JP2021155307A - Dielectric composition and electronic component - Google Patents

Abstract

To provide a dielectric composition exhibiting high dielectric breakdown voltage in a high temperature region, and an electronic component provided with a dielectric layer constituted of the dielectric composition.SOLUTION: A dielectric composition contains a tungsten bronze type composite oxide represented by a chemical formula Ba2LaZr2(Nb1-xTax)3O15+σ as a main component, where 0.35≤x≤0.65. The dielectric composition comprises crystalline particles constituted of the main component as a main phase. At least a part of the crystalline particles are crystalline particles having a first region and a second region having different niobium contents. When the content of niobium in the first region is C1Nb (at.%) and the content of niobium in the second region is C2Nb (at.%), C1Nb and C2Nb satisfy the relationship of 1.20≤C1Nb/C2Nb≤2.10.SELECTED DRAWING: Figure 4

Description

The present invention relates to a dielectric composition and an electronic component comprising a dielectric layer composed of the dielectric composition.

Multilayer ceramic capacitors are installed in many electronic devices due to their high reliability and low cost.

Specific examples of electronic devices include information terminals such as mobile phones, home appliances, and automobile electrical components. Among these, multilayer ceramic capacitors used for automobiles are required to be guaranteed to operate up to higher temperatures than multilayer ceramic capacitors used in home appliances and information terminals. Further, the multilayer ceramic capacitor for removing surge voltage mounted on an inverter circuit using a power semiconductor such as SiC or GaN, which is considered to be used in a high temperature range of 150 ° C. or higher, has a high dielectric breakdown voltage even at around 200 ° C. Is required.

Patent Document 1, by a composition formula _{(1-a) (K 1} -x Na x) (Sr 1-y-z Ba y Ca z) 2 Nb 5 O 15 -a (Ba 1-b Ca b) TiO 3 Dielectric ceramic composition containing a mixed crystal system of a represented tungsten bronze structural compound and a perovskite structural compound as a main component and containing 0.1 to 40 mol of sub-component M with respect to 100 mol of the main component. The thing is disclosed. Further, Patent Document 1 discloses that the log of the resistivity of the dielectric ceramic composition at 175 ° C. is 8.0 or more.

Patent Document 2, the composition formula _{(Na x K 1-x)} (Nb y Ta 1-y) 0.1~10 respect to 100 moles of the main component represented by _{O 3,} Li and F in LiF terms. It is disclosed that the ceramic particles containing 0 mol have a core-shell structure. Further, Patent Document 2 discloses that the insulation resistance at 200 ° C. of the dielectric ceramic composition is about 10 ⁹ Omega.

International Publication No. 2008/155945 Japanese Unexamined Patent Publication No. 2013-35746

However, the dielectric composition described in Patent Document 1 has not been evaluated for insulation characteristics, particularly dielectric breakdown voltage, in a high temperature range of 200 ° C. or higher.

Further, the dielectric porcelain composition described in Patent Document 2 has not been evaluated for insulation characteristics, particularly dielectric breakdown voltage, in a high temperature range of 200 ° C. or higher.

The present invention has been made in view of such an actual situation, and provides an electronic component including a dielectric composition exhibiting a high dielectric breakdown voltage in a high temperature range and a dielectric layer composed of the dielectric composition. With the goal.

In order to achieve the above object, the aspects of the present invention are as follows.
[1] _{A tungsten bronze type composite oxide represented by the chemical formula Ba 2} LaZr ₂ (Nb _1-x Ta _x ) ₃ O _{15 + σ} and satisfying the relationship that x is 0.35 ≦ x ≦ 0.65. A dielectric composition containing as a main component.
The dielectric composition has crystal particles composed of a main component as a main phase, and has
At least a part of the crystal particles are crystal particles having a first region and a second region having different niobium contents.
When the content of niobium in the first region is C1 _Nb (at.%) And the content of niobium in the second region is C2 _Nb (at.%), C1 _Nb and C2 _Nb are 1.20 ≦ C1. It is a dielectric composition that satisfies the relationship of _Nb / C2 _{Nb ≤ 2.10.}

[2] When the tantalum content in the first region is C1 _Ta (at.%), The _{relationship that C1 Nb} and C1 _Ta are 0.98 ≤ C1 _Nb / C1 _Ta ≤ 2.57 is satisfied.
When the tantalum content in the second region is C2 _Ta (at.%), C2 _Nb and C2 _Ta satisfy the relationship of 0.39 ≤ C1 _Nb / C2 _Nb ≤ 1.02 [1]. The described dielectric composition.

[3] When the ratio of the number of crystal particles having the first region and the second region to the total number of crystal particles contained in the dielectric composition is α, the relationship that α is α ≧ 50% is satisfied. The dielectric composition according to [1] or [2].

[4] An electronic component comprising a dielectric layer containing the dielectric composition according to any one of [1] to [3], an electrode, and the like.

According to the present invention, it is possible to provide an electronic component including a dielectric composition exhibiting a high dielectric breakdown voltage in a high temperature range and a dielectric layer composed of the dielectric composition.

FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention. FIG. 2 is a schematic view showing the existence states of the first region and the second region in the dielectric composition. FIG. 3 is a schematic diagram for explaining a method of calculating _{C1 Nb} , C2 _Nb , C1 _Ta, and C2 _Ta. FIG. 4 shows the results of mapping analysis of niobium and tantalum for crystal particles having a first region and a second region in an example of the present invention. FIG. 5 shows the results of point analysis of niobium and tantalum on the line segment shown in FIG.

Hereinafter, the present invention will be described in detail in the following order based on specific embodiments.
1. 1. Multilayer ceramic capacitors 1.1. Overall configuration of multilayer ceramic capacitors 1.2. Dielectric layer 1.3. Internal electrode layer 1.4. External electrode 2. Dielectric composition 2.1. Composite oxide 2.2. Prime Minister 3. Manufacturing method of multilayer ceramic capacitors 4. Summary of this embodiment 5. Modification example

(1. Multilayer ceramic capacitor)
(1.1. Overall configuration of multilayer ceramic capacitor)
A monolithic ceramic capacitor 1 as an example of an electronic component according to this embodiment is shown in FIG. The multilayer ceramic capacitor 1 has an element body 10 having a structure in which a dielectric layer 2 and an internal electrode layer 3 are alternately laminated. A pair of external electrodes 4 that conduct with the internal electrode layers 3 alternately arranged inside the element body 10 are formed at both ends of the element body 10. The shape of the element body 10 is not particularly limited, but is usually a rectangular parallelepiped shape. Further, the size of the element main body 10 is not particularly limited, and may be an appropriate size depending on the application.

(1.2. Dielectric layer)
The dielectric layer 2 is composed of the dielectric composition according to the present embodiment, which will be described later. As a result, the multilayer ceramic capacitor having the dielectric layer 2 can exhibit a high dielectric breakdown voltage under a high electric field strength even in a high temperature range.

The thickness of the dielectric layer 2 per layer (interlayer thickness) is not particularly limited, and can be arbitrarily set according to desired characteristics, applications, and the like. Usually, the interlayer thickness is preferably 100 μm or less, more preferably 30 μm or less. In the present embodiment, the lower limit of the interlayer thickness is not particularly limited, but is, for example, about 0.5 μm. The number of laminated dielectric layers 2 is not particularly limited, but in the present embodiment, it is preferably, for example, 20 or more, and more preferably 50 or more.

(1.3. Internal electrode layer)
In the present embodiment, the internal electrode layers 3 are laminated so that their end faces are alternately exposed on the surfaces of the two opposing ends of the element body 10.

The conductive material contained in the internal electrode layer 3 is not particularly limited. In this embodiment, Ni, Ni-based alloys, Cu or Cu-based alloys are preferable. More preferably, it is a Ni or Ni-based alloy. More preferably, it is a conductive material containing Ni or a Ni-based alloy as the main component of the internal electrode layer 3 and one or more selected from Al, Si, Li, Cr and Fe as subcomponents. The main component of the internal electrode layer 3 refers to a component contained in an amount of 85% by mass or more with respect to the entire internal electrode layer 3.

The internal electrode layer 3 is contained in the internal electrode layer 3 by containing Ni or a Ni-based alloy as a main component and at least one selected from Al, Si, Li, Cr and Fe as a sub component. Ni is less likely to be oxidized. Then, even if the multilayer ceramic capacitor 1 is continuously used at a high temperature of about 250 ° C., the continuity and conductivity of the internal electrode layer 3 are less likely to deteriorate due to the oxidation of the internal electrode layer 3.

The reason why Ni contained in the internal electrode layer 3 is less likely to be oxidized when the internal electrode layer 3 contains one or more selected from Al, Si, Li, Cr and Fe as subcomponents is as follows. .. When the internal electrode layer 3 contains one or more selected from Al, Si, Li, Cr and Fe, the above-mentioned subcomponents and oxygen are mixed before Ni reacts with oxygen in the atmosphere to become NiO. The reaction reacts to form an oxide film of the above-mentioned subcomponent on the surface of Ni contained in the internal electrode 3. As a result, oxygen in the atmosphere cannot react with Ni unless it passes through the oxide film, so that Ni is less likely to be oxidized.

The internal electrode layer 3 may contain various trace components such as P in an amount of about 0.1% by mass or less. Further, the internal electrode layer 3 may be formed by using a commercially available electrode paste. The thickness of the internal electrode layer 3 may be appropriately determined according to the application and the like.

(1.4. External electrode)
The conductive material contained in the external electrode 4 is not particularly limited. For example, known conductive materials such as Ni, Cu, Ag, Pd, Pt, Au, alloys thereof, and conductive resins may be used. The thickness of the external electrode 4 may be appropriately determined according to the application and the like.

(2. Dielectric composition)
The dielectric composition according to the present embodiment contains a composite oxide having a tungsten bronze type crystal structure as a main component. Specifically, the composite oxide is contained in an amount of more than 50 mol, preferably 75 mol or more, in 100 mol of the dielectric composition according to the present embodiment.

(2.1. Composite oxide)
The composite oxide is represented by the chemical formula Ba ₂ LaZr ₂ (Nb _1-x Ta _x ) ₃ O _{15 + σ} . Niobium (Nb) and tantalum (Ta) are pentavalent elements that occupy the B site of the tungsten bronze crystal structure. Niobium and tantalum occupy the B site at a predetermined ratio, and when the total number of niobium and tantalum existing at the B site is 1, the ratio of tantalum is x.

In this embodiment, x satisfies the relationship of 0.35 ≦ x ≦ 0.65. That is, based on the composition (x = 0.5) containing the same number of niobium and tantalum, a slightly niobium-rich composition range and a slightly tantalum-rich composition range are included.

In the tungsten bronze type crystal structure, oxygen is added to the oxygen octahedron formed by 6 coordination of oxygen to the tetravalent element (zirconium) that occupies the B site, and to the pentavalent element (niobium and tantalum) that occupies the B site. The oxygen octahedron formed by 6 coordination forms a three-dimensional network that shares the vertices of each other. Further, a divalent element (barium) and a trivalent element (lanthanum) occupying the A site are located in the gaps between these oxygen octahedrons.

(2.2. Prime Minister)
The dielectric composition according to the present embodiment is a polycrystalline material, and a large number of crystal particles composed of the above-mentioned composite oxides are bonded to each other via grain boundaries. Therefore, the crystal particles composed of the above-mentioned composite oxide form the main phase of the dielectric composition according to the present embodiment.

The crystal particles constituting the main phase usually have almost the same composition in any region within the particles. However, in the present embodiment, at least a part of the crystal particles constituting the main phase are crystal particles having a first region and a second region having different niobium contents in the particles.

That is, the particles as a whole have a composition represented by the above chemical formula, but the content of niobium in the first region and the second region deviates from the composition ratio of niobium represented by the chemical formula. .. Specifically, the first region is a region in which the content of niobium is the same as or higher than the composition ratio (1-x) of niobium in the above chemical formula. On the other hand, the second region is a region in which the content of niobium is lower than the composition ratio (1-x) of niobium in the above chemical formula.

In the present embodiment, the existence state of the first region and the second region in the crystal particles is not particularly limited. For example, as shown in FIG. 2, the crystal particle 21 having the first region and the second region may have a structure in which the second region 21b surrounds a part or the whole of the periphery of the first region 21a. However, the first region 21a may have a structure in which a part or all of the periphery of the second region 21b is surrounded by the first region 21a. Further, a plurality of first regions 21a and / or second regions 21b may exist.

In the present embodiment, when the content of niobium in the first region is C1 _Nb (at.%) And the content of niobium in the second region is C2 _Nb (at.%), C1 _Nb and C2 _Nb are The relationship of 1.20 ≦ C1 _Nb / C2 _Nb ≦ 2.10 is satisfied.

By satisfying the above relationship, it is considered that the movement of oxygen defects inside the crystal particles is suppressed. As a result, the dielectric breakdown voltage tends to improve under high electric field strength.

Further, in the present embodiment, when the tantalum content in the first region is C1 _Ta (at.%) And the tantalum content in the second region is C2 _Ta (at.%), In the first region, , C1 _Nb and C1 _Ta preferably satisfy the relationship of 0.98 ≤ C1 _Nb / C1 _Ta ≤ 2.57, and in the second region, 0.39 ≤ C2 _Nb / C2 _Ta ≤ 1.02. It is preferable to satisfy the relationship. _{That is, the content ratio of C1 Nb} and C1 _Ta is larger than the content ratio of niobium and tantalum (Nb / Ta = 0.35 / 0.65 to 0.65 / 0.35) in the chemical formula, and C2 _Nb The content ratio with C2 _{Ta is preferably small.} By greatly shifting the concentration difference between niobium and tantalum in the first region and the second region from the composition ratio of niobium and tantalum, the breakdown voltage under high electric field strength tends to be further improved.

In the present embodiment, when the ratio of the number of crystal particles having the first region and the second region to the total number of crystal particles contained in the dielectric composition is α, α is α ≧ 50%. It is preferable to be satisfied. By setting α within the above range, the dielectric breakdown voltage under high electric field strength tends to be further improved.

A method for identifying crystal particles having a first region and a second region in a dielectric composition, and a method for measuring _{C1 Nb} and C1 _Ta in the first region and C2 _{Nb and C2 Ta} in the second region. For example, the following method is exemplified.

For any cross section of the dielectric composition, a scanning transmission electron microscope (STEM) can be used to distinguish between the crystal particles that make up the main phase of the dielectric composition and the grain boundaries between the crystal particles. Observe at a discriminable magnification, identify the crystal particles existing in the observation field, and calculate the number of crystal particles. The magnification may be appropriately determined according to the crystal particle size, and is, for example, about 10,000 to 1,000,000 times.

Next, in the same observation field, mapping analysis is performed on niobium and tantalum using the energy dispersive X-ray spectrometer (EDS) attached to STEM. From the mapping analysis results, crystalline particles having a region in which the niobium concentration is the same as or higher than the composition ratio of niobium in the composite oxide and a region having a niobium concentration lower than the composition ratio of niobium in the composite oxide are contained in the same particle. It is specified as crystal particles having a first region and a second region, and the number thereof is calculated. From the number of crystal particles existing in the observation field of view and the number of crystal particles having the first region and the second region, the number ratio of the crystal particles having the first region and the second region is calculated, and the value is α. And. The magnification of the observation field of view is about 10,000 to 200,000 times, and the number of observation fields of view is preferably about 3 to 5.

Next, crystal particles having a predetermined number of first region and second region are extracted. The number to be extracted is, for example, about 5 to 200.

As shown in FIG. 3, with respect to the crystal particles 21 having the extracted first region and the second region, the crystal particles are crossed and passed through the center of gravity of the first region 21a (or the second region 21b) and the grain boundary. The longest line segment LS among the line segments having 30 and the common point P is set. Point analysis is performed using EDS at sufficiently close intervals for the set length of the line segment. In the present embodiment, for example, point analysis may be performed at intervals that divide the set line segment into 100 equal parts.

From the point analysis result, the average value of the niobium concentration at the point belonging to the first region 21a is defined as the niobium concentration in the first region, and the average value of the niobium concentration in the first region calculated for each crystal particle is defined as C1 _Nb . Similarly, C1 _Ta , C2 _Nb and C2 _Ta can be calculated. From the calculated C1 _Nb , C1 _Ta , C2 _Nb and C2 _Ta , C1 _Nb / C2 _Nb , C1 _Nb / C1 _Ta and C2 _Nb / C2 _Ta are calculated.

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

The multilayer ceramic capacitor 1 according to the present embodiment can be manufactured by a known method similar to that of a conventional multilayer ceramic capacitor. As a known method, for example, a method of producing a green chip using a paste containing a raw material of a dielectric composition and firing the green chip to produce a multilayer ceramic capacitor is exemplified. Hereinafter, the manufacturing method will be specifically described.

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

As a starting material for the calcined powder of the main component, oxides of each metal contained in the above-mentioned composite oxide which is the main component, or various compounds which are constituents of the composite oxide by firing may be used. can. Examples of various compounds include carbonates, oxalates, nitrates, hydroxides, organic metal compounds and the like.

For example, barium carbonate powder, lanthanum hydroxide powder, zirconium, niobium and tantalum oxide powder are prepared. The average particle size of each powder is, for example, in the range of 0.1 to 1.0 μm.

First, the raw material of barium and the raw material of niobium or the raw material of tantalum are weighed and mixed so as to have a molar ratio of 5: 4. The mixed powder is heat-treated at 600 to 800 ° C. for 1 to 10 hours under atmospheric conditions to obtain a composite oxide of barium and niobium or tantalum. In the case of a composite oxide of barium and niobium, this composite oxide is represented by, for example, the chemical formula Ba ₅ Nb ₄ O ₁₅ .

The obtained composite oxide of barium and niobium or tantalum is crushed, and the raw materials of barium, lanthanum, zirconium, tantalum and niobium are added to the crushed powder so as to have the above-mentioned composition and mixed. The mixed powder is heat-treated at 800 to 1200 ° C. for 2 to 10 hours under the conditions of a reducing atmosphere to obtain a calcined powder as a main component. As the reducing atmosphere, an atmosphere in which the oxygen partial pressure PO ₂ is in the range of 1.0 × ^{10-8 to 1.0 × 10-15} MPa is preferable.

By performing the two-step heat treatment as described above to obtain the calcined powder of the main component, it has a first region and a second region, and the niobium concentration and the tantalum concentration in each region satisfy the above-mentioned relationship. Crystal particles are easy to obtain.

Then, the obtained calcined powder of the main component is crushed to obtain a raw material powder of the dielectric composition. The average particle size of the dielectric composition raw material powder is, for example, 0.5 μm to 2.0 μm.

Subsequently, a paste for making green chips is prepared. The obtained dielectric composition raw material powder, a binder, and a solvent are kneaded and made into a paint to prepare a paste for a dielectric layer. Known binders and solvents may be used. Further, the paste for the dielectric layer may contain additives such as a plasticizer, if necessary.

The paste for the internal electrode layer is obtained by kneading the above-mentioned raw material of the conductive material, a binder, and a solvent. Known binders and solvents may be used. The paste for the internal electrode layer may contain additives such as a common material and a plasticizer, if necessary.

The paste for the external electrode can be prepared in the same manner as the paste for the internal electrode layer.

The content of the binder and the solvent in each of the above-mentioned pastes is not particularly limited, and may be any normal content. For example, the binder may be about 1% by mass to 5% by mass, and the solvent may be about 10% by mass to 50% by mass. Further, each paste may contain an additive selected from various dispersants, plasticizers, dielectric materials, insulator materials and the like, if necessary. The total content of these is preferably 10% by mass or less.

The type of dispersant is arbitrary. For example, a surfactant-type dispersant and a polymer-type dispersant can be used. The type of plasticizer is arbitrary. For example, dioctyl phthalate and dibutyl phthalate can be used. The type of dielectric material is arbitrary. For example, Ba ₃ ZrNb ₄ O ₁₅ system and Ca ₃ TiTa ₄ O ₁₅ system can be used. The type of insulator material is arbitrary. For example, Al ₂ O ₃ and SiO ₂ can be used.

Each of the obtained pastes is used to form a green sheet and an internal electrode pattern, which are laminated to obtain a green chip.

Before firing, the green chips are debindered. As the binder removal conditions, the temperature rising rate is preferably 5 ° C./hour to 300 ° C./hour, the holding temperature is preferably 400 ° C. to 800 ° C., and the temperature holding time is preferably 0.5 hour to 24 hours. The atmosphere is air or a reducing atmosphere. Further, in the above-mentioned debinder treatment, the atmosphere of the debinder treatment may be humidified. The method of humidification is arbitrary. For example, a wetter or the like may be used. In this case, the water temperature is preferably about 5 ° C to 75 ° C.

After the binder removal treatment, the green chip is fired to obtain an element body. Examples of firing conditions include the following conditions. The firing temperature is preferably 1100 ° C to 1400 ° C. If the firing temperature is too low, the element body will be insufficiently densified. If the firing temperature is too high, the electrode is likely to be interrupted due to abnormal sintering of the internal electrode layer, and the capacity change rate is likely to be deteriorated due to the diffusion of the material constituting the internal electrode layer. Further, the particles composed of the main components may become coarse and the high temperature load life may be shortened.

The rate of temperature rise is preferably 7,000 ° C./hour to 20,000 ° C./hour. By setting the temperature rising rate within the above range, it is easy to obtain crystal particles having a first region and a second region and satisfying the above-mentioned relationship between the niobium concentration and the tantalum concentration in each region. Further, the temperature holding time at the time of firing and the cooling rate after firing are arbitrary. The temperature holding time is preferably 0 in order to control the particle size distribution of the main phase particles composed of the main components after firing within the range of 0.5 μm to 5.0 μm and suppress the volume diffusion between the main phase particles. It is 1 hour to 1.0 hour, and the cooling rate is preferably 100 ° C./hour to 500 ° C./hour.

Further, as the firing atmosphere, it is preferable _{to use a mixed gas of humidified N 2} and H ₂ and have an oxygen partial pressure of ^10-2 to ^{10-6 Pa.} When the internal electrode layer contains Ni, if firing is performed in a state where the oxygen partial pressure is high, Ni may be oxidized and the conductivity may be lowered. However, by adding one or more kinds of sub-components for internal electrodes selected from Al, Si, Li, Cr, and Fe to the conductive material containing Ni as the main component, the oxidation resistance of Ni is improved. Even when firing in an atmosphere with a high oxygen partial pressure, it becomes easy to ensure the conductivity of the internal electrode layer.

After firing, the obtained element body is annealed as necessary. The annealing treatment conditions may be known conditions. For example, it is preferable that the oxygen partial pressure during the annealing treatment is higher than the oxygen partial pressure during firing and the holding temperature is 1100 ° C. or lower.

Further, the binder removal treatment, firing and annealing treatment may be performed independently or continuously.

The dielectric composition constituting the dielectric layer of the device body obtained as described above is the above-mentioned dielectric composition. The end face is polished on the element body, and the paste for the external electrode is applied and baked to form the external electrode 4. Then, if necessary, a coating layer is formed on the surface of the external electrode 4 by plating or the like.

In this way, the monolithic ceramic capacitor according to this embodiment is manufactured.

(4. Summary of this embodiment)
In the present embodiment, in the dielectric composition having a composite oxide having a tungsten bronze crystal structure as a main phase, the composition ratio of niobium and tantalum contained in the composite oxide is within the above range and within the same crystal particles. In the above, crystal particles having a region in which the concentration of niobium is the same as or higher than the composition ratio of niobium (first region) and a region in which the concentration of niobium is low (second region) are formed.

By doing so, the movement of oxygen defects is inhibited in the crystal particles having the first region and the second region. That is, the movement of electrons that accompanies oxygen defects is also inhibited. Therefore, in an electronic component having a dielectric layer composed of such a dielectric composition, an increase in the current flowing through the dielectric layer is suppressed, and heat generation of the dielectric layer itself is suppressed even under a high electric field strength. It is thought that it can be done. As a result, it is considered that pure thermal breakdown, which is a dielectric breakdown mode due to heat generation of the dielectric layer, is less likely to occur, and the dielectric breakdown voltage is improved.

The above effect is further improved by satisfying the above-mentioned relationship between the ratio of the crystal particles having the first region and the second region and the ratio of the niobium concentration and the tantalum concentration in the first region and the second region.

(5. Modification example)
In the above-described embodiment, the case where the electronic component according to the present embodiment is a multilayer ceramic capacitor has been described, but the electronic component according to the present embodiment is not limited to the multilayer ceramic capacitor and has the above-mentioned dielectric composition. Any electronic component may be used.

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

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples.

(Experiment 1)
First, each powder _{of BaCO 3} , La (OH) ₃ , ZrO ₂ , Nb ₂ O ₅ and Ta ₂ O _{5 having} an average particle size of 1.0 μm or less was prepared as a starting material for the main component. BaCO ₃ and Nb ₂ O ₅ were weighed and mixed so that the molar ratio of barium and niobium was 5: 4. The mixed powder was heat-treated at 700 ° C. for 4 hours under atmospheric conditions to obtain a composite oxide represented by the _{chemical formula Ba 5} Nb ₄ O _15.

_{The obtained composite oxide was pulverized, and BaCO 3} , La (OH) ₃ , ZrO ₂ , Nb ₂ O ₅ and Ta ₂ O ₅ were added to the pulverized powder so as to have the composition shown in Table 1. , Mixed. The mixed powder was heat-treated under the conditions of 1150 ° C. for 5 hours and an oxygen partial pressure PO ₂ of 1.0 × 10 ^-10 MPa to obtain a calcined powder as a main component.

The calcined powder of the main component obtained by the above method was crushed to obtain a raw material powder for a dielectric composition. Next, a toluene + ethanol solution (toluene: ethanol = 50: 50 (weight ratio)), a plasticizer (dioctyl phthalate (DOP) (manufactured by J-PLUS)) and dispersion were added to 1000 g of the raw material powder of the dielectric composition. 700 g of a solvent prepared by mixing an agent (Marialim AKM-0531 (manufactured by Nichiyu)) at a ratio of 90: 6: 4 (weight ratio) was added to obtain a mixture. Next, the obtained mixture was dispersed for 2 hours using a basket mill to prepare a paste for a dielectric layer. The viscosity of the dielectric layer paste was adjusted to about 200 cps in all the samples. Specifically, the viscosity was adjusted by adding a small amount of a toluene + ethanol solution.

As raw materials for the internal electrode layer, Ni powder having an average particle size of 0.2 μm, Al oxide powder having an average particle size of 0.1 μm or less, and Si oxide powder having an average particle size of 0.1 μm or less are used. Got ready. These powders were weighed and mixed so that the total of Al and Si was 5% by mass with respect to Ni. Then, it was heat-treated at 1200 ° C. or higher in a mixed gas of _{humidified N 2} and H _2. The powder after the heat treatment was crushed by a ball mill or the like to prepare a raw material powder for an internal electrode layer having an average particle size of 0.20 μm.

100% by mass of the raw material powder of the prepared 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 are kneaded by three rolls. , And a paste for the internal electrode layer was obtained.

Then, the prepared paste for the dielectric layer was applied onto the PET film to form a green sheet. At this time, the thickness of the green sheet after drying was adjusted to 10 μm. Next, a predetermined pattern of the internal electrode layer was printed on the green sheet using the internal electrode layer paste. Then, by peeling the green sheet from the PET film, a green sheet in which the internal electrode layer was printed in a predetermined pattern was produced. Next, a plurality of green sheets on which the internal electrode layer was printed in a predetermined pattern were laminated and pressure-bonded to obtain a green laminate. Further, a green chip was obtained by cutting the green laminate into a predetermined shape.

Next, the obtained green chips were subjected to a binder removal treatment, a firing treatment, and an annealing treatment to obtain a laminated ceramic fired body. The conditions for debinder treatment, firing and annealing are as shown below. In addition, a wetter was used for humidifying the atmospheric gas in the binder removal treatment, firing and annealing treatment.

(Binder removal processing)
Temperature rise rate: 100 ° C / hour Holding temperature: 400 ° C
Temperature holding time: 8.0 hours Atmospheric gas: Mixed gas of _{humidified N 2} and H ₂

(Baking)
Heating rate: 12000 ° C / hour Firing temperature: 1200 ° C to 1400 ° C
Temperature holding time: 0.5 hours Cooling rate: 300 ° C / hour Atmospheric gas: _{Mixed gas of humidified N 2} and H ₂ Oxygen partial pressure: ^10-5 to ^10-9 Pa

(Annealing process)
Holding temperature: 800 ° C to 1000 ° C
Temperature holding time: 2.0 hours Raising and lowering rate: 200 ° C / hour Atmospheric gas: Humidified N ₂ gas

As a result of composition analysis of the dielectric layer (dielectric composition) of each of the obtained laminated ceramic fired bodies using ICP emission spectroscopy, the compositions after the analysis are the compositions shown in Tables 1 and 2. It was confirmed that the composition was substantially the same as that of. Further, as a result of performing X-ray diffraction measurement on the dielectric composition, it was confirmed from the obtained X-ray diffraction pattern that the dielectric composition had a tungsten bronze type crystal structure.

After polishing the end face of the obtained laminated ceramic fired body by sandblasting, an In—Ga eutectic alloy was applied as an external electrode to obtain each laminated ceramic capacitor sample having the same shape as the laminated ceramic capacitor shown in FIG. The sizes of the obtained multilayer ceramic capacitor samples are 3.2 mm × 1.6 mm × 1.2 mm, the thickness of the dielectric layer is 7 μm, the thickness of the internal electrode layer is 2 μm, and the dielectric material sandwiched between the internal electrode layers. The number of layers was 50.

The cross section of the dielectric layer (dielectric composition) along the stacking direction of each of the obtained laminated ceramic capacitor samples is polished, and the polished cross section is observed at a magnification of 100,000 using a scanning transmission electron microscope (STEM). Then, the crystal particles constituting the main phase were identified. Next, mapping analysis was performed on niobium and tantalum using the energy dispersive X-ray spectrometer (EDS) attached to STEM. From the mapping analysis results, the crystal particles having a region having the same or high niobium concentration as the composition ratio of niobium and a region having a low niobium concentration were defined as crystal particles having the first region and the second region. The number ratio (α) of the crystal particles having the first region and the second region was calculated from the number of all crystal particles existing in the observation field of view and the number of crystal particles having the first region and the second region. The results are shown in Table 1.

Subsequently, 10 crystal particles having the first region and the second region are extracted, cross the crystal particles on the crystal particles, pass through the center of gravity of the first region, and end points share with the grain boundaries. A straight line to have was set, and point analysis was performed using EDS at intervals of dividing the set straight line into 100 equal parts. From the point analysis results for 10 particles, the average value of the niobium concentration of the points belonging to the first region was calculated and used as C1 _Nb . C2 _Nb , C1 _Ta and C2 _Ta were calculated by the same method. Further, from the obtained C1 _Nb , C2 _Nb , C1 _Ta and C2 _Ta , C1 _Nb / C2 _Nb , C1 _Nb / C1 _Ta and C2 _Nb / C2 _Ta were calculated. The results are shown in Table 1.

FIG. 4 shows the mapping analysis results of niobium and tantalum for the crystal particles having the first region and the second region existing in the sample number 32. From FIG. 4, it was confirmed that in the crystal particles having the first region and the second region existing in the sample number 32, the two first regions are surrounded by the second region.

Further, FIG. 5 shows the results of point analysis of niobium and tantalum on the line segment shown in FIG. _{For sample number 32, C1 Nb} , C2 _Nb , C1 _Ta and C2 _Ta were calculated based on the results shown in FIG.

With respect to the obtained multilayer ceramic capacitor sample, the relative permittivity, the specific resistance when a DC voltage was applied, the dielectric breakdown voltage and the high temperature load life were measured at 225 ° C. by the methods shown below.

(Relative permittivity at 225 ° C)
A signal having a frequency of 1 kHz and an input signal level (measurement voltage) of 1 Vrms was input to the multilayer ceramic capacitor sample at 225 ° C. with a digital LCR meter (4284A manufactured by YHP), and the capacitance was measured. Then, the relative permittivity (without unit) was calculated based on the thickness of the dielectric layer, the effective electrode area, and the capacitance obtained as a result of the measurement. The higher the relative permittivity, the better. In this example, a sample having a relative permittivity of 200 or more was judged to be good. The results are shown in Table 2.

(Specific resistance when DC voltage is applied at 225 ° C)
The insulation resistance of the multilayer ceramic capacitor sample was measured at 225 ° C. with a digital resistance meter (R8340 manufactured by ADVANTEST) under the conditions of a measurement voltage of 280 V (electric field strength 40 V / μm) and a measurement time of 60 seconds. The specific resistance was calculated from the obtained measured values of insulation resistance, the electrode area of the multilayer ceramic capacitor sample, and the thickness of the dielectric layer. Higher specific resistance is preferable. In this example, a sample having a measurement voltage of 280 V (electric field strength 40 V / μm) of 1.00 × 10 ¹² Ωcm or more was judged to be good. The results are shown in Table 2.

(Dielectric breakdown voltage at 225 ° C. (BDV))
The multilayer ceramic capacitor sample was placed in an oil bath at 225 ° C., a DC voltage was applied under the condition of a boosting speed of 100 V / sec, and the voltage value at the time when the leakage current exceeded 10 mA was taken as the withstand voltage. The withstand voltage per unit thickness (dielectric breakdown voltage) was calculated by dividing the obtained withstand voltage by the thickness of the dielectric layer. It is preferable that the dielectric breakdown voltage is high. In this example, a sample having a breakdown voltage of 250 V / μm or more was judged to be good. A sample having a breakdown voltage of 280 V / μm or more is more preferable. The results are shown in Table 2.

From Tables 1 and 2, a dielectric composition having a first region and a second region, and having a dielectric composition having a niobium content and a tantalum content in the above-mentioned ranges in the first and second regions is obtained. It was confirmed that the multilayer ceramic capacitor sample used as the dielectric layer showed a good dielectric breakdown voltage even at 225 ° C.

On the other hand, it was confirmed that the dielectric breakdown voltage was low when the crystal particles having the first region and the second region were not present and the niobium content and the tantalum content were out of the above ranges. ..

(Experiment 2)
A capacitor sample was prepared by the same method as in Experiment 1 except that the prepared starting materials were weighed so that the dielectric composition after firing had the composition shown in Table 3. In addition, the characteristics of the prepared capacitor sample at 225 ° C. were evaluated by the same method as in Experiment 1. The results are shown in Table 4.

From Tables 3 and 4, it was confirmed that the dielectric breakdown voltage was further improved when the niobium content and the tantalum content in the first region and the second region were within the above-mentioned ranges.

The dielectric composition according to the present embodiment can exhibit a high dielectric breakdown voltage in a high temperature range and even under a high electric field strength. Therefore, it can be suitably used for in-vehicle electronic components that are required to be used in a high temperature region of about 150 ° C. Further, it can be suitably used for a snubber capacitor for a power device using a SiC or GaN-based semiconductor, which is required to be used in a high temperature region of about 200 ° C. Further, it can be suitably used for a capacitor or the like used for removing noise in an engine room of an automobile, which is required to be used in a high temperature region of about 200 ° C.

1 ... Multilayer ceramic capacitor 10 ... Element body 2 ... Dielectric layer 3 ... Internal electrode layer 4 ... External electrode

Claims (4)

The main component is a tungsten bronze type composite oxide represented by the chemical formula Ba ₂ LaZr ₂ (Nb _1-x Ta _x ) ₃ O _{15 + σ} and satisfying the relationship that x is 0.35 ≦ x ≦ 0.65. A dielectric composition containing
The dielectric composition has crystal particles composed of the main components as the main phase.
At least a part of the crystal particles are crystal particles having a first region and a second region having different niobium contents.
When the content of niobium in the first region is C1 _Nb (at.%) And the content of niobium in the second region is C2 _Nb (at.%), C1 _Nb and C2 _Nb are 1.20. A dielectric composition that satisfies the relationship of ≦ C1 _Nb / C2 _{Nb ≦ 2.10.} When the tantalum content in the first region was C1 _Ta (at.%), The _{relationship that C1 Nb} and C1 _Ta were 0.98 ≤ C1 _Nb / C1 _Ta ≤ 2.57 was satisfied.
Claim 1 that satisfies the relationship that _{C2 Nb} and C2 _Ta are 0.39 ≤ C1 _Nb / C2 _Nb ≤ 1.02 when the tantalum content in the second region is C2 _Ta (at.%). The dielectric composition according to. When the ratio of the number of crystal particles having the first region and the second region to the total number of crystal particles contained in the dielectric composition is α, the relationship that α is α ≧ 50% is satisfied. The dielectric composition according to claim 1 or 2. An electronic component comprising a dielectric layer containing the dielectric composition according to any one of claims 1 to 3 and an electrode.

Images