JPH09270366A - Multilayer capacitors - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: An extremely economical material having a high relative dielectric constant and excellent insulating properties, a small temperature variation rate of capacitance over a wide temperature range, a small dielectric loss tangent, and a long high temperature load life. Provide a high-performance multilayer capacitor. A The BaTiO ₃ as a main component, Si, a dielectric layer containing a rare earth element and alkaline earth metal elements, in the multilayer capacitor formed by alternately stacking internal electrode layers mainly composed of Ni And the dielectric layer is Ba
It is composed of crystal grains containing TiO ₃ as a main component and grain boundaries between the crystal grains, and 80% or more of all grain boundaries in the fracture surface of the dielectric layer have Si, a rare earth element, an alkali. It is characterized by being an amorphous material containing an earth metal element and oxygen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention alternately stacks a dielectric layer containing BaTiO ₃ as a main component and containing Si, a rare earth element and an alkaline earth metal element, and an internal electrode layer containing Ni as a main component. The present invention relates to a multilayer capacitor formed by.

[0002]

2. Description of the Related Art Conventionally, in a multilayer ceramic capacitor, a plurality of dielectric green sheets containing BaTiO ₃ as a main component whose surface is coated with an internal electrode paste are laminated, and the internal electrodes of the sheets are alternately arranged in parallel. It is formed by connecting to a pair of electrodes for external connection and sintering and integrating them. Such laminated porcelain capacitors have been used in a wide variety of electronic circuits due to rapid miniaturization of electronic components with the recent development of electronics.

However, the conventional dielectric material containing BaTiO ₃ as a main component needs to be sintered at a high temperature, and the internal electrodes do not melt at the sintering temperature of the dielectric and are not oxidized. Noble metal such as palladium (melting point 1555 ° C.) or its alloy is used. Especially, in the case of a large capacitance, there is a problem that the number of internal electrodes is large and the cost is high. Therefore, the conventional multilayer capacitor has high volumetric efficiency, excellent dielectric characteristics, and high reliability, but its price is a major obstacle to its development.

Therefore, in recent years, it has been attempted to use an inexpensive base metal such as nickel as the internal electrode.
However, when a base metal such as nickel is used as the internal electrode, when the dielectric made of barium titanate (BaTiO ₃ ) and the base metal internal electrode are simultaneously sintered, the base metal is sintered as a metal film without being oxidized. Since the equilibrium oxygen partial pressure of Ni / NiO is about 0.03 Pa at 1300 ° C., the oxygen partial pressure should be lower than that. In this case, the dielectric made of BaTiO ₃ or its solid solution should generally have the above-mentioned content. It has a drawback that it is reduced under oxygen partial pressure and loses its insulating property, and as a result, practical dielectric properties as a laminated ceramic capacitor cannot be obtained.

On the other hand, a barium titanate solid solution (Ba, Ca, S) is used as a non-reducing dielectric ceramic composition which can be used as a laminated capacitor having an internal electrode such as nickel.
r) TiO ₃ is a basic oxide (Ba, C
The reason for making a, Sr) O in excess of the stoichiometric ratio with respect to TiO ₂ which is an acidic oxide is that it is disclosed in JP-B-57-42588.
It is proposed in Japanese Patent Publication No.

This is generally because in the ABO ₃ type crystal, the A ion having a 12-coordinate with respect to oxygen larger than the B ion is stoichiometric with respect to the B ion located at the center of the oxygen octahedral (perovskite) structure. It is known that when the amount is more than the stoichiometric ratio, the crystal lattice strongly attracts oxygen atoms and is difficult to reduce, and the invention described in the above publication is based on the deviation of the stoichiometric ratio, It is an improved non-reducing property.

[0007]

However, when the dielectric ceramic composition described in the above publication is used as a multilayer capacitor, there is a drawback that the high temperature load life is short. Further, there is a drawback that the temperature change rate of the capacitance is large and the dielectric property is deteriorated.

The present invention has a high relative permittivity and an excellent insulating property, has a small rate of change in capacitance over a wide temperature range, has a small dielectric loss tangent, has a high temperature load life, and is extremely economical. An object is to provide a multilayer capacitor.

[0009]

A multilayer capacitor of the present invention comprises BaTiO ₃ as a main component, a dielectric layer containing Si, a rare earth element and an alkaline earth metal element, and a Ni layer.
A multilayer capacitor in which internal electrode layers containing as a main component are alternately laminated, wherein the dielectric layer is BaTiO ₃
And a grain boundary between the crystal grains, and 80% or more of all grain boundaries in the fracture surface of the dielectric layer have Si, a rare earth element, or an alkaline earth element. It is characterized by being composed of an amorphous material containing a metal element and oxygen.

[0010]

The present inventors have studied the mechanism of deterioration of high-temperature load life of non-reducing dielectric ceramics, and as a result, the insulation resistance is deteriorated at high temperature load and the life is shortened. The inventors have found that this is due to an increase in electron concentration due to the movement of oxygen vacancies and uneven distribution, leading to the present invention.

That is, in the multilayer capacitor of the present invention, 80% or more of the total number of grain boundaries in the fracture surface of the dielectric layer has an amorphous structure containing Si, a rare earth element, an alkaline earth metal element and oxygen. Since it is made of a high quality material, the concentration of oxygen vacancies in the porcelain is reduced and the movement of oxygen vacancies during high temperature load is suppressed, so that a multilayer capacitor having a long high temperature load life can be provided.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the multilayer capacitor of the present invention, the dielectric layer is composed of crystal grains containing BaTiO ₃ as a main component and grain boundaries between the crystal grains, and the dielectric layer has a total cross section of the fracture surface. At least 80% of the grain boundaries are composed of an amorphous material containing Si, a rare earth element, an alkaline earth metal element and oxygen.

Here, the dielectric layer contains BaTiO ₃ as a main component and contains Si, a rare earth element, and an alkaline earth metal element. In the present invention, for example, BaTiO ₃ 8
6-99 mol%, MgO 0.2-2.0 mol%, MnO
0.01 to 2.0 mol%, Y ₂ O ₃ 0.5~2.0 mol%, Li ₂ O0~4 mol%, SiO ₂ 0.5 to 4 mol%
It consists of

Particularly, in order to obtain a high dielectric constant, BaTi
O ₃ 92 to 98.5 mol%, MgO0.2~1.0 mol%, MnO0.04~0.5 mol%, Y ₂ O ₃ 0.75
To 1.5 mol%, Li ₂ O0~0.5 mol%, SiO ₂
It is preferably composed of 0.5 to 4 mol%. Al, Zr, Fe, Na, etc. may be present as impurities in the dielectric layer, but if the amount is very small, there is no problem in terms of characteristics. Also,
In some cases, ball components may be mixed from the crushed balls during crushing.

The thickness of this dielectric layer is preferably 3 to 15 μm. This is because it is difficult to manufacture the dielectric layer if the thickness of the dielectric layer is thinner than 3 μm, and if the thickness is thicker than 15 μm, it becomes impossible to increase the capacity. The thickness of the dielectric layer of the present invention is 5 from the viewpoint of increasing the capacity and facilitating the production of the dielectric layer.
It is desirable that the thickness is 10 μm.

The dielectric layer of the present invention is composed of crystal grains containing BaTiO ₃ as a main component and grain boundaries between the crystal grains.

In the present invention, although Si, rare earth elements, and alkaline earth metal elements may be solid-dissolved in the crystal grains containing BaTiO ₃ as a main component, the amount is very small, and most of them are among the crystal grains. It exists in grain boundaries. this is,
This is because each powder containing Si, a rare earth element, and an alkaline earth metal element is mixed and calcined, and is fired at a high temperature of 1250 to 1300 ° C., which is higher than the melting temperature of the glass component.

The grain boundaries in which Si, the rare earth element and the alkaline earth metal element exist as an amorphous phase account for 80% of the total number of grain boundaries in the fracture surface of the dielectric layer.
It is necessary to be above. When the number of grain boundaries in which Si, the rare earth element and the alkaline earth metal element exist as an amorphous phase is less than 80% of the total number of grain boundaries,
This is because the high temperature load life becomes short. From the viewpoint of extending the high temperature load life, it is desirable that the number of grain boundaries in which Si, the rare earth element and the alkaline earth metal element exist as an amorphous phase is 90% or more of the total number of grain boundaries. The grain boundary in the present invention means a so-called triple point formed by three or more crystal grains.

As rare earth elements, Y, La, Ce, P
There are r, Nd, Sm, Dy, Ho, Er, Yb, etc.,
Of these, Y, Ho, Er, and Yb are preferable from the viewpoint of extending the high temperature load life. Further, as the alkaline earth metal element, there are Mg, Ca, Sr, Ba and the like,
Of these, Mg and Ba are preferable from the viewpoint of extending the high temperature load life. Further, Li, K, B or the like may be added as an element forming the dielectric layer of the present invention from the viewpoint of sinterability, but among these, Li is preferable from the viewpoint of temperature characteristic of capacitance. .

The internal electrodes in the multilayer capacitor of the present invention are mainly composed of Ni, but may be formed by adding Cu and Cr to Ni, for example.

In the present invention, the grain boundaries in which Si, the rare earth element and the alkaline earth metal element exist as an amorphous phase are 8 out of the total number of grain boundaries in the fracture surface of the dielectric layer.
In order to achieve 0% or more, oxide powders containing Si, a rare earth element, and an alkaline earth metal element are mixed, calcined and crushed, and the powder and BaTiO 3 are used.
₃ were mixed, Si, above the melting temperature of the glass component formed by alkaline earth metal elements such as, 1250-130
It is obtained by firing at a high temperature of 0 ° C.

Further, in the present invention, it is desirable that an amorphous phase composed of Si be present between the two BaTiO ₃ particles from the viewpoint of extending the high temperature load life. As described above, in order to allow the amorphous phase made of Si to exist between the two BaTiO ₃ particles, it is necessary to perform firing at the melting temperature of the glass component or higher.

In the multilayer capacitor of the present invention, first, S
800 to 1000 in the air by mixing the respective powders containing i, the rare earth element and the alkaline earth metal element.
The powder which is calcined at ℃ and pulverized is mixed with BaTiO ₃ powder and other desired powders, an organic binder and the like are added thereto, and the mixture is formed into a film by a doctor blade method or the like. An electrode paste containing Ni as a main component is printed on this film by, for example, screen printing.

A plurality of films having the electrode paste formed thereon are laminated to form a laminated molded body, which is subjected to a binder removal treatment and then subjected to a non-reducing oxygen partial pressure of 3 × 10 ^{−3 to} 3 × 10 ⁻⁷ Pa. In the atmosphere, a temperature above the melting temperature of the glass component,
By firing at 1250 to 1300 ° C. and forming external electrodes on this porcelain, the multilayer capacitor of the present invention is obtained. After calcination, it is desirable to perform reoxidation treatment at 800 to 1100 ° C. at an oxygen partial pressure of 1 × 10 ⁻² to 2 × 10 ⁴ Pa for 1 to 5 hours from the viewpoint of extending the high temperature load life.

The BaTiO ₃ particles of the dielectric layer in the present invention preferably have an average particle size of 0.3 to 1 μm from the viewpoint of temperature characteristics of resonance frequency and improvement of dielectric constant.

[0026]

【Example】

Example 1 BaCO ₃ powder having a purity of 99% or more and Ti as starting materials
After mixing with O ₂ powder, 1 at 1150 ° C in air
BaTiO ₃ powder is synthesized by solid-phase reaction by calcination for a while and finely pulverized. Next, Y ₂ O ₃ powder, Li ₂ CO ₃ powder, SiO ₂ powder, and MgO powder were weighed so as to have the composition shown in Table 1, mixed, and then calcined in the air at 1000 ° C. for 2 hours to obtain additives. To get Next, synthetic fine powder BaTiO ₃ and
The above additives were added to MnCO ₃ powder, and the results are shown in Table 1.
To obtain the composition of Z, together with the dispersant and dispersion medium, Z
A raw material slurry was prepared by mixing with a ball mill using rO ₂ balls.

An organic binder and a plasticizer were added to this slurry, and after sufficiently stirring, a film was formed by a doctor blade method. Ni, a dispersant, a dispersion medium,
An electrode paste made of an organic binder was screen-printed to print a counter electrode.

After stacking the films and thermocompression-bonding them, the film is vertically 3.
A laminated molded body having a size of 5 mm, a width of 1.8 mm and a thickness of 0.75 mm was obtained. This laminated molded body was exposed to the air at 300 ° C. for 4 hours,
After debinding, the oxygen partial pressure is 10 ⁻⁵ to 10 ⁻⁷ Pa
To 1,200 to 1 with nitrogen as the carrier gas.
It was baked at 350 ° C. for 2 hours. After barrel polishing,
Cu paste was applied to the end faces of the porcelain and baked in nitrogen at 850 ° C. to form terminal electrodes, and the multilayer capacitor of the present invention was obtained.

The obtained multilayer capacitor has 20 dielectric layers sandwiched by internal electrodes, and its dimension is 3 m in length.
The thickness was m, the width was 1.5 mm, and the thickness per layer was 13 μm. The effective electrode area is 2.86mm ² (2.6mm ×
It was 1.1 mm).

Next, the evaluation samples having these Cu terminal electrodes formed thereon were allowed to stand at room temperature for 48 hours, and then the frequency was 1.0 kH.
The capacitance and the dielectric loss tangent were measured at z and an input signal level of 1.0 Vrms. The relative permittivity was calculated from the capacitance. After that, DC 50V was applied for 1 minute, and the insulation resistance at that time was measured.

Also, in the temperature range of −55 to 125 ° C., the capacitance and the dielectric loss tangent were measured under the same conditions as above, and the rate of change of the capacitance at each temperature with respect to the capacitance at + 25 ° C. Was calculated.

Further, instead of the Cu terminal electrode of the obtained porcelain, an Au electrode was formed by sputtering on the end face of the porcelain to prepare a sample for high temperature load test. These samples are then placed at a temperature of 300
The life time until breakage was measured under conditions of ° C and voltage of 10V.

Further, after polishing the obtained dielectric layer into flakes, the number of triple points in 10 μm square was measured by a transmission electron microscope (TEM), and electron diffraction images of these grain boundaries were observed. The ratio of the grain boundaries of the amorphous phase in all grain boundaries was determined by determining whether or not it was amorphous, and the constituent elements of the grain boundaries of the amorphous phase were determined by an X-ray microanalyzer (EPMA). . Table 2 shows the results. However, the insulation resistance is represented by the product (CR, MΩ · μF) of the electrostatic capacity (C, μF) and the insulation resistance (R, MΩ).

[0034]

[Table 1]

[0035]

[Table 2]

As is apparent from Tables 1 and 2, the sample No. 3 whose triple point composition does not contain an alkaline earth element has a short high temperature load life and contains No. 5 containing no Si.
No.4, which has poor sinterability and does not contain rare earth elements
However, the high temperature load life is short. On the other hand, it can be seen that the sample of the present invention in which the composition of the triple points is the amorphous phase containing Si, the rare earth element and the alkaline earth element has a long high temperature load life.

Further, when the firing temperature is as low as 1200 ° C. (Sample No. 7), it is found that the proportion of amorphous is small and the high temperature load life is short. Furthermore, when the firing temperature is as high as 1350 ° C. (Sample No. 9), the proportion of amorphous is small,
Further, it can be seen that Si is dissolved in the crystal grains of BaTiO ₃ and the high temperature load life is short.

Further, the inventors of the present invention prepared a multilayer capacitor by batch-mixing and firing in the same manner as above without calcining the glass components, and the additive alone existed at the grain boundary. The amorphous content was 70%, and the high temperature load life was as short as 9 minutes. An example of this is described in Sample No. 8.

Further, the inventors of the present invention have determined the element existing between the two particles and the form of its existence in the sample No.1.
As a result of measurement by TEM and EPMA, it was found that Si was present as amorphous in the grain boundary between the two particles.

Example 2 In the same manner as in Example 1 above, a laminated molded body was prepared, fired, and then reoxidized at 1000 ° C. in nitrogen for 2 hours. After barrel polishing, Cu paste was applied to the end surface of the porcelain and baked in nitrogen at 850 ° C. to form a terminal electrode, and a multilayer capacitor having the same shape as in Example 1 was obtained.

Then, in the same manner as in Example 1, the relative permittivity, dielectric loss tangent, insulation resistance, temperature change rate of capacitance and high temperature load life were measured, and the number of grain boundaries and the amorphous state were measured. The ratio of a certain grain boundary and the constituent elements of the grain boundary were determined. The results are shown in Tables 3 and 4.

[0042]

[Table 3]

[0043]

[Table 4]

As is clear from Tables 3 and 4, it is understood that the high temperature load life is further improved when the reoxidation treatment is performed after firing.

[0045]

As described in detail above, the multilayer capacitor of the present invention exhibits excellent characteristics in high temperature load life even when fired under firing conditions in which the oxygen partial pressure is equal to or lower than the parallel oxygen partial pressure of Ni / NiO. Therefore, it is excellent as a multilayer capacitor using an internal electrode containing nickel as a main component.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01G 4/12 358 C04B 35/46 D

Claims (1)

[Claims] 1. A multilayer capacitor comprising a dielectric layer containing BaTiO ₃ as a main component and containing Si, a rare earth element and an alkaline earth metal element, and an internal electrode layer containing Ni as a main component, which are alternately laminated. Where the dielectric layer is Ba
It is composed of crystal grains containing TiO ₃ as a main component and grain boundaries between the crystal grains, and 80% or more of all grain boundaries in the fracture surface of the dielectric layer have Si, a rare earth element, an alkali. A multilayer capacitor comprising an amorphous material containing an earth metal element and oxygen.