JP5084657B2 - Multilayer ceramic capacitor - Google Patents

Description

  The present invention provides a capacitor body in which dielectric layers composed of dielectric ceramics mainly composed of barium titanate and internal electrode layers made of nickel as a conductive material are alternately laminated, and an end where the internal electrode layers of the capacitor body are exposed. The present invention relates to a multilayer ceramic capacitor composed of an external electrode provided in a portion.

  A multilayer ceramic capacitor is usually manufactured by laminating a ceramic green sheet for a dielectric layer and a conductor paste for an internal electrode layer by a sheet method, a printing method, or the like and simultaneously firing them. Palladium or palladium-silver alloy is generally used as the conductor material for the internal electrode, but since these noble metals are expensive, relatively inexpensive base metals such as nickel and nickel alloys are used. It has become like this.

Further, by using dielectric powder obtained by coating an additive such as vanadium, magnesium, rare earth elements and manganese on barium titanate as a material for forming the dielectric layer, X7R characteristics (−55 to 125 ° C.) of EIA standard are used. , It is proposed to use a dielectric ceramic satisfying a maximum capacitance change rate of within ± 15% based on 25 ° C. (see, for example, Patent Document 1). By the way, when a base metal is used as the conductor material for the internal electrode layer, the internal electrode layer is oxidized when fired in the atmosphere, and therefore, the simultaneous firing of the dielectric layer and the internal electrode layer is performed in a reducing atmosphere. There is a need.
JP 2006-8498 A

  However, when the multilayer ceramic capacitor described in Patent Document 1 is produced by firing in a reducing atmosphere, the dielectric layer is reduced and the insulation resistance is lowered, so that desired dielectric constant and capacitance-temperature characteristics can be obtained. There was no problem.

  Accordingly, an object of the present invention is to provide a multilayer ceramic capacitor having a high insulation resistance even after firing in a reducing atmosphere and having a high dielectric constant and excellent capacitance-temperature characteristics.

The multilayer ceramic capacitor of the present invention is formed by alternately laminating dielectric layers having a thickness of 1 to 3 μm made of dielectric ceramics having crystal grains mainly composed of barium titanate and internal electrode layers made of nickel as a conductive material. A multilayer ceramic capacitor composed of a capacitor body and an external electrode provided at an end portion where the internal electrode layer of the capacitor body is exposed,
The dielectric ceramic is one kind selected from 0.05 to 0.3 mol of vanadium in terms of V ₂ O ₅ and yttrium, dysprosium, holmium and erbium with respect to 100 mol of barium constituting the barium titanate. The rare earth element (RE) contains 0.5 to 1.5 mol in terms of RE ₂ O ₃ , magnesium contains 0 to 0.1 mol in terms of MgO, and manganese contains 0 to 0.5 mol in terms of MnO. X-ray In the diffraction chart, the diffraction intensity of the (004) plane showing the tetragonal barium titanate is larger than the diffraction intensity of the (400) plane showing the cubic barium titanate,
The crystal particles have an average particle size of 0.15 to 0.4 μm ,
EELS analysis was performed on the polished surface obtained by polishing a part of the capacitor body after heat-treating the capacitor body with oxygen partial pressure of 10 ⁻⁸ to 10 ⁻¹⁶ atmosphere at 1200 ° C. for 2 hours. In this case, the valence of titanium in the range of 10 to 50 nm from the interface between the conductor material and the crystal particles toward the crystal particles is tetravalent.

  In the multilayer ceramic capacitor, it is desirable that components dissolved in the barium titanate are substantially only vanadium and a rare earth element (RE).

  Note that the rare earth element RE is based on the rare earth element English representation (Rare earth) in the periodic table. In the present invention, yttrium is included in the rare earth element.

  According to the present invention, it is possible to obtain a multilayer ceramic capacitor having a high insulation resistance even after firing in a reducing atmosphere and having a high dielectric constant and excellent capacity-temperature characteristics.

  FIG. 1 is a schematic cross-sectional view showing an example of the multilayer ceramic capacitor of the present invention. FIG. 2 is a transmission electron micrograph showing the vicinity of the interface between the dielectric layer and the internal electrode layer of the capacitor body.

  The multilayer ceramic capacitor of the present invention is such that external electrodes 3 are provided at both ends of a capacitor body 1, and the capacitor body 1 is made of a laminate in which dielectric layers 5 and internal electrode layers 7 are alternately stacked. It is configured. Here, the external electrode 3 is electrically connected to the internal electrode layer 7 exposed on the end face of the capacitor body 1. In FIG. 1, the laminated state of the dielectric layer 5 and the internal electrode layer 7 is shown in a simplified manner. However, in the multilayer ceramic capacitor of the present invention, the dielectric layer 5 and the internal electrode layer 7 are several hundred layers. Is formed.

  The dielectric layer 5 is made of a dielectric ceramic composed of crystal particles 11 mainly composed of barium titanate and grain boundary phases 13 connecting the crystal particles 11 to each other.

  As a material for forming the internal electrode layer 7, nickel (Ni) is used in that the manufacturing cost can be suppressed even when the number of layers is increased, and simultaneous firing with the dielectric layer 5 can be achieved.

  The external electrode 4 is formed by baking, for example, Cu or an alloy paste of Cu and Ni.

  In the multilayer ceramic capacitor of the present invention, the dielectric layer 5 is composed of crystal particles 11 mainly composed of barium titanate, and the dielectric layer 5 has a thickness of 1 to 3 μm. The average grain size of the constituting crystal grains 11 is 0.15 to 0.4 μm.

The dielectric layer 5 is composed of 0.05 to 0.3 mol of vanadium in terms of V ₂ O ₅ and one kind of rare earth selected from yttrium, dysprosium, holmium and erbium with respect to 100 mol of barium constituting barium titanate. It consists of a dielectric ceramic containing 0.5 to 1.5 elements (RE) in terms of RE ₂ O ₃ , 0 to 0.1 mol of magnesium in terms of MgO, and 0 to 0.5 mol of manganese in terms of MnO.

The dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention will be further described. The capacitor body 1 is heat-treated at 1200 ° C. for 2 hours in an oxygen partial pressure of 10 ⁻⁸ to 10 ⁻¹⁶ atm. When EELS analysis was performed on a sample in which nickel which is a conductor material of the internal electrode layer 7 obtained by polishing a part of the capacitor body 1 and the crystal particles 11 are in contact, the conductor material (nickel) and the crystal particles 11 The valence of titanium in the range of 10 to 50 nm from the interface to the crystal particle 11 side is tetravalent.

As a result, the dielectric layer 5 has an insulation resistance of 1 × 10 ⁷ Ω or more even after firing in a reducing atmosphere, and the dielectric layer 5 has a relative dielectric constant of 3300 or more at room temperature (25 ° C.). A multilayer ceramic capacitor satisfying the above can be obtained. In this case, having an insulation resistance of 1 × 10 ⁷ Ω or more even after firing in a reducing atmosphere means that the step of re-oxidation treatment may be omitted in the production of the multilayer ceramic capacitor. The manufacturing cost can be reduced.

  On the other hand, when the thickness of the dielectric layer 5 is less than 1 μm, the electric field applied to the dielectric layer 5 when a voltage is applied becomes strong, so that the insulation resistance of the dielectric layer 5 decreases.

  On the other hand, when the thickness of the dielectric layer 5 is greater than 3 μm, a high insulation resistance can be obtained, but the rate of change in capacitance with temperature increases.

Further, the composition of the dielectric ceramic which is the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention is one kind of rare earth element selected from yttrium, dysprosium, holmium and erbium with respect to 100 moles of barium constituting barium titanate ( When the content of (RE) is less than 0.5 mol in terms of RE ₂ O ₃ , or when the content of magnesium is more than 0.1 mol in terms of MgO, the temperature characteristic of capacitance is EIA. The X7R characteristic of the standard is not satisfied.

Further, when the content of vanadium with respect to 100 mol of barium constituting barium titanate is less than 0.05 mol in terms of V ₂ O ₅ , the insulation resistance after heat treatment in a reducing atmosphere is 1 × 10 ^7. It is much lower than Ω.

When the content of vanadium with respect to 100 mol of barium constituting barium titanate is more than 0.3 mol in terms of V ₂ O ₅ , or from yttrium, dysprosium, holmium and erbium with respect to 100 mol of barium constituting barium titanate When the content of one selected rare earth element (RE) is more than 1.5 mol in terms of RE ₂ O ₃ or when the manganese content is more than 0.5 mol in terms of MnO, The relative dielectric constant at (25 ° C.) is lower than 3300.

  By the way, among rare earth elements, yttrium, dysprosium, holmium and erbium are less likely to form a different phase when dissolved in barium titanate, and can be suitably used because high insulation can be obtained. Yttrium is more preferable because the specific permittivity can be increased.

  In the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention, it is desirable that the components dissolved in barium titanate are substantially only vanadium and rare earth elements (RE). When the component dissolved in barium titanate is substantially only vanadium and rare earth elements (RE), the maximum rate of change in capacitance at −55 to 125 ° C. can be within ± 11%. become.

  Moreover, the dielectric ceramic in the present invention may contain a glass component and other additive components in the dielectric ceramic in an amount of 0.5 to 2% by mass as an auxiliary for enhancing the sinterability. As an unavoidable impurity, Zr mixed from zirconia balls used for mixing raw material powders and various trace components such as C, Na, K, Cl, etc. may be contained in a dielectric ceramic in an amount of 0.2 parts by mass or less. Good. In the present invention, the fact that the components that are dissolved in barium titanate are substantially only vanadium and rare earth elements (RE) are those that are positively added and that dissolve in barium titanate. It means only vanadium and rare earth elements (RE).

  Further, in the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention, when the average grain size of the crystal grains 11 constituting the dielectric layer 5 is smaller than 0.15 μm, the relative dielectric constant at room temperature (25 ° C.) is 3300. When the average particle size of the crystal grains 11 is larger than 0.4 μm, the maximum change in capacitance at −55 to 125 ° C. when the capacitance at room temperature (25 ° C.) is used as a reference. The rate may not satisfy within ± 15% (EIA standard X7R characteristic).

  Here, the average particle diameter of the crystal particles 11 is determined by polishing the fracture surface of the sample, which is a dielectric ceramic after firing, and then taking a picture of the internal structure using a scanning electron microscope. Draw 20 to 30 circles, select the crystal particles 11 in and around the circle, image the outline of each crystal particle 11 to obtain the area of each particle, and make circles with the same area. The diameter at the time of replacement is calculated and obtained from the average value.

  Further, the crystal particles 11 constituting the dielectric layer 5 will be described in more detail.

In the present invention, the capacitor body 1 is heat-treated in oxygen partial pressure of 10 ⁻⁸ to 10 ⁻¹⁶ atmosphere at 1200 ° C. for 2 hours, and then the valence of titanium (Ti) constituting the crystal particle 11 is EELS. Evaluate by analysis.

  The EELS analysis is one of analysis methods performed by an analyzer attached to a transmission electron microscope (TEM), and is electronic energy loss spectroscopy.

FIG. 3A is a reaction formula showing the generation of oxygen defects and surplus electrons in barium titanate (BaTiO ₃ ) when heat-treated in a reducing atmosphere. FIG. 3B is a reaction formula showing a state in which electrons generated by reduction are doped in barium titanate.

When the dielectric layer 5 composed of the crystal particles 11 mainly composed of barium titanate is heat-treated in a reducing atmosphere, oxygen defects and accompanying electrons are generated during reduction as shown in FIG. Generated. Next, as shown in FIG. 3B, surplus electrons generated by the reduction are doped into the Ti3d orbital from the band structure of BaTiO ₃ (Ti ⁴⁺ ), and change into Ti ³⁺ , so that the crystal particles 11 It is considered that the number of carriers increases in the inside, and as a result, the insulation resistance of the dielectric layer 5 changes.

FIG. 4A is an EELS spectrum of barium titanate (BaTiO ₃ ), and FIG. 4B is an enlarged view of Ti L _{2 and 3 in} the spectrum of FIG. In this case, a change in the number of electrons (valence) is examined from a specific EELS spectrum (TiL _2,3 : (energy loss: 460 to 472 ev)) of titanium (Ti) contained in the crystal particles 11 by EELS analysis. As shown in FIG. 4A, when the rise of the K spectrum of oxygen (O) is 530 eV, if the peak indicated by the arrow in FIG. 4B is 464 ± 0.1 eV, the valence of Ti is 4 If the peak is shifted to the low loss energy side, the valence of Ti will be less than 4.

  A sample for performing the EELS analysis on the crystal particles 11 constituting the dielectric layer 5 is produced as follows.

  First, a capacitor body 1 is prepared by removing the external electrode 3 from the multilayer ceramic capacitor.

Next, the capacitor body 1 is heat-treated in a reducing atmosphere. The reducing atmosphere at this time is prepared with a hydrogen-nitrogen mixed gas, and the oxygen partial pressure is 10 ⁻⁸ to 10 ⁻¹⁶ atm. The heat treatment temperature is 1200 ° C. and the holding time is 2 hours.

  Next, the reduced capacitor body 1 is cut into a predetermined size in a state where the dielectric layers 5 and the internal electrode layers 7 are alternately laminated, and then subjected to rough polishing, and finally an ion using argon gas. A sample that can be observed with a transmission electron microscope (TEM) is manufactured by milling. At this time, the ion milled sample is in a state in which nickel, which is a conductor material of the internal electrode layer 7, and crystal particles 11 mainly composed of barium titanate are adjacent to each other (FIG. 2).

  Next, the prepared sample is mounted in the TEM, and the place where the EELS analysis is performed is determined by looking at the TEM image. The place where EELS analysis is performed is in the range of 10 to 50 nm from the interface B between the nickel, which is a conductor material, and the crystal particle 11 toward the crystal particle 11 as shown by the dashed frame in FIG. Analyze with. The reason why the EELS analysis is made near the interface B between nickel and crystal particles 1 is that the portion closer to nickel as the conductor material is the portion where the valence of Ti is more likely to change.

Even after the capacitor body 1 is heat-treated in oxygen partial pressure of 10 ⁻⁸ to 10 ⁻¹⁶ at 1200 ° C. for 2 hours, the crystal grains on the side adjacent to nickel which is the conductor material of the internal electrode layer 7 When the valence of titanium in 11 is tetravalent (Ti ⁺⁴ ), the capacitor body 1 having an insulation resistance of 1 × 10 ⁷ Ω or more can be obtained even after firing in a reducing atmosphere.

In contrast, when the same heat treatment and analysis as described above were performed, the valence of titanium obtained from the EELS analysis in the range of 10 to 50 nm from the interface B between the nickel and the crystal particles toward the crystal particle 11 side was If it is smaller than tetravalent (Ti ^4−δ ), after firing in a reducing atmosphere, the insulation resistance may be less than 1 × 10 ⁷ Ω and the dielectric properties may not be measured.

  As described above, the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention is characterized in that the valence of titanium obtained from the EELS analysis of the crystal particles 11 is tetravalent. In the X-ray diffraction chart, the dielectric ceramic serving as the body layer 5 has a (004) plane diffraction intensity indicating tetragonal barium titanate and a (400) plane diffraction intensity indicating cubic barium titanate. And the Curie temperature is 100 to 120 ° C.

  Here, the crystal structure of the dielectric ceramic forming the dielectric layer 5 in the multilayer ceramic capacitor of the present invention will be described in more detail. The dielectric ceramic serving as the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention. Is occupied by a crystal phase close to a single phase exhibiting a tetragonal system even if additives such as vanadium and rare earth elements (RE) are dissolved in the crystal particles 11.

  FIG. 5A shows a sample No. 1 as an example of the multilayer ceramic capacitor of the present invention in Table 1 of Examples described later. 3 is an X-ray diffraction chart for the dielectric ceramic of No. 3, and FIG. 16 is an X-ray diffraction chart of 15 dielectric ceramics. 6 shows a sample No. in Table 1 of Examples described later. 3 and sample no. It is a graph which shows the temperature characteristic of the electrostatic capacitance of 15 multilayer ceramic capacitors. The dielectric porcelain of the present invention has a sample no. 3 having a capacitance temperature characteristic.

  Here, in the conventional multilayer ceramic capacitor which is the invention described in Patent Document 3, the crystal structure of the dielectric ceramic is a core-shell structure, which corresponds to the X-ray diffraction chart of FIG. The temperature characteristic of the capacitance is the sample No. in FIG. This corresponds to 15 characteristics.

  That is, in a dielectric ceramic composed of crystal grains having barium titanate as a main component and having a core / shell structure, titanium appearing between the (004) plane and (400) plane showing the tetragonal system of barium titanate. The diffraction intensity Ixc of the (400) plane showing the cubic system of barium oxide (the (040) plane and (004) plane overlap) is the diffraction intensity of the (004) plane showing the tetragonal system of barium titanate. It is larger than Ixt.

  In addition, as seen from the X-ray diffraction chart, dielectric ceramics composed of crystal particles having a core-shell structure have a higher proportion of cubic crystal phases than tetragonal crystal phases. Anisotropy is reduced. Therefore, in the X-ray diffraction chart, the (400) plane diffraction lines are shifted to the low angle side and the (004) plane diffraction lines are shifted to the high angle side, so that both diffraction lines overlap each other at least partially. It becomes a wide diffraction line.

  Such a dielectric porcelain is formed by molding a powder containing barium titanate as a main component and adding an oxide powder such as magnesium or a rare earth element, followed by reduction firing. In this case, the crystal particles having a core-shell structure are solid-dissolved with many components such as magnesium and rare earth elements (RE) in the shell portion, whereas the core portion is composed of components such as magnesium and rare earth elements (RE). It is a crystal phase of barium titanate that is close to pure due to the small amount of solid solution. Therefore, the Curie temperature is around 125 ° C. (122 to 126 ° C.) and has an inflection point P around 125 ° C. Yes.

A multilayer ceramic capacitor having a core-shell structure and having a dielectric ceramic layer 5 with a dielectric ceramic having a Curie temperature near 125 ° C. has a temperature of −55 to 125 ° C. with respect to room temperature (25 ° C.). Although the maximum rate of change of capacitance in the range is about ± 15%, the capacitor body 1 is heat-treated at 1200 ° C. for 2 hours in an oxygen partial pressure of 10 ⁻⁸ to 10 ⁻¹⁶ atm. In this case, the insulation resistance becomes lower than 1 × 10 ⁷ Ω by applying the voltage of the multilayer ceramic capacitor. Further, in such a sample, when EELS analysis is performed on a sample in which nickel obtained by polishing a part of the capacitor body and the crystal particle are in contact with each other, the interface between the nickel and the crystal particle is directed toward the crystal particle side. In addition, the valence of titanium in the range of 10 to 50 nm is smaller than the tetravalence.

  On the other hand, the dielectric ceramic forming the dielectric layer 5 in the multilayer ceramic capacitor of the present invention has a tetragonal barium titanate crystal in the X-ray diffraction chart of the dielectric ceramic as shown in FIG. The diffraction intensity Ixt of the (004) plane indicating the system is larger than the diffraction intensity Ixc of the (400) plane indicating the cubic system of barium titanate.

  That is, the dielectric ceramic which is the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention has a (004) plane (4) indicating a tetragonal system of barium titanate as seen in FIG. X-ray diffraction peaks of (2θ = 100 °) and (400) plane (2θ = 101 °) clearly appear and show the tetragonal system of barium titanate (004) plane and (400) plane The diffraction intensity Ixc of the (400) plane (the (040) plane and (400) plane overlap)) representing the cubic system of barium titanate appearing in between indicates the tetragonal system of barium titanate (004). ) Surface diffraction intensity Ixt.

That is, the crystal structure of the dielectric ceramic in the multilayer ceramic capacitor of the present invention is different from the X-ray diffraction pattern of the conventional core-shell structure, and the multilayer ceramic capacitor of the present invention (sample No. 3) in FIG. As described above, the dielectric characteristics are different from those of the multilayer ceramic capacitor in which the dielectric layer 5 is a dielectric ceramic having a core-shell structure with a Curie temperature (Tc) in the range of 98 to 120 ° C. and a Curie temperature of 125 ° C. . This is because at least a predetermined amount of vanadium and rare earth elements (RE) are solid-dissolved over the entire crystal particle 11 mainly composed of barium titanate. Thus, even after firing in a reducing atmosphere, the dielectric layer 5 has an insulation resistance of 1 × 10 ⁷ Ω or more, a dielectric constant of the dielectric layer 5 at room temperature (25 ° C.) of 3300 or more, and room temperature (25 ° C. The capacitance change rate in the temperature range of −55 to 125 ° C. with respect to the relative dielectric constant in (1) is within ± 15%. The Curie temperature of the multilayer ceramic capacitor is a temperature at which the electrostatic capacitance is measured in the range of −55 to 125 ° C. and exhibits the maximum capacitance in the measured temperature range.

Next, a method for producing the multilayer ceramic capacitor of the present invention will be described. First, in order to produce a ceramic green sheet that becomes the dielectric layer 5 after firing, the raw material powder is a barium titanate powder (hereinafter referred to as BT powder) having a purity of 99% or more, and the additive component is V ₂ O. ₅ powder, oxide powder of at least one rare earth element (RE) among Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder and Er ₂ O ₃ powder, MgO powder and MnCO ₃ as MnO Prepare the powder.

In the present invention, BT powder having a Curie temperature of 125 to 131 ° C. at the raw material powder stage is used as the BT powder used for producing the ceramic green sheet, and in particular, the Curie temperature is 128 to 131 ° C. It is desirable to use BT powder. By using BT powder having a Curie temperature of 125 ° C. to 131 ° C., it becomes easy to make the Curie temperature in the multilayer ceramic capacitor in the range of 98 to 120 ° C., and in particular, the Curie temperature of the BT powder is 128 to 131 ° C. This is because the capacity-temperature characteristic can be further stabilized. Since the Curie temperature of the BT powder is on the high temperature side, the dielectric ceramic obtained by dissolving the V ₂ O ₅ powder, rare earth element (RE) oxide powder, MgO powder and MnCO ₃ powder is 125 ° C. This is because the relative dielectric constant in the vicinity can be increased, and as a result, the temperature characteristics of the capacitance can be further stabilized. Note that the Curie temperature of the BT powder is measured by differential scanning calorimetry (DSC).

  The average particle size of the BT powder is preferably 0.1 to 0.18 μm. If the average particle size of the BT powder is 0.1 μm or more, grain growth during sintering can be suppressed, so that there is an advantage that a dielectric loss can be reduced as well as an increase in relative dielectric constant.

  On the other hand, when the average particle size of the BT powder is 0.18 μm or less, it becomes easy to solidify additives such as vanadium and rare earth elements to the inside of the crystal particles, and as described later, before and after firing. There is an advantage that the ratio of grain growth from BT powder to crystal grains can be increased to a predetermined range.

_V 2 _{O 5} powder is an _additive, oxide powder of Y 2 _{O 3} powder, _Dy 2 _{O 3} powder, _Ho 2 _{O 3} powder and _Er 2 _{O 3} of at least one rare earth element of powder (RE), MgO Regarding the powder and MnCO ₃ powder, it is preferable to use those having an average particle diameter equal to or less than that of the BT powder.

Subsequently, 0.05 to 0.3 mol of V ₂ O ₅ powder, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, and Ho ₂ O ₃ are used for these raw material powders with respect to 100 mol of barium constituting the BT powder. 0.5 to 1.5 mol of oxide powder of one kind of rare earth element (RE) selected from powder and Er ₂ O ₃ powder, 0 to 0.1 mol of MgO powder and 0 to 0. MnCO ₃ powder. A ceramic slurry is prepared by adding a special organic vehicle to these raw material powders at a ratio of 5 moles, and then ceramic slurry is formed into a ceramic slurry using a sheet forming method such as a doctor blade method or a die coater method. Form. In this case, the thickness of the ceramic green sheet is preferably 1.5 to 4 μm from the viewpoint of reducing the thickness of the dielectric layer for increasing the capacity and maintaining high insulation.

  When producing the ceramic green sheet, glass powder may be added as a sintering aid as long as the desired dielectric properties can be maintained, and the amount added is the same as that of the main raw material powder BT powder. 0.5-2 mass parts is good when the total amount is 100 mass parts.

  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 preferably Ni or an alloy powder containing Ni as a main component.

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

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

  Next, after degreasing the capacitor body molded body, the capacitor body 1 is manufactured by firing in a reducing atmosphere. The firing temperature is preferably 1050 to 1130 ° C. because it controls the solid solution of the additive in the BT powder and the grain growth of the crystal grains.

  That is, in order to obtain the above-described dielectric ceramic, a fine grained BT powder is used, and a predetermined amount of the above-mentioned additive is added thereto, and the crystal grains after firing with respect to the average particle size of the BT powder before firing. Bake so that the average particle size of No. 11 is 1.5 times or more. By firing so that the particle size of the BT powder becomes 1.5 times or more after firing, vanadium and other additive components are dissolved in the crystal particles 11 as a whole. As a result, oxygen vacancies are formed inside the crystal particles 11. It is considered that the generation of defects such as these is suppressed and the number of carriers that carry charges is reduced.

  Thus, the solid solution amount of various additives such as vanadium and rare earth elements (RE) is increased with respect to the BT powder, and as a result, the dielectric ceramic forming the dielectric layer 5 has a tetragonal system in the X-ray diffraction chart. The diffraction intensity of the (004) plane showing barium titanate is larger than the diffraction intensity of the (400) plane showing cubic barium titanate, and the Curie temperature is in the range of 98 to 120 ° C. Furthermore, in the multilayer ceramic capacitor, the valence of titanium in the range of 10 to 50 nm from the interface between nickel, which is a conductor material for the internal electrode layer 7, and the crystal particles 11 toward the crystal particles 1 is 4 Can be priced.

  Next, an external electrode paste is applied to the end of the capacitor body 1 where the internal electrode layer 7 is exposed, and baking is performed to form the external electrode 3. Further, a plating film may be formed on the surface of the external electrode 3 in order to improve mountability.

First, as the raw material powder, BT powder, MgO powder, MnCO3 _powder, Y 2 _{O 3} powder, _Dy 2 _{O 3} powder, _Ho 2 _{O 3} powder, _Er 2 _{O 3} were prepared powders and _V 2 _{O 5} powder, these Various powders were mixed in the proportions shown in Table 1. MgO powder, MnCO _{3 powder,} Y 2 _{O 3} powder, _Dy 2 _{O 3} powder, _Ho 2 _{O 3} powder, _Er 2 _{O 3} addition amount of the powder and _V 2 _{O 5} powder are ratio BT powder 100 mol. These raw material powders having a purity of 99.9% were used. In addition, the average particle diameter and Curie temperature of BT powder were as shown in Table 1. MgO powder, MnCO ₃ powder, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder and V ₂ O ₅ powder having an average particle diameter of 0.1 μm were used. The Ba / Ti ratio of the BT powder was 1. As the sintering aid, glass powder having a composition of SiO ₂ = 55, BaO = 20, CaO = 15, and Li ₂ O = 10 (mol%) was used. The addition amount of the glass powder was 1 part by mass with respect to 100 parts by mass of the BT powder.

  Next, these raw material powders were wet mixed by adding a mixed solution of toluene and alcohol as a solvent using zirconia balls having a diameter of 2 mm.

  Next, a polyvinyl butyral resin and a mixed solvent of toluene and alcohol are added to the wet-mixed powder, and a wet-mixed ceramic slurry is prepared using zirconia balls having a diameter of 2 mm. Ceramic greens of various thicknesses are prepared by the doctor blade method. A sheet was produced.

  Next, a plurality of rectangular internal electrode patterns were formed on the upper surface of the ceramic green sheet. The conductor paste used for the internal electrode pattern was prepared by using nickel powder having an average particle size of 0.3 μm and adding 15 parts by mass of BT powder used for the ceramic green sheet as a co-material to 100 parts by mass of nickel powder. A thing was used.

Next, 360 ceramic green sheets on which internal electrode patterns were printed were laminated, and 20 ceramic green sheets on which the internal electrode patterns were not printed were laminated on the upper and lower surfaces, respectively, using a press machine at a temperature of 60 ° C. and pressure Lamination was performed under the conditions of 10 ⁷ Pa and time 10 minutes, and cut into predetermined dimensions to form a laminated molded body.

Next, the multilayer molded body was treated to remove the binder at 300 ° C. in the atmosphere, and then fired in hydrogen-nitrogen at 1110 to 1140 ° C. for 2 hours to produce a capacitor body. The size of the capacitor body was 0.95 × 0.48 × 0.48 mm ³ , the thickness of the dielectric layer was 2 μm, and the effective area of one internal electrode layer was 0.3 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, the fired capacitor body was barrel-polished, and then an external electrode paste containing Cu powder and glass was applied to both ends of the capacitor body and baked at 850 ° C. to form external electrodes. Thereafter, using an electrolytic barrel machine, Ni plating and Sn plating were sequentially performed on the surface of the external electrode to produce a multilayer ceramic capacitor.

  Next, the following evaluation was performed on these multilayer ceramic capacitors. In each evaluation, the number of samples was 10 and the average value was obtained. The relative dielectric constant was measured by measuring the capacitance under the measurement conditions of a temperature of 25 ° C., a frequency of 1.0 kHz, and a measurement voltage of 1 Vrms. Calculated based on the rate. The temperature characteristics were evaluated by measuring the capacitance in the temperature range of −55 to 125 ° C. The temperature showing the maximum capacitance in the measured temperature range was taken as the Curie temperature, and the presence or absence of an inflection point found around 125 ° C. in the curve of the temperature characteristics of the capacitance was also confirmed.

  The average particle size of the crystal particles in the dielectric layer is determined by polishing the fracture surface of the capacitor body after firing and then taking a picture of the internal structure of the dielectric layer using a scanning electron microscope. A circle containing 20 to 30 pieces was drawn, and crystal grains applied within and around the circle were selected. Next, the contour of each crystal particle was image-processed to determine the area of each particle, the diameter when replaced with a circle having the same area was calculated, and the average value was determined.

Next, a capacitor body was prepared by removing the external electrode from the produced multilayer ceramic capacitor. Next, the capacitor body was heat-treated in a hydrogen-nitrogen reducing atmosphere. The heat treatment was performed at a maximum temperature of 1200 ° C., a holding time of 2 hours, and an oxygen partial pressure of 10 ⁻¹⁰ to 10 ⁻¹³ atm.

  For the capacitor body heat-treated in a reducing atmosphere, the insulation resistance was first evaluated. When evaluating the insulation resistance, an electrode for measurement was formed by applying In—Ga to the end of the capacitor body where the internal electrode layer was exposed. The insulation resistance was measured at a measurement voltage of 0 to 10 V (DC), and the insulation resistance at 10 V was read.

Next, the capacitor body treated in a reducing atmosphere is cut into a predetermined size in a state where dielectric layers and internal electrode layers are alternately laminated, and then rough polishing is performed, and finally an ion using argon gas is used. A sample capable of TEM observation was prepared by milling. At this time, the ion-milled sample was in a state where nickel, which is a conductor material of the internal electrode layer, and crystal particles mainly composed of barium titanate were adjacent to each other. Next, the prepared sample was mounted in the TEM, and the place where the EELS analysis was performed was determined by looking at the TEM image. The place where EELS analysis was performed was in the range of 10 to 50 nm from the interface between nickel, which is a conductor material, and crystal particles toward the crystal particle side, and analysis was performed at intervals of 15 to 25 nm. In this case, the change in the number of electrons (valence) was examined from the EELS spectrum (TiL ₃ : (energy loss: 455 to 463 ev)) of titanium (Ti) contained in the crystal particles. As shown in FIG. 4A, when the rise of the K spectrum of oxygen (O) is 530 eV, if the peak indicated by the black arrow in FIG. 4B is 464 ± 0.1 eV, the Ti valence is 4 The Ti valence was determined to be smaller than the tetravalence if the peak was shifted to the low loss energy side. One EELS analysis was evaluated for each sample.

  In FIG. 3 EELS spectrum and sample no. The EELS spectrum for 15 is shown. These EELS spectra were measured in the range of 10 to 50 nm from the interface between the conductor material and the crystal particles toward the crystal particles. All of the EELS spectra evaluated for the multilayer ceramic capacitor of the present invention were sample Nos. 3 showed the same spectrum.

  The composition analysis of the obtained dielectric ceramic sample was performed by ICP (Inductively Coupled Plasma) analysis or 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. Here, in the ICP analysis of the dielectric ceramic, the case where each component was below the detection limit (0.5 μg / g or less) was defined as 0 mol.

  Table 1 shows the composition and firing temperature, and Table 2 shows the characteristics. In addition, it confirmed from the said composition analysis that the composition of the produced dielectric ceramic was the same as a preparation composition.

As is apparent from the results in Tables 1 and 2, the sample No. 2 to 4, 6 to 9, 12, 13, 16 to 20, 22, 25, and 26, the valence of Ti in the crystal grains obtained by EELS analysis is tetravalent, and the relative dielectric constant at room temperature (25 ° C.) The rate of change is not less than 3300 and the maximum change rate of capacitance in the temperature range of −55 to 125 ° C. based on room temperature (25 ° C.) satisfies ± 15% or less, and after heat treatment in a reducing atmosphere The insulation resistance was 2 × 10 ⁷ Ω or more.

In particular, sample No. 1 in which the components dissolved in barium titanate were substantially only vanadium and rare earth elements (RE) except for inevitable impurities. 2 to 4, 6 to 9, 12, 13, 16 to 19, 25 and 26, the relative dielectric constant at room temperature (25 ° C.) is 3500 or more and the insulation resistance after heat treatment in a reducing atmosphere is 2 × 10 ⁷ Ω. While maintaining the above, the maximum change rate of the capacitance in the temperature range of −55 to 125 ° C. based on room temperature (25 ° C.) was within ± 11%.

On the other hand, sample no. In 1, 5, 10, 11, 14, 15, 21, 23, 24, 27, and 28, the relative dielectric constant is lower than 3300, or a temperature of −55 to 125 ° C. based on room temperature (25 ° C.). The maximum change rate of the relative dielectric constant in the range did not satisfy within ± 15%, or the insulation resistance after the heat treatment in the reducing atmosphere was lower than 1 × 10 ⁷ Ω.

It is a cross-sectional schematic diagram which shows the example of the multilayer ceramic capacitor of this invention. 2 is a transmission electron micrograph of the vicinity of an interface between a dielectric layer and an internal electrode layer of a capacitor body. (A) is a reaction formula showing the generation of oxygen defects and surplus electrons in barium titanate (BaTiO ₃ ) when heat-treated in a reducing atmosphere. (B) is a reaction formula showing a state in which electrons generated by reduction are doped in barium titanate. (A) is an EELS spectrum of barium titanate (BaTiO ₃ ), and (b) is an enlarged portion of Ti L _{2,3 in} the spectrum of (a). Sample No., which is an example of a multilayer ceramic capacitor. 3 shows an X-ray diffraction chart for the dielectric ceramic of No. 3, and (b) shows a sample No. 1 which is a multilayer ceramic capacitor of a comparative example. 16 is an X-ray diffraction chart of 15 dielectric ceramics. Sample No. in the examples. 3 and sample no. It is a graph which shows the temperature characteristic of the electrostatic capacitance of 15. Sample No. in the examples. 3 (solid line) and sample no. 15 (broken line) EELS spectrum.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer 11 Crystal particle

Claims (2)

Capacitor body in which dielectric layers made of dielectric ceramics having crystal grains mainly composed of barium titanate and having a thickness of 1 to 3 μm and internal electrode layers made of nickel as a conductive material are alternately laminated, and the capacitor body A multilayer ceramic capacitor composed of an external electrode provided at an exposed end of the internal electrode layer,
The dielectric ceramic is one kind selected from 0.05 to 0.3 mol of vanadium in terms of V ₂ O ₅ and yttrium, dysprosium, holmium and erbium with respect to 100 mol of barium constituting the barium titanate. The rare earth element (RE) contains 0.5 to 1.5 mol in terms of RE ₂ O ₃ , magnesium contains 0 to 0.1 mol in terms of MgO, and manganese contains 0 to 0.5 mol in terms of MnO. X-ray In the diffraction chart, the diffraction intensity of the (004) plane showing the tetragonal barium titanate is larger than the diffraction intensity of the (400) plane showing the cubic barium titanate,
The crystal particles have an average particle size of 0.15 to 0.4 μm ,
EELS analysis was performed on the polished surface obtained by polishing a part of the capacitor body after heat-treating the capacitor body with oxygen partial pressure of 10 ⁻⁸ to 10 ⁻¹⁶ atmosphere at 1200 ° C. for 2 hours. A monolithic ceramic capacitor characterized in that the valence of titanium in the range of 10 to 50 nm from the interface between the conductor material and the crystal particles toward the crystal particles is tetravalent.   2. The multilayer ceramic capacitor according to claim 1, wherein the components dissolved in the barium titanate are substantially only vanadium and a rare earth element (RE).