JPH0715855B2 - Ceramic capacitors - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to Pb (Zn _1/3 Nb
_2/3) The O ₃ as a main component the dielectric constant temperature coefficient (T.C.
C. ) A ceramic capacitor using a high dielectric constant porcelain composition having a small temperature change as a dielectric layer.

[0002]

2. Description of the Related Art Electrical properties required for dielectric materials include permittivity, permittivity temperature coefficient, permittivity loss, permittivity bias electric field dependency, capacitance resistance product, and the like.

In particular, the capacitance-resistance product (CR value) needs to have a sufficiently high value, and is a multilayer ceramic capacitor (chip type) standard RC- for electronic equipment of EIAJ (Japan Electronic Machinery Manufacturers Association).
3698B is specified as 500 MΩ · μF or more at room temperature.
It is required to maintain a high CR value even at high temperatures (for example, the US Department of Defense standard MIL-C 55681B defines a CR value at 125 ° C.) so that it can be used under more severe conditions.

Although it is required that the dielectric constant temperature coefficient is small, in general, in the case of a material having a large dielectric constant (K), the T.V.
C. C. Tends to be large, and K / T. C. C. Is large, that is, the relative value of the change in the dielectric constant is small.

Further, when considering a laminated type element, since the electrode layer and the dielectric layer are integrally fired, it is necessary to use an electrode material that is stable even at the firing temperature of the dielectric material. Therefore, if the firing temperature of the dielectric material is high, expensive materials such as platinum (Pt) and palladium (Pd) must be used, and in order to be able to use inexpensive materials such as silver (Ag), a temperature of 1100 ° C or lower It is required that firing at low temperature is possible.

[0006] As a conventionally known high dielectric constant porcelain composition, there is one in which barium titanate is used as a base and stannate, zirconate, titanate, etc. are solid-solved therein. Certainly, it is possible to obtain a material having a high dielectric constant, but if the dielectric constant becomes high, T.S. C. C. And the bias electric field dependency also becomes large. Furthermore, the firing temperature for barium titanate-based materials is
Since the temperature is as high as 1300 to 1400 ° C., it is necessary to use an expensive material such as platinum and palladium that can withstand the high temperature as an electrode material, which causes a high cost.

Various compositions have been studied in order to solve the problems of the barium titanate system. For example, those mainly containing lead iron niobate (JP-A-57-57204) and those mainly containing lead magnesium niobate (JP-A-55-51758)
No.), lead magnesium tungstate, and the like (JP-A-52-21699). Those mainly composed of lead iron niobate have a large change in the CR value depending on the firing temperature,
In particular, there is a problem that the CR value greatly decreases at high temperatures. Those mainly composed of magnesium / lead niobate have a relatively high firing temperature, and those mainly composed of magnesium / lead tungstate have a small dielectric constant when the CR value is large, and a CR value when the dielectric constant is large. There was a problem that it was small. In addition, the T.I. C. C. Is superior to the barium titanate system, but not sufficient.

Further, a material in which a part of lead is replaced with barium, strontium or calcium in a solid solution of lead magnesium niobate and lead titanate has been studied (JP-A-55-121959). However, the T.I. C. C. Is the best at -25 to 85 ℃.
It is 9.8%, which is not enough. Furthermore, the most important CR value as a capacitor material is not mentioned, and its usefulness as a capacitor material is not clear.

Further, Japanese Patent Application Laid-Open No. 57-25607 also studies a material of a solid solution of lead magnesium niobate and lead zinc niobate. However, the CR value and T.I.
C. C. Is not mentioned, and its usefulness as a capacitor material is not clear.

[0010]

The present invention has been made in consideration of the above points, and is a ceramic capacitor using a high dielectric constant porcelain composition having a large dielectric constant and a small temperature coefficient as a dielectric layer. The purpose is to provide.

[0011]

The present invention is represented by the general formula xPb (Zn _1/3 Nb _2/3 ) O ₃ -yPb (Mg _1/3 Nb _2/3 ) O ₃ -zPbTiO ₃ . Then, a (x = 0.50, y = 0.00, z = 0.50) b (x = 1.00, y = 0.00, z = 0.00) c (x = 0.20, y = 0.80) of the ternary diagram with each component as the vertex , Z = 0.00) d (x = 0.05, y = 0.90, z = 0.05) The composition within the line connecting the points (except on the line connecting ab) is 1 to 1 part of Pb. A ceramic capacitor in which a high dielectric constant porcelain composition substituted with at least one of 35 mol% Ba and Sr is used as a dielectric layer, and a pair of electrodes is formed through the dielectric layer. The porcelain composition contains at least one of Mn and Co.
A ceramic capacitor containing 0.5 wt% or less.

Various types of perovskite-type porcelain materials have been studied as dielectric materials. However, when zinc lead niobate (Pb (Zn _1/3 Nb _2/3 ) O ₃ ) is used as a porcelain, it is perovskite. It was considered to be unsuitable as a dielectric material because of its difficult structure (NEC Research & Deve
lopment No. 29 April 1973 p.15-21). According to the study by the present inventors, it was found that a stable perovskite structure can be formed in porcelain by substituting an appropriate amount of Pb site of Pb (Zn _1/3 Nb _2/3 ) O ₃ with Ba or Sr. Further, it has been found that such a porcelain composition exhibits a very high dielectric constant and insulation resistance, and its temperature characteristics are also very good. It was also found that the mechanical strength was also excellent. As a result of further research, by combining this lead zinc niobate with magnesium lead niobate and lead titanate, it is possible to obtain a high dielectric constant porcelain composition having a higher dielectric constant and insulation resistance. I found it.

The composition range of the composition of the present invention will be described below.

Me = Ba, Sr is an element necessary for forming the perovskite structure of the above general formula, and 1
When it is less than mol%, the pyrochlore structure is mixed and the high dielectric constant and high insulation resistance are not exhibited. If it is 35 mol% or more, the dielectric constant will be reduced to about 1000 or less, or the firing temperature will be increased to 1100 ° C or more. Therefore, M
The substitution amount of the component e is 0.01 <α <0.35 when expressed as (Pb _1-α Me _α ).

In order to increase the capacity of the dielectric material at room temperature, the Curie temperature is set near room temperature (0 to 30 ° C.). The Me component of the present invention is an essential component for forming the perovskite structure as described above,
Further, it has a function of a shifter for lowering the Curie temperature of the porcelain composition of the present invention. Furthermore, it significantly increases the insulation resistance,
It also improves the mechanical strength.

The amount of Pb replaced by the Me component can be set as appropriate in consideration of the Curie temperature and the like, but is a region where lead zinc niobate and lead titanate are abundant (x> 0.5, z
> 0.1), 10 mol% or more is preferable, and in the region containing a large amount of lead magnesium niobate (y> 0.6, z <0.05), 1 mol% or more sufficiently exhibits the effect of substitution.

FIG. 1 shows the composition range of the porcelain composition of the present invention.

On the outside of the line segment ad, the firing temperature becomes as high as 1100 ° C. or higher, and the insulation resistance decreases, so that a high CR value cannot be obtained.

On the outside of the line segment cd, since the Curie temperature is originally around room temperature, the Curie point is largely moved to the low temperature side by the replacement with the Me component, and the dielectric constant at room temperature is significantly lowered. Will end up. Also, d ₁ (x = 0.1
0, y = 0.80, z = 0.10), the line segment cd ₁
Is more preferable.

The effect of adding magnesium / lead niobate in a small amount is exhibited, but it is desirable to contain 1 mol% or more for practical use.

Considering the CR value, it is preferable that the content of zinc lead niobate is 15 mol% or more, and more preferably 20 mol% or more. 20 mol
%, The dielectric loss is particularly small.

Further, c ₁ (x = 0.40, y = 0.60, z =
0.00), d ₂ (x = 0.15, y = 0.70, z = 0.15
), D ₃ (x = 0.20, y = 0.60, z = 0.20),
When c ₂ (x = 0.45, y = 0.55, z = 0.00), it is relatively difficult to obtain a dense porcelain outside the line segment c ₁ d ₁ .

In this way, the CR value, T.S. C. C. , Considering sinterability etc., inside the line segment c ₁ d ₂ , especially line segment c ₂ d
₂ , more preferably inside the line segment c ₂ d ₃ . However, in consideration of the dielectric constant and the like, even a composition system divided by such line segments has sufficient characteristics.

FIG. 2 shows changes in the CR value and the dielectric constant depending on the amount of Me in a composition system of zinc / lead niobate 50 mol% and magnesium / lead niobate 50 mol%. As is clear from the figure, the characteristics are significantly improved by the addition of a small amount of the Me component. In particular, the effect on the CR value is remarkable, and the reliability as a ceramic capacitor is excellent.

The present invention is mainly based on the above-mentioned general formula, but the stoichiometric ratio may be slightly different. Converting this composition to an oxide, PbO 46.13 to 69.09 wt% BaO 0.00 to 18.10 wt% SrO 0.00 to 12.99 wt% ZnO 0.42 to 9.13 wt% Nb ₂ O ₅ 15.15 to 27.13 wt% TiO ₂ 0.00 to 14.31 wt% MgO 0.04 to 3.73 wt% (however, the total of BaO and SrO is 0.32 to 18.10 wt
%).

In addition, impurities, additives, substitutes, etc. may be contained within a range that does not impair the effects of the present invention. For example, M
nO ₂ , CoO, NiO, MgO, Sb ₂ O ₃ , ZrO
Examples include transition metals such as ₂ , La ₂ O ₃ and lanthanide elements. The content of these additives is at most about 1 wt%. Mn and Co are especially effective, and 0.01 to 0.5wt
%, It is effective to add a small amount such as%.

Next, a method for producing the composition of the present invention will be described.

As starting materials, Pb, Ba, Sr, Zn,
Oxides of Nb, Ti, Mg or carbonates, salts such as oxalates, hydroxides, organic compounds and the like which become oxides upon firing are weighed in a predetermined ratio, sufficiently mixed and then calcined. This calcination is performed at 700 ° C to 850 ° C. If the calcination temperature is too low, the sintering density will decrease, and if it is too high, the sintering density will also decrease and the insulation resistance will decrease. Next, the calcined product is crushed to produce a raw material powder. Average particle size is 0.8-2μ
m is preferable, and if it is too large, the pores increase in the sintered body, and if it is too small, the moldability decreases. A high dielectric constant ceramic is obtained by molding the raw material powder into a desired shape and firing it. By using the composition of the present invention, firing can be carried out at a relatively low temperature of 1100 ° C or lower, or about 980 to 1080 ° C.

When manufacturing a laminated type element, a binder, a solvent, etc. are added to the above-mentioned raw material powder to form a slurry, a green sheet is formed, and an internal electrode is printed on the green sheet. After that, a predetermined number of layers are laminated, pressure-bonded, and fired to manufacture. At this time, since the dielectric material of the present invention can be sintered at a low temperature, an inexpensive material mainly containing Ag can be used as the internal electrode material.

Since it can be fired at a low temperature as described above, it is also effective as a material for a thick film dielectric paste to be printed and fired on a circuit board or the like.

The porcelain composition of the present invention as described above has a high dielectric constant and T. C. C. Is good. Further, it has a large CR value, and has a sufficient value even at high temperatures, and has excellent reliability at high temperatures.

T. C. C. Is a major feature of the present invention, which is particularly noticeable for large dielectric constants such as K ≧ 10000. When the dielectric constant is large as described above, it is required that (dielectric constant) / (absolute value of temperature change rate) be large. The present invention is also very excellent in this respect.

Further, the dielectric constant bias electric field dependency is also excellent as compared with the conventional barium titanate-based material, and it is possible to obtain a material having a dielectric constant change rate of about 10% or less even at 4 kV / mm. Therefore, it is effective as a material for high pressure. It also has a small dielectric loss and is effective for AC and high frequency applications.

Further, the grain size during firing is also 1 to 3.
Since it is made uniform to μm, it has excellent pressure resistance.

The electrical characteristics have been described above, but the mechanical strength is also sufficiently excellent.

[0036]

EXAMPLES Examples of the present invention will be described below.

As starting materials, Pb, Ba, Sr, Zn,
Starting materials such as Nb, Ti, and Mg oxides and carbonates were mixed in a ball mill etc. at the compounding ratios shown in Table 1 and Table 2.
Calcination at 00-850 ℃. Then, the calcined body was pulverized by a ball mill or the like and dried, and then a binder was added thereto to granulate and press to form a disc-shaped element body having a diameter of 17 mm and a thickness of about 2 mm. The ball for mixing and crushing is to prevent the mixture of impurities.
It is preferable to use a ball having high hardness and high toughness such as partially stabilized zirconia ball.

This element was sintered in air under the conditions of 980 to 1080 ° C. for 2 hours, and silver electrodes were baked on both main surfaces to measure each characteristic. Dielectric loss and capacitance are measured values by a digital LCR meter under the conditions of 1 kHz, 1 Vrms, and 25 ° C, and the dielectric constant was calculated from these values. The insulation resistance was calculated from the value measured with an insulation resistance meter after applying a voltage of 100 V for 2 minutes. In addition, T. C. C. Is expressed as the rate of change at -25 ° C and 85 ° C, using the value at 25 ° C as a reference. The capacitive resistance product is (dielectric constant) × (insulation resistance) × at 25 ° C and 125 ° C.
It was calculated from (vacuum dielectric constant). The insulation resistance was measured in silicone oil to eliminate the effect of moisture in the air. The results are shown in Tables 3 and 4.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4] As is clear from Table 3, the porcelain composition of the present invention has a high dielectric constant (K = 2200 or more) and good temperature characteristics (-25 to 85 ° C).
And within -53%). CR value is also 1900 MΩ ・ μF (25
℃) or more, especially 350MΩ ・ μF even at 125 ℃
Above, it is excellent in reliability at high temperature. In addition, T.
C. C. Is small especially when the dielectric constant is large such that K ≧ 10000. When the dielectric constant is large as described above, it is required that (dielectric constant) / (absolute value of temperature change rate) be large. In the embodiment of the present invention, this value is 220 or more when K ≧ 10000, which is very excellent. Furthermore, the dielectric constant bias electric field dependence is excellent at 45% or less at 1 kV / mm. Also, the dielectric loss is small at 3.5% or less at 25 ° C and 1kHz.

Further, in the composition containing 15 mol% or more of zinc and lead niobate, the CR value is 2000 MΩ · μF or more, and at 20 mol% or more, it is an extremely excellent value of 3000 MΩ · μF or more. Also, when it is 20 mol% or more, the dielectric loss is 2% or less, which is a very small value.

The reference examples in Table 4 are outside the range of the composition of the present invention.

Those containing no Me component (refer to Reference Examples 1 to 1)
7), the dielectric constant is small, the CR value is also extremely small, and the dielectric loss is large. C. C. Will also grow. Reference Example 8 is an example in which the Me component is excessively added, but the dielectric constant is small and the temperature change is extremely large.

FIG. 3 shows the temperature characteristics of the dielectric constant. For comparison, the properties of commercially available barium titanate-based materials for multilayer capacitors are also shown (Reference Examples 9 and 10). Reference example 9
Although it shows a large dielectric constant of about 12000 at 25 ° C, it has a T.S. of more than -80% at -25 ° C and 85 ° C. C. C. Indicates. On the other hand, in the present invention, even when K = 11000 (25 ° C.) (Example 8), it was within −41%, and when K = 6500 (25 ° C.) (Example 3) was within −20%. Extremely small. This T. C. C. , The positive change is more important than the negative change with respect to the value at room temperature, and materials showing a change of + 30% or more do not satisfy any of the standards of EIA, EIAJ and JIS capacitors, and are completely practical as capacitor materials. There is no. For example, Reference Examples 1, 2, 3, 6, 7, and 8 are not practical as capacitor materials.

FIG. 4 is a diagram showing the DC bias electric field dependence. Generally, the dielectric constant tends to decrease as the bias electric field increases, and this tendency becomes more remarkable as the dielectric constant increases. Reference example 9 has a dielectric constant of about 12000, but 1kV
/ Mm shows -80%, and 2 kV / mm shows -93%, showing a very large decrease tendency. In contrast, Example 8 has a dielectric constant of 110.
Despite being almost the same size as 00, it is extremely small at -45% at 1 kV / mm and only about -64% at 2 kV / mm.

Further, barium titanate (Reference Example 10) shows a dielectric constant similar to that of Example 24, but shows a change of -50% at 4 kV / mm, whereas Example 24 shows an extremely high -10%. small. Thus, the composition of the present invention having a small DC bias electric field dependency is effective as a capacitor material for high voltage. Further, when considering a multilayer capacitor and considering the increase in capacity with the same shape, it is necessary to reduce the thickness per one dielectric layer, but in this case, the applied electric field per layer becomes high. However, since the composition of the present invention has excellent bias characteristics, the characteristics do not deteriorate even when applied to such an element. Further, the sample of Example 24 has a very small dielectric loss of 0.01% and is therefore suitable for alternating current.

FIG. 5 is an X-ray diffraction pattern of Example 8, which shows a nearly complete perovskite phase. Therefore, the dielectric constant is 11000, CR value is 34000 MΩ ・ μ
It shows excellent values of F (25 ℃) and 6000MΩ ・ μF (125 ℃). On the other hand, in the case of Reference Example 3 in which the Pb site was not replaced with Ba, a large amount of pyrochlore phase was observed as shown in FIG. Therefore, the dielectric constant is as small as 4500, and the CR value is as small as 620 MΩ · μF (25 ° C),
Not at all practical.

Next, an example in which a laminated ceramic capacitor is prepared by using the composition of Example 8 will be described. First, a binder and an organic solvent were added to roasted powder having such a composition to make a slurry, and then a doctor blade type caster was used to prepare a 30 μm green sheet. This green
An electrode paste of 80 Ag / 20Pd was printed on the sheet with a predetermined pattern, and 20 sheets of the sheet having such an electrode pattern were laminated and pressure-bonded. After that, it was cut into a predetermined shape, degreased, and fired at 1020 ° C. and 2H. After sintering,
An Ag paste was baked as an external electrode to manufacture a monolithic ceramic capacitor. The electrical characteristics are shown in Table 5.

[0051]

[Table 5] The dielectric constant of the obtained monolithic ceramic capacitor is approximately 11000.
It can be seen that each property is sufficiently excellent. Especially T. C. C. Is within ± 50% at -25 to 85 ° C.
E characteristics of EIA and Z5U characteristics of EIA are satisfied.

As described above, Mn in an amount of about 1 wt% or less, preferably 0.5 wt% or less, in a range that does not impair the effects of the present invention,
You may add Co etc. Such additives improve the withstand voltage, T.S. C. C. It is also possible to obtain effects such as improvement of the above and reduction of dielectric loss. Table 6 shows various characteristics when MnO and CoO are added.

[0053]

[Table 6] Also, as in Table 5, the composition of Example 8 was changed to 0.1 mol% MnO.
A monolithic ceramic capacitor was manufactured in the same manner by using those containing CoO and CoO. The results are shown in Table 7.

[0054]

[Table 7] As described above, the ceramic capacitor of the present invention has C.
C. It is excellent in various characteristics such as, and is particularly effective as a laminated ceramic capacitor.

[0055]

As described above, according to the present invention,
It is possible to obtain a ceramic capacitor having a high dielectric constant and excellent temperature characteristics and bias characteristics. In particular, since it is possible to obtain such a porcelain excellent in various characteristics by low temperature firing, it is suitable for application to a laminated ceramic capacitor.

[Brief description of drawings]

FIG. 1 is a composition diagram showing a composition range of a high dielectric constant porcelain composition used in the present invention.

FIG. 2 is a characteristic diagram showing changes in characteristics depending on the Me amount.

FIG. 3 is a temperature characteristic curve diagram of a dielectric constant.

FIG. 4 is a DC bias electric field characteristic curve diagram of a dielectric constant.

FIG. 5 is an X-ray diffraction pattern of the high dielectric constant porcelain composition of the present invention.

FIG. 6 is an X-ray diffraction pattern diagram of a high dielectric constant porcelain composition outside the composition range of the present invention.

Claims (2)

[Claims] 1. A general formula xPb (Zn _1/3 Nb _2/3 ) O ₃ -yPb (Mg _1/3 N
b _2/3 ) O ₃ −zPbTiO ₃ a (x = 0.50, y = 0.00, z = 0.50) b (x = 1.00, y = 0.00) of the ternary diagram with each component as a vertex z = 0.00) c (x = 0.20, y = 0.80, z = 0.00) d (x = 0.05, y = 0.90, z = 0.05) The composition within the line connecting the points (however, line connecting ab) A high dielectric constant porcelain composition obtained by substituting a part of Pb with 1 to 35 mol% of at least one of Ba and Sr is used as a dielectric layer, and a pair of electrodes are provided through this dielectric layer. A ceramic capacitor characterized by being formed. 2. The ceramic capacitor according to claim 1, wherein the high dielectric constant porcelain composition contains 0.5 wt% or less of at least one of Mn and Co.