JP5106626B2 - Multilayer ceramic capacitor - Google Patents

Description

  The present invention relates to a multilayer ceramic capacitor, and more particularly to a small-sized, high-capacity multilayer ceramic capacitor having a dielectric ceramic layer composed of barium titanate as a main component.

  In recent years, with the widespread use of mobile devices such as mobile phones and the high speed and high frequency of semiconductor devices, which are the main components of personal computers and the like, multilayer ceramic capacitors mounted on such electronic devices are required to be smaller and have higher capacities. The dielectric layer constituting the multilayer ceramic capacitor is required to be thin and highly multilayered.

  By the way, as a dielectric porcelain serving as a dielectric layer constituting a multilayer ceramic capacitor, a dielectric material having barium titanate as a main component has been conventionally used. However, in recent years, barium titanate powder has been made of magnesium. Dielectrics composed of so-called core-shell structure crystal particles in which magnesium or rare earth elements are dissolved in the vicinity of the surface of the crystal particles mainly composed of barium titanate by adding oxide powder of rare earth elements Porcelain has been developed and put into practical use as a multilayer ceramic capacitor.

  Here, the core-shell structure of the crystal particle refers to a structure in which the core part which is the center part of the crystal particle and the shell part which is the outer shell part form physically and chemically different phases. That is, in the crystal particles mainly composed of barium titanate, the core portion is occupied by a tetragonal crystal phase, while the shell portion is occupied by a cubic crystal phase.

A multilayer ceramic capacitor using a dielectric ceramic layer composed of such core-shell crystal grains as a dielectric layer is improved in relative dielectric constant and temperature characteristics of relative dielectric constant as X7R (based on 25 ° C.). The temperature change rate of the relative permittivity is within ± 15% at −55 to 125 ° C.), and the change in the relative permittivity when the applied AC voltage is increased is small. ing. However, when the thickness of the dielectric is reduced to, for example, about 2 μm, there is a problem that the life characteristics in the high temperature load test are greatly deteriorated.
JP 2001-220224 A

  The main objects of the present invention are excellent in stability of temperature characteristics of high dielectric constant and relative dielectric constant, small increase of relative dielectric constant when AC voltage is increased, and excellent life characteristics in high temperature load test. Another object of the present invention is to provide a multilayer ceramic capacitor having a dielectric layer.

The multilayer ceramic capacitor of the present invention is composed of (i) crystal particles mainly composed of barium titanate, and at least one selected from calcium, magnesium, vanadium, manganese, terbium, and yttrium, dysprosium, holmium, and erbium. It is formed by alternately laminating dielectric layers made of dielectric porcelain containing a rare earth element (RE) and (ii) internal electrode layers. In the dielectric ceramic, the vanadium is 0.02 to 0.2 mol in terms of V ₂ O _{5 and the} magnesium is 0.2 to 0.00 in terms of MgO with respect to 100 mol of titanium constituting the barium titanate. 8 mol, 0.1 to 0.5 mol of manganese in terms of MnO, 0.3 to 0.8 mol of rare earth element (RE) in terms of RE ₂ O ₃ , and terbium in terms of Tb ₄ O ₇ While containing 0.02 to 0.2 mol, the concentration of calcium in the crystal particles is 0.4 atomic% or more. In the X-ray diffraction chart of the dielectric ceramic, the diffraction intensity of the (200) plane showing cubic barium titanate is larger than the diffraction intensity of the (002) plane showing tetragonal barium titanate, And Curie temperature is 90-100 degreeC.

In particular, the dielectric porcelain is 0.02 to 0.08 mol in terms of V ₂ O ₅ and 0.3 to 0.3 mg in terms of MgO with respect to 100 mol of titanium constituting the barium titanate. 0.6 mol, the manganese is 0.2 to 0.4 mol in terms of MnO, and at least one rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium is 0 in terms of RE ₂ O ₃ It is desirable to contain 0.4 to 0.6 mol and 0.02 to 0.08 mol of terbium in terms of Tb ₄ O ₇ .

  Furthermore, the average crystal grain size of the crystal grains constituting the dielectric ceramic is preferably 0.22 to 0.28 μm. Alternatively, the average crystal grain size of the crystal particles is preferably 0.13 to 0.19 μm.

  According to the present invention, the temperature change rate of the dielectric constant can be reduced with a high dielectric constant, and the increase in the relative dielectric constant when the applied AC voltage is increased is small (the relative dielectric constant has an AC voltage dependency). Small) and a multilayer ceramic capacitor having a dielectric layer having a long life in a high-temperature load test can be obtained.

It is a schematic sectional drawing which shows the example of the multilayer ceramic capacitor of this invention. FIG. 2 is an enlarged view of a dielectric layer constituting the multilayer ceramic capacitor of FIG. 1, and is a schematic diagram showing crystal grains and grain boundary phases. Sample No. in the examples. 3 shows an X-ray diffraction chart of I-3. Sample No. in the examples. It is a graph which shows the temperature characteristic of the electrostatic capacitance of I-3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer 9 Crystal grain 11 Grain boundary phase

  The multilayer ceramic capacitor of the present invention will be described in detail based on the schematic sectional view of FIG. FIG. 1 is a schematic sectional view showing an example of the multilayer ceramic capacitor of the present invention, and FIG. 2 is an enlarged view of a dielectric layer constituting the multilayer ceramic capacitor of FIG. 1, showing crystal grains and grain boundary phases. It is a schematic diagram.

  In the multilayer ceramic capacitor of the present invention, 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 a plurality of dielectric layers 5 and internal electrode layers 7 made of dielectric ceramics. 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 laminated ceramic capacitor of the present invention has a laminated layer in which the dielectric layer 5 and the internal electrode layer 7 are several hundred layers. It is a body.

  The dielectric layer 5 made of dielectric porcelain is composed of crystal grains 9 and grain boundary phases 11, and the thickness is preferably 2 μm or less, particularly preferably 1 μm or less, thereby reducing the size and capacity of the multilayer ceramic capacitor. It becomes possible to do. In addition, when the thickness of the dielectric layer 5 is 0.4 μm or more, it is possible to reduce the variation in capacitance and stabilize the capacitance-temperature characteristic.

  The internal electrode layer 7 is preferably a base metal such as nickel (Ni) or copper (Cu) in that the manufacturing cost can be suppressed even when the number of layers is increased, and in particular, simultaneous firing with the dielectric layer 5 in the present invention can be achieved. In this respect, nickel (Ni) is more desirable.

  The dielectric ceramic constituting the dielectric layer 5 in the multilayer ceramic capacitor of the present invention is composed of crystal particles mainly composed of barium titanate, and includes calcium, magnesium, vanadium, and manganese, yttrium, dysprosium, and holmium. And a sintered body containing at least one rare earth element selected from erbium and terbium.

  The crystal particles 9 constituting the dielectric ceramic in the present invention have a calcium concentration of 0.4 atomic% or more, and particularly preferably 0.5 to 2.5 atomic%. When the concentration of calcium is within this range, the solid solution of calcium in barium titanate can be made sufficient. In addition, since the Ca compound remaining in the grain boundary or the like without being dissolved can be reduced, the dependency of the relative permittivity on the AC voltage is increased, so that the permittivity can be increased.

  Regarding the calcium concentration in the crystal particles 9, the transmission electron microscope provided with an elemental analysis device for the crystal particles 9 existing on the polished surface obtained by polishing the cross section of the dielectric layer 5 constituting the multilayer ceramic capacitor. Elemental analysis is performed using At this time, the spot size of the electron beam is set to 5 nm, and the location to be analyzed is 4 to 5 points at almost equal intervals from the grain boundary on the straight line drawn from the vicinity of the grain boundary to the center of the crystal grain 9. Obtain the ratio of calcium when the total amount of detected Ba, Ti, Ca, V, Mg, RE (rare earth element) and Mn is 100%, and calculate the average value of the ratio of calcium obtained at each measurement point. Calculate as concentration.

The dielectric ceramic is composed of 0.02 to 0.2 mol in terms of V ₂ O ₅ and 0.2 to 0.8 mol in terms of MgO with respect to 100 mol of titanium constituting barium titanate, Manganese is 0.1 to 0.5 mol in terms of MnO, and at least one rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium is 0.3 to 0.8 mol in terms of RE ₂ O _3. And 0.02 to 0.2 mol of terbium in terms of Tb ₄ O ₇ . Note that RE is an abbreviation that represents a rare earth element.

Further, the dielectric ceramic constituting the dielectric layer 5 in the multilayer ceramic capacitor of the present invention has a tetragonal crystal (200) plane diffraction intensity indicating cubic barium titanate in the X-ray diffraction chart of the dielectric ceramic. Greater than the diffraction intensity of the (002) plane of the barium titanate of
And Curie temperature is 90-100 degreeC. In the present invention, the Curie temperature is a temperature at which the relative dielectric constant becomes maximum in the range (−60 to 150 ° C.) in which the temperature characteristic of the relative dielectric constant is measured.

  As a result, the relative dielectric constant at room temperature (25 ° C.) is 3400 or more, the dielectric loss is 12.5% or less, and the temperature characteristic of the relative dielectric constant is X6S (the rate of temperature change of the relative dielectric constant when 25 ° C. is used as a reference). (Within ± 22% at −55 to 105 ° C.), the relative permittivity when the AC voltage is 1 V is less than twice the relative permittivity when the AC voltage is 0.01 V, and the high temperature load test (temperature : 105 ° C., voltage: 1.5 times the rated voltage, test time: 1000 hours), a highly reliable multilayer ceramic capacitor free from defects can be obtained.

That is, when the content of vanadium is less than 0.02 mol in terms of V ₂ O _{5 with} respect to 100 mol of titanium constituting barium titanate, reliability in a high temperature load test is lowered. On the other hand, when the content of vanadium is more than 0.2 mol in terms of V ₂ O ₅ , the relative dielectric constant at room temperature becomes low.

  When the content of magnesium is less than 0.2 mol in terms of MgO with respect to 100 mol of titanium constituting barium titanate, the temperature characteristic of the relative permittivity tends to be greatly deviated to the + side, and the capacitance temperature The X6S condition that is a characteristic is not satisfied. On the other hand, when the content of magnesium is more than 0.8 mol, the relative dielectric constant at room temperature becomes low.

  When the content of manganese is less than 0.1 mol in terms of MnO with respect to 100 mol of titanium constituting barium titanate, the insulation resistance of the dielectric layer 5 is lowered. Reliability decreases. On the other hand, when the content of manganese is more than 0.5 mol in terms of MnO, the relative dielectric constant at room temperature becomes low.

When the content of at least one rare earth element selected from yttrium, dysprosium, holmium and erbium is less than 0.3 mol in terms of RE ₂ O _{3 with} respect to 100 mol of titanium constituting barium titanate, In this case also, the reliability in the high temperature load test is lowered. On the other hand, if the content of the rare earth element is more than 0.8 mol in terms of RE ₂ O ₃ , the relative dielectric constant at room temperature becomes low.

When the content of terbium is less than 0.02 mol in terms of Tb ₄ O _{7 with} respect to 100 mol of titanium constituting barium titanate, the above vanadium, magnesium, manganese and rare earth to barium titanate as the main component The amount of solid solution of the element is reduced, and the Curie temperature of the dielectric porcelain is equivalent to the Curie temperature of barium titanate (about 125 ° C) showing the core-shell structure. Reliability decreases. On the other hand, when the terbium content is more than 0.2 mol in terms of Tb ₄ O ₇ , the solid solution amount of vanadium, magnesium, manganese and rare earth elements in the main component barium titanate increases. For this reason, the relative permittivity when the AC voltage is 1 V is increased (the relative permittivity has a large AC voltage dependency) as compared with the relative permittivity when the AC voltage is 0.01 V, and the rated voltage is The change in capacitance when changed is increased.

As a particularly preferable composition, vanadium is 0.02 to 0.08 mol in terms of V ₂ O ₅ and magnesium is 0.3 to 0.6 mol in terms of MgO, with respect to 100 mol of titanium constituting barium titanate, Manganese is 0.2 to 0.4 mol in terms of MnO, and at least one rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium is 0.4 to 0.6 mol in terms of RE ₂ O _3. And 0.02 to 0.08 mol of terbium in terms of Tb ₄ O ₇ is preferable.

  In the dielectric ceramic in this range, the relative dielectric constant at room temperature can be increased to 3900 or more, and the relative dielectric constant when the AC voltage is 1 V is 1 as the relative dielectric constant when the AC voltage is 0.01 V. .6 or less. As the rare earth element, yttrium is particularly preferable in that a higher relative dielectric constant is obtained and an insulation resistance is high.

  3 shows sample Nos. 1 to 3 in Examples 1 to 3 described later. 4 shows an X-ray diffraction chart of a dielectric ceramic constituting the multilayer ceramic capacitor of I-3. The multilayer ceramic capacitor of the present invention has a diffraction pattern as shown in the X-ray diffraction chart of FIG. 4 shows sample Nos. 1 to 4 in Examples 1 to 3 described later. It is a graph which shows the temperature characteristic of the electrostatic capacitance of the multilayer ceramic capacitor of I-3. The multilayer ceramic capacitor of the present invention has a capacitance temperature characteristic as shown in FIG.

  In the X-ray diffraction chart of FIG. 3, the (200) plane (about 2θ = 45.3 °) showing cubic barium titanate and the (002) plane (2θ = 45.1 °) showing tetragonal barium titanate. The (200) plane diffraction intensity (Ic) of cubic barium titanate indicates tetragonal barium titanate (002) plane. Is greater than the diffraction intensity (It). Although this crystal structure is similar to the X-ray diffraction pattern of the conventional core-shell structure, as shown in FIG. 4, the multilayer ceramic capacitor of the present invention has a Curie temperature (Tc) of 90 to 100 ° C. It has a dielectric characteristic different from that of a conventional dielectric ceramic having a core / shell structure with a temperature of 125 ° C.

  That is, a dielectric ceramic having a core-shell structure obtained by dissolving additive components such as magnesium, manganese and rare earth elements in barium titanate, which is the main component, has a Curie temperature (125 ° C.) of pure barium titanate. ) Shows a Curie temperature in the vicinity, whereas the dielectric ceramic constituting the dielectric layer 5 in the multilayer ceramic capacitor of the present invention is composed of vanadium and magnesium with respect to barium titanate containing calcium as described above. And manganese, at least one rare earth element selected from yttrium, dysprosium, holmium and erbium, and terbium are dissolved. For this reason, the X-ray diffraction chart has a crystal structure in which the diffraction intensity of the (200) plane showing cubic barium titanate is larger than the diffraction intensity of the (002) plane showing tetragonal barium titanate, The Curie temperature is 90-100 ° C., which is shifted to the room temperature side.

  This is because in addition to the additive components such as vanadium, magnesium, manganese and rare earth elements, the additive component diffuses into the dielectric ceramic by dissolving a small amount of terbium. Although it looks like a core-shell structure from the line diffraction pattern, the Curie temperature can be set to 90 to 100 ° C.

  In the multilayer ceramic capacitor of the present invention, the diffused element compensates for oxygen defects in the crystal grains 9, thereby increasing the insulation of the dielectric ceramic and improving the life in the high temperature load test.

  In other words, when the solid solution amount of magnesium and rare earth elements in the crystal particles is small, the ratio of the core portion containing many defects such as oxygen vacancies increases, so that when a DC voltage is applied, the dielectric ceramic is It is considered that oxygen vacancies or the like are likely to be carriers that carry electric charges inside the crystal grains 9 constituting the dielectric particles, and the insulating properties of the dielectric ceramic are lowered. However, in the dielectric ceramic constituting the dielectric layer 5 in the multilayer ceramic capacitor according to the present invention, terbium is added together with vanadium to increase the solid solution of the additive component containing these to bring the Curie temperature to a range of 90 to 100 ° C. is there. Therefore, the carrier density such as oxygen vacancies in the crystal particles 9 can be reduced, the rare earth elements and magnesium can be increased, and the inside of the crystal particles 9 can be reduced in oxygen vacancies. It is thought that it can be obtained.

  In the dielectric ceramic constituting the dielectric layer 5 in the multilayer ceramic capacitor of the present invention, the average crystal grain size of the crystal grains 9 may be 0.1 μm or more in terms of enabling a high dielectric constant. If the variation in capacitance is to be reduced, the range is preferably 0.3 μm or less. Preferably, the average particle diameter of the crystal particles 9 is 0.22 to 0.28 μm, or 0.13 to 0.33. It is good that it is 0.19 μm.

  When the average crystal grain size of the crystal grains 9 is 0.22 to 0.28 μm, the relative dielectric constant is 3400 or more, the dielectric loss is 12% or less, and the temperature characteristics of the relative dielectric constant is X6S (when 25 ° C. is used as a reference) Of the relative permittivity when the AC voltage is 1 V and the relative permittivity when the AC voltage is 0.01 V is satisfied. There is an advantage that reliability in a high temperature load test (temperature: 105 ° C., voltage: 1.5 times the rated voltage, test time: 1000 hours) can be satisfied by 1.8 times or less.

  Further, when the average crystal grain size of the crystal grains 9 is 0.13 to 0.19 μm, conditions under a more severe high temperature load test (for example, temperature: 125 ° C., voltage: 1.5 times the rated voltage, test time) : 1000 hours). In order to adjust the average crystal grain size of the crystal particles 9, for example, the specific surface area of a powder (BCT powder) in which calcium is solid-solved in barium titanate, which is a raw material powder as described later, may be adjusted.

  Here, the average crystal grain size of the crystal grains 9 constituting the dielectric layer 5 is obtained as follows. First, after the fracture surface of the dielectric layer 5 of the capacitor body 1 is polished, a picture of the internal structure is taken using a scanning electron microscope. A circle containing 20 to 30 crystal grains 9 is drawn on the photograph, crystal grains covering the circumference and the circumference are selected, and the contour of each crystal grain 9 is image-processed to determine the area of each grain. Then, the diameter when replaced with a circle having the same area as this is calculated and obtained from the average value.

  In the dielectric ceramic according to the present invention, a glass component may be included as an auxiliary for enhancing the sinterability as long as desired dielectric characteristics can be maintained.

Next, a method for producing the multilayer ceramic capacitor of the present invention will be described. First, as raw material powder, powder in which calcium is solid-solved in barium titanate having a purity of 99% or more (hereinafter referred to as BCT powder), V ₂ O ₅ powder and MgO powder, Y ₂ O ₃ powder, Dy _At least one rare earth element oxide powder selected from ₂ O ₃ powder, Ho ₂ O ₃ powder and Er ₂ O ₃ powder, Tb ₄ O ₇ powder and MnCO ₃ powder are added and mixed.

The BCT powder is a solid solution mainly composed of barium titanate in which a part of the A site is substituted with calcium (Ca), and is represented by (Ba _1-x Ca _x ) TiO ₃ . In this compound, the Ca substitution amount in the A site is preferably X = 0.01 to 0.2. When the Ca substitution amount is within this range, excellent capacitance temperature characteristics can be obtained in the operating temperature range when used as a multilayer ceramic capacitor. Note that Ca contained in the crystal particles 9 is dissolved in a state dispersed in the crystal particles 9.

The BCT powder to be used preferably has a specific surface area of ² to 6 m ² / g. When the specific surface area of the BCT powder is ² to 6 m ² / g, the crystal particles 9 maintain a crystal structure close to the core-shell structure, and the additive components are dissolved in these crystal particles to lower the Curie temperature. It becomes easy to shift to the side. In addition, the dielectric constant can be improved, and the insulating property of the dielectric ceramic can be enhanced, thereby improving the reliability in the high temperature load test. In the present invention, it is desirable to select a powder having a specific surface area greater than 5 m ² / g in order to make the average crystal grain size of the crystal grains 9 constituting the dielectric ceramic smaller than 0.19 μm.

In addition, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, and Er ₂ O ₃ powder, which are additives, oxide powder of at least one rare earth element selected from powders of T _{2 4} O ₇ , V _{For the 2} O ₅ powder, the MgO powder, and the MnCO ₃ powder, it is preferable to use those having a particle size (or specific surface area) equivalent to that of the dielectric powder.

Next, these raw material powders were prepared by using 0.02 to 0.2 mol of V ₂ O ₅ powder, 0.2 to 0.8 mol of MgO powder, and oxide powder of rare earth element with respect to 100 mol of BCT powder. 0.3 to 0.8 mole, 0.1 to 0.5 mole of MnCO ₃ powder, and 0.02 to 0.2 mole of Tb ₄ O ₇ powder are blended. A raw material powder is obtained by adding glass powder as a sintering aid to the extent that desired dielectric properties can be maintained. The addition amount of the glass powder is preferably 0.5 to 2 parts by mass when the BT powder is 100 parts by mass.

  Next, a ceramic slurry is prepared by adding a dedicated organic vehicle to the raw material powder, and then a ceramic green sheet is formed from the ceramic slurry using a sheet forming method such as a doctor blade method or a die coater method. In this case, the thickness of the ceramic green sheet is preferably 0.5 to 3 μm from the viewpoint of reducing the thickness of the dielectric layer 5 to increase the capacity and maintaining high insulation.

  Next, a rectangular internal electrode pattern is printed and formed on the main surface of the obtained ceramic green sheet. Ni, Cu, or an alloy powder thereof is suitable for the conductor paste that forms the internal electrode pattern.

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

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

Next, the capacitor body compact is degreased and fired. The firing temperature is preferably 1100 to 1200 ° C. because the solid solution of the additive in the BCT powder and the grain growth of the crystal grains are controlled in the present invention. In order to obtain the dielectric ceramic according to the present embodiment, a BCT powder having a specific surface area of ² to 6 m ² / g is used and, as described above, selected from magnesium, manganese and yttrium, dysprosium, holmium and erbium. A predetermined amount of each of the oxides of vanadium and terbium is added as an additive together with at least one kind of various oxide powders of the rare earth elements, and firing is performed at the above temperature. As a result, various additives are included in the crystal particles obtained using BCT powder as a main raw material, and the crystal structure shown by the crystal particles 9 is made close to the core-shell structure, while the Curie temperature is set to The range is lower than the Curie temperature of the dielectric ceramic showing the shell structure. By firing so that the Curie temperature after firing is in a range lower than the Curie temperature of the dielectric ceramic showing the conventional core-shell structure, the crystal particles 9 increase in the solid solution of the additive. And a dielectric ceramic having a long life in a high temperature load test can be obtained.

  Moreover, after baking, it heat-processes in a weak reducing atmosphere again. This heat treatment is performed to reoxidize the dielectric ceramic reduced in firing in a reducing atmosphere and recover the insulation resistance reduced and reduced during firing. The temperature is preferably 900 to 1100 ° C. for the purpose of increasing the amount of reoxidation while suppressing the grain growth of the crystal grains 9. Thus, the dielectric ceramic becomes highly insulating, and a multilayer ceramic capacitor exhibiting a Curie temperature of 90 to 100 ° C. can be manufactured.

  Next, an external electrode paste is applied to the opposing ends of the capacitor body 1 and baked to form the external electrodes 3. Further, a plating film may be formed on the surface of the external electrode 3 in order to improve mountability.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited by a following example.
<Example I>
First, as the raw material powder, BCT powder _{(composition: (Ba 1-x Ca x} ) TiO 3, X = 0.05), MgO _powder, Y 2 _{O 3} powder, _Dy 2 _{O 3} powder, _Ho 2 _{O 3} powder, Er ₂ O ₃ powder, Tb ₄ O ₇ powder, MnCO ₃ powder and V ₂ O ₅ powder were prepared. These various powders were mixed in the proportions shown in Table 1. At this time, the ratio of MgO powder, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder, Tb ₄ O ₇ powder, MnCO ₃ powder and V ₂ O ₅ powder is BT powder. Is the ratio when 100 moles. All of these raw material powders had a purity of 99.9%, and BCT powder having a specific surface area of 4 m ² / g was used. MgO powder, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder, Tb ₄ O ₇ powder, MnCO ₃ powder and V ₂ O ₅ powder have an average particle size of 0.1 μm. The thing of was used. As the sintering aid, glass powder having a composition of SiO ₂ = 55, BaO = 20, CaO = 15, 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 solvent of toluene and alcohol as a solvent using zirconia balls having a diameter of 5 mm.

  The wet-mixed 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 5 mm to prepare a ceramic slurry, and a thickness of 1.5 μm and 2. A 5 μm ceramic green sheet was prepared.

  A plurality of rectangular internal electrode patterns mainly composed of Ni were formed on the upper surface of 1.5 μm and 2.5 μm thick ceramic green sheets. The conductive paste for forming the internal electrode pattern was obtained by adding a small amount of 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 sheet laminate using a ceramic green sheet having a thickness of 1.5 μm and a sheet laminate using a ceramic green sheet having a thickness of 2.5 μm are prepared by closely adhering them at 10 ⁷ Pa for 10 minutes. Thereafter, each sheet laminate was cut into a predetermined size to form a capacitor body molded body.

Next, the capacitor body molded body was treated to remove the binder in the air, and then fired in hydrogen-nitrogen at 1125 to 1135 ° C. for 2 hours to produce a capacitor body. The sample was subsequently reoxidized at 1000 ° C. for 4 hours in a nitrogen atmosphere. The size of this capacitor body was 0.95 × 0.48 × 0.48 mm ³ , the thickness of the dielectric layer was 1 μm or 2 μm, and the effective area of one layer of the 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.

  After the sintered capacitor body was barrel polished, 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 all cases, the number of samples was 10, and the average value was obtained.

  The relative dielectric constant and dielectric loss were measured from a capacitance of 25 ° C., a frequency of 1.0 kHz, a measurement voltage of 0.01 Vrms or 1 Vrms, and obtained from the thickness of the dielectric layer and the effective area of the internal electrode layer.

  For the temperature characteristics of the relative dielectric constant, the capacitance was measured in a temperature range of −55 to 150 ° C. As for the temperature characteristics of the relative dielectric constant, a case where X6S (within ± 22% with respect to 25 ° C. in the range of −55 to 105 ° C.) is satisfied, and a case where it is not satisfied are indicated as x. The Curie temperature was determined as the temperature at which the relative dielectric constant was maximum in the range where the temperature characteristics of the relative dielectric constant were measured.

  The high temperature load test was performed under the conditions of a temperature of 105 ° C., an applied voltage of 6 V / μm, and 1000 hours. The number of samples in the high temperature load test was 20 for each sample, and those that had no defects up to 1000 hours were regarded as non-defective products.

  The average crystal grain size of the crystal grains constituting the dielectric layer is determined by polishing the fracture surface of the capacitor body sample after firing, then taking a picture of the internal structure using a scanning electron microscope, and Draw a circle containing 20 to 30 particles, select the crystal particles in and around the circle, perform image processing on the outline of each crystal particle, find the area of each particle, and have the same area The diameter at the time of replacement was calculated and obtained from the average value.

  The ratio of the diffraction intensity of the (200) plane showing cubic barium titanate and the diffraction intensity of the (002) plane showing tetragonal barium titanate was measured by X-ray diffraction with a Cukα tube. Using an apparatus, the angle was measured in the range of 2θ = 44 to 46 °, and obtained from the ratio of peak intensities.

  Moreover, the composition analysis of the sample which is the obtained sintered body 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.

  In addition, the concentration of calcium in the crystal particles is determined based on the elemental analysis equipment for the crystal particles present on the polished surface obtained by sampling three multilayer ceramic capacitors from each sample and polishing the cross section of the dielectric layer constituting the capacitor. Elemental analysis was carried out using a transmission electron microscope provided with. As the crystal particles to be selected, a circle containing 20 to 30 crystal particles was drawn on an image observed with a transmission electron microscope, and the crystal particles were placed in and around the circle. The spot size of the electron beam for performing elemental analysis was 5 nm. The points to be analyzed are 4 to 5 points at almost equal intervals from the grain boundary on the straight line drawn from the vicinity of the grain boundary toward the center, and Ba, Ti, Ca, V, Mg detected from each measurement point. , RE (rare earth element) and the total amount of Mn were taken as 100%, the calcium ratio was determined, and the average value of the calcium ratio determined from each measurement point was determined as the calcium concentration. As a result, all of the crystal particles formed using the BCT powder had a calcium concentration of 0.5 to 2 atomic%.

  Tables 1 and 2 show the preparation composition and firing temperature, Tables 3 and 4 show the oxide equivalent composition of each element in the sintered body, and the thickness, average crystal grain size, and X-rays of the dielectric layer after firing. Shows the results of peak intensity ratio and characteristics (specific permittivity, dielectric loss, temperature characteristics of relative permittivity (determined from the temperature characteristics of capacitance), life in high temperature load test) of diffraction and cubic crystals. Shown in 5 and 6, respectively.

表１〜６の結果から明らかなように、本発明の試料Ｎｏ．Ｉ−２〜５、８〜１３、１６〜１９、２２〜２５、２８〜３１および３３〜５５では、室温（２５℃）における比誘電率が３４００以上、誘電損失が１２．５％以下であり、比誘電率の温度特性がＸ６Ｓ（２５℃を基準にしたときの比誘電率の温度変化率が−５５〜１０５℃において±２２％以内）を満足し、また、ＡＣ電圧を１Ｖとしたときの比誘電率がＡＣ電圧を０．０１Ｖとしたときの比誘電率の２倍以下であり、さらに、高温負荷試験（温度：１０５℃、定格電圧の１．５倍、１０００時間）において不良が無かった。

As is apparent from the results of Tables 1 to 6, the sample No. In I-2 to 5, 8 to 13, 16 to 19, 22 to 25, 28 to 31, and 33 to 55, the relative dielectric constant at room temperature (25 ° C.) is 3400 or more, and the dielectric loss is 12.5% or less. When the temperature characteristic of the dielectric constant satisfies X6S (the temperature change rate of the dielectric constant with respect to 25 ° C. is within ± 22% at −55 to 105 ° C.), and the AC voltage is 1V The relative dielectric constant is less than twice the relative dielectric constant when the AC voltage is set to 0.01 V. Further, in the high temperature load test (temperature: 105 ° C., 1.5 times the rated voltage, 1000 hours) There was no.

Moreover, as a composition of the dielectric ceramic constituting the dielectric layer, vanadium is 0.02 to 0.08 mol in terms of V ₂ O ₅ and magnesium is in terms of MgO with respect to 100 moles of titanium constituting barium titanate. 0.3 to 0.6 mol, manganese to 0.2 to 0.4 mol in terms of MnO, and at least one rare earth element selected from yttrium, dysprosium, holmium, and erbium to an RE ₂ O ₃ equivalent of 0. Sample No. ₄ to 0.6 mol, and terbium 0.02 to 0.08 mol in terms of Tb ₄ O _{7 were} converted. In I-36 to 55, the relative dielectric constant was 3900 or more, and the relative dielectric constant when the AC voltage was 1 V was 1.6 times or less than the relative dielectric constant when the AC voltage was 0.01 V. .

  Further, Sample No. 2 in which the average crystal grain size of the crystal grains constituting the dielectric layer was in the range of 0.22 to 0.28 μm. In I-2 to 5, 8 to 12, 16 to 19, 22 to 25, 28 to 31, 33 to 52, 54 and 55, the dielectric loss was 12% or less.

On the other hand, sample no. In I-1, 6, 7, 14, 15, 20, 21, 26, 27 and 32, the relative dielectric constant at room temperature (25 ° C.) is 3400 or more, the dielectric loss is 12.5% or less, the temperature of the relative dielectric constant The characteristic satisfies X6S (the rate of change in temperature of the relative permittivity with respect to 25 ° C. is ± 22% at −55 to 105 ° C.), and the relative permittivity when the AC voltage is 1 V is the AC voltage. Either the dielectric constant is 2 times or less of the relative dielectric constant at 0.01 V, and the temperature is 105 ° C., 1.5 times the rated voltage, and the lifetime in the high temperature load test is zero defect at 1000 hours or more. The characteristics were not satisfied.
<Example II>
Each raw material powder was mixed in the ratio shown in Table 7 in the same manner as in Example 1 except that the BCT powder having a specific surface area of 6 m ² / g was used instead of the BCT powder having a specific surface area of 4 m ² / g. Thus, a ceramic green sheet was obtained, and the capacitor body molded body was fired at 1130 to 1160 ° C. to produce a capacitor body, and further a multilayer ceramic capacitor was produced. The obtained multilayer ceramic capacitor was evaluated in the same manner as in Example I. However, unlike the conditions of Example I (temperature: 105 ° C., voltage: 6 V, test time: 1000 hours), the high temperature load test satisfies temperature: 125 ° C., voltage: 6 V, test time: 1000 hours. Was evaluated.

  Table 7 shows the composition and firing temperature of each sample, Table 8 shows the oxide equivalent composition of each element in the sintered body, and the thickness, average crystal grain size, and X-ray diffraction of the dielectric layer after firing. Table 9 and Table 10 show the results of the peak intensity ratio and characteristics (relative permittivity, dielectric loss, temperature characteristics of relative permittivity, lifetime in high temperature load test) of cubic and tetragonal crystals, respectively.

表９、表１０から明らかなように、本発明の試料Ｎｏ．II−２〜５，８〜１３，１６〜１９，２２〜２５，２８〜３１および３３〜５０では、室温（２５℃）における比誘電率が３４００以上、誘電損失が１２．5％以下であり、比誘電率の温度特性がＸ６Ｓ（２５℃を基準にしたときの比誘電率の温度変化率が−５５〜１０５℃において±２２％）を満足し、また、ＡＣ電圧を１Ｖとしたときの比誘電率がＡＣ電圧を０．０１Ｖとしたときの比誘電率の２倍以下であり、さらに、高温負荷試験（温度：１２５℃、定格電圧の１．５倍、１０００時間）において不良が無かった。この結果、結晶粒子の平均結晶粒径が微粒化（０．１３〜０．１９μｍ）されると、高温負荷特性が向上することがわかる。

As is clear from Tables 9 and 10, the sample No. In II-2 to 5, 8 to 13, 16 to 19, 22 to 25, 28 to 31, and 33 to 50, the relative dielectric constant at room temperature (25 ° C.) is 3400 or more, and the dielectric loss is 12.5% or less. The temperature characteristics of the dielectric constant satisfy X6S (the temperature change rate of the dielectric constant with respect to 25 ° C. is ± 22% at −55 to 105 ° C.), and the AC voltage is 1V. The relative permittivity is less than twice the relative permittivity when the AC voltage is 0.01 V, and there is no defect in the high temperature load test (temperature: 125 ° C., 1.5 times the rated voltage, 1000 hours). It was. As a result, it can be seen that when the average crystal grain size of crystal grains is atomized (0.13 to 0.19 μm), the high temperature load characteristics are improved.

  On the other hand, Sample Nos. II-1, 21, and 27 that do not satisfy the high temperature load characteristics are those in which the blending amount of any of the raw materials does not satisfy the scope of the present invention. Even within the range of 0.13 to 0.19 μm, the high temperature load characteristics are not satisfied.

Sample No. II-50 was satisfactory in high temperature load characteristics at 105 ° C. because the average crystal grain size of crystal grains exceeded 0.19 μm, but had high temperature load characteristics at 125 ° C. I'm not satisfied.

Claims (4)

(I) A dielectric composed of crystal particles mainly composed of barium titanate and containing calcium, magnesium, vanadium, manganese and terbium and at least one rare earth element selected from yttrium, dysprosium, holmium and erbium A multilayer ceramic capacitor formed by alternately laminating dielectric layers made of a ceramic body and (ii) internal electrode layers,
The dielectric porcelain is 0.02 to 0.2 mol in terms of V ₂ O _{5 and the} magnesium is 0.2 to 0.00 in terms of MgO with respect to 100 mol of titanium constituting the barium titanate. 8 mol, 0.1 to 0.5 mol of manganese in terms of MnO, and at least one rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium in an amount of 0.3 in terms of RE ₂ O ₃ 0.8 mol, and the terbium well as 0.02 to 0.2 molar content in _Tb 4 _{O 7} terms,
The crystal particles have a calcium concentration of 0.4 atomic% or more;
In the X-ray diffraction chart of the dielectric ceramic, the diffraction intensity of the (200) plane showing cubic barium titanate is larger than the diffraction intensity of the (002) plane showing tetragonal barium titanate, and the Curie A multilayer ceramic capacitor having a temperature of 90 to 100 ° C. The dielectric porcelain is 0.02 to 0.08 mol in terms of V ₂ O ₅ and 0.3 to 0.005 in terms of MgO with respect to 100 mol of titanium constituting the barium titanate. 6 mol, 0.2 to 0.4 mol of manganese in terms of MnO, and at least one rare earth element selected from yttrium, dysprosium, holmium and erbium in an amount of 0.4 to 0.00 in terms of RE ₂ O ₃ . 6. The multilayer ceramic capacitor according to claim 1, comprising 6 mol and 0.02 to 0.08 mol of the terbium in terms of Tb ₄ O ₇ .   3. The multilayer ceramic capacitor according to claim 1, wherein an average crystal grain size of the crystal particles is 0.22 to 0.28 μm.   3. The multilayer ceramic capacitor according to claim 1, wherein an average crystal grain size of the crystal particles is 0.13 to 0.19 μm.

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