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WO2021171920A1 - コンデンサ - Google Patents

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Publication number
WO2021171920A1
WO2021171920A1 PCT/JP2021/003582 JP2021003582W WO2021171920A1 WO 2021171920 A1 WO2021171920 A1 WO 2021171920A1 JP 2021003582 W JP2021003582 W JP 2021003582W WO 2021171920 A1 WO2021171920 A1 WO 2021171920A1
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WO
WIPO (PCT)
Prior art keywords
crystal particles
crystal
particle
capacitor
additive element
Prior art date
Application number
PCT/JP2021/003582
Other languages
English (en)
French (fr)
Inventor
麻衣子 永吉
Original Assignee
京セラ株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 京セラ株式会社 filed Critical 京セラ株式会社
Priority to US17/799,092 priority Critical patent/US20230082288A1/en
Priority to JP2022503199A priority patent/JP7365488B2/ja
Priority to EP21760508.8A priority patent/EP4113552A4/en
Priority to KR1020227027623A priority patent/KR20220121886A/ko
Priority to CN202180015195.5A priority patent/CN115210832A/zh
Publication of WO2021171920A1 publication Critical patent/WO2021171920A1/ja

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G4/00—Fixed capacitors; Processes of their manufacture
    • H01G4/30—Stacked capacitors
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/46—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on titanium oxides or titanates
    • C04B35/462—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on titanium oxides or titanates based on titanates
    • C04B35/465—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on titanium oxides or titanates based on titanates based on alkaline earth metal titanates
    • C04B35/468—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on titanium oxides or titanates based on titanates based on alkaline earth metal titanates based on barium titanates
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Definitions

  • This disclosure relates to a multilayer capacitor.
  • Patent Document 1 An example of the prior art is described in Patent Document 1.
  • the capacitors of the present disclosure include a laminate in which dielectric layers and internal electrode layers are alternately laminated, and A capacitor located on the surface of the laminate and having an external electrode electrically connected to the internal electrode layer.
  • the dielectric layer is composed of a plurality of crystal particles containing barium titanate and an additive element.
  • the plurality of crystal particles include a first crystal particle and a second crystal particle having a particle size larger than that of the first crystal particle.
  • the composition is such that the additive element content of the second crystal particles is higher than the additive element content of the first crystal particles.
  • the capacitor having the basic configuration of the present disclosure which is one of the electronic components mounted on the electronic device, is required to have a high capacitance and various characteristics to be improved.
  • the multilayer ceramic capacitor described in Patent Document 1 is a dielectric layer composed of two types of particles having different average particle diameters, and high capacitance is achieved by satisfying a specific relationship between the average particle diameters of the dielectric layers.
  • the capacitance, withstand voltage and DC bias characteristics are improved.
  • capacitors disclosed in the present disclosure will be described with reference to the drawings.
  • the capacitors of the present disclosure are not limited to the specific embodiments described below.
  • the capacitors of the present disclosure include various aspects as long as they are in line with the spirit or scope of the general concept defined by the appended claims.
  • FIG. 1 is an external perspective view of the capacitor.
  • FIG. 2 is a cross-sectional view taken along the cutting plane line of FIG.
  • the capacitor 100 shown as an example of the embodiment of the present disclosure includes a laminate 1 and an external electrode 3 located on the surface thereof.
  • the laminated body 1 has a dielectric layer 5 and an internal electrode layer 7, and the dielectric layer 5 and the internal electrode layer 7 are alternately laminated in a plurality of layers.
  • the laminated body 1 of the present embodiment has, for example, a rectangular parallelepiped shape, and the dielectric layer 5 and the internal electrode layer 7 are both rectangular in a plan view when viewed from the stacking direction.
  • the number of layers of the dielectric layer 5 and the internal electrode layer 7 is simplified to several layers, but the number of layers of the dielectric layer 5 and the internal electrode layer 7 reaches, for example, several hundred layers. It may be the number of layers.
  • FIG. 3 is an enlarged schematic view of the cross section of the dielectric layer.
  • the dielectric layer 5 is composed of a plurality of crystal particles 6 containing barium titanate and an additive element.
  • the plurality of crystal particles 6 include a first crystal particle 6A and a second crystal particle 6B having a particle size larger than that of the first crystal particle 6A.
  • the crystal particles 6 are crystal particles containing barium titanate as a main component and contain an additive element.
  • the main component is the component contained most in the crystal particles 6.
  • barium titanate as a main component means that the crystal particles 6 contain a larger amount of titanium and barium than other components.
  • the additive element is one or more elements selected from, for example, dysprosium (Dy), magnesium (Mg), calcium (Ca), manganese (Mn) and silica (Si).
  • the additive element is present in the crystal particles 6 by diffusing into the barium titanate crystal, for example.
  • the plurality of crystal particles 6 include a small-diameter first crystal particle 6A and a large-diameter second crystal particle 6B, where the particle size of the first crystal particle 6A is d1 and the particle size of the second crystal particle 6B.
  • d2 0.13 ⁇ m ⁇ d1 ⁇ 0.30 ⁇ m, and 0.30 ⁇ m ⁇ d2 ⁇ 0.50 ⁇ m.
  • the method for measuring the particle size of the crystal particles 6 can be measured by image analysis of an electron micrograph of a cross section of the dielectric layer 5.
  • the crystal particles 6 constituting the dielectric layer 5 may include crystal particles having a particle size of less than 0.13 ⁇ m and crystal particles having a particle size of 0.50 ⁇ m or more.
  • the additive element content of the second crystal particles 6B is assumed to be higher than the additive element content of the first crystal particles 6A.
  • the relative permittivity of the dielectric layer 5 can be increased, and a desired capacitance can be obtained as the capacitor 100.
  • crystal particles having a relatively large particle size such as the second crystal particles 6B are present, the ratio of the grain boundaries in the unit volume of the dielectric layer 5 is small, and the capacitor characteristics are likely to be deteriorated. Deterioration of capacitor characteristics is said to be caused by the movement of oxygen vacancies between the internal electrode layers 7.
  • the capacitor characteristic in this embodiment is, for example, a DC voltage characteristic under high temperature conditions.
  • the additive element content of the second crystal particles 6B is higher than the additive content of the first crystal particles 6A, that is, the highest additive element content among the plurality of first crystal particles 6A and the plurality of first crystal particles 6A.
  • the content of the second crystal particle 6B which is the smallest is larger.
  • the additive element content of the first crystal particles 6A and the second crystal particles 6B was determined by using a transmission electron microscope (EDX-TEM) equipped with an elemental analysis device for the crystal particles existing in the cross section of the dielectric layer 5. It is measured by performing elemental analysis. The measurement point is 100 nm from the grain boundary, and the concentration (atomic%) of each additive element is measured.
  • the additive element content of the first crystal particles 6A and the second crystal particles 6B can be obtained by calculating the sum of the concentrations of each element.
  • the ratio of the second crystal particles 6B in the dielectric layer 5 for example, in the cross section of the dielectric layer 5, the ratio of the area occupied by the second crystal particles 6B per unit area should be 4% or more and 18% or less. Just do it.
  • the ratio of the area occupied by the second crystal particles 6B can be measured, for example, as follows. In the capacitor 100, the total area of a predetermined cross section (longitudinal cross section of an arbitrary dielectric layer 5 or the like) is S0, and the total cross-sectional area of the second crystal particles 6B included in the cross section is S2.
  • the cross-sectional area of the second crystal particle 6B can be measured by image analysis of an electron micrograph in the same manner as the measurement of the particle size.
  • the area ratio A2 (S2 / S0) ⁇ 100 [%] of the second crystal particles 6B.
  • the number of the second crystal particles 6B connected to each other may be 2 or less.
  • the larger the number of the second crystal particles 6B in a row the more the second crystal particles 6B are unevenly present.
  • the first crystal particles 6A are small and the ratio of grain boundaries is locally small.
  • the number of the second crystal particles 6B connected to each other is set to 2 or less, in other words, the number of the second crystal particles 6B connected to each other is set to 2 or less, so that deterioration of the characteristics is suppressed and the reliability of the capacitor is suppressed.
  • the sex can be further improved.
  • the first crystal particles 6A and the second crystal particles 6B are small-diameter particles having a particle size of less than 0.3 ⁇ m and large-diameter particles having a particle size of 0.3 ⁇ m or more. If the particle size of the crystal particles 6 in the dielectric layer 5 varies widely, the capacitor characteristics tend to vary, and there is a possibility that the characteristics may be significantly reduced. In order to reduce the variation in particle size, when the arithmetic mean particle size of the first crystal particle 6A is D1 and the arithmetic mean particle size of the second crystal particle 6B is D2, 2D1 ⁇ D2 ⁇ 3D1 may be set. ..
  • the arithmetic mean particle diameters D1 and D2 can be measured by image analysis of an electron micrograph of a cross section of the dielectric layer 5 in the same manner as the measurement of the particle diameters d1 and d2.
  • the arithmetic mean value of the particle size may be calculated for the crystal particles belonging to the first crystal particle 6A, and the arithmetic mean value of the particle size may be calculated for the crystal particles belonging to the second crystal particle 6B. If the arithmetic mean particle size D1 and D2 are 2D1 ⁇ D2, the particle size of the first crystal particle 6A and the second crystal particle 6B is appropriately different, and if D2 ⁇ 3D1, the particle size varies. It is kept small. This makes it possible to reduce variations in capacitor characteristics.
  • the internal electrode layer 7 is made of a metal material, and for example, nickel (Ni), copper (Cu), palladium (Pd), silver (Ag) and the like can be used. Also. Alloys containing these metallic materials can also be used.
  • the external electrode 3 the same metal material as the internal electrode layer 7 can be used.
  • the second crystal particles 6B have a core-shell structure, and the configurations other than the second crystal particles 6B are the same as the configurations of the above-described embodiment, and thus detailed description thereof will be omitted.
  • FIG. 4 is an enlarged schematic view of the second crystal particles of the present embodiment.
  • the core-shell structure is a structure in which one crystal particle has a core portion and a shell portion.
  • the core portion 6B1 is composed of barium titanate crystals
  • the shell portion 6B2 surrounds the core portion 6B1 and is a region in which the additive element is diffused in the barium titanate crystals. be.
  • the core-shell structure can be confirmed by an electron micrograph of a cross section of the dielectric layer 5.
  • a striped pattern showing a domain structure is observed in the core portion 6B1 composed of barium titanate crystals, but this striped pattern is not observed in the shell portion 6B2.
  • Additive elements are diffused in the shell portion 6B2, and the movement resistance of oxygen vacancies is large as in the grain boundaries, deterioration of characteristics can be suppressed, and the reliability of the capacitor can be further improved.
  • the thickness of the shell portion 6B2 may be, for example, 0.05 ⁇ m to 0.13 ⁇ m.
  • a method for manufacturing the capacitor of the present disclosure will be described.
  • a laminate is manufactured.
  • the raw material powder containing barium titanate as the main component two types having different Ba / Ti ratios are used. Further, the average particle size of the raw material powder having a large Ba / Ti ratio is made smaller than the particle size of the raw material powder having a small Ba / Ti ratio.
  • the raw material powder of barium titanate and additive elements is mixed with a dispersant or the like in a solvent to obtain a slurry.
  • a green sheet is prepared from the slurry by the doctor blade method.
  • a metal paste containing a metal material such as nickel as a main component is prepared.
  • a metal paste is printed on the surface of the green sheet to prepare a green sheet with the metal paste.
  • a green sheet with a metal paste is laminated and fired to obtain a laminate.
  • metal pastes for external electrodes are applied to both ends of the laminate and baked at a temperature of 800 ° C. to form external electrodes.
  • the metal paste for the external electrode one to which Cu powder and glass are added is used.
  • the plating layer may be provided on the surface of the external electrode with a single plating layer or may be provided with a plurality of plating layers.
  • Example 2 As the raw material powder of barium titanate, those having a Ba / Ti ratio of 1.006 (raw material 1) and those having a Ba / Ti ratio of 1.000 (raw material 2) were used. The average particle size of the raw material 1 and the raw material 2 was 0.15 ⁇ m and 0.3 ⁇ m, respectively.
  • additive elements diprosium and magnesium were added as Dy 2 O 3 and Mg 2 CO 3 , respectively.
  • the wet-mixed powder was put into a mixed solvent of toluene and alcohol in which polyvinyl butyral resin was dissolved, and wet-mixed using a zirconia ball having a diameter of 5 mm to prepare a ceramic rally, which was molded by the doctor blade method.
  • a ceramic green sheet having a thickness of about 3 ⁇ m was prepared on the film.
  • Nickel powder was used as the metal of the metal paste for forming the internal electrode layer.
  • Ethyl cellulose was used as the resin for preparing the metal paste.
  • As the solvent a dihydroterpineol solvent and a butyl cellosolve were mixed and used.
  • a metal paste was printed on the prepared ceramic green sheet to prepare a green sheet with the metal paste.
  • 200 layers of the prepared green sheet with metal paste were laminated, and ceramic green sheets were laminated as cover layers on the upper surface side and the lower surface side, respectively, to prepare a base laminate.
  • the base laminate was cut to prepare a molded body of the laminate.
  • the molded body of the laminated body was fired to prepare a laminated body.
  • the temperature was raised to 900 ° C./h in hydrogen-nitrogen, and the maximum temperature was set to 1190 ° C.
  • a resistance heating type firing furnace was used for this firing.
  • the laminate was subjected to a reoxidation treatment.
  • the conditions for the reoxidation treatment were set to a maximum temperature of 1000 ° C. and a holding time of 5 hours in a nitrogen atmosphere.
  • the size of the laminate was 1.0 mm ⁇ 0.5 mm ⁇ 0.5 mm.
  • the average thickness of the dielectric layer was 1.8 ⁇ m.
  • the average thickness of the internal electrode layer was 0.7 ⁇ m.
  • the design value of the capacitance of the produced capacitor was set to 1 ⁇ F.
  • external electrode paste was applied to both ends of the laminate and baked at a temperature of 800 ° C. to form an external electrode.
  • the external electrode paste one to which Cu powder and glass were added was used. Then, using an electrolytic barrel machine, Ni plating and Sn plating were sequentially formed on the surface of the external electrode to obtain a capacitor.
  • Capacitor characteristics were evaluated by high temperature load life (HALT).
  • HALT high temperature load life
  • the test conditions were set to a DC voltage of 45 V
  • the environmental temperature was set to 170 ° C.
  • the time when the failure probability reached 50% was determined as the mean time between failures (MTTF).
  • MTTF mean time between failures
  • the shape parameter (m value) in the Weibull plot was obtained.
  • the MTTF indicates that the longer the life, the longer the life, and the larger the m value, the smaller the variation in the life.
  • the MTTF may be 15 hours or more and the m value may be 3 or more.
  • Example 1 the mixing ratio of the raw material 1 (small particle size) and the raw material 2 (large particle size) was changed.
  • the raw material mixing ratio was the same as in Example 3, and the arithmetic mean particle size D1 of the first crystal particles 6A and the arithmetic mean particle size D2 of the second crystal particles 6B were different.
  • Comparative Example 1 only the raw material 1 is used, and the raw material 2 is not used.
  • Comparative Example 2 only the raw material 2 is used, and the raw material 1 is not used.
  • the evaluation results are shown in Table 1.
  • the raw material mixing ratio in Table 1 shows the ratio of the raw material 2 when the total amount of the raw material 1 and the raw material 2 is 100.
  • Comparative Example 1 and Comparative Example 2 when the crystal particles are only small-diameter particles or only large-diameter particles, the lifetime is short and the lifetime variation is large. As can be seen from Comparative Example 3, if the particle size of the small-diameter particles is too small, the life variation is large. On the other hand, in Examples 1 to 8, the life is long and the life variation is small. Further, Examples 2 to 5 in which the area ratio of the second crystal particles is 4% or more and 18% or less are capacitors having a life of 20 hours or more, an m value of 4 or more, and excellent reliability. It turns out that there is. In Examples 1 and 6, the area ratio was out of the range, and the result was inferior to Examples 2 to 5.
  • the average particle diameters of the first crystal particles 6A and the second crystal particles 6B are out of the range of 2D1 ⁇ D2 ⁇ 3D1, and the lifetime is sufficiently long, but the m value is about 3. Yes, there was some variation. It was confirmed that the second crystal particles of Examples 1 to 8 had a core-shell structure.
  • the capacitors of the present disclosure include a laminate in which dielectric layers and internal electrode layers are alternately laminated, and A capacitor located on the surface of the laminate and having an external electrode electrically connected to the internal electrode layer.
  • the dielectric layer is composed of a plurality of crystal particles containing barium titanate and an additive element.
  • the plurality of crystal particles include a first crystal particle and a second crystal particle having a particle size larger than that of the first crystal particle.
  • the composition is such that the additive element content of the second crystal particles is higher than the additive element content of the first crystal particles.
  • the capacitor of the present disclosure deterioration of characteristics can be suppressed and the reliability of the capacitor can be improved.

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Abstract

コンデンサは、積層体と、その表面に位置する外部電極とを備える。積層体は、誘電体層と内部電極層とを有しており、誘電体層と内部電極層とは交互に複数層積層されている。複数の結晶粒子は、小径の第１結晶粒子と、大径の第２結晶粒子とを含んでおり、第１結晶粒子の粒子径をｄ１とし、第２結晶粒子の粒子径をｄ２としたとき、０．１３μｍ≦ｄ１＜０．３０μｍであり、０．３０≦ｄ２＜０．５０μｍである。第２結晶粒子の添加物元素含有量を、第１結晶粒子の添加物元素含有量より多くする。

Description

コンデンサ
　本開示は、積層型のコンデンサに関する。
　従来技術の一例は、特許文献１に記載されている。
特開２００５－２４３８９０号公報
　本開示のコンデンサは、誘電体層と内部電極層とが交互に積層された積層体と、
　前記積層体の表面に位置し、前記内部電極層に電気的に接続された外部電極と、を有するコンデンサであって、
　前記誘電体層は、チタン酸バリウムと添加物元素とを含む複数の結晶粒子で構成されており、
　前記複数の結晶粒子は、第１結晶粒子と、前記第１結晶粒子より粒子径が大きい第２結晶粒子とを含み、
　前記第１結晶粒子の粒子径をｄ１とし、前記第２結晶粒子の粒子径をｄ２としたとき、０．１３μｍ≦ｄ１＜０．３０μｍであり、０．３０μｍ≦ｄ２＜０．５０μｍであり、
　前記第２結晶粒子の添加物元素含有量が、前記第１結晶粒子の添加物元素含有量より多い構成である。
　本開示の目的、特色、および利点は、下記の詳細な説明と図面とからより明確になるであろう。
コンデンサの外観斜視図である。 図１の切断面線における断面図である。 誘電体層断面の拡大模式図である。 第２結晶粒子の拡大模式図である。
　電子機器に搭載される電子部品の１つである本開示の基礎となる構成のコンデンサには、高い静電容量が求められるとともに、種々の特性向上が望まれている。
　例えば、特許文献１記載の積層セラミックコンデンサは、平均粒径が異なる２種類の粒子で構成された誘電体層であって、それぞれの平均粒径が特定の関係を満足することで、高い静電容量と、耐電圧性およびＤＣバイアス特性を向上させている。
　以下、本開示のコンデンサについて、図面を基に説明する。なお、本開示のコンデンサは、以下に記述する特定の実施形態に限定されるものではない。本開示のコンデンサは、添付の特許請求の範囲によって定義される総括的な概念の精神または範囲に沿ったものであれば、様々な態様を含むものとなる。
　図１は、コンデンサの外観斜視図である。図２は、図１の切断面線における断面図である。本開示の実施形態の一例として示すコンデンサ１００は、積層体１と、その表面に位置する外部電極３とを備える。積層体１は、誘電体層５と内部電極層７とを有しており、誘電体層５と内部電極層７とは交互に複数層積層されている。本実施形態の積層体１は、例えば、直方体形状であって、誘電体層５と内部電極層７とは、積層方向から見た平面視において、いずれも矩形状である。内部電極層７は、一辺が積層体１の側面に露出しており、外部電極３が、この側面を覆うことによって内部電極層７と外部電極３とが電気的に接続される。図２では、誘電体層５と内部電極層７との積層数を数層に簡略して描いているが、誘電体層５および内部電極層７の積層数は、例えば、数百層に及ぶ積層数であってもよい。
　図３は、誘電体層断面の拡大模式図である。誘電体層５は、チタン酸バリウムと添加物元素とを含む複数の結晶粒子６で構成されている。複数の結晶粒子６は、第１結晶粒子６Ａと、第１結晶粒子６Ａより粒子径が大きい第２結晶粒子６Ｂとを含む。結晶粒子６は、チタン酸バリウムを主成分とする結晶粒子であって、添加物元素を含む。ここで、主成分とは、結晶粒子６中に最も多く含まれている成分のことである。チタン酸バリウムを主成分とするとは、結晶粒子６中にチタンおよびバリウムの含有量が他の成分よりも多く含まれている状態のことである。
　添加物元素は、例えば、ジスプロシウム（Ｄｙ）、マグネシウム（Ｍｇ）、カルシウム（Ｃａ）、マンガン（Ｍｎ）およびシリカ（Ｓｉ）から選ばれる１種以上の元素である。添加物元素は、例えば、チタン酸バリウム結晶に拡散して結晶粒子６中に存在している。
　複数の結晶粒子６は、小径の第１結晶粒子６Ａと、大径の第２結晶粒子６Ｂとを含んでおり、第１結晶粒子６Ａの粒子径をｄ１とし、第２結晶粒子６Ｂの粒子径をｄ２としたとき、０．１３μｍ≦ｄ１＜０．３０μｍであり、０．３０μｍ≦ｄ２＜０．５０μｍである。結晶粒子６の粒子径の測定方法については、誘電体層５の断面の電子顕微鏡写真を画像解析することで測定することができる。例えば、断面の電子顕微鏡写真において、結晶粒子６が２００～３００個含まれる領域を指定し、既存の画像解析プログラムを用いて、領域内に含まれる各結晶粒子６の輪郭を抽出して断面積を求める。得られた断面積に基づいて、各結晶粒子６の円相当直径を算出し、粒子径とする。なお、誘電体層５を構成する結晶粒子６には、粒子径が０．１３μｍ未満の結晶粒子、粒子径が０．５０μｍ以上の結晶粒子が含まれていてもよい。
　このような第１結晶粒子６Ａおよび第２結晶粒子６Ｂにおいて、第２結晶粒子６Ｂの添加物元素含有量が、第１結晶粒子６Ａの添加物元素含有量より多いものとしている。第２結晶粒子６Ｂのような比較的粒子径が大きい結晶粒子を用いることによって、誘電体層５の比誘電率を高めることができ、コンデンサ１００として所望の静電容量を得ることができる。一方で、第２結晶粒子６Ｂのような比較的粒子径が大きい結晶粒子が存在すると、誘電体層５の単位体積における粒界の割合が小さく、コンデンサ特性の劣化が生じやすい。コンデンサ特性の劣化は、内部電極層７間で酸素空孔が移動することによって生じるとされている。結晶粒子６内は、酸素空孔が移動し易く、粒界は、酸素空孔の移動抵抗が大きいので、粒界の割合が小さいほど特性劣化が生じ易くなる。第２結晶粒子６Ｂの添加物元素含有量を第１結晶粒子６Ａより多くすることで、第２結晶粒子６Ｂ内における酸素空孔の移動抵抗が大きくなり、特性の劣化を抑制してコンデンサの信頼性を向上させることができる。本実施形態におけるコンデンサ特性は、例えば、高温条件下における直流電圧特性である。
　第２結晶粒子６Ｂの添加物元素含有量が、第１結晶粒子６Ａの添加物含有量より多いとは、複数の第１結晶粒子６Ａのうちで最も多い添加物元素含有量と、複数の第２結晶粒子６Ｂのうちで最も少ない添加物元素含有量とを比較したとき、第２結晶粒子６Ｂの最も少ない添含有量の方が多い場合を言う。
　第１結晶粒子６Ａおよび第２結晶粒子６Ｂの添加物元素含有量は、誘電体層５の断面に存在する結晶粒子に対して、元素分析機器を付設した透過電子顕微鏡（ＥＤＸ－ＴＥＭ）を用いて元素分析を行うことで測定する。測定箇所は、粒界から１００ｎｍとし、添加物元素ごとの濃度（atomic%）を測定する。第１結晶粒子６Ａおよび第２結晶粒子６Ｂの添加物元素含有量は、元素ごとの濃度の総和を算出することで得られる。
　また、誘電体層５における第２結晶粒子６Ｂの割合については、例えば、誘電体層５の断面において、単位面積あたりの第２結晶粒子６Ｂが占める面積の割合を４％以上１８％以下とすればよい。第２結晶粒子６Ｂが占める面積の割合は、例えば、次のようにして測定できる。コンデンサ１００において、予め定める断面（任意の誘電体層５の縦断面など）の全面積をＳ０とし、当該断面に含まれる第２結晶粒子６Ｂの断面積の総和をＳ２とする。第２結晶粒子６Ｂの断面積は、粒子径の測定と同様に電子顕微鏡写真を画像解析することで測定できる。これらの面積を用いて、第２結晶粒子６Ｂの面積割合Ａ２＝（Ｓ２／Ｓ０）×１００［％］で算出することができる。第２結晶粒子６Ｂの面積割合を上記の範囲内とすることで、特性の劣化を抑制してコンデンサの信頼性をさらに向上させることができる。なお、第２結晶粒子６Ｂの面積割合が上記の範囲外であっても、特性劣化の抑制効果が弱いものの実用上、問題は無い。
　さらに、誘電体層５における第２結晶粒子６Ｂの存在位置については、例えば、誘電体層５の断面において、第２結晶粒子６Ｂ同士が連なる個数が２個以下であればよい。第２結晶粒子６Ｂが連なる個数が多いほど、第２結晶粒子６Ｂが偏って存在していることとなる。第２結晶粒子６Ｂが偏って存在しているところでは、第１結晶粒子６Ａは少なく、粒界の割合が局所的に小さくなる。第２結晶粒子６Ｂ同士が連なる個数を２個以下とする、言い換えると、第２結晶粒子６Ｂ同士が３個以上は連なることがないようにすることで、特性の劣化を抑制してコンデンサの信頼性をさらに向上させることができる。
　第１結晶粒子６Ａおよび第２結晶粒子６Ｂは、上記のとおり、粒子径が０．３μｍ未満の小径粒子および粒子径が０．３μｍ以上の大径粒子である。誘電体層５における結晶粒子６の粒子径のばらつきが大きいと、コンデンサ特性にばらつきが生じ易くなり、特性が大きく低下するようなものが発生するおそれがある。粒子径のばらつきを小さくするためには、第１結晶粒子６Ａの算術平均粒子径をＤ１とし、第２結晶粒子６Ｂの算術平均粒子径をＤ２としたとき、２Ｄ１≦Ｄ２＜３Ｄ１とすればよい。算術平均粒子径Ｄ１，Ｄ２は、粒子径ｄ１，ｄ２の測定と同様に、誘電体層５の断面の電子顕微鏡写真を画像解析することで測定できる。第１結晶粒子６Ａに属する結晶粒子に対して粒子径の算術平均値を算出し、第２結晶粒子６Ｂに属する結晶粒子に対して粒子径の算術平均値を算出すればよい。算術平均粒子径Ｄ１，Ｄ２が、２Ｄ１≦Ｄ２であれば、第１結晶粒子６Ａおよび第２結晶粒子６Ｂの粒子径は、適度に差があり、Ｄ２＜３Ｄ１であれば、粒子径のばらつきが小さく抑えられている。これにより、コンデンサ特性のばらつきを低減させることができる。
　内部電極層７は、金属材料で構成されており、例えば、ニッケル（Ｎｉ）、銅（Ｃｕ）、パラジウム（Ｐｄ）および銀（Ａｇ）などを用いることができる。また。これらの金属材料を含む合金を用いることもできる。外部電極３も内部電極層７と同様の金属材料を用いることができる。
　本開示のコンデンサの他の実施形態について説明する。本実施形態は、第２結晶粒子６Ｂがコアシェル構造を有しており、第２結晶粒子６Ｂ以外の構成は、前述の実施形態の構成と同じであるので、詳細な説明は省略する。図４は、本実施形態の第２結晶粒子の拡大模式図である。コアシェル構造は、一つの結晶粒子がコア部とシェル部とを有する構造である。本実施形態の第２結晶粒子６Ｂにおいて、コア部６Ｂ１は、チタン酸バリウム結晶で構成されており、シェル部６Ｂ２は、コア部６Ｂ１を取り囲み、チタン酸バリウム結晶に添加物元素が拡散した領域である。コアシェル構造は、誘電体層５の断面の電子顕微鏡写真によって確認できる。チタン酸バリウム結晶で構成されるコア部６Ｂ１は、ドメイン構造を示す縞模様が観察されるが、シェル部６Ｂ２には、この縞模様が観察されない。シェル部６Ｂ２には、添加物元素が拡散されており、粒界と同様に酸素空孔の移動抵抗が大きく、特性の劣化を抑制してコンデンサの信頼性をさらに向上させることができる。第２結晶粒子６Ｂでは、シェル部６Ｂ２の厚さが、例えば、０．０５μｍ～０．１３μｍであればよい。
　次に、本開示のコンデンサの製造方法について説明する。まず、積層体を製造する。チタン酸バリウムを主成分とする原料粉末として、Ｂａ／Ｔｉ比が異なる２種類を用いる。また、Ｂａ／Ｔｉ比が大きい原料粉末の平均粒子径を、Ｂａ／Ｔｉ比が小さい原料粉末の粒子径より小さくする。添加物元素となるジスプロシウム（Ｄｙ）、マグネシウム（Ｍｇ）およびカルシウム（Ｃａ）は、それぞれＤｙ２Ｏ３、Ｍｇ２ＣＯ３、ガラス粉末（例えば、ＳｉＯ２＝５５ｍｏｌ％、ＢａＯ＝２０ｍｏｌ％、ＣａＯ＝１５ｍｏｌ％、Ｌｉ２Ｏ３＝１０ｍｏｌ％の組成を有するもの）として添加する。チタン酸バリウムおよび添加物元素の原料粉末と、分散剤などを溶媒中で混合し、スラリーを得る。スラリーからドクターブレード法によってグリーンシートを作製する。一方、ニッケルなどの金属材料を主成分とする金属ペーストを準備する。グリーンシート表面に金属ペーストを印刷し、金属ペースト付きグリーンシートを作製する。金属ペースト付きグリーンシートを積層し、焼成して積層体を得る。積層体をバレル研磨した後、積層体の両端部に外部電極用の金属ペーストを塗布し、８００℃の温度にて焼き付けを行って外部電極を形成する。外部電極用の金属ペーストは、Ｃｕ粉末およびガラスを添加したものを用いる。その後、電解バレル機を用いて、この外部電極の表面に順にＮｉめっき層及びＳｎめっき層を形成してコンデンサを得る。また、めっき層は、外部電極の表面上に、単一のめっき層で設けても、また、複数のめっき層で設けてもよい。
　（実施例）
　チタン酸バリウムの原料粉末には、Ｂａ／Ｔｉ比が１．００６のもの（原料１）とＢａ／Ｔｉ比が１．０００のもの（原料２）を用いた。原料１および原料２の平均粒子径は、それぞれ０．１５μｍおよび０．３μｍとした。添加物元素には、ジプロシウムとマグネシウムとをそれぞれＤｙ２Ｏ３、Ｍｇ２ＣＯ３として添加した。その他の添加剤として、炭酸カルシウム粉末（ＣａＣＯ３）、炭酸マンガン粉末（ＭｎＣＯ３）およびガラス粉末（ＳｉＯ２＝５５ｍｏｌ％、ＢａＯ＝２０ｍｏｌ％、ＣａＯ＝１５ｍｏｌ％、Ｌｉ２Ｏ３＝１０ｍｏｌ％の組成を有するもの）を用いた。これらを直径５ｍｍのジルコニアボールを用いて、溶媒としてトルエンとアルコールとからなる混合溶媒を添加し湿式混合した。
　次に、湿式混合した粉末を、ポリビニルブチラール樹脂を溶解させたトルエンおよびアルコールの混合溶媒中に投入し、直径５ｍｍのジルコニアボールを用いて湿式混合してセラミックスラリを調製し、ドクターブレード法により成形用フィルム上に厚さが約３μｍのセラミックグリーンシートを作製した。
　内部電極層を形成するための金属ペーストの金属としてニッケル粉末を用いた。金属ペーストを調製するための樹脂としてはエチルセルロースを用いた。溶媒としてはジヒドロターピネオール系溶媒とブチルセロソルブとを混合して用いた。
　次に、作製したセラミックグリーンシートに金属ペーストを印刷して金属ペースト付きグリーンシートを作製した。次に、作製した金属ペースト付きグリーンシートを２００層積層し、上面側および下面側にカバー層としてセラミックグリーンシートをそれぞれ重ねて母体積層体を作製した。この後、母体積層体を切断して積層体の成形体を作製した。
　次に、積層体の成形体を焼成して積層体を作製した。本焼成は、水素－窒素中、昇温速度を９００℃／ｈとし、最高温度を１１９０℃に設定した条件で焼成した。この焼成には抵抗加熱方式の焼成炉を用いた。続いて、積層体に対して再酸化処理を行った。再酸化処理の条件は、窒素雰囲気中、最高温度を１０００℃に設定し、保持時間を５時間とした。積層体のサイズは、１．０ｍｍ×０．５ｍｍ×０．５ｍｍであった。誘電体層の平均厚みは１．８μｍであった。内部電極層の平均厚みは０．７μｍであった。作製したコンデンサの静電容量の設計値は１μＦに設定した。
　次に、積層体をバレル研磨した後、積層体の両端部に外部電極ペーストを塗布し、８００℃の温度にて焼き付けを行って外部電極を形成した。外部電極ペーストは、Ｃｕ粉末およびガラスを添加したものを用いた。その後、電解バレル機を用いて、この外部電極の表面に順にＮｉめっきおよびＳｎめっきを形成してコンデンサを得た。
　コンデンサ特性は、高温負荷寿命（ＨＡＬＴ）によって評価した。高温負荷寿命は、試験条件を直流電圧４５Ｖ、環境温度を１７０℃に設定し、故障確率が５０％に達したときの時間を平均故障時間（ＭＴＴＦ）として求めた。また、ワイブルプロットにおける形状パラメータ（ｍ値）を求めた。ＭＴＴＦは、長時間であるほど寿命が長く、ｍ値が大きいほど寿命のばらつきが小さいことを示す。ＭＴＴＦが、１５時間以上であって、ｍ値が３以上であればよい。
　実施例１～６は、原料１（小粒径）と原料２（大粒径）の混合比を変えたものである。実施例７，８は、原料混合比を実施例３と同じとし、第１結晶粒子６Ａの算術平均粒子径Ｄ１と、第２結晶粒子６Ｂの算術平均粒子径Ｄ２を異ならせた。実施例７は、Ｄ２＝１．８Ｄ１であり、実施例８は、Ｄ２＝３．２Ｄ１であった。比較例１は、原料１のみを用い、原料２は用いていない。比較例２は、原料２のみを用い、原料１は用いていない。評価結果を表１に示す。表１における原料混合比は、原料１と原料２の全量を１００としたときの原料２の割合を示す。
Figure JPOXMLDOC01-appb-T000001
　比較例１および比較例２からわかるように、結晶粒子として、小径粒子のみまたは大径粒子のみである場合は、寿命が短く、寿命ばらつきも大きい。比較例３からわかるように、小径粒子の粒子径が小さ過ぎると、寿命ばらつきが大きい。これに対して、実施例１～８は、いずれも寿命が長く、寿命ばらつきも小さい。また、第２結晶粒子の面積割合が、４％以上１８％以下である実施例２～５は、寿命が、２０時間以上であり、ｍ値も４以上であり、信頼性に優れたコンデンサであることがわかる。実施例１，６は、面積割合が範囲外であり、実施例２～５より劣る結果となった。実施例７，８は、第１結晶粒子６Ａおよび第２結晶粒子６Ｂの平均粒子径が、２Ｄ１≦Ｄ２＜３Ｄ１の範囲外となっており、寿命は十分に長いが、ｍ値がおよそ３であり、ややばらつきが見られた。なお、実施例１～８の第２結晶粒子は、コアシェル構造を有していることが確認できた。
　本開示は次の実施の形態が可能である。
　本開示のコンデンサは、誘電体層と内部電極層とが交互に積層された積層体と、
　前記積層体の表面に位置し、前記内部電極層に電気的に接続された外部電極と、を有するコンデンサであって、
　前記誘電体層は、チタン酸バリウムと添加物元素とを含む複数の結晶粒子で構成されており、
　前記複数の結晶粒子は、第１結晶粒子と、前記第１結晶粒子より粒子径が大きい第２結晶粒子とを含み、
　前記第１結晶粒子の粒子径をｄ１とし、前記第２結晶粒子の粒子径をｄ２としたとき、０．１３μｍ≦ｄ１＜０．３０μｍであり、０．３０μｍ≦ｄ２＜０．５０μｍであり、
　前記第２結晶粒子の添加物元素含有量が、前記第１結晶粒子の添加物元素含有量より多い構成である。
　本開示のコンデンサによれば、特性の劣化を抑制してコンデンサの信頼性を向上させることができる。
　以上、本開示の実施形態について詳細に説明したが、また、本開示は上述の実施の形態に限定されるものではなく、本開示の要旨を逸脱しない範囲内において、種々の変更、改良等が可能である。上記各実施形態をそれぞれ構成する全部または一部を、適宜、矛盾しない範囲で組み合わせ可能であることは、言うまでもない。
　１　　　積層体
　３　　　外部電極
　５　　　誘電体層
　６　　　結晶粒子
　６Ａ　　第１結晶粒子
　６Ｂ　　第２結晶粒子
　７　　　内部電極層
　６Ｂ１　コア部
　６Ｂ２　シェル部
　１００　コンデンサ

Claims (6)

  1. 　誘電体層と内部電極層とが交互に積層された積層体と、
    　前記積層体の表面に位置し、前記内部電極層に電気的に接続された外部電極と、を有するコンデンサであって、
    　前記誘電体層は、チタン酸バリウムと添加物元素とを含む複数の結晶粒子で構成されており、
    　前記複数の結晶粒子は、第１結晶粒子と、前記第１結晶粒子より粒子径が大きい第２結晶粒子とを含み、
    　前記第１結晶粒子の粒子径をｄ１とし、前記第２結晶粒子の粒子径をｄ２としたとき、０．１３μｍ≦ｄ１＜０．３０μｍであり、０．３０μｍ≦ｄ２＜０．５０μｍであり、
    　前記第２結晶粒子の添加物元素含有量が、前記第１結晶粒子の添加物元素含有量より多いコンデンサ。
  2. 　前記誘電体層の断面における、単位面積あたりの前記第２結晶粒子が占める面積の割合が、４％以上１８％以下である、請求項１記載のコンデンサ。
  3. 　前記誘電体層の断面における、前記第２結晶粒子同士が連なる個数が２個以下である、請求項１または２記載のコンデンサ。
  4. 　前記第２結晶粒子は、チタン酸バリウム結晶で構成されるコア部と、前記コア部を取り囲み、チタン酸バリウム結晶に添加物元素が拡散したシェル部と、を含むコアシェル構造を有する、請求項１～３のいずれか１つに記載のコンデンサ。
  5. 　前記第１結晶粒子の算術平均粒子径をＤ１とし、前記第２結晶粒子の算術平均粒子径をＤ２としたとき、２Ｄ１≦Ｄ２＜３Ｄ１である、請求項１～４のいずれか１つに記載のコンデンサ。
  6. 　前記添加物元素が、ジスプロシウム、マグネシウムおよびカルシウムから選ばれる１種以上である、請求項１～５のいずれか１つに記載のコンデンサ。
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