JP5578881B2 - Multilayer ceramic capacitor - Google Patents

Description

  The present invention relates to a multilayer ceramic capacitor that is made of crystal grains 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, in the case of the X5R characteristic (or JIS standard B characteristic) of the EIA standard, as a dielectric material, for example, barium titanate is a main component, and oxides of rare earth elements, Mn, V, Cr, Mo, Fe, Reduction-resistant dielectric ceramic compositions to which acceptor-type and donor-type element compounds such as Ni, Cu, and Co are added are used. A dielectric crystal particle (for example, BaTiO ₃ ) in which a plurality of additive components are solid-dissolved in barium titanate has a tetragonal core part (usually pure BaTiO ₃ ) and a core part. And a shell portion in which the added component is dissolved (see, for example, Patent Document 1). Here, the X5R characteristic of the EIA standard indicates that the rate of change of the electrostatic capacity is within ± 15% with respect to 25 ° C. in the temperature range of −55 to 85 ° C. Means that the rate of change in capacitance is within ± 10% when 20 ° C. is used as a reference in the temperature range of −25 to 85 ° C.

  Furthermore, in recent years, with the trend toward smaller and higher density electronic circuits, multilayer ceramic capacitors are also required to be smaller and larger in capacity while satisfying the X5R characteristics of the EIA standard. In order to reduce the number of dielectric layers, the number of dielectric layers is increasing and the thickness is being reduced.

However, when the dielectric layer is thinned, the electric field strength per layer increases, and the multilayer ceramic capacitor has a problem that the capacitance decreases when a DC voltage is applied (DC bias characteristics). Here, the DC bias characteristic is ((C ₁ − −) when C _{0 is} the capacitance when no DC voltage is applied to the multilayer ceramic capacitor, and C ₁ is the capacitance when a DC voltage is applied. C ₀ ) / C ₀ ) × 100 (%)).

  For this reason, in the multilayer ceramic capacitor, the effective capacitance when a DC voltage is applied together with an AC voltage has been emphasized, and improvements for improving the DC bias characteristics of the multilayer ceramic capacitor have been made for many years. (For example, Patent Documents 2 to 5).

JP 2001-230150 A JP 2001-316176 A JP 2006-111468 A JP 2008-162818 A JP 2009-238885 A

  However, the problems associated with the thinning of the dielectric layer of the multilayer ceramic capacitor are not limited to the above-described deterioration of the DC bias characteristics accompanying the increase of the electric field strength per layer, but the multilayer ceramic capacitor is also subject to direct current. When voltage is continuously applied, there is also a problem that the capacitance gradually decreases (DC aging characteristics). Here, the DC aging characteristic is a rate of change (decrease) in capacitance with time when a constant DC voltage is continuously applied to the multilayer ceramic capacitor.

  Accordingly, an object of the present invention is to provide a multilayer ceramic capacitor having a high dielectric constant and excellent in DC bias characteristics and DC aging characteristics while satisfying the X5R characteristics of the EIA standard.

The multilayer ceramic capacitor of the present invention is provided on a capacitor body in which a plurality of dielectric layers and a plurality of internal electrode layers made of nickel as a conductive material are alternately stacked, and on the end face of the capacitor body where the internal electrode layers are exposed. A multilayer ceramic capacitor having an external electrode layer, wherein the dielectric layer is composed mainly of barium titanate, and is selected from calcium, magnesium, yttrium, dysprosium, holmium, terbium and ytterbium. The rare earth element (RE) is 0.6 to 1.2 mol in terms of MgO, and the rare earth element (RE) with respect to 100 mol of the total amount of barium and calcium constituting the barium titanate. ) as well as 0.6 to 1.0 moles contained in the terms _{of RE} 2 _{O 3,} the main crystal grain The barium titanate as a main component, and the calcium, and the magnesium, made of crystal grains of the core-shell structure in which a solid solution and the rare earth element, the crystal grains, the calcium 0.4-1.0 And the average particle size is 0.15 to 0.4 μm , the crystal structure of the core part is tetragonal, and the crystal structure of the shell part surrounding the core part is cubic. , and the average thickness of the shell portion was calculated based on the X-ray diffraction information Rutotomoni such a dielectric ceramic is a 5 to 15 nm, dielectric ceramic, characterized in that it contains no manganese.

  In the multilayer ceramic capacitor, it is desirable that the dielectric ceramic does not contain vanadium.

  In the multilayer ceramic capacitor, it is desirable that the dielectric ceramic does not contain manganese.

  According to the present invention, it is possible to obtain a multilayer ceramic capacitor having a high dielectric constant and excellent DC bias characteristics and DC aging characteristics while satisfying the X5R characteristics of the EIA standard.

(A) is a schematic sectional drawing which shows an example of the multilayer ceramic capacitor of this invention, (b) is an enlarged view of an 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 multilayer ceramic capacitor of the present invention.

The multilayer ceramic capacitor of the present invention will be described in detail based on the schematic sectional view of FIG. FIG. 1A is a schematic sectional view showing an example of the multilayer ceramic 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 multilayer ceramic capacitor of the present invention.

  In the multilayer ceramic 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 multilayer ceramic capacitor of this embodiment has several hundreds of dielectric layers 5 and internal electrode layers 7. It is a laminate.

  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 multilayer ceramic capacitor of this embodiment, the dielectric ceramic constituting the dielectric layer 5 is mainly composed of barium titanate, and at least one selected from calcium, magnesium, yttrium, dysprosium, holmium, terbium and ytterbium. Rare earth element (RE).

  Further, this dielectric porcelain has at least one rare earth element (RE) selected from 0.6 to 1.2 mol of magnesium, yttrium, dysprosium, holmium, terbium and ytterbium with respect to 100 mol of barium and calcium in total. ) Is contained in an amount of 0.6 to 1.0 mol.

  Further, the crystal grains 9 as the main crystal grains constituting the dielectric ceramic have an average particle diameter of 0.15 to 0.4 μm.

  Furthermore, the crystal particles 9 constituting the dielectric ceramic contain calcium in the crystal particles 9, the concentration of the calcium is 0.4 to 1.0 atomic%, and the calcium is contained in the entire crystal particles 9. Almost uniformly distributed and dissolved in barium titanate.

  Further, the crystal particles 9 constituting the dielectric ceramic have a core part 9a having a tetragonal crystal structure, and an additive component of magnesium and rare earth element (RE) that surrounds the core part 9a and has a crystal structure. The shell portion 9b has a cubic shell portion 9b, and the shell portion 9b has an average thickness t calculated from X-ray diffraction information of 5 to 15 nm. The average thickness t of the shell portion calculated based on the X-ray diffraction information is hereinafter referred to as an average thickness t of the shell portion.

The dielectric ceramic constituting the multilayer ceramic capacitor has the above composition, the crystal particles 9 have the above average particle diameter, and the crystal structure is a tetragonal core portion 9a and a cubic shell portion 9b. When the average thickness t of the shell portion 9b is within a specific range, the dielectric layer 5 constituting the multilayer ceramic capacitor has a relative dielectric constant at room temperature of 3600 or more, and a temperature characteristic of capacitance. Satisfies the EIA standard X5R characteristics (in which the capacitance change rate is within ± 15% with respect to 25 ° C in the temperature range of -55 to + 85 ° C) and DC bias characteristics (lamination) The capacitance change rate when a DC voltage is applied is within −55% of the capacitance when no DC voltage is applied to the ceramic capacitor, and the DC capacitor Ing characteristics (rate of change in capacitance with respect to time of the multilayer ceramic capacitor obtained by applying continuously a constant DC voltage) may be a stacked ceramic capacitor having excellent dielectric characteristics of within -20%.

  That is, the crystal particles 9 constituting the dielectric ceramic serving as the dielectric layer 5 in the multilayer ceramic capacitor of this embodiment contain calcium substantially uniformly throughout the crystal particles 9, and the concentration of calcium is 0.4 to 0.4. 1.0 atomic%. In this case, when the concentration of calcium in the crystal particles 9 is lower than 0.4 atomic%, the dielectric constant at room temperature of the dielectric layer 5 constituting the multilayer ceramic capacitor is lower than 3600.

  On the other hand, when the concentration of calcium in the crystal particles 9 is higher than 1.0 atomic%, the shell portion 9b is not formed in the crystal particles 9, and the core-shell structure cannot be obtained. As a result, the multilayer ceramic capacitor does not satisfy the EIA standard X5R characteristic with respect to the temperature characteristic of the capacitance, the DC bias characteristic becomes larger than −55%, and the DC aging characteristic becomes larger than −20%. .

  Further, the content of each element contained in the dielectric ceramic serving as the dielectric layer 5 in the multilayer ceramic capacitor of this embodiment is such that the magnesium content is 0.6 mol in terms of MgO with respect to 100 mol of the total amount of barium and calcium. If it is less, a shell portion is not formed in the crystal grain 9 and a core-shell structure cannot be obtained. Therefore, the temperature characteristic of the capacitance is increased, the EIA standard X5R characteristic is not satisfied, and the DC bias characteristic is −55. %, And DC aging characteristics are also larger than -20%.

  Here, the DC bias characteristic larger than −55% and the DC aging characteristic larger than −20% mean that the change in capacitance becomes larger on the negative side.

  On the other hand, when the content of magnesium with respect to 100 mol of the total amount of barium and calcium is more than 1.2 mol in terms of MgO, the relative dielectric constant at room temperature is lower than 3600 and the DC aging characteristic is larger than −20%. .

Next, when the content of rare earth element (RE) with respect to 100 mol of the total amount of barium and calcium is less than 0.6 mol in terms of RE ₂ O ₃ , the shell part is not formed in the crystal particles 9 in this case, A core-shell structure cannot be obtained, the temperature characteristics of capacitance do not satisfy the X5R characteristics of the EIA standard, the DC bias characteristics are greater than −55%, and the DC aging characteristics are also greater than −20%.

On the other hand, when the content of the rare earth element (RE) with respect to 100 mol of the total amount of barium and calcium is more than 1.0 mol in terms of RE ₂ O ₃ , the thickness t of the shell portion 9b becomes thicker than 15 nm. As the dielectric constant falls below 3600, the DC aging characteristics become greater than -20%.

  Furthermore, in the multilayer ceramic capacitor of this embodiment, it is important that the average thickness t of the shell portion 9b of the crystal particle 9 having the core-shell structure is 5 to 15 nm, and the average thickness t of the shell portion 9b is thinner than 5 nm. In this case, although the relative dielectric constant at room temperature is 3600 or more, the temperature change rate of the capacitance is larger than ± 15%, which does not satisfy the X5R characteristic of the EIA standard. On the other hand, when the average thickness t of the shell portion 9b is greater than 15 nm, the DC aging characteristic exceeds −20%.

  In the multilayer ceramic capacitor of this embodiment, it is important that the average particle size of the crystal particles 9 constituting the dielectric ceramic that is the dielectric layer 5 is 0.15 to 0.4 μm. When the average particle diameter of the crystal particles 9 is smaller than 0.15 μm, the relative dielectric constant at room temperature becomes lower than 3600. In this case, the average particle diameter of the crystal particles 9 is small, and the average of the shell portion 9b is diffused by the diffusion of the additive element. When the thickness t becomes thicker than 15 nm, the DC aging characteristic exceeds −20%. On the other hand, when the average grain size of the crystal grains 9 is larger than 0.4 μm, the DC bias characteristic becomes larger than −55%.

Further, in the multilayer ceramic capacitor of this embodiment, the dielectric ceramic serving as the dielectric layer 5 is 0 in terms of V ₂ O _{5 with} respect to 100 mol of the total amount of barium and calcium together with magnesium and rare earth elements (RE). Although it may be contained in a range of 1 mol or less, it is desirable that it does not contain vanadium. When the dielectric porcelain does not contain vanadium, the thickness of the shell portion 9b in the crystal particle 9 is reduced to 8 nm or less, and the relative dielectric constant of the dielectric layer 5 at room temperature can be increased to 3900 or more. Aging characteristics can be made to be 10.48% or less.

  Furthermore, in the multilayer ceramic capacitor of this embodiment, the dielectric ceramic serving as the dielectric layer 5 is 0.2 mol in terms of MnO with respect to the total amount of barium and calcium, together with magnesium and rare earth elements (RE), of 100 mol. Although it may be contained in the following range, it is preferable that it does not contain manganese. When the dielectric porcelain does not contain manganese, the average thickness t of the shell portion 9b is 6.1 to 7.3 nm, and the DC aging characteristic can be reduced to -10.04% or less.

  Further, in the multilayer ceramic capacitor of this embodiment, as long as desired dielectric characteristics can be maintained, a glass component or other additive component is added to the dielectric ceramic as an auxiliary for enhancing the sinterability to 4% by mass or less. You may make it contain in a ratio.

  Regarding the concentration of calcium in the crystal particles 9 (hereinafter sometimes referred to as “Ca concentration”), the crystal particles existing on the polished surface obtained by polishing the cross section of the dielectric porcelain are provided with an elemental analyzer. Elemental analysis is performed using an electron microscope. At this time, the spot size of the electron beam is set to 5 nm or less, and the points to be analyzed are 4 to 5 points at approximately equal intervals from the grain boundary on the straight line drawn from the vicinity of the grain boundary toward the center of the crystal grain 9. Calculating the ratio of calcium when the total amount of Ba, Ti, Ca, V, Mg, RE (rare earth element) and Mn detected from 100% is obtained, and averaging the ratio of calcium determined at each measurement point, Ca Calculate as concentration.

  Further, in the present invention, a method for measuring the average thickness t of the shell portion 9b of the crystal particle 9 is based on an evaluation method using an X-ray diffraction method disclosed in JP-A-2006-137647, as follows. It can be obtained from the equation.

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. In this case, the target diffraction data is tetragonal (h k l) and cubic (h ′ k ′ l ′) reflections. Then, parameters such as peak intensity (= integrated intensity), peak top 2θ position, half-value width, peak shape function, and the like are obtained from the diffraction peak.

Next, the peak half-value width (B) of the cubic crystal (h ′ k ′ l ′) obtained from the diffraction peak
Is substituted into equation (2) to determine the true half-value width (β), and then the true half-value width (β) and the Bragg angle (θ) obtained from the diffraction data are expressed in equation (1). The thickness (d _obs ) of the shell portion is determined by substitution, and this is set as the average thickness t of the shell portion. 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 °). Commercially available software can be used for peak separation, and the tools for peak separation are 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 9 is drawn on the photograph, and the crystal particles 9 in and around the circle are drawn. select. Next, the contour of each crystal particle 9 is image-processed to determine the area of each crystal particle 9, the diameter when replaced with a circle having the same area is calculated, and the average value is determined.

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

  Next, a method for manufacturing the multilayer ceramic 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 main component powder constituting the dielectric powder used in the method of manufacturing the multilayer ceramic capacitor of this embodiment is a BCT powder represented by (Ba _1-x Ca _x ) TiO ₃ as a barium titanate powder in which calcium is dissolved. (Ba + Ca / Ti molar ratio is 1.001 to 1.009). The average particle size of the BCT powder is preferably 0.06 to 0.2 μm. This facilitates the thinning of the dielectric layer 5, and as a BCT powder, a crystal having a high dielectric constant under the firing conditions described later and satisfying the X5R characteristics of the EIA standard, and suitable for DC bias characteristics and DC aging characteristics. The particles 9 can be obtained.

  Next, the dielectric powder to be used is prepared as follows. First, pH adjustment was performed on a suspension of BCT powder having a purity of 99.9% or more, a Ba / Ti molar ratio of 1.001 to 1.009, and an average particle size of 0.1 to 0.2 μm. Ammonia water is used as the agent, and the pH is in the range of 6 to 8, which is selected from lithium aqueous solution, silica sol, barium carbonate aqueous solution, magnesium hydroxide aqueous solution, calcium hydroxide aqueous solution and yttrium, dysprosium, holmium, terbium and ytterbium. A ceramic slurry is prepared by adding and mixing at least one rare earth element (RE) aqueous solution in this order. 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. Further, as a coating component, other additive components such as vanadium and manganese can be similarly added as a solution as required.

  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 the dielectric powder is then manufactured by heat-treating the precursor of the dielectric powder at a temperature higher than the temperature of the drying process.

The composition of the dielectric powder is selected from 0.6 to 1.2 mol, yttrium, dysprosium, holmium, terbium and ytterbium in terms of the amount of magnesium hydroxide aqueous solution converted to MgO when the BCT powder is 100 mol. The aqueous solution of at least one kind of rare earth element (RE) to be added is added so as to have a composition of 0.6 to 1.0 mol in terms of RE ₂ O ₃ .

Moreover, when using a sintering auxiliary agent, the addition amount is prepared so that it may become 0.5-2 mass parts with respect to 100 mass parts of BCT powder. Thereby, the sinterability of the dielectric ceramic can be further enhanced. As the sintering aid, it is preferable to use a low melting point glass containing lithium. For example, the composition is Li ₂ O = 1-15 mol%, SiO ₂ = 40-60 mol%, BaO = 15-35 mol%. , And CaO = 5 to 25 mol% is preferable.

  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.

  The multilayer ceramic capacitor of the present invention has a method of laminating after the internal electrode pattern is formed in advance on the main surface of the ceramic green sheet. Is printed, dried, and the ceramic green sheet without the internal electrode pattern printed thereon is temporarily adhered to the printed and dried internal electrode pattern, and the adhesion of the ceramic green sheet and the printing of the internal electrode pattern are sequentially performed. It can also be formed by a construction method.

  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 capacitor body 1 is formed by firing the capacitor body molded body in a predetermined atmosphere under temperature conditions. In some cases, 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 opposite end surface of the capacitor body 1.

  Next, the obtained capacitor body molded body is degreased and fired. Firing is preferably performed in a hydrogen-nitrogen atmosphere at a temperature increase rate of 1500 to 4000 ° C./h, a maximum temperature of 1030 to 1200 ° C., 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. 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 0.4 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 and manganese is dissolved, and the thickness of the shell portion 9b is 5 to 15 nm. The capacitor body 1 can be obtained.

  As described above, in the multilayer ceramic capacitor of this embodiment, in order to produce the dielectric layer 5, at least magnesium, rare earth elements, and sintering aids are used with respect to barium titanate containing calcium as a main component. 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. . On the other hand, even when barium titanate containing calcium is coated with a predetermined amount of at least magnesium, rare earth elements, and sintering aids, the temperature increase rate is slower than 1500 ° C./h. Then, the thickness of the shell portion 9b is increased, and a method in which glass powder is post-added as a sintering aid even when barium titanate is a main component and at least a predetermined amount of magnesium and rare earth elements are coated thereon. In either case, the DC aging characteristic is increased.

  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 multilayer ceramic capacitor of the present invention can be obtained.

First, as a raw material powder, a BCT powder containing calcium at a ratio shown in Table 1, having a purity of 99.9%, an average particle diameter of 0.06 to 2.0 μm, and a Ba + Ca / Ti molar ratio of 1.005 is prepared. did.

  Next, aqueous ammonia was used as a pH adjuster in the BCT powder suspension so that the pH was in the range of 6-8. Next, at least one rare earth 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 the 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. As a comparative example, 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. 37).

  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 molded body of the capacitor body was treated to remove the binder in the air, and then fired at 1100 in hydrogen-nitrogen to produce a capacitor body. In this firing, firing was performed using a roller hearth kiln under the conditions of the heating rate shown in Table 1.

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. Moreover, the temperature characteristic of the capacitance was measured in a temperature range of −55 to 85 ° C.

  The DC bias characteristics are C1, electrostatic capacity when a direct current (DC) voltage is not applied under conditions of a temperature of 25 ° C., a frequency of 1.0 kHz, and an AC voltage of 1.0 V / μm, a temperature of 25 ° C., a frequency of 1.0 kHz, It was determined from ((C2−C1) / C1) × 100 (%), where C2 is the capacitance when a direct current (DC) voltage is applied under the condition of AC voltage of 0.2 V / μm.

  DC aging characteristics are as follows: a direct current (DC) voltage of 4.5 V / μm is applied, the electrostatic capacity is measured when 1 hour and 10 hours have elapsed, and the electrostatic capacity after 10 hours is defined as C3. And ((C3-C2) / C1) × 100 (%).

  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.

The average shell thickness of the crystal grains was determined 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, tetragonal (002), (200) and cubic (200) were peak-separated from the diffraction peak using peak separation software 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 °.

  Moreover, the composition analysis of the sample which is the obtained sintered body 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 particle diameter and dielectric characteristics of the dielectric grains (dielectric constant, capacitance temperature characteristics, DC bias characteristics, DC aging) in the obtained multilayer ceramic capacitor The characteristic results are shown in Table 2, respectively.

  As is clear from the results in Tables 1 and 2, the sample No. 2 to 4, 10, 11, 13, 14, 17, 18, 20 to 22, 24 to 31, and 33 to 35, the relative dielectric constant at room temperature (25 ° C.) is 3600 or more, and the temperature characteristic of capacitance is X5R. In the measurement of DC bias characteristics satisfying (temperature change rate of relative permittivity with respect to 25 ° C. is ± 15% at −55 to 85 ° C.), a DC voltage is measured. When the non-application capacitance value is used as a reference, the decrease rate of the capacitance value when applied under the condition of 4.5 V / μm is 53.63% (−53.63%: sample No. 10) or less. Furthermore, in the DC aging characteristic in which a DC voltage is applied under the condition of 4.5 V / μm, the rate of decrease in capacitance until the lapse of 0.1 to 10 hours is 19.77% (−19.77% : Sample No. 2) or less.

In particular, in the samples (samples No. 20 and 28 to 31) in which the dielectric ceramic serving as the dielectric layer does not contain manganese, the capacitance until 0.1 to 10 hours elapses in the DC aging characteristics under the same conditions. The rate of decrease was 10.04% (-10.04%: Sample No. 30) or less.

  On the other hand, sample no. 1,5-9,12,15,16,19,23,32 and 36-39 have a relative dielectric constant of 3600 or more at room temperature (25 ° C) and a temperature characteristic of capacitance of X5R (based on 25 ° C) The temperature change rate of the relative permittivity is within ± 15% at −55 to 85 ° C.), and in the DC bias measurement in which a direct current of 4.5 V / μm is applied, no direct current voltage is applied. In terms of the DC aging characteristics in which the decrease rate of the capacitance value when applied with 4.5 V / μm is within 55% and a DC voltage is applied under the condition of 4.5 V / μm when the value is used as a reference, 0.1 to 10 The capacitance reduction rate until the passage of time did not satisfy any of the characteristics within 20%.

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

Claims (1)

A capacitor body in which a plurality of dielectric layers and a plurality of internal electrode layers made of nickel as a conductive material are alternately laminated, and an external electrode layer provided on an end surface of the capacitor body where the internal electrode layers are exposed In the multilayer ceramic capacitor, the dielectric layer has barium titanate as a main component, calcium, magnesium, and at least one rare earth element (RE) selected from yttrium, dysprosium, holmium, terbium, and ytterbium. And, with respect to a total amount of 100 mol of barium and calcium constituting the barium titanate, the magnesium is 0.6 to 1.2 mol in terms of MgO, and the rare earth element (RE) is in terms of RE ₂ O ₃ In addition to containing 0.6 to 1.0 mol, the main crystal particles are mainly composed of the barium titanate. And wherein the calcium, said magnesium, made of crystal grains of the core-shell structure in which a solid solution and the rare earth element, the crystal grains, as well as containing the calcium 0.4-1.0 atomic%, average particle size 0.15 to 0.4 μm , the crystal structure of the core part is tetragonal, and the crystal structure of the shell part surrounding the core part is cubic and calculated based on X-ray diffraction information multilayer ceramic capacitor average thickness of the shell portion that is Rutotomoni such a dielectric ceramic is a 5 to 15 nm, dielectric ceramic, characterized in that it contains no manganese.

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