Dielectric, electronic device, and multilayer ceramic capacitor

Abstract

The present invention relates to and provides a dielectric, an electronic device, and a multilayer ceramic capacitor. The dielectric of the present invention includes core-shell particles having a twin structure, wherein an interface of the twin structure of the core-shell particles extends from a shell on one side, through a core, and to a shell on another side. According to the present invention, the dielectric, the electronic device, and the multilayer ceramic capacitor can have improved reliability.

Description

TECHNICAL FIELD

[0001] An aspect of the present application relates to a dielectric, an electronic device, and a multilayer ceramic capacitor. BACKGROUND

[0002] As electronic devices are reduced in size and increased in capacity, the thickness of a dielectric layer of an electronic device such as a multilayer ceramic capacitor is reduced, and the number of dielectric layers is increased (see, for example, Japanese Patent Application Publication No. 2017-178684, Japanese Patent Application Publication No. 2017-178685, and Japanese Patent Application Publication No. 2002-362971). SUMMARY

[0003] However, when the thickness of a dielectric layer is reduced, the DC electric field strength applied to the dielectric layer is increased. Therefore, there is a demand for improving the reliability of the dielectric layer.

[0004] An object of the present application is to provide a dielectric, an electronic device, and a multilayer ceramic capacitor that can improve reliability.

[0005] According to one aspect of the present application, there is provided a dielectric including core-shell particles having a twin structure, wherein an interface of the twin structure of the core-shell particles extends from a shell on one side, through a core, and to a shell on the other side.

[0006] According to another aspect of the present application, there is provided an electronic device including the dielectric.

[0007] According to another aspect of the present application, there is provided a multilayer ceramic capacitor including a multilayer structure in which each dielectric layer and each internal electrode layer are alternately stacked, each dielectric layer including core-shell particles having a twin structure, wherein an interface of the twin structure of the core-shell particles extends from a shell on one side, through a core, and to a shell on the other side. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 A partial perspective view of a multilayer ceramic capacitor is shown;

[0009] Figure 2A A cross-sectional view of core-shell particles having a twin structure is shown;

[0010] Figure 2B Core-shell particles having a twin structure observed by a backscattered electron image are shown;

[0011] Figure 2C A cross-section of a dielectric layer is schematically shown;

[0012] Figure 3 A manufacturing method of a multilayer ceramic capacitor is shown; and

[0013] Figures 4A to 4C A stacking process is shown. DETAILED DESCRIPTION

[0014] Embodiments will be described with reference to the accompanying drawings.

[0015] [Embodiment]

[0016] Figure 1 is a perspective view of a multilayer ceramic capacitor 100 according to an embodiment, in which a partial cross section of the multilayer ceramic capacitor 100 is shown. As shown in Figure 1 the multilayer ceramic capacitor 100 includes a multilayer chip 10 having a cuboid shape, and a pair of external electrodes 20a and 20b provided on two end faces of the multilayer chip 10 opposite to each other, respectively. Of four faces of the multilayer chip 10 other than the two end faces, two faces other than the upper and lower faces in a stacking direction of the multilayer chip 10 are referred to as side faces. The external electrodes 20a and 20b extend to the upper and lower faces and the two side faces. However, the external electrodes 20a and 20b are spaced apart from each other.

[0017] The multilayer chip 10 has a structure designed to have dielectric layers 11 and internal electrode layers 12 alternately stacked. A main component of the dielectric layers 11 is a ceramic material serving as a dielectric material. A main component of the internal electrode layers 12 is a metal material, such as a base metal material. End edges of the internal electrode layers 12 are alternately exposed to a first end face of the multilayer chip 10 and a second end face of the multilayer chip 10 different from the first end face. In the present embodiment, the first end face is opposite to the second end face. The external electrode 20a is provided on the first end face. The external electrode 20b is provided on the second end face. Thereby, the internal electrode layers 12 are alternately connected to the external electrode 20a and the external electrode 20b. Thus, the multilayer ceramic capacitor 100 has a structure in which a plurality of the dielectric layers 11 are stacked and each two of the dielectric layers 11 sandwich the internal electrode layer 12. In the stacked structure of the dielectric layers 11 and the internal electrode layers 12, the outermost layer in the stacking direction is the internal electrode layer 12. The upper and lower faces of the stacked structure are the internal electrode layers 12, which are covered by a cover layer 13. A main component of the cover layer 13 is a ceramic material. For example, the main component of the cover layer 13 is the same as the main component of the dielectric layers 11.

[0018] For example, the multilayer ceramic capacitor 100 can be 0.25 mm long, 0.125 mm wide, and 0.125 mm high. The multilayer ceramic capacitor 100 can be 0.4 mm long, 0.2 mm wide, and 0.2 mm high. The multilayer ceramic capacitor 100 can be 0.6 mm long, 0.3 mm wide, and 0.3 mm high. The multilayer ceramic capacitor 100 can be 1.0 mm long, 0.5 mm wide, and 0.5 mm high. The multilayer ceramic capacitor 100 can be 3.2 mm long, 1.6 mm wide, and 1.6 mm high. The multilayer ceramic capacitor 100 can be 4.5 mm long, 3.2 mm wide, and 2.5 mm high. However, the size of the multilayer ceramic capacitor 100 is not limited.

[0019] The main component of the internal electrode layer 12 is a base metal such as nickel (Ni), copper (Cu), tin (Sn), or the like. A noble metal such as platinum (Pt), palladium (Pd), silver (Ag), gold (Au), or an alloy thereof can be used as the internal electrode layer 12.

[0020] The dielectric layer 11 is mainly composed of a ceramic material represented by a general formula ABO3and having a perovskite structure. The perovskite structure includes ABO 3-α For example, the ceramic material is, for example, BaTiO3(barium titanate), CaZrO3(calcium zirconate), CaTiO3(calcium titanate), SrTiO3(strontium titanate), Ba 1-x-y Ca x Sr y Ti 1-z Zr z O3(0≤x≤1, 0≤y≤1, 0≤z≤1).

[0021] According to the purpose, the dielectric layer 11 includes an additive compound in addition to the main component ceramic material. The additive compound can be an oxide of Mo (molybdenum), Nb (niobium), Ta (tantalum), W (tungsten), Mg (magnesium), Mn (manganese), V (vanadium), Cr (chromium), Zr (zirconium), or a rare earth element (Y (yttrium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium)), or an oxide of Co (cobalt), Ni (nickel), Li (lithium), B (boron), Na (sodium), K (potassium), and Si (silicon), or a glass.

[0022] As the size of the multilayer ceramic capacitor 100 decreases and the capacity of the multilayer ceramic capacitor 100 increases, it is required to reduce the thickness of the dielectric layer 11 and increase the number of stacks of the dielectric layer 11. However, when the thickness of the dielectric layer 11 is reduced, the DC electric field strength in the dielectric layer 11 increases. Therefore, it is required to improve the reliability of the dielectric layer 11.

[0023] The reliability of the dielectric layer 11 will be described. The dielectric layer 11 is formed by firing a ceramic material powder having a perovskite structure represented by a general formula ABO3 as a main component. The ceramic material powder is exposed to a reducing atmosphere during firing. Thus, oxygen vacancies occur in ABO3 of the ceramic material powder. During operation of the multilayer ceramic capacitor 100, a voltage is repeatedly applied to the dielectric layer 11. In this case, the oxygen vacancies migrate, and a potential barrier can be destroyed. That is, the oxygen vacancies in the perovskite structure are one of the reasons for the decrease in reliability of the dielectric layer 11.

[0024] Thus, in the present embodiment, at least a part of the grains of the ceramic that is the main component of the dielectric layer 11 has a core-shell structure in which both the shell and the core have a twin structure. Figure 2A A cross-sectional view of the core-shell particle 30 of the dielectric layer 11 is shown. In the drawing, hatching is omitted. The core-shell particle 30 is a grain of the ceramic that is the main component of the dielectric layer 11. When the ceramic that is the main component of the dielectric layer 11 is barium titanate, the core-shell particle 30 is a grain of barium titanate. Figure 2A As shown in FIG. 1, the core-shell particle 30 has a spherical core 31 and a shell 32 that surrounds and covers the core 31. The core 31 is a crystal portion in which no additive or a small amount of additive is solid-solved. The shell 32 has a crystal portion in which an additive is solid-solved and the concentration of the additive is higher than the additive concentration in the core 31.

[0025] Figure 2A As shown in FIG. 1, the core-shell particle 30 has a spherical core 31 and a shell 32 that surrounds and covers the core 31. The core 31 is a crystal portion in which no additive or a small amount of additive is solid-solved. The shell 32 has a crystal portion in which an additive is solid-solved and the concentration of the additive is higher than the additive concentration in the core 31.

[0026] The core-shell particle 30 has a twin structure. The interface 33 of the twin structure of the core-shell particle 30 extends from a grain boundary of the core-shell particle 30, through the shell 32 on one side, the core 31, and the shell 32 on the other side, and reaches the grain boundary of the core-shell particle 30. In this way, the interface 33 of the twin structure of the core-shell particle 30 continuously extends from the grain boundary of the core-shell particle 30 on one side, through the core 31, and reaches the grain boundary on the other side. In this way, the range of the interface 33 is wide. In Figure 2A In the drawing, one line of the interface 33 is shown. However, a plurality of interfaces 33 can be formed in a band shape. When a cross section of the core-shell particle 30 is observed, the grain boundary can be spaced apart from the interface of the twin structure. In this case, the spacing distance can be 5 nm to 25 nm.

[0027] ​The method for distinguishing between the core 31 and shell 32 in the core-shell particle 30 is not limited. The core 31 and shell 32 can be distinguished by: making the dielectric layer 11 thinner so that its surface can be observed using STEM (scanning transmission electron microscopy); observing the cross-section using STEM; obtaining an elemental mapping image using EDS (energy-dispersive X-ray spectroscopy); and confirming the contrast of the elemental mapping image. From the perspective of EDS observation, it is preferable to observe multiple fields of view at a magnification of 10,000 to 150,000 times. The method for calculating the cross-sectional area of ​​the core 31 and shell 32 is not limited. For example, the cross-sectional area of ​​each of the core 31 and shell 32 can be calculated by image processing of 20 elemental mapping images of the core-shell particle 30 obtained by EDS and counting the number of pixels in each region of the core 31 and shell 32. When calculating the total area of ​​the core 31 and shell 32, the proportion of the core 31 is preferably 20% to 95%. The proportion of the core 31 is more preferably 40% to 85%. The proportion of nuclear 31 is even more preferably 60% to 80%.

[0028] Atomic defects can form in interface 33. Therefore, oxygen vacancies can be trapped in interface 33. Interface 33 is widely formed in core-shell particles 30. Therefore, the performance of trapping oxygen vacancies is high. When the dielectric layer 11 includes core-shell particles 30, the reliability of the dielectric layer 11 is improved.

[0029] It is believed that increasing the proportion of the diffused phase in the dielectric layer 11 can ensure the reliability of the dielectric layer 11. Rare earth elements diffuse into the main component ceramic of this diffused phase. However, when the proportion of the diffused phase is too high, the temperature characteristics may deteriorate. On the other hand, when core-shell particles 30 are formed in the dielectric layer 11, the reliability is improved. Therefore, the deterioration of the temperature characteristics of the dielectric layer 11 can be suppressed.

[0030] By observing backscattered electron images using SEM (scanning electron microscopy), it is possible to determine whether core-shell particles possess a bicrystal structure. For example... Figure 2B As shown, in core-shell particles with a bicrystal structure, contrast differences caused by different crystal orientations at the twin interface and concentric contrast differences caused by different compositions between the core and shell are observed. Typically, the existence of a bicrystal structure can be confirmed by observing the crystal orientation using TEM (transmission electron microscopy). Therefore, the interface 33 can be confirmed by observing SEM or TEM. The object of observation is a cross-section of the core-shell particle.

[0031] Figure 2C A cross-section of the dielectric layer 11 is schematically shown. (e.g.) Figure 2C As shown, the dielectric layer 11 has multiple grains 14 whose main component is ceramic. At least a portion of the grains 14 are... Figure 2A 30 nucleo-shell particles.

[0032] When the proportion of the core-shell particles 30 in the dielectric layer 11 is small, sufficient capture of oxygen vacancies is not necessarily achieved. Therefore, it is preferable that the proportion of all the core-shell particles 30 in each dielectric layer 11 has a lower limit. For example, the proportion of the number of the core-shell particles 30 in each dielectric layer 11 with respect to all the crystal grains 14 is preferably 2% or more. The proportion is more preferably 8% or more. The proportion of the core-shell particles 30 can be calculated by confirming 300 randomly selected crystal grains in a plurality of fields of view of a backscattered electron image of a SEM (scanning electron microscope) image at a magnification of 10000 to 50000.

[0033] On the other hand, when the proportion of the core-shell particles 30 in each dielectric layer 11 is large, the temperature characteristics can be deteriorated due to the growth of the crystal grains. Therefore, it is preferable that the proportion of all the core-shell particles 30 in each dielectric layer 11 has an upper limit. For example, the proportion of all the core-shell particles 30 in each dielectric layer 11 is preferably 20% or less. The proportion is more preferably 12% or less.

[0034] The rare earth element in the added compound of the dielectric layer 11 improves the reliability of the dielectric layer 11. Therefore, it is preferable that the rare earth element is added to the dielectric layer 11. Therefore, it is preferable that the added amount of the rare earth element in each dielectric layer 11 has a lower limit. On the other hand, when the added amount of the rare earth element in the dielectric layer 11 is large, the proportion of the diffusion phase in which the rare earth element diffuses into the main component ceramic increases, and the temperature characteristics of the multilayer ceramic capacitor 100 can be deteriorated. Therefore, it is preferable that the added amount of the rare earth element in the dielectric layer 11 has an upper limit. In the present embodiment, when the amount of the main component ceramic of the dielectric layer 11 is 100 mol% and the rare earth element is converted into Re2O3, the amount of the rare earth element Re (Re represents at least one of the rare earth elements) is preferably 1.75 mol% to 3.50 mol%. The amount of the rare earth element Re is more preferably 2.00 mol% to 2.75 mol%. The amount of the rare earth element Re is still more preferably 2.25 mol% to 2.50 mol%. Even if Re2O3 diffuses during the firing of the multilayer chip 10, Re2O3 is present at an arbitrary position. Therefore, when the multilayer structure between the two cover layers 13 is analyzed by ICP analysis, Re2O3 is detected at this proportion.

[0035] The Mg, V, Mn, Zr, and Cr in the additive compound of the dielectric layer 11 promote sintering during firing of the dielectric layer 11. Therefore, it is preferable that the addition amount of Mg, V, Mn, Zr, and Cr in the dielectric layer 11 has a lower limit. On the other hand, when the addition amount of Mg and Zr in the dielectric layer 11 is large, grain growth is suppressed and formation of a twin crystal can be suppressed. When the addition amount of Mg, V, Mn, and Cr is large, a decrease in lifetime due to an increase in oxygen vacancy concentration caused by an excess of an acceptor can occur. When the addition amount of V, Mn, and Cr in the dielectric layer 11 is large, DC bias characteristics, aging characteristics, and the like can deteriorate. Therefore, it is preferable that the addition amount of Mg, V, Mn, Zr, and Cr in the dielectric layer 11 has an upper limit. In the present embodiment, when the amount of the main component ceramic of the dielectric layer 11 is 100 mol%, it is preferable that the total amount of oxides of Mg, V, Mn, Zr, and Cr is 0.02 mol% to 2.05 mol%, provided that the oxides of Mg, V, Mn, Zr, and Cr are converted into MgO, MnO2, ZrO2, V2O5, and Cr2O3. The addition amount is more preferably 0.10 mol% to 1.00 mol%. The addition amount is still more preferably 0.15 mol% to 0.80 mol%.

[0036] The Si in the additive compound added to the dielectric layer 11 serves as a sintering aid and lowers the sintering temperature. Therefore, it is preferable that the addition amount of Si in each of the dielectric layers 11 has a lower limit. On the other hand, when the addition amount of Si in each of the dielectric layers 11 is large, the dielectric constant of the dielectric layer 11 can decrease. Therefore, it is preferable that the addition amount of Si in each of the dielectric layers 11 has an upper limit. In the present embodiment, provided that the amount of the main component ceramic of the dielectric layer 11 is 100 mol%, the amount of the oxide of Si is preferably 0.25 mol% to 2.50 mol% when the oxide of Si is converted into SiO2. The amount of the oxide of Si is more preferably 1.00 mol% to 2.00 mol%. The amount of the oxide of Si is still more preferably 1.50 mol% to 1.80 mol%.

[0037] A method for manufacturing the multilayer ceramic capacitor 100 will be described. Figure 3 A method for manufacturing the multilayer ceramic capacitor 100 will be described.

[0038] (Manufacturing process of raw material powder) (S1) The A-site and B-site elements contained in the dielectric layer 11 are usually contained in the dielectric layer 11 in the form of a sintered structure of ABO3 particles. For example, BaTiO3 is a tetragonal compound with a perovskite structure and exhibits a high dielectric constant. BaTiO3 can usually be obtained by reacting a titanium raw material such as titanium dioxide with a barium raw material such as barium carbonate to synthesize barium titanate. As a method for synthesizing ceramics of the dielectric layer 11, various methods are known. For example, solid-state methods, sol-gel methods, hydrothermal methods, etc. are known. Any of the above methods can be used in this embodiment.

[0039] Next, depending on the purpose, additive compounds can be added to the ceramic powder material. The additive compounds can be oxides of Mo, Nb, Ta, W, Mg, Mn, V, Cr, or rare earth elements (Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), or oxides of Co, Ni, Li, B, Na, K, and Si, or glass.

[0040] For example, from the viewpoint of reducing the thickness of the dielectric layer 11, the average particle size of the ceramic powder is preferably 50 nm to 300 nm. For example, the particle size of the resulting ceramic can be adjusted by pulverizing the ceramic powder. Alternatively, the particle size can be adjusted by performing pulverization and classification processes. Through these processes, a dielectric material is obtained.

[0041] (Manufacturing Process of Metal Conductive Paste) (S2) The metal conductive paste is made by mixing a metal material, a co-material, and an organic binder. From the perspective of reducing the thickness of the internal electrode layer 12, the particle size of the metal material should be small. In this embodiment, the metal material is a metal with an average particle size of 120 nm or less (e.g., Ni). Ceramic particles, used as the co-material, are added to the metal conductive paste. The main component of the ceramic particles, ceramic, is not limited. Preferably, the main component ceramic of the ceramic particles is the same as the main component ceramic of the dielectric layer 11. Therefore, the co-material is barium titanate, etc.

[0042] (Stacking Process) (S3) Next, an adhesive such as polyvinyl butyral (PVB) resin, an organic solvent such as ethanol or toluene, and a plasticizer are added to the resulting dielectric material and wet-mixed. Figure 4A As shown, using the obtained slurry, a strip-shaped dielectric green sheet 41 with a thickness of less than 0.8 μm is coated onto a substrate by, for example, die coating or blade coating, and then dried. Figure 4A The substrate is not shown in the image.

[0043] Next, as Figure 4BAs shown, a metal conductive paste 42 for the internal electrode layer is formed on the surface of the dielectric green sheet 41 by screen printing or gravure printing. The metal conductive paste 42 contains an organic binder. Thus, a sheet member 43 is obtained.

[0044] Thereafter, as shown in FIG. 2, the sheet members 43 are stacked while peeling the substrate, so that the end edges of the metal conductive paste 42 are alternately exposed to both end faces of the dielectric green sheet 41 in the longitudinal direction. For example, 100 to 500 stacking units are stacked. Thereafter, a cover sheet to be a cover layer 13 is press-bonded to both upper and lower faces of the stacked sheet members 43 in the laminated structure, to obtain a ceramic laminated structure. Thereafter, a metal conductive paste is applied to both end faces of the ceramic laminated structure by a dip coating method, as external electrodes 20a and 20b. Thereafter, the metal conductive paste is dried. Thus, a molded body for forming a laminated ceramic capacitor 100 is obtained. Figure 4C The metal conductive paste 42 corresponding to the internal electrode layer 12 can be printed on a plurality of regions of a single dielectric green sheet 41. In this case, the obtained sheet members 43 are stacked. A cover sheet is clamped. Thereafter, the stacked sheet members 43 are cut into chips having a predetermined size (for example, 1.0 mm x 0.5 mm). A metal conductive paste to be a base layer of the external electrodes 20a and 20b is applied to both end faces of the chips by a dip coating method or the like, and dried.

[0045] (S4) Next, after removing the binder at 250°C to 500°C in a N2 atmosphere, the obtained molded body is fired at a temperature of 1100°C to 1300°C in a reducing atmosphere having an oxygen partial pressure of 10 -5 atm for 10 minutes to 2 hours. -8

[0046] (S5) Thereafter, the obtained molded body is held at a temperature of 300°C lower than the maximum temperature of the firing step (for example, 880°C) for 20 minutes in a reducing atmosphere having a higher oxygen partial pressure than that of the firing step. Thereafter, the obtained molded body is cooled. Thus, a sintered structure is obtained.

[0047] (S6) Thereafter, a re-oxidation step can be performed at 600°C to 1000°C in a N2 gas atmosphere.

[0048] (S7) Thereafter, a plating step is performed to apply a metal layer such as Cu, Ni or Sn to the base layer of the external electrodes 20a and 20b.

[0049]

[0050] ​​In the manufacturing method of the present embodiment, after the firing process, a temperature holding process of holding the temperature for a predetermined time at a temperature lower than the maximum temperature of the firing process is performed. Thereafter, cooling is performed. In this case, the particle growth of the main component ceramic of the dielectric material is promoted. Thereby, the core-shell particles 30 can be formed in the dielectric layer 11.

[0051] Preferably, the temperature and time of the temperature holding process are adjusted according to the degree of particle growth of the main component ceramic. For example, it is preferable to adjust the temperature and time of the temperature holding process so that the average grain diameter of the crystal grains 14 in the dielectric layer 11 is 3 times or more of the average particle diameter of the main component ceramic of the dielectric material. As the additive compound, when Mg oxide for suppressing particle growth is added to the dielectric material, it is preferable to consider the amount of addition of the Mg oxide.

[0052] In the above embodiments, the multilayer ceramic capacitor has been described as an example of the ceramic electronic device. However, the ceramic electronic device is not limited to the multilayer ceramic capacitor. For example, the ceramic electronic device can be other electronic devices such as a pressure-sensitive resistor and a thermistor.

[0053] Example

[0054] In Example 1, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted into BaTi03, the amount of Dy oxide was 2.00 mol% when converted into Dy203, the amount of Mg oxide was 0.10 mol% when converted into MgO, the amount of V oxide was 0.075 mol% when converted into V205, and the amount of Si oxide was 1.50 mol% when converted into Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours.

[0055] Next, the mixed material was dried and calcined at 800°C in air. Thereby, a calcined powder was obtained. The average particle diameter of the calcined particles was 97 nm. The calcined powder was wet pulverized in ethanol and dried. An organic binder and a solvent were added to the resulting calcined powder. The resulting slurry was formed into a ceramic green sheet having a thickness of 4 μm by a doctor blade method. Next, an internal electrode pattern was printed on the ceramic green sheet using a conductive slurry whose main component was Ni powder. Ten sheets were stacked and subjected to hot pressing. Thereby, a multilayer structure was obtained. The multilayer structure was punched into a 1005 shape (length 1.0 mm x width 0.5 mm x height 0.5 mm). A multilayer structure having a chip shape was obtained. Next, a Ni external electrode was formed on the chip-shaped multilayer structure. The binder was removed from the resulting chip-shaped multilayer structure under a N2 atmosphere. The chip-shaped multilayer structure was fired at 1200°C for 2 hours under a N2 atmosphere at a pressure of 10 MPa. Thereby, a multilayer ceramic capacitor was obtained. -5 to 10 -8atm for 15 minutes. Thereafter, as a temperature holding step, the chip-shaped layered structure was held at 800°C for 10 minutes under an oxygen partial pressure of 10 -4 to 10 - 7 atm for 20 minutes. Thereafter, the chip-shaped layered structure was cooled. A chip-shaped sintered structure was obtained. Next, a re-oxidation step was performed on the chip-shaped sintered structure at 800°C to 1000°C in a N2 atmosphere. Thereby, a multilayer ceramic capacitor was obtained. The thickness of one layer of the multilayer ceramic capacitor was about 3 μm. The average grain diameter of the crystal grains 14 in the sintered structure was 352 nm, which was more than three times the size of the material powder.

[0056] Next, the multilayer ceramic capacitor was embedded in an epoxy resin. The multilayer ceramic capacitor was polished so that the cross portion of the internal electrode was exposed. The backscattered electron image of the dielectric layer between the internal electrode layers obtained by SEM was observed. The proportion of the core-shell particles 30 in 300 crystal grains 14 randomly selected from the backscattered electron image was determined.

[0057] (Example 2) In Example 2, the firing temperature was 20°C higher than that of Example 1. The other conditions were the same as those of Example 1. In Example 2, the average particle diameter of the calcined powder was 97 nm. The average grain diameter of the crystal grains 14 was 467 nm.

[0058] (Example 3) In Example 3, the average particle diameter of BaTi03 was 20 nm larger than that of Example 1. The other conditions were the same as those of Example 1. In Example 3, the average particle diameter of the calcined powder was 122 nm. The average grain diameter of the crystal grains 14 was 263 nm.

[0059] (Example 4) In Example 4, the firing temperature was 20°C higher than that of Example 3. The other conditions were the same as those of Example 3. In Example 4, the average particle diameter of the calcined powder was 122 nm. The average grain diameter of the crystal grains 14 was 315 nm.

[0060] (Example 5) In Example 5, the firing temperature was 20°C higher than that of Example 4. The other conditions were the same as those of Example 1. In Example 5, the average particle diameter of the calcined powder was 122 nm. The average grain diameter of the crystal grains 14 was 417 nm.

[0061] (Example 6) In Example 6, the average particle diameter of BaTi03 was 120 nm larger than that of Example 1. The other conditions were the same as those of Example 2. In Example 6, the average particle diameter of the calcined powder was 218 nm. The average grain diameter of the crystal grains 14 was 316 nm.

[0062] (Comparative Example 1) In Comparative Example 1, the process of maintaining the temperature at 880°C for 20 minutes was not performed compared to Example 6, but cooling was performed from the maximum temperature of the firing process. The other conditions were the same as in Example 1. In Comparative Example 1, the average particle diameter of the calcined powder was 218 nm. The average grain diameter of the crystal grains 14 was 254 nm.

[0063] (Comparative Example 2) In Comparative Example 2, the process of maintaining the temperature at 880°C for 20 minutes was not performed compared to Example 1, but cooling was performed from the maximum temperature of the firing process. The average particle diameter of BaTi03 was 220 nm larger than the average particle diameter of Example 1. The other conditions were the same as in Example 2. In Comparative Example 2, the average particle diameter of the calcined powder was 321 nm. The average grain diameter of the crystal grains 14 was 343 nm.

[0064] (Comparative Example 3) In Comparative Example 3, the firing temperature was 20°C higher than in Comparative Example 2. The other conditions were the same as in Comparative Example 2. In Comparative Example 3, the average particle diameter of the calcined powder was 321 nm. The average grain diameter of the crystal grains 14 was 387 nm.

[0065] In Example 1, the proportion of the number of core-shell particles 30 with respect to the total crystal grains 14 in the dielectric layer 11 was 15.9%. In Example 2, the proportion was 23.7%. In Example 3, the proportion was 2.7%. In Example 4, the proportion was 8.5%. In Example 5, the proportion was 21.4%. In Example 6, the proportion was 0.6%. In Comparative Examples 1 to 3, the core-shell particles 30 were not formed. That is, in Comparative Examples 1 to 3, the proportion was 0%. Table 1 shows the results.

[0066] [Table 1]

[0067]

[0068]

[0069] (Lifetime measurement test) Next, the lifetime of each of Examples 1 to 6 and Comparative Examples 1 to 3 was measured. When the lifetime was 800 minutes or more under the accelerated conditions of 150°C and -240V, the sample was determined to be good "O". When the lifetime was less than 800 minutes, the sample was determined to be poor "X".

[0070] In the measurement of the lifetime, Comparative Examples 1 to 3 were determined to be poor "X". It is considered that this is because the core-shell particles 30 were not contained in the dielectric layer 11, and the oxygen vacancies were not trapped. On the other hand, Examples 1 to 6 were determined to be good "O" in the measurement of the lifetime. It is considered that this is because the core-shell particles 30 were contained in the dielectric layer 11, and the oxygen vacancies were trapped.

[0071] It was confirmed that the life becomes longer as the proportion of the core-shell particles 30 in the dielectric layer 11 increases relative to the total crystal grains 14. It was confirmed that, in order to extend the life to 1000 minutes or more, the proportion is preferably 2% or more.

[0072] (Temperature change rate) Next, the temperature change rate was measured for each of Examples 1 to 6 and Comparative Examples 1 to 3. The capacity change rate at 125°C was measured relative to the standard capacity at 25°C. When the capacity change rate was -33%, the sample was judged to be good.

[0073] The capacity change rates of Examples 2 and 5 were less than -33%. However, Examples 1, 3, 4, and 6 were judged to be good. It is considered that this is because the proportion of the core-shell particles 30 in the dielectric layer 11 was 20% or less. Even if the capacity change rate is less than -33%, the sample can be used as a product when the upper limit of the temperature compensation range is reduced from 125°C to 105°C or 85°C.

[0074] It was confirmed from the results that the proportion of the core-shell particles 30 in the dielectric layer 11 is preferably 2% or more and 20% or less. It was confirmed that, from the viewpoint of achieving a more preferable capacity change rate and a more preferable life characteristic, the proportion of the core-shell particles 30 in the dielectric layer 11 is preferably 5% to 16%.

[0075] (Example 7) In Example 7, other rare earth elements than Dy were added. In Example 7, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Ho oxide was 1.75 mol% when converted to Ho203, the amount of Mg oxide was 0.15 mol% when converted to MgO, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.50 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 7, the average particle diameter of the calcined powder was 115 nm. The average crystal grain diameter of the sintered structure was 317 nm. The other conditions were the same as in Example 1.

[0076] (Example 8) In Example 8, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Ho oxide was 2.00 mol% when converted to Ho203, the amount of Mg oxide was 0.15 mol% when converted to MgO, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.50 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 8, the average particle diameter of the calcined powder was 115 nm. The average crystal grain diameter of the sintered structure was 422 nm. The other conditions were the same as in Example 1.

[0077] (Example 9) In Example 9, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Ho oxide was 2.50 mol% when converted to Ho203, the amount of Mn oxide was 0.15 mol% when converted to Mn02, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.50 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 9, the average particle diameter of the calcined powder was 115 nm. The average grain diameter of the sintered structure was 342 nm. The other conditions were the same as in Example 1.

[0078] (Example 10) In Example 10, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Ho oxide was 2.50 mol% when converted to Ho203, the amount of Zr oxide was 0.15 mol% when converted to Zr02, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.50 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 10, the average particle diameter of the calcined powder was 115 nm. The average grain diameter of the sintered structure was 252 nm. The other conditions were the same as in Example 1.

[0079] (Example 11) In Example 11, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Ho oxide was 2.50 mol% when converted to Ho203, the amount of Mg oxide was 0.15 mol% when converted to MgO, the amount of Cr oxide was 0.05 mol% when converted to Cr203, and the amount of Si oxide was 1.50 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 11, the average particle diameter of the calcined powder was 115 nm. The average grain diameter of the sintered structure was 316 nm. The other conditions were the same as in Example 1.

[0080] (Example 12) In Example 12, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Y oxide was 1.75 mol% when converted to Y203, the amount of Ho oxide was 1.75 mol% when converted to Ho203, the amount of Mg oxide was 0.15 mol% when converted to MgO, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.50 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 12, the average particle diameter of the calcined powder was 127 nm. The average grain diameter of the sintered structure was 328 nm. The other conditions were the same as in Example 1.

[0081] (Example 13) In Example 13, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Y oxide was 1.00 mol% when converted to Y203, the amount of Ho oxide was 1.75 mol% when converted to Ho203, the amount of Mg oxide was 0.15 mol% when converted to MgO, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.50 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 13, the average particle diameter of the calcined powder was 127 nm. The average grain diameter of the sintered structure was 387 nm. The other conditions were the same as in Example 1.

[0082] (Example 14) In Example 14, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Ho oxide was 2.50 mol% when converted to Ho203, the amount of Mn oxide was 0.50 mol% when converted to Mn02, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.20 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 14, the average particle diameter of the calcined powder was 115 nm. The average grain diameter of the sintered structure was 284 nm. The other conditions were the same as in Example 1.

[0083] (Example 15) In Example 15, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Ho oxide was 2.50 mol% when converted to Ho203, the amount of Mn oxide was 1.50 mol% when converted to Mn02, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.00 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 15, the average particle diameter of the calcined powder was 115 nm. The average grain diameter of the sintered structure was 237 nm. Other conditions were the same as in Example 1.

[0084] (Example 16) In Example 16, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Ho oxide was 2.50 mol% when converted to Ho203, the amount of Mg oxide was 2.00 mol% when converted to MgO, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.20 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Example 16, the average particle diameter of the calcined powder was 115 nm. The average grain diameter of the sintered structure was 251 nm. Other conditions were the same as in Example 1.

[0085] (Comparative Example 4) In Comparative Example 4, each material was weighed so that the amount of oxides of Ba and Ti was 100 mol% when converted to BaTi03, the amount of Ho oxide was 3.50 mol% when converted to Ho203, the amount of Mn oxide was 0.15 mol% when converted to Mn02, the amount of V oxide was 0.05 mol% when converted to V205, and the amount of Si oxide was 1.70 mol% when converted to Si02. The materials were wet mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Comparative Example 4, the process of maintaining the temperature at 880°C for 20 minutes was not performed. Cooling was performed from the maximum temperature of the firing process. Other conditions were the same as in Example 1. In Comparative Example 4, the average particle diameter of the calcined powder was 253 nm. The average grain diameter of the sintered structure was 302 nm.

[0086] (Comparative Example 5) In Comparative Example 5, each material was weighed such that, when converted to BaTiO3, the amount of Ba and Ti oxides was 100 mol%, when converted to Ho2O3, the amount of Ho oxides was 2.50 mol%, when converted to ZrO2, the amount of Zr oxides was 0.10 mol%, when converted to V2O5, the amount of V oxides was 0.05 mol%, and when converted to SiO2, the amount of Si oxides was 1.90 mol%. The materials were wet-mixed and pulverized in a ball mill for 15 to 24 hours. In Comparative Example 5, the process of maintaining the temperature at 880°C for 20 minutes was not performed. Cooling was performed from the highest temperature of the firing process. Other conditions were the same as in Example 1. In Comparative Example 5, the average particle size of the calcined powder was 253 nm. The average grain diameter of the sintered structure was 284 nm.

[0087] (Comparative Example 6) In Comparative Example 6, each material was weighed such that, when converted to BaTiO3, the amount of Ba and Ti oxides was 100 mol%, when converted to Y2O3, the amount of Y oxide was 1.75 mol%, when converted to Ho2O3, the amount of Ho oxide was 1.75 mol%, when converted to MgO, the amount of Mg oxide was 0.075 mol%, when converted to V2O5, the amount of V oxide was 0.05 mol%, and when converted to SiO2, the amount of Si oxide was 1.80 mol%. The materials were wet-mixed and pulverized into a mixture in a ball mill for 15 to 24 hours. In Comparative Example 6, the process of maintaining the temperature at 880°C for 20 minutes was not performed. Cooling was performed from the highest temperature of the firing process. Other conditions were the same as in Example 1. In Comparative Example 6, the average particle size of the calcined powder was 252 nm. The average grain diameter of the sintered structure was 279 nm.

[0088] In Example 7, the proportion of core-shell particles 30 in the dielectric layer 11 relative to all grains 14 was 9.7%. In Example 8, this proportion was 18.1%. In Example 9, this proportion was 10.2%. In Example 10, this proportion was 3.2%. In Example 11, this proportion was 7.4%. In Example 12, this proportion was 8.5%. In Example 13, this proportion was 17.5%. In Example 14, this proportion was 8.1%. In Example 15, this proportion was 2.2%. In Example 16, this proportion was 2.9%. In Comparative Examples 4 to 6, no core-shell particles 30 were formed. That is, in Comparative Examples 4 to 6, this proportion was 0%. Tables 2 and 3 show the results.

[0089] [Table 2]

[0090]

[0091]

[0092] [Table 3]

[0093]

[0094]

[0095] Next, the life of each of Examples 7 to 16 and Comparative Examples 4 to 6 was measured. When the life was 800 minutes or more under accelerated conditions of 150°C and -240V, the sample was determined to be good "0". When the life was less than 800 minutes, the sample was determined to be poor "X".

[0096] In the life measurement test, Comparative Examples 4 to 6 were determined to be poor "X". It is considered that this is because the core-shell particles 30 were not contained in the dielectric layer 11, and oxygen vacancies were not trapped. On the other hand, Examples 7 to 16 were determined to be good "0" in the life measurement test. It is considered that this is because the core-shell particles 30 were contained in the dielectric layer 11, and oxygen vacancies were trapped.

[0097] It was confirmed that the life becomes longer as the proportion of the number of the core-shell particles 30 in the dielectric layer 11 with respect to the total number of the crystal grains 14 increases. It was confirmed that, in order to extend the life to 1000 minutes or more, the proportion is preferably 2% or more.

[0098] Next, the temperature change rate of each of Examples 7 to 16 and Comparative Examples 4 to 6 was measured. The capacity change rate at 125°C was measured with respect to the standard capacity at 25°C. When the capacity change rate was -33%, the sample was determined to be good.

[0099] Examples 7 to 16 were determined to be good. It is considered that this is because the proportion of the core-shell particles 30 in the dielectric layer 11 was 20% or less.

[0100] From the above results, it is preferable that the proportion of the core-shell particles 30 in the dielectric layer 11 be 2% or more and 20% or less. Furthermore, from the viewpoint of achieving a more preferable capacity change rate and a more preferable life characteristic, it is preferable that the proportion of the core-shell particles 30 in the dielectric layer 11 be 5% to 16%.

[0101] It is also known that when the amount of the ceramic that is the main component of the dielectric layer 11 is 100 mol% and the oxide of Re is converted to Re2O3, it is preferable to add 1.75 mol% to 3.50 mol% of the oxide of Re to the dielectric layer 11. Also, when the amount of the ceramic that is the main component of the dielectric layer 11 is 100 mol% and the oxides of Mg, V, Mn, Zr, and Cr are converted to MgO, MnO2, ZrO2, V2O5, and Cr2O3, it is preferable to add the oxides of Mg, V, Mn, Zr, and Cr in a total amount of 0.02 mol% to 2.05 mol% to the dielectric layer 11. Further, when the amount of the ceramic that is the main component of the dielectric layer 11 is 100 mol% and the oxide of Si is converted to SiO2, it is preferable to add the oxide of Si in an amount of 0.25 mol% to 2.50 mol% to the dielectric layer 11.

[0102] While the embodiments of the present application have been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the application.

Claims

1. A dielectric, comprising: core-shell particles having a twin structure, wherein an interface of the twin structure of the core-shell particles extends from a shell on one side, through a core, and to a shell on the other side.

2. The dielectric according to claim 1, wherein the interface of the twin structure contacts a grain boundary of the core-shell particles.

3. The dielectric according to claim 1 or 2, wherein a proportion of the core-shell particles relative to the crystal grains in the dielectric is 2% or more and 20% or less.

4. The dielectric according to any one of claims 1 to 3, wherein a main component of the core-shell particles is an oxide of Ba and Ti.

5. The dielectric according to any one of claims 1 to 4, wherein the core-shell particles include an oxide of a rare earth element and include at least one of oxides of Mg, V, Mn, Zr, and Cr.

6. The dielectric according to any one of claims 1 to 3, further comprising: 1.75 mol% to 3.50 mol% of an oxide of a rare earth element Re, where Re represents at least one of rare earth elements, when an amount of a main component ceramic of the dielectric is assumed to be 100 mol% and the oxide of the rare earth element Re is converted to Re2O3; and oxides of Mg, V, Mn, Zr, and Cr in a total amount of 0.02 mol% to 2.05 mol% when an amount of a main component ceramic of the dielectric is assumed to be 100 mol% and the oxides of Mg, V, Mn, Zr, and Cr are converted to MgO, MnO2, ZrO2, V2O5, and Cr2O3.

7. The dielectric according to any one of claims 1 to 6, further comprising an oxide of Si.

8. The dielectric according to claim 7, further comprising 0.25 mol% to 2.50 mol% of an oxide of Si when an amount of a main component ceramic of the dielectric is assumed to be 100 mol% and Si is converted to SiO2.

9. An electronic device, comprising the dielectric according to any one of claims 1 to 8.

10. A multilayer ceramic capacitor, comprising: a multilayer structure in which each of dielectric layers and each of internal electrode layers are alternately stacked, each of the dielectric layers including core-shell particles having a twin structure, wherein an interface of the twin structure of the core-shell particles extends from a shell on one side, through a core, and to a shell on the other side.

11. The multilayer ceramic capacitor according to claim 10, wherein the interface of the twin structure contacts a grain boundary of the core-shell particles.

12. The multilayer ceramic capacitor according to claim 10 or 11, wherein a proportion of the core-shell particles relative to the crystal grains in one of the dielectric layers is 2% or more and 20% or less.

13. The multilayer ceramic capacitor according to any one of claims 10 to 12, wherein a main component of the core-shell particles is an oxide of Ba and Ti.

14. The multilayer ceramic capacitor according to any one of claims 10 to 13, wherein the core-shell particles include an oxide of a rare earth element and include at least one of oxides of Mg, V, Mn, Zr, and Cr.

15. The multilayer ceramic capacitor of any one of claims 10 to 12, wherein one of the dielectric layers comprises: an oxide of a rare earth element Re in an amount of 1.75 mol% to 3.50 mol% when the amount of the ceramic that is a main component of the dielectric layer is assumed to be 100 mol% and the rare earth element Re is converted into Re2O3, where Re represents at least one of the rare earth elements; and wherein the one dielectric layer includes: oxides of Mg, V, Mn, Zr, and Cr in a total amount of 0.02 mol% to 2.05 mol% when the amount of the ceramic that is a main component of the dielectric layer is assumed to be 100 mol% and the oxides of Mg, V, Mn, Zr, and Cr are converted into MgO, MnO2, ZrO2, V2O5, and Cr2O3.

16. The multilayer ceramic capacitor according to any one of claims 10 to 15, wherein the dielectric layer includes an oxide of Si.

17. The multilayer ceramic capacitor according to claim 16, wherein the dielectric layer includes an oxide of Si in an amount of 0.25 mol% to 2.50 mol% when the amount of the ceramic that is a main component of the dielectric layer is assumed to be 100 mol% and Si is converted into SiO2.

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