JP5087938B2 - Dielectric ceramic composition and multilayer ceramic capacitor - Google Patents

Description

The present invention relates to a dielectric ceramic composition and a multilayer capacitor. More specifically, the present invention relates to a dielectric ceramic composition based on KSr ₂ Nb ₅ O ₁₅ having a tungsten bronze structure and a multilayer using the dielectric ceramic composition. It relates to ceramic capacitors.

  The multilayer ceramic capacitor which is the main use of the present invention is generally manufactured as follows.

  First, a ceramic green sheet containing a dielectric ceramic raw material, which is provided with a conductive material serving as an internal electrode with a desired pattern on its surface, is prepared.

  Next, a plurality of ceramic green sheets including the ceramic green sheet provided with the conductive material described above are laminated and thermocompression bonded, thereby producing an integrated raw laminate.

  The raw laminate is then fired, thereby obtaining a sintered laminate. An internal electrode made of the above-described conductive material is formed inside the laminate.

  Next, external electrodes are formed on the outer surface of the laminate so as to be electrically connected to specific ones of the internal electrodes. The external electrode is formed, for example, by applying and baking a conductive paste containing conductive metal powder and glass frit on the outer surface of the laminate. In this way, a multilayer ceramic capacitor is completed.

  In order to reduce the manufacturing cost of the multilayer ceramic capacitor, it is desirable that Ni, which is inexpensive, is used for the internal electrode. At this time, since Ni is a base metal, the atmosphere during firing needs to be a reducing atmosphere in order to prevent oxidation of Ni during firing of the laminate.

In order to fire in a reducing atmosphere, the dielectric ceramic material is required to have reduction resistance. As a material having reduction resistance and excellent electrical characteristics, Patent Document 1 discloses a KSr ₂ Nb ₅ O ₁₅ based ceramic composition. This is quite different from barium titanate having a tungsten bronze structure and a perovskite structure.
WO 2006/114914 A1 (full text)

The KSr ₂ Nb ₅ O ₁₅ based ceramic composition of Patent Document 1 shows an excellent dielectric constant in a multilayer ceramic capacitor having a Ni internal electrode.

However, although the KSr ₂ Nb ₅ O ₁₅ ceramic composition of Patent Document 1 has a sufficient resistivity at room temperature, the resistivity is slightly insufficient at a high temperature of 150 ° C. or higher. For this reason, there is a concern that the operation becomes unstable in an environment at a high temperature such as an automobile.

  The present invention has been made in view of such problems, and provides a dielectric ceramic composition exhibiting sufficient resistivity even at a high temperature of 150 ° C. or higher, and a multilayer ceramic capacitor using the same. It is aimed.

That is, the dielectric ceramic composition of the present invention has a composition formula {(K _1−x Na _x ) Sr ₂ } _m Nb ₅ O ₁₅ (where 0 ≦ x ≦ 0.2, 0.96 ≦ m ≦ 1. 16 ) a dielectric ceramic composition containing a tungsten bronze-type composite oxide as a main component, and 0.05 to 20 mol parts of Mn with respect to 100 mol parts of the main component as a subcomponent ; 0.25 to 30 mol parts of Li, and at least one content selected from Cr, Co, Fe, Ni, Zn, Mg, and Si is 100 parts by weight of the main component, It is 5.0 parts by weight or less (including 0) .

In the dielectric ceramic composition of the present invention, 70 mol% or less of Sr in the main component may be substituted with at least one selected from Ba and Ca.

  The dielectric ceramic composition of the present invention is electrically connected to the plurality of laminated dielectric ceramic layers of the present invention, internal electrodes disposed between these dielectric ceramic layers, and these internal electrodes. In addition, the present invention is also directed to a multilayer ceramic capacitor having an external electrode, and particularly to a multilayer ceramic capacitor in which the main component of the internal electrode is Ni.

  According to the dielectric ceramic composition of the present invention, a sufficiently high resistivity can be obtained even at a high temperature due to the synergistic action of the subcomponents Mn and Li. Therefore, it is possible to obtain a multilayer ceramic capacitor having stable characteristics even at high temperatures such as for automotive applications.

  First, a multilayer ceramic capacitor, which is the main use of the dielectric ceramic of the present invention, will be described. FIG. 1 is a cross-sectional view showing a general multilayer ceramic capacitor 1.

  The multilayer ceramic capacitor 1 includes a rectangular parallelepiped ceramic multilayer body 2. The ceramic laminate 2 includes a plurality of laminated dielectric ceramic layers 3 and a plurality of internal electrodes 4 and 5 formed along an interface between the plurality of dielectric ceramic layers 3. The internal electrodes 4 and 5 are formed so as to reach the outer surface of the ceramic laminate 2, but are drawn to the internal electrode 4 and the other end surface 7 that are drawn to one end face 6 of the ceramic laminate 2. The internal electrodes 5 are alternately arranged inside the ceramic laminate 2 so that electrostatic capacity can be obtained via the dielectric ceramic layer 3.

  The conductive material for the internal electrodes 4 and 5 is preferably nickel or a nickel alloy, which is low cost.

  In order to take out the above-described capacitance, on the outer surface of the ceramic laminate 2 and on the end faces 6 and 7, so as to be electrically connected to any one of the internal electrodes 4 and 5, External electrodes 8 and 9 are respectively formed. As the conductive material contained in the external electrodes 8 and 9, the same conductive material as in the case of the internal electrodes 4 and 5 can be used, and silver, palladium, a silver-palladium alloy, and the like can also be used. The external electrodes 8 and 9 are formed by applying and baking a conductive paste obtained by adding glass frit to such metal powder.

  Further, first plating layers 10 and 11 made of nickel, copper, or the like are formed on the external electrodes 8 and 9 as required, and a second plating layer made of solder, tin, or the like is further formed thereon. Plating layers 12 and 13 are formed, respectively.

  Next, details of the dielectric ceramic of the present invention will be described.

The main component (K _1-x Na _x ) Sr ₂ Nb ₅ O ₁₅ (where 0 ≦ x <0.2) has a tungsten bronze type crystal structure, which is represented by barium titanate. It is completely different from the perovskite structure.

The molar ratio of each K site, Sr site, Nb site, and O site in the main component is basically 1: 2: 5: 15, but may be slightly increased or decreased as long as the tungsten bronze structure can be maintained. . However, when the composition formula is (KSr ₂ ) _m Nb ₅ O ₁₅ , if m is larger than 1.16 or smaller than 0.96, the sinterability is deteriorated.

  The subcomponents Mn and Li are contained in an amount of 0.05 to 20 mol parts and 0.25 to 30 mol parts, respectively, with respect to 100 mol parts of the main component. If any of the contents of Mn and Li is outside the scope of the present invention, the resistivity at high temperatures is low.

The K site in the main component is preferably not substituted with Na, but the substitution amount may be 20 mol% or less .
If the amount of Na substitution exceeds 20 mol% , not only the dielectric constant decreases, but also the effect of improving the high temperature resistivity by the synergistic action of Mn and Li is suppressed.

  Part of the Sr site in the main component may be substituted with Ba and / or Ca. The permissible amount of substitution can be appropriately designed according to the required characteristics, but the upper limit of the permissible amount is about 70 mol% in total of Ba and Ca.

  Furthermore, the dielectric ceramic composition of the present invention preferably contains at least one selected from Cr, Co, Fe, Ni, Zn, Mg, and Si as an accessory component in addition to Mn and Li. These subcomponents have the effect of reducing the dielectric loss of the dielectric ceramic composition. These contents are preferably 5.0 parts by weight or less with respect to 100 parts by weight of the main component. When the content exceeds 5.0 parts by weight, dielectric loss increases and resistivity at high temperatures decreases.

Although it is a manufacturing method of the dielectric ceramic composition of this invention, this may be a conventionally existing method. For example, it can be obtained by a solid phase method in which starting materials such as oxide powder and carbonate are mixed and the obtained mixed powder is heat-treated and synthesized. Further, a wet synthesis method such as an oxalic acid method, a hydrothermal synthesis method, or a hydrolysis method may be used. In general, a method of first synthesizing a powder of a tungsten bronze type compound KSr ₂ Nb ₅ O ₁₅ , mixing subcomponents such as MnO and Li ₂ CO ₃ with the main component powder, molding, and firing is used. . However, KSr ₂ Nb ₅ when synthesizing a powder of O _15, by previously by mixing subcomponents raw materials in advance to the main component of the raw materials, KSr ₂ Nb ₅ O ₁₅ modified with secondary components This powder may be obtained and used as a ceramic raw material powder.

[Experimental Example 1] In this experimental example, the contents of subcomponents Mn and Li were changed with respect to the main component (KSr ₂ Nb ₅ O ₁₅ ), and the influence on the electrical characteristics was examined. Sample numbers are 1 to 18, and the results of composition and electrical characteristics are shown in Table 1. Details will be described below.

K ₂ CO ₃ , SrCO ₃ , Nb ₂ O ₅ as starting materials of main components are weighed so as to satisfy (KSr ₂ ) _m Nb ₅ O ₁₅ satisfying m of sample numbers 1 to 18 in Table 1. After being mixed in a ball mill, it was dried and then subjected to heat treatment synthesis at 1000 ° C. for 2 hours to obtain a main component powder composed of (KSr ₂ ) _m Nb ₅ O ₁₅ .

MnO and Li ₂ CO ₃ were weighed so that Mn and Li correspond to mole parts of sample numbers corresponding to 100 mole parts of the main ingredients with respect to the principal powders of sample numbers 1 to 18 in Table 1. These were mixed in a solvent by a ball mill and then dried to obtain ceramic raw material powders of sample numbers 1 to 18.

  Next, a polyvinyl butyral binder and ethanol were added to the ceramic raw material powders of Sample Nos. 1 to 18, and then wet mixed by a ball mill to prepare ceramic slurries. Each ceramic slurry is formed into a sheet by a doctor blade method to obtain a rectangular ceramic green sheet having a thickness of 8 μm, and then a conductive paste mainly composed of Ni is formed on the ceramic green sheet for each sample. Printing was performed to form a conductive paste film for internal electrodes.

Subsequently, for each ceramic green sheet of each sample, as shown in FIG. 1, a plurality of stacked end portions from which the conductive paste films were drawn were alternately stacked to obtain a raw laminate. These raw laminates were heated to a temperature of 350 ° C. in an N ₂ gas atmosphere to decompose and burn the binder, and then H ₂ —N ₂ —H _{2 with} an oxygen partial pressure of 10 ⁻⁹ to 10 ⁻¹² MPa. The ceramic laminate was obtained by firing at a temperature shown in Table 1 for 2 hours in a reducing atmosphere composed of O gas. Thereafter, an Ag paste containing B ₂ O ₃ —SiO ₂ —BaO glass frit is applied to both end faces of each sample laminate, and baked at a temperature of 800 ° C. in an N ₂ gas atmosphere. Connected external electrodes were formed.

In this way, samples of multilayer ceramic capacitors of sample numbers 1 to 18 were obtained. The outer diameters of these multilayer ceramic capacitors were 3.2 mm in width, 4.5 mm in length, 0.5 mm in thickness, and the thickness of the dielectric ceramic layer interposed between the internal electrodes was 6 μm. . The number of effective dielectric ceramic layers was 5, and the area of the counter electrode per layer was 2.5 × 10 ⁻⁶ m ² .

  For each of the above samples, the capacitance C and the dielectric loss DF were measured under the conditions of 25 ° C., frequency 1 kHz, 1 Vrms using an automatic bridge type measuring device, and the dielectric constant was obtained from the obtained capacitance C. ε was calculated. Moreover, about each sample, the direct current voltage of 30V was applied for 1 minute at 25 degreeC and 150 degreeC using the insulation resistance meter, the insulation resistance R was measured, and resistivity (rho) was computed from the obtained insulation resistance R. The results are shown in Table 1.

  According to the results shown in Table 1, among the sample numbers 1 to 18, the samples in which the contents of Mn and Li and m are within the scope of the present invention are mainly composed of Ni at a temperature of 1100 ° C. or lower in a reducing atmosphere. The internal electrode and the dielectric ceramic layer can be fired at the same time, and a high dielectric constant ε and resistivity ρ can be obtained. It became more than 8.0.

  On the other hand, Sample Nos. 1 and 9 whose Mn and Li contents are outside the scope of the present invention have a log ρ (ρ / Ω · m) value of resistivity ρ at a high temperature of 150 ° C. of 8. It was a low value of less than 0.

  Further, Sample No. 18 in which the value of m was smaller than the range of the present invention was not sufficiently sintered at the firing temperature of 1100 ° C., and the desired characteristics could not be measured.

[Experimental Example 2] In this experimental example, Cr, Co, Fe, Ni, Zn, Mg, a composition containing subcomponents Mn and Li with respect to the main component (KSr ₂ Nb ₅ O ₁₅ ) were added. This shows the effect of containing at least one selected from Si as a subcomponent. Sample numbers are 101 to 118, and Table 2 shows the results of composition and electrical characteristics. Details will be described below.

K ₂ CO ₃ , SrCO ₃ , Nb ₂ O ₅ as starting materials of main components are weighed so as to satisfy (KSr ₂ ) _m Nb ₅ O ₁₅ satisfying m of sample numbers 101 to 118 in Table 2. After being mixed in a ball mill, the mixture was dried and then heat-treated and synthesized at 1100 ° C. for 2 hours to obtain a main component powder composed of (KSr ₂ ) _m Nb ₅ O ₁₅ .

MnO and Li ₂ CO ₃ were weighed so that Mn and Li correspond to the molar part of the corresponding sample number with respect to 100 parts by mole of the main ingredient powder of sample numbers 101 to 118 in Table 2. Furthermore, Cr ₂ O ₃ , Co ₂ O ₃ so that at least one selected from Cr, Co, Fe, Ni, Zn, Mg, Si corresponds to the weight part of the corresponding sample number with respect to 100 parts by weight of the main component. Fe ₂ O ₃ , NiO, ZnO, MgO, and SiO ₂ were weighed. These were mixed in a solvent by a ball mill and then dried to obtain ceramic raw material powders of sample numbers 101 to 118.

Next, using the ceramic raw material powders of sample numbers 101 to 118, a raw laminate was obtained through the same steps as in Experimental Example 1. This raw laminate is heated to a temperature of 350 ° C. in an N ₂ gas atmosphere to decompose and burn the binder, and then H ₂ —N ₂ —H ₂ O having an oxygen partial pressure of 10 ⁻⁹ to 10 ⁻¹² MPa. The ceramic laminate was obtained by firing for 2 hours at a temperature shown in Table 2 in a reducing atmosphere composed of gas.

  An external electrode electrically connected to the internal electrode was formed on the obtained ceramic laminate through the same steps as in Experimental Example 1. Thus, samples of the multilayer ceramic capacitors of sample numbers 101 to 118 were obtained.

  For each of the above samples, the dielectric constant ε, dielectric loss DF, and resistivity ρ at 25 ° C. and 150 ° C. were evaluated in the same manner as in Experimental Example 1. The results are shown in Table 2.

  According to the results shown in Table 2, sample numbers 101 to 103, 105 to 113, and 115 to 117 within the composition range of the present invention are internal electrodes mainly composed of Ni at a temperature of 1100 ° C. or lower in a reducing atmosphere. And a dielectric ceramic layer can be fired at the same time, and a high dielectric constant ε and high resistivity ρ can be obtained. In particular, the log ρ (ρ / Ω · m) value of the resistivity ρ at a high temperature of 150 ° C. That's it. Furthermore, since at least one selected from Cr, Co, Fe, Ni, Zn, Mg, and Si is contained, the dielectric loss DF tends to decrease as a whole as compared with the sample of Experimental Example 1. It was seen.

  On the other hand, the sample numbers 104, 114, in which the content of at least one selected from Cr, Co, Fe, Ni, Zn, Mg, Si exceeded 5.0 parts by weight with respect to 100 parts by weight of the main component, In 118, the dielectric loss DF was as high as 10% or more, and the log ρ (ρ / Ω · m) value of the resistivity ρ at a high temperature of 150 ° C. was as low as less than 8.0.

[Experimental Example 3] In this experimental example, the effect of substituting Na for a part of the K site in the composition containing the minor components Mn and Li with respect to the main component (KSr ₂ Nb ₅ O ₁₅ ) is shown. It is. Sample numbers are 201 to 224, and the results of composition and electrical characteristics are shown in Table 3. Details will be described below.

As starting materials, K ₂ CO ₃ , Na ₂ CO ₃ , SrCO ₃ , and Nb ₂ O ₅ satisfy x and m of sample numbers 201 to 224 in Table 2 {(K _1-x Na _x ) Sr ₂ } _m Nb ₅ O ₁₅ was weighed, and MnO and Li ₂ CO ₃ were weighed so that Mn and Li correspond to the mole number of the sample number corresponding to 100 mole parts of the main component. These were mixed in a ball mill in a solvent, dried and then heat-treated and synthesized at 1000 ° C. for 2 hours to obtain a main component powder of (KSr ₂ ) _m Nb ₅ O ₁₅ modified with Mn and Li.

At least selected from Cr, Co, Fe, Ni, Zn, Mg, and Si with respect to 100 parts by weight of the main component, based on 100 parts by weight of the main component powder of sample numbers 201 to 224 in Table 3 Cr ₂ O ₃ , Co ₂ O ₃ , Fe ₂ O ₃ , NiO, ZnO, MgO, and SiO ₂ were weighed so that one type was a part by weight of the corresponding sample number. These were mixed in a solvent by a ball mill and then dried to obtain ceramic raw material powders of sample numbers 201 to 224.

Subsequently, using the ceramic raw material powders of sample numbers 201 to 224, a raw laminate was obtained through the same steps as in Experimental Example 1. This raw laminate is heated to a temperature of 350 ° C. in an N ₂ gas atmosphere to decompose and burn the binder, and then H ₂ —N ₂ —H ₂ O having an oxygen partial pressure of 10 ⁻⁹ to 10 ⁻¹² MPa. The ceramic laminate was obtained by firing at a temperature shown in Table 3 for 2 hours in a reducing atmosphere composed of gas.

  An external electrode electrically connected to the internal electrode was formed on the obtained ceramic laminate through the same steps as in Experimental Example 1. Thus, samples of the multilayer ceramic capacitors of sample numbers 201 to 224 were obtained.

  For each of the above samples, the dielectric constant ε, dielectric loss DF, and resistivity ρ at 25 ° C. and 150 ° C. were evaluated in the same manner as in Experimental Example 1. The results are shown in Table 2.

  According to the results shown in Table 3, sample numbers 201 to 203, 205 to 208, and 210 to 217 within the composition range of the present invention are internal electrodes mainly composed of Ni at a temperature of 1100 ° C. or lower in a reducing atmosphere. And a dielectric ceramic layer can be fired simultaneously, and a high dielectric constant ε and resistivity ρ can be obtained. In particular, the log ρ (ρ / Ω · m) value of the resistivity ρ at a high temperature of 150 ° C. is 8.0 or more It became.

On the other hand, Sample Nos. 204, 209, and 218 to 224 in which the Na substitution amount x exceeds 0.2 or the other subcomponents exceed 5.0 parts by weight have Mn and Li contents of the present invention. Despite being within the range, the log ρ (ρ / Ω · m) value of the resistivity ρ at a high temperature of 150 ° C. was a low value of less than 8.0.

1 is a cross-sectional view schematically showing a multilayer ceramic capacitor 1 according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic capacitor 2 Ceramic multilayer body 3 Dielectric ceramic layer 4,5 Internal electrode 8,9 External electrode

Claims (3)

Tungsten bronze type complex oxide represented by the compositional formula {(K _1−x Na _x ) Sr ₂ } _m Nb ₅ O ₁₅ (where 0 ≦ x ≦ 0.2, 0.96 ≦ m ≦ 1.16 ) the a dielectric ceramic composition comprising as a main component, as a subcomponent, the Mn of 0.05 to 20 parts by mole with respect to the 100 parts by mol of the main ingredient, and Li of 0.25 to 30 molar parts, and In addition, the content of at least one selected from Cr, Co, Fe, Ni, Zn, Mg, and Si is 5.0 parts by weight or less (including 0) with respect to 100 parts by weight of the main component. ) that dielectric ceramic composition characterized. 2. The dielectric ceramic composition according to claim 1 , wherein 70 mol% or less of Sr in the main component is substituted with at least one selected from Ba and Ca. A plurality of laminated dielectric ceramic layers, internal electrodes disposed between the dielectric ceramic layers, and external electrodes electrically connected to the internal electrodes, the dielectric ceramic layer comprising: formed by the dielectric ceramic composition according to any one of claims 1 to 2, also, the internal electrodes, multilayer ceramic capacitor, characterized in that it is formed of Ni as a main component.