Dielectric composition and electronic component

Abstract

The invention provides a dielectric composition which has good relative dielectric constant and dielectric loss tangent and shows high AC withstand voltage in a wide temperature range. The dielectric composition contains, as a main component, a composite oxide containing Ba, Zr, and Ta, with respect to 100 mol% of the composite oxide, 48.5 mol% to 53.2 mol% of Ba in terms of BaO, 3.5 mol% to 25.2 mol% of Zr in terms of ZrO2, 26.2 mol% to 48.0 mol% of Ta in terms of Ta2O5, and the balance of the composite oxide. At least a part of the crystal particles comprising the composite oxide have a first region containing Ta and a second region containing Ta and having a lower Ta content ratio than the first region, the second region surrounds a part or all of the periphery of the first region, and the Ta content ratio in the first region is C1Ta mol% in terms of Ta2O5, and the Ta content ratio in the second region is C1Ta mol% in terms of Ta2O5. When the content ratio of Ta in the second region is represented by C2Ta mol% in terms of Ta2O5, C1Ta-C2Ta > = 0.5 mol%.

Description

Technical Field

[0001] The present invention relates to a dielectric composition and an electronic component including a dielectric layer composed of the dielectric composition. Background Art

[0002] Patent Document 1 describes an invention related to a dielectric composition containing Sr and Ta as main components.

[0003] Patent Document 2 describes an invention relating to a dielectric ceramic composition comprising a first component and a second component containing a Mn oxide, wherein the first component contains, as essential components, at least one selected from Ca oxides, Sr oxides, and Ba oxides; at least one selected from Ti oxides and Zr oxides; and at least one selected from Nb oxides and Ta oxides.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2022-111642

[0007] Patent Document 2: International Publication No. 2018 / 074290 Summary of the Invention

[0008] Technical problem to be solved by the invention

[0009] An object of the present invention is to provide a dielectric composition having a favorable relative dielectric constant and dielectric loss tangent over a wide temperature range and exhibiting a high AC withstand voltage, and an electronic component including a dielectric layer formed of the dielectric composition.

[0010] Technical solutions to technical problems

[0011] In order to achieve the above-mentioned object, the present invention has the following aspects.

[0012] [1] A dielectric composition comprising a composite oxide containing barium, zirconium, and tantalum as a main component,

[0013] In the composite oxide, barium is converted to BaO, zirconium is converted to ZrO2, and tantalum is converted to Ta2O5. When the total of BaO, ZrO2 and Ta2O5 is set to 100 mol%,

[0014] The content of barium is 48.5 mol% or more and 53.2 mol% or less in terms of BaO.

[0015] The zirconium content is 3.5 mol% or more and 25.2 mol% or less in terms of ZrO2.

[0016] The tantalum content is 26.2 mol% or more and 48.0 mol% or less in terms of Ta2O5.

[0017] The dielectric composition has crystal particles composed of a complex oxide as a main phase,

[0018] At least a portion of the crystal grains is a crystal grain having a first region containing tantalum and a second region containing tantalum with a tantalum content ratio lower than that of the first region.

[0019] The second area surrounds part or all of the first area.

[0020] The content ratio of tantalum in the first region is converted to Ta2O5 and is defined as C1 Ta (mol%), the tantalum content in the second region is converted to C2 Ta (mol%), C1 Ta and C2 Ta Satisfy C1 Ta -C2 Ta ≥0.5 (mol %).

[0021] [2] The dielectric composition according to [1], wherein the dielectric composition satisfying C1 Ta -C2 Ta When the number ratio of the crystal particles having the relationship of ≥0.5 (mol %) to the total number of crystal particles composed of the composite oxide is α, α ≥ 25%.

[0022] [3] An electronic component comprising a dielectric layer formed by laminating the dielectric composition according to [1] or [2], and an electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a cross-sectional view of a multilayer capacitor according to one embodiment of the present invention.

[0024] Figure 2 It is a schematic diagram showing the existence state of the first region and the second region in the dielectric composition.

[0025] Figure 3 It is used to illustrate the calculation of C1 Ta and C2 Ta Schematic diagram of the method.

[0026] Figure 4 Observation images of crystal particles obtained by line analysis of tantalum in an example of the present invention are shown.

[0027] Figure 5 express Figure 4 Line analysis results for tantalum on the line segment shown.

[0028] Explanation of symbols:

[0029] 1…Multilayer capacitor

[0030] 10…Component body

[0031] 2…Dielectric composition

[0032] 2a…Crystalline particles

[0033] 21…First Area

[0034] 22…Second Area

[0035] 3…Internal electrode layer

[0036] 4…External electrodes DETAILED DESCRIPTION

[0037] Hereinafter, the present invention will be described in detail based on specific embodiments in the following order.

[0038] 1. Electronic components

[0039] 1.1. Overall Structure of Multilayer Capacitors

[0040] 1.2. Dielectric layer

[0041] 1.3. Internal electrode layer

[0042] 1.4. External electrodes

[0043] 2. Dielectric composition

[0044] 2.1. Composite oxides

[0045] 2.2. Main phase

[0046] 3. Method for manufacturing multilayer capacitors

[0047] 4. Summary of this Implementation

[0048] 5. Modifications

[0049] (1. Electronic components)

[0050] The electronic component of this embodiment is an electronic component having a dielectric layer and electrodes that exhibit predetermined dielectric properties. Such an electronic component may have a structure in which a single dielectric layer is sandwiched between electrodes, or may be a stacked electronic component in which multiple dielectric layers are stacked with electrodes interposed therebetween. In this embodiment, a stacked capacitor is described as an example of a stacked electronic component.

[0051] (1.1. Overall Structure of Multilayer Capacitor)

[0052] Figure 1 A multilayer capacitor 1 is shown as an example of a multilayer electronic component according to this embodiment. Multilayer capacitor 1 includes a component body 10 having a structure in which dielectric layers 2 and internal electrode layers 3 are alternately stacked. A pair of external electrodes 4 are formed at both ends of component body 10, each electrically conductive to the internal electrode layers 3 alternately arranged within component body 10. The shape of component body 10 is not particularly limited, but is typically a rectangular parallelepiped. Furthermore, the dimensions of component body 10 are also not particularly limited and can be appropriately sized depending on the intended use.

[0053] (1.2. Dielectric layer)

[0054] The dielectric layer 2 is formed by forming a dielectric composition described later into a layer. As a result, the multilayer capacitor including the dielectric layer 2 can exhibit a high dielectric breakdown voltage under high electric field strength even in a high temperature region.

[0055] The thickness of each layer of the dielectric layer 2 (interlayer thickness) is not particularly limited and can be arbitrarily set according to the desired characteristics or application. Generally, the interlayer thickness is preferably 100 μm or less, and more preferably 30 μm or less. In addition, the number of stacked layers of the dielectric layer 2 can also be arbitrarily set. For example, in the case of a stacked capacitor used for characteristic evaluation, the number of stacked layers can be several layers. On the other hand, in the case of a stacked capacitor assembled into a specific product, the number of stacked layers can be, for example, 20 or more.

[0056] (1.3. Internal Electrode Layer)

[0057] In this embodiment, if Figure 1 As shown, the internal electrode layers 3 are stacked so that their ends are exposed on a pair of opposing surfaces of the element body 10. Specifically, the internal electrode layers 3 are arranged so that their ends are exposed on the same surface within a pair of opposing surfaces of the element body 10.

[0058] The internal electrode layer 3 is made of a conductive material. As the conductive material, for example, a conductive metal can be exemplified. In the present embodiment, examples of the metal used as the conductive material include palladium (Pd), platinum (Pt), silver-palladium (Ag-Pd) alloy, nickel (Ni), nickel-based alloys, copper (Cu), copper-based alloys, etc. In addition, nickel, nickel-based alloys, copper, or copper-based alloys may contain various trace components such as phosphorus (P) and / or sulfur (S) in an amount of approximately 0.1% by mass or less. In addition, the internal electrode layer 3 can also be formed using a commercially available electrode paste. The thickness of the internal electrode layer 3 can be appropriately determined according to the intended use, etc.

[0059] (1.4. External Electrode)

[0060] The external electrodes 4 are made of a conductive material. For example, known conductive materials such as nickel (Ni), copper (Cu), tin (Sn), silver (Ag), palladium (Pd), platinum (Pt), gold (Au), alloys thereof, and conductive resins can be used as the external electrodes 4. The thickness of the external electrodes 4 can be appropriately determined depending on the intended use, etc.

[0061] (2. Dielectric composition)

[0062] In this embodiment, the dielectric composition contains a composite oxide comprising at least barium (Ba), zirconium (Zr), and tantalum (Ta). The composite oxide is a main component comprising more than 50 mol% of the dielectric composition (100 mol%). In this embodiment, the composite oxide preferably comprises 75 mol% or more, and more preferably 90 mol% or more, of the dielectric composition (100 mol%).

[0063] The composite oxide preferably has a tungsten bronze crystal structure. When the composite oxide has a tungsten bronze crystal structure, oxygen octahedra formed by hexacoordinated oxygen on the tetravalent element (zirconium) occupying the B site and oxygen octahedra formed by hexacoordinated oxygen on the pentavalent element (tantalum) occupying the B site form a three-dimensional network that shares vertices. Furthermore, the divalent element (barium) occupying the A site is located in the gaps between these oxygen octahedra.

[0064] (2.1. Composite oxides)

[0065] In this embodiment, in the composite oxide, when the total of BaO, ZrO2, and Ta2O5 is 100 mol%, the barium content is 48.5 mol% to 53.2 mol% when converted to BaO, the zirconium content is 3.5 mol% to 25.2 mol% when converted to ZrO2, and the tantalum content is 26.2 mol% to 48.0 mol% when converted to Ta2O5. Since the content ratios of each element are within the above ranges, the composite oxide is easily sintered. As a result, the resulting dielectric composition has low power loss (dielectric loss tangent) and improved AC withstand voltage. In addition, heterogeneity is less likely to occur.

[0066] The barium content, calculated as BaO, may be 50.2 mol% to 53.2 mol%. The zirconium content, calculated as ZrO2, may be 4.0 mol% to 20.0 mol%, or 4.0 mol% to 15.4 mol%. The tantalum content, calculated as Ta2O5, may be 26.8 mol% to 45.8 mol%, or 31.4 mol% to 45.8 mol%.

[0067] (2.2. Main Phase)

[0068] The dielectric composition of this embodiment is a polycrystalline body, and a plurality of crystal grains composed of the composite oxide are bonded via grain boundaries. Therefore, the crystal grains composed of the composite oxide constitute the main phase of the dielectric composition of this embodiment.

[0069] The crystal grains constituting the main phase generally have substantially the same composition in all regions within the grain. However, in this embodiment, at least some of the crystal grains constituting the main phase are crystal grains having first and second regions with different tantalum content ratios within the grain.

[0070] That is, while the crystal grain as a whole has a predetermined composition, the tantalum content in the first region differs from the tantalum content in the second region. Specifically, the tantalum content in the first region is greater than the tantalum content in the second region. Furthermore, the tantalum content in the first region is approximately constant, and the tantalum content in the second region is also approximately constant. That is, in this crystal grain, the variation in the tantalum content near the interface between the first and second regions is greater than the variation in the tantalum content in the first region and the variation in the tantalum content in the second region.

[0071] In this embodiment, it is preferable that the change in the tantalum content ratio near the interface between the first region and the second region is large. Specifically, when the tantalum content ratio in the first region is converted to C1 Ta (mol%), the tantalum content in the second region is converted to C2 Ta (mol%), C1 Ta and C2 Ta Satisfy C1 Ta -C2 Ta Thus, when the tantalum content changes greatly, the difference between the composition constituting the first region and the composition constituting the second region becomes clear, and both the characteristics shown in the first region and the characteristics shown in the second region can be fully enjoyed.

[0072] In addition, in this embodiment, if Figure 2As shown, a crystal grain 2a having a first region and a second region has a structure in which the second region 22 surrounds part or all of the perimeter of the first region 21. In other words, the first region forms the so-called core, and the second region forms the so-called shell. The second region 22 preferably surrounds at least 70% of the perimeter of the first region 21, and more preferably surrounds 100% of the perimeter of the first region 21, that is, surrounds the entire perimeter of the first region 21. Multiple first regions may exist in a crystal grain, as long as they are surrounded by second regions.

[0073] By having the composite oxide having the above-mentioned composition, the tantalum content ratio satisfying the above-mentioned relationship, and the structures of the first region and the second region being the above-mentioned structures, a dielectric composition is obtained that has good relative dielectric constant and dielectric loss tangent within a wide temperature range (for example, -55 to 150°C), and a high AC voltage value (AC withstand voltage) at which dielectric breakdown of crystal particles occurs when an AC voltage is applied.

[0074] Such characteristic is thought to be because, owing to the shell portion where electric field is concentrated when voltage is applied, there is the second region where resistance is higher than the first region, so as the AC withstand voltage of the entire crystalline particle becomes higher. In addition, it is thought that the first region has improved the sintering property of the second region of difficult sintering because of sintering property higher than the second region, so the entire crystalline particle becomes easy to sinter, and the pores (holes) formed due to insufficient sintering are reduced. As a result, it is thought that power loss (dielectric loss tangent) can be reduced while maintaining a high dielectric constant.

[0075] C1 Ta -C2 Ta It may be 2.0 mol% or more, 5.2 mol% or more, or 10.0 mol% or more. Ta -C2 Ta The upper limit value is, for example, 40.0 mol %.

[0076] In this embodiment, when satisfying C1 Ta -C2 Ta When the ratio of the number of crystal particles having a relationship of ≥0.5 (mol %) to the total number of crystal particles composed of the composite oxide is α, preferably α ≥ 25%. When α is within the above range, the AC withstand voltage tends to be further improved.

[0077] α may be 30.0% or more.

[0078] In a dielectric composition, a method for determining a crystal particle having a first region and a second region, and measuring C1 in the first region Ta and C2 in the second region Ta The method can be exemplified as follows.

[0079] Using a scanning transmission electron microscope (STEM), it is possible to distinguish the crystal grains that constitute the main phase of the dielectric composition and the grain boundaries between the crystal grains. Each crystal grain is observed at a magnification that allows for identification, and the number of crystal grains within the observation field is determined and counted. The magnification can be appropriately determined based on the particle size of the crystal grains, and can be, for example, approximately 10,000 to 1,000,000 times.

[0080] Next, in the same observation field, tantalum is mapped and analyzed using an energy dispersive X-ray spectrometer (EDS) attached to the STEM. In the tantalum mapping image obtained by the mapping analysis, the area composed of pixels with high brightness is the area with a high tantalum content, and the area composed of pixels with low brightness is the area with a low tantalum content. The area with a high tantalum content and the area with a low tantalum content can also be distinguished based on the tantalum content calculated from the entire dielectric composition, for example. Therefore, based on the tantalum mapping image, the crystal grains in which the area with a low tantalum content surrounds part or all of the area with a high tantalum content are judged as crystal grains having the first area and the second area.

[0081] Next, a predetermined number of crystal grains having the first region and the second region determined as described above are extracted. The number of extracted grains is, for example, about 5 to 200.

[0082] like Figure 3 As shown, for the extracted crystal grain 2a having the first region and the second region, a line segment L is set that traverses the first region 21 and has the second region 22 as its starting and ending points. EDS is used to perform point analysis at sufficiently close intervals along the length of the set line segment. In this embodiment, for example, point analysis can be performed at intervals of 40 or more equal parts along the set line segment.

[0083] Based on the point analysis results, calculate the Ta2O5 content at each point. Arrange the analyzed points in order from highest to lowest Ta2O5 content. The first five points with the highest Ta2O5 content fall within the first region, so the average of the Ta2O5 content of these five points is used as the Ta2O5 content in the first region. Similarly, the last five points with the lowest Ta2O5 content fall within the second region, so the average of the Ta2O5 content of these five points is used as the Ta2O5 content in the second region.

[0084] The above-mentioned point analysis is performed on each of the extracted crystal particles, and the average value of the content ratio of Ta2O5 in the first region is set as C1. Ta The average value of the content ratio of Ta2O5 in the second region is set as C2 Ta According to the obtained C1Ta and C2 Ta Calculate C1 Ta -C2 Ta .

[0085] According to the number of crystal particles composed of composite oxides in the observation field and C1 Ta -C2 Ta The number of crystal particles with a concentration of 0.5 (mol%) or more is calculated as C1 Ta -C2 Ta The number ratio of crystal particles is 0.5 (mol%) or more, and its value is defined as α. Ta -C2 Ta Calculations based on cross-sectional images of the dielectric composition indicate that even for crystal grains with first and second regions, there may be crystal grains with only the second region in the cross-sectional image. Furthermore, the magnification of the observation field is preferably approximately 10,000 to 200,000 times, and the number of observation fields is preferably approximately 3 to 5.

[0086] The dielectric composition of this embodiment may contain other components in addition to the main component. The other components can be determined based on the desired properties. Examples of other components include Si oxides, V oxides, Mn oxides, and Al oxides. The proportions of these other components can be determined based on the desired properties.

[0087] (3. Method for Manufacturing Multilayer Capacitor)

[0088] Next, Figure 1 An example of a method for manufacturing the multilayer capacitor 1 shown will be described.

[0089] The multilayer capacitor 1 of this embodiment can be manufactured using the same known methods as conventional multilayer capacitors. For example, a method of manufacturing a multilayer capacitor by preparing a green chip using a paste containing a raw material of a dielectric composition and then firing the green chip can be exemplified. The manufacturing method is described in detail below.

[0090] First, a starting material for the dielectric composition is prepared. In this embodiment, the starting material is preferably a powder. As the starting material for the dielectric composition, a calcined powder of the main component constituting the main phase is prepared.

[0091] As the starting material for the calcined powder as the main component, oxides of the metals contained in the composite oxide as the main component, or various compounds that become components of the composite oxide by calcination can be used. Examples of the various compounds include carbonates, oxalates, nitrates, hydroxides, and organometallic compounds.

[0092] For example, barium carbonate powder and zirconium and tantalum oxide powders are prepared, and the average particle size of each powder is, for example, in the range of 0.1 to 1.0 μm.

[0093] First, barium and tantalum raw materials are weighed and mixed so that the molar ratio of barium to tantalum is 1:2. The mixed powder is heat-treated in air at 800-1100°C for 0.5-3.0 hours to produce a composite oxide of barium and tantalum. This composite oxide is represented by the chemical formula BaTa2O6, for example.

[0094] The obtained composite oxide of barium and tantalum is pulverized, and the raw materials of barium, zirconium, and tantalum are added to the pulverized powder so as to obtain the above-mentioned composition and mixed. The mixed powder is heat-treated at 900-1400°C for 0.5-10.0 hours in a reducing atmosphere to obtain a calcined powder of the main component. As a reducing atmosphere, an oxygen partial pressure PO2 of 1.0×10 -8 ~1.0×10 -15 atmosphere within the range of MPa.

[0095] By performing the two-step heat treatment as described above to obtain a calcined powder of the main component, it is easy to obtain crystal particles having a first region and a second region, wherein the tantalum concentration in each region satisfies the above-mentioned relationship.

[0096] The obtained calcined powder of the main component is then pulverized to obtain a raw material powder of the dielectric composition. The raw material powder of the dielectric composition has an average particle size of, for example, 0.5 μm to 2.0 μm.

[0097] When the dielectric composition contains components other than the main component, raw material powders of the other components are also prepared. The raw material powders of the other components may be added to the raw material powder of the main component before calcination, or the raw material powders of the other components may be added to the calcined powder of the main component.

[0098] Next, a paste for making green chips is prepared. The resulting dielectric composition raw material powder, a binder, and a solvent are mixed and applied to form a coating to prepare a dielectric layer paste. Known binders and solvents can be used. The dielectric layer paste may also contain additives such as plasticizers as needed.

[0099] The internal electrode layer paste is obtained by mixing the above-mentioned conductive material raw materials, a binder, and a solvent. Known binders and solvents can be used. The internal electrode layer paste may also contain additives such as common materials and plasticizers as needed.

[0100] The external electrode paste can be prepared in the same manner as the internal electrode layer paste.

[0101] The binder and solvent contents in each of the above-mentioned pastes are not particularly limited; typical contents are sufficient. For example, the binder content can be approximately 1% to 5% by mass, and the solvent content can be approximately 10% to 50% by mass. Furthermore, each paste may contain additives selected from various dispersants, plasticizers, dielectric materials, insulators, and the like, as needed. The total content of these additives is preferably 10% by mass or less.

[0102] As the dispersant, for example, a surfactant-type dispersant or a polymer-type dispersant can be used. As the plasticizer, for example, dioctyl phthalate or dibutyl phthalate can be used.

[0103] Green sheets and internal electrode patterns were formed using the obtained pastes, and these were stacked to obtain green chips.

[0104] Before firing, the green chip is subjected to a debinding treatment. As debinding conditions, the heating rate is preferably set to 5°C / hour to 300°C / hour, the holding temperature is preferably set to 180°C to 500°C, and the temperature holding time is preferably set to 0.5 hours to 24 hours. In addition, the atmosphere is air or a reducing atmosphere. In addition, in the above-mentioned debinding treatment, the atmosphere of the debinding treatment can also be humidified. The method of humidification is arbitrary. For example, a humidifier can be used. In this case, the water temperature is preferably about 5°C to 75°C.

[0105] After the binder removal treatment, the green chip is fired to obtain the component body. As firing conditions, the following conditions can be exemplified. For example, it can be set to a heating rate of 100 to 5000°C / hour, a holding temperature of 1200 to 1450°C, a temperature holding time of 0.5 to 2.0 hours, and a cooling rate of 100 to 5000°C / hour. The atmosphere during firing can be air or a reducing atmosphere. In the case of a reducing atmosphere, it can also be set to an oxygen partial pressure of 10 -2 ~10 -7 Pa atmosphere. A humidified N2 and H2 mixed gas, humidified N2 gas, or the like can also be used as the reducing atmosphere. The humidification method is arbitrary. For example, a humidifier can be used. In this case, the water temperature can be approximately 5°C to 75°C.

[0106] After firing, the obtained component body is annealed as needed. The annealing conditions can be any known conditions. For example, the heating rate can be 100 to 5000°C / hour, the holding temperature can be 850 to 1150°C, the temperature holding time can be 0.5 to 30 hours, and the cooling rate can be 100 to 5000°C / hour. It is preferred that the oxygen partial pressure during annealing is higher than the oxygen partial pressure during firing, and the holding temperature is set to below 1150°C. As the atmosphere gas during annealing, humidified N2 gas, humidified N2 and H2 mixed gas, etc. can also be used. The humidification method is arbitrary. For example, a humidifier can be used. In this case, the water temperature can also be set to about 5°C to 75°C.

[0107] The above-mentioned binder removal treatment, firing and annealing treatment may be performed independently or continuously.

[0108] The dielectric composition constituting the dielectric layer of the component body obtained as described above is the dielectric composition described above. The component body is end-face polished, and an external electrode paste is applied and sintered to form the external electrodes 4. Subsequently, a coating layer is formed on the surface of the external electrodes 4 by plating or the like, as needed.

[0109] In this manner, the multilayer capacitor of this embodiment is manufactured.

[0110] (4. Summary of this embodiment)

[0111] In this embodiment, in a dielectric composition having a composite oxide containing at least barium, zirconium, and tantalum, the composition of the composite oxide is controlled within the above range. Furthermore, at least a portion of the crystal particles composed of the composite oxide has a tantalum content ratio C1 in the first region. Ta The tantalum content ratio C2 in the second region Ta The above relationship is satisfied, and the second region surrounds a portion or all of the first region.

[0112] Thus, owing to the peripheral portion (shell portion) of the crystalline particles that electric field easily concentrates when voltage is applied, the second region of insulation resistance is configured, so it is difficult to produce the dielectric breakdown of crystalline particles. In addition, the composition constituting the first region is compared with the composition constituting the second region, and sinterability is higher, easily densification. The sinterability of the second region connected with the region with such high sinterability also improves, and the second region is close to the grain boundary, and therefore, the pores formed because of sintering deficiency also easily arrive at the grain boundary and are discharged. Therefore, it is difficult to produce the reduction (the reduction of relative dielectric constant, the rising of dielectric loss tangent) of the characteristic caused by sintering deficiency.

[0113] As a result, a dielectric composition is obtained that has a good relative dielectric constant and dielectric loss tangent over a wide temperature range, and a high voltage value (AC withstand voltage) at which dielectric breakdown of the crystalline particles occurs when an AC voltage is applied. That is, by arranging two regions with different compositions in a specific positional relationship within the same particle, it is possible to suppress the unpreferable properties of each of the two regions, and to provide preferred properties with a good balance. The greater the difference in composition between the two regions, the more these properties are improved.

[0114] When the number ratio (α) of crystal particles having the above structure in the crystal particles composed of the above composite oxide is within the above range, the AC withstand voltage is further improved.

[0115] (5. Modification)

[0116] In the above embodiment, the electronic component of this embodiment is described as a multilayer capacitor. However, the electronic component of this embodiment is not limited to a multilayer capacitor, and any electronic component may be used as long as it includes the above-mentioned dielectric composition.

[0117] As mentioned above, although embodiment of this invention was demonstrated, this invention is not limited to the said embodiment, It can also be changed in various aspects within the scope of this invention.

[0118] Example

[0119] Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples. However, the present invention is not limited to the following Examples.

[0120] (Experiment 1)

[0121] First, as starting materials for the main components, powders of BaCO₃, ZrO₂, and Ta₂O₅ were prepared, each with an average particle size of 1.0 μm or less. BaCO₃ and Ta₂O₅ were weighed and mixed to a molar ratio of 1:2 between barium and tantalum. The mixed powders were heat-treated at 900°C for 3 hours in air to produce a composite oxide represented by the chemical formula BaTa₂O₆.

[0122] The obtained composite oxide was pulverized, and BaCO3, ZrO2, and Ta2O5 were added to the pulverized powder to form the composition shown in Table 1, and the mixture was mixed. The mixed powder was heated at 1200°C for 4 hours at an oxygen partial pressure of PO2 of 1.0×10 -10 MPa under the conditions of heat treatment to obtain the main component of the calcined powder.

[0123] The calcined powder of the main component obtained by the above method was crushed to obtain a raw material powder of the dielectric composition. Then, 700g of a solvent was added to 1000g of the raw material powder of the dielectric composition, which was a mixture of toluene + ethanol solution (toluene: ethanol = 50:50 (weight ratio)), a plasticizer (dioctyl phthalate (DOP) (made by J-PLUS CO., LTD.) and a dispersant (MALIALIM AKM-0531 (made by NOF)) in a ratio of 90:6:4 (weight ratio) to obtain a mixture. Next, the obtained mixture was dispersed for 2 hours using a basket mill to prepare a paste for the dielectric layer. In addition, the viscosity of the dielectric layer paste was adjusted to approximately 200cps in all samples. Specifically, the viscosity was adjusted by adding a small amount of toluene + ethanol solution.

[0124] As raw materials for the internal electrode layers, Ni powder with an average particle size of 0.2 μm, Al oxide powder with an average particle size of 0.1 μm or less, and Si oxide powder with an average particle size of 0.1 μm or less were prepared. These powders were weighed and mixed so that the combined Al and Si content relative to Ni was 5% by mass. Subsequently, they were heat treated at a temperature of 1200°C or higher in a humidified mixture of N₂ and H₂. The heat-treated powder was pulverized using a ball mill, etc., to prepare raw material powder for the internal electrode layers with an average particle size of 0.20 μm.

[0125] 100% by mass of the prepared raw material powder for the internal electrode layer, 30% by mass of an organic vehicle (8% by mass of ethyl cellulose resin dissolved in 92% by mass of butyl carbitol), and 8% by mass of butyl carbitol were kneaded using three rolls to form a paste to obtain an internal electrode layer paste.

[0126] The dielectric layer paste is then applied to a PET film to form a green sheet. The thickness of the dried green sheet is 4.2 μm. Next, an internal electrode layer paste is used to print a predetermined pattern of internal electrode layers on the green sheet. The green sheet is then peeled off from the PET film to produce a green sheet with internal electrode layers printed in a predetermined pattern. Multiple green sheets with internal electrode layers printed in a predetermined pattern are then stacked and bonded together under pressure to form a green laminate. The green laminate is then cut into a predetermined shape to produce a green chip.

[0127] Next, the resulting green chip was subjected to a binder removal process, firing, and annealing process to obtain a laminated ceramic fired body. The conditions for the binder removal, firing, and annealing processes are shown below. During the binder removal, firing, and annealing processes, a humidifier was used to humidify the atmosphere.

[0128] (Binder removal treatment)

[0129] Heating rate: 100℃ / hour

[0130] Maintaining temperature: 400°C

[0131] Temperature holding time: 8.0 hours

[0132] Atmosphere gas: humidified N2 and H2 mixed gas

[0133] (Firing)

[0134] Heating rate: 500℃ / hour

[0135] Firing temperature: 1200℃~1450℃

[0136] Temperature holding time: 2.0 hours

[0137] Cooling speed: 100℃ / hour

[0138] Atmosphere gas: humidified N2 and H2 mixed gas

[0139] Oxygen partial pressure: 10 -2 ~10 -7 Pa

[0140] (Annealing treatment)

[0141] Heating rate: 200℃ / hour

[0142] Maintaining temperature: 800℃~1000℃

[0143] Temperature holding time: 2.0 hours

[0144] Cooling rate: 200℃ / hour

[0145] Atmosphere gas: humidified N2 gas

[0146] Oxygen partial pressure: 10 -1 Pa

[0147] Composition analysis of the dielectric layer (dielectric composition) of each sintered body obtained was performed using ICP emission spectroscopy, and it was confirmed that the analyzed composition was the same as the composition described in Table 1. Furthermore, X-ray diffraction measurement of the dielectric composition confirmed that the dielectric composition had a tungsten bronze-type crystal structure based on the obtained X-ray diffraction pattern.

[0148] After the end faces of the obtained sintered body were polished by sandblasting, an In-Ga eutectic alloy was applied as an external electrode to obtain a Figure 1The multilayer capacitor samples shown have the same shape as the multilayer capacitors shown. The dimensions of the obtained multilayer capacitor samples are 3.2 mm × 1.6 mm × 1.2 mm, the thickness of the dielectric layer is 3 μm, the thickness of the internal electrode layer is 1.5 μm, and the number of dielectric layers sandwiched by the internal electrode layers is 10.

[0149] A cross-section of the dielectric layer (dielectric composition) along the stacking direction of each obtained multilayer ceramic capacitor sample was polished and observed at 100,000x magnification using a scanning transmission electron microscope (STEM) to identify the crystal grains that constitute the main phase. Tantalum mapping analysis was then performed using an energy-dispersive X-ray spectrometer (EDS) attached to the STEM. Based on the mapping analysis results, crystal grains in which a region with a low tantalum content surrounds part or all of a region with a high tantalum content were considered to have first and second regions.

[0150] Next, 10 crystal particles with a first region and a second region were extracted. A straight line was set on the crystal particle, crossing the first region and with its starting point and end point located in the second region. The set straight line was divided into 41 equal intervals and point analysis was performed using EDS. In each particle, the average value of the first 5 points with a high Ta2O5 content ratio was taken as the Ta2O5 content ratio in the first region, and the average value of the last 5 points with a low Ta2O5 content ratio was taken as the Ta2O5 content ratio in the second region. Based on the point analysis results of the 10 particles, the average value of the Ta2O5 content ratio in the first region was calculated as C1 Ta Similarly, the average value of the content ratio of Ta2O5 in the second region is calculated as C2 Ta According to the obtained C1 Ta and C2 Ta , calculate C1 Ta -C2 Ta The results are shown in Table 1.

[0151] Next, according to the number of all crystal particles in the observation field and C1 Ta -C2 Ta The number of crystal particles with a concentration of 0.5 (mol%) or more is used to calculate C1 Ta -C2 Ta The results are shown in Table 1.

[0152] Figure 4 This is a STEM observation image of a crystal particle obtained by performing line analysis of tantalum in sample number 17. Figure 4 The crystal grain shown has two regions due to the contrast difference, and it can be confirmed that one region is surrounded by the other region.

[0153] Figure 5 express Figure 4 The analysis results of the tantalum points on the line segment shown. It can be confirmed that the tantalum content ratio is high in the enclosed area and low in the enclosed area. In other words, it can be confirmed that Figure 4 A first region of the crystalline grain is shown surrounded by a second region.

[0154] [Table 1]

[0155]

[0156] The obtained multilayer capacitor samples were measured for relative dielectric constant and dielectric loss tangent in the temperature range of -55 to 150° C., and withstand voltage when AC voltage was applied (AC withstand voltage) by the methods described below.

[0157] (Relative dielectric constant and dielectric loss tangent)

[0158] For the stacked capacitor sample, a digital LCR meter (4284A manufactured by YHP Company) was used in the temperature range of -55 to 150°C, with an input frequency of 1kHz and an input signal level (measurement voltage) of 1Vrms, to measure the electrostatic capacitance and dielectric loss tangent. Then, the relative dielectric constant (unitless) was calculated based on the thickness of the dielectric layer, the effective electrode area, and the electrostatic capacitance obtained in the measurement results. In the temperature range of -55 to 150°C, the smallest relative dielectric constant among the calculated relative dielectric constants was set as the relative dielectric constant of this embodiment. The relative dielectric constant is preferably high. In this embodiment, the sample with a relative dielectric constant of 90 or more was judged to be good. In addition, in the temperature range of -55 to 150°C, the largest dielectric loss tangent among the measured dielectric loss tangents was set as the dielectric loss tangent in this embodiment. The dielectric loss tangent is preferably low. In this embodiment, the sample with a dielectric loss tangent of less than 1% was judged to be good. The results are shown in Table 1.

[0159] (AC withstand voltage)

[0160] An AC voltage was applied to the multilayer ceramic capacitor samples at 25°C. The voltage at which the leakage current exceeded 10 mA was measured. The withstand voltage per unit thickness was calculated by dividing the voltage by the thickness of the dielectric layer. A higher AC withstand voltage is preferred. In this example, samples with an AC withstand voltage of 90 V / μm or greater were considered good. More preferably, samples with an AC withstand voltage of 100 V / μm or greater were considered good. The results are shown in Table 1.

[0161] Table 1 confirms that multilayer capacitor samples containing a dielectric composition having a composition of a composite oxide containing barium, zirconium, and tantalum within the above-mentioned range, and having crystal grains having a first region and a second region in a main phase composed of the composite oxide, wherein the tantalum content ratio in the first region and the second region satisfies the above-mentioned relationship, have excellent relative permittivity and dielectric loss tangent over a wide temperature range, and exhibit higher AC withstand voltage.

Claims

1. A dielectric composition, wherein: The dielectric composition contains a composite oxide containing barium, zirconium and tantalum as a main component, In the composite oxide, barium is converted to BaO, zirconium is converted to ZrO2, and tantalum is converted to Ta2O5. When the total of BaO, ZrO2 and Ta2O5 is set to 100 mol%, The content of barium is 48.5 mol% or more and 53.2 mol% or less in terms of BaO. The zirconium content is 3.5 mol% or more and 25.2 mol% or less in terms of ZrO2. The tantalum content is 26.2 mol% or more and 48.0 mol% or less in terms of Ta2O5. The dielectric composition has crystal particles composed of the composite oxide as a main phase, At least a portion of the crystal grains includes a first region containing tantalum and a second region containing tantalum with a tantalum content ratio lower than that of the first region. The second area surrounds a part or all of the first area. The content ratio of tantalum in the first region is converted to Ta2O5 and is defined as C1 Ta The content ratio of tantalum in the second region is converted to Ta2O5 as C2 Ta When C1 Ta and C2 Ta Satisfy C1 Ta -C2 Ta ≥0.5 mol%, where C1 Ta 、C2 Ta The unit is mole %.

2. The dielectric composition according to claim 1, wherein In will satisfy C1 Ta -C2 Ta When the number ratio of the crystal particles having a relationship of ≥0.5 mol % to the total number of crystal particles composed of the composite oxide is α, α ≥ 25%.

3. An electronic component, wherein: The present invention comprises a dielectric layer formed by forming the dielectric composition according to claim 1 or 2 into a layer, and an electrode.

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