Dielectric composition and electronic component

Abstract

To provide a dielectric composition that exhibits a good relative dielectric constant and dielectric loss tangent over a wide temperature range and shows high AC withstand voltage.SOLUTION: A dielectric composition comprises, as a main component, a composite oxide including Ba, Zr, and Ta, wherein: in 100 mol% of the composite oxide, Ba is contained in an amount of 48.5 mol% or more and 53.2 mol% or less in terms of BaO, Zr is contained in an amount of 3.5 mol% or more and 25.2 mol% or less in terms of ZrO2, and Ta is contained in an amount of 26.2 mol% or more and 48.0 mol% or less in terms of Ta2O5; at least a part of crystal particles composed of the composite oxide includes a first region containing Ta and a second region containing Ta and having a lower Ta content than the first region; and the second region surrounds a part or all of the periphery of the first region. When the Ta content of the first region is defined as C1Ta mol% in terms of Ta2O5 and the Ta content of the second region is defined as C2Ta mol% in terms of Ta2O5, the dielectric composition satisfies the condition C1Ta-C2Ta≥0.5 mol%.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Patent Document 1 describes an invention relating 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 containing, as essential components, one or more selected from an oxide of Ca, an oxide of Sr, and an oxide of Ba, one or more selected from an oxide of Ti and an oxide of Zr, and at least one selected from an oxide of Nb and an oxide of Ta, and a second component containing an oxide of Mn. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-111642 [Patent Document 2] International Publication No. 2018 / 074290 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a dielectric composition that has a good relative permittivity and dielectric loss tangent over a wide temperature range and further exhibits a high AC withstand voltage, and an electronic component including a dielectric layer formed of the dielectric composition in a layered form. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention is embodied as follows.

[0007] [1] A dielectric composition containing a composite oxide containing barium, zirconium, and tantalum as a main component, In the composite oxide, when barium is converted to BaO, zirconium is converted to ZrO2, and tantalum is converted to Ta2O5, and the total of BaO, ZrO2, and Ta2O5 is taken as 100 mol%, The barium content 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, as a main phase, crystal grains composed of a composite oxide, at least some of the crystal particles are crystal particles having a first region containing tantalum and a second region containing tantalum and having a lower tantalum content than the tantalum content in the first region, The second region surrounds a part or all of the periphery of the first region, The tantalum content in the first region is calculated as C1 Ta (mol%), and the content of tantalum in the second region is C2 Ta (mol%), C1 Ta and C2 Ta But C1 Ta -C2 Ta ≧0.5 (mol %).

[0008] [2] C1 Ta -C2 Ta The dielectric composition according to [1], wherein α is a ratio of the number of crystal particles satisfying the relationship of α≧0.5 (mol %).

[0009] [3] An electronic component comprising a dielectric layer in which the dielectric composition according to [1] or [2] is formed in a layered form, and an electrode. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of a multilayer capacitor according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the state in which the first region and the second region exist in the dielectric composition. [Figure 3] FIG. 3 is a schematic diagram for explaining a method for calculating C1Ta and C2Ta. [Figure 4] FIG. 4 shows an observed image of crystal particles obtained by line analysis of tantalum in an example of the present invention. [Figure 5] FIG. 5 shows the results of a line analysis of tantalum on the line segment shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below based on specific embodiments in the following order. 1. Electronic Components 1.1. Overall structure of multilayer capacitor 1.2.Dielectric Layer 1.3. Internal electrode layer 1.4.External electrode 2. Dielectric composition 2.1. Complex oxides 2.2. Main phase 3. Manufacturing method of multilayer capacitors 4. Summary of this embodiment 5. Variations

[0012] (1. Electronic Components) The electronic component according to this embodiment is an electronic component having a dielectric layer exhibiting predetermined dielectric properties and electrodes. Such an electronic component may be an electronic component having a configuration in which one dielectric layer is sandwiched between electrodes, or may be a multilayer electronic component in which multiple dielectric layers are stacked with electrode layers interposed therebetween. In this embodiment, a multilayer capacitor will be described as an example of a multilayer electronic component.

[0013] (1.1. Overall structure of multilayer capacitor) FIG. 1 shows a multilayer capacitor 1 as an example of a multilayer electronic component according to this embodiment. The multilayer capacitor 1 has an element body 10 configured with dielectric layers 2 and internal electrode layers 3 alternately stacked. A pair of external electrodes 4 is formed on both ends of the element body 10, and is electrically connected to the internal electrode layers 3 alternately arranged inside the element body 10. There are no particular restrictions on the shape of the element body 10, but it is usually a rectangular parallelepiped. There are also no particular restrictions on the dimensions of the element body 10, and the dimensions may be appropriate depending on the application.

[0014] (1.2. Dielectric Layer) The dielectric layer 2 is a layer of a dielectric composition described below. As a result, a multilayer capacitor having the dielectric layer 2 can exhibit a high breakdown voltage under a high electric field strength even in a high temperature range.

[0015] The thickness of each dielectric layer 2 (interlayer thickness) is not particularly limited and can be set arbitrarily depending on the desired properties, applications, etc. Usually, the interlayer thickness is preferably 100 μm or less, more preferably 30 μm or less. The number of laminated layers of the dielectric layers 2 can also be set arbitrarily. For example, in the case of a multilayer capacitor used for property evaluation, the number of laminated layers may be on the order of several layers. On the other hand, in the case of a multilayer capacitor to be incorporated into a specific product, the number of laminated layers may be, for example, 20 or more.

[0016] (1.3. Internal electrode layer) 1, in this embodiment, 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 the ends of every other layer are exposed on the same surface of the pair of opposing surfaces of the element body 10.

[0017] The internal electrode layers 3 are made of a conductive material. Examples of the conductive material include conductive metals. In this embodiment, examples of metals used as the conductive material include palladium (Pd), platinum (Pt), silver-palladium (Ag-Pd) alloys, nickel (Ni), nickel-based alloys, copper (Cu), and copper-based alloys. Note that nickel, nickel-based alloys, copper, or copper-based alloys may contain trace components such as phosphorus (P) and / or sulfur (S) in an amount of about 0.1 mass % or less. The internal electrode layers 3 may also be formed using a commercially available electrode paste. The thickness of the internal electrode layers 3 may be determined appropriately depending on the application, etc.

[0018] (1.4.External electrode) The external electrodes 4 are made of a conductive material. Known conductive materials such as nickel (Ni), copper (Cu), tin (Sn), silver (Ag), palladium (Pd), platinum (Pt), gold (Au), alloys of these, conductive resins, etc. may be used as the external electrodes 4. The thickness of the external electrodes 4 may be determined appropriately depending on the application, etc.

[0019] (2. Dielectric Composition) In this embodiment, the dielectric composition contains a composite oxide containing at least barium (Ba), zirconium (Zr), and tantalum (Ta). The composite oxide is a main component that accounts for more than 50 mol% of the dielectric composition (100 mol%). In this embodiment, the composite oxide accounts for preferably 75 mol% or more, and more preferably 90 mol% or more of the dielectric composition (100 mol%).

[0020] The composite oxide preferably has a tungsten bronze crystal structure. When the composite oxide has a tungsten bronze crystal structure, an oxygen octahedron formed by hexacoordinated oxygen to a tetravalent element (zirconium) occupying the B site and an oxygen octahedron formed by hexacoordinated oxygen to a pentavalent element (tantalum) occupying the B site share their vertices to form a three-dimensional network. Furthermore, a divalent element (barium) occupying the A site is located in the gaps between these oxygen octahedra.

[0021] (2.1. Complex oxides) In this embodiment, when the composite oxide is calculated by converting barium to BaO, zirconium to ZrO2, and tantalum to Ta2O5, and the total of BaO, ZrO2, and Ta2O5 is taken as 100 mol%, the barium content is 48.5 mol% to 53.2 mol% in BaO terms, the zirconium content is 3.5 mol% to 25.2 mol% in ZrO2 terms, and the tantalum content is 26.2 mol% to 48.0 mol% in Ta2O5 terms. By ensuring that the content of each element falls within the above ranges, the composite oxide is easily sintered. As a result, the resulting dielectric composition has low electrical energy loss (dielectric dissipation factor) and improved AC withstand voltage. Furthermore, heterogeneous phases are less likely to form.

[0022] The barium content may be 50.2 mol% or more and 53.2 mol% or less in terms of BaO. The zirconium content may be 4.0 mol% or more and 20.0 mol% or less, or 4.0 mol% or more and 15.4 mol% or less, in terms of ZrO. The tantalum content may be 26.8 mol% or more and 45.8 mol% or less, or 31.4 mol% or more and 45.8 mol% or less, in terms of TaO.

[0023] (2.2. Main phase) The dielectric composition according to this embodiment is a polycrystalline body, in which a large number of crystal grains made of the above-mentioned complex oxide are bonded via grain boundaries, and therefore the crystal grains made of the above-mentioned complex oxide constitute the main phase of the dielectric composition according to this embodiment.

[0024] The crystal grains constituting the main phase usually have substantially the same composition in every region within the grain. However, in this embodiment, at least some of the crystal grains constituting the main phase are crystal grains having a first region and a second region within the grain that have different tantalum content ratios.

[0025] That is, the crystal particle as a whole has a predetermined composition, but the tantalum content in the first region is different 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 the crystal particle, the change in the tantalum content near the interface between the first region and the second region is greater than the change in the tantalum content in the first region and the change in the tantalum content in the second region.

[0026] In this embodiment, it is preferable that the change in the content ratio of tantalum in the vicinity of the interface between the first region and the second region is large. Specifically, the content ratio of tantalum in the first region is preferably C1 Ta (mol%), and the content of tantalum in the second region is C2 Ta (mol%), C1 Ta and C2 Ta But C1 Ta -C2 Ta ≧0.5. When the change in the tantalum content is large, the difference between the composition constituting the first region and the composition constituting the second region becomes clear, and it is possible to fully enjoy the properties exhibited by both the first region and the second region.

[0027] Furthermore, in this embodiment, as shown in FIG. 2, the crystal grain 2a having the first region and the second region has a structure in which the second region 22 surrounds part or all of the periphery of the first region 21. That is, the first region forms a so-called core portion, and the second region forms a so-called shell portion. The second region 22 preferably surrounds 70% or more of the periphery of the first region 21, and more preferably surrounds 100% of the periphery of the first region 21, i.e., the entire periphery of the first region 21. A crystal grain may have a plurality of first regions, as long as they are surrounded by the second region.

[0028] When the composite oxide has the above composition, the tantalum content satisfies the above relationship, and the first and second regions have the above structure, a dielectric composition is obtained that has a good relative permittivity and dielectric dissipation factor over a wide temperature range (for example, −55 to 150°C), and a high AC voltage value (AC withstand voltage) at which dielectric breakdown occurs in the crystal particles when an AC voltage is applied.

[0029] These characteristics are thought to be due to the presence of the second region, which has a higher resistance than the first region, in the shell where the electric field concentrates when voltage is applied, resulting in a higher AC withstand voltage for the entire crystal particle. Furthermore, the first region has a higher sinterability than the second region, improving the sinterability of the second region, which is difficult to sinter. This makes it easier for the entire crystal particle to sinter, and is thought to reduce the number of pores that form due to insufficient sintering. As a result, it is thought that it is possible to maintain a high relative permittivity while lowering electrical energy loss (dielectric dissipation factor).

[0030] C1 Ta -C2 Ta may be 2.0 mol% or more, 5.2 mol% or more, or 10.0 mol% or more. Ta -C2 Ta The upper limit is, for example, 40.0 mol %.

[0031] In this embodiment, C1 Ta -C2Ta When the number ratio of crystal grains satisfying the relationship ≧0.5 (mol%) is defined as α, it is preferable that α≧25%. By setting α within the above range, the AC withstand voltage tends to be further improved.

[0032] α may be 30.0% or more.

[0033] A method for identifying a crystalline particle having a first region and a second region in a dielectric composition, and a method for identifying a C1 in the first region Ta and C2 in the second area Ta Examples of methods for measuring the above include the following.

[0034] An arbitrary cross section of the dielectric composition is observed using a scanning transmission electron microscope (STEM) at a magnification that allows the crystal grains constituting the main phase of the dielectric composition and the grain boundaries between the crystal grains to be distinguished and each crystal grain to be distinguished, the crystal grains present within the observation field are identified, and their number is calculated. The magnification may be appropriately determined depending on the crystal grain size, and is, for example, about 10,000 to 1,000,000 times.

[0035] Next, a mapping analysis of tantalum is performed in the same observation field using an energy dispersive X-ray spectrometer (EDS) attached to the STEM. In the tantalum mapping image obtained by the mapping analysis, regions consisting of pixels with high brightness are regions with high tantalum content, and regions consisting of pixels with low brightness are regions with low tantalum content. The regions with high tantalum content and the regions with low tantalum content may be distinguished, for example, based on the tantalum content calculated from the entire dielectric composition. Therefore, from the tantalum mapping image, crystal particles in which the regions with low tantalum content surround part or all of the regions with high tantalum content are determined to be crystal particles having first and second regions.

[0036] Next, a predetermined number of crystal particles having the first and second regions identified as described above are extracted, for example, about 5 to 200 particles.

[0037] As shown in Figure 3, a line segment L is set for the extracted crystal particle 2a having the first and second regions, crossing the first region 21 and having the second region 22 as its starting and ending points. Point analysis is performed using EDS at sufficiently close intervals along the length of the set line segment. In this embodiment, point analysis may be performed at intervals of 40 or more equal parts along the set line segment, for example.

[0038] The Ta2O5 content ratio at each point is calculated from the point analysis results. The points analyzed are sorted in order from highest to lowest Ta2O5 content ratio. The top five points with the highest Ta2O5 content ratios are points within the first region, so the average value of the Ta2O5 content ratios at these five points is taken as the Ta2O5 content ratio in the first region. Similarly, the bottom five points with the lowest Ta2O5 content ratios are points within the second region, so the average value of the Ta2O5 content ratios at these five points is taken as the Ta2O5 content ratio in the second region.

[0039] The above point analysis was performed on each extracted crystal particle, and the average value of the content ratio of Ta2O5 in the first region was calculated as C1 Ta The average content of Ta2O5 in the second region is defined as C2 Ta The obtained C1 Ta and C2 Ta Tokara C1 Ta -C2 Ta Calculate.

[0040] The number of crystalline particles composed of complex oxides present in the observation field and C1 Ta -C2 Ta From the number of crystal grains having a value of 0.5 (mol%) or more, C1 Ta -C2 Ta The number ratio of crystal particles having a value of 0.5 (mol%) or more is calculated, and this value is defined as α. Ta -C2 Tais calculated based on a cross-sectional image of the dielectric composition, so even if a crystal particle has a first region and a second region, there will be crystal particles in which only the second region appears in the cross-sectional image. Note that the magnification of the observation field is preferably about 10,000 to 200,000 times, and the number of observation fields is preferably about 3 to 5.

[0041] The dielectric composition according to this embodiment may contain other components in addition to the main component. The other components may be determined depending on the desired properties. Examples of the other components include oxides of Si, V, Mn, and Al. The content ratio of the other components may be determined depending on the desired properties.

[0042] (3. Manufacturing method of multilayer capacitor) Next, an example of a method for manufacturing the multilayer capacitor 1 shown in FIG. 1 will be described below.

[0043] The multilayer capacitor 1 according to this embodiment can be manufactured by a known method similar to that used for conventional multilayer capacitors. An example of such a known method is a method in which a green chip is produced using a paste containing raw materials for a dielectric composition, and then fired to manufacture a multilayer capacitor. The manufacturing method will now be described in detail.

[0044] First, starting materials for the dielectric composition are prepared. In this embodiment, the starting materials are preferably powders. As the starting materials for the dielectric composition, calcined powders of the main components that constitute the main phase are prepared.

[0045] The starting materials for the calcined powder of the main component can be oxides of the metals contained in the above-mentioned composite oxide, which is the main component, or various compounds that will become components of the composite oxide upon firing. Examples of various compounds include carbonates, oxalates, nitrates, hydroxides, and organometallic compounds.

[0046] For example, barium carbonate powder and zirconium and tantalum oxide powders are prepared, each having an average particle size in the range of 0.1 to 1.0 μm.

[0047] First, the barium raw material and the tantalum raw material are weighed and mixed so that the molar ratio of barium to tantalum is 1:2. The mixed powder is heat-treated at 800-1100°C for 0.5-3.0 hours in air to obtain a composite oxide of barium and tantalum. This composite oxide is expressed, for example, by the chemical formula BaTa2O6.

[0048] The resulting barium and tantalum composite oxide is pulverized, and the barium, zirconium, and tantalum raw materials are added to and mixed with the pulverized powder to achieve the above-mentioned composition. 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. The reducing atmosphere is an oxygen partial pressure PO2 of 1.0 x 10 -8 ~1.0×10 -15 An atmosphere in the range of MPa is preferred.

[0049] By performing the two-stage heat treatment as described above to obtain calcined powder of the main component, it is easy to obtain crystal particles having first and second regions, in which the tantalum concentrations in each region satisfy the above-mentioned relationship.

[0050] Thereafter, the obtained calcined powder of the main component is crushed 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.

[0051] 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, and then calcined, or the raw material powders of the other components may be added to the calcined powder of the main component.

[0052] Next, a paste for producing a green chip is prepared. The obtained dielectric composition raw material powder is kneaded with a binder and a solvent to form a paint, thereby preparing a dielectric layer paste. Known binders and solvents may be used. The dielectric layer paste may also contain additives such as plasticizers, if necessary.

[0053] The internal electrode layer paste is obtained by kneading the above-mentioned raw materials of the conductive material, a binder, and a solvent. Known binders and solvents may be used. The internal electrode layer paste may contain additives such as co-materials and plasticizers as necessary.

[0054] The external electrode paste can be prepared in the same manner as the internal electrode layer paste.

[0055] The binder and solvent contents in each of the above pastes are not particularly limited, and may be ordinary contents. For example, the binder may be about 1% to 5% by mass, and the solvent may be about 10% to 50% by mass. Furthermore, each paste may contain additives selected from various dispersants, plasticizers, dielectric materials, insulating materials, etc., as needed. The total content of these is preferably 10% by mass or less.

[0056] The dispersant may be, for example, a surfactant-type dispersant or a polymer-type dispersant, and the plasticizer may be, for example, dioctyl phthalate or dibutyl phthalate.

[0057] Using each of the obtained pastes, green sheets and internal electrode patterns are formed, and these are laminated to obtain a green chip.

[0058] Before firing, the green chip is subjected to a binder removal treatment. The binder removal conditions are a temperature rise rate of preferably 5°C / hour to 300°C / hour, a holding temperature of preferably 180°C to 500°C, and a temperature holding time of preferably 0.5 hours to 24 hours. The atmosphere is air or a reducing atmosphere. In the binder removal treatment described above, the atmosphere may be humidified. Any method for humidification may be used. For example, a wetter or the like may be used. In this case, the water temperature is preferably about 5°C to 75°C.

[0059] After the binder removal process, the green chip is fired to obtain the element body. The firing conditions are exemplified as follows. For example, the temperature rise rate may be 100 to 5000°C / hour, the holding temperature may be 1200 to 1450°C, the temperature holding time may be 0.5 to 2.0 hours, and the temperature drop rate may be 100 to 5000°C / hour. The firing atmosphere may be air or a reducing atmosphere. In the case of a reducing atmosphere, the oxygen partial pressure may be 10 -2 ~10 -7 The atmosphere may be a reduced atmosphere, for example, a mixed gas of humidified N2 and H2, or humidified N2 gas. Any method for humidification may be used. For example, a wetter may be used. In this case, the water temperature may be about 5°C to 75°C.

[0060] After firing, the obtained element body is annealed as needed. The annealing conditions may be well-known. For example, the temperature may be increased at a rate of 100 to 5000°C / hour, maintained at a temperature of 850 to 1150°C, maintained for 0.5 to 30 hours, and decreased at a rate of 100 to 5000°C / hour. It is preferable that the oxygen partial pressure during annealing is higher than that during firing, and that the maintained temperature is 1150°C or lower. The atmospheric gas used during annealing may be humidified N2 gas or a mixture of humidified N2 and H2 gas. Any method of humidification may be used. For example, a wetter or the like may be used. In this case, the water temperature may be about 5°C to 75°C.

[0061] The above-mentioned binder removal treatment, firing and annealing treatment may be carried out independently or successively.

[0062] The dielectric composition constituting the dielectric layer of the element body obtained as described above is the dielectric composition described above. The end faces of this element body are polished, and an external electrode paste is applied and baked to form the external electrodes 4. Then, if necessary, a coating layer is formed on the surface of the external electrodes 4 by plating or the like.

[0063] In this manner, the multilayer capacitor according to this embodiment is manufactured.

[0064] (4. Summary of this embodiment) In this embodiment, in the dielectric composition having a complex oxide containing at least barium, zirconium, and tantalum, the composition of the complex oxide is controlled to be within the above-mentioned range. Furthermore, at least some of the crystal particles made of the complex oxide have a tantalum content C1 Ta and the tantalum content in the second region C2 Ta The above relationship is satisfied, and the second region surrounds the first region partially or entirely.

[0065] As a result, the second region with high insulation resistance is located at the periphery (shell) of the crystal grains, where the electric field tends to concentrate when a voltage is applied, making the crystal grains less susceptible to dielectric breakdown. Furthermore, the composition of the first region has a higher sinterability and is more easily densified than the composition of the second region. The sinterability of the second region, which is adjacent to this highly sinterable region, is also improved, and because the second region is close to the grain boundary, pores formed due to insufficient sintering are more likely to reach the grain boundary and be expelled. Therefore, deterioration of properties due to insufficient sintering (a decrease in the dielectric constant and an increase in the dielectric loss tangent) is less likely to occur.

[0066] As a result, a dielectric composition is obtained that has a good dielectric constant and dielectric loss tangent over a wide temperature range and a high voltage value (AC withstand voltage) at which the crystal grains break down 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 undesirable characteristics of each of the two regions and achieve a balanced combination of desirable characteristics. The greater the difference in composition between the two regions, the more improved these characteristics become.

[0067] By setting the proportion (α) of the number of crystal particles having the above-mentioned structure among the crystal particles made of the above-mentioned composite oxide within the above-mentioned range, the AC withstand voltage can be further improved.

[0068] (5. Modifications) In the above-described embodiment, the case where the electronic component according to the present embodiment is a multilayer capacitor has been described. However, the electronic component according to the present embodiment is not limited to a multilayer capacitor, and may be any electronic component having the above-described dielectric composition.

[0069] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention. [Example]

[0070] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0071] (Experiment 1) First, powders of BaCO3, ZrO2, and Ta2O5 with an average particle size of 1.0 μm or less were prepared as starting materials for the main components. BaCO3 and Ta2O5 were weighed and mixed so that the molar ratio of barium to tantalum was 1:2. The mixed powders were heat-treated at 900°C for 3 hours in air to obtain a composite oxide with the chemical formula BaTa2O6.

[0072] The obtained composite oxide was pulverized, and BaCO3, ZrO2, and Ta2O5 were added to the pulverized powder and mixed to obtain the composition shown in Table 1. The mixed powder was heated at 1200°C for 4 hours at an oxygen partial pressure of PO2 of 1.0 × 10 -10 The powder was then heat-treated under the condition of 2000 kJ / cm2 and 1000 kJ / cm2, and calcined powder of the main component was obtained.

[0073] The calcined powder of the main component obtained by the above method was crushed to obtain the raw powder of the dielectric composition. Next, 700 g of a solvent consisting of a toluene / ethanol solution (toluene:ethanol = 50:50 (weight ratio)), a plasticizer (dioctyl phthalate (DOP) (manufactured by J-Plus)), and a dispersant (Marialim AKM-0531 (manufactured by NOF Corp.)) mixed in a 90:6:4 (weight ratio) was added to 1,000 g of the raw powder of the dielectric composition to obtain a mixture. The resulting mixture was then dispersed using a basket mill for two hours to prepare a dielectric layer paste. The viscosity of the dielectric layer paste for all samples was adjusted to approximately 200 cps. Specifically, the viscosity was adjusted by adding a small amount of toluene / ethanol solution.

[0074] 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 total of Al and Si was 5 mass% relative to Ni. Then, the mixture was heat-treated at 1200°C or higher in a humidified N2 and H2 mixed gas. The heat-treated powder was crushed using a ball mill or the like to prepare raw material powder for the internal electrode layers with an average particle size of 0.20 μm.

[0075] 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 and formed into a paste using a three-roll mill to obtain a paste for the internal electrode layer.

[0076] The prepared dielectric layer paste was then applied to a PET film to form a green sheet. At this time, the thickness of the green sheet after drying was adjusted to 4.2 μm. Next, a predetermined pattern of internal electrode layers was printed on the green sheet using the internal electrode layer paste. The green sheet was then peeled off from the PET film to produce a green sheet on which the internal electrode layers were printed in the predetermined pattern. Next, multiple green sheets on which the internal electrode layers were printed in the predetermined pattern were stacked and pressure-bonded to form a green laminate. Furthermore, the green laminate was cut into a predetermined shape to obtain a green chip.

[0077] The green chip was then subjected to binder removal, firing, and annealing to obtain a multilayer ceramic fired body. The conditions for the binder removal, firing, and annealing were as follows. A wetter was used to humidify the atmospheric gas during the binder removal, firing, and annealing processes.

[0078] (Debinding process) Heating rate: 100°C / hour Holding temperature: 400℃ Temperature holding time: 8.0 hours Atmospheric gas: Humidified N2 and H2 mixed gas

[0079] (Firing) Heating rate: 500°C / hour Firing temperature: 1200℃~1450℃ Temperature holding time: 2.0 hours Cooling rate: 100℃ / hour Atmospheric gas: Humidified N2 and H2 mixed gas Oxygen partial pressure: 10 -2 ~10 -7 Pa

[0080] (annealing treatment) Heating rate: 200°C / hour Holding temperature: 800℃~1000℃ Temperature holding time: 2.0 hours Cooling rate: 200℃ / hour Atmospheric gas: Humidified N2 gas Oxygen partial pressure: 10 -1 Pa

[0081] The dielectric layers (dielectric compositions) of the obtained fired bodies were subjected to composition analysis using ICP atomic emission spectroscopy, and the analyzed compositions were confirmed to be the same as those listed in Table 1. Furthermore, X-ray diffraction measurements were performed on the dielectric compositions, and the obtained X-ray diffraction patterns confirmed that the dielectric compositions had a tungsten bronze-type crystal structure.

[0082] The end faces of the obtained sintered body were polished by sandblasting, and then an In-Ga eutectic alloy was applied as an external electrode to obtain multilayer capacitor samples with the same shape as the multilayer capacitor shown in Figure 1. The size of the obtained multilayer capacitor samples was 3.2 mm x 1.6 mm x 1.2 mm, with dielectric layer thicknesses of 3 μm, internal electrode layers of 1.5 μm, and 10 dielectric layers sandwiched between the internal electrode layers.

[0083] A cross section of the dielectric layer (dielectric composition) along the lamination direction of each obtained multilayer ceramic capacitor sample was polished, and the polished cross section was observed at 100,000x magnification using a scanning transmission electron microscope (STEM) to identify the crystal grains that make up the main phase. Next, a mapping analysis of tantalum was performed using an energy dispersive X-ray spectrometer (EDS) attached to the STEM. From the mapping analysis results, crystal grains in which a region with a low tantalum content partially or entirely surrounds a region with a high tantalum content were defined as crystal grains having a first region and a second region.

[0084] Next, 10 crystal particles having a first region and a second region were extracted, and a line was drawn on the crystal particle, crossing the first region and with its start and end points located within the second region. Point analysis was then performed using EDS at intervals that divided the drawn line into 41 equal parts. For each particle, the average value of the top 5 points with the highest Ta2O5 content was taken as the Ta2O5 content in the first region, and the average value of the bottom 5 points with the lowest Ta2O5 content was taken as the Ta2O5 content in the second region. From the point analysis results for the 10 particles, the average value of the Ta2O5 content in the first region was calculated, and C1 Ta Similarly, the average content of Ta2O5 in the second region was calculated, and C2 Ta The obtained C1 Ta and C2 Ta So, C1 Ta -C2 Ta The results are shown in Table 1.

[0085] Next, the number of all crystal grains present in the observation field and C1 Ta -C2 Ta From the number of crystal grains having a value of 0.5 (mol%) or more, C1 Ta -C2 Ta The number ratio (α) of crystal particles having a value of 0.5 (mol %) or more was calculated. The results are shown in Table 1.

[0086] Figure 4 is a STEM image of one of the crystal grains subjected to line analysis of tantalum in sample number 17. The crystal grain shown in Figure 4 has two regions due to the contrast difference, and it was confirmed that one region is surrounded by the other region.

[0087] Figure 5 shows the results of a point analysis of tantalum on the line segment shown in Figure 4. It was confirmed that the tantalum content was high in the surrounded region and low in the surrounding region. That is, it was confirmed that the crystal particle shown in Figure 4 has a first region surrounded by a second region.

[0088] [Table 1]

[0089] The obtained multilayer capacitor samples were measured for their relative permittivity and dielectric loss tangent in the temperature range of −55 to 150° C., and their withstand voltage when an AC voltage was applied (AC withstand voltage) by the methods described below.

[0090] (relative permittivity and dielectric loss tangent) The capacitance and dielectric loss tangent of the multilayer capacitor samples were measured using a digital LCR meter (YHP 4284A) at a temperature range of -55 to 150°C by inputting a signal with a frequency of 1 kHz and an input signal level (measurement voltage) of 1 Vrms. The dielectric constant (unitless) was then calculated based on the thickness of the dielectric layer, the effective electrode area, and the capacitance obtained from the measurement. The minimum dielectric constant among the calculated dielectric constants in the temperature range of -55 to 150°C was used as the dielectric constant in this example. A higher dielectric constant is preferable. In this example, samples with a dielectric constant of 90 or more were considered to be good. Furthermore, the maximum dielectric loss tangent among the measured dielectric loss tangents in the temperature range of -55 to 150°C was used as the dielectric loss tangent in this example. A lower dielectric loss tangent is preferable. In this example, samples with a dielectric loss tangent of less than 1% were considered to be good. The results are shown in Table 1.

[0091] (AC withstand voltage) An AC voltage was applied to the multilayer ceramic capacitor sample at 25°C, and the voltage value measured when the leakage current exceeded 10 mA was divided by the thickness of the dielectric layer to determine the AC withstand voltage per unit thickness. A higher AC withstand voltage is preferable. In this example, samples with an AC withstand voltage of 90 V / μm or more were judged to be good. Samples with an AC withstand voltage of 100 V / μm or more are more preferable. The results are shown in Table 1.

[0092] From Table 1, it was confirmed that a multilayer capacitor sample having a dielectric composition having crystal particles in which the composition of a composite oxide containing barium, zirconium, and tantalum is within the above-mentioned range, the main phase composed of the composite oxide has first and second regions, and the content ratios of tantalum in the first and second regions satisfy the above-mentioned relationship, has a good relative dielectric constant and dielectric loss tangent over a wide temperature range, and further exhibits a high AC withstand voltage. [Explanation of symbols]

[0093] 1... Multilayer capacitor 10... Element body 2... Dielectric composition 2a...Crystal particles 21…First area 22…Second area 3… Internal electrode layer 4… External electrode

Claims

1. A dielectric composition containing a composite oxide containing barium, zirconium, and tantalum as a main component, In the composite oxide, barium is converted to BaO and zirconium is converted to ZrO 2 and convert tantalum to Ta 2 O 5 Converted to BaO, ZrO 2 and Ta 2 O 5 When the total is 100 mol%, The barium content is 48.5 mol % or more and 53.2 mol % or less in terms of BaO, The zirconium content is ZrO 2 converted to 3.5 mol % or more and 25.2 mol % or less, The tantalum content is Ta 2 O 5 converted to 26.2 mol % or more and 48.0 mol % or less, the dielectric composition has, as a main phase, crystal grains composed of the composite oxide, at least some of the crystal particles have a first region containing tantalum and a second region containing tantalum and having a lower tantalum content than the tantalum content in the first region, the second region surrounds a part or the whole of the periphery of the first region, The content of tantalum in the first region is Ta 2 O 5 Converted to C1 Ta (mol %), and the content of tantalum in the second region is Ta 2 O 5 Converted to C2 Ta (mol%), C1 Ta and C2 Ta But C1 Ta -C2 Ta ≧0.5 (mol %).

2. C1 relative to the total number of crystal particles composed of the composite oxide Ta -C2 Ta 2. The dielectric composition according to claim 1, wherein when the number ratio of crystal grains satisfying the relationship .gtoreq.0.5 (mol %) is taken as .alpha., .alpha.

3. An electronic component comprising: a dielectric layer in which the dielectric composition according to claim 1 or 2 is formed in a layered form; and an electrode.

Images