.0 μm, and the effective area of one internal electrode layer was 1.78 mm ² . The effective area is the area of the overlapping portion of the internal electrode layers that are alternately formed in the stacking direction so as to be exposed at different end faces of the capacitor body.

  Next, after barrel-polishing the capacitor body, 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 ceramic capacitor.

  Next, the following evaluation was performed on these multilayer ceramic capacitors. The dielectric constant at room temperature (25 ° C.) was measured by using an LCR meter (manufactured by Hewlett-Packard Co.) with a capacitance of 25 ° C., a frequency of 1.0 kHz, and an AC voltage of 1.0 V / μm. And the effective area of the internal electrode layer.

  Dielectric loss was also measured under the same conditions as the capacitance using the same LCR meter. Moreover, the temperature characteristic of the capacitance was measured in a temperature range of −55 to 85 ° C.

  The AC bias characteristic is that the capacitance when an alternating current (AC) voltage of 0.01 V / μm is applied is C1, and the temperature is 25 at a temperature of 25 ° C., a frequency of 1.0 kHz, and an AC voltage of 0.01 to 3.5 V / μm. The capacitance was determined from ((C2−C1) / C1) × 100 (%), where C2 was the electrostatic capacity when applying an AC voltage of 3.5 V / μm at a temperature of 1.0 ° C.

  The average particle size of the crystal particles constituting the dielectric layer is determined by polishing the fracture surface of the sample that is the capacitor body after firing, and then taking a picture of the internal structure using a scanning electron microscope. Draw a circle that contains 30 circles, select the crystal particles that fall within and around the circle, image the outline of each crystal particle, determine the area of each particle, and replace it with a circle with the same area Was calculated from the average value.

  Next, whether or not the crystal particles having the core portion and the shell portion are those in which the shell portion surrounds the core portion was confirmed by analysis using a transmission electron microscope provided with an element analyzer (EDS). As an analyzed sample, 10 to 20 crystal particles in a range of ± 30% of the average particle diameter were extracted from a TEM sample manufactured by processing a multilayer ceramic capacitor. The spot size of the electron beam at the time of performing the elemental analysis was 1 to 3 nm, and the site to be analyzed was the region from the grain boundary to the central part which is the surface of the crystal grain. In this case, the concentration of the rare earth element was determined every 5 to 10 nm from the grain boundary, which is the surface of the crystal grain, to the center, and a graph was created with the horizontal axis representing the distance and the vertical axis representing the element concentration. Here, in the graph, three points were taken in order from the measurement point closest to the grain boundary, and an approximate straight line was drawn using these three points, and the slope of the straight line was taken as the concentration gradient of the element on the surface layer side. In addition, from the measurement points within the range of 30 to 100 nm from the grain boundary of the crystal grain, three points are taken in order from the measurement point closest to the center of the crystal grain, and an approximate line is drawn from these three points, and the slope of the straight line is obtained. Is the concentration gradient of the element on the center side. In this case, when the concentration gradient of the element on the grain boundary side is 0.15 atomic% / nm or more and the concentration gradient of the element on the center side is 0.5 atomic% / nm or less, the core-shell structure is obtained. It was supposed to be.

  Next, the respective crystal structures of the core portion and the shell portion constituting the crystal particles were determined by an X-ray diffraction method. First, from the X-ray diffraction pattern of the sample obtained by grinding the dielectric layer, the cubic system of barium titanate appearing between the (004) plane and the (400) plane showing the tetragonal system of barium titanate is shown (004). The diffraction intensity of the plane (the (040) plane and (400) plane overlap) is the diffraction intensity of any one of the (400) plane and (004) plane showing the tetragonal system of barium titanate. The crystal grains had tetragonal and cubic crystal structures when they were equal or larger.

  And the analysis result by the transmission electron microscope which confirmed that the crystal particle has a core part and a shell part surrounding the core part, and that the crystal particle has a tetragonal crystal system and a cubic crystal structure From the results, it was determined that the crystal particles had a tetragonal core part and a cubic shell part surrounding the core part.

  Next, the thickness of the shell portion of the crystal particle was determined by the following method for the crystal particle 9 determined to have a tetragonal core portion and a cubic shell portion surrounding the core portion.

  The shell thickness of the crystal grains was obtained using the above-described Equation 1 and Equation 2. At this time, X′Pertpro manufactured by Panallytical was used as the X-ray diffractometer. At this time, the crystal structure of the target crystal particle is that the selected X-ray diffraction pattern is reflected in pure tetragonal (h k l) or cubic (h ′ k ′ l ′) in the measured X-ray diffraction pattern. In comparison, the peak was identified, and the one containing tetragonal (h k l) and cubic (h ′ k ′ l ′) reflections was selected.

  The diffraction peaks of tetragonal (002) and (200) and cubic (200) were measured. The size of the beam was 0.5 mm in the vertical direction and 5 mm in the horizontal direction. The wavelength was 1.54982 mm. In the measurement of the dielectric ceramic, the step width was 0.02 °, and the counting time per point was 5.0 seconds. Further, the number of repetitions was 10, and the integration for 10 times was defined as the diffraction intensity. In the evaluation, peak separation was performed for tetragonal (002), (200), and cubic (200) from the diffraction peak using peak separation software (PROFIT) under the following conditions. The conditions for peak separation are as follows: background function: 0th order polynomial, synchrotron radiation: Kα1, profile function: the psedo-Voigt function, half width: different half width for all reflections, profile subjectivity: subject, data resolution: Sharp (minimum half width: about 0.1 °) and analysis range: 44 ° <2θ <47 °.

  The composition analysis of the obtained sintered body sample was performed by ICP (Inductively Coupled Plasma) 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. The composition of the dielectric layer constituting the obtained multilayer ceramic capacitor matched the composition shown in Table 1.

The composition and firing conditions are shown in Table 1, and the average grain size and dielectric characteristics (relative permittivity, capacitance temperature characteristics, AC bias characteristics, dielectric loss) of the dielectric particles in the obtained multilayer ceramic capacitor ) Shows the results in Table 2. In Tables 1 and 2, the sample Nos. I-5, I-11, I-14, I-20, I-25, I-30, I-34 and I-35 are reference samples.

  As is apparent from the results in Tables 1 and 2, sample No. Room temperature (25 ° C.) for I-1-4, I-6-10, I-12, I-13, I-15-19, I-21-24, I-26-29 and I-31-34 The relative dielectric constant at 3950 was 3950 or more, and the temperature characteristics of the capacitance satisfied the X5R characteristics.

  Sample No. At I-2-4, I-6-10, I-12, I-13, I-16-19, I-22-22, I-27-29, I-31 and I-32, room temperature (25 The relative dielectric constant at 4 ° C. was 4500 or more, the temperature characteristics of the capacitance satisfied the X5R characteristics, the AC bias characteristics were 30% or less, and the dielectric loss was 5% or less.

In particular, with respect to 100 mol of barium titanate, the vanadium is 0.04 to 0.1 mol in terms of V ₂ O ₅ , the magnesium is 0.5 to 1.2 mol in terms of MgO, and the rare earth element (RE) Is a dielectric ceramic layer containing a dielectric ceramic containing 0.3 to 0.48 mol in terms of RE ₂ O ₃ and 0.05 to 0.35 mol in terms of MnO in terms of manganese. No. For I-2 to 3, I-6 to 10, I-12, I-13, I-16 to 19, I-22 to 24, I-27 to 29, I-31 and I-32, room temperature (25 The relative dielectric constant at 4 ° C. was 4500 or more, the temperature characteristic of the capacitance satisfied the X5R characteristic, the AC bias characteristic was 29.00% or less, and the dielectric loss was 5% or less.

  In contrast, sample no. In I-5, I-11, I-14, I-20, I-25, I-30, and I-35, the relative dielectric constant at room temperature (25 ° C.) is 3950 or more, and the temperature characteristic of capacitance is X5R. Any of the characteristics of satisfying the characteristics was not satisfied.

  Next, in the firing process, after degreasing the produced capacitor molded body, and before firing at the maximum temperature, heat treatment was performed at the temperature shown in Table 3 for 1 hour, and all the results were as in Example 1. A sample was prepared by the same method, the same evaluation was performed, and the capacitance at 85 ° C. was measured to determine the variation (CV). The variation in capacitance was determined from 32 samples.

  The concentrations of rare earth elements, magnesium and silicon in the interfacial grain boundary phase and triple point grain boundary phase in the dielectric ceramic were determined by an X-ray microanalyzer (XMA) attached to the transmission electron microscope. In this case, the sample used for the analysis was a thin plate-shaped dielectric ceramic cut out from the dielectric layer of the produced multilayer ceramic capacitor and subjected to ion milling. The region to be analyzed is a crystal grain group in which the maximum diameter of at least three crystal grains is within a range of ± 20% of the average grain size when the cross-sectional view of the intergranular grain boundary phase and the triple point grain boundary phase is viewed. 5 locations were selected. Then, using an X-ray microanalyzer (XMA), as shown in FIG. 3, the concentrations of rare earth elements, magnesium and silicon at the position S1 of the intergranular grain boundary phase and the position S2 of the triple point grain boundary phase are determined, The average value of the ratio C2 / C1 between the element concentration C1 in the interfacial grain boundary phase and the element concentration C2 in the triple-point grain boundary phase was determined. At this time, the position S1 of the intergranular phase to be analyzed was set to be approximately the center of the width of the grain boundary phase, and the position S2 of the triple point grain boundary phase was set to the center of the triple point grain boundary phase. The position S1 of the intergranular grain boundary phase was set at a position about 50 nm away from the position where the position S2 of the triple point grain boundary phase was determined. The production conditions are shown in Table 3, and the evaluation results such as dielectric properties are shown in Table 4. Sample No. Each of II-1 to 28 had a core-shell structure, and the core portion was tetragonal and the shell portion was confirmed to be cubic.

  As is clear from the results in Tables 3 and 4, the prepared samples (Sample Nos. II-1 to 28) are all in the same ratio as that of the sample prepared by the method of Example 1 at room temperature (25 ° C.). The dielectric constant was 3950 or more, and the temperature characteristic of the capacitance satisfied the X5R characteristic. The AC bias characteristic was 30% or less, and the dielectric loss was 5% or less. In this, after degreasing the obtained capacitor body molded body during manufacturing, before the maximum temperature is reached in a hydrogen-nitrogen atmosphere, a laminated layer produced by adding a heat treatment step held at the temperature shown in Table 3 The ceramic capacitor samples (Sample Nos. II-1 to 23, 25 to 28) are more variable in capacitance (CV) than the samples (Sample No. II-24) fired without the heat treatment step. Are both as small as 2% or less, and in particular, in the samples (sample Nos. II-1 to 21, 25 to 28) in which the temperature of the heat treatment step is 900 to 1000 ° C., the variation in capacitance (CV) is all It was 1.5% or less.

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer 9 Crystal grain 9a Core part 9b Shell part 11 Grain boundary phase 11a Interfacial grain boundary phase 11b Triple point grain boundary phase

Claims (5)

The dielectric layer is composed of crystal particles having a barium titanate as a main component, a crystal structure having a tetragonal core part, and a crystal structure having a cubic structure and a shell part in which vanadium is dissolved , The thickness of the shell portion is 11.8 to 2 4 . A capacitor comprising a dielectric ceramic having an average particle diameter of 5 nm and a crystal grain size of 0.15 to 0.35 μm. The dielectric ceramic contains vanadium, magnesium, at least one rare earth element (RE) selected from yttrium, dysprosium, holmium, terbium and ytterbium, and manganese, Vanadium is 0.04 to 0.10 mol in terms of V ₂ O ₅ , the magnesium is 0.4 to 1.2 mol in terms of MgO, and the rare earth element (RE) is 0.12 to 0 in terms of RE ₂ O _3. The capacitor according to claim 1, wherein .48 mol and manganese are contained in an amount of 0.05 to 0.35 mol in terms of MnO. The dielectric ceramic contains vanadium, magnesium, at least one rare earth element (RE) selected from yttrium, dysprosium, holmium, terbium and ytterbium, and manganese, Vanadium is 0.04 to 0.10 mol in terms of V ₂ O ₅ , the magnesium is 0.4 to 1.2 mol in terms of MgO, and the rare earth element (RE) is 0.30 to 0 in terms of RE ₂ O _3. The capacitor according to claim 1, containing .48 mol and 0.05 to 0.35 mol of manganese in terms of MnO.   The dielectric ceramic has a grain boundary phase between the crystal grains, and the grain boundary phase is composed of a two-sided grain boundary phase formed by a plurality of the crystal grains and a triple point grain boundary phase. The rare earth element, the magnesium and silicon, and the concentration of each of the rare earth element, the magnesium and the silicon in the interfacial grain boundary phase is C1, the rare earth element in the triple point grain boundary phase, the magnesium and The concentration ratio C2 / C1 of two kinds of elements when the respective concentrations of silicon are C2 is 0.8 to 1.2. Capacitor described in. The dielectric ceramic has a grain boundary phase between the crystal grains, and the grain boundary phase is composed of a two-sided grain boundary phase formed by a plurality of the crystal grains and a triple point grain boundary phase. The rare earth element, the magnesium and silicon, and the concentration of each of the rare earth element, the magnesium and the silicon in the interfacial grain boundary phase is C1, the rare earth element in the triple point grain boundary phase, the magnesium and 5. The capacitor according to claim 1, wherein the concentration ratio C2 / C1 of each element is 0.8 to 1.2 when the concentration of each silicon is C2. .

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