JP7491837B2 - Dielectric composition and electronic component - Google Patents

Description

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

Multilayer ceramic capacitors are used 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 automotive electrical equipment. Among these, laminated ceramic capacitors used in vehicles are required to be guaranteed to operate at higher temperatures than laminated ceramic capacitors used in home appliances and information terminals. For example, at high temperatures of 175°C or higher, laminated ceramic capacitors for vehicles are required to have not only high reliability but also a high breakdown voltage of at least 2.5 times the rated voltage.

Patent Document 1 discloses a dielectric composition containing a tungsten bronze type complex oxide represented by the chemical formula (Sr _1.00-s-t Ba _{s Cat} ) _6.00-x R _x (Ti _1.00-a Zr _a ) _x+2.00 (Nb _1.00-b Ta _b ) _8.00-x O _30.00 as a main component, in which s, t, x, a, and b are within a predetermined range. Patent Document 1 also describes that the dielectric composition has a good relative dielectric constant, resistivity, and withstand voltage at 200°C. Furthermore, Patent Document 1 describes that the dielectric composition has a good high-temperature load life at 250°C.

Patent Document 2 discloses a dielectric composition containing a tungsten bronze type complex oxide represented by the chemical formula (A1) _a (A2) _b (B1) _c (B2) _{dO15 +σ} as a main component, where A1 is Ba or the like, A2 is Y or the like, B1 is Ti or the like, B2 is Nb or the like, and a, b, c, and d are within predetermined ranges. Patent Document 2 also describes that the dielectric composition has good relative dielectric constant, resistivity, and breakdown voltage at 225°C.

International Publication No. 2017/163843 JP 2020-037490 A

However, the dielectric composition described in Patent Document 1 has not been evaluated for its high-temperature load life in the high-temperature range exceeding 250°C.

Furthermore, the dielectric composition described in Patent Document 2 has not been evaluated for its high-temperature load life.

The present invention has been made in consideration of these circumstances, and aims to provide a dielectric composition that has a long high-temperature load life and a high dielectric breakdown voltage in high temperature ranges, and an electronic component that includes a dielectric layer and electrodes made of the dielectric composition.

In order to achieve the above object, the dielectric composition of the present invention comprises:
[1] A dielectric composition containing, as a main component, a tungsten bronze type composite oxide represented by the chemical formula (A1) _a (A2) _b (A3) _c (B1) ₂ (B2) _{3O15 +σ} ,
A1 is at least one element selected from the group consisting of Ba, Sr and Ca;
A2 is at least one element selected from the group consisting of La, Pr, Nd and Sm;
A3 is at least one element selected from the group consisting of Yb, Lu, Sc and Al;
B1 is at least one element selected from the group consisting of Ti and Zr;
B2 is at least one element selected from the group consisting of Nb and Ta;
a, b and c are each
2.600≦a+b+c≦2.980,
1.003≦b+c≦1.500,
0.003≦c≦0.100,
The dielectric composition satisfies the following relationship:

[2] b and c are
1.250≦b+c≦1.400,
The dielectric composition according to [1] satisfies the following relationship:

[3] An electronic component comprising a dielectric layer containing the dielectric composition described in [1] or [2] and an electrode.

The present invention provides a dielectric composition that has a long high-temperature load life and a high dielectric breakdown voltage in the high temperature range, and an electronic component that includes a dielectric layer and electrodes made of the dielectric composition.

FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor according to one embodiment of the present invention.

The present invention will now be described in detail based on specific embodiments in the following order.
1. Multilayer ceramic capacitor 1.1 Overall configuration of multilayer ceramic capacitor 1.2 Dielectric layer 1.3 Internal electrode layer 1.4 External electrode 2. Dielectric composition 2.1 Complex oxide 3. Manufacturing method of multilayer ceramic capacitor 4. Summary of this embodiment 5. Modifications

(1. Multilayer ceramic capacitors)
(1.1 Overall structure of multilayer ceramic capacitor)
A multilayer ceramic capacitor 1 is shown in Fig. 1 as an example of an electronic component according to this embodiment. The multilayer ceramic capacitor 1 has an element body 10 in which dielectric layers 2 and internal electrode layers 3 are alternately laminated. A pair of external electrodes 4 are formed on both ends of the element body 10, and are electrically connected to the internal electrode layers 3 arranged alternately inside the element body 10. There is no particular restriction on the shape of the element body 10, but it is usually a rectangular parallelepiped. There is also no particular restriction on the dimensions of the element body 10, and the dimensions may be appropriate depending on the application.

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

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

(1.3 Internal electrode layer)
In this embodiment, the internal electrode layers 3 are laminated so that their end faces are alternately exposed on the surfaces of 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 alloy, Pd, Ag, Pd-Ag alloy, Cu or Cu-based alloy is preferable. Ni or Ni-based alloy is more preferable. Even more preferable is a conductive material whose main component of the internal electrode layer 3 is Ni or Ni-based alloy and whose secondary component is one or more selected from Al, Si, Li, Cr and Fe. The main component of the internal electrode layer 3 refers to a component contained in an amount of 85 mass% or more of the entire internal electrode layer 3.

The internal electrode layer 3 contains Ni or a Ni-based alloy as the main component and one or more selected from Al, Si, Li, Cr and Fe as the secondary component, so that the Ni contained in the internal electrode layer 3 is less likely to oxidize. 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 oxidation of the internal electrode layer 3.

The reason why the Ni contained in the internal electrode layer 3 is less likely to be oxidized when the internal electrode layer 3 contains one or more types selected from Al, Si, Li, Cr, and Fe as minor components is as follows. When the internal electrode layer 3 contains one or more types selected from Al, Si, Li, Cr, and Fe, the minor components react with oxygen before the Ni reacts with oxygen in the air to become NiO, forming an oxide film of the minor components on the surface of the Ni contained in the internal electrode 3. As a result, oxygen in the air cannot react with Ni without passing through the oxide film, making the Ni less likely to be oxidized.

The internal electrode layer 3 may contain various trace components such as P at about 0.1 mass % or less. The internal electrode layer 3 may be formed using a commercially available electrode paste. The thickness of the internal electrode layer 3 may be appropriately determined depending on the application, etc.

(1.4 External Electrodes)
There is no particular limitation on the conductive material contained in the external electrodes 4. For example, known conductive materials such as Ni, Cu, Ag, Pd, Pt, Au, alloys of these, conductive resins, etc. may be used. The thickness of the external electrodes 4 may be appropriately determined depending on the application, etc.

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

(2.1 Complex oxides)
The composition of a composite oxide having a tungsten bronze crystal structure is represented by the chemical formula _A3B5O15 . In the tungsten bronze crystal structure, oxygen octahedra formed by six-coordination of oxygen to atoms occupying the B site form a _three -dimensional network sharing _each other's vertices. Furthermore, atoms occupying the A site are located in the gaps between the oxygen octahedra.

In order to balance the charges, an example of an oxide represented by the chemical formula A ₃ B ₅ O ₁₅ is an oxide in which the atoms occupying the A site are two elements with a divalent oxidation number and one element with a trivalent oxidation number, and the atoms occupying the B site are two elements with a tetravalent oxidation number and three elements with a pentavalent oxidation number. This oxide is represented by the chemical formula (A1) ₂ (A2) ₁ (B1) ₂ (B2) ₃ O _15. In this chemical formula, A1 is an element with a divalent oxidation number, A2 is an element with a trivalent oxidation number, B1 is an element with a tetravalent oxidation number, and B2 is an element with a pentavalent oxidation number. That is, the composition ratio of each element in the above oxide is divalent oxidation number: trivalent oxidation number: tetravalent oxidation number: pentavalent oxidation number=2:1:2:3.

In this embodiment, the composite oxide is represented by the chemical formula (A1) _a (A2) _b (A3) _c (B1) ₂ (B2) _{3O15 +σ} . The metal elements contained in the composite oxide, that is, the "A1" element, the "A2" element, the "A3" element, the "B1" element, and the "B2" element, are classified based on their stable oxidation numbers.

The sites occupied by the "A1", "A2", "A3", "B1" and "B2" elements that make up the above composite oxide are not particularly limited, so long as the composite oxide has a tungsten bronze type crystal structure. However, taking into consideration the oxidation number and ionic radius, the "A1", "A2" and "A3" elements usually tend to occupy the A site, and the "B1" and "B2" elements tend to occupy the B site.

The "A1" element is an element with an oxidation number of divalent. In this embodiment, the "A1" element is at least one element selected from the group consisting of Ba (barium), Sr (strontium), and Ca (calcium). The "A1" element preferably contains at least Ba, and is more preferably Ba.

The "A2" element is an element with an oxidation number of three. In this embodiment, the "A2" element is at least one element selected from the group consisting of La (lanthanum), Pr (praseodymium), Nd (neodymium) and Sm (samarium). The "A2" element preferably includes at least La, and is more preferably La.

The "A3" element is an element with an oxidation number of three. In this embodiment, the "A3" element is at least one element selected from the group consisting of Yb (ytterbium), Lu (lutetium), Sc (scandium) and Al (aluminum). It is preferable that the "A3" element contains at least Yb, and it is more preferable that it is Yb.

"A2" elements tend to have a larger ionic radius than "A3" elements.

The "B1" element is an element with an oxidation number of 4. In this embodiment, the "B1" element is at least one element selected from the group consisting of Ti (titanium) and Zr (zirconium). It is preferable that the "B1" element is Zr.

The "B2" element is an element with an oxidation number of five. In this embodiment, the "B2" element is at least one element selected from the group consisting of Nb (niobium) and Ta (tantalum). It is preferable that the "B2" element is Nb.

In the chemical formula, "a" indicates the number of atoms of the "A1" element relative to the total atomic number of the "B1" and "B2" elements, which is 5. Also, "b" indicates the number of atoms of the "A2" element relative to the total atomic number of the "B1" and "B2" elements, which is 5. Also, "c" indicates the number of atoms of the "A3" element relative to the total atomic number of the "B1" and "B2" elements, which is 5.

In this embodiment, "a", "b" and "c" satisfy the relationship 2.600≦a+b+c≦2.980.

"a+b+c" indicates the total number of atoms of elements that tend to occupy the A site ("A1" element, "A2" element, and "A3" element) relative to the total number of atoms of elements that tend to occupy the B site ("B1" element and "B2" element), which is _5. Therefore, the total number of atoms of elements that tend to occupy the A site in the above complex oxide tends to be smaller than the number of atoms in the A site in the complex _oxide represented by the chemical formula _A3B5O15 (3).

As a result, cation vacancies are more likely to occur in the above-mentioned composite oxide. These cation vacancies compensate for oxygen vacancies that are likely to be generated, for example, during reduction firing of the composite oxide. Therefore, when "a+b+c" is within the above range, the high-temperature load life of the dielectric composition tends to be improved.

If "a+b+c" is too small, the tungsten bronze crystal structure becomes unstable, and the breakdown voltage tends to decrease. On the other hand, if "a+b+c" is too large, fewer cation vacancies are generated, which tends to inhibit improvement in high-temperature load life.

In this embodiment, "b" and "c" satisfy the relationship 1.003≦b+c≦1.500. It is preferable that "b+c" is 1.250 or more. On the other hand, it is preferable that "b+c" is 1.400 or less.

"b + c" indicates the total number of atoms of the elements with an oxidation number of three (the "A2" element and the "A3" element) that tend to occupy the A site out of the total number of atoms of the "B1" element and the "B2" element, which is 5.

When comparing the "a+b+c" range with the "b+c" range, there are relatively more elements with an oxidation number of three ("A2" element and "A3" element) that tend to occupy the A site, and conversely, there are relatively fewer elements with an oxidation number of two ("A1" element).

Elements with an oxidation number of three have a higher degree of covalent bonding than elements with an oxidation number of two, so by having "b + c" within the above range, the tungsten bronze crystal structure becomes stronger and the breakdown voltage tends to improve.

If "b+c" is too small, the covalent bond is low, which tends to suppress the improvement of the dielectric breakdown voltage. On the other hand, if "b+c" is too large, the tungsten bronze crystal structure becomes unstable, which tends to reduce the dielectric breakdown voltage.

In this embodiment, "c" satisfies the relationship 0.003≦c≦0.100. It is preferable that "c" is 0.005 or more. On the other hand, it is preferable that "c" is 0.050 or less.

"c" indicates the number of atoms of the "A3" element, which tends to occupy the A site, relative to the total number of atoms of the "B1" and "B2" elements, which is 5. The "A3" element tends to have a higher degree of covalent bonding than the "A2" element. Therefore, by having "c" within the above range, the tungsten bronze type crystal structure becomes stronger, and the dielectric breakdown voltage tends to improve.

If "c" is too small, the covalent bond is low, which tends to suppress the improvement of the dielectric breakdown voltage. On the other hand, if "c" is too large, the tungsten bronze crystal structure becomes unstable, which tends to reduce the dielectric breakdown voltage.

In this composite oxide, the amount of oxygen (O) may vary depending on the composition ratio of "A1", "A2", "A3", "B1" and "B2", oxygen defects, etc. Therefore, in this embodiment, the stoichiometric ratio in the composite oxide represented by the chemical formula (A1) ₂ (A2, A3) ₁ (B1) ₂ (B2) ₃ O ₁₅ is used as a reference, and the deviation of oxygen from the stoichiometric ratio is represented by "σ". The range of "σ" is not particularly limited, and is, for example, about -0.900 or more and 0.925 or less.

The dielectric composition according to this embodiment may contain other components in addition to the above-mentioned main components within the range in which the above-mentioned effects are achieved. The content of the other components is preferably 1.00 mol or less, and more preferably 0.50 mol or less, per 100 mol of the dielectric composition.

(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 this embodiment can be manufactured by a known method similar to that used for conventional multilayer ceramic capacitors. One known method is, for example, a method in which a green chip is made using a paste containing the raw materials of a dielectric composition, and then fired to manufacture a multilayer ceramic capacitor. The manufacturing method is described in detail below.

First, the 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 is prepared.

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

For example, prepare carbonate powder "A1", hydroxide or oxide powder "A2", oxide powder "A3", oxide powder "B1", and oxide powder "B2". It is preferable that the average particle size of each powder is 1.0 μm or less.

Next, the prepared starting materials are weighed in a predetermined ratio and then wet mixed for a predetermined time using a ball mill or the like. After drying the mixed powder, it is heat-treated in air at 1000°C or less to obtain a calcined powder of the composite oxide, which is the main component.

The calcined powder of the main component is then crushed to obtain the dielectric composition raw material powder. The average particle size of the dielectric composition raw material powder is arbitrary. For example, it is 0.5 μm to 2.0 μm.

Next, a paste for producing the green chip is prepared. The obtained dielectric composition raw material powder is kneaded with a binder and a solvent to form a paint, and a paste for the dielectric layer is prepared. The binder and the solvent may be publicly known. The paste for the dielectric layer may also contain additives such as a plasticizer, if necessary.

The internal electrode layer paste is obtained by kneading the above-mentioned conductive material raw material, a binder, and a solvent. The binder and the solvent may be publicly known. The internal electrode layer paste may contain additives such as co-materials and plasticizers as necessary.

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

The binder and solvent contents in each of the above pastes are not particularly limited and may be normal contents. For example, the binder may be about 1% to 5% by mass, and the solvent may be about 10% to 50% by mass. In addition, each paste may contain additives selected from various dispersants, plasticizers, dielectric materials, insulating materials, etc., as 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 or a polymer type dispersant can be used. The type of plasticizer is arbitrary. For example, dioctyl phthalate or dibutyl phthalate can be used. The type of dielectric material is arbitrary. For example, _BaTiO3- based or _CaZrO3- based can be used. The type of insulator material is arbitrary. For example, _{Al2O3 or SiO2} can be used.

The resulting pastes are used to form green sheets and internal electrode patterns, which are then stacked to obtain green chips.

Before firing, the green chip is subjected to a binder removal process. 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 process 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.

After the binder removal process, the green chip is fired to obtain the element body. There are no particular restrictions on the firing conditions. The holding temperature is preferably 1100°C to 1400°C. If the holding temperature is too low, the element body will not be sufficiently densified. If the holding temperature is too high, abnormal sintering of the internal electrode layer will cause the electrodes to break, and the material that makes up the internal electrode layer will diffuse, making it more likely that the rate of capacitance change will deteriorate. Furthermore, particles made up of the main component will become coarse, which may shorten the high-temperature load life.

The heating rate is preferably 200°C/hour to 5000°C/hour. The temperature holding time during sintering and the cooling rate after sintering are optional. In order to control the particle size distribution of the main phase particles composed of the main components after sintering to within the range of 0.5 μm to 5.0 μm and to suppress volume diffusion between the main phase particles, the temperature holding time is preferably 0.5 hours to 2.0 hours and the cooling rate is preferably 100°C/hour to 500°C/hour.

In addition, the firing atmosphere is preferably a mixture of humidified _N2 and _H2 gas, with an oxygen partial pressure of ^10-2 to ^10-6 Pa. When the internal electrode layer contains Ni, firing under high oxygen partial pressure conditions may result in Ni being oxidized and the electrical conductivity may be reduced. However, by adding one or more types of internal electrode subcomponents selected from Al, Si, Li, Cr, and Fe to a conductive material mainly composed of Ni, the oxidation resistance of Ni is improved, and it is easy to ensure the electrical conductivity of the internal electrode layer even when firing in an atmosphere with a high oxygen partial pressure.

After firing, the obtained element body is annealed as necessary. The annealing conditions may be known conditions, and for example, it is preferable that the oxygen partial pressure during the annealing is higher than the oxygen partial pressure during firing, and that the holding temperature is 1150°C or less.

The above-mentioned binder removal process, firing and annealing processes may be carried out independently or consecutively.

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 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 manner, the multilayer ceramic capacitor according to this embodiment is manufactured.

(4. Summary of the present embodiment)
In this embodiment, in a tungsten bronze type composite oxide in which the composition ratio of each element is divalent element: trivalent element: tetravalent element: pentavalent element = 2:1:2:3, the number of atoms of the elements occupying the A site is reduced to generate cation vacancies. The generated cation vacancies can compensate for oxygen vacancies generated during reduction firing of the dielectric composition. As a result, the high temperature load life is improved.

Furthermore, by making the number of trivalent elements in the A site greater than the number of divalent elements, the covalent bond in the tungsten bronze crystal structure is increased, making the tungsten bronze crystal structure more stable. As a result, the breakdown voltage is improved. This effect is further improved by including an element with higher covalent bond strength as a trivalent element within the above-mentioned range.

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

Furthermore, the above-mentioned dielectric composition may contain a subcomponent according to the desired characteristics within the range in which the above-mentioned effects are obtained. Examples of the subcomponent include oxides of Si, oxides of V, oxides of Mn, and oxides of Al. The content ratio of the subcomponent may be determined according to the desired characteristics.

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.

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

(Experimental Example 1)
First, powders of BaCO ₃ , SrCO ₃ , CaCO ₃ , La(OH) ₃ , Pr ₆ O ₁₁ , Nd ₂ O ₃ , Sm ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ , Sc ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , Nb ₂ O ₅ , and Ta ₂ O ₅ with an average particle size of 1.0 μm or less were prepared as starting materials for the main components. These raw materials were weighed so that the main components (composite oxides) contained in the finally obtained dielectric composition had the compositions shown in Table 1. Then, the materials were wet mixed for 24 hours using ethanol as a dispersion medium in a ball mill. The mixture obtained was then dried to obtain a mixed raw material powder. Then, heat treatment was performed in the air at a holding temperature of 900° C. and a holding time of 2 hours to obtain a calcined powder of the main components.

The calcined powder of the main component obtained by the above method was mixed and crushed to obtain a dielectric composition raw material powder. Next, 700 g of a solvent containing 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 ratio of 90:6:4 (weight ratio) was added to 1000 g of the dielectric composition raw material powder to obtain a mixture. Next, the obtained mixture was dispersed for 2 hours using a basket mill to prepare a dielectric layer paste. In all examples and comparative examples, the viscosity of the dielectric layer paste was adjusted to about 200 cps. 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 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 powder was heat-treated at 1200 ° C or more 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 raw material powder for the internal electrode layer with an average particle size of 0.20 μm.

100% by mass of the 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 made into a paste using a three-roll mill to obtain a paste for the internal electrode layer.

The prepared dielectric layer paste was then applied onto a PET film to form a green sheet. At this time, the thickness of the green sheet after drying was set to 10 μm. Next, a predetermined pattern of internal electrode layers was printed onto 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.

Then, the obtained green chip was subjected to a binder removal process, firing and annealing process to obtain a multilayer ceramic fired body (element body). The conditions for the binder removal process, firing and annealing are as shown below. In addition, a wetter was used to humidify the atmospheric gas during the binder removal process, firing and annealing processes.

(Debinding process)
Heating rate: 100°C/hour Holding temperature: 400°C
Temperature retention time: 8.0 hours Atmospheric gas: mixed gas of humidified _N2 and _H2

(Firing)
Heating rate: 500°C/hour Holding temperature: 1200°C to 1350°C
Temperature retention time: 2.0 hours Cooling rate: 100°C/hour Atmosphere gas: mixed gas of humidified _N2 and _H2 Oxygen partial pressure: ^10-5 to ^10-9 Pa

(Annealing treatment)
Holding temperature: 800°C to 1000°C
Temperature retention time: 2.0 hours Temperature increase and decrease rate: 200°C/hour Atmospheric gas: humidified _N2 gas

The composition of the dielectric layers (dielectric compositions) of each of the obtained fired laminated ceramic bodies was analyzed using ICP atomic emission spectroscopy, and it was confirmed that the composition after analysis was the same as the composition shown in Table 1. In addition, X-ray diffraction measurements were performed on the dielectric compositions, and the obtained X-ray diffraction pattern confirmed that the dielectric compositions had a tungsten bronze type crystal structure.

The end faces of the obtained fired laminated ceramic body were polished by sandblasting, and then 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 Figure 1. The size of each of the obtained laminated ceramic capacitor samples was 3.2 mm x 1.6 mm x 1.2 mm, with a dielectric layer thickness of 7 μm, an internal electrode layer thickness of 2 μm, and 50 dielectric layers sandwiched between the internal electrode layers.

The dielectric breakdown voltage at 175°C and the high-temperature load life at 280°C of the obtained multilayer ceramic capacitor samples were measured using the method described below.

(Breakdown voltage at 175°C)
The multilayer ceramic capacitor sample was placed in an oil bath at 175°C, and a DC voltage was applied at a voltage rise rate of 100V/sec. The voltage value at the point where the leakage current exceeded 10mA was taken as the withstand voltage. The obtained withstand voltage was divided by the thickness of the dielectric layer to calculate the withstand voltage per unit thickness (dielectric breakdown voltage). A higher dielectric breakdown voltage is preferable, and in this example, samples with a dielectric breakdown voltage of 270V/μm or more were judged to be good. Samples with a dielectric breakdown voltage of 290V/μm or more are more preferable. The results are shown in Table 1.

(High temperature load life at 280°C)
At 280°C, a DC voltage was applied to the dielectric layer of the multilayer ceramic capacitor sample so that an electric field strength of 40 V/μm was applied, and the change in insulation resistance over time was measured. The time from the insulation resistance value at the start of DC voltage application until the insulation resistance value dropped by one digit was defined as the failure time. The 50% mean time to failure (MTTF) was calculated from a Weibull analysis of the failure time. For each sample number, the mean time to failure was measured for 20 samples, and the average value was defined as the high temperature load life. The longer the high temperature load life, the better. In this example, samples with a high temperature load life of 9.0 hours or more were determined to be good. The results are shown in Table 1.

From Table 1, it was confirmed that multilayer ceramic capacitor samples in which A1, A2, A3, B1 and B2 were appropriately selected and "a", "b" and "c" were within the above-mentioned ranges had good dielectric breakdown voltage at 175°C and high-temperature load life at 280°C.

In contrast, it was confirmed that when "a", "b" and "c" are outside the above-mentioned ranges, at least one of the dielectric breakdown voltage at 175°C and the high temperature load life at 280°C deteriorates.

The dielectric composition according to this embodiment has a long high-temperature load life and a high dielectric breakdown voltage in the high-temperature range. Therefore, it can be suitably used for electronic components for automotive applications that require use in high-temperature ranges of 175°C or higher.

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

Claims (3)

A dielectric composition comprising, as a main component, a tungsten bronze type composite oxide represented by the chemical formula (A1) _a (A2) _b (A3) _c (B1) ₂ (B2) _{3O15 +σ,}
A1 is at least one element selected from the group consisting of Ba, Sr and Ca;
A2 is at least one element selected from the group consisting of La, Pr, Nd and Sm;
A3 is at least one element selected from the group consisting of Yb, Lu, Sc and Al;
B1 is at least one element selected from the group consisting of Ti and Zr;
B2 is at least one element selected from the group consisting of Nb and Ta;
a, b and c are each
2.600≦a+b+c≦2.980,
1.003≦b+c≦1.500,
0.003≦c≦0.100,
A dielectric composition which satisfies the following relationship: b and c are 1.250≦b+c≦1.400;
2. The dielectric composition according to claim 1, which satisfies the following relationship: An electronic component comprising a dielectric layer containing the dielectric composition according to claim 1 or 2 and an electrode.

Images