JP2009249257A - Dielectric ceramic and laminated ceramic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep high dielectric constant without damaging temperature characteristics and to secure required reliability and AC electric field characteristics. <P>SOLUTION: The dielectric ceramic comprises crystal particles 1 and a crystal grain boundary 2. When observed in an optional cross-section, ≥70% of the crystal particles 1 has a first region 3 consisting essentially of BaTiO<SB>3</SB>and a second region 4 consisting essentially of (Ba, Ca)TiO<SB>3</SB>, wherein the peripheral length L1 of an exposed part of the first region 3 to the crystal grain boundary 2 is formed longer than the peripheral length L2 of an exposed part of the second region 4 to the crystal grain boundary, and the second regions 4 are surrounded with the first region 3. It is preferable that at least one kind selected from a group of Si, Mg, Mn and V as an accessory ingredient and further at least one kind selected from a group of Sm, Gd, Dy, Er, Ho, Y and Zr are added if need. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a dielectric ceramic and a multilayer ceramic capacitor, and more particularly, a dielectric ceramic suitable for a dielectric material of a small and large capacity multilayer ceramic capacitor, and a multilayer ceramic capacitor manufactured using the dielectric ceramic. About.

  Multilayer ceramic capacitors are electronic components used in circuits of a wide variety of electronic devices, and with the miniaturization of electronic devices, miniaturization of multilayer ceramic capacitors is also required.

  This type of multilayer ceramic capacitor is usually formed by laminating a dielectric layer and a dielectric layer with an internal electrode interposed therebetween and sintering the multilayer body. In order to reduce the size of the multilayer ceramic capacitor without reducing the capacitance, it is necessary to make the dielectric layer thinner.

  By the way, with the thinning of the dielectric layer, there is a demand for a dielectric ceramic having a high dielectric constant and high reliability that can withstand long-time driving at high temperatures.

As a dielectric ceramic material having a high dielectric constant and good reliability, a (Ba, Ca) TiO ₃ (hereinafter referred to as “BCT”)-based material is known. In this BCT, by replacing a part of Ba of BaTiO ₃ (hereinafter referred to as “BT”) with Ca, the interstitial distance is reduced as compared with BT, and thereby oxygen vacancy, which is considered to cause a decrease in reliability. The movement of the hole can be suppressed. Therefore, BCT is more reliable than BT.

  As a prior art using this BCT, for example, it is a dielectric ceramic (dielectric ceramic) having BCT crystal particles and BT crystal particles, and the average particle diameter of the BT crystal particles is the BCT system. From the composite oxide containing an alkaline earth element, a rare earth element, and Si on the surface of the BT crystal particle, and Mg and Mn are present over the entire area of the BT crystal particle, which is smaller than the average particle diameter of the crystal particle. There is known a dielectric ceramic having a coating layer of which the BCT crystal particles have a core-shell structure (Patent Document 1).

  The dielectric ceramic disclosed in Patent Document 1 has a mixed crystal structure of BT crystal grains having a high dielectric constant and good temperature characteristics, and BCT crystal grains having good DC bias characteristics. It is possible to obtain better DC bias characteristics compared to a uniform-structured dielectric ceramic made of system crystal grains, and a higher dielectric constant and better static performance than a uniform-structured dielectric ceramic made of BCT-type crystal grains. It becomes possible to obtain the temperature characteristic of the capacitance.

JP 2003-63863 A

  However, in Patent Document 1, although the ceramic structure of the dielectric ceramic is a mixed crystal structure of BCT crystal particles and BT crystal particles, the BT crystal particles are unevenly present locally, There is a case where the crystal particles are locally biased, and the local bias becomes relatively remarkable as the dielectric layer is thinned. That is, when the dielectric layer is thinned, when the cross section of the internal electrode is observed from the thickness direction, the probability of existence of a portion composed of only one of the BT crystal particles and the BCT crystal particles increases.

  Therefore, for example, when the ratio of the portion formed only of the BT crystal particles having poor reliability is increased, a short path made of the BT crystal particles is formed between the internal electrode and the internal electrode. When applied, depending on the load, the electrical resistance value may be reduced.

  In this case, it is possible to avoid the above problem by reducing the particle diameter of the crystal particles, but miniaturization of the crystal particles may cause a decrease in the relative dielectric constant.

  Further, in order to make the crystal particles fine, it is necessary to make the particle diameter of the ceramic powder as a raw material fine. However, if the particle diameter of the ceramic powder is made fine, the particles tend to aggregate. And as a result, when the ceramic powder is formed into a sheet, there is a possibility that the packing property is lowered and the forming density is lowered, and there is a possibility that local crystal particles are coarsened even after firing. It is difficult to ensure desired reliability.

  In addition, with the recent thinning of the dielectric layer, the applied AC voltage may be reduced to 0.1 V or less in a multilayer ceramic capacitor used around the IC. Therefore, it is necessary to suppress the fluctuation of the capacitance as much as possible even when the AC applied voltage is lowered. That is, realization of a dielectric ceramic having good AC electric field characteristics is desired.

  The present invention has been made in view of such a problem, and maintains a high dielectric constant without impairing temperature characteristics, and can ensure reliability and AC electric field characteristics. An object of the present invention is to provide a multilayer ceramic capacitor using a dielectric ceramic.

In order to achieve the above object, the dielectric ceramic according to the present invention is a dielectric ceramic having crystal grains and crystal grain boundaries, and 70% or more of the crystal grains are observed when any cross section is observed. ₃ and a second region mainly composed of (Ba, Ca) TiO ₃ , and the periphery of the exposed portion of the first region to the crystal grain boundary The length is longer than the peripheral length of the exposed portion of the second region to the grain boundary.

  In the present invention, the “crystal grain boundary” includes “crystal triple point”.

  The dielectric ceramic of the present invention is characterized in that the second region is surrounded by the first region.

  The dielectric ceramic of the present invention is characterized in that it contains at least one element selected from the group consisting of Si, Mg, Mn, and V.

  Furthermore, the dielectric ceramic of the present invention is characterized in that it contains at least one element selected from the group consisting of Sm, Gd, Dy, Er, Ho, Y, and Zr.

  The multilayer ceramic capacitor according to the present invention includes a ceramic sintered body in which dielectric layers and internal electrodes are alternately stacked, and external electrodes are formed at both ends of the ceramic sintered body. In the multilayer ceramic capacitor in which the internal electrode and the internal electrode are electrically connected, the dielectric layer is formed of any one of the above dielectric ceramics.

According to the dielectric ceramic of the present invention, when an arbitrary cross section is observed, 70% or more of the crystal grains are composed of the first region mainly composed of BaTiO ₃ and the main component composed of (Ba, Ca) TiO _3. And the peripheral length of the exposed portion of the first region to the crystal grain boundary is longer than the peripheral length of the exposed portion of the second region to the crystal grain boundary. In addition, it is possible to reduce the ratio at which the crystal grains have a BCT or BT uniform structure, and to realize a structure in which the BT surrounding the BCT that contributes to improving the reliability surrounds the BCT. As a result, even when the dielectric layer is thinned, the AC electric field characteristics can be improved while maintaining a high dielectric constant without impairing the temperature characteristics and having high reliability.

  In addition, at least one element selected from the group of Si, Mg, Mn, and V is included, and at least one element selected from the group of Sm, Gd, Dy, Er, Ho, Y, and Zr is included. Therefore, the relative permittivity can be further improved, and the reliability can be further improved.

  According to the multilayer ceramic capacitor of the present invention, since the dielectric layer is formed of any one of the above dielectric ceramics, the dielectric layer is thinned (for example, 2 μm or less). Even in such a case, it is possible to obtain a desired multilayer ceramic capacitor having both AC electric field characteristics and reliability, excellent temperature characteristics, and high dielectric constant.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view schematically showing a main part of one embodiment (first embodiment) of a dielectric ceramic according to the present invention.

The dielectric ceramic of the present invention includes crystal grains 1 and crystal grain boundaries 2, and 70% or more of the crystal grains 1 satisfy the following requirements (1) and (2) when an arbitrary cross section is observed. Yes. That is,
(1) having a first region 3 containing BT as a main component and a second region 4 containing BCT as a main component, and (2) a crystal of the first region 3 as shown in FIG. The peripheral length L1 of the exposed portion to the grain boundary 2 and the peripheral length L2 of the exposed portion of the second region 4 to the crystal grain boundary 2 have a relationship of L1> L2.

  As a result, a dielectric ceramic capable of achieving both AC electric field characteristics and reliability can be obtained.

  That is, BCT can reduce the interstitial distance by substituting a part of Ba of BT with Ca, thereby suppressing the movement of oxygen vacancies that cause a decrease in reliability. On the other hand, BT has a high dielectric constant and excellent temperature characteristics, and further contributes to improvement of AC electric field characteristics as compared with BCT.

  Therefore, the high dielectric constant can be maintained without impairing the temperature characteristics by coexisting the first region 3 mainly composed of BT and the second region 4 mainly composed of BCT in the same crystal grain. In addition, it is considered that both reliability and AC electric field characteristics can be achieved.

  However, according to the research results of the present inventors, L1 <L2, that is, the peripheral length L2 of the exposed portion of the second region 4 to the crystal grain boundary is set to the peripheral length of the exposed portion of the first region 3 to the crystal grain boundary. When it is longer than L1, it is difficult to cover almost the entire periphery of the first region 3 with the second region 4, and the exposed portion of the first region 3 to the crystal grain boundary 2 is not a little. I understood that.

  Therefore, in this case, when an electric field is applied to the multilayer ceramic capacitor, the electric field does not propagate along the crystal grain boundary 2 but propagates through the central portion of the crystal grain 1, that is, the first region 3 having low reliability. be able to. That is, a short path made of the BT crystal grains is formed between the internal electrode and the internal electrode, and an electric field propagates through the short path, so that it is difficult to improve reliability.

  On the other hand, when L1> L2, that is, the peripheral length L1 of the exposed portion of the first region 3 to the crystal grain boundary is longer than the peripheral length L2 of the exposed portion of the second region 4 to the crystal grain boundary 2, The second region 4 can be surrounded by the first region 3. And since the center part of the crystal grain 1 is the 2nd area | region 4 which has highly reliable BCT as a main component, an electric field must propagate along the crystal grain boundary 2, and internal electrode-internal electrode It is difficult to form a short path between them. As a result, high reliability can be obtained.

  With such a structure, it is possible to achieve both reliability and AC electric field characteristics.

  The reason why the crystal grains satisfying the requirements (1) and (2) are set to 70% or more is as follows.

  Even if crystal grains satisfying the requirements of (1) and (2) above exist in the crystal grains, if the ratio is less than 70%, the ratio of crystal grains in which BCT is not sufficiently surrounded by BT is relative This is because the desired reliability cannot be improved.

  The dielectric ceramic satisfying the requirements (1) and (2) can be manufactured by controlling the manufacturing conditions of the raw material powder. That is, as described later, for example, after preparing the BCT powder, the BaCT and BT are added to the BCT powder so that the BCT and BT have a predetermined blending amount, and the calcining temperature is adjusted to adjust the calcining temperature. (1) A dielectric ceramic that satisfies the requirements of (2) can be easily manufactured.

  FIG. 3 is a cross-sectional view schematically showing the second embodiment of the dielectric ceramic. When observed in an arbitrary cross section, 70% or more of crystal grains are as shown in FIG. A second region 4 is formed inside the first region 3.

  That is, also in this second embodiment, when observed in an arbitrary cross section, 70% or more of the crystal grains are the first region 3 containing BT as the main component and the second region containing BCT as the main component. Region 4. Only the periphery of the first region 3 is exposed at the crystal grain boundary 2, and the periphery of the second region 4 is not exposed at the crystal grain boundary 2. That is, the second region 4 is surrounded by the first region 3. Therefore, as in the first embodiment, the peripheral length L1 of the exposed portion of the first region 3 to the crystal grain boundary 2 is larger than the peripheral length L2 of the exposed portion of the second region 3 to the crystal grain boundary 2. It will be formed long.

  In the second embodiment as well, for the same reason as described in the first embodiment (FIGS. 1 and 2), a high dielectric constant is maintained without impairing temperature characteristics, and high reliability is achieved. Thus, the AC electric field characteristics can be improved.

  Moreover, although this dielectric ceramic has BT and BCT as main components, it is also preferable to add a subcomponent as needed within the range which does not affect a characteristic. In particular, at least one element selected from the group consisting of Si, Mg, Mn, and V, and at least one element selected from the group consisting of Sm, Gd, Dy, Er, Ho, Y, and Zr are added as sub-elements. By adding it as a component, it is possible to further improve the dielectric constant while maintaining good temperature characteristics and AC electric field characteristics, and it is possible to greatly improve the reliability.

  In addition, these subcomponents may be dissolved in the main component in a crystal grain, and may exist in a crystal grain boundary.

  Next, a multilayer ceramic capacitor manufactured using this dielectric ceramic will be described in detail.

  FIG. 4 is a cross-sectional view schematically showing an embodiment of the multilayer ceramic capacitor.

  In the multilayer ceramic capacitor, internal electrodes 6a to 6f are embedded in the ceramic sintered body 5, and external electrodes 7a and 7b are formed at both ends of the ceramic sintered body 5, and the external electrodes 7a and 7b are further formed. The first plating films 8a and 8b and the second plating films 9a and 9b are formed on the surface.

  That is, the ceramic sintered body 5 is formed by alternately laminating and firing the dielectric layers 10a to 10g and the internal electrode layers 6a to 6f made of the dielectric ceramic, and the internal electrode layers 6a, 6c, and 6e. Are electrically connected to the external electrode 7a, and the internal electrode layers 6b, 6d, 6f are electrically connected to the external electrode 7b. An electrostatic capacitance is formed between the opposing surfaces of the internal electrode layers 6a, 6c, 6e and the internal electrode layers 6b, 6d, 6f.

  Next, an example of a method for manufacturing the multilayer ceramic capacitor will be described in detail.

First, BaCO ₃ , CaCO ₃ , and TiO ₂ are prepared as ceramic raw materials, and a predetermined amount is weighed.

  Next, this weighed product is put into a ball mill together with cobblestones such as PSZ (Partially Stabilized Zirconia) balls and pure water, sufficiently mixed and pulverized in a wet manner, calcined at a temperature of 1000 ° C. or higher, and BCT Make a powder.

Next, a predetermined amount of BCT powder, BaCO ₃ , and TiO ₂ are weighed so that the ratio of BCT and BT in the main component raw material powder becomes a predetermined ratio. Then, this weighed product is put into a ball mill together with cobblestones such as PSZ balls and pure water, sufficiently mixed and pulverized in a wet manner, calcined at a temperature of about 1000 to 1150 ° C., and a main component raw material powder consisting of BCT and BT Is made.

  Furthermore, if necessary, the above-mentioned auxiliary component compound is added to the main component raw material powder, wet-mixed by a ball mill, and then dried to obtain a ceramic raw material powder.

  Next, this ceramic raw material powder is put into a ball mill together with an organic binder and an organic solvent and wet-mixed, thereby producing a ceramic slurry. Thereafter, the ceramic slurry is formed using a doctor blade method or the like to produce a ceramic green sheet.

  Next, screen printing is performed on the ceramic green sheet using the internal electrode conductive paste, and a conductive film having a predetermined pattern is formed on the surface of the ceramic green sheet.

  As the conductive material contained in the internal electrode conductive paste, it is preferable to use a base metal material mainly composed of Ni, Cu or an alloy thereof from the viewpoint of cost reduction.

Next, a plurality of ceramic green sheets on which a conductive film is formed are laminated in a predetermined direction, sandwiched between ceramic green sheets on which a conductive film is not formed, pressure-bonded, and cut into predetermined dimensions to produce a ceramic laminate. Thereafter, the binder removal treatment is performed at a temperature of 300 ° C. to 500 ° C., and the reducing atmosphere is made of H ₂ —N ₂ —H ₂ O gas whose oxygen partial pressure is controlled to 10 ⁻⁹ to 10 ⁻¹² MPa. Then, a baking treatment is performed at a temperature of 1200 to 1300 ° C. for about 2 hours. Thereby, the conductive film and the ceramic green sheet are co-sintered, and the ceramic sintered body 5 in which the internal electrodes 6a to 6f and the dielectric layers 10a to 10g are alternately laminated is obtained.

  Next, a conductive paste for external electrodes is applied to both end faces of the ceramic sintered body 5 and subjected to a baking treatment, whereby external electrodes 7a and 7b are formed.

  In addition, it is preferable to use base metal materials, such as Cu, also about the electroconductive material contained in the electroconductive paste for external electrodes from a viewpoint of cost reduction.

  In addition, as a method of forming the external electrodes 7a and 7b, a conductive paste for external electrodes may be applied to both end faces of the ceramic laminate, and then fired at the same time as the ceramic laminate.

  Finally, electrolytic plating is performed to form first plating films 8a and 8b made of Ni or the like on the surfaces of the external electrodes 7a and 7b, and solder and tin are further formed on the surfaces of the first plating films 8a and 8b. The second plating films 9a and 9b made of the like are formed, whereby a multilayer ceramic capacitor is manufactured.

  As described above, in the present multilayer ceramic capacitor, the dielectric layers 10a to 10g are manufactured using the dielectric ceramic, so that even if the dielectric layers 10a to 10g are thinned, the temperature characteristics are not impaired. In addition, it is possible to obtain a multilayer ceramic capacitor that can maintain a high dielectric constant, ensure good AC electric field characteristics, and have a good high temperature load life and excellent reliability.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the main components BCT and BT are produced by a solid phase synthesis method, but they may be produced by a hydrolysis method, a hydrothermal synthesis method, a coprecipitation method, or the like. Furthermore, the ceramic raw material can be appropriately selected according to the form of the synthesis reaction, such as nitrate, hydroxide, organic acid salt, alkoxide, chelate compound, etc. in addition to carbonate and oxide.

  Further, the internal electrode component may diffuse into the crystal grains or the crystal grain boundaries during the firing process of the multilayer ceramic capacitor. However, in this case, the electrical characteristics of the multilayer ceramic capacitor are not affected at all.

  Next, examples of the present invention will be specifically described.

[Production and preparation of main ingredient raw material powder]
[Sample No. 1]
A BaTiO ₃ powder having an average particle size of 200 nm was prepared and used as a main component raw material powder of sample number 1.

[Sample No. 2]
(Ba _0.95 Ca _0.05 ) TiO ₃ powder having an average particle diameter of 200 nm was prepared and used as the main component raw material powder of sample number 2.

[Sample No. 3]
(Ba _0.95 Ca _0.05 ) TiO ₃ powder having an average particle diameter of 200 nm was prepared. (Ba _0.95 Ca _0.05 ) TiO ₃ (BCT) and BaTiO ₃ (BT) are (Ba _0.95 Ca _0.05 ) TiO ₃ , BaCO ₃ and TiO ₂ so that the molar ratio is BCT: BT = 8: _2. Were weighed and put into a ball mill with PSZ balls and pure water and mixed. Subsequently, after drying this, it calcined for 2 hours at the temperature of 1000 degreeC, and produced the main component raw material powder of the sample number 3.

[Sample No. 4]
A main component raw material powder of Sample No. 4 was produced in the same manner as Sample No. 3 except that the calcining temperature was 1050 ° C.

[Sample No. 5]
A main component raw material powder of Sample No. 5 was produced in the same manner as Sample No. 3 except that the calcining temperature was 1100 ° C.

[Sample No. 6]
A main component raw material powder of Sample No. 6 was produced in the same manner as Sample No. 3 except that the calcining temperature was 1150 ° C.

[Sample No. 7]
BaTiO ₃ powder having an average particle size of 200 nm was prepared. Then, BaTiO ₃ , BaCO ₃ , CaCO ₃ and TiO ₂ are weighed so that (Ba _0.95 Ca _0.05 ) TiO ₃ (BCT) and BaTiO ₃ (BT) have a molar ratio of BCT: BT = 8: 2. Then, it was put into a ball mill with PSZ balls and pure water and mixed. Subsequently, after drying this, it calcined for 2 hours at the temperature of 1000 degreeC, and produced the main component raw material powder of the sample number 7.

[Production of multilayer ceramic capacitors]
1 mol part of MgO and 0.3 mol part of MnO are put into a ball mill together with PSZ balls and pure water and mixed with 100 mol parts of the main component raw material powders of the above sample numbers 1 to 7, and then dried to be ceramic. The raw material was obtained.

  Next, an organic solvent such as a polyvinyl butyral binder and ethanol was added to the ceramic raw material, and the mixture was wet mixed with a ball mill for a predetermined time to prepare a ceramic slurry. This ceramic slurry was formed into a sheet by a doctor blade method to produce a rectangular ceramic green sheet having a thickness of 2.5 μm. An internal electrode conductive paste containing Ni as a main component was prepared, and the internal electrode conductive paste was screen-printed on the ceramic green sheet to form a conductive layer on the ceramic green sheet.

Next, a plurality of ceramic green sheets on which conductive layers were formed were stacked so that the sides from which the conductive layers were drawn were staggered to obtain a stacked body. After heating this laminated body at a temperature of 300 ° C. in a nitrogen atmosphere to burn the binder, a reducing atmosphere composed of H ₂ —N ₂ —H ₂ O gas having an oxygen partial pressure of 10 ⁻⁹ to 10 ⁻¹² MPa. Inside, it baked at 1200-1300 degreeC for 2 hours, and obtained the ceramic sintered compact.

Next, a conductive paste for external electrodes containing Cu as a main component and containing B ₂ O ₃ —Li ₂ O—SiO ₂ —BaO glass frit was prepared. And this electroconductive paste for external electrodes is apply | coated to the both end surfaces of a ceramic sintered compact, and it bakes at the temperature of 800 degreeC in nitrogen atmosphere, and forms an external electrode, Thereby, the multilayer ceramic capacitor of the sample numbers 1-7 is obtained. Obtained.

The multilayer ceramic capacitor thus obtained has outer dimensions of length: 2.0 mm, width: 1.2 mm, thickness: 1.0 mm, and the dielectric ceramic layer interposed between the internal electrodes. The thickness was 2 μm. The total number of effective dielectric layers was 100, and the counter electrode area per layer was 1.8 mm ² .

[Structural analysis of dielectric ceramics]
Element by STEM-EDX method using scanning transmission electron microscopy (hereinafter referred to as “STEM”) and energy dispersive x-ray spectroscopy (hereinafter referred to as “EDX”). Analysis was performed to identify the composition of the crystal particles.

  Specifically, 10 points were sampled evenly at the periphery of about 15 nm inward from the outer periphery of the crystal grain, and it was identified whether the composition was mainly composed of BT or BCT. That is, at each sampling point, the molar ratio Ca / Ti between Ca and Ti is measured, and when the molar ratio Ca / Ti is 1% or more, BCT, and when the molar ratio Ca / Ti is less than 1%, BT. The case where seven or more locations identified as BT existed was regarded as crystal particles within the scope of the present invention.

  Thus, the structural analysis of 10 crystal grains was performed, and the number ratio of crystal grains within the scope of the present invention was examined.

(Characteristic evaluation)
For each of the sample numbers 1 to 7, the relative dielectric constant εr, AC electric field characteristics, and reliability were evaluated.

  That is, using an automatic bridge type measuring device, the capacitance C was measured under the conditions of a frequency of 1 kHz, an effective voltage of 1.0 Vrms, and a temperature of 25 ° C., and a relative dielectric constant εr was calculated from the sample dimensions and the capacitance C.

For AC electric field characteristics, the capacitance of the effective voltage 1.0Vrms as a reference, determine the voltage change rate [Delta] C _0.1 / C _1.0 in capacitance when the effective voltage was 0.1 Vrms, the voltage change rate [Delta] C _0.1 / C _1.0 within ± 20% was evaluated as a non-defective product.

  Reliability was evaluated by a high temperature load test and a high temperature load life. That is, a DC voltage of 16 V (8 kV / mm in terms of electric field) was applied to 10 samples at a high temperature of 150 ° C. And the time-dependent change of the insulation resistance was measured, it was judged that the failure occurred when the insulation resistance decreased to 200 kΩ, and the reliability was evaluated using the average value for each sample as the average failure time.

  Table 1 shows the structures of the dielectric ceramics of sample numbers 1 to 7 and the measurement results. In Table 1, L1 is the peripheral length of the exposed portion of the first region containing BT as a main component to the crystal grain boundary, and L2 is the exposure of the second region containing BCT as the main component to the same crystal grain boundary. The peripheral length of the part.

In Sample No. 1, since the dielectric ceramic crystal particles have a uniform structure of BT, the capacitance voltage change rate ΔC _0.1 / C _1.0 is −17% and the AC electric field characteristics are good, but the average It was found that the failure time was as short as 5 hours and the reliability was poor.

In Sample No. 2, the dielectric ceramic crystal particles have a BCT uniform structure, so the average failure time is 40 hours and the reliability is good, but the capacitance voltage change rate ΔC _0.1 / C _1.0 It was found to be inferior to the AC electric field characteristics.

Sample No. 7 has a capacitance voltage change rate ΔC _0.1 / C _1.0 of −18%, and the AC electric field characteristics are good, but the average failure time is as short as 10 hours, which may be inferior in reliability. I understood. This is because although BT and BCT coexist in the crystal grains, there are only 50% of the crystal grains in which L1> L2 is established, and therefore the percentage of crystal grains in which BCT is surrounded by BT is small, For this reason, it seems that sufficient reliability was not obtained.

In contrast, Sample Nos. 3 to 6 have a crystal structure in which the crystal particles satisfying L1> L2 are 70 to 100% and the surface exposed portions of the crystal particles are sufficiently covered with BT. Voltage change rate ΔC _0.1 / C _1.0 of −13 to −19%, average failure time is 30 to 45 hours, and it is possible to achieve both AC electric field characteristics and reliability while maintaining a high relative dielectric constant of 1600 to 1800. I understood that.

  In addition, about the sample numbers 3-6, when the change rate of the electrostatic capacitance was measured in the range of -55 degreeC-+85 degreeC on the basis of the temperature of 25 degreeC, all were suppressed within +/- 15%. That is, it was confirmed that the X5R characteristic of the EIA standard was satisfied.

 Subcomponents were added to the main component raw material powder of Sample No. 3 in Example 1, and the characteristics were evaluated.

That is, subcomponent _{compounds, SiO 2, MgO, MnO,} V 2 O 5, Sm 2 O 3, Gd 2 O 3, Dy 2 O 3, Er 2 O 3, Ho 2 O 3, Y 2 O 3 and BaZrO ₃ powders were prepared.

  Then, these subcomponent compounds were weighed so that the subcomponent compounds were in the mol parts shown in Table 2 with respect to 100 mol parts of the main component raw material powder of sample number 3. Then, the main component raw material powder and the auxiliary component compound were put into a ball mill together with PSZ balls and pure water and mixed. Next, this was dried to obtain a ceramic raw material.

  Thereafter, multilayer ceramic capacitors of sample numbers 11 to 23 were obtained by the same method and procedure as in [Example 1].

Next, the dielectric constant εr, the capacitance voltage change rate ΔC _0.1 / C _1.0 , and the average failure time were measured in the same manner and procedure as in Example 1.

  Moreover, the temperature change rate of the capacitance was measured in the range of −55 ° C. to + 125 ° C. with reference to the capacitance of + 25 ° C.

  If the temperature change rate is within ± 15% in the range of −55 ° C. to + 85 ° C., the X5R characteristic of the EIA standard is satisfied, and if the temperature change rate is within ± 15% in the range of −55 ° C. to + 105 ° C., EIA The standard X6R characteristic is satisfied, and if the temperature change rate is within ± 15% within the range of −55 ° C. to + 125 ° C., the X7R characteristic of the EIA standard is satisfied. Then, temperature characteristics were evaluated using these as indices.

  Table 2 shows the mole parts of the subcomponent elements of Sample Nos. 11 to 23 with respect to 100 mole parts of the main component raw material powder and the measurement results.

  As is apparent from Table 2, it was found that the AC electric field characteristics and reliability equal to or higher than those of Example 1 can be obtained by adding the subcomponent element to the main component raw material powder. It was also found that the temperature characteristics can be secured more than the X5R characteristics.

  In particular, sample numbers 15 to 23 to which rare earth elements such as Sm, Gd, Dy, Er, Ho, and Y and Zr are added can further improve the relative permittivity, and the average failure time is 100 hours or more. It was found that the reliability can be improved significantly.

It is sectional drawing which showed typically the principal part of one Embodiment of the dielectric ceramic which concerns on this invention. FIG. 4 is a diagram showing the relationship between the peripheral length L1 of the exposed portion of the first region 3 to the crystal grain boundary and the peripheral length L2 of the exposed portion of the second region 4 to the crystal grain boundary. It is sectional drawing which showed typically the principal part of other embodiment of the dielectric ceramic which concerns on this invention. It is sectional drawing which shows one Embodiment of the laminated ceramic capacitor manufactured using the dielectric ceramic of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystal grain 2 Crystal grain boundary 3 1st area | region 4 2nd area | region 5 Ceramic sintered compact 6a-6f Internal electrode 7a, 7b External electrode 10a-10g Dielectric layer

Claims (5)

A dielectric ceramic having crystal grains and crystal grain boundaries,
When an arbitrary cross section is observed, 70% or more of crystal grains have a first region mainly composed of BaTiO ₃ and a second region mainly composed of (Ba, Ca) TiO ₃ ,
The dielectric ceramic according to claim 1, wherein a peripheral length of a portion exposed to the crystal grain boundary of the first region is longer than a peripheral length of a portion exposed to the crystal grain boundary of the second region.   The dielectric ceramic according to claim 1, wherein the second region is surrounded by the first region.   3. The dielectric ceramic according to claim 1, wherein at least one element selected from the group consisting of Si, Mg, Mn, and V is contained.   4. The dielectric according to claim 1, comprising at least one element selected from the group consisting of Sm, Gd, Dy, Er, Ho, Y, and Zr. 5. ceramic. The ceramic sintered body is formed by alternately laminating dielectric layers and internal electrodes, external electrodes are formed at both ends of the ceramic sintered body, and the external electrodes and the internal electrodes are electrically connected. In multilayer ceramic capacitors
A multilayer ceramic capacitor, wherein the dielectric layer is formed of the dielectric ceramic according to any one of claims 1 to 4.

Images