JP2018145075A - Dielectric composition and electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dielectric composition having small DC-bias-voltage dependence of relative dielectric constant and small temperature dependence of relative dielectric constant to high temperature and to provide an electronic component using the dielectric composition.SOLUTION: There is provided a dielectric composition which comprises Ba, Sr, Ti, Bi, X (X is at least one selected from the group consisting of Na and K) and Y (Y is at least one selected from the group consisting of Zn, Mg, Ca, Mn, Co, Ni, Cu and Sn), wherein the dielectric composition comprises crystalline particles having a perovskite structure, at least a part of the crystalline particles is a core-shell particle composed of a core part and a shell part existing around the core part and the content of Bi existing in the core part is 1.01 or more times and 1.19 or less times of the content of Bi existing in the shell part.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a dielectric composition and an electronic component including a dielectric layer containing the dielectric composition.

  In recent years, due to increasing global interest in energy problems, demand for electric vehicles (EV) and hybrid vehicles (HEV) with low carbon dioxide emissions, or power generation devices using natural energy such as solar cells has increased. Yes. These are equipped with power devices such as converters, inverters, and power conditioners, and their energy conversion efficiency greatly affects the performance of the apparatus.

  Therefore, research on next-generation power semiconductors such as SiC (silicon carbide) and GaN (gallium nitride) with high conversion efficiency instead of conventional Si (silicon) based semiconductors as power semiconductors suitable for such power devices. It is actively done. Since these next-generation power semiconductors have lower on-resistance than conventional Si-based semiconductors, power loss is small, and the device can be made smaller and more efficient.

  In particular, SiC has the advantage that the cooling device can be simplified and miniaturized because it can be driven at a high temperature of about 250 ° C. as a semiconductor element. Such an advantage is particularly great when applied to an automotive power device that requires high-voltage driving and the cooling device is currently a large water-cooled type.

  In power devices using these semiconductor elements, a multilayer ceramic capacitor is used as a smoothing capacitor or a snubber capacitor in order to eliminate surge voltage and noise. Especially when a power device is installed in the engine room of an automobile, and when a SiC semiconductor is used for the power device, it is assumed that it will be used in a high temperature environment and a high voltage. Must be used.

  To deal with this problem, Patent Document 1 discloses that the material can be fired at a low temperature of 1150 ° C. or less, the relative dielectric constant εr is as high as 2000 or more, and the temperature characteristic is X8R characteristic (capacity change rate is ± 15% at −55 ° C. to + 150 ° C. In a reliability test typified by a high temperature load life, a dielectric ceramic that is greatly improved as compared with a conventional product is disclosed. However, regarding the temperature characteristics, the measurement temperature is evaluated up to 150 ° C., and the DC bias voltage dependency is not evaluated at all.

Japanese Patent Laid-Open No. 2001-240465

  In view of the above situation, the present invention provides a dielectric composition having a low dielectric constant dependency on the DC bias voltage and a low dielectric constant temperature dependency up to a high temperature (for example, 250 ° C.), and the dielectric composition thereof. An object of the present invention is to provide an electronic component using an object.

In order to achieve the above object, the dielectric composition of the present invention comprises:
[1] Ba, Sr, Ti, Bi, X (X is at least one selected from the group consisting of Na and K) and Y (Y is Zn, Mg, Ca, Mn, Co, Ni, Cu and Sn) A dielectric composition comprising at least one selected from the group consisting of:
The dielectric composition includes crystal particles having a perovskite structure,
At least a part of the crystal particles is a core-shell particle composed of a core part and a shell part existing around the core part,
A dielectric composition characterized in that the Bi content in the core part is 1.01 to 1.19 times the Bi content in the shell part.

  [2] The dielectric composition according to [1], wherein 0.10 ≦ α, where α is a ratio of the number of core-shell particles to the total number of crystal particles contained in the dielectric composition. is there.

  [3] When the total of Ba, Sr, Ti, Bi, X and Y contained in the dielectric composition is 100 atomic%, the total of Ba, Sr and Bi is 28 atomic% or more and 53 atomic% or less. When the total of Ba, Sr and Bi is 1.00, x is the total composition ratio of Ba and Sr, and y is the composition ratio of Bi. It is a dielectric composition as described in [1] or [2] characterized by these.

[4] When the crystal particles are in the first phase, the dielectric composition has a second phase having a composition different from the first phase,
In the second phase, when the total of Ba, Sr, Ti, Bi, X and Y is 100 atomic%, the total of Bi and X is 56 atomic% or more. The dielectric according to any one of [1] to [3], wherein a ratio of Bi content (Bi content / X content) is β, and 5 ≦ β ≦ 50 It is a composition.

  [5] The dielectric composition according to [4], wherein 0 <γ ≦ 0.20 when the area ratio occupied by the second phase is γ in the cross section of the dielectric composition is there.

  [6] An electronic component comprising a dielectric layer containing the dielectric composition according to any one of [1] to [5].

  Since the dielectric composition of the present invention has the above-described characteristics, the dependency of the relative permittivity on the DC bias voltage is small, and the temperature dependency of the relative permittivity up to a high temperature can be decreased.

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 diagram for explaining an example of the content of Bi present in the core part and the shell part of the core-shell particles contained in the dielectric composition according to the embodiment of the present invention, and a method for measuring the Bi content. FIG. FIG. 3 is a perspective view of a single-layer ceramic capacitor according to another embodiment of the present invention.

Hereinafter, the present invention will be described in detail in the following order based on specific embodiments.
1. Multilayer Ceramic Capacitor 1.1 Overall Configuration of Multilayer Ceramic Capacitor 1.2 Dielectric Layer 1.2.1 Dielectric Composition 1.2.2 Core Shell Particles 1.2.3 Second Phase 1.3 Internal Electrode Layer 4 Terminal electrode 2. Manufacturing method of multilayer ceramic capacitor Effect of the present embodiment 4. Modified example

(1. Multilayer ceramic capacitor)
(1.1 Overall structure of multilayer ceramic capacitor)
As shown in FIG. 1, the multilayer ceramic capacitor 200 according to this embodiment includes a multilayer body 24 having a configuration in which dielectric layers 21 and internal electrode layers 22A and 22B are alternately stacked. A pair of terminal electrodes 23 </ b> A and 23 </ b> B are formed at both ends of the laminate 24 so as to be electrically connected to the internal electrode layers 22 </ b> A and 22 </ b> B arranged alternately in the laminate 24. Although there is no restriction | limiting in particular in the shape of the laminated body 24, Usually, it is set as a rectangular parallelepiped shape. Moreover, there is no restriction | limiting in particular also in the dimension, What is necessary is just to set it as a suitable dimension according to a use.

(1.2 Dielectric layer)
The dielectric layer 21 is composed of a dielectric composition according to this embodiment described later. As a result, the multilayer ceramic capacitor having the dielectric layer 21 has a relatively high relative permittivity and a small dependence of the relative permittivity on the DC bias voltage, and further has a relative permittivity up to a high temperature (for example, 250 ° C.). Temperature dependence can be reduced. The thickness per layer of the dielectric layer 21 is not particularly limited, and can be arbitrarily set according to desired characteristics, applications, and the like. Usually, it can be made into thickness of 1-100 micrometers, for example.

(1.2.1 Dielectric composition)
The dielectric composition according to this embodiment includes a plurality of crystal particles having a perovskite structure. The crystal particles are Ba, Sr, Ti, Bi, X (X is at least one selected from the group consisting of Na and K) and Y (Y is Zn, Mg, Ca, Mn, Co, Ni, Cu and And at least one selected from the group consisting of Sn). In the present embodiment, the crystal particle is preferably a compound of a metal element and another element, and the metal element is composed of a compound composed of Ba, Sr, Ti, Bi, X, and Y. The compound is preferably an oxide.

The oxide having a perovskite structure is represented by the general formula ABO ₃ , and the above Ba, Sr, Ti, Bi, X, and Y are present at the A site or the B site depending on factors such as charge balance and ionic radius in the perovskite structure. Distributed. In this embodiment, at least Ba, Sr, Bi and X are allocated to the A site (occupies the A site), and at least Ti is allocated to the B site (occupies the B site). Y may occupy either the A site or the B site, or may occupy both. With such a dielectric composition, since the dielectric domain is small and the domain wall is difficult to move, the dependency of the relative permittivity on the DC bias voltage can be reduced.

  In the present embodiment, when the total of Ba, Sr, Ti, Bi, X and Y contained in the dielectric composition is 100 atomic%, the total of Ba, Sr and Bi is 28 atomic% or more and 53 atomic% or less. When the total of Ba, Sr, and Bi is 1.00, the total composition ratio of Ba and Sr, that is, the composition ratio of (Ba + Sr) is expressed as x, and the composition ratio of Bi is expressed as y. Is preferably 0.06 or more and 0.92 or less. The total of Ba, Sr and Bi is preferably 30 atomic% or more, and preferably 50 atomic% or less. Further, x is more preferably 0.34 or more. Furthermore, x is more preferably 0.85 or less.

  On the other hand, since x + y = 1.00 holds, y is preferably 0.08 or more and 0.94 or less. By doing in this way, the dielectric constant of a dielectric composition can be improved.

  The reason why the relative permittivity is improved by setting x within the above range is currently unknown, but the present inventors have determined that when x is within the above range, the core portion or the shell It is presumed that the relative permittivity is improved by mixing a phase containing a large amount of Ba or Sr and a phase containing a large amount of Bi in the order of nanometers and generating a phase that easily moves at the interface. .

(1.2.1 Core-shell particles)
In the present embodiment, as at least a part of the crystal particles constituting the dielectric composition, there are particles having two regions in which the content ratio of the element occupying the A site and the content ratio of the element occupying the B site are different from each other. To do. Specifically, for example, in the particles, the average content ratio of elements occupying the A site is such that Ba is 40%, Sr is 10%, Bi is 40%, and X is 10%; There is a region where the average content ratio of elements occupying 30%, Sr is 10%, Bi is 45%, and X is 15%, and the other region is around one region. Existing. That is, the particle is a core-shell particle having a shell part around the core part.

The core-shell particle is a particle in which the entire particle has a composition represented by the general formula ABO ₃ , but the content ratio of elements occupying the A site and the B site is biased between the core part and the shell part. This compositional deviation occurs in a region of at least several tens of nanometers.

  Moreover, it is preferable that rare earth elements are not substantially contained in both the core part and the shell part.

  In the present embodiment, in the core-shell particles, the Bi content present in the core part is 1.01 to 1.19 times the Bi content present in the shell part. That is, the content rate of Bi existing in the core part is larger than the content rate of Bi existing in the shell part. Due to the difference between the Bi content in the core part and the Bi content in the shell part, the temperature dependence of the relative dielectric constant in the core part is different from the temperature dependence of the relative dielectric constant in the shell part. And the temperature characteristics of each other are offset to some extent. As a result, the temperature dependence of the dielectric constant of the dielectric composition can be reduced.

  The Bi content present in the core part is more preferably 1.06 times or more the Bi content present in the shell part. The Bi content in the core part is more preferably 1.14 times or less the Bi content in the shell part. If the Bi content in the core part is too large, the difference between the temperature dependence of the relative dielectric constant in the core part and the temperature dependence of the relative dielectric constant in the shell part becomes too large, and the temperature characteristics of each other are good. As a result, the temperature dependence of the dielectric constant of the dielectric composition tends to increase.

  In addition, the effect mentioned above is not acquired when Bi is diffused to a crystal grain and the content rate of Bi which exists in a shell part is made larger than the content rate of Bi which exists in a core part.

  In the present embodiment, when the number ratio of the core-shell particles to the total number of crystal particles contained in the dielectric composition is α, 0.10 ≦ α is preferable, and 0.15 ≦ α is preferable. More preferred. Further, α ≦ 0.90 is preferable. By setting α within the above range, the temperature characteristics of the dielectric constant can be further improved.

  In general, it is determined whether or not the crystal particles are core-shell particles based on a cross-sectional photograph of the dielectric composition. Therefore, although it is actually a core-shell particle, there are crystal particles in which only the shell portion appears in the cross-sectional photograph. Since such particles are not determined to be core-shell particles, the upper limit of the number ratio (α) of the core-shell particles is about 0.98 based on a cross-sectional photograph. However, even when α is 1.00, that is, when all the crystal particles are core-shell particles, the above-described effects can be obtained.

  In the present embodiment, the content ratio of Bi present in the core part and the shell part, and the number ratio α of the core-shell particles to the crystal particles may be measured as follows.

  First, a sample for a multilayer ceramic capacitor is microsampled using FIB (Focused Ion Beam), and a sample for a transmission electron microscope (TEM) is produced from the dielectric layer. The produced sample is observed with a scanning transmission electron microscope (STEM), and a BF image is acquired. Crystal particles present in the acquired STEM-BF (Scanning Transmission Electron Microscopy-Bright Field) image are specified, and the number thereof is calculated. The visual field area of the BF image may be appropriately determined according to the number of crystal particles included in the BF image, and may be, for example, about 5 μm × 5 μm to 10 μm × 10 μm. Moreover, it is preferable to observe 10 or more fields for each sample.

  Furthermore, by performing STEM-EDS (Energy Dispersive X-ray Spectrometry) mapping analysis in the same visual field, each content of Ba, Sr, Ti, Bi, X and Y in the crystal particles present in the STEM-BF image By calculating the bias, it can be determined whether or not it is a core-shell particle. Α can be calculated from the total number of crystal particles thus obtained and the number of the core-shell particles.

  Further, for example, as shown in FIG. 2, by arbitrarily setting measurement points for each of the core part 31 and the shell part 32 of the core-shell particle and performing STEM-EDS point analysis, each element at each measurement point is measured. The content of can be calculated. Furthermore, by averaging the content of each element at each measurement point, the content of each element present in the core portion 31 and the content of each element present in the shell portion 32 can be calculated. The actual number of measurement points is preferably set to 10 or more measurement points per core part. Moreover, it is preferable to set 10 or more measurement points per shell part.

  There are no particular restrictions on the method of setting the measurement points. For example, it is possible to measure the Bi content in all the pixels in the region where the Bi content is measured by STEM-EDS mapping analysis, and calculate the Bi content in each region from the Bi content in all the pixels.

  As described above, from the calculated Bi content, whether or not the Bi content in the core part is 1.01 to 1.19 times the Bi content in the shell part in the core-shell particles. It is possible to determine whether. For example, when the Bi content in the core part is larger than the Bi content in the shell part, a Bi concentration distribution as shown in FIG. 2 is shown.

(1.2.3 Phase 2)
In the present embodiment, when the crystal particle is the first phase, the dielectric composition may have a phase different from the first phase. As such a phase, a phase in which Bi and X (X is at least one selected from the group consisting of Na and K) is present in a high concentration, specifically, Ba, Sr, Ti, Bi, X, and Y When the total is 100 atomic%, it is preferable that (Bi + X) is a phase of 56 atomic% or more. In the present embodiment, it is preferable that the phase in which Bi and X exist at a high concentration exist between the crystal grains that are the first phase.

  In the present embodiment, among the phases in which Bi and X are present at a high concentration, if the ratio of the Bi content to the X content in the phase (Bi content / X content) is β, 5 ≦ A phase satisfying β ≦ 50 is defined as a second phase. β is more preferably 30 or less. By having the second phase where β is in the above range, the DC bias voltage dependency of the dielectric constant can be further improved.

  The reason why the dependence of the relative permittivity on the DC bias voltage is improved by having the second phase is that the second phase has a higher specific resistance and a lower relative permittivity than the first phase, and the DC bias It is presumed that the influence of the DC bias voltage on the relative dielectric constant is reduced when the DC electric field due to the voltage is applied to the second phase rather than the first phase having a high relative dielectric constant.

  Furthermore, in the cross section of the dielectric composition, it is preferable that 0 <γ ≦ 0.20, where γ is the area ratio of the second phase with respect to the entire cross section (1.00). By setting γ within the above range, it is possible to improve the relative permittivity while improving the dependency of the relative permittivity on the DC bias voltage. In addition, although a pore may exist in a cross section, it is preferable that the area ratio of a pore is 0.05 or less with respect to the whole cross section.

  Further, the average value of the Bi content in the second phase relative to the average value of the Bi content in the entire dielectric composition is preferably 2.50 times or more, and more preferably 50.0 times or less.

  In the present embodiment, β, which is the Bi content relative to the X content in the second phase, and γ, which is the area ratio of the second phase, may be calculated by STEM-EDS analysis as described above.

  Specifically, a phase having a composition different from that of the first phase can be determined from the STEM-EDS mapping analysis. By analyzing the composition of this phase by STEM-EDS point analysis, the second phase of 5 ≦ β ≦ 50 among the phases can be discriminated. The area ratio of the second phase can be calculated from STEM-EDS mapping analysis.

  Further, the dielectric composition according to the present embodiment may contain a very small amount of impurities and subcomponents as long as the good dielectric properties that are the effects of the present invention are not significantly deteriorated. For example, Cr, Rb, Mo, etc. Therefore, the content of the main component is not particularly limited, but is, for example, 50 mol% or more and less than 100 mol% with respect to the entire dielectric composition containing the main component.

(1.3 Internal electrode layer)
In this embodiment, the internal electrode layers 22A and 22B are provided in parallel to each other as shown in FIG. The internal electrode layer 22A is formed so that one end is exposed on the end surface of the multilayer body 24 where the terminal electrode 23A is formed. Further, the internal electrode layer 22B is formed so that one end thereof is exposed on the end surface of the multilayer body 24 where the terminal electrode 23B is formed. Furthermore, the internal electrode layer 22A and the internal electrode layer 22B are arranged so that most of them overlap in the stacking direction.

  There is no restriction | limiting in particular as a material of internal electrode layer 22A, 22B. For example, metals such as Au, Pt, Ag, Ag—Pd alloy, Cu or Ni are used, but other metals can also be used.

(1.4 Terminal electrode)
In the present embodiment, the terminal electrodes 23A and 23B are in contact with the end portions of the internal electrode layers 22A and 22B exposed at the end surfaces at the end surfaces of the laminate 24 provided with the terminal electrodes 23A and 23B, respectively. doing. Thereby, the terminal electrodes 23A and 23B are electrically connected to the internal electrode layers 22A and 22B, respectively. The terminal electrodes 23A and 23B can be made of a conductive material whose main component is Ag, Au, Cu or the like. The thickness of the terminal electrodes 23A and 23B is not particularly limited. It is set as appropriate depending on the application and the size of the multilayer ceramic capacitor. The thickness of the terminal electrodes 23A and 23B can be set to 10 to 50 μm, for example.

(2. Manufacturing method of multilayer ceramic capacitor)
Next, an example of a method for manufacturing the multilayer ceramic capacitor 200 shown in FIG. 1 will be described below.

  There is no limitation in particular in the manufacturing method of the multilayer ceramic capacitor 200 which concerns on this embodiment. For example, as with a conventional multilayer ceramic capacitor, a green chip is produced by a normal printing method or sheet method using a paste, fired, and then printed or transferred and fired by external electrodes. .

  There is no particular limitation on the type of dielectric layer paste. For example, an organic paint obtained by kneading a dielectric material for forming a dielectric layer and an organic vehicle may be used, or an aqueous paint obtained by kneading a dielectric material and an aqueous vehicle may be used.

  As the dielectric material, a metal oxide, a mixture thereof, or a composite oxide contained in the above-described dielectric composition can be used. In addition, various compounds that are converted into the above-described oxides or composite oxides by firing, such as carbonates, oxalates, nitrates, hydroxides, organometallic compounds, and the like, can be appropriately selected and mixed for use. In the present embodiment, the dielectric material may be a calcined powder obtained by calcining a mixture obtained by mixing the above-described materials.

  In this embodiment, it is preferable to control the average particle size of the Ba and Sr raw material powders to 0.5 times or less of the average particle size of the Bi raw material powders. By doing so, the number ratio α of the core-shell particles and the Bi content existing in the core part and the shell part can be appropriately controlled. Furthermore, it is preferable to control the ratio of the Bi raw material powder having a particle size of 500 nm or more to 50% to 100%. In this way, the presence / absence of the second phase and the area ratio γ can be appropriately controlled.

  When the dielectric layer paste is an organic paint, an organic vehicle in which a binder or the like is dissolved in an organic solvent and a dielectric material may be kneaded. The binder used for the organic vehicle is not particularly limited, and can be appropriately selected from various usual binders such as ethyl cellulose and polyvinyl butyral. Moreover, the organic solvent used for the organic vehicle is not particularly limited, and can be appropriately selected from various organic solvents such as terpineol, butyl carbitol, acetone, and toluene depending on the method used, such as a printing method and a sheet method.

  In addition, when the dielectric layer paste is used as a water-based paint, a water-based vehicle in which a water-soluble binder, a dispersant or the like is dissolved in water and a dielectric material may be kneaded. The water-soluble binder used in the water-based vehicle is not particularly limited, and can be appropriately selected from various binders such as polyvinyl alcohol, cellulose, and a water-soluble acrylic resin.

  The internal electrode layer paste is made of Au, Pt, Ag, Pd, Ag-Pd alloy, conductive material made of metal such as Cu or Ni, or various oxides, organometallic compounds, resinates, etc. that become the conductive material described above after firing. And the above-mentioned organic vehicle or aqueous vehicle. The external electrode paste can be prepared in the same manner as the internal electrode layer paste described above.

  When an organic vehicle is used for the preparation of each paste described above, the content of the organic vehicle is not particularly limited. For example, the binder can be about 1 to 5% by weight, and the organic solvent can be about 10 to 50% by weight. Each paste may contain additives selected from various dispersants, plasticizers, dielectrics, insulators, and the like as necessary. The total content of these additives is preferably 10% by weight or less.

  When using the printing method, the dielectric layer paste and the internal electrode layer paste are laminated and printed on a substrate such as polyethylene terephthalate (PET), cut into a predetermined shape, and then peeled off from the substrate to form a green chip and To do. When using the sheet method, a dielectric layer paste is used to form a green sheet, and after printing the internal electrode layer paste on the green sheet, the green sheet is peeled off, laminated, and cut. Use green chips.

  Before firing the green chip, a binder removal process is performed. There are no particular restrictions on the binder removal processing conditions, and normal conditions may be used.

In the case where a base metal or an alloy containing a base metal such as Cu or Cu alloy is used as the conductive material of the internal electrode layer, it is preferable to perform a binder removal treatment in a reducing atmosphere. There is no particular limitation on the type of reducing atmosphere, and for example, humidified N ₂ gas, a mixed gas of humidified N ₂ and H ₂ , or the like can be used.

  There are no particular restrictions on the rate of temperature rise, holding speed, and temperature holding time in the binder removal process. The rate of temperature rise is preferably 0.1 to 100 ° C./hour, more preferably 1 to 10 ° C./hour. The holding temperature is preferably 200 to 500 ° C, more preferably 300 to 450 ° C. The temperature holding time is preferably 1 to 48 hours, more preferably 2 to 24 hours. It is preferable to remove organic components such as a binder component to about 300 ppm by binder removal treatment, and it is more preferable to remove to about 200 ppm.

  What is necessary is just to determine suitably the atmosphere when baking a green chip | tip and obtaining a laminated body according to the kind of electrically conductive material in the paste for internal electrode layers.

When using a base metal or an alloy containing a base metal such as Cu or Cu alloy as the conductive material in the internal electrode layer paste, the oxygen partial pressure in the firing atmosphere should be 10 ⁻⁶ to 10 ⁻⁸ atm. Is preferred. By setting the oxygen partial pressure to 10 ⁻⁸ atm or higher, decomposition of components constituting the dielectric layer and a decrease in resistivity can be suppressed. Moreover, the oxidation of the internal electrode layer can be suppressed by setting the oxygen partial pressure to 10 ⁻⁶ atm or less.

  In the present embodiment, it is preferable to control the rate of temperature increase when firing the green chip within a range of 1000 ° C./hour or more. By doing so, the number ratio α of the core-shell particles and the Bi content existing in the core part and the shell part can be appropriately controlled.

  Moreover, the holding temperature at the time of baking is 900-1400 degreeC, Preferably it is 900-1100 degreeC, More preferably, it is 950-1050 degreeC. By setting the holding temperature to 900 ° C. or higher, densification by firing can be sufficiently facilitated. Further, when the holding temperature is 1100 ° C. or lower, abnormal sintering of the internal electrode layer and diffusion of various materials constituting the internal electrode layer can be easily suppressed. By suppressing abnormal sintering of the internal electrode layer, it becomes easy to prevent the internal electrode from being interrupted. By suppressing diffusion of various materials constituting the internal electrode layer, it becomes easy to prevent deterioration of the DC bias voltage characteristics.

  In particular, by controlling the firing temperature of the green chip in the range of 900 ° C. to 1000 ° C., the presence / absence of the generation of the second phase and the area ratio γ can be appropriately controlled.

There is no particular limitation on the firing atmosphere. The firing atmosphere is preferably a reducing atmosphere in order to suppress oxidation of the internal electrode layer. There is no particular limitation on the atmospheric gas. As the atmospheric gas, it is preferable to use a wet mixed gas of N ₂ and H ₂ , for example. Moreover, there is no restriction | limiting in particular in baking time.

Annealing (reoxidation) can be performed after firing the green chip. Annealing may be performed under normal conditions. There is no particular limitation on the annealing atmosphere. As the atmospheric gas, humidified N ₂ gas, a mixed gas of N ₂ and H ₂ that is humidified, or the like can be used.

In the above-described binder removal processing, firing and annealing, for example, a wetter or the like may be used to wet the N ₂ gas or a mixed gas of N ₂ and H ₂ or the like. In this case, the water temperature is preferably about 20 to 90 ° C.

The binder removal treatment, firing and annealing may be performed continuously or independently. When performing these continuously, it is preferable that after the binder removal treatment, the atmosphere is changed without cooling, and then the temperature is raised to a holding temperature at the time of firing to perform firing. On the other hand, when these are carried out independently, it is preferable to raise the temperature in the N ₂ gas atmosphere up to the holding temperature at the time of the binder removal, and then continue to raise the temperature by changing the atmosphere. After cooling to the holding temperature during the binder treatment, it is preferable to change to the N ₂ gas atmosphere again and continue cooling. Note that the N ₂ gas may or may not be humidified.

The laminated body sintered body (capacitor element main body) obtained as described above is subjected to end face polishing, for example, by barrel polishing or sand blasting, etc., and terminal electrode paste is printed or transferred and fired to form terminal electrodes. To do. The terminal electrode paste is preferably baked, for example, in a humidified mixed gas of N ₂ and H ₂ at 600 to 800 ° C. for about 10 minutes to 1 hour. Then, if necessary, a coating layer is formed on the surface of the terminal electrode by plating or the like. The multilayer ceramic capacitor 200 shown in FIG. 1 can be manufactured by the above method.

  The multilayer ceramic capacitor according to the embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, a dielectric layer made of the dielectric composition according to the present invention can be used as a dielectric element of a semiconductor device. In the present invention, a known configuration can be freely used as the configuration other than the dielectric composition. In addition, for example, in the method for manufacturing a multilayer ceramic capacitor described above, the calcined powder can be manufactured by a known method such as a hydrothermal synthesis method.

(3. Effects in the present embodiment)
In the present embodiment, by controlling the structure of at least a part of the crystal particles having a perovskite structure included in the dielectric composition and having a specific element, the crystal particles have a specific composition as a whole crystal particle. However, the core part and the shell part are present as core-shell particles having slightly different compositions, and the Bi content in the core part is made higher than the Bi content in the shell part. Yes. By doing so, it is possible to improve the temperature characteristics and DC bias voltage dependency of the relative permittivity while maintaining the relative permittivity relatively high.

  Such an effect can be further enhanced by setting the ratio of the core-shell particles in the dielectric particles constituting the dielectric composition to a predetermined ratio.

  In addition, as a phase different from the crystal particles, in the phase in which Bi and X are present at a high concentration, the above-described effect can be obtained by allowing the second phase in which the Bi content and the X content are in a predetermined ratio to exist. Can be further enhanced. In addition, by setting the abundance ratio (area ratio) of the second phase in the cross section of the dielectric composition to a predetermined ratio, the relative permittivity, the temperature characteristics of the relative permittivity, and the DC bias voltage dependency characteristics are balanced Can be good.

(4. Modifications)
In the above-described embodiment, the multilayer ceramic capacitor has been described. However, a single-layer ceramic capacitor shown in FIG. 3 may be used. The single-layer ceramic capacitor has a disk-shaped dielectric 11 and a pair of electrodes 10A and 10B. Similar to the multilayer ceramic capacitor, the shape of the dielectric 11 and the electrodes 10A and 10B is not particularly limited. Moreover, there is no restriction | limiting in particular also in the dimension, What is necessary is just to set it as a suitable dimension according to a use.

  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.

(Examples 1-35 and Comparative Examples 1-2)
As starting materials, bismuth oxide (Bi ₂ O ₃ ), sodium carbonate (Na ₂ CO ₃ ), strontium carbonate (SrCO ₃ ), barium carbonate (BaCO ₃ ), magnesium carbonate (MgCO ₃ ), titanium oxide (TiO ₂ ) A powder was prepared. In addition, in order to control Bi content rate etc. which exist in a core part and a shell part, the average particle diameter of bismuth oxide, strontium carbonate, and barium carbonate was adjusted suitably.

  The powder raw material was weighed so that the dielectric composition (sintered body) after the main firing had the composition shown in Table 1.

  Next, each raw material powder weighed was wet mixed by a ball mill, and the obtained mixture was calcined at 750 ° C. for 2 hours in the air to obtain a calcined product. Then, the obtained calcined product was wet pulverized by a ball mill to obtain a calcined powder.

  An organic solvent and an organic vehicle were added to the obtained calcined powder and wet mixed by a ball mill to prepare a dielectric layer paste. On the other hand, Pd powder was kneaded with an organic vehicle as a conductive material powder to prepare a Pd internal electrode layer paste.

  The produced dielectric layer paste was formed into a sheet by a sheet forming method to obtain a ceramic green sheet. The produced internal electrode layer paste was applied on a ceramic green sheet by screen printing to print the internal electrode layer. After stacking the ceramic green sheets on which the internal electrode layers were printed, a laminated green chip was produced by cutting into square shapes. Each laminated green chip was debindered at 500 ° C. to remove organic components to about 300 ppm. After the binder removal, firing was performed in the atmosphere at a firing temperature of 900 to 1100 ° C. to obtain a sintered body of a laminate. The heating rate and firing time were changed as appropriate.

  After polishing the end surface of the sintered body of the obtained multilayer body by sand blasting, an In—Ga eutectic alloy was applied as a terminal electrode to obtain a multilayer ceramic capacitor sample having the same shape as the multilayer ceramic capacitor shown in FIG. . The size of the obtained multilayer ceramic capacitor was 3.2 mm × 1.6 mm × 0.6 mm, the thickness of the dielectric layer was 20 μm, and the thickness of the internal electrode layer was 1.5 μm. The number of dielectric layers sandwiched between the internal electrode layers was four.

  As a result of the composition analysis of each sample using ICP emission spectroscopic analysis for each of the obtained multilayer ceramic capacitors, it was confirmed that the values were almost the same as the weighed composition.

  A cross section where the internal electrodes intersect was cut out from the obtained multilayer ceramic capacitor, and the crystal structure of the dielectric layer in the cross section was measured and analyzed by an X-ray diffraction method using an XRD measuring apparatus (Rigaku, Smartlab). As a result, it was confirmed that the dielectric layer had a perovskite crystal structure.

  Next, a TEM sample of a dielectric layer was produced from the cross section of the multilayer ceramic capacitor by FIB. The obtained TEM sample was identified using STEM (JEOL, JEM-2100F) for crystal particles present in the observation field. Next, STEM-EDS mapping analysis was performed in the same observation field to identify core-shell particles. For the identified core-shell particles, the composition analysis of the core part and the shell part is performed by STEM-EDS point analysis, and the ratio of the Bi content present in the core part and the Bi content present in the shell part is calculated. did. In addition, the magnitude | size of the observation visual field was 7 micrometers x 7 micrometers, and 10 or more visual fields were observed with respect to each sample. Moreover, the STEM-EDS point analysis of the core-shell particles was performed at 10 points or more for each core-shell particle.

  Next, from the STEM-EDS mapping, a phase different from the crystal particle is discriminated, and a composition analysis by STEM-EDS point analysis is performed on this phase, and the total of Ba, Sr, Ti, Bi, X and Y is set to 100. When the atomic percent is (Bi + X) high-concentration phase containing a total of 56 atomic percent or more of Bi and Na as X, and the ratio of Bi to Na as X is β, 5 ≦ The phase satisfying β ≦ 50 was defined as the second phase. Furthermore, from the STEM-EDS mapping, γ which is the area ratio of the second phase with respect to the entire observation field was calculated.

  Next, the relative dielectric constant was measured. First, the relative dielectric constant ε1 (no unit) of the multilayer ceramic capacitor sample is measured using a digital LCR meter (Hewlett-Packard, 4284A) at room temperature 25 ° C., frequency 1 kHz, input signal level (measurement voltage) 1.0 Vrms. It calculated from the electrostatic capacitance measured on condition, the distance between electrodes of a multilayer ceramic capacitor, and the effective area of an electrode. It is preferable that the relative dielectric constant ε1 is high. In this example, 800 or more was good, and 1000 or more was particularly good.

  Next, the temperature dependence of the dielectric constant was measured. The multilayer ceramic capacitor sample was placed in a transparent electric furnace (Ishikawa Sangyo), heated at a rate of 300 ° C. per hour, and heated to 250 ° C. The temperature was measured with a digital thermometer (ADVANTEST). The relative dielectric constant ε2 at 250 ° C. was calculated by the same method as the method for measuring the relative dielectric constant ε1.

The temperature dependence of the dielectric constant was calculated from the following equation (1) using the dielectric constant ε1 and the dielectric constant ε2. In this example, the case where the temperature dependency was −22% to + 22% was good, and the case where it was −15% to + 15% was particularly good.
Temperature dependency (%) = 100 × (ε2−ε1) / ε1 (1)

  Next, the DC bias voltage dependency of the relative dielectric constant was measured. The relative dielectric constant ε3 of the multilayer ceramic capacitor is obtained by connecting a DC bias generator (GLASSMAN HIGH VOLTAGE, WX10P90) to a digital LCR meter (Hewlett-Packard, 4284A) and applying a DC bias of 5 kV / mm to the multilayer ceramic capacitor sample. Was calculated from the capacitance, effective electrode area, interelectrode distance, and vacuum dielectric constant measured at room temperature of 25 ° C., frequency of 1 kHz, and input signal level (measurement voltage) of 1.0 Vrms. ).

The dependence of the relative permittivity on the DC bias voltage was calculated from the following equation (2) using the relative permittivity ε1 and the relative permittivity ε3. In this example, the case where the DC bias voltage characteristic was −30% to + 30% was good, and the case where it was −20% to + 20% was particularly good.
DC bias voltage dependency (%) = 100 × (ε3-ε1) / ε1 (2)

  In each of the examples and comparative examples, the ratio of Bi contained in the core and shell in the core-shell particles, the ratio of the core-shell particles to the crystal particles: α, the ratio of Bi and Na in the second phase: β, and the relative dielectric constant ( Table 1 shows the temperature dependence of ε1), the relative permittivity, and the dependence of the relative permittivity on the DC bias voltage.

  Note that “−” in the table indicates that there is no (Bi + X) high concentration phase.

  From Examples 1 to 5, 11, 12 and Comparative Examples 1 and 2 in Table 1, the Bi content in the core part is 1.01 to 1.19 times the Bi content in the shell part. In this case, it was confirmed that the relative dielectric constant was 800 or more, the temperature dependence of the relative dielectric constant was within ± 22%, and the DC bias voltage dependence of the relative dielectric constant was within ± 30%.

  From Examples 3 and 6 to 12 in Table 1, it was confirmed that when the ratio of the core-shell particles: α was 0.10 or more, the temperature dependence of the relative dielectric constant was within ± 15%.

  From Examples 3 and 13 to 18 in Table 1, it was confirmed that the relative dielectric constant was 900 or more when x was 0.06 or more and 0.92 or less. From Examples 3 and 32-35 in Table 1, it was confirmed that the relative dielectric constant was 900 or more when the total of Ba, Sr, and Bi was 28 atomic% or more and 53 atomic% or less.

  From Examples 3, 19 to 24, and 28 to 31 in Table 1, the sum of Bi and Na as X is a (Bi + X) high-concentration phase that is 56 atomic% or more, and Bi relative to Na as X When β, which is the content ratio, has a second phase where 5 ≦ β ≦ 50, it was confirmed that the DC bias voltage dependency of the relative dielectric constant was within ± 20%.

  From Examples 3, 21, 25 to 31 in Table 1, it can be confirmed that the relative dielectric constant is 1000 or more when γ is 0 <γ ≦ 0.20 as the area ratio of the second phase with respect to the entire cross section. It was.

(Examples 36 to 46)
Next, a multilayer ceramic capacitor produced in the same manner as in Example 3 was evaluated in the same manner as in Example 3 except that X and Y were changed as shown in Table 2 as metal elements. The results are shown in Table 2.

  From Table 2, when X is at least one selected from Na and K, and Y is at least one selected from Zn, Mg, Ca, Mn, Co, Ni, Cu and Sn, the relative dielectric constant is It was 800 or more, and it was confirmed that the temperature dependence of the dielectric constant was within ± 22%, and the DC bias voltage dependence of the dielectric constant was within ± 30%.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the embodiment mentioned above at all, and can be variously modified within the range which does not deviate from the summary of this invention.

  According to the present invention, there are provided a dielectric composition and an electronic component that are most suitable for electronic components such as ceramic capacitors and piezoelectric actuators used in the vicinity of SiC and GaN-based power devices and in high-temperature environments such as in an automobile engine room. can get.

10A, 10B Electrode 11 Dielectric 21 Dielectric layers 22A, 22B Internal electrode layers 23A, 23B Terminal electrode 24 Laminated body 31 Core portion 32 Shell portion 100 Ceramic capacitor 200 Multilayer ceramic capacitor

Claims (6)

Ba, Sr, Ti, Bi, X (X is at least one selected from the group consisting of Na and K) and Y (Y is a group consisting of Zn, Mg, Ca, Mn, Co, Ni, Cu and Sn) A dielectric composition comprising at least one selected from
The dielectric composition includes crystal particles having a perovskite structure,
At least a part of the crystal particles is a core-shell particle composed of a core part and a shell part existing around the core part,
The dielectric composition, wherein the Bi content in the core portion is 1.01 to 1.19 times the Bi content in the shell portion.   2. The dielectric composition according to claim 1, wherein 0.10 ≦ α, where α is a ratio of the number of the core-shell particles to the total number of crystal particles contained in the dielectric composition. When the total of Ba, Sr, Ti, Bi, X, and Y contained in the dielectric composition is 100 atomic%, the total of Ba, Sr, and Bi is 28 atomic% or more 53 Less than atomic percent,
When the total of Ba, Sr, and Bi is 1.00, the total composition ratio of Ba and Sr is represented by x, and the composition ratio of Bi is represented by y, x is 0.06. The dielectric composition according to claim 1, wherein the dielectric composition is 0.92 or less. When the crystal grains are in the first phase, the dielectric composition has a second phase having a composition different from that of the first phase;
In the second phase, when the total of Ba, Sr, Ti, Bi, X, and Y is 100 atomic%, the total of Bi and X is 56 atomic% or more, The ratio of the Bi content to the X content in the second phase (Bi content / X content) is β, and 5 ≦ β ≦ 50. 4. The dielectric composition according to any one of items 1 to 3.   5. The dielectric composition according to claim 4, wherein 0 <γ ≦ 0.20 when the area ratio of the second phase is γ in the dielectric composition.   An electronic component comprising a dielectric layer comprising the dielectric composition according to claim 1.

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