JPH04363012A - Ceramic capacitor - Google Patents

Abstract

PURPOSE:To realize a high dielectric constant and to improve temperature characteristics and bias characteristics by mixing, calcinating and milling oxides of Pb, Ba, Sr, Zn, Nb, Ti, Mg at specified proportions to manufacture raw powders, by forming a desired shape using the raw powders and by burning it thereafter. CONSTITUTION:A high dielectric constant ceramic composition is used as a dielectric layer, which is formed by replacing a part of Pb of a composition (excepting on a segment connecting a and b) inside a line which connects each point shown by 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, z=0.00), d(x=0.05, y=0.90, z=0.05) of a phase diagram whose top is each component when expressed by a formula xPb(Zn1/3Nb2/3)O3-yPb(Mg1/3 Nb2/3)O3-zPbTiO3 with at least one kind of Ba and Sr of 1 to 35mol%. It is mixed by a ball mill, etc., at the composition ratio and calcinated at 700 to 850 deg.C. Then, it is milled by a ball mill, etc., and then dried. The element is sintered in air at 980 to 1080 deg.C for 2 hours.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides Pb(Zn1/3N
b2/3) Temperature coefficient of dielectric constant (T.
C. C. ) It relates to a ceramic capacitor using a high dielectric constant ceramic composition with small temperature changes as a dielectric layer.

0002

2. Description of the Related Art Electrical properties required for dielectric materials include dielectric constant, temperature coefficient of dielectric constant, dielectric loss, dependence of dielectric constant on electric field, and capacitance-resistance product.

In particular, the capacitance-resistance product (CR value) must take a sufficiently high value, and the RC-
3698B specifies a resistance of 500MΩ・μF or more at room temperature. Furthermore, in order to enable use under even more severe conditions, high temperatures (for example, according to the U.S. Department of Defense standard MIL-C 55681B, 1
The CR value at 25°C is determined. ) is required to maintain a high CR value.

[0004]Although a small temperature coefficient of dielectric constant is required, materials with a large dielectric constant (K) generally have a low temperature coefficient of T.
C. C. tends to be large, and K/T. C. C. is required to be large, that is, the relative value of the change in dielectric constant is required to be small.

Furthermore, when a multilayer type element is considered, since the electrode layer and the dielectric layer are fired integrally, 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. It is required that firing can be performed at low temperatures.

Conventionally known high-permittivity ceramic compositions include those based on barium titanate, in which stannate, zirconate, titanate, etc. are solidly dissolved. It is certainly possible to obtain a material with a high dielectric constant, but the higher the dielectric constant, the higher the T. C. C. There is a problem in that the voltage becomes large and the dependence on the bias electric field also becomes large. Furthermore, the firing temperature of barium titanate-based materials is 13
The temperature is as high as about 00 to 1400°C, and as an electrode material, it is necessary to use an expensive material such as platinum or palladium that can withstand high temperatures, which causes high costs.

[0007] In order to solve the problems of barium titanate, various compositions have been studied. For example, those based on lead iron niobate (Japanese Patent Application Laid-open No. 57-57204)
, one based on magnesium/lead niobate (Japanese Patent Application Laid-open No. 51758/1983), and one based on magnesium/lead tungstate (Japanese Patent Application Laid-open No. 21699/1982). Those containing lead iron niobate as a main component have a problem in that the CR value changes greatly depending on the firing temperature, and the CR value decreases particularly at high temperatures. Products mainly composed of magnesium and lead niobate have a relatively high firing temperature, and
Those mainly composed of magnesium and lead tungstate are
When the CR value is large, the dielectric constant is small, and when the dielectric constant is large, the C
There was a problem that the R value was small. Furthermore, the T. C. C. Although it is superior to the barium titanate type, it is not sufficient.

[0008] Further, research has also been conducted on materials in which a solid solution of lead magnesium niobate and lead titanate is used, in which part of the lead is replaced with barium, strontium, or calcium as required (Japanese Patent Laid-Open Publication No. 121959/1982). However, the T. C. C. Even the best value is -59.8% at -25 to 85°C, which is not sufficient. Furthermore, the most important CR value for a capacitor material is not mentioned, and its usefulness as a capacitor material is not clear.

[0009] Further, in JP-A-57-25607, solid solution materials of magnesium lead niobate and zinc lead niobate are also studied. However, the CR value and T. C. C. There is no mention of this, and its usefulness as a capacitor material is unclear.

0010

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

[0011]

[Means and effects for solving the problems] The present invention provides the general formula xPb(Zn1/3 Nb2/3)O3 -yPb(
Mg1/3 Nb2/3 )O3 -zPbTiO3
When expressed as 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=0.8
0, z= 0.00) d(x= 0.05, y=
0.90, z = 0.05) of the composition within the line connecting each point (excluding the line segment connecting ab)
A ceramic capacitor in which a high permittivity ceramic composition in which part of b is replaced with at least one of 1 to 35 mol% of Ba and Sr is used as a dielectric layer, and a pair of electrodes are formed through this dielectric layer. 0.5wt of at least one of Mn and Co.
% or less.

Various perovskite-type porcelain materials have been studied as dielectric materials, but zinc-lead niobate (Pb(Zn1/3 Nb2/3)O3) has a perovskite structure when made into porcelain. It was considered difficult to use as a dielectric material (NEC R
search & Development No.
．． 29 April 1973 p. 15-21
reference). According to the research of the present inventors, Pb(Zn1/3
Nb2/3)O3 Pb site is Ba or Sr
It was found that a stable perovskite structure can be formed in porcelain by substituting an appropriate amount of . Furthermore, it has been found that such a ceramic composition exhibits extremely high dielectric constant and insulation resistance, and also has extremely good temperature characteristics. It was also found that the mechanical strength was excellent. Further research revealed that by combining this zinc lead niobate with magnesium lead niobate and lead titanate, a high dielectric constant porcelain composition with even higher dielectric constant and insulation resistance could be obtained. I found it.

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

Me=Ba, Sr are elements necessary to form the perovskite structure of the above general formula, and 1
If it is less than mol %, a pyrochlore structure is mixed, and high dielectric constant and high insulation resistance are not exhibited. 35 mol%
If this is the case, the dielectric constant will be as low as about 1,000 or less, or the firing temperature will be as high as 1,100° C. or more. Therefore, the amount of substitution with the Me component is (Pb1-α
Meα), 0.01 <α< 0.35.

In dielectric materials, in order to increase the capacity at room temperature, the Curie temperature should be around room temperature (0 to 30°C).
Make sure to come. The Me component of the present invention is an essential component for forming a perovskite structure as described above, but it also functions as a shifter to lower the Curie temperature of the ceramic composition of the present invention. Furthermore, it significantly increases insulation resistance and improves mechanical strength.

[0016] The amount of Pb replaced by the Me component can be appropriately set in consideration of the Curie temperature, etc.;
z>0.1), preferably 10 mol% or more,
Region with a lot of magnesium/lead niobate (y > 0.6,
z<0.05), 1 mol % or more is sufficient to exhibit the effect of the substitution.

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

[0018] Outside the line segment ad, the firing temperature is 1100°C.
Insulation resistance also decreases, resulting in high C.
Unable to obtain R value.

[0019] Furthermore, outside the line segment cd, the Curie temperature is originally near room temperature, so the substitution with the Me component significantly shifts the Curie point to the lower temperature side, and the dielectric constant at room temperature decreases significantly. It ends up. Also, d1 (x= 0
．． 10, y=0.80, z=0.10), the inside of the line segment cd1 is more preferable.

[0020] Magnesium/lead niobate exhibits its effect even when added/contained in small amounts, but in practice it is limited to 1 mol%.
It is desirable to contain the above amount.

[0021] Furthermore, in consideration of the CR value, it is preferable to contain zinc/lead niobate in an amount of 15 mol% or more, and more preferably 20 mol% or more. When the content is 20 mol% or more, the dielectric loss is also particularly small.

[0022] Also, c1 (x= 0.40, y= 0
．． 60, z= 0.00), d2 (x= 0.1
5, y=0.70, z=0.15), d3 (
x= 0.20, y= 0.60, z= 0.20
), c2 (x= 0.45, y= 0.55,
z=0.00), it is relatively difficult to obtain dense porcelain outside the line segment c1 d1.

[0023] In this way, the CR value, T. C. C. , considering sinterability, etc., the inside of line segment c1 d2, especially line segment c
2 d2 , and more preferably inside the line segment c2 d3 . However, when the dielectric constant and the like are taken into consideration, even a composition system divided by such line segments has sufficient characteristics.

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

Although the present invention is mainly based on the compound represented by the above general formula, the stoichiometric ratio may be slightly different. When this composition is converted into oxide, PbO
46.13 ~69.09 wt%BaO
0.00 ~ 18.10 wt%SrO
0.00 ~12.99 wt%ZnO
0.42 ~ 9.13 wt%Nb2O
5 15.15 ~27.13 wt%TiO2
0.00 ~14.31 wt%MgO
0.04 to 3.73 wt% (however,
The total of BaO and SrO is 0.32 to 18.10
wt%).

[0026] Furthermore, impurities, additives, substitutes, etc. may be included within a range that does not impair the effects of the present invention. For example, M
nO2, CoO, NiO, MgO, Sb2O3,
Examples include transition metals such as ZrO2 and La2O3 and lanthanide elements. The content of these additives is about 1 wt% at most. Mn and Co are particularly effective;
Addition of a small amount of about 0.01 to 0.5 wt% is effective.

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

[0028] As starting materials, Pb, Ba, Sr, Zn,
Oxides of Nb, Ti, and Mg or salts such as carbonates and oxalates that become oxides by firing, hydroxides, organic compounds, etc. are weighed out in predetermined proportions, thoroughly mixed, and then calcined. This calcination is performed at about 700°C to 850°C. If the calcination temperature is too low, the sintered density will decrease, and if it is too high, the sintered density will also decrease and the insulation resistance will decrease. Next, the calcined product is pulverized to produce raw material powder. Average particle size is 0
．． The diameter is preferably about 8 to 2 μm; if it is too large, pores will increase in the sintered body, and if it is too small, moldability will deteriorate. A high dielectric constant ceramic is obtained by molding such raw material powder into a desired shape and firing it. By using the composition of the present invention, firing can be performed at 1100°C or less, 980-1
It can be carried out at a relatively low temperature of about 0.80°C.

When manufacturing a multilayer type element, a binder, a solvent, etc. are added to the raw material powder described above to form a slurry, a green sheet is formed, and internal electrodes are printed on this green sheet. After that, a predetermined number of sheets are laminated and pressed together, and then fired. At this time, since the dielectric material of the present invention can be sintered at a low temperature, for example, A
An inexpensive material mainly composed of g can be used.

Furthermore, since it can be fired at such a low temperature, it is also effective as a material for thick film dielectric paste to be printed and fired on circuit boards and the like.

The ceramic composition of the present invention has a high dielectric constant and a T. C. C. is good. In addition, the CR value is large, particularly sufficient even at high temperatures, and has excellent reliability at high temperatures.

[0032]T. C. C. A small characteristic of the present invention is that K is small, and this is particularly noticeable in the case of a large dielectric constant such as K≧10,000. When the dielectric constant is large like this, it is required that (permittivity)/(absolute value of temperature change rate) be large. The present invention is also very superior in this respect.

Furthermore, the bias electric field dependence of the dielectric constant is superior to that of conventional barium titanate-based materials, and even at a rate of change in dielectric constant of 4 kV/mm, it is possible to obtain a material with a dielectric constant change rate of about 10% or less. Therefore, it is effective as a material for high pressure. Furthermore, it has low dielectric loss and is effective for alternating current and high frequency applications.

[0034] Furthermore, the grain size during firing is 1 to 3.
It also has excellent pressure resistance because it is uniform in μm.

Although the electrical properties have been described above, the mechanical strength is also sufficiently excellent.

[0036]

[Examples] Examples of the present invention will be described below.

[0037] As starting materials, Pb, Ba, Sr, Zn,
Starting materials such as oxides and carbonates of Nb, Ti, and Mg are mixed in a ball mill etc. at the compounding ratio shown in Tables 1 and 2,
Calcinate at 700-850°C. Next, this calcined body is
After pulverizing with Lumil etc. and drying, add a binder and granulate.
This was pressed to form a disc-shaped element having a diameter of 17 mm and a thickness of about 2 mm. As the balls for mixing and grinding, it is preferable to use balls with high hardness and high toughness, such as partially stabilized zirconia balls, in order to prevent the mixing of impurities.

[0038] This element body was heated to 980 to 1080°C in air.
It was sintered for 2 hours, silver electrodes were baked on both main surfaces, and each characteristic was measured. Dielectric loss and capacity are 1kHz, 1Vrm
The dielectric constant was calculated from this value, which was measured using a digital LCR meter under conditions of 25° C. Moreover, the insulation resistance was calculated from the value measured using an insulation resistance meter after applying a voltage of 100 V for 2 minutes. In addition, T. C.
C. is expressed as a rate of change at -25°C and 85°C with the value at 25°C as a reference. The capacitance-resistance product is 25℃ and 12
(Dielectric constant) x (insulation resistance) x (vacuum permittivity) at 5℃
I asked for it from Insulation resistance measurements were performed in silicone oil to eliminate the effect of atmospheric moisture. Table 3 shows the results.
and shown in Table 4.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4] As is clear from Table 3, the ceramic composition of the present invention has a high dielectric constant (K=2200 or more) and good temperature characteristics (-25
-53% at ~85°C). CR value is also 1900M
It has a high resistance of Ω·μF (at 25°C) or more, and in particular, it has a resistance of 350MΩ·μF or more even at 125°C, and has excellent reliability at high temperatures. Also, T. C. C. The smallness of is K≧
This is especially true for large dielectric constants such as 10,000. When the dielectric constant is large like this, (permittivity)/(
(absolute value of temperature change rate) is required to be large. In the embodiment of the present invention, when K≧10000, this value is 22
It is 0 or more, which is very excellent. Furthermore, the dielectric constant bias electric field dependence is excellent, being within 45% at 1 kV/mm. Furthermore, the dielectric loss is low at 3.5% or less at 25°C and 1kHz.

[0043] Furthermore, 15 mol of zinc/lead niobate
% or more, the CR value is 2000MΩ・μF
and more than 20 mol%, 3000M
It takes an extremely excellent value of Ω・μF or more. Also, 20 m
At ol% or more, the dielectric loss also shows a very small value of 2% or less.

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

Those containing no Me component (Reference Examples 1 to 7)
), the dielectric constant is small, the CR value is also extremely small, the dielectric loss is large, and furthermore, T. C. C. It also gets bigger. Further, in Reference Example 8, an excessive amount of Me component was added, but the dielectric constant was small and the temperature change thereof was also extremely large.

FIG. 3 shows the temperature characteristics of the dielectric constant. For comparison, the characteristics of commercially available barium titanate materials for multilayer capacitors are also shown (Reference Examples 9 and 10). Reference example 9
exhibits a large dielectric constant of about 12,000 at 25°C, but a T. of more than -80% at -25°C and 85°C. C. C
．． shows. On the other hand, in the present invention, K=11000(
Even when K = 6500 (25°C) (Example 8) it is within -41%, and when K = 6500 (25°C) (Example 3)
It is extremely small, within -20%. This T. C. C. Positive changes are more important than negative changes relative to the value at room temperature, and materials that show a change of +30% or more are EIA, EIAJ.
Also, it does not satisfy any of the JIS capacitor standards, and is completely impractical as a capacitor material. For example, Reference Examples 1, 2, 3, 6, 7, 8, etc. are not practical at all as capacitor materials.

FIG. 4 is a diagram showing the dependence on the DC bias electric field. Generally, the dielectric constant tends to decrease as the bias electric field increases, and this tendency becomes more pronounced as the dielectric constant increases. Reference Example 9 has a dielectric constant of about 12,000, but shows a very large tendency to decrease by -80% at 1 kV/mm and -93% at 2 kV/mm. On the other hand, in Example 8, although the dielectric constant is approximately the same as 11000, it is extremely small at -45% at 1 kV/mm, and only about -64% at 2 kV/mm.

Furthermore, barium titanate (Reference Example 10) shows a dielectric constant similar to that of Example 24, but shows a -50% change at 4 kV/mm, whereas Example 24 shows a -10% change in dielectric constant.
%, which is extremely small. As described above, the composition of the present invention having a small dependence on a DC bias electric field is effective as a material for a high-voltage capacitor. In addition, when considering a multilayer capacitor, in order to increase the capacitance with the same shape, it is necessary to reduce the thickness of each dielectric layer, but in this case, the applied electric field per layer increases. However, since the composition of the present invention has excellent bias characteristics, the characteristics will not deteriorate even when applied to such devices. Further, the sample of Example 24 has an extremely small dielectric loss of 0.01%, so it is suitable for AC use.

FIG. 5 is an X-ray diffraction pattern diagram of Example 8, which shows an almost perfect perovskite phase. Therefore, the dielectric constant is 11000, and the CR value is 340.
00MΩ・μF (25℃), 6000MΩ・μF (1
25°C), which is an excellent value. On the other hand, in the case of Reference Example 3 in which the Pb site was not replaced by Ba, a large amount of pyrochlore phase was observed as shown in FIG. Therefore, the dielectric constant is as low as 4500, and the CR value is 620MΩ・
It is extremely small at μF (25°C) and is not practical at all.

Next, an example in which a multilayer ceramic capacitor was manufactured 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 form a slurry, and then a 30 μm green sheet was prepared using a doctor blade type caster. An 80Ag/20Pd electrode paste was printed in a predetermined pattern on this green sheet, and 20 sheets having such an electrode pattern were laminated and pressure-bonded. Thereafter, it was cut into a predetermined shape, degreased, and fired at 1020° C. for 2 hours. After sintering, Ag paste was baked as an external electrode to produce a multilayer ceramic capacitor. Its electrical characteristics are shown in Table 5.

[0051]

[Table 5] The dielectric constant of the obtained multilayer ceramic capacitor is approximately 11
000, and it can be seen that each characteristic is sufficiently excellent. Especially T. C. C. is within ±50% at -25 to 85°C, satisfying JIS E characteristics and EIA Z5U characteristics.

As described above, Mn, Co, etc. may be added in an amount of about 1 wt % or less, preferably 0.5 wt % or less, within a range that does not impair the effects of the present invention. Such additives are
Improved pressure resistance, T. C. C. It is also possible to obtain effects such as improvement of dielectric loss and reduction of dielectric loss, and these effects appear with a small amount of about 0.01 wt%. Table 6 shows various properties when MnO and CoO are added.

[0053]

[Table 6] Similarly to Table 5, 0.1 mol% was added to the composition of Example 8.
A multilayer ceramic capacitor was manufactured in the same manner using a capacitor to which MnO and CoO were added. The results are shown in Table 7.

[0054]

[Table 7] As described above, the ceramic capacitor of the present invention has T. C.
C. It has excellent properties such as, and is particularly effective as a multilayer ceramic capacitor.

[0055]

[Effects of the Invention] As explained above, according to the present invention,
A ceramic capacitor with a high dielectric constant and excellent temperature characteristics and bias characteristics can be obtained. In particular, since porcelain with such excellent properties can be obtained by firing at low temperatures, it is suitable for application to multilayer ceramic capacitors.

[Brief explanation of the drawing]

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

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

[Figure 3] Temperature characteristic curve diagram of permittivity.

[Figure 4] DC bias electric field characteristic curve diagram of dielectric constant.

FIG. 5 is an X-ray diffraction pattern diagram of a high dielectric constant ceramic composition according to the present invention.

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

Claims (2)

[Claims] Claim 1: General formula xPb(Zn1/3 Nb2/3)O3 -yPb(
Mg1/3 Nb2/3 )O3 -zPbTiO3
When expressed as 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=0.8
0, z= 0.00) d(x= 0.05, y=
0.90, z = 0.05) of the composition within the line connecting each point (excluding the line segment connecting ab)
A high dielectric constant ceramic composition in which part of b is replaced 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 formed through this dielectric layer. ceramic capacitor. 2. The ceramic capacitor according to claim 1, wherein the high dielectric constant ceramic composition contains at least 0.5 wt % of at least one of Mn and Co.