JP5159682B2 - Multilayer ceramic capacitor - Google Patents

Description

  The present invention relates to a multilayer ceramic capacitor using a dielectric ceramic composed of crystal particles mainly composed of barium titanate as a dielectric layer.

  In general, an electronic circuit board having an active circuit such as a transistor amplifier or various LSIs is provided with a power supply line and a ground separately from a transmission line for the purpose of improving high-frequency characteristics. In such an electronic circuit board, a bypass capacitor is mounted between the power supply line and the ground in order to avoid fluctuations in the DC power supply voltage when the circuit operates, but the bypass capacitor is connected to the ground of the power supply line. In addition to lowering the AC impedance, it plays a role of filtering so that noise components are not transmitted to subsequent circuits.

  In recent years, as mobile computing devices such as mobile phones have become smaller and more functional, electronic circuit boards used in such electronic devices have been increased in the density of electronic components to be mounted. For this reason, multilayer ceramic capacitors, which are one of the electronic components mounted on electronic circuit boards, are not only reduced in size and increased in capacity, but also in a wider temperature range against the increase in the amount of heat generated due to the higher frequency of active circuits. There is also a demand for stable capacitance.

  In response to such a problem, the present applicant has a high dielectric constant by forming a dielectric ceramic with crystal particles mainly composed of barium titanate and adding magnesium, rare earth elements, manganese, and the like to the dielectric ceramic. In addition, a multilayer ceramic capacitor was proposed in which the temperature change in capacitance satisfies the EIA standard X5R characteristics (−55 to 85 ° C., ΔC = ± 15% or less) (see, for example, Patent Document 1).

  In addition to this, the present applicant, as the multilayer ceramic capacitor described in the above-mentioned Patent Document 1, has a high dielectric constant and the temperature characteristics of the dielectric constant satisfy the X5R characteristics of the EIA standard. Have proposed a multilayer ceramic capacitor as disclosed in US Pat.

  The multilayer ceramic capacitor disclosed in Patent Document 2 includes magnesium, a rare earth element, manganese, and the like contained in barium titanate whose main component is a dielectric ceramic that constitutes a dielectric layer. It is formed by crystal grains having a core-shell structure composed of a shell phase having an element concentration gradient and an inner core surrounded by the shell phase and having a low content of magnesium and rare earth elements.

JP 2006-156450 A JP-A-2005-217000

  However, although the multilayer ceramic capacitors disclosed in Patent Documents 1 and 2 have a high dielectric constant as described above and the temperature change of the relative dielectric constant satisfies the X5R characteristic of the EIA standard, the applied AC voltage has changed. Since the change rate of the relative permittivity is large in some cases, the decrease in the relative permittivity is large even in a high-frequency region, and in an electronic circuit board having a transistor amplifier or an LSI with a low AC voltage for reducing power consumption. However, there was a problem that it was difficult to obtain the necessary capacitance.

  Therefore, the present invention provides a multilayer ceramic capacitor having a high dielectric constant and a change in temperature of the relative dielectric constant satisfying the X5R characteristic of the EIA standard, and a small change rate of the relative dielectric constant even with respect to an AC voltage change. Objective.

The multilayer ceramic capacitor of the present invention includes a capacitor body in which dielectric layers and internal electrode layers are alternately stacked, and a multilayer ceramic capacitor provided on an end surface of the capacitor body and connected to the internal electrode layer. The dielectric layer is composed of crystal particles mainly composed of barium titanate, and includes a rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium, and vanadium. The dielectric porcelain contains one rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium with respect to 100 moles of barium constituting barium titanate in terms of RE ₂ O _3. 1.8 mole, the vanadium _V 2 _{O 5} in terms of 0 to 0.30 mol contain together The crystal particle has an inner core that occupies the center of the crystal particle and an outer shell that surrounds the inner core, and a molar ratio Ba / Ti of barium to titanium in the inner core is 0.98 to 1.10. The molar ratio Ba / Ti between barium and titanium in the outer shell is 0.90 to 0.97, and the average particle size is 0.18 to 0.27 μm.

  In the multilayer ceramic capacitor of the present invention, the crystal particles constituting the dielectric layer are mainly composed of barium titanate, and the molar ratio between barium and titanium is different between the inner core and the outer shell of the crystal particles. Specifically, the molar ratio of the inner core is 0.98 to 1.10, the molar ratio of the outer shell is 0.90 to 0.97, and the molar ratio of the outer shell is smaller than the molar ratio of the inner core. As described above, in the present invention, since the molar ratio Ba / Ti of the outer shell is smaller than 1, the amount of additive components such as rare earth elements (RE) and vanadium is reduced, so that the crystal particles are barium titanate. As a result, the change rate of the relative permittivity when the AC voltage is changed (hereinafter referred to as the AC voltage dependency of the relative permittivity). Can be reduced.

  On the other hand, the molar ratio Ba / Ti is larger than 1 in the inner core so as to compensate for the deficiency of barium in the outer shell. For this reason, since the molar ratio of barium titanate necessary to form a perovskite structure is maintained between the outer shell and the inner core, the crystal particles can exhibit their original ferroelectricity and can have a high dielectric constant. it can.

  As described above, in the present invention, the dielectric ceramic contains a predetermined additive component, and the crystal grains have different molar ratios Ba / Ti so as to have different functions between the central portion and the periphery of the crystal particles. As a result, it is possible to obtain a multilayer ceramic capacitor having a high dielectric constant, a temperature change of the dielectric constant satisfying the X7R characteristic of the EIA standard, and a low dielectric constant AC voltage dependency of the dielectric constant.

The dielectric porcelain may include 0.03 to 0.30 mol of vanadium in terms of V ₂ O ₅ and 100% of barium constituting the barium titanate and RE ₂ O of the rare earth element (RE). It is desirable to contain 0.4-1.8 mol in ₃ conversions.

  In this case, when the vanadium and rare earth element (RE) contained in the dielectric ceramic are in the above range, the life characteristics in the high temperature load test can be improved.

Further, the dielectric ceramic is configured such that the vanadium is 0.03 to 0.15 mol in terms of V ₂ O _{5 and the} rare earth element (RE) is RE ₂ O with respect to 100 mol of barium constituting the barium titanate. It is desirable to contain 0.4-1.0 mol in ₃ conversions.

  In this case, when the vanadium and rare earth element (RE) contained in the dielectric ceramic are in the above range, the dielectric constant of the dielectric ceramic at room temperature (25 ° C.) can be further increased.

  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 dielectric constant and a change in temperature of the relative dielectric constant satisfying the X7R characteristic of the EIA standard and a small change rate of the relative dielectric constant even with respect to a change in AC voltage. .

It is a schematic sectional drawing which shows an 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. FIG. 3 is a schematic diagram showing the internal structure of crystal grains constituting the dielectric layer in the multilayer ceramic capacitor of the present invention and the change in the molar ratio Ba / Ti of barium and titanium in the inner core and outer shell of the crystal grains.

  The multilayer ceramic capacitor of the present invention will be described. FIG. 1 is a schematic cross-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 and schematically showing crystal grains and grain boundary phases. FIG.

  In the multilayer ceramic capacitor of the present invention, external electrodes 3 are formed at both ends of a capacitor body 1 in which dielectric layers 5 and internal electrode layers 7 made of dielectric ceramics are alternately stacked. The electrode layer 7 is electrically connected. The external electrode 3 is formed by baking, for example, Cu or an alloy paste of Cu and Ni.

  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 ceramic forming the dielectric layer 5 is composed of crystal grains 9 and grain boundary phases 11. The thickness of the dielectric layer 5 is 2 μm or less in the case of a thin layer. When the thickness of the dielectric layer 5 is within this range, the change rate of the relative permittivity can be stabilized, the life characteristics in the high temperature load test can be improved, and the capacity can be increased.

  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 mainly composed of barium titanate, and one kind of rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium, and vanadium. It consists of a sintered compact containing.

In this dielectric ceramic, one kind of rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium is converted into RE ₂ O ₃ with respect to 100 mol of barium which is a constituent of barium titanate which is a main component. 0.4 to 1.8 mol, composed of vanadium terms _{of V} 2 _{O 5} in 0 to 0.3 molar containing crystal grains 9.

  In addition, the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention has an inner core 9a in which the crystal particles 9 constituting the same occupy the center of the crystal particle 9 and an outer shell 9b surrounding the inner core 9a. The molar ratio Ba / Ti of barium and titanium in the inner core 9a is 0.98 to 1.10, and the molar ratio Ba / Ti of barium and titanium in the outer shell 9b is 0.90 to 0.97. And the average particle size is 0.18 to 0.27 μm. In the following, when the molar ratio Ba / Ti is simply described, it represents the molar ratio of barium and titanium.

  As a result, the relative permittivity at room temperature (25 ° C.) is 3000 or more, the temperature change of the relative permittivity satisfies the X5R characteristic of the EIA standard, and the AC voltage relative to the relative permittivity when the AC voltage is 0.1V. The AC voltage dependency represented by the ratio of the relative permittivity when 1 is 1 V can be made smaller than twice.

The dielectric ceramic constituting the dielectric layer 5 in the multilayer ceramic capacitor of the present invention is composed of crystal particles 9 mainly composed of barium titanate, the composition of which is 100 mol of barium constituting barium titanate. One kind of rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium is 0.4 to 1.8 mol in terms of RE ₂ O ₃ , and vanadium is 0 to 0.30 mol in terms of V ₂ O _5. Including.

That is, when one kind of rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium with respect to 100 mol of barium constituting barium titanate is less than 0.4 mol in terms of RE ₂ O ₃ , an alternating voltage The dependency is more than doubled.

When the content of vanadium with respect to 100 mol of barium constituting barium titanate is more than 0.30 mol in terms of V ₂ O ₅ , or selected from yttrium, dysprosium, holmium and erbium with respect to 100 mol of barium constituting barium titanate When one kind of rare earth element (RE) is more than 1.8 mol in terms of RE ₂ O ₃ , the dielectric constant of the dielectric ceramic at room temperature (25 ° C.) is lower than 3000.

  By the way, among rare earth elements (RE), yttrium, dysprosium, holmium, and erbium can be suitably used because they are unlikely to form a different phase when dissolved in barium titanate and high insulation is obtained. Yttrium is more preferable because the relative dielectric constant of the dielectric ceramic can be increased.

In the present invention, the dielectric porcelain includes 0.03 to 0.30 mol of vanadium in terms of V ₂ O ₅ and RE ₂ O of rare earth element (RE) with respect to 100 mol of barium constituting barium titanate. It is desirable to contain 0.4-1.8 mol in ₃ conversions. Thus, in addition to satisfying the EIA standard X5R characteristic with a high dielectric constant and relative dielectric constant temperature change, the life characteristic of the high temperature load test of 85 ° C., 10 V, 1000 hours can be satisfied.

  In the present invention, by containing vanadium in the dielectric ceramic, oxygen vacancies and trivalent vanadium existing in the crystal grains 9 form defect pairs, and as a result, the oxygen vacancies in the grains of the oxygen vacancies. Since the movement is restricted, the life characteristics in the high temperature load test can be enhanced.

In the present invention, the dielectric porcelain, with respect to 100 moles of barium constituting the barium titanate, 0.03 to 0.15 moles of vanadium in terms _{of V} 2 _{O 5,} rare earth elements and _(RE) RE 2 O It is desirable to contain 0.4-1.0 mol in ₃ conversions. Thereby, the dielectric constant of the dielectric ceramic at room temperature (25 ° C.) can be increased to 3100 or more.

  When the composition of the dielectric porcelain contains only vanadium and rare earth elements (RE) with respect to barium titanate, for example, a dielectric having a lower dielectric loss than that obtained by adding manganese or the like Porcelain can be obtained.

  FIG. 3 is a schematic diagram showing the internal structure of the crystal grains constituting the dielectric layer in the multilayer ceramic capacitor of the present invention and the change in the molar ratio Ba / Ti of barium and titanium in the inner core and outer shell of the crystal grains. .

  As described above, the crystal particles 9 constituting the dielectric layer 5 in the multilayer ceramic capacitor of the present invention have the inner core 9a that occupies the center of the crystal particles 9, and the outer shell 9b that surrounds the inner core 9a, The molar ratio Ba / Ti in the inner core 9a is 0.98 to 1.10, and the molar ratio Ba / Ti in the outer shell 9b is 0.9 to 0.97.

  In the multilayer ceramic capacitor of the present invention, as described above, the crystal grains 9 constituting the dielectric layer 5 have different molar ratios Ba / Ti between the inner core 9a and the outer shell 9b. In this case, since the outer shell 9b has a molar ratio Ba / Ti smaller than 1, the amount of solid solution of additive components such as rare earth elements (RE) and vanadium as additive components is small. The characteristic close to the characteristic of the AC voltage dependence inherent in barium can be expressed, and as a result, the AC voltage dependence of the relative permittivity can be reduced.

  On the other hand, the molar ratio Ba / Ti of the inner core 9a of the crystal particle 9 is close to 1 or larger than 1, and the molar ratio Ba / Ti is increased so as to compensate for the amount of barium deficiency in the outer shell 9b. For this reason, since the molar ratio of barium titanate necessary for constructing the perovskite structure is maintained between the outer shell 9b and the inner core 9a, the crystal grains 9 can exhibit the intrinsic ferroelectricity and increase the dielectric constant. Can be planned.

  The crystal particle 9 in the present invention has a structure in which the amount of solid solution of the additive component is different between the inner core 9a and the outer shell 9b, and the conventionally known core-shell structure is a molar ratio Ba / inside of the crystal particle 9 inside. The change of Ti is different.

  Here, in the dielectric ceramic constituting the dielectric layer in the conventional multilayer ceramic capacitor described in Patent Documents 1 and 2, the molar ratio Ba / Ti of the crystal particles is a value close to 1 in the crystal particles 9. And it is uniform. As will be apparent from the examples described later, such a multilayer ceramic capacitor has a higher relative dielectric constant AC voltage dependency than the multilayer ceramic capacitor having crystal grains 9 in the present invention.

  In contrast, in the multilayer ceramic capacitor of the present invention, as shown in FIG. 3, the crystal grains 9 constituting the dielectric ceramic have a structure in which the molar ratio Ba / Ti is different between the inner core 9a and the outer shell 9b. By forming the crystal grains 9 so as to have different functions between the central portion and the periphery thereof, the dielectric constant is high and the change rate of the relative permittivity is small, and the relative permittivity is less dependent on the AC voltage. A multilayer ceramic capacitor can be obtained.

  However, when the molar ratio Ba / Ti of the inner core 9a of the crystal grain 9 is smaller than 0.98, the relative dielectric constant of the dielectric ceramic at room temperature (25 ° C.) is lower than 3000, and the molar ratio Ba / Ti of the inner core 9a. When Ti is greater than 1.10, the AC voltage dependency of the relative dielectric constant is twice or more.

  When the molar ratio Ba / Ti of the outer shell 9b is smaller than 0.90, the dielectric constant of the dielectric ceramic at room temperature (25 ° C.) is lower than 3000, and the molar ratio Ba / Ti of the outer shell 9b is 0.00. If it is greater than 97, the AC voltage dependence of the dielectric constant will be twice or more.

  Here, the molar ratio Ba / Ti in the crystal particles 9 is obtained as follows. First, a laminated ceramic capacitor serving as a sample to be analyzed is polished or cut to produce a thin plate sample. Next, this thin plate-like sample is processed by ion milling to prepare a sample for observation with a transmission electron microscope. For this analysis, a transmission electron microscope equipped with an elemental analysis instrument is used. At this time, the spot size of the electron beam is about 5 nm, and analysis is performed at intervals of 20 to 50 nm from the grain boundary to the center of the crystal grain 9 as indicated by an arrow in FIG. And a region smaller than 1, respectively, and an average value is obtained to obtain the molar ratio Ba / Ti of the inner core 9a and the outer shell 9b in the crystal grain 9. Here, the inner core 9a of the crystal grain 9 is a region where the molar ratio Ba / Ti obtained as described above is larger than 1, and a region where the molar ratio Ba / Ti is smaller than 1 is defined as an outer shell 9b.

  The crystal particle 9 to be selected is a crystal particle 9 having a ratio (aspect ratio) between the maximum diameter and the minimum diameter of the crystal particle 9 of 1.3 or less and in the range of ± 60% of the average particle diameter. The crystal grains 9 in the range of ± 60% of the average grain size are obtained by calculating the area from the contour of the crystal grain 9 by image processing, and the diameter when the diameter is replaced with a circle having the same area as the area is the average grain size. It is in the range of ± 60%. Such an analysis for obtaining the molar ratio Ba / Ti is performed on five or more crystal grains 9, and the molar ratio Ba / Ti is obtained from the average value thereof.

  Further, it is important that the average particle size of the crystal particles 9 is 0.18 to 0.27 μm. By setting the average particle size of the crystal particles 9 within the above range, the dielectric constant at room temperature (25 ° C.) of the dielectric ceramic, the temperature characteristics of the capacitance, and the AC voltage dependency of the dielectric constant are set to the above-described values. can do.

  That is, when the average particle size of the crystal particles 9 is smaller than 0.18 μm, the dielectric constant of the dielectric ceramic at room temperature (25 ° C.) is lower than 3000, and the average particle size of the crystal particles 9 is 0.00. When it is larger than 27 μm, the AC voltage dependency of the relative dielectric constant is more than doubled.

  Here, the average grain size of the crystal particles 9 is determined by polishing the fracture surface of the sample, which is a fired multilayer ceramic capacitor, and then taking a picture of the internal structure of the dielectric ceramic using a scanning electron microscope. Draw a circle containing 20 to 30 crystal grains 9, select the crystal grains 9 in and around the circle, perform image processing on the outline of each crystal grain 9, and determine the area of each grain. Calculate the diameter when it is replaced with a circle with, and find the average value.

  Further, the dielectric ceramic of the present invention may contain a glass component or other additive component in the dielectric ceramic in an amount of 0.5 to 2% by mass as an auxiliary for enhancing the sinterability. The dielectric ceramic constituting the dielectric layer 5 in the multilayer ceramic capacitor of the present invention is mainly composed of barium calcium titanate except for the above-mentioned additive components, inevitable impurities, and auxiliary agents for enhancing the sinterability. Yes.

Next, a method for producing the multilayer ceramic capacitor of the present invention will be described. First, barium titanate powder (hereinafter referred to as BT powder) and at least one rare earth selected from Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder and Er ₂ O ₃ powder as an additive component An oxide powder of element (RE) and a V ₂ O ₅ powder are prepared. The BT powder used has a molar ratio Ba / Ti in the inner core 9a occupying the central portion of the BT powder larger than that of the outer shell 9b and a molar ratio Ba / Ti of the outer shell 9b smaller than 1.

  The BT powder in which the molar ratio Ba / Ti in the inner core 9a occupying the center of the powder is larger than the outer shell 9b and the molar ratio Ba / Ti of the outer shell 9b is smaller than 1, the molar ratio Ba / Ti is the outer shell. A BT powder having an average particle size of about 100 nm is prepared which is larger than the molar ratio Ba / Ti of the BT powder forming 9b, and the molar ratio Ba / Ti is more than 1 with respect to the BT powder having an average particle size of about 100 nm. It is obtained by mixing a small BT powder having an average particle size of about 30 nm so as to be 30 to 70% by mass and then calcining at about 700 to 800 ° C.

  The molar ratio of barium and titanium in the BT powder is measured using a transmission electron microscope equipped with an energy dispersive element analyzer (EDS). At the time of analysis, BT powder is dispersed on a carbon mesh for a transmission electron microscope, about 10 BT powders in the range of ± 30% of the average particle diameter of BT powder are extracted, and an average value thereof is obtained. In the observation, the spot size of the electron beam is 5 nm, and the same analysis is performed from the surface of the BT powder to the center.

  The average particle size of the BT powder is preferably 0.11 to 0.17 μm. If the average particle size of the BT powder is 0.11 μm or more, grain growth during sintering can be suppressed, so that there is an advantage that the dielectric constant can be improved and the dielectric loss can be reduced. When it is 0.17 μm or less, it becomes easy to dissolve an additive such as a rare earth element to the inside of the crystal particles 9.

Regarding the additive, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder and Er ₂ O ₃ powder, at least one rare earth element (RE) oxide powder and V ₂ O ₅ powder It is preferable to use an average particle size equal to or less than that of BT powder.

Next, these raw material powders are obtained by adding 0 to 0.3 mol of V ₂ O ₅ powder, Y ₂ O ₃ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder and 100 mol of barium constituting BT powder. A rare earth element (RE) selected from Er ₂ O ₃ powder is blended at a ratio of 0.4 to 1.8 mol in terms of RE ₂ O ₃ and, if necessary, sintered within a range where desired dielectric properties can be maintained. Glass powder is added as a binder to obtain a raw material powder. The addition amount of the glass powder is preferably 0.5 to 2 parts by mass when the total amount of BT powder as the main raw material 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 1.2 to 4 μm from the viewpoint of reducing the thickness of the dielectric layer for increasing 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 then fired in a reducing atmosphere. The firing temperature is preferably 1050 to 1150 ° C. for the purpose of controlling the solid solution of the additive in the BT powder used in the present invention and the grain growth of the crystal grains 9.

In addition, after firing, the capacitor body 1 may be subjected to heat treatment (reoxidation treatment) again in a weak reducing atmosphere. The reason for this heat treatment is that the insulation resistance of the multilayer ceramic capacitor, which was about 5 × 10 ⁶ Ω after firing, can be increased to 10 ⁷ Ω or more. 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. In this way, it is possible to produce a multilayer ceramic capacitor in which the dielectric ceramic is highly insulating.

  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.

First, as raw material powders, BT powders having different molar ratios Ba / Ti in the inner core and outer shell, 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 Powders were prepared, and these various powders were mixed in the proportions shown in Table 1. The addition amount of 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 is a ratio to 100 mol of BT powder. These raw material powders having a purity of 99.9% were used. The average particle size of the BT powder was 0.14 μm. Further, 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. 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 total amount of BT powder.

  Next, polyvinyl alcohol and ion-exchanged water were added to these raw material powders and wet mixed using zirconia balls having a diameter of 5 mm.

  Next, the wet-mixed powder is put into a mixed solvent of toluene and alcohol in which polyvinyl butyral resin is dissolved, wet-mixed using a zirconia ball having a diameter of 5 mm, and a ceramic slurry is prepared. A ceramic green sheet of 0.0 μm was produced.

  Next, a plurality of rectangular internal electrode patterns mainly composed of Ni were formed on the upper surfaces of these ceramic green sheets. The conductor paste for forming the internal electrode pattern was obtained by adding 15 parts by mass 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 about 30 ceramic green sheets on which no internal electrode patterns were printed were laminated on each of the upper and lower surfaces. A sheet laminated body using a ceramic green sheet having a thickness of 2.0 μm was produced by closely adhering under a pressure of 10 ⁷ Pa and a time of 10 minutes, and then each sheet laminated body was cut into a predetermined size to obtain a capacitor body. A molded body was formed.

Next, after debinding the capacitor body molded body in the atmosphere, it was fired in hydrogen-nitrogen at 1110 to 1130 ° C. for 2 hours to produce a capacitor body (for sample No. 23, 1110 ° C., sample No. 24 is 1130 ° C, and other samples are 1120 ° C). Further, the sample was subsequently subjected to a reoxidation treatment at 1000 ° C. for 4 hours in a nitrogen atmosphere. The size of the capacitor body was 0.95 mm × 0.48 mm × 0.48 mm, the thickness of the dielectric layer was 1.5 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 all cases, the number of samples was 10, and the average value was obtained. The relative dielectric constant and dielectric loss were determined from the thickness of the dielectric layer and the effective area of the internal electrode layer, measured at a capacitance of 25 ° C., a frequency of 1.0 kHz, and a measurement voltage of 1 Vrms. Moreover, the temperature characteristic of the capacitance was obtained by measuring the capacitance in a temperature range of −55 to 85 ° C., and obtaining a value at which the change rate of the capacitance was maximum with respect to 25 ° C. in this temperature range.

The high temperature load test was conducted up to 1000 hours under the conditions of a temperature of 85 ° C. and an applied voltage of 10V. The life characteristics in the high-temperature load test were 20 samples each, and any one of the multilayer ceramic capacitors having an insulation resistance of less than 10 ⁶ Ω was considered defective.

  The AC voltage dependence of the relative dielectric constant was determined from the ratio between the relative dielectric constant obtained from the electrostatic capacity when the AC voltage was 0.1 V and the relative dielectric constant obtained from the electrostatic capacity when the AC voltage was 1 V. . The number of samples at this time was 10 for each sample.

  The average grain size of the crystal particles constituting the dielectric layer is determined by polishing the fracture surface of the sample that is the capacitor body after firing, and then taking a picture of the internal structure using a scanning electron microscope. When drawing 20 to 30 circles, selecting crystal grains in and around the circle, processing the image of the outline of each crystal particle, finding the area of each particle, and replacing it with a circle with the same area The diameter was calculated from the average value.

  Regarding the molar ratio Ba / Ti in the crystal particles, first, a laminated ceramic capacitor serving as a sample to be analyzed was polished or cut to produce a thin plate sample. Next, this thin plate-like sample was processed by ion milling to prepare a sample for observation with a transmission electron microscope. For this analysis, a transmission electron microscope equipped with an elemental analysis instrument was used. At this time, the spot size of the electron beam is about 5 nm, and analysis is performed at intervals of 20 to 50 nm from the grain boundary to the center as shown in FIG. It was divided into small regions, and the average value was determined for each to determine the molar ratio Ba / Ti of the inner core and outer shell in the crystal grains. The crystal grains to be selected were crystal grains 9 having a ratio (aspect ratio) between the maximum diameter and the minimum diameter of the crystal grains of 1.3 or less and in the range of ± 60% of the average particle diameter. The crystal grains 9 in the range of ± 60% of the average grain size are obtained by calculating the area by image processing from the outline of the crystal grains, and the diameter when replaced with a circle having the same area as the area is ± the average grain size. It was supposed to be in the range of 60%. The analysis for obtaining such a molar ratio Ba / Ti was performed on five crystal grains, and the molar ratio Ba / Ti was obtained from the average value thereof.

  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 multilayer ceramic capacitor mixed with boric acid and sodium carbonate and dissolved is dissolved in hydrochloric acid. First, qualitative analysis of the elements contained in the dielectric ceramic is performed 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, it confirmed from the said composition analysis that the composition of the produced dielectric ceramic was the same as a preparation composition. Table 1 shows the composition, the firing temperature, and the characteristics after firing.

  As is clear from the results in Table 1, sample No. 1 to 6, 9, 10, 12 to 15, 17, 20, and 21 have a relative dielectric constant of 3010 or more at room temperature (25 ° C.) and a temperature of −55 to 85 ° C. based on room temperature (25 ° C.). The maximum rate of change of the relative permittivity in the range was within ± 14%, and the AC voltage dependency of the relative permittivity obtained by setting the AC voltage to 1.0 V and 0.1 V was 1.7 times or less.

Further, the composition of the dielectric ceramic constituting the dielectric layer is 0.03 to 0.3 mole of vanadium in terms of V ₂ O ₅ with respect to 100 moles of barium constituting barium titanate, rare earth element (RE). Sample No. in which 0.4 to 1.8 mol in terms of RE ₂ O ₃ was contained. No. 2 to 6, 9, 10, 12 to 15, 17, 20, and 21 have a relative dielectric constant of 3010 or more at room temperature (25 ° C.) and a temperature of −55 to 85 ° C. based on room temperature (25 ° C.). The maximum change rate of the relative permittivity in the range is within ± 14%, and the AC voltage dependency of the relative permittivity obtained by setting the AC voltage to 1.0 V / 0.1 V is 1.7 times or less. The high temperature load test at 85 ° C. and 10 V satisfied 1000 hours.

Further, the composition of the dielectric ceramic constituting the dielectric layer is 0.03 to 0.15 mole in terms of V ₂ O ₅ with respect to 100 moles of barium constituting barium titanate, rare earth element (RE). Sample No. in which 0.4 to 1.0 mol in terms of RE ₂ O ₃ was contained. 2 to 4, 9, 12 to 15, 17, 20, and 21 had a relative dielectric constant of 3100 or more at room temperature (25 ° C.).

  On the other hand, samples (sample Nos. 7, 8, 11, 16, 18, 19 and 22 to 24) outside the scope of the present invention have a relative dielectric constant of 3000 or more at room temperature (25 ° C.) and room temperature (25 AC) with a relative permittivity obtained by assuming that the maximum change rate of the relative permittivity within a temperature range of −55 to 85 ° C. is within ± 15% and the AC voltage is 1.0 V / 0.1 V. It did not satisfy any of the characteristics that the dependence was less than twice.

  The multilayer ceramic capacitor according to the present invention has been described in detail above. However, the scope of the present invention is not limited to these descriptions, and can be appropriately changed or improved without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer 9 Crystal grain 9a Inner core 9b Outer shell 11 Grain boundary phase

Claims (3)

A multilayer ceramic capacitor having a capacitor body in which dielectric layers and internal electrode layers are alternately stacked, and an external electrode provided on an end face of the capacitor body and connected to the internal electrode layer, wherein the dielectric layer Is composed of dielectric ceramics composed of crystal particles mainly composed of barium titanate, and containing one kind of rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium, and vanadium. In addition, one rare earth element (RE) selected from yttrium, dysprosium, holmium and erbium is added in an amount of 0.4 to 1.8 mol in terms of RE ₂ O ₃ and vanadium is added to 100 mol of barium constituting barium titanate. as well as 0 to 0.30 molar content in terms _of V ₂ O _5, wherein the crystal grains, the center of the crystal grains And an outer shell surrounding the inner core, the molar ratio Ba / Ti of barium and titanium in the inner core is 0.98 to 1.10, and the molar ratio of barium and titanium in the outer shell. A multilayer ceramic capacitor having a ratio Ba / Ti of 0.9 to 0.97 and an average particle diameter of 0.18 to 0.27 μm. The dielectric porcelain is 0.03 to 0.30 mol in terms of V ₂ O _{5 and the} rare earth element (RE) in terms of RE ₂ O ₃ with respect to 100 mol of barium constituting the barium titanate. The multilayer ceramic capacitor according to claim 1, which is contained in an amount of 0.4 to 1.8 mol. The dielectric porcelain is 0.03 to 0.15 mol in terms of V ₂ O _{5 and the} rare earth element (RE) in terms of RE ₂ O ₃ with respect to 100 mol of barium constituting the barium titanate. The multilayer ceramic capacitor according to claim 1, which is contained in an amount of 0.4 to 1.0 mol.

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