JPH06208804A - Dielectric material and ceramic component - Google Patents

Abstract

PURPOSE:To provide a ceramic component in which a dielectric layer can be baked simultaneously with an Ag electrode by providing a dielectric material, in which the rate of temperature change in the dielectric constant is small, the dielectric loss of which is small, and which can be baked at a low temperature, and by using the dielectric materials. CONSTITUTION:Bismuth oxide, magnesium oxide, tantalum oxide and/or niobium oxide are contained, at the mol ratio expressed by the sides and the inside of a triangle with three vertices X, Y, Z, in a diagram of three-component composition, where 0<=Nb2O5/(Ta2O5+Nb2O5)<=1, is satisfied and the main phase is an oxide phase having a pyrochlore type structure.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a dielectric material and a ceramic component having a dielectric layer containing the same.

[0002]

2. Description of the Related Art In developing a dielectric material used for a temperature compensating capacitor, the following are important points.

Dielectric constant (ε) is large Dielectric loss (tanδ) is small Change in temperature coefficient (ε ・ TC) of dielectric constant is small over a wide temperature range, and ε ・ TC with small absolute value can be obtained depending on the application. Being low baking temperature

However, these characteristics are in a mutually contradictory relationship, and it is extremely difficult to improve all the characteristics at the same time. For this reason, at present, development is being carried out by narrowing down the application, selecting the most important characteristic in the application, and focusing on improving the characteristic.

Conventional dielectric materials such as SrTiO 3
₃ , SrZrO ₃ , CaTiO ₃ , Ba (Ti, Zr)
_{O 3, MgTiO 3, (Sr} , Ca) TiO 3 , etc. are some of the advantages and disadvantages of such a situation.
In particular, since these material systems require a high temperature of 1200 ° C. or higher for sintering, thermal fatigue of the firing furnace and high energy cost are problems. Further, in recent years, a multilayer ceramic capacitor that can be downsized and have a large capacity has become common, but when manufacturing a multilayer ceramic capacitor,
It is necessary to fire the dielectric material and the internal electrode material at the same time, and when the above-mentioned dielectric material is used, the firing temperature becomes high, so it is necessary to use a metal having a high melting point for the internal electrode material. Under these circumstances, Pd is conventionally used in most of the temperature-compensated multilayer ceramic capacitors. However, Pd has an electric conductivity lower than that of Ag by about one digit, which is one of the limits of capacitor performance such as an increase in loss at high frequencies. Also, Pd is very expensive.

On the other hand, Pb-based and Bi-based dielectric materials that can be fired at low temperatures have not been completed as materials that are sufficiently satisfactory in terms of the rate of change in dielectric constant with temperature and dielectric loss.

In order to develop a material which satisfies the above items (1) to (3) on average, the dielectric constant ε is generally high and the dielectric loss is high.
A method is adopted in which a material having a small tan δ is used as a base material and an additive is added to the base material. Materials with high ε and small tanδ
Since most of the changes in the dielectric constant with temperature have a negative slope, in order to correct this, an additive with a large dielectric loss but with a positive slope in the temperature change of the dielectric constant is added unintentionally. Of.

Therefore, if the rate of change in dielectric constant with temperature can be reduced and the dielectric loss can be reduced, a useful dielectric material which has never been obtained can be obtained. If low temperature firing is possible, Ag
The co-firing with the system electrode material becomes possible, and the usefulness is further enhanced.

[0009]

The present invention has been made under such circumstances, and provides a dielectric material which has a small rate of change in dielectric constant with temperature, a small dielectric loss, and can be fired at a low temperature. It is also an object of the present invention to provide a ceramic component capable of cofiring a dielectric layer with an Ag-based electrode by using this dielectric material.

[0010]

These objects are achieved by the present invention described in (1) to (5) below. (1) Bismuth oxide and magnesium oxide and tantalum oxide and / or niobium oxide are contained, and bismuth oxide is converted to Bi ₂ O ₃ , magnesium oxide is MgO, tantalum oxide is converted to Ta ₂ O ₅ , and niobium oxide is converted to Nb ₂ O ₅ . When the molar ratio is (Bi ₂ O ₃ , MgO, Ta ₂ O
₅ + Nb ₂ O ₅ ) in a three-component composition diagram, X (0.16, 0.28, 0.56), Y (0.16, 0.76, 0.08) and Z (0.64, 0. 28, 0.08) on the inside and inside of a triangle with the apex being 0, and 0 ≦ Nb ₂ O ₅ / (Ta ₂ O ₅ + Nb ₂ O ₅ ) ≦ 1. material. (2) The dielectric material according to (1), which has an oxide phase having a pyrochlore structure as a main phase. (3) The oxide phase having the pyrochlore structure is B
i ₂ Mg (Nb, Ta) ₂ O ₉ , Bi ₃ Mg ₂ (Nb,
The dielectric material according to the above (2), containing at least one selected from Ta) O ₉ and Bi ₅ (Nb, Ta) ₃ O ₁₅ . (4) A ceramic part having a dielectric layer and an electrode, wherein the dielectric layer contains the dielectric material according to any one of (1) to (3). (5) The ceramic component according to (4) above, wherein the electrode contains Ag as a main component.

[0011]

FUNCTION AND EFFECT The dielectric material of the present invention is Bi ₂ (M
g, Ta, Nb) ₂ O ₆ , Bi ₂ (Mg, Nb) ₂ O ₆
Alternatively, it is produced using a compounding composition centered on Bi ₂ (Mg, Ta) ₂ O ₆ and has a pyrochlore type oxide phase as a main phase. With such a configuration, it is possible to make the dielectric loss extremely small while reducing the temperature change rate of the dielectric constant. For example, the temperature change rate of dielectric constant is ± 500ppm
The dielectric loss can be 0.5% or less, and particularly 0.1% or less in the range of / ° C. Further, since low temperature firing is also possible, when applied to a ceramic component such as a monolithic ceramic capacitor, it is possible to simultaneously fire an inexpensive Ag-based electrode and a dielectric layer having good electrical characteristics.

Therefore, the dielectric material of the present invention is very suitable for a compact, thin, laminated type temperature compensating capacitor or feedthrough capacitor.

The pyrochlore type oxide which has been conventionally known as a dielectric material is represented by the general formula A ₂ B ₂ O ₇ , and specifically, {A = Ba, Ca,
Sr, B = Ti, Nb} system and {A = Pb, B = Nb,
The Ta} system is known and is intended for use as a microwave dielectric material. However, there is a problem that the above-mentioned material system requires a high temperature of 1200 ° C. or more for firing, and the above-mentioned material system has a large negative temperature coefficient (ε · TC) of the dielectric constant.

In addition, Bi ₂ (Ni _1/3 Nb _2/3 ) ₂ O ₇
And Bi ₂ (Mg _1/3 Nb _2/3 ) ₂ O ₇ are Soviet phy
As described in sics-solid state vol.14, No.10 pp2539, these materials have high dielectric constant but large dielectric loss.

[0015]

Specific Structure The specific structure of the present invention will be described in detail below.

The dielectric material of the present invention contains bismuth oxide and magnesium oxide and tantalum oxide and / or niobium oxide. When bismuth oxide is converted to Bi ₂ O ₃ , magnesium oxide is converted to MgO, tantalum oxide is converted to Ta ₂ O ₅ , and niobium oxide is converted to Nb ₂ O ₅ , the molar ratio is (B
In the three-component composition diagram of i ₂ O ₃ , MgO, Ta ₂ O ₅ + Nb ₂ O ₅ (FIG. 1), X (0.16, 0.28, 0.56), Y (0.16, 0.76) , 0.08) and Z (0.64, 0.28, 0.08) are represented on and inside the sides of a triangle having vertices, and preferably X ′ (0.2, 0.4, 0. 4), Y '(0.2,0.72,0.08) and Z' (0.52,0.4,0.08) are represented on and inside the sides of a triangle having vertices. If the composition deviates from the above range, the dielectric loss becomes significantly large and the absolute value of the temperature coefficient of the dielectric constant becomes large.

The ratio of Ta ₂ O ₅ and Nb ₂ O ₅ is 0 ≦ Nb ₂ O ₅ / (Ta ₂ O ₅ + Nb ₂ O ₅ ) ≦ 1, preferably 0.2 ≦ Nb ₂ O ₅ / (Ta ₂ O ₅ + Nb ₂ O ₅ ) ≦
1, more preferably 0.5 ≦ Nb ₂ O ₅ / (Ta ₂ O ₅ + Nb ₂ O ₅ ) ≦ 1. If Nb ₂ O ₅ is not contained, the firing temperature is 95.
Becomes relatively high as 0 ℃ about more, Nb ₂ O ₅ sintering temperature by the solid solution can be lowered to about 900 ° C., and also dielectric constant when increasing amount of solid solution Nb ₂ O ₅ improves.

The dielectric material of the present invention has a pyrochlore oxide phase as a main phase, but it may have a mixed crystal structure having two or more pyrochlore structures.
Bi ₂ Mg (Nb, Ta) ₂ O ₉ , Bi ₃ Mg ₂ (N
b, Ta) O ₉ and Bi ₅ (Nb, Ta) ₃ O ₁₅ and at least one pyrochlore phase. Such a tissue structure can be confirmed by X-ray diffraction.

The average crystal grain size of the dielectric material of the present invention is
It is about 0.7 to 3.0 μm.

Next, a method of manufacturing the dielectric material of the present invention will be described.

As a starting material, oxides of metal elements constituting the dielectric material, such as Bi ₂ O ₃ , MgO and Ta _{2 are used.}
O ₅ , Nb ₂ O ₅ or the like may be used. Alternatively, a compound such as a carbonate which becomes an oxide after heat treatment may be used. The mixing ratio of the starting materials is selected so that the ratio of each metal element is the same as the final composition.

It is preferable to mix the powders of the starting materials by a wet method using a ball mill or the like. After mixing, calcination is performed. The calcination is preferably performed in air at a temperature of about 650 to 850 ° C. for about 1 to 2 hours. After calcination, it is crushed by a ball mill or the like. The average particle size of the calcined powder may be about 0.5 to 2.0 μm.

Next, a binder such as polyvinyl alcohol is added to the calcined powder to shape it into a predetermined shape, and then it is fired. The firing may be performed in air, but may be performed in an atmosphere in which the oxygen partial pressure is controlled, if necessary. In the present invention, firing at a low temperature of 1000 ° C. or lower is possible, but preferably 850 to 1000 ° C., more preferably 900 to 950.
Bake at ° C. If the firing temperature is too low, sintering tends to be insufficient, and if it is too high, it tends to react with the setter and cause welding to the setter. The temperature holding time during firing may be usually about 2 hours.

When the dielectric material of the present invention is applied to a monolithic ceramic capacitor, a vehicle containing an organic binder and an organic solvent is added to the above calcined powder to prepare a dielectric layer paste, and a paste for the dielectric layer is prepared. An electrode layer paste is laminated by a printing method, a sheet method, or the like, and then simultaneously fired, and terminal electrodes are further provided to obtain a laminated ceramic capacitor in which dielectric layers and internal electrode layers are alternately laminated.
As the conductive material used for the internal electrode layer, an inexpensive low melting point metal such as Ag-based, Ni-based, or Al-based can be used, and Ag-based metal is particularly preferable. In addition, as the Ag-based metal, it is preferable to use a silver content of 90% by weight or more, for example, Ag, Ag-Pd, Ag-.
It is preferable to use Pt or the like. The amount of Pd or Pt added is at most 3% by weight, and usually 1% by weight or less. These are added to prevent Ag migration.

The present invention is not limited to such a laminated ceramic capacitor, but various ceramic parts having a dielectric layer and an electrode, for example, a laminated LC part, a multilayer wiring board containing a capacitor part, and a resonance having a triplate line. Suitable for vessels and the like.

[0026]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Bi ₂ O ₃ , MgO, Ta as starting materials
₂ O ₅ and Nb ₂ O ₅ are used, and the composition is represented by points A to K in the three-component composition diagram of FIG. 1 and Nb ₂ O ₅ /
(Ta ₂ O ₅ + Nb ₂ O ₅ ) was weighed and blended so as to have the values shown in Table 2 below. The compositions of points A to K are shown in Table 1 below.

[0028]

[Table 1]

Next, these were wet mixed in a polyethylene pot for 10 hours and calcined in air at 650 to 850 ° C. for 2 hours. The obtained calcined body was crushed with a ball mill to obtain a calcined body powder having an average particle diameter of 0.5 μm.

Then, an organic binder was added to the calcined powder, and the powder was molded at a pressure of ² ton / cm ² to obtain a disk-shaped molded product having a diameter of 12 mm and a thickness of 0.6 mm. The molded body was fired in the air at the temperature shown in Table 2 for 2 hours. In order to prevent compositional deviation due to evaporation and to prevent insufficient sintering, the compact was embedded in the calcined powder in a closed cask and fired. The average crystal grain size of the obtained sintered body was 0.8 to 2 μm. Ag is vapor-deposited on both main surfaces of each sintered body to form electrodes,
The dielectric samples shown in Table 2 were obtained.

For these dielectric samples, the dielectric constant ε, the temperature coefficient ε · TC of the dielectric constant, and the dielectric loss tan δ were measured. The results are shown in Table 2. In Table 2, ε and
tan δ is the value at 20 ℃, 1MHz, and ε ・ TC is
{(Ε at 85 ° C.) − (Ε at −25 ° C.)} /
(Ε at 20 ° C.) / {85 − (− 25)}.

[0032]

[Table 2]

From the results shown in Table 2, the effect of the present invention is clear. That is, the dielectric material of the present invention has an extremely small rate of change in dielectric constant with temperature and also has an extremely small dielectric loss. Moreover, the sintering containing Nb ₂ O ₅ was completed at 900 ° C. for 2 hours.

Next, for sample Nos. 1 and 2,
X-ray diffraction was performed. The X-ray diffraction chart of Sample No. 1 is shown in the bottom row of FIG. 2, and the X-ray diffraction chart of Sample No. 2 is shown in the top row of FIG. For these, the crystal phase was identified as follows. Bi ₂ O ₃ , MgO and Nb ₂ O ₅ were mixed so as to have an appropriate integer ratio, and a sintered body was obtained by adjusting conditions such as calcination temperature and time. X-ray diffraction analysis was performed on these sintered bodies, and further, the conditions were adjusted so as to obtain a single phase, to prepare sintered bodies. The X-ray diffraction chart of the obtained sintered body is shown in FIGS. 2 and 3 together with the chart of the sample of the present invention.

In the uppermost row of FIG. 2 and the third row of FIG. 3, the compounding composition ratio is set to Bi ₂ MgNb ₂ O ₉ and
It is a chart of a sintered body obtained by firing at 00 ° C. for 2 hours, and it can be synthesized in a substantially single phase although there are some different phases. The peaks in this chart correspond well to the peaks marked with ↓ in the chart of the sample of the present invention. Furthermore, it can be seen from the pattern of peaks that this phase exhibits a pyrochlore structure belonging to the space group Fd3m. Since the sample of the present invention contains Nb ₂ O ₅ and / or Ta ₂ O ₅ ,
Considering that Ta is substituted at the position of Nb, it is understood that the ↓ phase has a pyrochlore structure represented by the chemical formula Bi ₂ Mg (Nb, Ta) ₂ O ₉ and belonging to the space group Fd3m.

In the second step of FIG. 2 and the second step of FIG. 3, the compounding composition ratio is set to Bi ₃ Mg ₂ NbO ₉ and 800
It is a chart of a sintered body obtained by firing at ℃ for 2 hours,
It can be synthesized in almost single phase. The peak of this chart is
It corresponds well to the peak marked with a circle in the chart of the sample of the present invention. Further, the peak pattern shows that this phase has a structure similar to BiDyO ₃ . However, the space group is unknown, and the crystal structure is not well understood. The sample of the present invention is Nb ₂ O
₅ and / or Ta ₂ O ₅ , it is considered that Ta is substituted at the position of Nb, and the phase of ○ has the chemical formula Bi
₃ Mg ₂ (Nb, Ta) represented by O ₉ is understood to have a structure similar to BiDyO _3.

The third row of FIG. 2 and the fourth row of FIG. 3 are charts of the sintered body obtained by firing at 800 ° C. for 2 hours with the composition ratio of Bi ₅ Nb ₃ O _15. Yes, it can be synthesized in almost single phase. The peaks in this chart correspond well to the peaks marked with ∇ in the chart of the sample of the present invention. Further, this is registered in the ASTM card, and it can be seen that it has a pyrochlore structure. Since the sample of the present invention contains Nb ₂ O ₅ and / or Ta ₂ O ₅ , considering that Ta is substituted at the Nb position, the phase of ∇ is Bi ₅ (Nb, Ta) ₃ O.
Considered to be ₁₅ .

In summary, sample No. 1 shown in FIG. 2 has a chemical formula Bi ₂ Mg (Nb, Ta) ₂ O ₉ and a phase belonging to the space group Fd3m and having a pyrochlore structure, and a chemical formula Bi ₃ It is considered to include a phase represented by Mg ₂ (Nb, Ta) O ₉ and having a similar structure to BiDyO _3, and further, a small amount of a pyrochlore phase represented by the chemical formula Bi ₅ (Nb, Ta) ₃ O _15. . The sample No. 2 shown in FIG. 3 is Bi ₅ (Nb, Ta) ₃ O ₁₅
Since no phase peak is observed, the chemical formula Bi ₂ Mg (N
b, Ta) ₂ O ₉ , a phase belonging to the space group Fd3m and having a pyrochlore structure, and a chemical formula Bi ₃ Mg ₂ (Nb,
Ta) O ₉ and represented by BiDyO ₃ and having a structure similar to that of BiDyO ₃ .

[Brief description of drawings]

FIG. 1 is a three-component composition diagram showing the composition of a dielectric material of the present invention.

FIG. 2 is an X-ray diffraction chart of a dielectric material and an X-ray diffraction chart for identifying a crystal phase.

FIG. 3 is an X-ray diffraction chart for identifying a dielectric material and an X-ray diffraction chart for identifying a crystal phase.

Claims (5)

[Claims] 1. Containing bismuth oxide and magnesium oxide and tantalum oxide and / or niobium oxide,
Bi ₂ O _{3 for} bismuth oxide, Mg for magnesium oxide
O, tantalum oxide is Ta ₂ O ₅ , niobium oxide is Nb ₂ O
When converted to ₅ , the molar ratio is (Bi ₂ O ₃ , Mg
In the three-component composition diagram of O, Ta ₂ O ₅ + Nb ₂ O ₅ ), X (0.16, 0.28, 0.56), Y (0.16, 0.76, 0.08) and Z (0 .64, 0.28, 0.08) on the inside and inside of a triangle with the apex being 0, and 0 ≦ Nb ₂ O ₅ / (Ta ₂ O ₅ + Nb ₂ O ₅ ) ≦ 1. Characteristic dielectric material. 2. The dielectric material according to claim 1, wherein an oxide phase having a pyrochlore structure is a main phase. 3. The oxide phase having a pyrochlore structure is Bi ₂ Mg (Nb, Ta) ₂ O ₉ , Bi ₃ Mg ₂
(Nb, Ta) O ₉ and Bi ₅ (Nb, Ta) ₃ O ₁₅
The dielectric material of claim 2, comprising at least one selected from: 4. A ceramic component having a dielectric layer and an electrode, wherein the dielectric layer contains the dielectric material according to any one of claims 1 to 3. 5. The ceramic component according to claim 4, wherein the electrode contains Ag as a main component.