JP3008408B2 - Dielectric ceramic composition for multilayer ceramic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL APPLICATION The present invention has a high dielectric constant, high insulation resistance, high dielectric breakdown voltage,
The present invention relates to a dielectric ceramic composition for a multilayer ceramic capacitor which has excellent quality factor Q, has a small capacitance temperature coefficient, and can suppress the occurrence of chip standing.

2. Description of the Related Art Conventionally, the following system has been known as a dielectric ceramic composition having a high dielectric constant, a high insulation resistance, an excellent quality factor Q, and a small capacitance temperature coefficient.

And issues BaO-TiO ₂ -Nd ₂ O ₃ based _{· BaO-TiO 2 -Sm 2 O} 3 system to be Solved by the Invention However, these compositions, for example, 0.09BaO-0.55TiO ₂
When a disc-shaped porcelain capacitor is manufactured using a dielectric material having a composition ratio of −0.36 NdO _3/2 , the average value of the insulation resistance is:
8.0 × 10 ¹² Ω, average value of dielectric breakdown strength: 30 Kv / mm,
Not a satisfactory value. Although the density of this dielectric porcelain is 5.6 g / cm ³ , in general, in reflow soldering of a multilayer ceramic capacitor having a length of L3.2 × width W1.6 mm or less, especially in a vapor reflow soldering, a chip ( Usually, the tombstone phenomenon and the Funhattan phenomenon are easily generated), and there is a problem that the density of the dielectric porcelain for preventing the chip from standing must be increased.

Means for Solving the Problems Accordingly, the dielectric ceramic composition for a multilayer ceramic capacitor of the present invention has a general formula xBaO-y ｛(TiO ₂ ) _(1-m) (SnO ₂ )
_m ｝ −zReO _3/2 (however, x + y + z = 1.00, 0.01 ≦ m
≦ 0.20, Re is one or more rare earth elements selected from La, Pr, Nd, and Sm. ), X, y, z are the main components 1 consisting of a range of molar ratios surrounded by points a, b, c, d, e, f shown in the following table.
It contains 0.1 to 10.0 parts by weight of Ta ₂ O ₅ as an auxiliary component with respect to 00 parts by weight.

According to the action this configuration, cation vacancies generated by replacing a part of tetravalent Ti and Sn in the dielectric ceramic composition in pentavalent Ta, e due to oxygen defect during firing ^- compensating for And Ti
O ₂ can be suppressed from being reduced. Therefore, when producing a multilayer ceramic capacitor, it is possible to prevent the formation of a compound of Ti and Pd and other metals forming an internal electrode in the dielectric layer, and to improve the adhesion at the interface between the dielectric layer and the internal electrode, A multilayer ceramic capacitor having a large capacitance and a large Q value and a small variation can be obtained.

Also, the conventional dielectric ceramic composition was reduced during firing.
Although TiO ₂ is reoxidized to some extent during the cooling process, the inside of the dielectric layer and the inside of each crystal particle are hardly reoxidized and remain in an oxygen-deficient state. This oxygen deficiency contributes to electrical conduction,
It degrades the insulation resistance and dielectric breakdown strength of the dielectric ceramic composition. The dielectric porcelain composition of the present invention compensates for e ⁻ due to oxygen vacancies during sintering, by cation vacancies generated by partially replacing tetravalent Ti and Sn with pentavalent Ta.

Therefore, it is possible to obtain a multilayer ceramic capacitor having improved insulation resistance and dielectric breakdown strength as compared with the prior art.

Further, by substituting a part of Ti with Sn, the density of the dielectric ceramic composition is improved. Therefore, when a multilayer ceramic capacitor is used, the occurrence of chip standing can be suppressed.

EXAMPLES Hereinafter, the present invention will be described with reference to specific examples.

(Example 1) Chemically high purity BaCo ₃ , TiO ₂ , SnO ₂ , La ₂ O was used as a starting material.
₃ , Pr ₆ O ₁₁ , Nd ₂ O ₃ , Sm ₂ O ₃ and Ta ₂ O ₅ powders are weighed so as to have the composition ratios shown in Table 1 below, and purified in a rubber-lined ball mill equipped with an agate ball. It was put together with water, wet-mixed, and dehydrated and dried. The dried powder was placed in a high alumina crucible and calcined in air at 1100 ° C. for 2 hours. The calcined powder was put together with pure water in a rubber-lined ball mill equipped with an agate ball, wet pulverized, and then dehydrated and dried.
An organic binder was added to the pulverized powder, and the mixture was homogenized, sieved through a 32-mesh sieve, and molded into a diameter of 15 mm and a thickness of 0.4 mm using a mold and a hydraulic press at a molding pressure of 1 ton / cm ² . Next, the molded disc was placed in an alumina sheath covered with zirconia powder and fired in air at a temperature shown in Table 1 for 2 hours to obtain a dielectric ceramic having a composition ratio shown in Table 1. .

The thickness, diameter and weight of the thus obtained dielectric porcelain disk were measured, and the weight was divided by the volume calculated from the thickness and diameter to obtain the density of the dielectric porcelain.

In addition, the sample for measuring dielectric constant, goodness Q, and temperature coefficient of capacitance was prepared by baking silver electrodes on both sides of the dielectric porcelain disk, and the sample for measuring insulation resistance and dielectric strength was the same as that of the dielectric porcelain disk. A portion having no silver electrode with a width of 1 mm was provided inside the outer periphery, and the silver electrode was baked. The dielectric constant, goodness Q, and capacitance temperature coefficient are the YHP digital LCR meter model 4275A.
Measurement temperature 20 ℃, measurement voltage 1.0Vrms, measurement frequency
It was determined from measurement at 1 MHz. Note that the capacitance temperature coefficient is
The capacitances at 20 ° C. and 85 ° C. were measured and determined by the following equation.

TC = (C-Co) / Co × 1/65 × 10 ⁶ TC: Temperature coefficient of capacitance (ppm / ° C) Co: Capacitance at 20 ° C (pF) C: Capacitance at 85 ° C ( pF) The dielectric constant was determined by the following equation.

K = 143.8 × Co × t / D ² K: dielectric constant Co: capacitance at 20 ° C. (pF) D: diameter of dielectric porcelain (mm) t: thickness of dielectric porcelain (mm) Is YHP HR meter model 4329A
And a measurement voltage of 50 V DC for a measurement time of 1 minute.

The dielectric breakdown strength was measured by using a high voltage power supply PHS35K-3 manufactured by Kikusui Electronics Co., Ltd., placing the sample in silicon oil, and dividing the dielectric breakdown voltage obtained at a step-up speed of 50 V / sec by the dielectric thickness. And the dielectric breakdown strength per 1 mm.

The test conditions are shown in Table 1, and the test results are shown in Table 2 below.

FIG. 1 is a ternary diagram showing the composition range of the main component of the composition according to the present invention. The reason for limiting the composition range of the main component will be described with reference to FIG. That is, sintering is extremely difficult in the region A. Further, in the region B, the degree of goodness Q is reduced and is not practical. Furthermore, in the C and D regions, the temperature coefficient of capacitance becomes too large on the minus side, which is not practical. Then, in the E region, the capacitance temperature coefficient shifts in the positive direction, but the dielectric constant is too small to be practical. Also, by selecting Re from La, Pr, Nd, and Sm, La, P
It is possible to shift the capacitance temperature coefficient in the positive direction without greatly lowering the dielectric constant in the order of r, Nd, Sm,
The capacitance temperature coefficient can be adjusted by one or a combination of La, Pr, Nd, and Sm.

In addition, by replacing TiO ₂ with SnO ₂ , the effect of increasing the density of the dielectric porcelain without significantly changing the values of the dielectric constant, the quality factor Q, the temperature coefficient of capacitance, the insulation resistance, and the dielectric breakdown strength. When the substitution rate m is less than 0.01, there is no substitution effect. On the other hand, when it exceeds 0.20, the dielectric constant and the goodness Q decrease, and the temperature coefficient of capacitance becomes too large on the minus side, which is not practical.

In addition, by containing a sub-component Ta ₂ O ₅ with respect to the main component, there is an effect of improving insulation resistance and dielectric breakdown strength,
When the content of Ta ₂ O ₅ is less than 0.1 part by weight with respect to 100 parts by weight of the main component, the dielectric breakdown strength is not so large and is excluded from the scope of the present invention. On the other hand, the content of Ta ₂ O ₅
If the amount exceeds 0.0 parts by weight, the degree of goodness Q and insulation resistance decrease, and the temperature coefficient of capacitance increases to the minus side, which is not practical.

Note that in the method of manufacturing the dielectric porcelain in the example, Ba
CO ₃ , TiO ₂ , SnO ₂ , La ₂ O ₃ , Pr ₆ O ₁₁ , Nd ₂ O ₃ , Sm ₂ O ₃ and Ta ₂ O ₃
However, the method is not limited to this method, and BaO, Ti is heated by heating in the air such as a compound such as BaTiO ₃ or a carbonate or a hydroxide so as to obtain a desired composition ratio.
Even if a compound that becomes O ₂ , SnO ₂ , La ₂ O ₃ , Pr ₆ O ₁₁ , Nd ₂ O ₃ , Sm ₂ O ₃ and Ta ₂ O ₅ can be used, the same characteristics as those of the example can be obtained. .

Further, even if the main component is calcined in advance and the subcomponent is added, the same characteristics as those of the embodiment can be obtained.

Further, in addition to the above basic composition, SiO ₂ , MnO ₂ , Fe ₂ O ₃ , Zn
Salts, oxides, and the like, which are generally considered to be fluxes, such as O, can be added as long as the properties are not impaired.

Effects of the Invention According to the present invention, tetravalent Ti in a dielectric porcelain composition is
And cation vacancies generated by substituting a part of Sn with pentavalent Ta to compensate for e ⁻ due to oxygen deficiency during firing,
The reduction of TiO ₂ can be suppressed. Therefore, when manufacturing a multilayer ceramic capacitor, it is possible to prevent the generation of a compound of Ti in the dielectric layer and a metal forming an internal electrode such as Pd,
In order to improve the adhesion at the interface between the dielectric layer and the internal electrode,
A multilayer ceramic capacitor having a large capacitance and a large Q value and a small variation can be obtained.

Also, the conventional dielectric ceramic composition was reduced during firing.
Although TiO ₂ is reoxidized to some extent during the cooling process, the inside of the dielectric layer and the inside of each crystal particle are hardly reoxidized and remain in an oxygen-deficient state. This oxygen deficiency contributes to electrical conduction,
It degrades the insulation resistance and dielectric breakdown strength of the dielectric ceramic composition. The dielectric porcelain composition of the present invention compensates for e ⁻ due to oxygen vacancies during sintering, by cation vacancies generated by partially replacing tetravalent Ti and Sn with pentavalent Ta.

Therefore, it is possible to obtain a multilayer ceramic capacitor having improved insulation resistance and dielectric breakdown strength as compared with the prior art.

Further, by replacing a part of Ti with Sn, the density of the dielectric ceramic composition is improved, so that when a multilayer ceramic capacitor is used, occurrence of chip standing can be suppressed, and mountability can be improved. it can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a ternary diagram illustrating a composition range of a main component of a composition according to the present invention.

Claims (1)

(57) [Claims] 1. The formula xBaO-y ｛(TiO ₂ ) _(1-m) (SnO ₂ )
_m ｝ −zReO _3/2 (where x + y + z = 1.0
0, 0.01 ≦ m ≦ 0.20, and Re is one or more rare earth elements selected from La, Pr, Nd, and Sm. ), X, y, and z are principal components 1 composed of a range of molar ratios surrounded by points a, b, c, d, e, and f shown in the following table.
A dielectric ceramic composition for a multilayer ceramic capacitor, comprising 0.1 to 10.0 parts by weight of Ta ₂ O ₅ as an auxiliary component with respect to 00 parts by weight.