JP2014162709A - Dielectric porcelain composition, electronic component using the same, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dielectric porcelain composition having a high specific permittivity and to provide an electronic component using the dielectric porcelain composition.SOLUTION: The provided dielectric porcelain composition includes: a three-dimensional network wherein multiple substrate particles BT are joined; and a surface layer KN covering the surface of the three-dimensional network wherein the interface MPB thereof with the substrate particles is a heteroepitaxial interface comprising continuous crystal lattices, whereas the heteroepitaxial interface embodies a matrix. A dielectric porcelain composition having improved dielectric characteristics for obtaining a high-capacity electricity storage appliance is especially favored.

Description

  The present invention relates to a dielectric ceramic composition, and more particularly to a dielectric ceramic composition having improved dielectric characteristics in order to obtain a large-capacity capacitor or the like. The present invention also relates to an electronic component using the dielectric ceramic composition. And a manufacturing method thereof.

  Conventionally, lead zirconate titanate has been used as a dielectric ceramic composition. However, since it contains lead, there is a problem of causing environmental pollution.

  Barium titanate is mainly used as a dielectric porcelain composition not containing lead, and is applied to dielectric elements, capacitors, multilayer capacitors and the like.

On the other hand, Patent Document 1 discloses a dielectric ceramic composition having a composite structure of a niobic acid compound represented by (K _1-x Na _x ) NbO ₃ and a barium titanate represented by BaTiO ₃ . It is disclosed that there is little variation in the dielectric constant.

JP 2013-28478 A

However, even a dielectric ceramic composition having a composite structure of the niobic acid compound represented by (K _1-x Na _x ) NbO ₃ and the barium titanate represented by BaTiO ₃ is sufficient in relative dielectric constant. There was a problem that it cannot be said that it has.

  The present invention is for solving such problems, and provides a dielectric ceramic composition having a high relative dielectric constant, and an electronic component using the dielectric ceramic composition.

  The dielectric ceramic composition of the present invention covers a three-dimensional network in which a plurality of substrate particles are joined and the surface of the three-dimensional network, and the interface with the substrate particles is a heteroepitaxial interface in which a crystal lattice is continuous. The heteroepitaxial interface is in a matrix form.

  The dielectric ceramic composition of the present invention is a heteroepitaxial interface in which a plurality of substrate particles are joined and a surface of the three-dimensional network is coated, and the interface with the substrate particles is a continuous crystal lattice. A surface layer, and the three-dimensional network is provided with a junction such that an average angle formed by the surfaces of the plurality of substrate particles is an obtuse angle around the three-dimensional network.

  According to another aspect of the present invention, there is provided an electronic component comprising the above-described dielectric ceramic composition, wherein a charge is induced on a surface of the dielectric material by an electric field applied to the dielectric material.

  The method for producing a dielectric ceramic composition according to the present invention includes a step of producing a green compact as substrate particles, a step of performing a necking process for joining the green compact, and a step of adding an Nb source from the outside And a step of epitaxially forming the surface layer by a solvothermal method.

  According to the present invention, a dielectric ceramic composition having a high dielectric constant can be provided. Further, by using the dielectric material, an electronic component capable of inducing a large amount of charge can be provided.

FIG. 3 is a schematic diagram showing MPB. These are schematic diagrams of a polarization rotation mechanism. These are the results of analyzing changes in the structural gradient region (SGR) from Rietveld analysis. These are figures which show the relationship between KN / BT of a dielectric ceramic composition by Example 1 of this invention, a dielectric constant, and the thickness of a structure inclination area | region (SGR). These are graphs showing the relationship between the volume density of ceramics and the relative dielectric constant. These are the schematic diagrams explaining the parallel structure of the dielectric material ceramic composition by Example 1 of this invention. These are the graphs which show the result of the dielectric property by introduction | transduction of a parallel structure of the dielectric material ceramic composition by Example 1 of this invention. These are the schematic diagrams of the flow of the manufacturing method of the dielectric material ceramic composition by Example 2 of this invention. These are graphs showing the results of KN lamination amount and relative dielectric constant of KN / BT nanocomposite ceramics using the solvothermal method. These are the flowcharts from the weighing to necking of the manufacturing method of the dielectric ceramic composition by Example 2 of this invention. These are the measurement results of the scanning electron microscope (SEM) of the sample after necking of the dielectric ceramic composition according to Example 2 of the present invention. It is a schematic diagram of the flow from Nb addition to heat processing of the manufacturing method of the dielectric ceramic composition by Example 2 of this invention. These are the XRD measurement results of what was performed from the hydrolysis to the heat treatment of the dielectric ceramic composition according to Example 2 of the present invention. It is a flowchart from the solvothermal synthesis to drying of the manufacturing method of the dielectric material ceramic composition by Example 2 of this invention. These are the qualitative analysis results by X-ray analysis (XRD) of the powder after the necking treatment of the Nb-added sample 5 times, the Nb addition, and the solvothermal synthesis of the dielectric ceramic composition according to Example 2 of the present invention. . These are the schematic diagrams of the process for aiming at the electrical property of the dielectric material ceramic composition by Example 2 of this invention. These are the measurement results of the frequency dependence and temperature dependence of the relative permittivity of the dielectric ceramic composition according to Example 2 of the present invention. FIG. 9 shows the results obtained by superimposing the results of the KN lamination amount obtained from the KN / BT ratio and the relative permittivity of 1 MHz and RT on the dielectric ceramic composition according to Example 2 of the present invention in FIG. These are schematic diagrams of dielectric ceramic compositions according to Example 2 and Example 3 of the present invention. These are the flowcharts of the manufacturing method of the dielectric material ceramic composition by Example 3 of this invention. These are the SEM images of BT after necking of the dielectric ceramic composition according to Example 3 of the present invention. These are the powder XRD measurement results of the dielectric ceramic composition according to Example 3 of the present invention after necking treatment, before solvothermal synthesis, and after solvothermal synthesis. These are graphs showing the frequency dependence and temperature dependence of the dielectric ceramic composition according to Example 3 of the present invention. Is the dielectric ceramic composition according to Example 3 of the present invention, the d ₃₃ * constants The apparent obtained from the slope of the resulting strain measurements and strain by hysteresis measurement, it is a graph showing a PE hysteresis curve. These are figures which show the structure of the dielectric material ceramic composition by Example 4 of this invention. These are figures which show the structure of the capacitor using the dielectric material ceramic composition by Example 1 to 4 by Example 5 of this invention. These are figures which show the structure of the multilayer capacitor using the dielectric ceramic composition by Example 1 to 4 by Example 5 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

As an example of the present invention, an example in which barium titanate (BaTiO ₃ , hereinafter referred to as BT) is used for substrate particles and potassium niobate (KNbO ₃ , hereinafter referred to as KN) is used as a surface layer will be described.

  Many materials conventionally used as dielectric ceramic compositions have a composition phase boundary (hereinafter referred to as MPB). MPB is a state in which two different crystal phases coexist in one grain. At the interface between the different crystal phases, there is a portion called a structure-gradient region (hereinafter also referred to as SGR) in which the spontaneous polarization direction is distorted. A schematic diagram of MPB is shown in FIG.

  At the interface, the two phases coexist and have an epitaxial interface. Epitaxial is a state in which two phase lattices are continuously grown. The cause of high dielectric properties in MPB is considered to be a phenomenon called polarization rotation mechanism in SGR. A schematic diagram of the polarization rotation mechanism is shown in FIG. Originally, the direction of spontaneous polarization depends on the phase, but in SGR it is possible to align the direction of spontaneous polarization freely along the external field within a certain range due to the external field. Have.

  KN exists in orthorhombic crystals at room temperature and has a high Curie temperature. BT exists in tetragonal form at room temperature and has high dielectric properties. Furthermore, the lattice constants of KN and BT are values close to those of cubic crystals, and an epitaxial interface is easily formed. KN / BT nanocomposite ceramics can be obtained by epitaxially growing KN by a method such as solvothermal method. The crystal lattice near the interface between BT and KN is distorted, creating an epitaxial interface.

  The solvothermal method is a synthesis method in which an organic solvent is used for reaction under high pressure. By using the solvothermal method, synthesis can be performed at a low temperature of 300 ° C. or lower. In the solvothermal method, crystal growth called heteroepitaxial growth occurs. The heteroepitaxial growth is a crystal growth of another kind of phase with a continuous lattice around one phase.

  Figure 3 shows the result of analyzing the change in SGR from Rietveld analysis by measuring the relative permittivity by changing the ratio of KN and BT. FIG. 4 shows the relationship between KN / BT, relative permittivity, and SGR thickness. FIG. 4 shows that the relative dielectric constant is improved with an increase in SGR.

  In ceramics, when the volume density exceeds the close-packed structure, the relative permittivity is greatly improved by changing the particles from point contact to surface contact. In addition, the particles can be brought into surface contact by necking the particles, and the relative dielectric constant can be improved even at a low density. A graph of the volume density and relative dielectric constant of the ceramic is shown in FIG.

  In this example, a parallel structure was adopted in which SGR was made continuous by epitaxially growing KN on the necked BT. The parallel structure means that the particles have a necking structure and the interface has a matrix structure. A schematic diagram of the parallel structure is shown in FIG.

When pellets are made of BT and niobium oxide (Nb ₂ O ₅ ), and KN is synthesized by the solvothermal method after heating necking, the relative permittivity can be increased about 1.5 times by necking. did it. FIG. 7 shows the result of the dielectric characteristics by introducing the parallel structure.

In Example 1 described above, pellets were prepared from BT and niobium oxide (Nb ₂ O ₅ ), and KN was synthesized by solvothermal method after heating necking treatment. In Example 2, after making green compact with only BT and performing necking treatment, Nb source is added from outside, Nb ₂ O ₅ is introduced, and KN is synthesized by solvothermal method without generating impurities. An example of synthesizing KN / BT composite ceramics with a parallel structure will be described.

  FIG. 8 shows a schematic diagram of the flow of the method for producing the dielectric ceramic composition of the present example.

  KN / BT nanocomposite ceramics using the solvothermal method have an optimum amount of KN laminated on BT, with an optimum KN / BT ratio of 0.5 and a laminated amount of 22 nm. FIG. 9 shows the results of KN stacking amount and relative dielectric constant.

  In order to add Nb later so that KN / BT = 0.5, the density of the green compact with only BT is high, so in this example, carbon black (hereinafter referred to as CB) is used together with BT in the production of the green compact. By mixing and removing CB together by debinding, porous BT pellets can be made and a large amount of Nb can be added.

  As a starting material, 30% (30 vol%) of CB is added to BT (Sakai Chemical, 300 nm) by volume, and this material, 200 g of zirconia balls, and ethanol are placed in a resin container and mixed at 300 rpm for 17 hours.

  The mixed raw material and solution are transferred to a fluororesin sheet and dried in a dryer at 80 ° C. for 3 hours to evaporate ethanol.

  After drying, pulverize using a mortar and pestle and add 2% (2 wt%) of the binder. Polyvinyl butyral (PVB) is used as the binder. Add raw materials and binder in ethanol and mix in a mortar and sift through (250μm) to make the powder particles the same size.

  About 0.15 g of the powder was weighed and packed into a mold, and a pressure of about 2 t was applied using a hydraulic press to form a disk with a diameter of 10 mm. This sample was placed on an alumina plate, and the binder was removed by heat treatment at 600 ° C. for 10 hours in an electric furnace. After the binder removal treatment, necking treatment at 1000 ° C. for 2 hours was performed in an electric furnace to produce BT porous pellets. A flowchart of the procedure from weighing to necking is shown in FIG. FIG. 11 shows the results of scanning electron microscope (SEM) measurement of the sample after necking.

The alkoxide is then added. Since the alkoxide reacts with moisture in the air to cause hydrolysis, the work is performed in the glove box. Metallic alkoxide pentaethoxyniobium (Nb (OC ₂ H ₅ ) ₅ ) is dissolved in ethanol at a molar ratio of 3:10, and BT porous pellets are placed in the solution and vacuum degassed to alkoxide inside the pellets. Impregnate.

The pellet impregnated with the alkoxide is allowed to stand in water to hydrolyze the alkoxide in the pellet, thereby producing niobium hydroxide (Nb (OH) ₅ ) in the pellet. This keeps the Nb source in the pellet.

This pellet is heated in an electric furnace at 600 ° C. for 5 hours to produce niobium oxide (Nb ₂ O ₅ ). A schematic diagram from Nb addition to heat treatment is shown in FIG.

FIG. 13 shows the XRD measurement results of the sample from hydrolysis to heat treatment. By using this method, we succeeded in adding Nb inside the pellet. The amount of Nb ₂ O ₅ added is controlled by performing the operation from the impregnation to the heat treatment from 1 to 5 times.

Next, solvothermal synthesis is performed. Potassium hydroxide (KOH) and potassium carbonate (K ₂ CO ₃ ) were used as raw materials for solvothermal synthesis, and ethanol was used as a solvent. As the container, a 25 mL fluororesin container and an autoclave were used. A fluororesin container is used because KOH, which is a K source, dissolves in a solvent and exhibits high alkalinity. Therefore, a fluororesin container that is resistant to alkali is used.

First, ethanol is placed in a fluororesin container so that the Nb concentration is 0.1 M based on the mass of the Nb ₂ O ₅ / BT compact, and weighed so that K / Nb = 10 (KOH / K ₂ CO ₃ = 0.22). After the addition, stir with a stirrer for 10 minutes. After 10 minutes, place the Nb ₂ O ₅ / BT green compact on the pedestal, place it in a fluororesin container, place the fluororesin container in an autoclave, and react by holding at 230 ° C for 20 hours. KN / BT ceramics Was synthesized. At this time, the reaction is performed on the pedestal in order to prevent the supersaturated raw material and the green compact from coming into contact with each other and a difference in reaction concentration between the front and back of the green compact.

  After the reaction, it was cooled to room temperature, and the sample taken out was washed with ethanol and dried at 200 ° C. for 5 hours. A flowchart from solvothermal synthesis to drying is shown in FIG. The dielectric ceramic composition can be manufactured by the flow described above.

Table 1 shows the density measurement results by the Archimedes method after the necking treatment, the addition of Nb, and the synthesis of the produced dielectric ceramic composition. In addition, FIG. 16 shows the qualitative analysis results by X-ray analysis (XRD) of the powder after necking of the Nb-added sample 5 times, after Nb addition, and after solvothermal synthesis. From the results shown in Table 1 and FIG. 15, the formation of Nb ₂ O ₅ was confirmed by adding Nb, and the peak of Nb ₂ O ₅ disappeared after the synthesis, so the synthesis of KN can also be confirmed. In addition, a peak swelling called a bridge structure can be confirmed between the 200 and 002 faces of the BT lattice after synthesis. This is because the lattice near the interface is distorted by the epitaxial growth of KN on BT present in tetragonal form at room temperature. It can be seen that the bridge structure is increased by increasing the amount of KN laminated.

  The obtained dielectric ceramic composition was polished to a thickness of 0.4 mm, a gold electrode was sputtered, heat-treated at 300 ° C., cut to 2 mm × 2 mm, and vacuum-dried at 200 ° C. for 24 hours, and then the electrical characteristics were measured. . A schematic diagram of the processing is shown in FIG.

  The measurement results of the frequency dependence and temperature dependence of the relative permittivity are shown in FIG. In the case of BT that has been necked, the dielectric ceramic composition of KN / BT = 0.42 with a relative permittivity of about 200 at room temperature and 1 MHz and Nb added 5 times is improved to about 350. FIG. 18 shows the result of superimposing the results of the KN stacking amount obtained from the KN / BT ratio and the relative permittivity of 1 MHz and RT on FIG. This result shows the same behavior as KN / BT nanocomposite ceramics without parallel structure.

  In Example 2 described above, since porous BT pellets were prepared using CB, necking was weak, and SGR was not continuous and seems to be scattered. It is thought that there is no significant structural change from KN / BT nanocomposite ceramics without necking.

  In the third embodiment, a manufacturing method that does not use CB will be described. A schematic diagram of the dielectric ceramic composition according to Example 2 and Example 3 is shown in FIG.

  A flowchart of this embodiment is shown in FIG. Unlike Example 2, CB is not used. Nb was added up to 5 times, and after hydrolysis and heat treatment, solvothermal synthesis was performed.

  The SEM image of BT after necking is shown in FIG. 21, the results of density measurement by Archimedes method are shown in Table 2, and the powder XRD measurement results after necking, before solvothermal synthesis, and after solvothermal synthesis are shown in FIG.

  From FIG. 21, it can be seen that BT pellets that do not use CB have much stronger necking than pellets to which 30 vol% of CB has been added. From the results shown in Table 2 and FIG. 22, the KN / BT ratio is 0.25, and the stacking amount of KN is 11 nm. The bridge structure can also be confirmed from the BT 200 peak.

  The frequency dependence and temperature characteristics of relative permittivity were measured. FIG. 23 shows frequency dependency and temperature dependency. From FIG. 23, the relative dielectric constant at 1 MHz and RT was increased by about 1600 for KN / BT nanocomposite ceramics compared to about 800 for BT subjected to necking treatment. Regarding the temperature dependence, a very high dielectric constant can be obtained by laminating KN.

FIG. 24 shows the apparent d ₃₃ * constant obtained from the strain measurement result obtained by the hysteresis measurement, the slope of the strain, and the PE hysteresis curve. KN / BT nanocomposite ceramic d ₃₃ * Whereas 161.9pC / N of BT subjected to necking process from Figure 24 it can be seen that with a is approximately twice the d ₃₃ * 318.4pC / N. It can be seen that the piezoelectric characteristics are greatly improved by epitaxially growing KN.

  FIG. 25 shows a dielectric ceramic composition as Example 4 in which substrate particles are arranged in a lattice pattern, adjacent substrate particles are connected by SGR, and a surface layer is formed in a gap. In Example 4, a uniform composition can be obtained, and the dielectric properties can be controlled by controlling the interval between the substrate particles and the size of the gap forming the surface layer.

  FIG. 26 shows an example of a capacitor as an electronic component using the dielectric ceramic composition described in Examples 1 to 3 according to the present invention. A dielectric ceramic composition 1 according to the present invention is formed into a flat plate shape, and a first electrode 2 and a second electrode 3 are provided on both sides. Here, a silver electrode is used. The shape of the dielectric porcelain composition is not limited, but it is preferably a flat plate shape in consideration of the amount of charge that can be stored. In addition, the electrode material may be any material as long as it is conductive, and it does not matter whether it is a metal or a doped semiconductor. Therefore, an electronic component such as a capacitor cell of a DRAM (Dynamic Random Access Memory) is used. It may be a thing. Further, it may be a variable capacitance element that can change the capacitance by changing the capacitor structure or the applied bias.

  When a voltage is applied between the electrodes 2 and 3, the SGR polarization of the dielectric ceramic composition changes according to the electric field generated in the dielectric material, and positive and negative charges are respectively applied to the surface of the dielectric ceramic composition at the interface with the electrode. Is induced. Since the dielectric ceramic composition according to the present invention exhibits high dielectric properties as described above, a capacitor having a large capacity can be obtained.

  FIG. 27 is a sectional view of a multilayer capacitor using the dielectric ceramic composition according to the present invention. The dielectric ceramic composition 1 according to the present invention is formed in a multilayer sheet shape, and the first electrode 2 and the second electrode 3 are alternately provided between the respective layers. Each of the first electrode and the second electrode includes external electrodes 4 and 5 so as to be connected to an external circuit. Electric charge is stored according to the voltage applied between the electrodes, but because it is a dielectric ceramic composition with a high relative dielectric constant, the area can be reduced and the number of layers can be reduced, contributing to the downsizing of the device. .

  ADVANTAGE OF THE INVENTION According to this invention, the dielectric ceramic composition which has a high dielectric constant can be provided, and the electronic component using the dielectric ceramic composition can be provided.

DESCRIPTION OF SYMBOLS 1 ... Dielectric ceramic composition 2 ... 1st electrode 3 ... 2nd electrode 4 ... External electrode 5 ... External electrode

Claims (4)

  A heterogeneous interface including a three-dimensional network in which a plurality of substrate particles are joined and a surface of the three-dimensional network covering the surface of the three-dimensional network, and the interface with the substrate particles being a heteroepitaxial interface having a continuous crystal lattice; A dielectric ceramic composition characterized in that an epitaxial interface is in a matrix form.   A three-dimensional network in which a plurality of substrate particles are joined, and a surface layer that covers the surface of the three-dimensional network and that is a heteroepitaxial interface in which a crystal lattice is continuous with the substrate particles. A dielectric ceramic composition, characterized in that the network has a junction such that an average angle formed by the surfaces of the plurality of substrate particles is an obtuse angle in the periphery.   3. An electronic component comprising the dielectric ceramic composition according to claim 1 or 2, wherein a charge is induced on a surface of the dielectric material by an electric field applied to the dielectric material. A step of producing a green compact as substrate particles, a step of performing a necking process for joining the green compact, a step of adding an Nb source, and a step of forming a surface layer epitaxially by a solvothermal method. A method for producing a dielectric ceramic composition, comprising: