Ceramic powder for multilayer ceramic capacitor, method for producing ceramic powder for multilayer ceramic capacitor, and method for manufacturing multilayer ceramic capacitor

Abstract

This ceramic powder for a multilayer ceramic capacitor is composed of a perovskite-type oxide. The perovskite-type oxide contains barium (Ba), titanium (Ti), and a rare earth (Re) element, and may additionally contain at least one of calcium (Ca) and strontium (Sr). The ceramic powder for a multilayer ceramic capacitor has a BET specific surface area of 4.0 m2 / g to 21.0 m2 / g, and has a Re / Ti weight concentration ratio distribution in which the arithmetic mean value μ is 0.02-0.08 wt% and the variation σ is 0.15 or less.

Description

Ceramic powder for multilayer ceramic capacitors, method for manufacturing ceramic powder for multilayer ceramic capacitors, and method for manufacturing multilayer ceramic capacitors

[0001] This invention relates to ceramic powder for multilayer ceramic capacitors, a method for producing ceramic powder for multilayer ceramic capacitors, and a method for producing multilayer ceramic capacitors.

[0002] Patent Document 1 discloses a multilayer ceramic capacitor in which a dielectric layer composed of barium titanate crystal particles with a calcium concentration of 0.2 atomic percent or less and barium calcium titanate crystal particles with a calcium concentration of 0.4 atomic percent or more, and an internal electrode layer are alternately stacked. In the multilayer ceramic capacitor described in Patent Document 1, the barium titanate crystal particles and the barium calcium titanate crystal particles contain magnesium, two rare earth elements (one of yttrium and holmium, and one of terbium and dysprosium), and vanadium, and the ratio of the content of magnesium and the rare earth element (one of yttrium and holmium) contained in the central part of the barium titanate crystal particles to the content of magnesium and the rare earth element (one of yttrium and holmium) on the surface side of the barium titanate crystal particles is greater than the ratio of the content of magnesium and the rare earth element (one of yttrium and holmium) contained in the central part of the barium calcium titanate crystal particles to the content of magnesium and the rare earth element (one of yttrium and holmium) contained in the central part of the barium calcium titanate crystal particles to the content of magnesium and the rare earth element (one of yttrium and holmium) on the surface side of the barium calcium titanate crystal particles.

[0003] Japanese Patent Publication No. 2008-135638

[0004] According to Patent Document 1, the dielectric layer constituting the multilayer ceramic capacitor is made of barium titanate crystal particles and barium calcium titanate crystal particles, and these crystal particles contain magnesium along with two rare earth elements and vanadium, so that the ratio of the content of magnesium and one of the rare earth elements (from magnesium, yttrium, and holmium) in the central part of the barium titanate crystal particles to the content of magnesium and one of the rare earth elements (from magnesium, yttrium, and holmium) on the surface side of the barium titanate crystal particles is greater than the ratio of the content of magnesium and one of the rare earth elements (from magnesium, yttrium, and holmium) in the central part of the barium calcium titanate crystal particles to the content of magnesium and one of the rare earth elements (from magnesium, yttrium, and holmium) on the surface side of the barium calcium titanate crystal particles, thereby making the barium titanate crystal particles highly cubic in the core-shell structure. By coexisting highly cubic barium titanate crystal particles with barium calcium titanate crystal particles in this manner, it is possible to obtain a multilayer ceramic capacitor that, regarding dielectric ceramics composed of barium titanate crystal particles and barium calcium titanate crystal particles, has high insulation resistance even after firing and exhibits little decrease in insulation resistance with time changes during high-temperature load testing.

[0005] However, in multilayer ceramic capacitors, as described in Patent Document 1, in which the dielectric layer (hereinafter also referred to as the dielectric ceramic layer) is composed of crystalline particles based on a core-shell structure, there are regions in the particles constituting the dielectric ceramic layer where rare earth elements are not solid-dissolved. Therefore, there is a risk that the insulation resistance will decrease over time during high-temperature load testing. Consequently, from the viewpoint of improving the high-temperature reliability of multilayer ceramic capacitors, there is still room for improvement. Furthermore, in order to obtain excellent high-temperature reliability as a multilayer ceramic capacitor, it is necessary to pay attention to the amount of solid-dissolved rare earth elements and the variation in the amount of solid-dissolved rare earth elements at the stage of the ceramic powder for multilayer ceramic capacitors, which serves as the precursor.

[0006] The present invention has been made to solve the above problems, and an object thereof is to provide a ceramic powder for a multilayer ceramic capacitor for obtaining a multilayer ceramic capacitor having excellent high-temperature reliability. Further, an object of the present invention is to provide a method for producing the ceramic powder for a multilayer ceramic capacitor and a method for producing a multilayer ceramic capacitor using the ceramic powder for a multilayer ceramic capacitor.

[0007] The ceramic powder for a multilayer ceramic capacitor of the present invention is composed of a perovskite-type oxide. The perovskite-type oxide contains barium (Ba), titanium (Ti), and a rare earth (Re) element, and may further contain at least one of calcium (Ca) and strontium (Sr). The ceramic powder for a multilayer ceramic capacitor has a BET specific surface area of 4.0 m ２ / g or more and 21.0 m ２ / g or less, and in the distribution of the weight concentration ratio of Re / Ti, the arithmetic mean value μ is 0.02 wt% ratio or more and 0.08 wt% ratio or less, and the variation σ is 0.15 or less.

[0008] The method for producing a ceramic powder for a multilayer ceramic capacitor of the present invention includes a step of obtaining a first slurry by performing wet pulverization of a rare earth (Re) powder alone until the cumulative volume-based particle size D90 becomes 0.60 μm or less; a step of obtaining a second slurry by adding the first slurry to a mixed slurry in which a barium (Ba) compound, a titanium (Ti) compound, and at least one of a calcium (Ca) compound and a strontium (Sr) compound are mixed so that the addition amount of the rare earth (Re) is more than 1.0 mol% and less than 10.0 mol% with respect to 100 mol% of titanium (Ti), or to a raw material slurry of barium titanate powder in which at least one of calcium (Ca) and strontium (Sr) may be partially substituted, and further performing wet pulverization; a step of obtaining a dry powder by removing a solvent from the second slurry; and a step of performing heat treatment using the dry powder, to obtain a calcined powder having a BET specific surface area of 4.0 m ２ / g or more and 21.0 m ２ / g or less.

[0009] The manufacturing method of the multilayer ceramic capacitor of the present invention is characterized by using the ceramic powder for the multilayer ceramic capacitor or the ceramic powder for the multilayer ceramic capacitor obtained by the above method.

[0010] According to the present invention, it is possible to provide a ceramic powder for a multilayer ceramic capacitor for obtaining a multilayer ceramic capacitor excellent in high-temperature reliability. Furthermore, according to the present invention, it is possible to provide a method for manufacturing the ceramic powder for the multilayer ceramic capacitor and a method for manufacturing a multilayer ceramic capacitor using the ceramic powder for the multilayer ceramic capacitor.

[0011] FIG. 1 is a perspective view schematically showing an example of a multilayer ceramic capacitor related to the present invention. FIG. 2 is an example of an LT cross-sectional view including the length direction L and the thickness direction T along the line II-II of the multilayer ceramic capacitor shown in FIG. 1. FIG. 3 is an example of a WT cross-sectional view including the width direction W and the thickness direction T along the line III-III of the multilayer ceramic capacitor shown in FIG. 1.

[0012] Hereinafter, the ceramic powder for the multilayer ceramic capacitor, the manufacturing method of the ceramic powder for the multilayer ceramic capacitor, and the manufacturing method of the multilayer ceramic capacitor of the present invention will be described. Note that the present invention is not limited to the following embodiments, and can be appropriately modified and applied without changing the gist of the present invention. In addition, a combination of two or more of the individual preferable configurations described in the following embodiments is also the present invention.

[0013] [Ceramic Powder for Multilayer Ceramic Capacitor] The ceramic powder for the multilayer ceramic capacitor of the present invention is composed of a perovskite-type oxide.

[0014] The perovskite-type oxide constituting the ceramic powder for a multilayer ceramic capacitor of the present invention contains barium (Ba), titanium (Ti), and a rare earth (Re) element, and may further contain at least one of calcium (Ca) and strontium (Sr). The perovskite-type oxide preferably contains at least Ca among Ca and Sr.

[0015] That is, the perovskite-type oxide constituting the ceramic powder for a multilayer ceramic capacitor of the present invention is composed of a barium titanate (BaTiO ３ )-based compound. BaTiO ３ shows a tetragonal crystal structure at room temperature and is a ferroelectric body showing a high dielectric constant. Therefore, it becomes possible to increase the capacitance of the multilayer ceramic capacitor.

[0016] BaTiO ３ -based compounds are not particularly limited as long as they are perovskite-type oxides mainly containing Ba and Ti. For example, the BaTiO ３ -based compound may be a compound in which part of Ba and / or Ti contained in BaTiO ３ is substituted with other elements. For example, part of Ba may be substituted with an alkaline earth metal element such as Ca or Sr, or part of Ti may be substituted with a transition metal element such as zirconium (Zr) or hafnium (Hf). Furthermore, the molar ratio of the A-site element (Ba, Ca, Sr, etc.) to the B-site element (Ti, Zr, Hf, etc.) of the BaTiO ３ -based compound (hereinafter also referred to as the A / B ratio) is not strictly limited to 1:1, and a deviation in the molar ratio of the A-site element to the B-site element is allowed as long as the perovskite-type crystal structure is maintained.

[0017] The rare earth (Re) element is a general term for elements constituting the group consisting of scandium (Sc) having an atomic number of 21, yttrium (Y) having an atomic number of 39, and lanthanum (La) having an atomic number of 57 to lutetium (Lu) having an atomic number of 71 in the periodic table. The perovskite-type oxide may contain one type of rare earth (Re) element, or may contain a combination of multiple types of rare earth (Re) elements.

[0018] BaTiO３ The inclusion of rare earth (Re) elements in the compound system can improve the reliability and various properties of multilayer ceramic capacitors, such as the temperature characteristics of the dielectric constant. ３ The compound may contain many oxygen vacancies generated during the calcination process. These oxygen vacancies tend to reduce the insulation resistance when accompanied by electronic compensation, and they also tend to move under an electric field, leading to a decrease in insulation resistance over time. Therefore, BaTiO ３ If the compound system contains rare earth elements (Re), then BaTiO ３ It tends to dissolve in the A site (Ba site) or B site (Ti site) of the compound. The dissolved rare earth (Re) element acts as a donor or acceptor, hindering the movement of oxygen vacancies or suppressing the generation of conduction electrons. As a result, the degradation of insulation resistance is reduced and the high-temperature load life is improved. Also, BaTiO ３ The compound exhibits a large temperature dependence of its dielectric constant near the Curie temperature Tc. Therefore, BaTiO ３ By solid-solving rare earth (Re) elements in the compound system, it becomes possible to flatten the temperature dependence of the dielectric constant over a wide range, including the Curie temperature Tc.

[0019] The type of rare earth (Re) element is not particularly limited, but it is preferable that the rare earth (Re) element includes at least one selected from the group consisting of lanthanum (La), yttrium (Y), 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 more preferably at least Dy. Dy is an element located near the middle of the lanthanide group in the periodic table, and its ionic radius is also of an intermediate size. Therefore, BaTiO ３ It can be solid-solved in both the A site (Ba site) and the B site (Ti site) of the compound, which is effective in improving reliability. The perovskite-type oxide may contain only Dy as the rare earth (Re) element, or it may contain other rare earth (Re) elements along with Dy.

[0020] In the ceramic powder for multilayer ceramic capacitors of the present invention, the BET specific surface area is 4.0 m². ２ / g or more 21.0m ２ It is characterized by being less than or equal to / g, and in the distribution of the weight concentration ratio of Re / Ti, the arithmetic mean μ is between 0.02 wt% and 0.08 wt%, and the variability σ is 0.15 or less.

[0021] BET specific surface area is 4.0 m² ２ If the amount is less than 1 / g, the high-temperature reliability of the multilayer ceramic capacitor manufactured using the ceramic powder will decrease due to the presence of condensed particles. On the other hand, if the BET specific surface area is 21.0 m² ２ If the concentration exceeds / g, high-temperature reliability decreases due to abnormal grain growth and insufficient solid solution of rare earth elements. The BET specific surface area is 8.0 m². ２ / g or more 13.0m ２ It is preferable that the amount is less than or equal to / g.

[0022] If the arithmetic mean μ in the Re / Ti weight concentration ratio distribution is less than 0.02 wt%, insufficient solid solution of rare earth elements will result in heterogeneous grain growth in multilayer ceramic capacitors manufactured using the ceramic powder, thus reducing the high-temperature reliability of the multilayer ceramic capacitors. On the other hand, if the arithmetic mean μ in the Re / Ti weight concentration ratio distribution exceeds 0.08 wt%, segregation of rare earth elements will reduce the high-temperature reliability.

[0023] When the variation σ in the weight concentration ratio distribution of Re / Ti exceeds 0.15, the solid solution variation of rare earth elements increases, leading to a decrease in the high-temperature reliability of multilayer ceramic capacitors manufactured using the ceramic powder. On the other hand, the variation σ in the weight concentration ratio distribution of Re / Ti is, for example, 0.01 or higher.

[0024] Based on the above, the ceramic powder for multilayer ceramic capacitors of the present invention has a BET specific surface area of ​​4.0 m². ２ / g or more 21.0m ２By having a ratio of less than or equal to / g, and by having an arithmetic mean μ in the weight concentration ratio distribution of Re / Ti between 0.02 wt% and 0.08 wt%, and a variation σ of 0.15 or less, it is possible to obtain a multilayer ceramic capacitor with a long high-temperature load life and high high-temperature reliability.

[0025] [Multilayer Ceramic Capacitors] Below, an example of a multilayer ceramic capacitor manufactured using the multilayer ceramic powder of the present invention will be described.

[0026] The following diagrams are schematic representations, and their dimensions, aspect ratios, and scales may differ from those of the actual product. The same reference numerals are used for identical or equivalent parts in the diagrams. Furthermore, identical elements are denoted by the same reference numerals in each diagram, and redundant explanations are omitted.

[0027] Figure 1 is a schematic perspective view showing an example of a multilayer ceramic capacitor related to the present invention.

[0028] The multilayer ceramic capacitor 1 shown in Figure 1 comprises a base body 10 and external electrodes 11 and 12 provided on the surface of the base body 10. In the base body 10, the length direction, width direction, and thickness direction are defined by double arrows L, W, and T, respectively.

[0029] The base body 10 is, for example, a rectangular parallelepiped. In this case, the base body 10 has a first main surface 10a and a second main surface 10b that are opposite to the thickness direction T, a first side surface 10c and a second side surface 10d that are opposite to the width direction W which is perpendicular to the thickness direction T, and a first end surface 10e and a second end surface 10f that are opposite to the length direction L which is perpendicular to the thickness direction T and the width direction W.

[0030] At least one of the corners and edges of the base body 10 may be rounded. Here, the corners are the parts where the three faces of the base body 10 intersect, and the edges are the parts where the two faces of the base body 10 intersect.

[0031] The external electrode 11 is provided on the first end face 10e of the base body 10. The external electrode 11 may wrap around to a part of the first main surface 10a, the second main surface 10b, the first side surface 10c, and the second side surface 10d of the base body 10.

[0032] The external electrode 12 is provided on the second end face 10f of the base body 10. The external electrode 12 may wrap around to a part of the first main surface 10a, the second main surface 10b, the first side surface 10c, and the second side surface 10d of the base body 10.

[0033] The dimensions of the multilayer ceramic capacitor 1 are not particularly limited. For example, the length L is 0.2 mm or more and 5.7 mm or less, the width W is 0.1 mm or more and 5.0 mm or less, and the thickness T is 0.1 mm or more and 5.0 mm or less.

[0034] Figure 2 is an example of a cross-sectional view (LT) of the multilayer ceramic capacitor shown in Figure 1, including the length direction L and thickness direction T along the line II-II. Figure 3 is an example of a cross-sectional view (WT) of the multilayer ceramic capacitor shown in Figure 1, including the width direction W and thickness direction T along the line III-III.

[0035] The base body 10 includes a plurality of dielectric ceramic layers 20 and a plurality of internal electrode layers 30 stacked in the thickness direction T.

[0036] The internal electrode layer 30 includes a first internal electrode layer 31 and a second internal electrode layer 32 that are alternately arranged in the thickness direction T.

[0037] The first internal electrode layer 31 extends to the first end face 10e of the base body 10, where it is electrically connected to the external electrode 11.

[0038] The second internal electrode layer 32 extends to the second end face 10f of the base body 10, where it is electrically connected to the external electrode 12.

[0039] The first internal electrode layer 31 and the second internal electrode layer 32, which face each other with the dielectric ceramic layer 20 in between, are not electrically connected. Therefore, when a voltage is applied between the first internal electrode layer 31 and the second internal electrode layer 32 via the external electrodes 11 and 12, charge accumulates. The accumulated charge generates capacitance, thereby enabling the device to function as a capacitive element.

[0040] An outer layer portion 25, consisting only of dielectric ceramic layers 20, may be provided on the outside of the plurality of dielectric ceramic layers 20 and plurality of internal electrode layers 30 that are stacked in the thickness direction T. The outer layer portion 25 is located on both main surfaces of the base body 10 and is a dielectric ceramic layer located between each main surface and the internal electrode layer 30 closest to that main surface. On the other hand, the region sandwiched between both outer layer portions 25 can also be called the inner layer portion.

[0041] The dielectric ceramic layer 20 is composed of ceramic. Specifically, the dielectric ceramic layer 20 mainly contains a sintered body of ceramic powder for the multilayer ceramic capacitor of the present invention. Therefore, the dielectric ceramic layer 20 is composed of BaTiO ３ It can also be said that it is composed of sintered bodies of compound systems.

[0042] In this specification, the main component means the component that accounts for the largest mass percentage in the ceramic. The mass percentage of the main component is not particularly limited as long as it is less than 100% by mass, and may be, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more.

[0043] The thickness of the dielectric ceramic layer 20 is not particularly limited and may be, for example, 5.0 μm or less, 4.0 μm or less, 3.5 μm or less, 2.5 μm or less, 1.0 μm or less, or 0.8 μm or less. On the other hand, the thickness of the dielectric ceramic layer 20 may be, for example, 0.3 μm or more, 0.4 μm or more, 0.5 μm or more, 0.6 μm or more, or 0.7 μm or more. If the thickness of the dielectric ceramic layer 20 is within the above range, deterioration of the insulating properties can be prevented. Furthermore, if the thickness of the dielectric ceramic layer 20 is within the above range, the dielectric ceramic layer 20 can be made thinner, and the capacitance can be improved.

[0044] The number of dielectric ceramic layers 20 is, for example, 50 or more and 1000 or less.

[0045] The average particle size of the ceramic grains contained in the dielectric ceramic layer 20 is not particularly limited, but is preferably 100 nm or more and 400 nm or less, and more preferably 150 nm or more and 300 nm or less.

[0046] The internal electrode layer 30 contains a conductive metal. Examples of conductive metals include nickel (Ni), copper (Cu), silver (Ag), palladium (Pd), and alloys containing at least one of these metals. The internal electrode layer 30 may also contain other components besides the conductive metal. Examples of other components include ceramic components that act as co-materials. Examples of ceramic components include BaTiO contained in the dielectric ceramic layer 20. ３ Examples include compound systems.

[0047] The thickness of the internal electrode layer 30 is not particularly limited, and is, for example, 0.3 μm or more and 0.7 μm or less. When the thickness of the internal electrode layer 30 is within the above range, defects such as electrode breaks are suppressed. Furthermore, when the thickness of the internal electrode layer 30 is within the above range, the decrease in the proportion of the electrically functional dielectric ceramic layer 20 in the capacitor is suppressed, making it possible to suppress a decrease in capacitance.

[0048] The thickness of the dielectric ceramic layer 20 and the internal electrode layer 30 is determined by observing the WT cross-section of the exposed substrate 10 by polishing using a scanning electron microscope (SEM). The thickness is measured along a center line passing through the center of the WT cross-section along the thickness direction T, and along a total of five lines drawn at equal intervals on both sides of this center line. The average of these five measured values ​​is then used.

[0049] Furthermore, the average particle size of the ceramic grains contained in the dielectric ceramic layer 20 can be measured by analyzing cross-sectional images scanned with a SEM. For example, the average particle size of the ceramic grains can be measured using software that measures the average particle size in accordance with the JIS G 0551:2013 standard.

[0050] The configuration of the external electrodes 11 and 12 is not particularly limited. The external electrodes 11 and 12 may have a laminated structure consisting of a base layer, a first plating layer, and a second plating layer, starting from the end face side of the multilayer ceramic capacitor 1. The base layer contains a metal such as nickel (Ni) or copper (Cu). The base layer may also contain ceramic powder 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. A conductive resin layer may be provided between the base layer 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 11 and 12 are not limited in their form as long as they are electrically connected to the internal electrode layer 30 and function as external input / output terminals.

[0051] [Method for Manufacturing Ceramic Powder for Multilayer Ceramic Capacitors] The method for manufacturing ceramic powder for multilayer ceramic capacitors according to the present invention comprises the steps of obtaining a first slurry, obtaining a second slurry, obtaining dried powder, and performing heat treatment. Details of each step are described below.

[0052] <Step to obtain the first slurry> A first slurry is obtained by wet grinding rare earth (Re) powder alone until the cumulative 90% particle size D90 by volume is 0.60 μm or less. As a result, the Re powder is finely pulverized (also called fine powdering), making it easier for the Re element to dissolve in solid solution.

[0053] As the Re powder, known ceramic raw materials such as Re oxides, carbonates, acetates, and hydroxides can be used.

[0054] Re preferably contains at least one selected from the group consisting of La, Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and more preferably contains at least Dy.

[0055] In the step of obtaining the first slurry, it is preferable that the Re powder is an oxide and that wet grinding is performed using a wet mill. The method of wet grinding is not particularly limited, and general grinding methods such as ball mills and bead mills can be used. Specific grinding conditions can be appropriately set depending on the grinding equipment and the type and particle size of the Re powder to be ground. A finer powder can be obtained by using a bead mill than by using a ball mill.

[0056] In the step of obtaining the first slurry, the grinding time of the Re powder is preferably more than 0.2 hours, and more preferably 5 hours or more and 24 hours or less.

[0057] <Step to obtain the second slurry> The first slurry is added to a mixed slurry or raw material slurry such that the amount of rare earth elements (Re) added is greater than 1.0 mol% but less than 10.0 mol% relative to 100 mol% of titanium (Ti), and then wet grinding is performed to obtain the second slurry.

[0058] The mixed slurry is a slurry in which a barium (Ba) compound, a titanium (Ti) compound, and optionally at least one of a calcium (Ca) compound and a strontium (Sr) compound are mixed. Preferably, the mixed slurry contains at least a Ca compound among the Ca and Sr compounds.

[0059] As the Ba compound, known ceramic raw materials such as Ba oxides, carbonates, acetates, hydroxides, and chlorides can be used.

[0060] As the Ti compound, known ceramic raw materials such as Ti oxides, acetates, and chlorides can be used.

[0061] As the Ca compound, known ceramic raw materials such as Ca oxides and carbonates can be used.

[0062] As the Sr compound, known ceramic raw materials such as Sr oxides and carbonates can be used.

[0063] The raw material slurry is a slurry of barium titanate powder, which may be partially substituted with at least one of calcium (Ca) and strontium (Sr). The raw material slurry may also be a slurry of barium titanate powder.

[0064] In the step of obtaining the second slurry, it is preferable that the amount of Re added is 1.5 mol% or more and 7.0 mol% or less.

[0065] In the step of obtaining the second slurry, wet grinding is preferably performed using a wet mill. The method of wet grinding is not particularly limited, and general grinding methods such as ball mills and bead mills can be used. Specific grinding conditions can be appropriately set according to the grinding equipment and the type and particle size of the powder to be ground. A finer powder can be obtained by using a bead mill than by using a ball mill.

[0066] <Step to obtain dried powder> Dry powder is obtained by removing the solvent from the second slurry. In the step to obtain dried powder, it is sufficient to evaporate the solvent in the second slurry, and the drying method is not particularly limited and can be carried out using known methods.

[0067] In the process of obtaining the dried powder, drying may be performed at room temperature, but from the viewpoint of manufacturing efficiency, heating drying is preferred. The drying temperature is preferably 50°C to 400°C, more preferably 80°C to 300°C, and even more preferably 100°C to 180°C, from the viewpoint of drying efficiency, maintaining the fineness of the dried powder, and ease of handling. From the same viewpoint, the drying time is preferably 6 hours to 60 hours, more preferably 10 hours to 50 hours, and even more preferably 12 hours to 48 hours. The drying atmosphere may be an atmospheric atmosphere.

[0068] <Heat treatment process> After that, heat treatment is performed using the dried powder. This results in BaTiO ３ The compound is synthesized.

[0069] To facilitate the solid solution of elements such as Re, it is preferable to repeat the wet grinding and heat treatment process of the heat-treated dried powder.

[0070] Based on the above, the BET specific surface area is 4.0 m². ２ / g or more 21.0m ２ A calcined powder (ceramic powder for multilayer ceramic capacitors) with a concentration of less than / g is obtained.

[0071] [Method for Manufacturing Multilayer Ceramic Capacitors] The method for manufacturing multilayer ceramic capacitors of the present invention is characterized by using the ceramic powder for multilayer ceramic capacitors of the present invention.

[0072] The manufacturing method of the multilayer ceramic capacitor of the present invention is, for example, BaTiO ３ The process comprises the steps of: preparing a green sheet containing a compound (green sheet preparation step); applying a conductive paste to the surface of the green sheet to obtain a green sheet with an internal electrode pattern (electrode pattern formation step); stacking and pressing multiple green sheets to obtain a stacked block (stacking step); cutting the obtained stacked block to obtain a stacked chip (cutting step); performing a binder removal process and a firing process on the obtained stacked chip to obtain a base body (firing step); and forming external electrodes on the obtained base body (external electrode formation step). Details of each step are described below.

[0073] <Green Sheet Manufacturing Process> In the green sheet manufacturing process, BaTiO ３ A green sheet containing a compound is prepared. The green sheet is a precursor to a dielectric ceramic layer and contains the main component raw material and additive raw materials for the dielectric ceramic layer. The method for preparing the green sheet is not particularly limited. For example, a dielectric raw material can be prepared by mixing the main component raw material with the additive raw material, a binder and a solvent can be added and mixed to the obtained dielectric raw material to form a slurry, and a green sheet can be formed from the obtained slurry.

[0074] The ceramic powder for multilayer ceramic capacitors of the present invention is used as the main component raw material.

[0075] The additive raw materials may also include raw materials for other additive components such as Mn, Mg, Si, Al, and V. Furthermore, the main component is BaTiO ３ To adjust the composition of the compound system, barium carbonate (BaCO3) is used.３ ) and titanium dioxide (TiO ２ Ba raw materials and Ti raw materials such as ) may be added to the additive raw materials.

[0076] Slurry formation can be carried out by known methods; for example, by mixing an organic binder and an organic solvent with the dielectric material. As the organic binder, known binders such as polyvinyl butyral-based binders can be used. As the organic solvent, known solvents such as toluene and ethanol can be used. Additives such as plasticizers may be added to the slurry as needed. Furthermore, the green sheet can be formed by known methods such as the doctor blade method or the lip method.

[0077] <Electrode Pattern Formation Process> In the electrode pattern formation process, a conductive paste is applied to the surface of a green sheet to obtain a green sheet with an internal electrode pattern formed on it. The internal electrode pattern becomes the internal electrode layer after firing. Conductive metals included in the conductive paste include, for example, conductive materials such as nickel (Ni), copper (Cu), silver (Ag), palladium (Pd), and alloys containing these. In addition, ceramic components that act as co-materials may be added to the conductive paste. As ceramic components, for example, the main component raw materials of dielectric ceramic layers may be used. The conductive paste can be applied by known methods such as screen printing or gravure printing.

[0078] <Lamination Process> In the lamination process, multiple green sheets are laminated and compressed to obtain a laminated block. Green sheets with internal electrode patterns are used as the green sheets, but some green sheets without internal electrode patterns may also be used. Lamination and compression can be carried out by known methods.

[0079] <Cutting Process> In the cutting process, the obtained laminated block is cut to obtain a laminated chip. The cutting should be performed in such a way that a chip of a predetermined size is obtained and at least a portion of the internal electrode pattern is exposed on the end face of the laminated chip.

[0080] <Firing Process> In the firing process, the obtained laminated chip is subjected to a binder removal process and a firing process to obtain a base material. The firing process causes the green sheet and the internal electrode pattern to co-sinter, forming the dielectric ceramic layer and the internal electrode layer, respectively. The conditions for the binder removal process should be determined according to the type of organic binder contained in the green sheet and the internal electrode pattern. The firing process should be performed at a temperature at which the laminated chip becomes sufficiently dense. The firing process is performed, for example, with the main component BaTiO ３ The process is carried out in an atmosphere that prevents the reduction of the compound and suppresses the oxidation of the conductive metal. Furthermore, additional heat treatment may be performed after firing at an appropriate temperature and atmosphere.

[0081] <External Electrode Formation Process> In the external electrode formation process, external electrodes are formed on the obtained base material. The external electrodes can be formed by known methods. For example, they can be formed by applying and baking a conductive paste containing a metal such as silver (Ag), copper (Cu), and / or nickel (Ni) onto the end face of the base material exposed after the internal electrode layer has been drawn out. Alternatively, they can be formed by applying a conductive paste to both end faces of the laminated chip before firing and then performing a firing process. Furthermore, the formed electrodes can be used as a base layer, and a plating film of nickel (Ni) or tin (Sn) can be formed on top of it. A multilayer ceramic capacitor is then manufactured.

[0082] This specification discloses the following:

[0083] <1> A ceramic powder for multilayer ceramic capacitors, composed of a perovskite-type oxide, wherein the perovskite-type oxide contains barium (Ba), titanium (Ti), and rare earth (Re) elements, and may further contain at least one of calcium (Ca) and strontium (Sr), and has a BET specific surface area of ​​4.0 m². ２ / g or more 21.0m ２ A ceramic powder for multilayer ceramic capacitors, wherein the concentration is less than or equal to / g, and the arithmetic mean μ in the distribution of the weight concentration ratio of Re / Ti is between 0.02 wt% and 0.08 wt%, and the variation σ is 0.15 or less.

[0084] <2> The ceramic powder for multilayer ceramic capacitors according to <1>, wherein the rare earth (Re) element is selected from the group consisting of lanthanum (La), yttrium (Y), 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).

[0085] <3> The ceramic powder for multilayer ceramic capacitors according to <2>, wherein the rare earth (Re) element is at least Dy.

[0086] <4> The perovskite-type oxide is a ceramic powder for multilayer ceramic capacitors according to any one of <1> to <3>, comprising at least Ca among Ca and Sr.

[0087] <5> A step to obtain a first slurry by wet grinding rare earth (Re) powder alone until the cumulative 90% particle size D90 by volume is 0.60 μm or less; a step to obtain a second slurry by adding the first slurry to a mixed slurry in which barium (Ba) compound, titanium (Ti) compound, and optionally at least one of calcium (Ca) compound and strontium (Sr) compound are mixed, or a raw material slurry of barium titanate powder in which a portion may be substituted with at least one of calcium (Ca) and strontium (Sr), such that the amount of rare earth (Re) added is more than 1.0 mol% but less than 10.0 mol% relative to 100 mol% of titanium (Ti), and further wet grinding; a step to obtain a dry powder by removing the solvent from the second slurry; and a step to perform heat treatment using the dry powder, wherein the BET specific surface area is 4.0 m². ２ / g or more 21.0m ２ A method for producing ceramic powder for multilayer ceramic capacitors, which yields calcined powder with a concentration of less than / g.

[0088] <6> The method for producing ceramic powder for multilayer ceramic capacitors according to <5>, wherein in the step of obtaining the first slurry, the rare earth (Re) powder is an oxide, and the wet grinding is performed using a wet mill.

[0089] <7> The method for producing ceramic powder for multilayer ceramic capacitors according to <5> or <6>, wherein in the step of obtaining the second slurry, the amount of rare earth (Re) added is 1.5 mol% or more and 7.0 mol% or less.

[0090] <8> A method for producing ceramic powder for multilayer ceramic capacitors according to any one of <5> to <7>, wherein in the step of obtaining the first slurry, the grinding time of the rare earth (Re) powder exceeds 0.2 hours.

[0091] <9> The method for producing ceramic powder for multilayer ceramic capacitors according to <8>, wherein in the step of obtaining the first slurry, the grinding time of the rare earth (Re) powder is 5 hours or more and 24 hours or less.

[0092] <10> A method for producing ceramic powder for multilayer ceramic capacitors according to any one of <5> to <9>, wherein the above-mentioned heat treatment of the dried powder is repeated in the process of wet grinding and heat treatment.

[0093] A method for manufacturing a multilayer ceramic capacitor, characterized by using the ceramic powder for multilayer ceramic capacitors described in any one of <1> to <4>, or the ceramic powder for multilayer ceramic capacitors obtained by the method described in any one of <5> to <10>.

[0094] The following are examples that more specifically disclose the present invention. However, the present invention is not limited to these examples.

[0095] 1. Fabrication of multilayer ceramic capacitors First, Dy ２ O ３ Weigh the powder and ZrO ２ Wet ball mill dispersion was performed using balls with varying dispersion times. ３ Powder, TiO ２ Powder and CaCO2 ３Mixed slurry obtained by weighing the powder (however, only in Example 18: BaTiO ３ Dy, which was dispersed in the powdered raw material slurry by itself. ２ O ３ A predetermined amount of the dispersed slurry (first slurry) is added as shown in Tables 1 to 7, and then ZrO ２ A wet ball mill was performed using balls for 24 hours. The powder obtained by drying the prepared slurry (second slurry) was heated in air at a rate of 600°C / hour to 990°C (however, in Examples 16, 17, Comparative Example 16, and Comparative Example 17, the calcination temperature was changed), and after holding for 2 hours, it was cooled to obtain calcined powder. This calcined powder was then used again in ZrO ２ A 24-hour wet ball mill was performed using balls to produce a dry powder, which was then synthesized at the same temperature as before. The heat treatment at a predetermined temperature and the subsequent wet ball milling were repeated a total of three times to obtain the final calcined powder (ceramic powder for multilayer ceramic capacitors).

[0096] TiO in calcined powder ２ : BaCO3 per 100 moles ３ Powder: 1.0 mol part, MgCO ３ Powder: 1.0 mol part, MnCO ３ Powder: 0.3 moles, and SiO ２ Sol: 1.5 moles were added to the calcined powder, and the mixture was wet-mixed and dried to obtain dielectric powder.

[0097] A polyvinyl butyral-based binder and a plasticizer are added to the obtained dielectric powder, and then toluene and ethyl alcohol are added, resulting in ZrO ２ The material was slurryed using a wet ball mill with balls, and this slurry was molded to obtain a green sheet. The thickness of the green sheet was adjusted to 1.7 μm after sintering and densification.

[0098] A conductive paste, primarily composed of nickel, was screen-printed onto the surface of the obtained green sheet to form a pattern of conductive paste layers that would serve as the internal electrode layers.

[0099] Subsequently, 201 layers of green sheets, each with a conductive paste layer formed on its surface, were stacked so that the sides with the conductive paste layer extended were staggered. Further layers of green sheets without a conductive paste layer were placed above and below the stacked sheets, and the entire assembly was then compressed to produce a laminated block.

[0100] The resulting multilayer blocks were cut into green multilayer chips. The cutting was done so that the length × width of the manufactured multilayer ceramic capacitors would be 3.2 mm × 1.6 mm.

[0101] The obtained green multilayer chips are N ２ The binder was removed by heat treatment at 280°C in an airflow. Subsequently, N ２ -H ２ -H ２ O-flow at 1260°C, oxygen partial pressure 1.6 × 10⁻⁶ －９ The firing process was carried out for two hours under MPa conditions.

[0102] In the fired laminated chip, a conductive paste mainly composed of Cu was applied to the end face portion where the internal electrode layer was drawn out, and the external electrode was formed by baking at 800°C. Furthermore, a Ni plating layer and an Sn plating layer were formed on the surface of the external electrode.

[0103] In this manner, a multilayer ceramic capacitor was fabricated. The resulting multilayer ceramic capacitor had external dimensions of 3.2 mm in length, 1.6 mm in width, and 1.6 mm in thickness. The number of dielectric ceramic layers sandwiched between the internal electrode layers was 200, and the thickness of each dielectric ceramic layer was 1.7 μm.

[0104] 2. Evaluation First, the final calcined powders (ceramic powders for multilayer ceramic capacitors) obtained in Examples 1 to 18 and Comparative Examples 1 to 17 were evaluated for various properties as follows.

[0105] <SSA Analysis> The specific surface area (SSA) was determined using the BET method.

[0106] <LA-960 Particle Size Distribution Analysis> The cumulative 90% particle size D90 was measured using the LA-960 laser diffraction / scattering particle size distribution analyzer manufactured by Horiba, Ltd., and the particle size that represents 90% of the volume-based cumulative particle size distribution was determined from the obtained particle size distribution.

[0107] <Press SEM / EDX Analysis> The final calcined powder was observed using a scanning electron microscope (SEM) after press molding, and component analysis of the fine regions was performed using an energy-dispersive X-ray spectrometer (EDX). The observation samples were prepared by ion milling after resin solidification. The observation and analysis were performed under the following conditions: - Equipment: Hitachi High-Tech Regulus 8230 (SEM), Bruker Japan XFlash 5060 FlatQUAD (EDX) - Field of view: n=1 - Magnification: 30000x - Measurement time: 1800s - Map area: 512*384 From the Dy / Ti ratio distribution (wt% ratio) obtained from the analysis results, the arithmetic mean μ and variability σ were calculated.

[0108] Next, the various characteristics of the multilayer ceramic capacitors obtained in Examples 1 to 18 and Comparative Examples 1 to 17 were evaluated as follows.

[0109] <Reliability (MTTF, B1 Life)> Highly accelerated lifetime testing (HALT) was performed on multilayer ceramic capacitors to determine the mean time to failure (MTTF). In the HALT test, a high-temperature load was applied to the sample under the conditions of temperature: 175°C and test voltage: 50V. The time at which the insulation resistance fell below 200kΩ was defined as the failure time. The failure time was measured for 72 samples prepared under the same conditions.

[0110] Next, the obtained data was plotted on Weibull probability paper to obtain the Weibull distribution. The relationship between failure time and cumulative failure rate was linearly regressed on the obtained Weibull distribution, and its slope was determined as the shape parameter m. Samples with an m value of 7.0 or higher were judged as acceptable. Furthermore, 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 50V was determined using this failure time and the shape parameter m corresponding to the slope of the regression line. Samples with an MTF of 50 hours or higher were judged as acceptable.

[0111] 3. Evaluation Results The evaluation results obtained for Examples 1 to 18 and Comparative Examples 1 to 17 are shown in Tables 1 to 7. Note that the MTTF and m values ​​shown in Tables 1 to 7 were measured under a test voltage of 50V.

[0112] In the evaluation when the thickness of the dielectric ceramic layer is 1.7 μm, Dy ２ O ３ The particle size (D90) is 0.60 μm or less, the arithmetic mean μ of the Dy / Ti ratio is between 0.02 wt% and 0.08 wt%, the variation σ is 0.15 or less, and the BET specific surface area is 4.0 m². ２ / g or more 21.0m ２ In the samples with values ​​of less than / g (Examples 1 to 17), the MTF was 50 hours or more and the m value was 7.0 or more. On the other hand, Dy ２ O ３ In samples (Comparative Examples 1 to 17) where the particle size, arithmetic mean μ, variability σ, and BET specific surface area fell outside the above-mentioned ranges, the MTF was less than 50 hours or the m value was less than 7.0.

[0113] Furthermore, in the ceramic powder manufacturing method described above, Dy ２ O ３ The slurry obtained by wet-disintegrating the powder is processed by BaTiO ３ In a sample (Example 18) in which the powder was added to a weighed slurry and subjected to dispersion and heat treatment, it was confirmed that the same reliability improvement effect as described above could be obtained.

[0114] Based on these results, the arithmetic mean μ in the distribution of the weight concentration ratio of Re / Ti should be between 0.02 wt% and 0.08 wt%, the variability σ should be 0.15 or less, and the BET specific surface area should be 4.0 m². ２ / g or more 21.0m ２ / g or less (preferably 8.0 m) ２ / g or more 13.0m ２ It can be seen that by setting the coefficient to less than or equal to 1 / g, a multilayer ceramic capacitor with high high-temperature reliability can be obtained.

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[0122] 1 Multilayer ceramic capacitor 10 Base body 10a First main surface 10b Second main surface 10c First side surface 10d Second side surface 10e First end surface 10f Second end surface 11, 12 External electrodes 20 Dielectric ceramic layer 25 Outer layer 30 Internal electrode layer 31 First internal electrode layer 32 Second internal electrode layer L Length direction T Thickness direction W Width direction

Claims

1. A ceramic powder for multilayer ceramic capacitors, composed of a perovskite-type oxide, wherein the perovskite-type oxide contains barium (Ba), titanium (Ti), and rare earth (Re) elements, and may further contain at least one of calcium (Ca) and strontium (Sr), and has a BET specific surface area of ​​4.0 m². ２ / g or more 21.0m ２ A ceramic powder for multilayer ceramic capacitors, wherein the concentration is less than or equal to / g, and the arithmetic mean μ in the distribution of the weight concentration ratio of Re / Ti is between 0.02 wt% and 0.08 wt%, and the variation σ is 0.15 or less.

2. The ceramic powder for multilayer ceramic capacitors according to claim 1, wherein the rare earth (Re) element comprises at least one selected from the group consisting of lanthanum (La), yttrium (Y), 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).

3. The ceramic powder for multilayer ceramic capacitors according to claim 2, wherein the rare earth (Re) element comprises at least Dy.

4. The ceramic powder for multilayer ceramic capacitors according to any one of claims 1 to 3, wherein the perovskite-type oxide contains at least Ca among Ca and Sr.

5. The process comprises: obtaining a first slurry by wet grinding rare earth (Re) powder alone until the cumulative 90% particle size D90 by volume is 0.60 μm or less; adding the first slurry to a mixed slurry containing barium (Ba) compound, titanium (Ti) compound, and optionally at least one of calcium (Ca) compound and strontium (Sr) compound, such that the amount of rare earth (Re) added is greater than 1.0 mol% but less than 10.0 mol% relative to 100 mol% of titanium (Ti), or to a raw material slurry of barium titanate powder in which a portion may be substituted with at least one of calcium (Ca) and strontium (Sr), and further wet grinding to obtain a second slurry; obtaining a dry powder by removing the solvent from the second slurry; and performing heat treatment using the dry powder, wherein the BET specific surface area is 4.0 m². ２ / g or more 21.0m ２ A method for producing ceramic powder for multilayer ceramic capacitors, which yields calcined powder with a concentration of less than / g.

6. The method for producing ceramic powder for multilayer ceramic capacitors according to claim 5, wherein in the step of obtaining the first slurry, the rare earth (Re) powder is an oxide, and the wet grinding is performed using a wet mill.

7. The method for producing ceramic powder for multilayer ceramic capacitors according to claim 5 or 6, wherein in the step of obtaining the second slurry, the amount of rare earth (Re) added is 1.5 mol% or more and 7.0 mol% or less.

8. A method for producing ceramic powder for multilayer ceramic capacitors according to any one of claims 5 to 7, wherein in the step of obtaining the first slurry, the grinding time of the rare earth (Re) powder exceeds 0.2 hours.

9. The method for producing ceramic powder for multilayer ceramic capacitors according to claim 8, wherein in the step of obtaining the first slurry, the grinding time of the rare earth (Re) powder is 5 hours or more and 24 hours or less.

10. A method for producing ceramic powder for multilayer ceramic capacitors according to any one of claims 5 to 9, comprising repeating the wet grinding and heat treatment of the dried powder that has undergone the heat treatment.

11. A method for manufacturing a multilayer ceramic capacitor, characterized by using the ceramic powder for multilayer ceramic capacitors described in any one of claims 1 to 4, or the ceramic powder for multilayer ceramic capacitors obtained by the method described in any one of claims 5 to 10.

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