Multilayer ceramic capacitor

Abstract

To provide a multilayer ceramic capacitor with high reliability, in which the insulating characteristic is high while advancing layer thinning, and the deterioration is small even under a high-temperature and high-humidity environment.SOLUTION: A multilayer ceramic capacitor includes: an element assembly part 6 including a plurality of dielectric ceramic layers 2 and a plurality of internal electrode layers 4 that are stacked in a thickness direction; and a pair of external electrodes 8a and 8b provided on a first end surface 14a and a second end surface 14b, respectively, and electrically connected to the internal electrode layers. The dielectric ceramic layer includes, as a main component, a crystal particle composed of a perovskite type composite oxide containing barium (Ba) and titanium (Ti), and further includes a rare earth element (Re). In a cross section including the thickness direction, a rare-earth high-concentration region in which a molar ratio (Re / Ti ratio) of the rare-earth element (Re) to the titanium (Ti) is 0.04 or more and 0.30 or less is included in an area ratio of 50% or more.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a multilayer ceramic capacitor.

Background Art

[0002] With the miniaturization of electronic devices such as mobile phones and the increase in the speed of CPUs, the demand for multilayer ceramic capacitors (MLCCs) is increasing more and more. A multilayer ceramic capacitor has a structure in which dielectric layers and internal electrode layers are alternately laminated, and due to the thin high-permittivity dielectric layers, it has a large capacitance while being small in size. Multilayer ceramic capacitors using various materials are known, but those using a barium titanate (BaTiO3)-based compound for the dielectric layer and a base metal such as nickel (Ni) for the internal electrode layer are widely used because they are inexpensive and exhibit high characteristics.

[0003] In realizing the miniaturization and large capacitance of multilayer ceramic capacitors, it is important to make the dielectric layers thinner. However, when the dielectric layers are made thinner, there is a problem that the insulation resistance life between the internal electrode layers is shortened, leading to a decrease in reliability. To address such a problem, a technique has been proposed in which additives such as rare earth elements (RE) and magnesium (Mg) are added to the dielectric layer made of a BaTiO3-based compound to extend the insulation resistance life and improve the reliability.

[0004] For example, Patent Document 1 discloses a dielectric ceramic composition comprising barium titanate, at least one selected from europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide and ytterbium oxide, barium zirconate, magnesium oxide, and manganese oxide, and containing a main component represented by a specific composition formula (Claim 1 of Patent Document 1). Patent Document 1 also describes applying the ceramic composition to the dielectric ceramic layer of a multilayer ceramic capacitor in which the internal electrode is made of nickel or a nickel alloy, and when used at a high electric field strength, having a high product of insulation resistance and capacitance (CR product), high dielectric breakdown voltage, and excellent weather resistance such as high-temperature load and moisture resistance (Claims 4 and

[0007] of Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] With the progress of electronic components and electronic devices, further miniaturization and increased capacitance of multilayer ceramic capacitors are expected. Also, as the applications of multilayer ceramic capacitors expand, the demand for improving their reliability is increasing. Therefore, there is a demand for multilayer ceramic capacitors that are excellent in reliability, having high insulation characteristics and less deterioration even under high temperature and high humidity, while promoting thinning. However, although the conventionally proposed technologies have certain effects, there is still room for improvement.

[0007] In view of such problems, the present inventors have conducted intensive studies. As a result, they have obtained the knowledge that by controlling the region containing rare earth elements in the dielectric ceramic layer, it is possible to significantly improve the reliability of multilayer ceramic capacitors.

[0008] The present invention has been completed based on such findings, and an object thereof is to provide a multilayer ceramic capacitor having excellent reliability.

Means for Solving the Problems

[0009] The present invention includes the following aspects. In this specification, the expression "~" includes the numerical values at both ends thereof. That is, "X~Y" is synonymous with "X or more and Y or less".

[0010] According to one aspect of the present invention, there is provided a multilayer ceramic capacitor having a first main surface and a second main surface facing each other in the thickness direction, a first side surface and a second side surface facing each other in the width direction, and a first end surface and a second end surface facing each other in the length direction. The multilayer ceramic capacitor includes a body portion including a plurality of dielectric ceramic layers and a plurality of internal electrode layers laminated in the thickness direction, and a pair of external electrodes provided on each of the first end surface and the second end surface and electrically connected to the plurality of internal electrode layers. The dielectric ceramic layer contains crystal particles mainly composed of a perovskite-type composite oxide containing barium (Ba) and titanium (Ti), and further contains a rare earth element (Re). The dielectric ceramic layer includes a rare earth high-concentration region having a molar ratio (Re / Ti ratio) of the rare earth element (Re) to titanium (Ti) of 0.04 or more and 0.30 or less in an area ratio of 50% or more in a cross section including the thickness direction.

Effects of the Invention

[0011] According to the present invention, a multilayer ceramic capacitor having excellent reliability is provided.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying out the Invention

[0013] Specific embodiments of the present invention (hereinafter referred to as "the present embodiment") will be described. Note that the present invention is not limited to the following embodiments, and various modifications are possible without changing the gist of the present invention.

[0014] <<1. Multilayer Ceramic Capacitor>> The multilayer ceramic capacitor of the present embodiment has a first main surface and a second main surface facing each other in the thickness direction, a first side surface and a second side surface facing each other in the width direction, and a first end surface and a second end surface facing each other in the length direction, and includes a body portion including a plurality of dielectric ceramic layers and a plurality of internal electrode layers laminated in the thickness direction, and a pair of external electrodes provided on each of the first end surface and the second end surface and electrically connected to the plurality of internal electrode layers. Further, the dielectric ceramic layer contains crystal particles mainly composed of a perovskite-type composite oxide containing barium (Ba) and titanium (Ti), and further contains a rare earth element (Re). The dielectric ceramic layer includes a rare earth high-concentration region where the molar ratio of the rare earth element (Re) to titanium (Ti) (Re / Ti ratio) is 0.04 or more and 0.30 or less in an area ratio of 50% or more in a cross section including the thickness direction.

[0015] One aspect of the multilayer ceramic capacitor will be described with reference to FIGS. 1 to 3. FIG. 1 is a perspective view showing the outer shape of the multilayer ceramic capacitor. FIGS. 2 and 3 are cross-sectional views showing the inside of the multilayer ceramic capacitor. The multilayer ceramic capacitor (100) includes a body portion (6) including a plurality of stacked dielectric ceramic layers (2) and a plurality of internal electrode layers (4), and a pair of external electrodes (8a, 8b) provided on both end faces (14a, 14b) of the body portion (6). The multilayer ceramic capacitor (100) and the body portion (6) have a substantially rectangular parallelepiped shape. The substantially rectangular parallelepiped includes not only a rectangular parallelepiped but also a rectangular parallelepiped with rounded corners and / or edges. Further, the multilayer ceramic capacitor (100) and the body portion (6) have a first main surface (10a) and a second main surface (10b) facing each other in the thickness direction T, a first side surface (12a) and a second side surface (12b) facing each other in the width direction W, and a first end face (14a) and a second end face (14b) facing each other in the length direction L. Here, the thickness direction T refers to the direction in which the plurality of dielectric ceramic layers (2) and the plurality of internal electrode layers (Four) are stacked. The length direction L is orthogonal to the thickness direction T and orthogonal to the end faces (14a, 14b) provided with the external electrodes (8a, 8b). The width direction W is a direction orthogonal to the thickness direction T and the length direction L. A plane including the thickness direction T and the width direction W is defined as a WT plane, a plane including the width direction W and the length direction L is defined as an LW plane, and a plane including the length direction L and the thickness direction T is defined as an LT plane.

[0016] The external electrodes (8a, 8b) are composed of a first external electrode (8a) provided on the first end face (14a) and a second external electrode (8b) provided on the second end face (14b). The first external electrode (8a) may extend not only to the first end face (14a) but also to a part of the first main surface (10a), the second main surface (10b), the first side surface (12a) and the second side surface (12b). Further, the second external electrode (8b) may extend not only to the second end face (14b) but also to a part of the first main surface (10a), the second main surface (10b), the first side surface (12a) and the second side surface (12b). However, the first external electrode (8a) and the second external electrode (8b) are not in contact with each other and are electrically separated.

[0017] The internal electrode layer (4) is composed of a plurality of first internal electrode layers (4a) and a plurality of second internal electrode layers (4b). The plurality of first internal electrode layers (4a) extend to the first end face (14a), where they are electrically connected to the first external electrode (8a). Also, the plurality of second internal electrode layers (4b) extend to the second end face (14b), where they are electrically connected to the second external electrode (8b). The first internal electrode layer (4a) and the second internal electrode layer (4b) facing each other with the dielectric ceramic layer (2) in between are not electrically connected. Therefore, when a voltage is applied between the first internal electrode layer (4a) and the second internal electrode layer (4b) via the external electrodes (8a, 8b), charges are accumulated. The accumulated charges generate a capacitance, thereby realizing the function as a capacitive element.

[0018] The dimensions of the multilayer ceramic capacitor (100) are not particularly limited. However, it is preferable that the dimension in the length direction L is 0.4 mm or more and 5.7 mm or less, the dimension in the width direction W is 0.2 mm or more and 5.0 mm or less, and the dimension in the stacking direction T is 0.125 mm or more and 5.0 mm or less.

[0019] <Dielectric ceramic layer> The dielectric ceramic layer is composed of ceramic. The dielectric ceramic layer mainly contains crystal particles composed of a perovskite-type composite oxide containing barium (Ba) and titanium (Ti). That is, the main crystal particles are composed of a perovskite-type composite oxide. These main crystal particles are composed of a barium titanate (BaTiO3)-based compound. Therefore, it can also be said that the dielectric ceramic layer is composed of a sintered body of a BaTiO3-based compound. BaTiO3 is a perovskite-type oxide represented by the general formula: ABO3. BaTiO3 exhibits a tetragonal crystal structure at room temperature and is a ferroelectric with a high dielectric constant. Therefore, by using a BaTiO3-based compound as the main component, the dielectric constant of the dielectric ceramic can be increased, and it becomes possible to increase the capacitance of the capacitor. In this specification, the main component means the component with the highest content ratio in the ceramic. The content ratio of the main component may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or even 90% by mass or more.

[0020] The barium titanate (BaTiO3)-based compound is not particularly limited as long as it is a perovskite-type composite oxide mainly containing barium (Ba) and titanium (Ti). That is, this compound may be BaTiO3, or a part of Ba and / or Ti contained in BaTiO3 may be substituted with other elements. Specifically, a part of barium (Ba) may be substituted with other elements such as strontium (Sr) and calcium (Ca), and a part of titanium (Ti) may also be substituted with other elements such as zirconium (Zr) and hafnium (Hf). Furthermore, the ratio of the A-site element (Ba, Sr, Ca, etc.) to the B-site element (Ti, Zr, Hf, etc.) of the BaTiO3-based compound is not strictly limited to 1:1. As long as the perovskite-type crystal structure is maintained, a deviation in the ratio of the A-site element to the B-site element is allowed.

[0021] The dielectric ceramic layer further contains a rare earth element (Re) in addition to barium (Ba) and titanium (Ti). The rare earth element (Re) is a general term for elements constituting the group consisting of scandium (Sc) with an atomic number of 21, yttrium (Y) with an atomic number of 39, and lanthanum (La) with an atomic number of 57 to lutetium (Lu) with an atomic number of 71 in the periodic table. The dielectric ceramic layer may contain one type of rare earth element, or may contain a combination of a plurality of types of rare earth elements. Further, the rare earth element may be contained only in the BaTiO3-based compound which is the main crystal particle, or may be contained in grain boundaries, triple points, etc. together with the main crystal particle. When contained in the main crystal particle, it may occupy the Ba site (A site) of the BaTiO3-based compound, may occupy the Ti site (B site), or may occupy both sites.

[0022] By adding a rare earth element (Re) to the dielectric ceramic layer, various properties such as the reliability of the multilayer ceramic capacitor and the temperature characteristics of the dielectric constant can be improved. That is, the BaTiO3-based compound which is the main component may contain many oxygen vacancies generated in the firing process. These oxygen vacancies tend to reduce the insulation resistance when accompanied by electron compensation, and also tend to move under an electric field and cause a time-dependent decrease in the insulation resistance. When a rare earth element is added to the dielectric ceramic layer, it tends to dissolve in the Ba site or Ti site of the BaTiO3-based compound. The dissolved rare earth element acts as a donor or acceptor, preventing the movement of oxygen vacancies or suppressing the generation of conduction electrons. Therefore, the deterioration of the insulation resistance is reduced and the high-temperature load life is improved. In addition, the BaTiO3-based compound has a large temperature dependence of the dielectric constant near the Curie temperature Tc. By dissolving a rare earth element, it becomes possible to make the temperature change of the dielectric constant flatter in a wide range including the Curie temperature Tc.

[0023] The type of rare earth element (Re) contained in the dielectric ceramic layer is not particularly limited. However, it preferably contains at least one selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), and particularly preferably contains dysprosium (Dy). Dy is an element located near the middle of the lanthanoid group in the periodic table, and its ionic radius is also of medium size. Therefore, it can dissolve in both the Ba site (A site) and the Ti site (B site) of the BaTiO3-based compound, which is effective in improving reliability. The dielectric ceramic layer may contain only Dy as the rare earth element, or may contain other rare earth elements together with Dy.

[0024] By adding an appropriate amount of rare earth element (Re) to the dielectric ceramic layer, it becomes possible to more significantly exert the effect of improving various properties. The dielectric ceramic layer preferably contains the rare earth element (Re) in a proportion of 0.1 mol or more and 35.0 mol or less, more preferably 0.5 mol or more and 30.0 mol or less, and even more preferably 3.5 mol or more and 25.0 mol or less, based on 100 mol of titanium (Ti). Note that these molar amounts are the molar amounts as raw materials.

[0025] The dielectric ceramic layer may contain other additive components in addition to the rare earth element (Re). Examples of such components include manganese (Mn), magnesium (Mg), silicon (Si), aluminum (Al), and vanadium (V). The form of existence of the additive components is not limited. It may be contained in any of the main crystal particles, grain boundaries, and triple points.

[0026] Preferably, the thickness of the dielectric ceramic layer is 0.5 μm or more and 7.0 μm or less. By setting the thickness of the dielectric ceramic layer to 0.5 μm or more, deterioration of insulation characteristics can be prevented, leading to improved reliability. On the other hand, by setting the thickness to 7.0 μm or less, the dielectric ceramic layer is thinned, making it possible to increase the capacitance. The number of layers of the dielectric ceramic layer is preferably 50 or more and 1000 or less.

[0027] In the multilayer ceramic capacitor of the present embodiment, the dielectric ceramic layer includes a rare earth high-concentration region with an area ratio of 50% or more in a cross section including the thickness direction. Here, the thickness direction is the stacking direction of the dielectric ceramic layer and the internal electrode layer. Therefore, the cross section including the thickness direction is a plane passing through the inside of the multilayer ceramic capacitor, and a plane whose perpendicular line is orthogonal to the thickness direction, for example, the LT plane or the WT plane. The rare earth high-concentration region is a region where the molar ratio (Re / Ti ratio) of the rare earth element (Re) to titanium (Ti) is 0.04 or more and 0.30 or less. That is, when the cross section of the dielectric ceramic layer is classified into a rare earth ultra-high-concentration region where the Re / Ti ratio exceeds 0.30, a rare earth high-concentration region where the Re / Ti ratio is 0.04 or more and 0.30 or less, and a rare earth low-concentration region where the Re / Ti ratio is less than 0.04, the ratio of the area occupied by the rare earth high-concentration region to the total area of the rare earth ultra-high-concentration region, the rare earth high-concentration region, and the rare earth low-concentration region is 50% or more.

[0028] By increasing the area ratio of the rare earth high-concentration region to 50% or more, it becomes possible to more significantly improve the reliability of the multilayer ceramic capacitor. Although the detailed reason is unknown, the following speculation is made. A high rare earth concentration means that the average distance between the positions where rare earths exist becomes shorter. Rare earth elements have an effect of hindering the movement of oxygen vacancies. By shortening the average distance between rare earth elements, the effect of suppressing the movement of oxygen vacancies increases, resulting in improved reliability. From the perspective of improving reliability, the higher the area ratio of the rare earth high-concentration region, the more preferable. The area ratio may be 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, or even 100%. However, if the area ratio is excessively high, the dielectric constant may decrease. From the perspective of improving the dielectric constant, the area ratio may be 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, or 60% or less.

[0029] Preferably, in a cross-section including the thickness direction, the coefficient of variation (CV) value of the Re / Ti ratio in the high rare earth concentration region is 45% or less. The CV value serves as an indicator of variation. The smaller the CV value of the Re / Ti ratio, the smaller the variation in the Re / Ti ratio for each location in the high rare earth concentration region. By limiting the CV value of the Re / Ti ratio to 45% or less, the variation in reliability can be suppressed. Although the detailed reasons are unclear, the following speculation is made. Even if the average value of the Re / Ti ratio is the same, a large CV value may mean that there is a region where the Re / Ti ratio is extremely lower than the average value, or that the total size of the dispersed low Re / Ti ratio regions is large. Low Re / Ti ratio regions may reduce reliability. Therefore, a small CV value of the Re / Ti ratio means that it is difficult for the reliability to decrease, and the variation in reliability can be reduced. From the perspective of suppressing the variation in reliability, the smaller the CV value, the more preferable. The CV value may be 40% or less, 35% or less, 30% or less, 25% or less, 20% or less, 15% or less, or 10% or less. The CV value of the Re / Ti ratio can be obtained by dividing the high rare earth concentration region into minute regions, measuring the Re / Ti ratio of each region by a method such as transmission electron microscopy (TEM)-energy dispersive X-ray spectroscopy (EDX), and using the average value and the standard deviation σ according to the following formula (1).

[0030]

Number

[0031] The reliability and its variation of a multilayer ceramic capacitor can be evaluated by examining the high-temperature load life. The high-temperature load life can be evaluated using the mean time to failure (MTTF) and B1 life obtained by performing a high-temperature load test on the capacitor. Specifically, a high-temperature load test is performed on a plurality of capacitors, and the time when the insulation resistance sharply decreases is defined as the failure time. The failure times of each capacitor are subjected to Weibull analysis to obtain the failure time when the cumulative failure rate reaches 63.2% and the shape parameter m, and the mean time to failure (MTTF) is determined from these. Also, the failure time when the cumulative failure rate reaches 1% is defined as the B1 life. It can be judged that the higher the MTTF, the higher the reliability. Also, it can be judged that the larger the B1 life / MTTF, the smaller the variation in reliability.

[0032] The distribution of the rare-earth high-concentration regions contained in the dielectric ceramic layer is not particularly limited. The dielectric ceramic layer may have an island structure in cross-section, and each of the rare-earth high-concentration region and the other regions may constitute a sea portion and an island portion. Specifically, a mode in which other regions, for example, rare-earth low-concentration regions, are dispersedly arranged in the rare-earth high-concentration region may be used. Alternatively, the rare-earth high-concentration region and the other regions may extend in layers, and each layer of the dielectric ceramic layer may have a laminated structure of the layer-shaped rare-earth high-concentration region and the other regions.

[0033] Preferably, in a cross-section including the thickness direction, the dielectric ceramic layer includes a rare earth low-concentration region, and this rare earth low-concentration region is composed of a plurality of sub-regions surrounded by a high-concentration region. Also preferably, the average value (average equivalent circle diameter) of the equivalent circle diameter of each sub-region in the cross-section is 130 nm or more. That is, it is preferable that the dielectric ceramic layer has an island structure in its cross-section, the rare earth high-concentration region forms the sea part, the rare earth low-concentration region forms the island part, and the average equivalent circle diameter of the island part is a predetermined value or more. In this way, by dispersing and arranging the rare earth low-concentration regions having a desired size in an island shape in the rare earth high-concentration region, it becomes possible to improve the dielectric constant while ensuring the reliability of the multilayer ceramic capacitor. The detailed reason is unknown, but it is speculated as follows. The Curie temperature Tc of the rare earth high-concentration region may be lower than room temperature depending on the Re / Ti ratio, and at this time the dielectric constant will decrease. However, by mixing a rare earth low-concentration region where the Curie temperature Tc is sufficiently higher than room temperature, a decrease in the dielectric constant can be avoided. Also, since the dielectric constant is accompanied by a size effect, a higher dielectric constant can be obtained by increasing the average equivalent circle diameter of the rare earth low-concentration region to a predetermined value or more. From the viewpoint of improving the dielectric constant, the larger the size of the sub-regions arranged in a dispersed manner, the more preferable. The average equivalent circle diameter of the sub-regions may be 140 nm or more, 150 nm or more, 160 nm or more, 170 nm or more, 180 nm or more, 190 nm or more, 200 nm or more, 210 nm or more, or 220 nm or more. On the other hand, in order to more effectively exert the effect of improving the reliability, it is preferable that the size of the rare earth low-concentration region can be suppressed to a certain size. The average equivalent circle diameter of the sub-regions may be 300 nm or less, 290 nm or less, 280 nm or less, 270 nm or less, 260 nm or less, 250 nm or less, 240 nm or less, 230 nm or less, 220 nm or less, 210 nm or less, 200 nm or less, 190 nm or less, 180 nm or less, 170 nm or less, or 160 nm or less. Note that the average equivalent circle diameter (D50) is the diameter of a circle having the same area as the cumulative 50% area. Also, the cumulative 50% area is the area of the sub-regions when, with the total area of each sub-region being 100%, the areas of the sub-regions are accumulated in ascending order and reach 50% cumulatively with respect to the total area.On the other hand, the equivalent diameter of the average circle can be calculated according to the following formula (2) using the cumulative 50% area.

[0034]

Number

[0035] Preferably, in a cross-section including the thickness direction, the average value (average circularity) of the circularity of each sub-region constituting the rare-earth low-concentration region is 0.70 or more. Circularity is an index representing the complexity of the region shape, being 1 for a perfect circle and becoming smaller as the shape becomes more complex. By making the shape of the dispersed rare-earth low-concentration regions approximately circular, it becomes possible to suppress the voltage dependence of the high-temperature load life. Although the detailed reason is unknown, it is speculated as follows. By increasing the circularity of the sub-regions constituting the rare-earth low-concentration region, the probability of the existence of a site having an extremely high curvature at the boundary with the rare-earth high-concentration region can be reduced. Since the insulation resistance changes with the rare-earth concentration, it is considered that the change in the insulation resistance is particularly large at the boundary between the rare-earth low-concentration region and the rare-earth high-concentration region. Therefore, the smoother this boundary, that is, the higher the circularity of the sub-regions constituting the rare-earth low-concentration region, the more the electric field concentration can be suppressed, and as a result, the voltage dependence of the high-temperature load life becomes smaller. The average circularity of the sub-regions may be 0.75 or more, 0.80 or more, or 0.85 or more. The average circularity can be obtained by calculating the circularity according to the following formula (3) using the area and perimeter of each sub-region obtained by TEM observation or the like, and calculating the average value thereof.

[0036]

Number

[0037] Preferably, at least one of the crystal particles composed of a perovskite-type composite oxide contained in the dielectric ceramic layer includes two or more sub-regions that are not connected to each other. That is, there are main crystal particles including a plurality of independent sub-regions. By adopting such a configuration, it is possible to obtain the effect of improving the DC bias characteristics of the dielectric constant. Although the detailed reason is unknown, it is presumed that a rare earth high-concentration region exists between the sub-regions that are not connected to each other within the same crystal particle, so that the ratio of the DC voltage applied to the sub-regions is reduced.

[0038] <Internal electrode layer> The internal electrode layer contains a conductive metal. As the conductive metal, known electrode materials such as nickel (Ni), copper (Cu), silver (Ag), palladium (Pd), and alloys thereof may be used. The internal electrode layer may also contain other components other than the conductive metal. Examples of other components include ceramic components that act as co-materials. Examples of the ceramic component include BaTiO3-based compounds contained in the dielectric ceramic layer.

[0039] Preferably, the thickness of the internal electrode layer is 0.3 μm or more and 0.7 μm or less. By setting the thickness of the internal electrode layer to 0.3 μm or more, defects such as electrode disconnection are suppressed. Also, by setting the thickness of the internal electrode layer to 0.7 μm or less, it is possible to suppress a decrease in the ratio of the dielectric ceramic layer that functions electrically in the capacitor and a resulting decrease in capacitance.

[0040] <External electrode> As the external electrodes, a known configuration can be adopted. For example, a laminated structure composed of an underlayer, a first plating layer, and a second plating layer can be formed from the end face side of the multilayer ceramic capacitor. The underlayer contains a metal such as nickel (Ni) or copper (Cu), for example. Also, ceramic powder may be included as a co-material in addition to the metal. The first plating layer is, for example, a nickel (Ni) plating layer. The second plating layer is, for example, a tin (Sn) plating layer. Also, a conductive resin layer may be provided between the underlayer and the first plating layer. The conductive resin layer is a layer containing conductive metal particles such as copper (Cu), silver (Ag), and nickel (Ni) and resin. The form of the external electrodes is not limited as long as they are electrically connected to the internal electrode layer and function as external input / output terminals.

[0041] <<2. Manufacturing method of multilayer ceramic capacitor>> The manufacturing method of the multilayer ceramic capacitor of the present embodiment is not limited as long as it satisfies the above-described requirements. An exemplary manufacturing method includes the following steps: a step of producing a green sheet containing at least barium (Ba), titanium (Ti), and a rare earth element (Re) (green sheet production step); a step of applying a conductive paste to the surface of the green sheet to obtain a green sheet with an internal electrode pattern formed thereon (electrode pattern formation step); a step of laminating and pressing a plurality of green sheets to obtain a laminated block (lamination step); a step of cutting the obtained laminated block to obtain a laminated chip (cutting step); a step of subjecting the obtained laminated chip to a debinding treatment and a firing treatment to obtain a body part (firing step); and a step of forming external electrodes on the obtained body part (external electrode formation step). Details of each step will be described below.

[0042] <Green sheet production step> In the green sheet manufacturing process, a green sheet containing at least barium (Ba), titanium (Ti), and rare earth elements (Re) is manufactured. The green sheet is a precursor of the dielectric ceramic layer of the capacitor and includes the main component raw material and the additive raw material of the dielectric ceramic layer. The green sheet can be manufactured by a known method and is not particularly limited. The additive raw material may be mixed with the main component raw material to produce a dielectric raw material, a binder and a solvent may be added to and mixed with the obtained dielectric raw material to form a slurry, and a green sheet may be formed from the obtained slurry.

[0043] Powder of a BaTiO3-based compound is used as the main component raw material. The BaTiO3-based compound may be synthesized using known ceramic raw materials such as oxides, carbonates, hydroxides, nitrates, organic acid salts, alkoxides, and / or chelate compounds, and using known ceramic synthesis methods such as the solid-phase reaction method, the hydrothermal synthesis method, and the alkoxide method. The additive raw material includes at least a rare earth element (Re) raw material. As the Re raw material, known ceramic raw materials such as Re oxides, carbonates, hydroxides, nitrates, organic acid salts, alkoxides, and / or chelate compounds may be used. The additive raw material may include raw materials of other additive components such as Mn, Mg, Si, Al, and V. Further, in order to adjust the composition of the BaTiO3-based compound as the main component, Ba raw materials and Ti raw materials such as barium carbonate (BaCO3) and titanium oxide (TiO2) may be added to the additive raw material.

[0044] The raw material mixing can be carried out by known methods. For example, there is a method of wet mixing and pulverizing the weighed main component raw material, additive raw material, and water together with a pulverizing medium using a ball mill. When wet mixing is performed, the obtained mixture may be dried. Further, if necessary, the dielectric raw material obtained after drying may be calcined. The slurrying can also be carried out by known methods, and an organic binder and an organic solvent may be mixed with the dielectric raw material. As the organic binder, a known binder such as a polyvinyl butyral-based binder may be used. As the organic solvent, a known solvent such as toluene or ethanol may be used. Additives such as plasticizers may be added to the slurry as necessary. Furthermore, the forming of the green sheet may be carried out by known methods such as the doctor blade method or the lip method.

[0045] <Electrode Pattern Forming Step> In the electrode pattern forming step, a conductive paste is applied to the surface of the green sheet to obtain a green sheet having an internal electrode pattern formed thereon. The internal electrode pattern becomes an internal electrode layer after firing. As the conductive metal contained in the conductive paste, conductive materials such as nickel (Ni), copper (Cu), silver (Ag), palladium (Pd), and alloys containing these may be used. Further, a ceramic component that acts as a co-material may be added to the conductive paste. As the ceramic component, the main component raw material of the dielectric ceramic layer can be used. The application of the conductive paste may be carried out by known methods such as screen printing or gravure printing.

[0046] <Laminating Step> In the laminating step, a plurality of green sheets are laminated and pressed to obtain a laminated block. As the green sheet, a green sheet having an internal electrode pattern formed thereon is used, but a part of the green sheet without the internal electrode pattern formed thereon may also be used. The lamination and pressing may be carried out by known methods.

[0047] <Cutting Step> In the cutting step, the obtained laminated block is cut to obtain a laminated chip. The cutting may be carried out so that a chip of a predetermined size is obtained and at least a part of the internal electrode pattern is exposed on the end face of the laminated chip.

[0048] <Firing Process> In the firing process, the obtained laminated chip is subjected to a debinding process and a firing process to obtain a green body. By the firing process, the green sheet and the internal electrode pattern are co-sintered to become a dielectric ceramic layer and an internal electrode layer, respectively. The conditions for the debinding process may be determined according to the type of organic binder contained in the green sheet and the internal electrode pattern. Also, the firing process may be performed at a temperature at which the laminated chip is sufficiently densified. For example, it may be performed under the condition of holding at a temperature of 1200 °C or higher and 1300 °C or lower for 1 hour or longer and 10 hours or shorter. Also, the firing is performed in an atmosphere in which the BaTiO3-based compound as the main component is not reduced and the oxidation of the conductive metal is suppressed. For example, in a N2-H2-H2O gas stream with an oxygen partial pressure of 1.9×10 -11 MPa or higher and 6.4×10 -9 MPa or lower. Further, an annealing process may be performed after firing.

[0049] <External Electrode Formation Process> In the external electrode formation process, an external electrode is formed on the obtained green body. The external electrode may be formed by a known method. For example, a conductive paste containing a metal such as silver (Ag), copper (Cu), and / or nickel (Ni) may be applied and baked on the end face of the green body where the internal electrode is drawn out and exposed. Alternatively, it may be formed by a method in which a conductive paste is applied to both end faces of the laminated chip before firing and then a firing process is performed. Also, a plating film such as nickel (Ni) or tin (Sn) may be formed on the formed electrode as an underlayer. Thereby, a multilayer ceramic capacitor is manufactured.

Examples

[0050] The present invention will be described in more detail using the following examples and comparative examples. However, the present invention is not limited to the following examples.

[0051] (1) Fabrication of Multilayer Ceramic Capacitor [Examples 1 to 15, Examples 19 to 21, and Examples 24 to 28] Samples of multilayer ceramic capacitors were fabricated according to the procedure shown below.

[0052] First, BaTiO3 powder with a BET diameter of 190 nm and a tetragonality of 1.0099 was prepared as BT-A powder. Here, the tetragonality is an index of the degree of tetragonality in the tetragonal crystal structure and is represented by the ratio of the c-axis length to the a-axis length (c / a axis ratio) in the tetragonal crystal. The tetragonality can be determined by the powder X-ray diffraction (XRD) method. The BET diameter is the average primary particle diameter obtained by conversion from the BET specific surface area of the BaTiO3 powder assuming that the particles are spherical.

[0053] Separately, BaTiO3 powder with a BET diameter of 100 nm and a tetragonality of 1.007 was prepared as BT-B powder, which was then wet-milled to obtain finely milled BT-B powder. The BET specific surface area of the finely milled BT-B powder was 50 m 2 / g.

[0054] Furthermore, Dy2O3 powder, BaCO3 powder, and TiO2 powder were individually wet-milled to obtain finely milled Dy2O3 powder, finely milled BaCO3 powder, and finely milled TiO2 powder. The BET specific surface areas of the finely milled Dy2O3 powder, finely milled BaCO3 powder, and finely milled TiO2 powder were in the range of 50 m 2 / g to 56 m 2 / g.

[0055] Next, the BT-A powder, finely milled BT-B powder, finely milled Dy2O3 powder, finely milled BaCO3 powder, and finely milled TiO2 powder were mixed using a wet mill so as to obtain the composition shown in Table 1 below, and then dried to obtain a mixed powder. Table 1 also shows the A / B ratio, which is the molar ratio of the A-site element to the B-site element of the perovskite-type oxide (ABO3). For Dy, in terms of the formulation composition, it was treated as entering both the A-site and the B-site so as to obtain the A / B ratio shown in Table 1.

[0056] The obtained mixed powder was heat-treated at a heating rate of 600 °C / hour in the atmosphere until it reached 1100 °C and then held for 2 hours to obtain a calcined powder.

[0057] To 100 mol parts of TiO2 in the calcined powder, 1.0 mol part of MgCO3 powder, 0.3 mol part of MnCO3 powder, and 1.3 mol parts of SiO2 sol were added to the calcined powder, followed by wet mixing and drying to obtain dielectric powder.

[0058] A polybutyral-based binder and a plasticizer were added to the obtained dielectric powder, and further toluene and ethyl alcohol were added, and the mixture was slurried using a wet mill, and this slurry was molded to obtain a green sheet. The obtained green sheet had a thickness of 1.7 μm after sintering densification.

[0059] A conductive paste mainly composed of nickel was screen-printed on the surface of the obtained green sheet to form a pattern of a conductive paste layer serving as an internal electrode layer.

[0060] Thereafter, 201 green sheets having a conductive paste layer formed on the surface were laminated such that the sides from which the conductive paste layers were drawn out were staggered, and further green sheet layers without a conductive paste layer were provided above and below, and then the whole was pressure-bonded to produce a laminated block.

[0061] The obtained laminated block was cut into green laminated chips. The cutting was performed so that the size of the laminated ceramic capacitor after manufacturing would be 3.2 mm × 1.6 mm.

[0062] The obtained green laminated chips were heat-treated at 280 °C in a N2 gas stream to burn off the binder. Subsequently, firing was performed at 1260 °C in a N2-H2-H2O gas stream under the condition of an oxygen partial pressure of 1.6 × 10 -9 MPa for 2 hours.

[0063] In the fired laminated chip, a conductive paste primarily composed of Cu was applied to the end surface where the internal electrode layer was drawn out, and baked at 800°C to form an external electrode, and then a Ni-Sn plating layer was formed on the surface of the external electrode.

[0064] In this way, a multilayer ceramic capacitor was fabricated. The resulting multilayer ceramic capacitor had an external dimension of 3.2 mm long x 1.6 mm wide x 1.6 mm thick. The number of dielectric ceramic layers sandwiched between the internal electrode layers was 200, and each dielectric ceramic layer was 1.7 μm thick.

[0065] [Examples 16 to 18] As the BT-A powder, BaTiO3 powder having a BET diameter of 250 nm and a tetragonal crystallinity of 1.0100 was used. Except for this, multilayer ceramic capacitors were fabricated in the same manner as in Examples 1 to 15, 19 to 21, and 24 to 28.

[0066] [Example 22] As the BT-A powder, BaTiO3 powder having a BET diameter of 150 nm and a tetragonal crystallinity of 1.0095 was used. Except for this, multilayer ceramic capacitors were fabricated in the same manner as in Examples 1 to 15, 19 to 21, and 24 to 28.

[0067] [Example 23] As the BT-A powder, BaTiO powder having a BET diameter of 250 nm and a tetragonal crystallinity of 1.0100 was used, which was wet-pulverized until the BET diameter reached 200 nm. Except for this, multilayer ceramic capacitors were fabricated in the same manner as in Examples 1 to 15, 19 to 21, and 24 to 28.

[0068] [Examples 29 to 32] We prepared rare earth oxides (Gd2O3, Y2O3, Ho2O3, and Er2O3) corresponding to the rare earth element (Re) species shown in Table 1. We then individually analyzed these rare earth oxides using a BET specific surface area of 50 m 2 / g~60m 2Wet grinding was performed until it fell within the range of / g to obtain a finely ground Re oxide powder. The raw material powders (BT-A powder, finely ground BT-B powder, finely ground Re oxide powder, finely ground BaCO3 powder, and finely ground TiO2 powder) were mixed and dried so as to obtain the compositions shown in Table 1 below to obtain a mixed powder. In terms of the preparation composition, the rare earth element (Re) was treated as entering both the A-site and the B-site, and the raw materials were prepared so as to obtain the A / B ratio shown in Table 1 below. Otherwise, multilayer ceramic capacitors were produced in the same manner as in Examples 1 to 15, Examples 19 to 21, and Examples 24 to 28.

[0069] [Examples 33 to 37] Rare earth oxides (Dy2O3, La2O3, Nd2O3, Tb4O7, Yb2O3, Lu2O3, Eu2O3, Sm2O3, CeO2, Pr6O 11 , and Tm2O3) corresponding to the rare earth element (Re) species shown in Table 1 were prepared. Then, these rare earth oxides were individually wet-ground until the BET specific surface area fell within the range of 50 m 2 / g to 60 m 2 / g to obtain a finely ground Re oxide powder. The raw material powders (BT-A powder, finely ground BT-B powder, finely ground Re oxide powder, finely ground BaCO3 powder, and finely ground TiO2 powder) were mixed and dried so as to obtain the compositions shown in Table 1 below to obtain a mixed powder. When preparing the raw materials, the addition amounts of rare earth elements other than Dy were all set to 0.1 mole parts. Also, for La, Nd, Eu, Sm, Ce, and Pr, they were treated as entering the A-site in terms of the preparation composition. For Tb, Yb, Lu, and Tm, they were treated as entering the B-site in terms of the preparation composition. For Dy, it was treated as entering both the A-site and the B-site in terms of the preparation composition. Considering these, the raw materials were prepared so as to obtain the A / B ratio shown in Table 1 below. Otherwise, multilayer ceramic capacitors were produced in the same manner as in Examples 1 to 15, Examples 19 to 21, and Examples 24 to 28.

[0070] (2) Evaluation Regarding the multilayer ceramic capacitors obtained in Examples 1 to 37, evaluations of various characteristics were performed as follows.

[0071] <TEM Observation / EDX Analysis> The dielectric ceramic layer of the multilayer ceramic capacitor was observed using a field emission transmission electron microscope (FE-TEM), and component analysis of the fine region was performed using an energy dispersive X-ray spectrometer (EDX) attached to the TEM. The observation sample was prepared by thinning the dielectric ceramic layer by the FIB lift-out method. The observation and analysis were carried out under the following conditions.

[0072] - Equipment: JEOL Ltd., JEM-2200FS / Noran System 7 - Field of view: n = 2 - Magnification: 60,000 times - Pixel size: 9.2 nm / 1 pixel - Spot diameter: 1 nmφ - Measurement: EDX integration count 100 times

[0073] Also, during the observation, the dielectric ceramic layer within the observation field of view was extracted, and a region with a Re / Ti ratio of 0.04 or more and 0.30 or less was defined as the rare earth high-concentration region. According to the following formula (4), the area ratio was calculated. Furthermore, the Re / Ti ratio at each pixel in the rare earth high-concentration region was measured, and the CV value was calculated according to the following formula (1) from the average value and the standard deviation σ.

[0074]

Equation

Equation

[0075] Also, a region where the Re / Ti ratio is less than 0.04 was defined as a rare earth low-concentration region, and the equivalent circle diameter and circularity of the sub-regions constituting the rare earth low-concentration region were determined. Specifically, the boundary line between the sub-regions constituting the rare earth low-concentration region and the rare earth high-concentration region was drawn with a touch pen. Then, the obtained data was analyzed using image analysis software (Miyaya Shoko Co., Ltd., WINROOF) to obtain the area and perimeter length of each sub-region. Further, the total area of each sub-region was set to 100 (100%), and the areas of the sub-regions were integrated in ascending order. When the cumulative value reached 50 (50%), the area of the sub-region at that time (cumulative 50% area) was determined. Then, using this cumulative 50% area, the average equivalent circle diameter (D50) was calculated according to the following formula (2). Also, the circularity of each sub-region was determined according to the following formula (3), and the average value was calculated.

[0076]

Number

Number

[0077] <Dielectric property> For the obtained multilayer ceramic capacitor, the capacitance (C) was measured using an automatic bridge type measuring instrument under the conditions of an AC voltage of 1 V and a frequency of 1 kHz. Then, the relative dielectric constant (ε r ) was calculated using the area of the opposing electrodes of the multilayer ceramic capacitor, as well as the number and layer thickness of the dielectric ceramic layers. Measurements were performed on 72 samples fabricated under the same conditions, and the average value of the obtained values was calculated.

[0078] <Reliability (MTTF, B1 life)> A high-accelerated life test (HALT) was performed on the multilayer ceramic capacitor to obtain the mean time to failure (MTTF). In the high-accelerated life test, a high-temperature load was applied to the sample under the conditions of a temperature of 175°C and a test voltage of 50 V. Then, the time when the insulation resistance became 200 kΩ or less was defined as the failure time. The failure times of 72 samples fabricated under the same conditions were measured.

[0079] Next, the obtained data was plotted on Weibull probability paper to obtain the Weibull distribution. In the obtained Weibull distribution, the relationship between the failure time and the cumulative failure rate was linearly regressed, and the slope was determined as the shape parameter m. Also, the failure time at which the cumulative failure rate reached 63.2% was read, and the mean time to failure (MTTF) at a test voltage of 50 V was determined using this failure time and the shape parameter m corresponding to the slope of the regression line. Samples with an MTTF of 50 hours or more were judged as qualified products. Also, the failure time at which the cumulative failure rate reached 1% was defined as the B1 life. And B1 life / MTTF was calculated in percentage notation.

[0080] Furthermore, a highly accelerated life test was conducted under the same conditions except that the test voltage was changed to 60 V. The mean time to failure (MTTF) at a test voltage of 60 V was obtained, and the decrease in MTTF was calculated according to the following formula (5).

[0081] [Number]

[0082] (3) Evaluation Results The evaluation results obtained for Examples 1 to 37 are summarized in Table 1. The MTTF shown in Table 1 is the value measured under the condition of a test voltage of 50 V except for the decrease in MTTF.

[0083] For the example samples (Examples 1 to 9, Examples 13 to 27, and Examples 29 to 37) with an area ratio of the rare earth high-concentration region of 50% or more, the MTTF was 52 hours or more. In particular, for the samples (Examples 6, 8, 13, 19, and 20) in which the rare earth element (Re) was Dy and the area ratio was 80% or more, the MTTF was as long as 149 hours or more. On the other hand, for the comparative example samples (Examples 10 to 12 and Example 28) with an area ratio of less than 50%, the MTTF was short at 39 hours or less. From these results, it was found that a highly reliable multilayer ceramic capacitor can be obtained by increasing the area ratio of the rare earth high-concentration region to 50% or more.

[0084] Example samples with a CV value of the Re / Ti ratio of 45% or less (Examples 1 to 9, Examples 13 to 24, Example 26, Example 27, and Examples 29 to 37) had a B1 life / MTTF of 25% or more, and the variation in failure time was small. Also, example samples with a circle equivalent diameter of 130 nm or more in the low rare earth concentration region (Examples 1 to 9, Examples 13 to 18, Example 20, Example 21, Examples 23 to 27, and Examples 29 to 37) had a relative dielectric constant ε r of 2500 or more. Furthermore, example samples with a circularity of 0.70 or more in the low rare earth concentration region (Examples 1 to 9, Examples 13 to 18, Examples 20 to 22, and Examples 24 to 27, and Examples 29 to 37) had a decrease in MTTF of 60% or less. From these results, it was found that by keeping the CV value of the Re / Ti ratio, the circle equivalent diameter and / or circularity in the low rare earth concentration region within a predetermined range, it is possible to suppress the variation in reliability and voltage dependence, and to improve the dielectric constant.

[0085] The fine structure and element distribution of the cross-section of the multilayer ceramic capacitor obtained in the examples are schematically shown in FIGS. 4(a) and 4(b). FIG. 4(a) is a diagram showing the cross-sectional fine structure. Points A and C in the figure indicate the internal electrode layer, and point B indicates the dielectric ceramic layer. FIG. 4(b) is an element distribution diagram showing the distribution of Dy. In FIG. 4(b), regions with a high Dy concentration in the dielectric ceramic layer are shown brightly, and regions with a low concentration are shown darkly. As shown in FIG. 4(a), the dielectric ceramic layer is composed of a large number of crystal particles. Also, as shown in FIG. 4(b), the Dy distribution is non-uniform, and low Dy concentration regions are distributed in an island shape in the high Dy concentration region. Furthermore, there are crystal particles containing a plurality of independent low rare earth concentration regions.

[0086] [Table 1]

Claims

1. It has a first main surface and a second main surface that face each other in the thickness direction, a first side surface and a second side surface that face each other in the width direction, and a first end surface and a second end surface that face each other in the length direction, a body portion including a plurality of dielectric ceramic layers and a plurality of internal electrode layers laminated in the thickness direction, and a pair of external electrodes provided on each of the first end surface and the second end surface and electrically connected to the plurality of internal electrode layers. A multilayer ceramic capacitor comprising: The dielectric ceramic layer contains crystal particles mainly composed of a perovskite-type composite oxide containing barium (Ba) and titanium (Ti), and further contains a rare earth element (Re). The dielectric ceramic layer includes a rare earth high-concentration region where the molar ratio (Re / Ti ratio) of the rare earth element (Re) to titanium (Ti) is 0.04 or more and 0.30 or less in a cross section including the thickness direction with an area ratio of 50% or more. Multilayer ceramic capacitor.

2. The dielectric ceramic layer includes the rare earth high-concentration region in the cross section with an area ratio of 60% or more. The multilayer ceramic capacitor according to claim 1.

3. In the cross section, the CV value of the Re / Ti ratio in the rare earth high-concentration region is 45% or less. The multilayer ceramic capacitor according to claim 1 or 2.

4. In the cross section, the CV value of the Re / Ti ratio in the rare earth high-concentration region is 20% or less. The multilayer ceramic capacitor according to any one of claims 1 to 3.

5. The dielectric ceramic layer includes a rare earth low-concentration region in the cross section where the ratio (Re / Ti ratio) of the rare earth element (Re) to titanium (Ti) is less than 0.

04. The rare earth low-concentration region is composed of a plurality of sub-regions surrounded by the rare earth high-concentration region. The average value (average equivalent circle diameter) of the equivalent circle diameter of each of the sub-regions in the cross section is 130 nm or more. The multilayer ceramic capacitor according to any one of claims 1 to 4.

6. The average value (average circularity) of the circularity of each of the sub-regions in the cross section is 0.70 or more. The multilayer ceramic capacitor according to claim 5.

7. At least one of the crystal particles includes two or more of the sub-regions that are not connected to each other. The multilayer ceramic capacitor according to claim 5 or 6.

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