JP2008081351A - Dielectric ceramics, multilayer ceramic capacitor, and manufacturing method thereof - Google Patents

Abstract

Disclosed is a dielectric ceramic for a multilayer ceramic capacitor, which satisfies the B characteristic and the X7R characteristic of the temperature characteristic of the capacitance, and has excellent reliability even when it is thinned.
SOLUTION: It consists of barium titanate, a rare earth oxide composed of at least one of Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, calcium oxide and silicon oxide. Dielectric ceramics, wherein the barium titanate, rare earth oxide, calcium oxide, silicon oxide and zirconium oxide are Ba _m TiO ₃ , RO _3/2 (where R is a rare earth element), CaO, SiO ₂ and ZrO, respectively. ₂ and containing 100 moles of Ba _m TiO ₃ , RO _3/2 contains a mole, CaO contains b mole, SiO ₂ contains c mole and dZrO ₂ contains d mole, and m, a, b, c and d Satisfy the relationships 0.990 ≦ m ≦ 1.030, 0.5 ≦ a ≦ 30, 0.1 ≦ b ≦ 30, 0.5 ≦ c ≦ 30, and 0.075 ≦ d ≦ 0.38, respectively. Dielectric ceramics characterized by that.
[Selection] Figure 1

Description

  The present invention relates to a dielectric ceramic and a multilayer ceramic capacitor using the dielectric ceramic.

  Conventionally, a multilayer ceramic capacitor is generally manufactured as follows.

First, a sheet-like dielectric material is prepared by applying an electrode material to be an internal electrode on its surface. As the dielectric material, for example, a material mainly composed of BaTiO ₃ is used.

  Next, a dielectric material having an internal electrode is obtained by laminating and thermocompression bonding the sheet-like dielectric material coated with this electrode material, and firing the integrated material.

  A multilayer ceramic capacitor can be obtained by baking an external electrode electrically connected to the internal electrode on the end face of the dielectric ceramic.

  In addition, noble metals such as platinum, gold, palladium, and silver-palladium alloys that are not oxidized even when fired at the same time as the dielectric material have been used as the internal electrode material.

  However, while these electrode materials have excellent characteristics, they are extremely expensive, which has been a major factor in increasing the manufacturing cost of multilayer ceramic capacitors.

  Therefore, relatively inexpensive base metals such as nickel and copper have come to be used as internal electrode materials, but these base metals are easily oxidized in a high-temperature oxidizing atmosphere and do not function as electrodes. In order to use it as an internal electrode, it is necessary to fire in a neutral or reducing atmosphere together with a dielectric ceramic layer.

  However, when firing in such a neutral or reducing atmosphere, the dielectric ceramic layer is reduced to become a semiconductor.

  In order to overcome this disadvantage, in the barium titanate solid solution, dielectric ceramics (see, for example, Patent Document 1) in which the ratio of barium site / titanium site exceeds the stoichiometric ratio, or La barium titanate solid solution is La. Dielectric ceramics to which rare earth oxides such as Nd, Sm, Dy, and Y are added have been proposed (see, for example, Patent Document 2).

Further, examples of methods that reduce the change in dielectric constant with temperature include, for example, the BaTiO ₃ —CaZrO ₃ —MnO—MgO system disclosed in Japanese Patent Laid-Open No. Sho 62-256422 and the BaTiO ₃ — shown in Japanese Patent Publication No. Sho 61-14611. (Mg, Zn, Sr, Ca) O—B ₂ O ₃ —SiO ₂ dielectric ceramics have been proposed.

  With such a dielectric ceramic, a dielectric ceramic that does not become a semiconductor even when fired in a reducing atmosphere can be obtained, and a multilayer ceramic capacitor using a base metal such as nickel as an internal electrode can be manufactured.

  However, with the recent development of electronics, miniaturization of electronic components has rapidly progressed, and the tendency of miniaturization and increase in capacity of multilayer ceramic capacitors has become remarkable. For this reason, there is a growing demand for dielectric ceramics that have a high dielectric constant, a small change in temperature of the dielectric constant, and have high insulation properties and excellent reliability even in a thin layer.

  However, since conventional dielectric ceramics are designed on the assumption that they are used under a low electric field strength, when they are used in a thin layer, that is, under a high electric field strength, the insulation resistance value, the dielectric strength and the reliability are extremely low. It had the problem of decreasing.

  For this reason, in the conventional dielectric ceramics, when the ceramic dielectric layer is thinned, it is necessary to lower the rated voltage according to the degree of thinning.

  Specifically, although the dielectric ceramics shown in Patent Document 1 and Patent Document 2 can obtain a large dielectric constant, the crystal grains of the obtained ceramic are large, and the thickness of the dielectric ceramic layer in the multilayer ceramic capacitor is 10 μm. When the following thin film is formed, the number of crystal grains present in one layer is reduced, and there is a disadvantage that the insulation reliability is lowered.

In addition, there is a problem that the temperature change of the dielectric constant is large, and it cannot be said that it can sufficiently meet market demand.

In addition, the dielectric ceramic proposed in Patent Document 3 has a relatively high dielectric constant, small crystal grains of the obtained ceramic laminate, and small change in temperature of the dielectric constant, but it is generated in the CaZrO ₃ or firing process. Since CaTiO ₃ that easily forms a secondary phase together with MnO or the like, there was a problem in reliability at a high temperature particularly when the layer was thinned.

  In addition, the dielectric ceramic proposed in Patent Document 4 does not satisfy the X7R characteristic defined by the EIA standard, that is, the rate of change in capacitance is within ± 15% within the temperature range of −55 to + 125 ° C. There was a problem.

In order to solve the above problems, a BaTiO ₃ —R ₂ O ₃ —Co ₂ O ₃ composition (where R is a rare earth element) has been proposed (see, for example, Patent Documents 5, 6, and 7). .

_{Furthermore, BaTiO 3 -R 2 O 3 -CaO} -SiO 2 based composition (wherein, R is a rare earth element) has been proposed (e.g., see Patent Document 8.).
Japanese Examined Patent Publication No. 57-42588 Japanese Patent Laid-Open No. 61-101458 Kaisho 62-256422 Japanese Patent Publication No. 61-14611 Japanese Patent Laid-Open No. 5-9066 Japanese Patent Laid-Open No. 5-9067 Japanese Patent Laid-Open No. 5-9068 JP 2001-143955 A

  However, the compositions described in Patent Documents 5 to 7 have a problem that the demands of the market cannot be sufficiently satisfied in terms of reliability when the dielectric ceramic layer is thinned.

  Further, the composition described in Patent Document 6 does not satisfy the X7R characteristic when the thickness of the dielectric ceramic layer interposed between the internal electrodes is reduced to 2 μm.

  In particular, the insulation resistance has a problem that the rate of decrease in the insulation resistance value under high temperature and high voltage after 100 hours is large and the insulation resistance value cannot be maintained for a long time.

  Therefore, an object of the present invention is to satisfy the B characteristic defined by the JIS standard and the X7R characteristic defined by the EIA standard, the dielectric loss is as small as 2.5% or less, and the temperature characteristic of the capacitance is high under high temperature and high voltage. An object of the present invention is to provide a dielectric ceramic that is capable of constituting a dielectric ceramic layer of a multilayer ceramic capacitor that has excellent reliability even when it is thinned because it has a small decrease in insulation resistance in an accelerated test and has a long life. .

  Another object of the present invention is to provide a multilayer ceramic capacitor in which such a dielectric ceramic is used as a dielectric ceramic layer and an internal electrode is composed of a base metal.

The dielectric ceramic of the present invention includes barium titanate, a rare earth oxide composed of at least one of Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, calcium oxide, and oxidation. A dielectric ceramic comprising silicon, wherein the barium titanate, rare earth oxide, calcium oxide, silicon oxide and zirconium oxide are Ba _m TiO ₃ , RO _3/2 (where R is a rare earth element), CaO, When expressed in terms of SiO ₂ and ZrO ₂ , 100 mol of Ba _m TiO ₃ contains a mol of RO _3/2 , b mol of CaO, c mol of SiO ₂ and d mol of ZrO ₂ , m, a, b, c and d are respectively
0.990 ≦ m ≦ 1.030
0.5 ≦ a ≦ 30
0.1 ≦ b ≦ 30
0.5 ≦ c ≦ 30
0.075 ≦ d ≦ 0.38
It is characterized by satisfying the relationship.

Further, as a sintering aid, an oxide containing at least one of B element and Si element as a main component is contained in an amount of 2 to 15 parts by mass with respect to 100 parts by mass of Ba _m TiO ₃ . It is preferable.

Further, it is preferable that a compound containing an Mn element is contained as an auxiliary component in an amount of 0.1 to 5.0 mol with respect to 100 mol of the Ba _m TiO ₃ in terms of MnO.

Further, as a subcomponent, a compound containing at least one kind X of Ba, Ca and Sr elements and at least one kind Y among Zr and Hf elements is converted into XYO ₃ , and the above Ba _m TiO ₃ 100 mol. It is preferable to contain 0.1-0.2 mol with respect to.

  The ceramic capacitor of the present invention is a multilayer ceramic capacitor comprising a plurality of dielectric ceramic layers, an internal electrode formed between the dielectric ceramic layers, and an external electrode electrically connected to the internal electrode. The dielectric ceramic layer is made of the dielectric ceramic according to any one of claims 1 to 4, and the internal electrode is made of a base metal as a main component.

  The dielectric ceramic layer includes BT crystal particles, the BT crystal particles include Zr, and the Zr concentration in the BT crystal particles is highest near the surface of the BT crystal particles, toward the BT crystal particle center. It is preferred to have a decreasing concentration gradient.

  The method for producing a multilayer ceramic capacitor of the present invention comprises a powder obtained by coating a surface of a barium titanate powder with zirconia oxide, and at least one of Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb. A step of preparing a dielectric green sheet containing one kind of rare earth oxide powder, calcium oxide powder and silicon oxide powder, and a step of forming an internal electrode pattern containing base metal powder on the surface of the dielectric green sheet A plurality of dielectric green sheets on which the internal electrode patterns are formed, and a capacitor body molded body in which internal electrode patterns are alternately exposed in the stacking direction on opposite end faces; and And a step of firing.

  The method for producing a multilayer ceramic capacitor according to the present invention includes: Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb on the surface of a barium titanate powder coated with zirconia oxide. A step of preparing a dielectric green sheet comprising a powder coated with a rare earth oxide comprising at least one of the following, a calcium oxide powder, and a silicon oxide powder; and an internal electrode comprising a base metal powder on the surface of the dielectric green sheet A step of forming a pattern, a step of laminating a plurality of dielectric green sheets on which the internal electrode pattern is formed, and a step of producing a capacitor body molded body in which internal electrode patterns are alternately exposed in the laminating direction on opposite end surfaces; And firing the capacitor body molded body.

The dielectric ceramic of the present invention includes barium titanate, a rare earth oxide composed of at least one of Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, calcium oxide, and oxidation. A dielectric ceramic comprising silicon, wherein the barium titanate, rare earth oxide, calcium oxide, silicon oxide and zirconium oxide are Ba _m TiO ₃ , RO _3/2 (where R is a rare earth element), CaO, Expressed as SiO ₂ and ZrO ₂ , with respect to 100 moles of Ba _m TiO ₃ , RO _3/2 contains a mole, CaO contains b mole, SiO ₂ contains c mole and dZrO ₂ contains d mole, m, a, b , C and d are respectively
0.990 ≦ m ≦ 1.030
0.5 ≦ a ≦ 30
0.1 ≦ b ≦ 30
0.5 ≦ c ≦ 30
0.075 ≦ d ≦ 0.38
By satisfying this relationship, the temperature characteristic of the capacitance satisfies the B characteristic specified by the JIS standard and the X7R characteristic specified by the EIA standard, and has a flat temperature characteristic. The multilayer ceramic capacitor can be used in any electronic device used in a place where the temperature changes greatly.

In addition, the dielectric ceramic of the present invention has a dielectric loss as small as 2.5% or less, and the product (CR product) of insulation resistance (R) and capacitance (C) when 4 kVDC / mm is applied at room temperature is 10,000 Ω · By containing zirconium oxide that is F or more, in particular, the accelerated life of the insulation resistance under a high temperature and high voltage is long, so that it is excellent in reliability even if it is thinned.

  Therefore, it is possible to reduce the size and increase the capacity of the capacitor by reducing the thickness of the dielectric ceramic, and it is not necessary to reduce the rated voltage of the capacitor even if the thickness is reduced.

That is, it is possible to obtain a small and large capacity monolithic ceramic capacitor in which the thickness of the dielectric layer is reduced to, for example, 2 μm or less.

  By using a powder in which the surface of the barium titanate powder is coated with zirconia oxide, a multilayer ceramic capacitor is manufactured, so that the surface of the BT crystal particles in the dielectric ceramic layer of the manufactured multilayer ceramic capacitor has a high concentration of zirconia. A solid solution phase can be formed, whereby the insulating properties of the surfaces of the BT crystal particles having poor insulating properties are increased, and deterioration of insulating properties can be suppressed even under high temperature and high voltage.

  Also, since the diffusion of zirconia can be suppressed by producing a multilayer ceramic capacitor using a powder in which the surface of the barium titanate powder is coated with zirconia oxide and the surface of the powder is coated with rare earth oxide, the produced multilayer ceramic A zirconia solid solution phase can be more stably formed at a high concentration on the surface of the BT crystal particles in the dielectric ceramic layer of the capacitor, thereby increasing the insulation of the surface of the BT crystal particles having poor insulation, Insulation deterioration can be further suppressed even under high temperature and high voltage.

  A structure of a multilayer ceramic capacitor according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing an example of a multilayer ceramic capacitor.

  As shown in FIG. 1, the multilayer ceramic capacitor 1 according to the present embodiment includes a rectangular parallelepiped ceramic multilayer body 3 obtained by laminating a plurality of dielectric ceramic layers 2 via internal electrodes 4.

  External electrodes 5 are respectively formed on both end faces of the ceramic laminate 3 so as to be electrically connected to specific ones of the internal electrodes 4, and a first plating such as nickel or copper is formed thereon. A layer 6 is formed, and a second plating layer 7 such as solder or tin is further formed thereon. And, the dielectric ceramic layer of the present invention, barium titanate, and a rare earth oxide composed of at least one of Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, It is composed of a composite oxide composed of calcium oxide and silicon oxide.

And this barium titanate, rare earth oxide, calcium oxide, silicon oxide and zirconium oxide are represented by Ba _m TiO ₃ , RO _3/2 (where R is a rare earth element), CaO, SiO ₂ and ZrO ₂ , respectively. 100 mol of Ba _m TiO ₃ contains a mol of RO _3/2 , b mol of CaO, c mol of SiO ₂ and d mol of dZrO ₂ , and m, a, b, c and d are each in a range of 0. It is important to satisfy the following relationships: 990 ≦ m ≦ 1.030, 0.5 ≦ a ≦ 30, 0.1 ≦ b ≦ 30, 0.5 ≦ c ≦ 30, 0.075 ≦ d ≦ 0.38 is there.

Further, the dielectric ceramic contains an oxide containing at least one of B element and Si element as a main component in an amount of 2 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the Ba _m TiO _3. Thus, the CR product can be increased by making the dielectric ceramic more dense.

Furthermore, the dielectric ceramic is fired in a reducing atmosphere by containing a compound containing Mn element in terms of MnO in an amount of 0.1 to 5.0 mol with respect to 100 mol of Ba _m TiO _3. Even so, deterioration of the characteristics can be further suppressed. In addition, there exist Zn, Ni, Co, and Cu as an element which has the same effect.

Further, in the dielectric ceramic, a compound containing at least one type X of Ba, Ca and Sr elements and at least one type Y of Zr and Hf elements is converted to XYO ₃ , and the Ba _m TiO ₃ By containing 0.1 to 0.2 mol with respect to 100 mol, the accelerated life of the insulation resistance under high temperature and high voltage is extended.

  By using such a dielectric ceramic as a dielectric ceramic layer, the temperature characteristics of the capacitance are not affected by the JIS standard B characteristics and EIA standards without deterioration of the characteristics even when fired in a reducing atmosphere. Satisfy specified X7R characteristics, dielectric loss is as small as 2.5% or less, and product (CR product) of insulation resistance (R) and capacitance (C) when 4kVDC / mm is applied at room temperature is 10000Ω · F or more Thus, since the accelerated life under a high temperature and high voltage is long, it is possible to obtain a multilayer ceramic capacitor having excellent reliability even if the layer is thinned.

  Further, as the internal electrode of the multilayer ceramic capacitor, a base metal such as nickel, nickel alloy, copper, or copper alloy can be appropriately used.

  Moreover, in order to prevent structural defects, a small amount of ceramic powder can be added to these internal electrode materials.

The external electrode may be a sintered layer of various conductive metal powders such as silver, palladium, silver-palladium, copper, and copper alloy, or the conductive metal powder and B ₂ O ₃ —Li ₂ O—SiO ₂ —. It is composed of a sintered layer containing various glass frit such as BaO, B ₂ O ₃ —SiO ₂ —BaO, Li ₂ O—SiO ₂ —BaO, and B ₂ O ₃ —SiO ₂ —ZnO. be able to.

  Furthermore, a plated layer of nickel, copper, or the like is formed on the external electrode made of these sintered layers, but this plated layer may be omitted depending on the application.

  The average particle diameter of the coating BT is not particularly limited, but is preferably 0.1 to 0.4 μm when the dielectric thickness is 1 to 3 μm.

  By using a powder in which the surface of the barium titanate powder is coated with zirconia oxide, a multilayer ceramic capacitor is manufactured, so that the surface of the BT crystal particles in the dielectric ceramic layer of the manufactured multilayer ceramic capacitor has a high concentration of zirconia. A solid solution phase can be formed, whereby the insulating properties of the surfaces of the BT crystal particles having poor insulating properties are increased, and deterioration of insulating properties can be suppressed even under high temperature and high voltage.

  Also, since the diffusion of zirconia can be suppressed by producing a multilayer ceramic capacitor using a powder in which the surface of the barium titanate powder is coated with zirconia oxide and the surface of the powder is coated with rare earth oxide, the produced multilayer ceramic A more stable solid solution phase of zirconia can be formed at a high concentration on the surface of the BT crystal particles in the dielectric ceramic layer of the capacitor, thereby increasing the insulation of the surface of the BT crystal particles having poor insulation, Insulation deterioration can be further suppressed even under high temperature and high voltage.

(Example 1) First, TiCl ₄ and Ba (NO 3) ₂ were prepared as starting materials, weighed to obtain an aqueous solution, oxalic acid was added, and titanyl barium oxalate {BaTiO (C ₂ O ₄ ) · 4H ₂ O} was precipitated.

Then, the precipitate was decomposed under heat at 1000 ° C. or higher, as the main component material to synthesize barium titanate (BaTiO _3).

Moreover, as rare earth oxides (RO _3/2 ), Y ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , CaO and ZrO ₂ were prepared as calcium oxide and coated on the surface of barium titanate (BaTiO ₃ ). The coating is Y ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O as a rare earth oxide (RO _3/2 ). ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , CaO and ZrO ₂ metal salts and alkali salts as calcium oxide were dropped into the barium titanate suspension and deposited on the barium titanate surface. However, the coating method is not limited to the coprecipitation method, and other methods such as a solid phase method and a sol-gel method may be used.

  Furthermore, MgO was prepared as magnesium oxide.

Subsequently, these raw material powders were blended so as to have the composition shown in Table 1 (excluding the SiO ₂ component) and pulverized to a maximum particle size of 1 μm or less.

Next, SiO ₂ was prepared as silicon oxide, and weighed so as to obtain the composition shown in Table 1 together with the previously calcined product, to obtain a blend.

As an example of an oxide containing B element as a main component as a sintering aid, 0.55B ₂ O ₃ -0.25Al ₂ O ₃ -0.03MnO-0.17BaO (however, the coefficient is a molar ratio, Hereinafter, the oxides, carbonates or hydroxides of the respective components were weighed, mixed and ground, and then evaporated to dryness to obtain a powder.

  This powder was heated and melted at 1300 ° C. in an alumina crucible, and then rapidly cooled and pulverized to obtain an oxide glass powder as a sintering aid having an average particle size of 1 μm or less.

  Thereafter, a polyvinyl butyral binder and an organic solvent such as ethanol were added to this blend and wet mixed by a ball mill to prepare a ceramic slurry.

The ceramic slurry was formed into a sheet by a doctor blade method to obtain a green sheet.

  Next, a conductive paste mainly composed of nickel was screen-printed on the ceramic green sheet to form a conductive paste layer for constituting internal electrodes. Thereafter, a plurality of ceramic green sheets on which the conductive paste layer was formed were stacked so that the side from which the conductive paste layer was drawn was alternated to obtain a stacked body.

Then, the resulting laminate was heated at a temperature of 350 ° C. in a _{N 2} atmosphere, after burning a binder, the oxygen partial pressure ^{_{10 -9 ~10 -12 MPa H 2 -N}} 2 -H 2 O The ceramic sintered body was obtained by firing at a temperature shown in Table 2 for 2 hours in a reducing atmosphere composed of gas.

Next, a silver paste containing B ₂ O ₃ —Li ₂ O—SiO ₂ —BaO-based glass frit is applied to both end faces of the obtained sintered body, and baked at a temperature of 600 ° C. in an N ₂ atmosphere. An external electrode electrically connected to the internal electrode was formed.

  The outer dimensions of the multilayer capacitor obtained as described above are 1.6 mm in width, 3.2 mm in length, and 1.2 mm in thickness. The thickness of the dielectric ceramic layer interposed between the internal electrodes is 5 μm. It was.

The total number of effective dielectric ceramic layers was 100, and the counter electrode area per layer was 2.1 mm ² .

Next, the electrical characteristics of the obtained multilayer ceramic capacitor were measured. That is, the capacitance (C) and the dielectric loss (tan δ) were measured at a frequency of 1 kHz, 1 Vrms, and a temperature of 25 ° C., and the relative dielectric constant (ε _r ) was calculated from the capacitance.

  Next, at a temperature of 25 ° C., a 20V DC voltage was applied for 2 minutes to measure the insulation resistance under an electric field strength of 4 kV / mm, and the product of capacitance (C) and insulation resistance (R), The CR product was determined.

Moreover, the change rate of the electrostatic capacitance with respect to the temperature change was measured. Regarding the temperature change rate of the capacitance, the change rate (ΔC / C ₂₀ ) from −25 ° C. to 85 ° C. based on the capacitance at ₂₀ ° C. and the capacitance at 25 ° C. as a reference. percent change from -55 ° C. to 125 ° C. and (ΔC _{/ C 25)} was obtained.

  Further, as a high temperature load life test, 36 samples were applied at a temperature of 150 ° C. and a DC voltage of 100 V was applied so that the electric field strength was 20 kV / mm, and the change over time in the insulation resistance was measured.

  And about each sample, the time when insulation resistance value (R) became 200 kohm or less was made into lifetime, and the average lifetime was calculated | required. The change in the insulation resistance value was measured after 100 hours when DC 100 V was applied to the capacitor sample.

The results are shown in Table 1. In Table 1, the sample number marked with * is outside the scope of the present invention, and the others are within the scope of the present invention.

  According to Table 2, in the dielectric ceramics within the scope of the present invention, the temperature characteristics of the capacitance satisfy the B characteristic defined by the JIS standard and the X7R characteristic defined by the EIA standard, and the dielectric loss is 2.5. %, The product (CR product) of insulation resistance (R) and capacitance (C) when applied at 4 kVDC / mm at room temperature is 10000Ω · F or more, and the rate of change in resistance is 100% after 100 hours. Is obtained (54% or less) monolithic ceramic capacitor.

  The concentration distribution of the Zr component in the BT crystal particles was measured using a transmission electron microscope apparatus equipped with an elemental analysis instrument. As a sample, a multilayer ceramic capacitor whose cross section was cut and the sample was further subjected to FIB processing to obtain a thin piece was used. In the transmission electron microscope, a BT crystal constituting the dielectric layer was selected so that the entire particle could be clearly seen. For such BT crystal particles, elemental analysis was performed by applying EDS at intervals of about 10 nm from the grain boundary side to the center of the BT crystal particles. EDS specified the Ba, Ti, Mg, Mn, Y, and Zr components contained in the dielectric layer and determined the Zr amount relative to the total amount. The measurement was performed on five BT crystal particles in one sample, and an averaged result was obtained.

  As a result, the Zr concentration in the BT crystal particles of the sample of the present invention was the highest near the surface of the BT crystal particles, and the concentration gradient decreased from the highest Zr concentration toward the BT crystal particle center. In addition, when the position where the Zr concentration becomes maximum in the BT crystal is within 10% of the radius of the BT crystal particle from the surface of the BT crystal particle, the Zr concentration becomes maximum near the particle surface.

  Next, the reasons for limiting the composition are shown below.

The reason _why RO _3/2 amount a is limited to 0.5 ≦ a ≦ 30 is that, as in sample number 1, when a <0.5, the rate of change in capacitance with temperature changes the B characteristic and X7R characteristic. This is because the high temperature load life is shortened as it is detached, and when a> 30 as in sample number 17, the firing temperature becomes high and the high temperature load life is shortened.

  The reason why the CaO amount b is limited to 0.1 ≦ b ≦ 30 is as shown in Sample No. 3, and when b <0.1, the high temperature load life is shortened. In the case of> 30, the sinterability is lowered and the high temperature load life is shortened.

The reason why SiO ₂ amount c is limited to 0.5 ≦ a ≦ 30 is that, as in sample number 5, when c <0.5, the sinterability is reduced and the high temperature load life is shortened. This is because, in the case of c> 30 as in number 6, as in sample number 6, the temperature change rate of the capacitance deviates from the B characteristic and the X7R characteristic and the high temperature load life is shortened.

The amount of ZrO ₂ is limited to 0.075 ≦ d ≦ 0.38 because the high temperature load life is shortened when d <0.075, and the electrostatic capacity when d> 0.38. This is because the rate of change in temperature deviates from the B characteristic and the X7R characteristic.

  Further, as apparent from comparison between Sample No. 13 and Sample No. 40, the dielectric ceramic composition of the present invention that does not contain MgO has superior high temperature load life characteristics as compared with the case of containing MgO. It will be a thing.

It is sectional drawing which shows the multilayer ceramic capacitor by one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Multilayer ceramic capacitor 2 ... Dielectric ceramic layer 3 ... Ceramic laminated body 4 ... Internal electrode 5 ... External electrode 6, 7 ... Plating layer

Claims (8)

A dielectric ceramic comprising barium titanate, a rare earth oxide composed of at least one of Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, calcium oxide, and silicon oxide. The barium titanate, rare earth oxide, calcium oxide, silicon oxide and zirconium oxide were expressed by Ba _m TiO ₃ , RO _3/2 (where R is a rare earth element), CaO, SiO ₂ and ZrO ₂ , respectively. When, relative to 100 moles of Ba _m TiO ₃ , RO _3/2 contains a mole, CaO contains b mole, SiO ₂ contains c mole and ZrO ₂ contains d mole, and m, a, b, c and d are respectively
0.990 ≦ m ≦ 1.030
0.5 ≦ a ≦ 30
0.1 ≦ b ≦ 30
0.5 ≦ c ≦ 30
0.075 ≦ d ≦ 0.38
Dielectric ceramics characterized by satisfying the above relationship. Further, as a sintering aid, an oxide containing at least one of B element and Si element as a main component is contained in an amount of 2 to 15 parts by mass with respect to 100 parts by mass of Ba _m TiO ₃ . The dielectric ceramic according to claim 1. Furthermore, as a subcomponent, the compound containing Mn element is contained in an amount of 0.1 to 5.0 mol in terms of MnO with respect to 100 mol of Ba _m TiO _3. 2. The dielectric ceramic according to 2. Further, as a subcomponent, a compound containing at least one kind X of Ba, Ca and Sr elements and at least one kind Y among Zr and Hf elements is converted into XYO ₃ , and the above Ba _m TiO ₃ 100 mol. The dielectric ceramic according to claim 1, wherein the dielectric ceramic is contained in an amount of 0.1 to 0.2 mol. In a multilayer ceramic capacitor comprising a plurality of dielectric ceramic layers, an internal electrode formed between the dielectric ceramic layers, and an external electrode electrically connected to the internal electrode, the dielectric ceramic layer is the claim. A multilayer ceramic capacitor comprising the dielectric ceramic according to any one of Items 1 to 4, wherein the internal electrode is composed mainly of a base metal. The dielectric ceramic layer includes BT crystal particles, the BT crystal particles include Zr, and the Zr concentration in the BT crystal particles is highest near the surface of the BT crystal particles, toward the BT crystal particle center. The multilayer ceramic capacitor of claim 5, wherein the multilayer ceramic capacitor has a decreasing concentration gradient. A powder of barium titanate powder coated with zirconia oxide; a rare earth oxide powder comprising at least one of Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb; and oxidation A step of preparing a dielectric green sheet containing calcium powder and silicon oxide powder, a step of forming an internal electrode pattern containing a base metal powder on the surface of the dielectric green sheet, and a dielectric formed with the internal electrode pattern Characterized in that it comprises a step of producing a capacitor body molded body in which a plurality of green sheets are laminated, and internal electrode patterns are alternately exposed in the laminating direction on opposite end surfaces, and a step of firing the capacitor body molded body. To manufacture multilayer ceramic capacitors. The surface of the barium titanate powder coated with zirconia oxide is coated with a rare earth oxide composed of at least one of Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb. A step of preparing a dielectric green sheet containing the prepared powder, a calcium oxide powder, and a silicon oxide powder, a step of forming an internal electrode pattern including a base metal powder on the surface of the dielectric green sheet, and the internal electrode pattern A plurality of dielectric green sheets formed with a capacitor body, and a step of producing a capacitor body molded body in which internal electrode patterns are alternately exposed in the stacking direction on opposite end faces; and a step of firing the capacitor body molded body A method for producing a multilayer ceramic capacitor, characterized in that:

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