Multilayer ceramic capacitor

Abstract

Provided is a laminated ceramic capacitor having superior reliability. This laminated ceramic capacitor comprises: an element part that has a first main surface and second main surface opposing each other in the thickness direction of the capacitor, a first side surface and second side surface opposing each other in the width direction, and a first end surface and second end surface opposing each other in the longitudinal direction, and includes a plurality of dielectric ceramic layers and a plurality of internal electrode layers laminated in the thickness direction; and a pair of external electrodes that are respectively provided on the first end surface and second end surface and electrically connected to the plurality of internal electrode layers. The dielectric ceramic layers contain, as a principle component, crystalline particles formed from a perovskite-type composite oxide including barium (Ba) and titanium (Ti), and additionally contain a rare-earth element (Re). In a cross section including the thickness direction thereof, the dielectric ceramic layers include a rare-earth high-concentration region, where the molar ratio (Re / Ti) of the rare earth element (Re) to titanium (Ti) is 0.04-0.30, in an area ratio of 50% or more.

Description

[Technical field]

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

[0002] As electronic devices such as mobile phones become smaller and CPU speeds increase, the demand for multilayer ceramic capacitors (MLCCs) is increasing. Multilayer ceramic capacitors have a structure in which dielectric layers and internal electrode layers are alternately laminated, and due to the thinned high-permittivity dielectric layers, they have a large capacitance despite their small size. There are known multilayer ceramic capacitors using various materials, but the most popular is one that uses barium titanate (BaTiO 3 )-based compounds and internal electrode layers made of base metals such as nickel (Ni) are widely used because they are inexpensive and exhibit high performance.

[0003] In order to realize a multilayer ceramic capacitor with a smaller size and a larger capacitance, it is important to make the dielectric layers thinner. However, when the dielectric layers are made thinner, the insulation resistance life between the internal electrode layers is shortened, which leads to a decrease in reliability. To address this issue, BaTiO 3 A technology has been proposed that aims to extend the insulation resistance life and improve reliability by adding additives such as rare earth elements (RE) and magnesium (Mg) to a dielectric layer made of a ferroelectric compound.

[0004] For example, Patent Document 1 discloses a dielectric ceramic composition that contains a main component represented by a specific composition formula, which comprises 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 (claim 1 of Patent Document 1). Patent Document 1 also describes that the ceramic composition is applied to a dielectric ceramic layer of a multilayer ceramic capacitor whose internal electrodes are made of nickel or a nickel alloy, and that when used at high electric field strength, the product of insulation resistance and capacitance (CR product) is high, dielectric strength is high, and weather resistance such as high temperature load and humidity load is excellent (claim 4 and

[0007] of Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3334607 Summary of the Invention [Problem to be solved by the invention]

[0006] With the progress of electronic components and electronic devices, multilayer ceramic capacitors are expected to become smaller and have larger capacitance. In addition, as the applications of multilayer ceramic capacitors expand, there is an increasing demand for improved reliability. Therefore, there is a demand for multilayer ceramic capacitors that are thinner while still having high insulation properties and excellent reliability with little deterioration even under high temperature and high humidity. However, although the techniques proposed so far have had a certain effect, there is still room for improvement.

[0007] In view of these problems, the present inventors have conducted extensive research and have found that the reliability of a multilayer ceramic capacitor can be significantly improved by controlling the region containing a rare earth element in a dielectric ceramic layer.

[0008] The present invention has been completed based on these findings, and an object of the present invention is to provide a multilayer ceramic capacitor with excellent reliability. [Means for solving the problem]

[0009] The present invention encompasses the following aspects. In this specification, the expression "to" includes both ends of the expression. In other words, "X to Y" is synonymous with "X or more and Y or less."

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

[0011] According to the present invention, a multilayer ceramic capacitor with excellent reliability is provided. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a perspective view showing the outer shape of the multilayer ceramic capacitor. [Diagram 2] 1 is a cross-sectional view that illustrates a schematic internal structure of a multilayer ceramic capacitor. [Diagram 3] 1 is a cross-sectional view that illustrates a schematic internal structure of a multilayer ceramic capacitor. [Figure 4] 1 is a schematic cross-sectional view showing a microstructure of a multilayer ceramic capacitor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A specific embodiment 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 embodiment, and various modifications are possible within the scope of the present invention.

[0014] <<1. Multilayer ceramic capacitors>> The multilayer ceramic capacitor of this embodiment has a first main surface and a second main surface opposite to each other in the thickness direction, a first side surface and a second side surface opposite to each other in the width direction, and a first end surface and a second end surface opposite to 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 stacked 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 layers contain, as a main component, crystal grains composed of a perovskite-type complex oxide containing barium (Ba) and titanium (Ti), and further contain a rare earth element (Re). The dielectric ceramic layers include, in a cross section including the thickness direction, a rare earth high concentration region in which 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, with an area ratio of 50% or more.

[0015] One embodiment 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) comprises an element body (6) including a plurality of laminated 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 element body (6). The multilayer ceramic capacitor (100) and the element body (6) have a substantially rectangular parallelepiped shape. The term "substantially rectangular parallelepiped" includes not only rectangular parallelepipeds but also rectangular parallelepipeds with rounded corners and / or edges. The multilayer ceramic capacitor (100) and the element part (6) have a first main surface (10a) and a second main surface (10b) facing in a thickness direction T, a first side surface (12a) and a second side surface (12b) facing in a width direction W, and a first end surface (14a) and a second end surface (14b) facing in a length direction L. Here, the thickness direction T refers to the direction in which the dielectric ceramic layers (2) and the internal electrode layers (4) are laminated. The length direction L refers to a direction perpendicular to the thickness direction T and perpendicular to the end surfaces (14a, 14b) on which the external electrodes (8a, 8b) are provided. The width direction W is a direction perpendicular 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 surface (14a) and a second external electrode (8b) provided on the second end surface (14b). The first external electrode (8a) may extend not only to the first end surface (14a) but also to parts of the first main surface (10a), the second main surface (10b), the first side surface (12a), and the second side surface (12b). The second external electrode (8b) may extend not only to the second end surface (14b) but also to parts 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 from each other.

[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 a first end face (14a) and are electrically connected to a first external electrode (8a) at that point. The plurality of second internal electrode layers (4b) extend to a second end face (14b) and are electrically connected to a second external electrode (8b) at that point. The first internal electrode layer (4a) and the second internal electrode layer (4b), which face each other across the dielectric ceramic layer (2), 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), electric charges are accumulated. The accumulated electric charges generate electrostatic capacitance, which allows the device to function as a capacitive element.

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

[0019] <Dielectric ceramic layer> The dielectric ceramic layer is made of ceramic. The dielectric ceramic layer contains, as a main component, crystal grains made of a perovskite-type complex oxide containing barium (Ba) and titanium (Ti). In other words, the main crystal grains are made of a perovskite-type complex oxide. These main crystal grains are barium titanate (BaTiO 3 )-based compounds. Therefore, the dielectric ceramic layer is BaTiO 3 It can also be said that it is made of a sintered body of BaTiO 3 is the general formula: ABO 3 It is a perovskite-type oxide represented by BaTiO 3 It is a ferroelectric material that has a tetragonal crystal structure at room temperature and exhibits a high dielectric constant. 3By using a ZnO-based compound as the main component, the dielectric constant of the dielectric ceramic can be increased, and the capacitance of the capacitor can be increased. In this specification, the main component refers to the component that is contained in the ceramic at the highest ratio. The content of the main component may be 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, or 90 mass% or more.

[0020] Barium titanate (BaTiO 3 The BaTiO compound is not particularly limited as long as it is a perovskite-type composite oxide that mainly contains barium (Ba) and titanium (Ti). 3 or BaTiO 3 A part of Ba and / or Ti contained in BaTiO may be replaced by other elements. Specifically, a part of barium (Ba) may be replaced by other elements such as strontium (Sr) and calcium (Ca), and a part of titanium (Ti) may be replaced by other elements such as zirconium (Zr) and hafnium (Hf). 3 The ratio of A-site elements (Ba, Sr, Ca, etc.) to B-site elements (Ti, Zr, Hf, etc.) in the perovskite-based compounds is not strictly limited to 1:1. As long as the perovskite crystal structure is maintained, deviations in the ratio of A-site elements to B-site elements are permitted.

[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 a group consisting of scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71 in the periodic table. The dielectric ceramic layer may contain one type of rare earth element, or may contain a combination of multiple types of rare earth elements. The rare earth element is also present in the BaTiO 3 They may be contained only in the BaTiO system compound, or may be contained together with the main crystal grains at grain boundaries or triple junctions. When contained in the main crystal grains, BaTiO 3It may occupy the Ba site (A site) of the compound, or it may occupy the Ti site (B site), or it may occupy both sites.

[0022] By adding rare earth elements (Re) to the dielectric ceramic layers, it is possible to improve the reliability of the multilayer ceramic capacitor and various other characteristics such as the temperature characteristics of the dielectric constant. 3 BaTiO compounds may contain many oxygen vacancies generated during the firing process. These oxygen vacancies tend to reduce the insulation resistance when accompanied by electronic compensation, and tend to migrate under an electric field, causing a decrease in the insulation resistance over time. When rare earth elements are added to the dielectric ceramic layer, BaTiO 3 Rare earth elements tend to dissolve in the Ba and Ti sites of Ba-based compounds. The dissolved rare earth elements act as donors and acceptors, preventing the movement of oxygen vacancies or suppressing the generation of conduction electrons. This reduces the deterioration of insulation resistance and improves the high-temperature load life. BaTiO 3 In rare earth compounds, the dielectric constant is highly dependent on temperature near the Curie temperature Tc. By incorporating rare earth elements into the solid solution, it becomes possible to make the temperature change in the dielectric constant flatter over 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 is preferable to include 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 it is particularly preferable to include dysprosium (Dy). Dy is an element located near the middle of the lanthanoid group in the periodic table, and its ionic radius is also about medium. Therefore, BaTiO 3The rare earth element Dy can be dissolved in both the Ba site (A site) and the Ti site (B site) of the 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 is possible to more significantly improve the various characteristics. The dielectric ceramic layer preferably contains 0.1 to 35.0 moles of rare earth element (Re) per 100 moles of titanium (Ti), more preferably 0.5 to 30.0 moles, and even more preferably 3.5 to 25.0 moles. Note that these mole numbers are the mole numbers of the raw material.

[0025] The dielectric ceramic layer may contain other additive elements besides the rare earth element (Re). Such elements include manganese (Mn), magnesium (Mg), silicon (Si), aluminum (Al), and vanadium (V). The form of the additive element is not limited. It is sufficient that the additive element is contained in the main crystal grains, grain boundaries, or triple points.

[0026] Preferably, the thickness of the dielectric ceramic layer is 0.5 μm or more and 7.0 μm or less. By making the thickness of the dielectric ceramic layer 0.5 μm or more, deterioration of the insulation characteristics can be prevented, leading to improved reliability. On the other hand, by making the thickness 7.0 μm or less, the dielectric ceramic layer is made thinner, making it possible to improve the capacity. In addition, the number of layers of the dielectric ceramic layer is preferably 50 layers or more and 1000 layers or less.

[0027] In the multilayer ceramic capacitor of this 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 lamination direction of the dielectric ceramic layers and the internal electrode layers. Therefore, the cross section including the thickness direction is a plane passing through the inside of the multilayer ceramic capacitor, and a perpendicular line to the thickness direction is a plane, for example, an LT plane or a WT plane. The rare earth high concentration region is a region in which 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 an ultra-high concentration region with a Re / Ti ratio of more than 0.30, a high concentration region with a Re / Ti ratio of 0.04 or more and 0.30 or less, and a low concentration region with a Re / Ti ratio of less than 0.04, the ratio of the area occupied by the high concentration region to the total area of ​​the ultra-high concentration region, the high concentration region, and the 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 is possible to improve the reliability of the multilayer ceramic capacitor more significantly. Although the detailed reason is unclear, it is speculated as follows. A high rare earth concentration means that the average distance between the positions where rare earths exist is shortened. Rare earth elements have the effect of preventing the movement of oxygen vacancies. By shortening the average distance between rare earth elements, the effect of suppressing the movement of oxygen vacancies is increased, and as a result, reliability is improved. From the viewpoint of improving reliability, the higher the area ratio of the rare earth high concentration region, the more preferable it is. 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 may be 100%. However, if the area ratio is excessively high, the dielectric constant may decrease. From the viewpoint 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 CV value of the Re / Ti ratio in the rare earth high concentration region is 45% or less. The CV value is an index of variation. The smaller the CV value of the Re / Ti ratio, the smaller the variation of the Re / Ti ratio for each location in the rare earth high concentration region. By limiting the CV value of the Re / Ti ratio to 45% or less, the variation of the reliability can be suppressed. The details of the reason are unclear, but it is speculated as follows. Even if the average 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, or the total size of the low Re / Ti ratio regions that are distributed is large. The low Re / Ti ratio region may reduce the reliability. Therefore, if the CV value of the Re / Ti ratio is small, the reliability variation can be reduced in the sense that the reliability is less likely to decrease. From the viewpoint of suppressing the reliability variation, the smaller the CV value, the more preferable it is. 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 calculated by dividing the rare earth-rich region into minute regions, measuring the Re / Ti ratio of each region using a method such as transmission electron microscope (TEM)-energy dispersive X-ray spectroscopy (EDX), and using the average value and standard deviation σ according to the following formula (1).

[0030]

number

[0031] The reliability and variation of multilayer ceramic capacitors can be evaluated by examining their high-temperature accelerated life. High-temperature accelerated life can be evaluated by conducting a high-temperature accelerated test on a capacitor and using the resulting mean time to failure (MTTF) and B1 life. Specifically, a high-temperature accelerated test is conducted on multiple capacitors, and the time at which the insulation resistance drops drastically is defined as the failure time. A Weibull analysis is performed on the failure time of each capacitor to determine the failure time at which the cumulative failure rate is 63.2% and the shape parameter m, from which the mean time to failure (MTTF) is determined. The failure time at which the cumulative failure rate is 1% is defined as the B1 life. The longer the MTTF, the higher the reliability can be determined. Furthermore, the larger the B1 life / MTTF, the smaller the variation in reliability can be determined.

[0032] The distribution of the rare earth high concentration region contained in the dielectric ceramic layer is not particularly limited. The dielectric ceramic layer may have a sea-island structure in cross section, with the rare earth high concentration region and the other region constituting a sea portion and an island portion, respectively. Specifically, the rare earth high concentration region may have other regions, for example, rare earth low concentration regions, dispersed therein. Alternatively, the rare earth high concentration region and the other region may extend in layers, and each layer of the dielectric ceramic layer may have a laminated structure of the rare earth high concentration region and the other region in layers.

[0033] Preferably, in a cross section including the thickness direction, the dielectric ceramic layer includes a low rare earth concentration region, and the low rare earth concentration region is composed of a plurality of sub-regions surrounded by a high concentration region. Also preferably, the average value of the circle equivalent diameter of each of the sub-regions in the cross section (average circle equivalent diameter) is 130 nm or more. That is, it is preferable that the dielectric ceramic layer has a sea-island structure in its cross section, the high rare earth concentration region constitutes the sea portion, the low rare earth concentration region constitutes the island portion, and the average circle equivalent diameter of the island portion is a predetermined value or more. In this way, by distributing the low rare earth concentration regions having a desired size in the high rare earth concentration region in an island shape, it is possible to improve the dielectric constant while ensuring the reliability of the multilayer ceramic capacitor. Although the detailed reason is unknown, it is speculated as follows. The Curie temperature Tc of the high rare earth concentration region may be lower than room temperature depending on the Re / Ti ratio, and in this case, the dielectric constant decreases. However, by mixing a low rare earth concentration region whose Curie temperature Tc is sufficiently higher than room temperature, the decrease in the dielectric constant can be avoided. In addition, 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 dispersed sub-regions, the more preferable it is. 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 reliability, it is preferable that the size of the rare earth low concentration region is 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. The average equivalent circle diameter (D50) is the diameter of a circle that has the same area as the cumulative 50% area. The cumulative 50% area is the area of ​​a sub-region when the total area of ​​each sub-region is taken as 100%, and the area of ​​the sub-region is cumulatively added up in ascending order to the total area, reaching 50%.On the other hand, the average equivalent circle diameter can be calculated using the cumulative 50% area according to the following formula (2).

[0034]

number

[0035] Preferably, in a cross section including the thickness direction, the average circularity (average circularity) of each of the sub-regions constituting the rare earth low concentration region is 0.70 or more. The circularity is an index that indicates the complexity of the region shape, and is 1 for a perfect circle, and the more complex the shape, the smaller the circularity. By making the shape of the dispersed rare earth low concentration regions approximately circular, it is possible to suppress the voltage dependency of the high temperature load life. Although the detailed reason is unclear, it is speculated as follows. By increasing the circularity of the sub-regions constituting the rare earth low concentration region, it is possible to reduce the probability of the existence of a portion having an extremely high curvature at the boundary with the rare earth high concentration region. Since the insulation resistance changes depending on the rare earth concentration, it is considered that the change in 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 is, 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 dependency of the high temperature load life is reduced. 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 determined by calculating the circularity according to the following formula (3) using the area and perimeter of each sub-region determined by TEM observation or the like, and then calculating the average value.

[0036]

number

[0037] Preferably, at least one of the crystal grains made of 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 is a main crystal grain that includes a plurality of independent sub-regions. By adopting such a configuration, it is possible to obtain an effect of improving the DC bias characteristic of the dielectric constant. Although the detailed reason is unclear, it is speculated that the presence of a rare earth-rich region between the sub-regions that are not connected to each other in the same crystal grain reduces the proportion of the DC voltage applied to the sub-regions.

[0038] <Internal electrode layer> The internal electrode layers contain 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 layers may contain other components in addition to the conductive metal. As the other components, a ceramic component acting as a co-material may be mentioned. As the ceramic component, BaTiO contained in the dielectric ceramic layer may be used. 3 Compounds based on the above-mentioned compounds are also included.

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

[0040] <External electrode> A known structure can be adopted as the external electrode. For example, the laminated structure can be made up of an underlayer, a first plating layer, and a second plating layer from the end face side of the multilayer ceramic capacitor. The underlayer contains metals such as nickel (Ni) and copper (Cu). It may also contain ceramic powder as a co-material in addition to metals. The first plating layer is, for example, a nickel (Ni) plating layer. The second plating layer is, for example, a tin (Sn) plating layer. A conductive resin layer may also 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 external electrodes are not limited in their form as long as they are electrically connected to the internal electrode layers and function as external input / output terminals.

[0041] <<2. Manufacturing method of multilayer ceramic capacitors>> The multilayer ceramic capacitor of this embodiment is not limited in its manufacturing method as long as it satisfies the above-mentioned requirements. An exemplary manufacturing method includes the following steps: a step of preparing a green sheet containing at least barium (Ba), titanium (Ti), and a rare earth element (Re) (green sheet preparation step), a step of applying a conductive paste to the surface of the green sheet to obtain a green sheet on which an internal electrode pattern is formed (electrode pattern formation step), a step of stacking and pressing a plurality of green sheets to obtain a laminated block (stacking step), a step of cutting the obtained laminated block to obtain a laminated chip (cutting step), a step of performing a binder removal process and a firing process on the obtained laminated chip to obtain an element part (firing step), and a step of forming an external electrode on the obtained element part (external electrode formation step). Details of each step are described below.

[0042] <Green sheet manufacturing process> In the green sheet preparation process, a green sheet containing at least barium (Ba), titanium (Ti), and a rare earth element (Re) is prepared. The green sheet is a precursor of the dielectric ceramic layer of the capacitor, and contains the main component raw material and the additive raw material of the dielectric ceramic layer. The preparation of the green sheet may be performed by a known method, and is not particularly limited. The main component raw material is mixed with the additive raw material to prepare a dielectric raw material, and a binder and a solvent are added and mixed to the obtained dielectric raw material to form a slurry, and the obtained slurry is molded into a green sheet.

[0043] BaTiO as the main component 3 Powder of BaTiO 3 The compound may be synthesized by using known ceramic raw materials such as oxides, carbonates, hydroxides, nitrates, organic acid salts, alkoxides and / or chelate compounds, and by using known ceramic synthesis methods such as solid-phase reaction, hydrothermal synthesis and alkoxide methods. The additive raw materials include 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 materials may include raw materials of other additive components such as Mn, Mg, Si, Al and V. Furthermore, the main component BaTiO 3 To adjust the composition of the system compounds, barium carbonate (BaCO 3 ) and titanium dioxide (TiO 2 ) may be added to the additive raw materials.

[0044] The raw material mixing may be performed by a known method, for example, a method of wet mixing and grinding the weighed main component raw material, additive raw material, and water together with a grinding medium using a ball mill. When the wet mixing is performed, the resulting mixture may be dried. If necessary, the dielectric raw material obtained after drying may be calcined. The slurry may also be performed by a known method, and an organic binder and an organic solvent may be mixed into the dielectric raw material. As the organic binder, a known binder such as a polyvinyl butyryl binder may be used. As the organic solvent, a known solvent such as toluene or ethanol may be used. If necessary, an additive such as a plasticizer may be added to the slurry. Furthermore, the green sheet may be formed by a known method such as a doctor blade method or a lip method.

[0045] <Electrode pattern formation process> In the electrode pattern forming process, a conductive paste is applied to the surface of the green sheet to obtain a green sheet with an internal electrode pattern. The internal electrode pattern becomes an internal electrode layer after firing. The conductive metal contained in the conductive paste may be a conductive material such as nickel (Ni), copper (Cu), silver (Ag), palladium (Pd), or an alloy containing these. A ceramic component that acts as a co-material may also be added to the conductive paste. The main component raw material of the dielectric ceramic layer may be used as the ceramic component. The conductive paste may be applied by a known method such as screen printing or gravure printing.

[0046] <Lamination process> In the lamination process, a plurality of green sheets are laminated and pressed to obtain a laminated block. Green sheets having internal electrode patterns are used as the green sheets, but green sheets having no internal electrode patterns may also be used. The lamination and pressing may be performed by a known method.

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

[0048] <Firing process> In the firing process, the obtained laminated chip is subjected to a binder removal process and a firing process to obtain an element part. The green sheet and the internal electrode pattern are co-sintered by the firing process to become a dielectric ceramic layer and an internal electrode layer, respectively. The conditions for the binder removal process can be determined according to the type of organic binder contained in the green sheet and the internal electrode pattern. The firing process can be performed at a temperature at which the laminated chip is sufficiently densified. For example, the firing process can be performed under conditions of a temperature of 1200°C to 1300°C, held for 1 hour to 10 hours. The firing process can also be performed by removing the binder from the main component BaTiO 3 The reaction is carried out in an atmosphere in which the compound is not reduced and the oxidation of the conductive metal is suppressed. For example, the oxygen partial pressure is 1.9×10 -11 MPa or more 6.4×10 -9 N below MPa 2 -H 2 -H 2 The firing may be performed in an O2 atmosphere. Annealing may also be performed after firing.

[0049] <External electrode formation process> In the external electrode formation step, external electrodes are formed on the obtained element part. The external electrodes may be formed by a known method. For example, the external electrodes may be formed by applying and baking a conductive paste containing a metal such as silver (Ag), copper (Cu) and / or nickel (Ni) to the end faces of the element part where the internal electrodes are drawn out and exposed. Alternatively, the external electrodes may be formed by applying a conductive paste to both end faces of the laminated chip before firing, followed by a firing process. The formed electrodes may be used as a base layer, and a plating film such as nickel (Ni) or tin (Sn) may be formed thereon. This produces a laminated ceramic capacitor. EXAMPLES

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

[0051] (1) Fabrication of multilayer ceramic capacitors [Examples 1 to 15, 19 to 21, and 24 to 28] A sample of a multilayer ceramic capacitor was prepared according to the following procedure.

[0052] First, BaTiO with a BET diameter of 190 nm and a tetragonality of 1.0099 3 Powder was prepared as BT-A powder. Tetragonality is an index of the degree of tetragonality in a tetragonal crystal structure, and is expressed as the ratio of the c-axis length to the a-axis length in a tetragonal crystal (c / a-axis ratio). The tetragonality can be determined by powder X-ray diffraction (XRD). The BET diameter was calculated by assuming that the particles are spherical, and was calculated using BaTiO 3 The average primary particle size is calculated from the BET specific surface area of ​​the powder.

[0053] In addition, BaTiO has a BET diameter of 100 nm and a tetragonality of 1.007. 3 The powder was prepared as BT-B powder, which was then wet-milled to produce finely ground BT-B powder. The BET specific surface area of ​​the finely ground BT-B powder was 50 m 2 / g.

[0054] Furthermore, Dy 2 O 3 Powder, BaCO 3 Powder, and TiO 2 The powders were individually wet-milled to produce finely ground Dy 2 O 3 Powder, finely ground BaCO 3 Powder and finely ground TiO 2 Powdered. Finely ground Dy 2 O 3 Powder, finely ground BaCO 3 Powder and finely ground TiO 2 The BET specific surface area of ​​the powder is 50m 2 / g~56m 2 / g.

[0055] Next, BT-A powder, finely ground BT-B powder, and finely ground Dy 2 O3 Powder, finely ground BaCO 3 Powder and finely ground TiO 2 The powders were mixed using a wet mill to obtain the composition shown in Table 1 below, and then dried to obtain a mixed powder. 3 The A / B ratio, which is the molar ratio of A-site elements to B-site elements, is also shown. Dy was treated as being present in both the A and B sites in the compounded composition so that the A / B ratio shown in Table 1 was obtained.

[0056] The resulting mixed powder was heated in air at a heating rate of 600° C. / hour up to 1100° C. and then maintained at that temperature for 2 hours, thereby obtaining a calcined powder.

[0057] TiO in calcined powder 2 : MgCO per 100 mole parts 3 Powder: 1.0 mol part, MnCO 3 Powder: 0.3 mol parts, and SiO 2 The sol was added in an amount of 1.3 moles to the calcined powder, wet-mixed and dried to obtain a dielectric powder.

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

[0059] A conductive paste containing nickel as a main component was screen-printed on the surface of the obtained green sheet to form a pattern of a conductive paste layer that would become an internal electrode layer.

[0060] Then, 201 green sheets with conductive paste layers formed on their surfaces were stacked so that the sides on which the conductive paste layers were exposed were staggered, and green sheet layers without conductive paste layers were placed on top and bottom, and the whole was then pressed together to produce a laminated block.

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

[0062] The obtained green laminated chip was 2 The binder was burned off by heat treatment at 280°C in a stream of N 2 -H 2 -H 2 In an O2 stream at 1260°C, oxygen partial pressure 1.6×10 -9 The mixture was fired for 2 hours under the condition of 100 MPa.

[0063] In the fired laminated chip, a conductive paste mainly composed of Cu was applied to the end surface from which 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 produced. The resulting multilayer ceramic capacitor had an external dimension of 3.2 mm in length × 1.6 mm in width × 1.6 mm in thickness. The number of dielectric ceramic layers sandwiched between the internal electrode layers was 200, and each dielectric ceramic layer had a thickness of 1.7 μm.

[0065] [Example 16 to Example 18] The BT-A powder was BaTiO with a BET diameter of 250 nm and a tetragonal crystallinity of 1.0100. 3 Other than that, multilayer ceramic capacitors were produced in the same manner as in Examples 1 to 15, 19 to 21, and 24 to 28.

[0066] [Example 22] The BT-A powder was BaTiO with a BET diameter of 150 nm and a tetragonal crystallinity of 1.0095. 3 Other than that, multilayer ceramic capacitors were produced in the same manner as in Examples 1 to 15, 19 to 21, and 24 to 28.

[0067] [Example 23] The BT-A powder was BaTiO with a BET diameter of 250 nm and a tetragonal crystallinity of 1.0100. 3 The powder was wet-pulverized until the BET diameter became 200 nm, and then used. Except for the above, the multilayer ceramic capacitors were fabricated in the same manner as in Examples 1 to 15, 19 to 21, and 24 to 28.

[0068] [Example 29 to Example 32] The rare earth oxides (Gd 2 O 3 , Y 2 O 3 , Ho 2 O 3 , and Er 2 O 3 ) were prepared. These rare earth oxides were then individually mixed to prepare SiO2 powders with a BET specific surface area of ​​50 m 2 / g~60m 2 The raw powders (BT-A powder, finely ground BT-B powder, finely ground Re oxide powder, finely ground BaCO 3 Powder and finely ground TiO 2 Powder) were mixed and dried to obtain a mixed powder with the composition shown in Table 1 below. In terms of the composition, the rare earth element (Re) was treated as occupying both the A site and the B site, and the raw materials were mixed to obtain the A / B ratio shown in Table 1 below. Other than that, 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] [Example 33 to Example 37] The rare earth oxides (Dy) corresponding to the rare earth element (Re) species shown in Table 1 2 O 3 , La 2 O 3 , Nd 2 O 3 , Tb 4 O 7 , Yb 2 O 3 , Lu 2 O 3 ,EU 2 O 3 , Sm2 O 3 , CeO 2 , Pr 6 O 11 , and Tm 2 O 3 ) were prepared. Then, these rare earth oxides were individually wet-ground until the BET specific surface area was within the range of 50 m 2 / g to 60 m 2 / g to obtain finely ground Re oxide powders. The raw material powders (BT-A powder, finely ground BT-B powder, finely ground Re oxide powders, finely ground BaCO 3 powder, and finely ground TiO 2 powder) were mixed and dried to obtain a mixed powder so that the composition shown in Table 1 below was obtained. 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 formulation composition. For Tb, Yb, Lu, and Tm, they were treated as entering the B site in terms of the formulation composition. For Dy, it was treated as entering both the A site and the B site in terms of the formulation composition. Considering these, the raw materials were formulated so that the A / B ratio shown in Table 1 was obtained. Otherwise, multilayer ceramic capacitors were fabricated 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 type transmission electron microscope (FE-TEM), and component analysis of a 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. Also, the observation and analysis were performed under the following conditions.

[0072] - Apparatus: JEOL Ltd., JEM-2200FS / Noran System 7 - Field of view: n=2 -Magnification: 60000x -Pixel size: 9.2nm / 1 pixel - Spot diameter: 1 nmφ - Measurement: EDX integration number 100 times

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

[0074]

number

number

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

[0076]

number

number

[0077] <Dielectric properties> The capacitance (C) of the obtained multilayer ceramic capacitor was measured using an automatic bridge type measuring device under the condition of an AC voltage of 1 V and 1 kHz. The relative dielectric constant (ε r ) was calculated. Measurements were carried out on 72 samples prepared under the same conditions, and the average value was calculated.

[0078] <Reliability (MTTF, B1 life)> A highly accelerated life test (HALT) was conducted on the multilayer ceramic capacitor to determine the mean time to failure (MTTF). In the highly accelerated life test, a high temperature load was applied to the sample at a temperature of 175°C and a test voltage of 50V. The time to failure was defined as the time when the insulation resistance fell to 200kΩ or less. The time to failure was measured for 72 samples produced under the same conditions.

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

[0080] Furthermore, a highly accelerated life test was performed under the same conditions except that the test voltage was changed to 60V, the mean time to failure (MTTF) at a test voltage of 60V 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 values ​​shown in Table 1 are values ​​measured under the condition of a test voltage of 50 V, excluding any decrease in MTTF.

[0083] The example samples (Examples 1 to 9, 13 to 27, and 29 to 37) in which the area ratio of the rare earth-rich region was 50% or more had an MTTF of 52 hours or more. In particular, 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 had a long MTTF of 149 hours or more. On the other hand, the comparative example samples (Examples 10 to 12, and 28) in which the area ratio was less than 50% had a short MTTF of 39 hours or less. These results show that a highly reliable multilayer ceramic capacitor can be obtained by increasing the area ratio of the rare earth-rich region to 50% or more.

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

[0085] The microstructure and element distribution of the cross section of the multilayer ceramic capacitor obtained in the embodiment are shown in Fig. 4(a) and (b). Fig. 4(a) is a diagram showing the cross-sectional microstructure, in which points A and C indicate the internal electrode layers, 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), the areas with high Dy concentration in the dielectric ceramic layer are shown bright, and the areas with low concentration are shown dark. As shown in Fig. 4(a), the dielectric ceramic layer is composed of many crystal grains. As shown in Fig. 4(b), the Dy distribution is non-uniform, and low Dy concentration areas are distributed in islands in the high Dy concentration areas. In addition, there are crystal grains containing multiple independent low rare earth concentration areas.

[0086] [Table 1]

Claims

1. a first main surface and a second main surface facing each other in a thickness direction, a first side surface and a second side surface facing each other in a width direction, and a first end surface and a second end surface facing each other in a length direction; a multilayer ceramic capacitor comprising: a body portion including a plurality of dielectric ceramic layers and a plurality of internal electrode layers stacked in the thickness direction; and a pair of external electrodes provided on the first end face and the second end face, respectively, and electrically connected to the plurality of internal electrode layers, The dielectric ceramic layer contains, as a main component, crystal grains constituted of a perovskite-type complex 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 of rare earth element (Re) to titanium (Ti) (Re / Ti ratio) of 0.04 or more and 0.30 or less at an area ratio of 50% or more in a cross section including the thickness direction, the dielectric ceramic layer includes a rare earth low concentration region in which a ratio of rare earth element (Re) to titanium (Ti) (Re / Ti ratio) is less than 0.04 in the cross section; 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 of the equivalent circle diameters of the subregions in the cross section (average equivalent circle diameter) is 130 nm or more.

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

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

4. 4. The multilayer ceramic capacitor according to claim 1, wherein in the cross section, a CV value of the Re / Ti ratio in the rare earth high concentration region is 20% or less.

5. 5. The multilayer ceramic capacitor according to claim 1, wherein an average value of the circularity of each of said subregions in said cross section (average circularity) is 0.70 or more.

6. 6. The multilayer ceramic capacitor according to claim 1, wherein at least one of the crystal grains includes two or more of the sub-regions that are not connected to each other.

Images