JP2907437B2 - Multilayer ceramic capacitors - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multilayer ceramic capacitor having an internal electrode containing palladium.

Description of the Related Art For example _{0.11BaO-0.88TiO 2 -0.21Nd 2 BaO-} TiO 2 of O _3,
Forming a dielectric layer using -Nd ₂ O ₃ based dielectric material,
It was a multilayer ceramic capacitor using palladium as an internal electrode.

Problems to be Solved by the Invention In the multilayer ceramic capacitor having the above structure, the internal electrodes are made thin in order to prevent the occurrence of delamination of the internal electrodes. However, when the dielectric layer containing a large amount of TiO ₂ such as a material having a small Ba / Ti ratio is generally fired,
The organic binder contained in the dielectric layer allows TiO ₂
Is reduced. And the Ti generated by the reduction is
Perhaps because of the formation of a compound with Pd, the internal electrode expands in volume, and as a result, the internal electrode looks like a bead, causing the internal electrode to break, and the adhesion at the interface between the dielectric layer and the internal electrode containing Pd is reduced. descend. As a result, there has been a problem that the capacitance and the Q value decrease and the variation increases.

Therefore, an object of the multilayer ceramic capacitor of the present invention is to provide a multilayer ceramic capacitor having a large capacitance and a large Q value and a small variation by suppressing disconnection of internal electrodes.

Means for Solving the Problems In order to achieve this object, a multilayer ceramic capacitor according to the present invention includes a laminated body in which dielectric layers and internal electrodes are alternately laminated, and an exposed end face of the internal electrode of the laminated body. And an external electrode provided in the dielectric layer, wherein the dielectric layer has a general formula xBaO
−yTiO ₂ −zRe ₂ O ₃ (where x + y + z = 1.00, Re ₂ O
₃ is an oxide of at least one rare earth element selected from La ₂ O ₃ , Pr ₂ O _11/3 , Nd ₂ O ₃ , and Sm ₂ O ₃ . ), X,
y, z is 100 parts by weight of the main component consisting of a range of molar ratios surrounded by points a, b, c, d, e, f shown in the following table,
b ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅
The internal electrode contains palladium in an amount of from 0.01 to 0.010 mol part.

Action According to this configuration, a part of the tetravalent Ti in the dielectric layer is reduced to 5%.
Substitution with two or more types selected from monovalent Nb, Ta and V suppresses the reduction of TiO ₂ and prevents the formation of a compound of Ti and Pd. As a result, the adhesion at the interface between the dielectric layer and the internal electrode is improved, so that a multilayer ceramic capacitor having a large capacitance and a large Q value and a small variation is obtained.

In the conventional dielectric layer, TiO ₂ reduced by firing is reoxidized to some extent during the cooling process, but the inside of the dielectric layer and the inside of each crystal grain are hardly reoxidized and remain in an oxygen-deficient state. Therefore, by neutralizing the effective charge + 2e of the oxygen atom with 3d electrons on the titanium atom, two Ti ³⁺ are formed for each oxygen vacancy, and electron hopping via the Ti ³⁺ causes the dielectric layer Degrades insulation resistance and dielectric breakdown strength. Therefore, the present invention provides a cation vacancy formed by substituting a part of tetravalent Ti in a dielectric layer with two or more kinds selected from pentavalent Nb, Ta, and V.
e ^- to compensate for. As a result, it is possible to obtain a multilayer ceramic capacitor having improved insulation resistance and dielectric breakdown strength as compared with conventional ones.

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

(Example 1) As starting materials, chemically pure BaCO ₃ , TiO ₂ , ZrO ₂ , La ₂ O
₃ , Pr ₆ O ₁₁ , Nd ₂ O ₅ , Sm ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and V ₂ O ₅ powders are weighed so as to have the composition ratios shown in Table 1 below, and agate. Pure water was put into a rubber-lined ball mill equipped with balls, 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 into 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, sized 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 disk was placed in an alumina sheath covered with zirconia powder, and a dielectric ceramic having a composition ratio shown in Table 1 below was obtained in air. The dielectric ceramic disk thus obtained was measured for thickness and diameter, and the dielectric constant, goodness Q, and capacitance temperature coefficient measurement sample were baked with silver electrodes on both surfaces of the dielectric ceramic disk. The sample for measuring the insulation resistance and the dielectric breakdown strength was provided with a portion having no silver electrode with a width of 1 mm inside the outer periphery of the dielectric porcelain disk, and the silver electrode was baked. And the dielectric constant, goodness Q and capacitance temperature coefficient are
Using a digital LCR meter model 4275A manufactured by YHP, measurement was performed at a measurement temperature of 20 ° C., a measurement voltage of 1.0 Vrms, and a measurement frequency of 1 MHz. The capacitance temperature coefficient is 20 ℃ and 85 ℃
Was obtained by the following equation using the capacitance of

TC = (C−C ₀ ) C ₀ × 1/65 × 10 ⁶ TC: Capacitance temperature coefficient (ppm / ° C) C ₀ : Capacitance at 20 ° C (pF) C: Electrostatic at 85 ° C Capacitance (pF) The dielectric constant was determined by the following equation.

K = 143.8 × C ₀ × t / D ² K: Dielectric constant C ₀ : Capacitance at 20 ° C (pF) D: Diameter of dielectric ceramic (mm) t: Thickness of dielectric ceramic (mm) Insulation resistance 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. Further, the crystal grain size was determined by observation with an optical microscope at a magnification of 400.

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

Here, FIG. 1 is a ternary diagram showing the composition range of the main component of the dielectric layer, and 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 ₂ O ₃ from La ₂ O ₃ , Pr ₂ O _11/3 , Nd ₂ O ₃ , Sm ₂ O ₃ , La ₂ O ₃ , Pr ₂ O _11/3 , Nd ₂ O ₃ , Without significantly lowering the dielectric constant in the order of Sm ₂ O ₃ , it is possible to shift the temperature coefficient of capacitance in the positive direction, La ₂ O ₃ , Pr ₂ O _11/3 , Nd ₂ O ₃ , Sm _Two
The capacitance temperature coefficient can be adjusted by one or a combination of O ₃ .

(Example 2) As starting materials, chemically pure BaCO ₃ , TiO ₂ , Nd ₂ O ₅ , Nb ₂
Using O ₅ , Ta ₂ O ₅ and V ₂ O ₅ powder, the main component is 0.11 BaO−0.6
100 parts by weight of 8TiO ₂ −0.21Nd ₂ O ₃ , (Nb ₂ O ₅ ) _0.4 (T
a ₂ O ₅ ) _0.3 (V ₂ O ₅ ) _0.3 is 0,0.0001,0.0010,0.0100,0.020
A calcined powder containing 0 mole part is produced in the same manner as in Example 1. However, (Nb ₂ O ₅ ) _0.4 (Ta ₂ O ₅ ) _0.3 (V ₂ O ₅ ) _0.3
Is within the range of the present invention, and 0.0010,0.0100 mol parts is within the range of the present invention.

An organic binder, a plasticizer, a dispersant, and an organic solvent were added to the calcined and pulverized powder, and mixed with a polyethylene pot equipped with alumina balls to prepare a slurry. After mixing
Filtration was performed using a 300 mesh nylon cloth. The slurry after filtration was formed into a sheet on a polyester film that had been subjected to a mold release treatment by a doctor blade so that the dielectric thickness after sintering was 12 μm.

Next, ten sheets peeled from the polyester film were laminated on a support. On this, an internal electrode palladium paste ML-3724 manufactured by Shoei Chemical Co., Ltd. was screen-printed such that the internal electrode thickness after sintering became 2 μm, and dried. One sheet peeled from the polyester film was laminated thereon. On this, the printing position was shifted so that the internal electrode overlapping dimension after sintering was 1.2 mm × 0.7 mm, the internal electrode palladium paste was printed, and after drying, one sheet peeled off from the polyester film was laminated. These operations were repeated until the number of dielectric layers reached 19. On this, 10 sheets peeled from the polyester film were laminated. After sintering this laminate, the internal electrode overlap dimension
The multilayer ceramic capacitor was cut into a laminated ceramic capacitor having a laminated structure of 1.2 mm × 0.7 mm, a dielectric thickness of 12 μm, and 19 dielectric layers. The cut sample is placed in an alumina sheath covered with zirconia powder, and is heated from room temperature to 350 ° C. in air.
Up to 5 ° C / hr, from 350 ° C at 100 ° C / hr,
After firing at 1270 ° C for 2 hours, the temperature was lowered to room temperature at 100 ° C / hr.
Next, the fired sample is put together with pure water into a polyethylene pot with a waterproof sandpaper stuck on the inside, and the polyethylene pot is rotated to polish the fired sample surface to sufficiently expose the internal electrode portion to be joined to the external electrode. Was. This sample was taken out of the polyethylene pot and dried, and then a silver external electrode was baked on the exposed portion of the internal electrode to make conduction with the internal electrode, thereby producing a multilayer ceramic capacitor.

The capacitance, goodness Q, capacitance temperature coefficient, insulation resistance, and dielectric breakdown strength of these samples were determined by measurement under the same conditions as in Example 1. In addition, the confirmation of the laminated structure was performed by polishing about 断面 of the length and width directions of the multilayer ceramic capacitor in a polished cross section, the overlap size of the internal electrodes was 100, and the dielectric thickness and internal electrode thickness were 400 magnifications. It was determined by microscopic observation.

FIG. 2 shows the measurement results. With reference to FIG. 2, the reason why the content range of the auxiliary component Ta ₂ O _{5 in} the dielectric layer is limited will be described with a graph. As shown in FIG. ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅
The effect of improving the insulation resistance and the dielectric breakdown strength, increasing the capacitance and the goodness Q, and reducing the variation in the capacitance and the goodness Q are obtained by containing. And Nb ₂ O
₅ , Ta ₂ O ₅ and V ₂ O ₅ improve the insulation resistance and dielectric breakdown strength, but the total content of Nb ₂ O ₅ , Ta ₂ O ₅ and V ₂ O ₅ is 10
If the amount is less than 0.001 mol part, the dielectric breakdown strength is not so large, the capacitance and the goodness Q are low, and the variation in the capacitance and the goodness Q is large, so that it is excluded from the scope of the present invention. . On the other hand, if the total content of Nb ₂ O ₅ , Ta ₂ O ₅ , and V ₂ O ₅ exceeds 0.010 mol parts with respect to the main component, the degree of goodness Q, insulation resistance is reduced, and the temperature coefficient of capacitance is negative. And become impractical. _{Further, Nb 2 O 5, Ta 2} O 5, Nb by containing two or more selected from _{V 2 O 5 2 O 5,} Ta 2 O 5, V 2 O 5
The dielectric constant, the insulation resistance, and the dielectric breakdown voltage are higher than those containing one selected from the group consisting of:

Incidentally, in the method of manufacturing dielectric ceramics and multilayer ceramic capacitors in the examples, BaCO ₃ , TiO ₂ , La ₂ O ₃ , Pr ₆ O ₁₁ ,
Nb ₂ O ₃ , Sm ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and V ₂ O ₅ were used, but it is not limited to this method, such as BaTiO ₃ so as to have a desired composition ratio BaO, TiO ₂ , La ₂ O ₃ , Pr ₆ O ₁₁ , Nb
_Even when a compound that becomes ₂ O ₃ , Sm ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and V ₂ O ₅ is 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.

Furthermore, in addition to the above-mentioned main components and sub-components, SiO ₂ , MnO ₂ , Fe
Salts, oxides, and the like, which are generally considered to be fluxes, such as ₂ O ₃ and ZnO, can also be added as long as the properties are not impaired.

Effects of the Invention According to the present invention, cation vacancies generated by replacing a part of tetravalent Ti in a dielectric layer with two or more kinds selected from pentavalent Nb, Ta, and V are described above. , due to oxygen defect during firing e ^- order to compensate for and suppress the TiO ₂ is reduced,
Generation of a compound of Ti and Pb can be prevented. As a result, the adhesion at the interface between the dielectric layer and the internal electrode is improved, so that a multilayer ceramic capacitor having a large capacitance and a large Q value and a small variation can be obtained.

Further, in the conventional dielectric layer, TiO ₂ reduced during firing is reoxidized to some extent during the cooling process, but 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 electric conduction and degrades the insulation resistance and dielectric breakdown strength of the dielectric layer. The dielectric layer of the present invention is a cation vacancy generated by replacing a part of tetravalent Ti with two or more types selected from pentavalent Nb, Ta, V,
Due to oxygen defect during firing e ^- to compensate for. Therefore, it is possible to obtain a multilayer ceramic capacitor having improved insulation resistance and dielectric breakdown strength as compared with the prior art.

[Brief description of the drawings]

FIG. 1 is a ternary diagram illustrating the composition range of the composition of the main component of the dielectric layer according to the present invention, and FIG. 2 is the ternary diagram of the main component of the dielectric layer according to the present invention, 0.11BaO-0.63TiO ₂ -0.21Nd. _The effect of sub-component (Nb ₂ O ₅ ) _0.4 (Ta ₂ O ₅ ) _0.3 (V ₂ O ₅ ) _0.3 with respect to ₂ O _{3 was obtained by} measuring the dielectric thickness: 12 μm and the internal electrode overlap dimension: 1.2 mm ×
6 is a graph showing electrical characteristics of a multilayer ceramic capacitor having a multilayer structure of 0.7 mm and the number of dielectric layers: 19;

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-56361 (JP, A) JP-A-62-83364 (JP, A) JP-A-62-17069 (JP, A) JP-A 57-56 90808 (JP, A) JP-A-59-154703 (JP, A) JP-A-63-246810 (JP, A) JP-A-63-298910 (JP, A) JP-A-63-292509 (JP, A)

Claims (1)

(57) [Claims] 1. A laminate comprising alternately laminated dielectric layers and internal electrodes, and an external electrode provided on an exposed end face of the internal electrode of the laminate, wherein the dielectric layer has a general formula xBaO −
yTiO ₂ -zRe ₂ O ₃ (where x + y + z = 1.00, Re ₂ O ₃ is L
_{a 2 O 3, Pr 2 O} 11/3, Nd 2 O 3, Sm oxide of at least one or more rare earth elements selected from ₂ O _3. ), X, y, z are the sub-components for 100 parts by weight of the main component consisting of the molar ratio range surrounded by the points a, b, c, d, e, f shown in the table below. Nb
Two or more selected from ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ are 0.00 in total
A multilayer ceramic capacitor containing 1 to 0.010 mol part, wherein the internal electrode contains palladium.