JP2022177748A - Ceramic material and capacitor - Google Patents

Abstract

To provide a dielectric having a high dielectric constant in a temperature range of 225°C or less, a small change rate of dielectric constant, and high insulating properties.SOLUTION: A ceramic material comprises, by mol: 0-15% of P2O5; 0-25% of GeO2; and 75-95% of Nb2O5, wherein the ceramic material further has: a dielectric constant of 700 or more in a temperature range of 225°C or less; a change rate of the dielectric constant of 30% or less; and an electrical conductivity of 10-8 S/cm or less. The ceramic material further includes (P(1-x)Gex)Nb9O25-α (0<x≤1, α>0) as a crystal phase.SELECTED DRAWING: Figure 1

Description

The present invention relates to a ceramic material that can be used as a dielectric. More specifically, the present invention relates to a ceramic material that has a high dielectric constant in a temperature range of 225° C. or less, a small change in dielectric constant with temperature, and a high insulating property. and a capacitor using the ceramic material.

With the spread of electronic devices such as smartphones and tablets, there is a demand for smaller and higher performance electronic components used in these devices. Thus, there is a demand for small size and large capacity.

In recent years, with the spread of electric vehicles, there has been a demand for mounting electrical boards directly around motors, which are subject to high temperatures, in order to improve motor performance and make motors more compact. Along with this, MLCCs are also required to have high capacitance and good capacitance-temperature characteristics even at higher temperatures (200° C. or higher). That is, it is required that the dielectric material constituting the capacitor has a high dielectric constant even in a high temperature range exceeding 200° C. and that the variation of the dielectric constant with respect to temperature is small.

In recent years, there has also been an increasing demand for capacitors with high energy storage densities used in excimer lasers used in semiconductor processing and vision correction surgery, medical X-rays, power storage devices, and power transmission equipment. In order to obtain a high energy storage density, the dielectric used in such capacitors is required to have both a high dielectric constant and a high dielectric breakdown strength, and at the same time, it is also required to have a small temperature change in capacitance even at high temperatures. .

However, _BaTiO3 , which is widely used as a dielectric, has a Curie temperature of around 130°C, so the dielectric constant drops significantly in the temperature range of 150°C or higher, and the above requirements cannot be satisfied. I had a problem.

Document 1 describes that the Curie temperature can be increased in a BaTiO ₃ composite oxide, and good temperature characteristics of capacitance can be obtained up to 200°C. , has the disadvantage that a large capacity cannot be obtained.

In addition, KNbO ₃ , K _0.5 Na _0.5 NbO ₃ and the like are being studied as dielectric materials having good capacity-temperature characteristics. However, these dielectric materials have the problem that potassium (K) scatters (sublimes) during the firing process, causing lattice defects in the resulting dielectric material, which lowers the insulating properties. Here, if the insulating property is low, semiconductorization progresses and dielectric breakdown is likely to occur. Therefore, when the dielectric material is applied to a ceramic electronic component such as a capacitor, the reliability of the ceramic electronic component decreases. There is a problem of storage. In addition, splashing of potassium (K) makes it difficult to manage the production process, resulting in a decrease in productivity.

JP 2017-119607 A

An object of the present invention is to solve the above problems. That is, an object of the present invention is to provide a dielectric having a high dielectric constant in a temperature range of 225° C. or less, a small change in the dielectric constant with temperature, and a high insulating property.

In order to solve the above problem, the present inventors conducted extensive research and found that the dielectric constant in a temperature range of 225° C. or lower in ceramics containing _five P ₂ O components, _two GeO components, and _five Nb ₂ O components is 700 or more and the electrical conductivity is 10 ⁻⁸ S/cm or less, which led to the completion of the present invention.
The present invention is the following (1) to (6).
(1) It contains 0 to 15% P ₂ O ₅ , 0 to 25% GeO ₂ and 75 to 95% Nb ₂ O ₅ in terms of mol %, and has a dielectric constant of 700 or more in a temperature range of 225° C. or lower. , a ceramic material having a conductivity of 10 ⁻⁸ S/cm or less.
(2) The ceramic material according to (1) above, characterized by containing (P _(1-x) Ge _x )Nb ₉ O _25-α (0<x≦1, α>0) as a crystal phase. .
(3) The ceramic material according to (1) or (2) above, wherein the temperature change rate of the dielectric constant is 30% or less in a temperature range of 225° C. or less.
(4) The ceramic material according to any one of (1) to (3) above, characterized by containing 10% or less in total of SiO ₂ , fluoride and transition metal oxide.
(5) A capacitor containing the ceramic material according to any one of (1) to (4) above.

According to the present invention, it is possible to provide a ceramic material having a high dielectric constant in a temperature range of 225° C. or lower, excellent temperature characteristics, and high insulating properties, and a capacitor containing the ceramic material.

The XRD patterns of Examples 1-3 and Comparative Example 1 are shown. 1 shows the frequency dependence of permittivity of Examples 1, 2, 4, 5 and Comparative Example 1 at room temperature. 1 shows the dielectric constant and dielectric loss of Examples 1, 2, 4 and 5 at 1 kHz in the temperature range from room temperature to 250°C. 1 shows temperature change rates of dielectric constants of Examples 1, 2, 4 and 5 in the temperature range from room temperature to 250.degree. As a representative example, the relationship between conductivity and temperature for Examples 1, 2, 4 and 5 is shown.

<Dielectric of the present invention>
The ceramic material of the present invention will be explained.
The ceramic material of the present invention is useful as a dielectric, and is a P ₂ O ₅ -GeO ₂ -Nb ₂ O ₅ system containing GeO ₂ and/or Nb ₂ O ₅ components. A dielectric constant of 700 or more, a small change in dielectric constant with temperature, and a conductivity of 10 ⁻⁸ S/cm or less can be realized.

For high dielectric properties, 0-15%, more preferably 0-12%, most preferably 0-10% P ₂ O ₅ and 0-25% GeO ₂ , more preferably It contains 0-20%, most preferably 0-18%, and Nb ₂ O ₅ content of 75-97%, more preferably 78-95%, most preferably 80-90%.

In addition, the inclusion of the P ₂ O ₅ component and the GeO ₂ component at the same time improves the dielectric properties, increases the insulating properties, and reduces the dielectric loss particularly at high temperatures. Furthermore, since the sintering temperature is also lowered, it can be expected to have the effect of reducing the oxidation of metals used as electrodes when manufacturing multilayer capacitors. Therefore, it is preferable to contain the P ₂ O ₅ component and the GeO ₂ component at the same time, and the total content of both components is preferably in the range of 5 to 25%, more preferably in the range of 8 to 22%. , in the range of 10-20%.

The ceramic material of the present invention can obtain high characteristics by containing (P _(1-x) Ge _x )Nb ₉ O _25-α (0<x≦1, α>0) crystals. α in the above formula represents the amount of oxygen defects. In order to maintain electrical neutrality in this crystal, oxygen vacancies must exist, so α is a value greater than zero. Since the presence of oxygen defects increases dielectric loss and causes a problem of deterioration of insulation properties, it is preferable to make the value of α as small as possible. As can be seen from the above formula, α takes the maximum value when x=1, so in order to obtain good characteristics, it is preferable to make x smaller than 1, more preferably smaller than 0.99. Most preferably less than 0.97.

Effective methods for reducing α include introduction of SiO ₂ component or/and fluoride component or/and transition metal oxide ions such as MnO ₂ and/or annealing treatment in an oxygen atmosphere. The introduction of these components significantly improves the dielectric loss at high temperatures.

_SiO2 , _{B2O3 , Al2O3} , ZnO, _Bi2O3 , _{TiO2 , ZrO2 , Ta2O5} , _WO3 , alkali metal oxides are added to the ceramic material of _the present invention in addition to the above crystal constituents. materials, alkaline earth metal oxides, rare earth oxides, transition metal oxides, fluorides, and the like. These components serve as sintering aids and may exist alone, may be dissolved in the above-mentioned crystals, or form new crystals with the elements constituting the above-mentioned crystals. may By introducing these components, the sintering temperature can be lowered and the dielectric properties can be improved by forming a solid solution. Among these components, SiO ₂ component or/and fluoride or/and transition metal oxide such as MnO ₂ in particular increase the sintering density of the present ceramic material, reduce oxygen defects, and improve dielectric loss and insulating properties. is remarkable, the total amount is preferably 10% or less, more preferably 5% or less, and most preferably 3% or less.

Glass may be added to the ceramic material of the present invention. Glass serves as a sintering aid and has the effect of lowering the firing temperature.

The ceramic material of the present _invention can be composited with other dielectric crystals such as tungsten bronze crystals, perovskite crystals, _CaZrO3 crystals, _SrZrO3 crystals, _BaTi2O5 crystals, _CaTi2O5 crystals, and the like _. . By combining these dielectrics, it is possible to approach the designed dielectric properties. The tungsten bronze type crystals mentioned above include MNb ₂ O ₆ (M: Ca, Sr, Ba), M ₂ RNb ₅ O ₁₅ (M: Ca, Sr, Ba; R: Na, K), K ₂ LnNb ₅ It is particularly preferable to contain one or more selected from the group consisting of O ₁₅ (Ln: Y, Ce, Sm, Eu, La, Gd, Tb, Dy, Ho, Bi) crystals and solid solutions thereof. Examples of the perovskite type include RNbO ₃ , RTaO ₃ , (Bi _0.5 , R _0.5 )TiO ₃ (R: Na, K), MTiO ₃ (M: Ca, Sr, Ba) crystals and solid solutions thereof. It is particularly preferable to include one or more selected from the group consisting of:

The ceramic material of the present invention preferably has a dielectric constant of 700 or more, more preferably 750 or more, and most preferably 800 or more in the frequency range of 100 Hz to 100 kHz at room temperature. The dielectric loss at a frequency of 1 kHz is preferably 10% or less, more preferably 5% or less, and most preferably 3% or less.

The ceramic material of the present invention preferably has a dielectric constant of 700 or more at 1 kHz in a temperature range of 225° C. or less and a rate of change in dielectric constant with respect to temperature of 30% or less, and a dielectric constant of 800 or more in a temperature range of 200° C. or less. It is more preferable that the rate of change in dielectric constant with respect to temperature is 25% or less.

Since the ceramic material of the present invention has a high dielectric constant over a wide temperature range of 225° C. or less and a small rate of change in dielectric constant with respect to temperature, it can be suitably used as a high-temperature capacitor. Specifically, electronic components used in high-temperature environments such as power devices based on SiC and GaN, which are expected to be used in vehicles, and electronic components used to eliminate noise in the engine compartment of automobiles. are mentioned.

In addition, some of the ceramic materials of the present invention can be ferroelectrics, and good piezoelectric properties (for example, piezoelectric constant: d, electromechanical coupling coefficient: k) are expected, so they are suitable for piezoelectric elements. Available.

<Manufacturing method>
A method for manufacturing the ceramic material of the present invention will be described.

First, raw materials for each component constituting the ceramic material of the present invention are prepared. The raw material of each component is not particularly limited, and the oxides and composite oxides of the above components, or various compounds that become these oxides and composite oxides by firing, such as carbonates, nitrates, hydroxides, and fluorides. It can be used by appropriately selecting from chemical compounds, organometallic compounds, and the like.

Next, the prepared raw materials are weighed and mixed so as to have a predetermined composition ratio to obtain a raw material mixture. Mixing methods include, for example, wet mixing using a ball mill and dry mixing using a dry mixer.

The raw material mixture thus obtained may be granulated by adding a binder resin thereto, or may be made into a paste together with a binder resin and a solvent to form a slurry. Moreover, the raw material mixture may be calcined before being made into granules or slurry.

The method for molding the granules or slurry is not particularly limited, and includes sheet method, printing method, dry molding, wet molding, extrusion molding, and the like. For example, when dry molding is employed, the granules are molded by filling them in a mold and compressing and pressurizing (pressing) them. The shape of the molded body is not particularly limited, and may be appropriately determined according to the application.

By sintering the obtained molded body by any method such as normal pressure sintering, hot press sintering, hot isostatic pressure sintering, discharge plasma sintering, microwave sintering, etc. , a ceramic dielectric can be obtained. The firing conditions may be appropriately determined according to the firing method, composition, etc. The firing temperature is preferably 800° C. to 1400° C., and the holding time is preferably several minutes to 24 hours.

The fired ceramic dielectric may be heat treated in the air in an oxygen or reducing atmosphere, if necessary. Such heat treatment reduces defects and improves the dielectric properties of the dielectric. The heat treatment temperature is preferably in the range of 700° C. to 1200° C., and the treatment time is preferably in the range of 1 to 24 hours.

Although the method for producing the disk-shaped ceramic material of the present invention has been described above, a ceramic capacitor constituting dielectric layers of laminated electronic components can also be produced by the green sheet method or the like. Specifically, the dielectric powder of the present invention is made into a paste, and a dielectric green sheet layer is formed on a carrier film by a doctor blade method or the like. A ceramic capacitor can be produced by peeling off the layers one by one, laminating them, applying pressure to integrally mold them, and baking them at a temperature of about 800°C to 1200°C.

Also, the ceramic material of the present invention can be made into a thin film dielectric by using a normal thin film formation method. For example, a vacuum deposition method, a high-frequency sputtering method, a pulse laser deposition method (PLD), a MOCVD (Metal Organic Chemical Vapor Deposition) method, a MOD (Metal Organic Decomposition) method, a sol-gel method, a hydrothermal method, etc. are used to form a thin film dielectric. can be formed.

Therefore, the ceramic material of the present invention may be used for electronic parts such as a single plate type capacitor, may be used for electronic parts such as a laminated type capacitor, or may be used for thin film electronic parts. Alternatively, it may be used for a piezoelectric element.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.
(Example 1-12)

Production of Ceramic Material A ceramic material containing (P _(1-x) Ge _x )Nb ₉ O _25-α (0<x≦1, α>0) was produced by the following steps.
(1-1) Mixing in a Ball Mill First, raw materials NH ₄ H ₂ PO ₄ , GeO ₂ , Nb ₂ O ₅ , SiO ₂ and MnO ₂ were mixed in a predetermined ratio, and mixed together with zirconia balls having diameters of 5 mm and 10 mm. A polypot was filled and more ethanol was added. It was then ball milled and mixed for 18 hours.
(1-2) Temporary firing
The mixed batch was dried for 24 hours, placed in a quartz crucible, and calcined at 800° C. to 1000° C. in the atmosphere in an electric furnace for 2 to 4 hours.
(1-3) Grinding with a ball mill
The calcined powder was dried and coarsely ground, and then ground again in a ball mill for 24 to 36 hours. As in (1-1) above, 2 mm and 5 mm zirconia balls and ethanol were added to the powder before ball milling.
(1-4) Molding by biaxial pressure
After drying the calcined material, 1.5 g was taken, filled in a metal mold having an inner diameter of 20 mm, and molded into pellets by a biaxial press. The pressurization conditions were 10 MPa and 1 min.
(1-5) Isotropic pressurization
The pellets were placed in a vinyl bag, evacuated, and isotropically pressurized with a CIP device (cold isostatic pressure device). Pressurization conditions were 200 MPa and 2 min.
(1-6) Main firing
The pellets were sintered in the air at 1180° C. to 1250° C. for 4 to 8 hours and then slowly cooled to complete a disk-shaped ceramic material.

1. Evaluation of ceramic material The disk-shaped ceramic material produced in the above item 1 was polished to a thickness of about 1.5 mm, and then XRD and dielectric properties (dielectric constant and dielectric loss) were measured. The XRD was measured in the range of 2θ=10 to 60° using an X-ray diffractometer (BRUKER, D8 DISCOVER). Dielectric properties were measured in the frequency range of 100 Hz to 10 ⁵ Hz using an impedance analyzer (Solartron SI1260) after depositing gold electrodes on both sides of the sample. The temperature dependence of the dielectric properties was measured in the temperature range from room temperature to 250°C in the same frequency range. The rate of change (ε _T ) of the dielectric constant with respect to temperature was calculated by the following formula by determining how much the dielectric constant changes at each temperature with reference to the dielectric constant at 25°C.

ε _T (%) = [(dielectric constant at target temperature−dielectric constant at 25° C.)/dielectric constant at 25° C.]×100%

Tables 1 to 3 show the compositions, manufacturing conditions and dielectric properties of Examples 1 to 12. Analysis of the XRD patterns of each sample revealed that all Examples had similar diffraction patterns. The XRD patterns of Examples 1 to 3 and Comparative Example 1 are shown in FIG. By identifying the diffraction peaks, the formation of PNb ₉ O ₂₅ crystals in Comparative Example 1 can be confirmed. The diffraction peaks observed in the examples containing _two GeO components almost coincide with those of PNb ₉ O ₂₅ , and the substitution of P with Ge shifts the diffraction peaks to the low-angle side. is composed of a (P _(1−x) Ge _x )Nb ₉ O ₂₅ (0<x≦1) solid solution. In addition, since oxygen defects must exist in the crystal in order to maintain electrical neutrality as described above, the crystal contained in the present ceramic material is (P _(1−x) Ge _x )Nb ₉ It is expressed as O _25-α (0<x≦1, α>0).

FIG. 2 shows the frequency dependence of the permittivity of Examples 1, 2, 4, 5 and Comparative Example 1 at room temperature. From this figure, it can be confirmed that the dielectric constant of Comparative Example 1 is 600 or less in the frequency range of 100 Hz to 100 kHz, while the dielectric constant of Example is 800. FIG.

FIG. 3 shows the dielectric constant and dielectric loss of Examples 1, 2, 4 and 5 at 1 kHz in the temperature range from room temperature to 250.degree. From this figure, it can be confirmed that the composition containing both P and Ge or the composition containing SiO ₂ exhibits a high dielectric constant and exhibits a smaller dielectric constant in a temperature range exceeding 170°C.
Further, when the rate of change in dielectric constant with respect to temperature was obtained, it was found that the rate of change was 25% or less in the temperature range up to 225°C, and 20% or less in the temperature range up to 200°C.

FIG. 4 shows the temperature change rate of dielectric constant in the temperature range from room temperature to 250° C. for Examples 1, 2, 4 and 5 as representative examples. From this figure, it was found that the temperature change rate of the dielectric constant in the temperature range of 225° C. or less was 30% or less in any of the examples.

FIG. 5 shows the relationship between conductivity and temperature in Examples 1, 2, 4 and 5 as representative examples. It was found that all the examples exhibited a conductivity of 10 ⁻⁸ S/cm or less at 225° C. or less and had high insulating properties. It was also found that the composition containing both P and Ge and the composition further containing SiO ₂ had higher insulating properties.

Claims (5)

It contains 0 to 15% P ₂ O ₅ , 0 to 25% GeO ₂ and 75 to 97% Nb ₂ O ₅ in terms of mol %, and has a dielectric constant of 700 or more in a temperature range of 225° C. or less, and an electrical conductivity. is 10 ⁻⁸ S/cm or less. 2. The ceramic material according to claim 1, containing (P _(1-x) Ge _x )Nb ₉ O _25-α (0<x≦1, α>0) as a crystal phase. 3. The ceramic material according to claim 1, wherein the temperature change rate of the dielectric constant is 30% or less in a temperature range of 225[deg.] C. or less. 4. The ceramic material according to any one of claims 1 to 3, wherein the total content of SiO ₂ , fluoride and transition metal oxide is 10% or less. A capacitor comprising the ceramic material according to any one of claims 1 to 4.

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