JP2004111951A - Laminated ceramic capacitor and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated ceramic capacitor with a small size and a large capacitance. <P>SOLUTION: The capacitor comprises a laminated body in which dielectric layers and internal electrodes are alternately stacked, and an external electrode 12 which is provided on the outer periphery of the laminated body. A dielectric layer 10 is composed of particles of a core shell structure in which a shell 101 is composed of accessary components on a surface of a core 100 made of barium titanate. As the dielectric layer 10 decreases in thickness, a relative dielectric constant increases. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a multilayer ceramic capacitor and a method for manufacturing the same.

The dielectric layer of a multilayer ceramic capacitor with a small rate of temperature change of the capacitance is formed of particles with a core-shell structure consisting of a core part centered on barium titanate, which is the main component, and a shell part, in which subcomponents diffuse to the surface of the core part. It is known to

積 層 In addition, multilayer ceramic capacitors are required to have a small size and a large capacity.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
JP-A-10-308321

According to the above method, a high relative dielectric constant and a good rate of temperature change of capacitance can be obtained by controlling the depth at which Mg diffuses into the crystal grain surface.

However, in the conventional dielectric layer composed of particles having a core-shell structure, the particle diameter of the constituent particles is almost uniform, and the thickness of the shell portion existing in the particles is uniform, so that the temperature change rate is small but the relative dielectric constant is small. There was a problem that the rate became small.

In recent years, in order to obtain a small and large-capacity multilayer ceramic capacitor, there is a method of increasing the number of stacked layers by making the dielectric layer thinner, but it has been difficult to reduce the size.

Therefore, an object of the present invention is to provide a multilayer ceramic capacitor having a small size and a large capacity.

達成 In order to achieve this object, the present invention has the following configuration.

The invention according to claim 1 of the present invention comprises particles having a core-shell structure having a core portion centered on barium titanate and a shell portion on the surface thereof, and in particular, a shell portion present on the particle surface portion. The thickness varies depending on the particle size of the particles, and a small-sized and large-capacity multilayer ceramic capacitor can be obtained.

The invention according to claim 2 of the present invention is particularly directed to a multilayer ceramic capacitor having a small size and a high capacity, in which the shell portion present on the surface of the particles constituting the dielectric layer has a smaller thickness as the particle size is larger. Can be obtained.

According to the third aspect of the present invention, in particular, particles having no shell portion are present, so that a multilayer ceramic capacitor having a small size and a large capacity can be obtained.

According to the invention described in claim 4 of the present invention, in particular, a particle having only a core portion is present, and a small-sized and large-capacity multilayer ceramic capacitor can be obtained.

The invention according to claim 5 of the present invention particularly includes a Mg compound or a Mg compound and a rare earth compound as subcomponents forming a dielectric layer, and the total amount of these is 1. 6 mol% or more and 3.0 mol% or less, the content of the Mg compound is 3.0 mol% or less (excluding 0 mol%), and the content of the rare earth compound is less than 3.0 mol%. Therefore, a small-sized and large-capacity multilayer ceramic capacitor can be obtained.

In the invention according to claim 6 of the present invention, in particular, the rare earth compound is at least one selected from the compounds of Dy, Ho, Er, and Yb, and a small-sized and large-capacity multilayer ceramic capacitor can be obtained. .

The invention according to claim 7 of the present invention provides a first step of mixing powders of barium titanate having a uniform particle size, a Mg compound, and a rare earth compound, and performing a heat treatment at 800 ° C to 1100 ° C; A second step of pulverizing the mixture so as to have a specific surface area larger than the specific surface area of the powder at the time of the mixing in the first step, and preparing a ceramic sheet using the pulverized powder, and alternately laminating with the internal electrodes And a fourth step of firing the laminate to form an external electrode, whereby a small-sized, large-capacity multilayer ceramic capacitor can be obtained.

According to the present invention, it is possible to provide a small-sized and large-capacity multilayer ceramic capacitor having a small rate of temperature change of capacitance.

(Embodiment 1)
Hereinafter, a first embodiment of the present invention will be described.

FIG. 1 is a partially enlarged cross-sectional view of a dielectric layer according to the present embodiment, where 100 is a core portion made of barium titanate, 101 is a shell portion covering the surface of the core portion 100, and 102 is only the core portion 100 Alternatively, the particles are composed of a core part 100 and a shell part 101. FIG. 2 is a partially cutaway perspective view of a general multilayer ceramic capacitor, in which 10 is a dielectric layer, 11 is an internal electrode, and 12 is an external electrode.

First, with respect to the average particle diameter 0.5μm or less of BaTiO ₃ 100 mol% as starting material for the dielectric layer 10, 1.0 mol% of MgO as an auxiliary component, 0.3 mol% of Dy ₂ O _3, the Ho ₂ O ₃ Weigh 0.3 mol%, SiO ₂ 0.6 mol%, and Mn ₃ O ₄ 0.05 mol%, respectively.

Next, put it together with pure water into a ball mill equipped with zirconia balls and wet mix. Then, it dehydrated and dried at 120 degreeC.

Next, the dried powder is put into a high-purity alumina crucible and calcined in air at 800 ° C. to 1100 ° C. for 2 hours.

After calcination, macroscopically, it is in a lightly solidified state, but when analyzed by X-ray diffraction, barium titanate reacts with each other or with the above-described additive and barium titanate to form a slightly solid solution. It is considered to be.

(5) Thereafter, the calcined powder was put together with pure water into a ball mill equipped with zirconia balls having a particle diameter of 3 mm, and wet milled. Then, it dehydrated and dried at 120 degreeC.

In the pulverization, the particles bonded by calcination are adjusted so that the maximum particle size is 0.6 μm or less and the average particle size is 0.5 μm or less. With this size, components other than barium titanate are likely to react, improving sinterability and effectively obtaining a desired dielectric layer 10.

Next, the ground powder is mixed with an alcohol such as ethanol so that the surface of the ground powder particles is coated with the alcohol.

Next, a slurry was prepared by mixing a solvent component composed of n-butyl acetate and a plasticizer component composed of benzyl butyl phthalate, and then an organic binder component composed of polyvinyl butyral resin.

凝集 As described above, the surface of the pulverized powder particles is first coated with alcohol, and then mixed with a binder, a solvent, and a plasticizer, whereby aggregation of the pulverized powder particles can be suppressed.

However, if the amount of alcohol added is too large, a desired ceramic sheet cannot be obtained. Therefore, the amount of the alcohol added is such that the surface of the ground powder particles can be coated so as not to agglomerate, and is smaller than the total amount of the binder, the solvent and the plasticizer.

Thereafter, the slurry is formed into a ceramic green sheet to be the dielectric layer 10 by a doctor blade method.

Next, screen printing is performed on this ceramic green sheet using an internal electrode paste made of Ni powder having an average particle size of about 0.4 μm so as to form a desired pattern.

Next, three ceramic green sheets on which the internal electrode patterns have been formed are overlapped with each other so that the internal electrode patterns face each other with the ceramic green sheets interposed therebetween, and heated and pressed to be integrated, and then 2.4 mm wide and 1.3 mm long. To obtain a green laminate.

The unsintered laminate is placed in a zirconia sheath covered with zirconia powder, heated to 350 ° C. in nitrogen to burn the organic binder, and then fired at 1250 ° C. for 2 hours in N ₂ + H ₂ for firing. I got a body.

At this time, if the firing temperature is 1300 ° C. or higher, the dielectric layer 10 composed of large and small particles having a core-shell structure, which is a feature of the present invention, cannot be manufactured, and the capacitance change rate of the dielectric layer 10 is large. Become.

(4) When the firing temperature is 1200 ° C. or lower, the insulation resistance of the multilayer ceramic capacitor decreases.

Therefore, it is desirable that the firing temperature be 1200 to 1300 ° C.

Next, a copper paste for baking in a nitrogen atmosphere at 900 ° C. was applied as an external electrode 12 to the exposed end face of the internal electrode 11 of the obtained sintered body, and baked in a continuous belt furnace of a mesh type, as shown in FIG. A simple multilayer ceramic capacitor is obtained.

The thickness of the internal electrode 11 of each multilayer ceramic capacitor is about 1.5 μm or less.

As shown in FIG. 1, the dielectric layer 10 of the multilayer ceramic capacitor has a core shell 100 of particles 102 made of barium titanate and a shell 101 made of the above-mentioned subcomponents (Mg, Dy, Ho, etc.). It has a structure.

Also, the entire surface of the core portion 100 is not always covered with the shell portion 101, and there are also particles 102 from which the core portion 100 is exposed.

{Circle around (4)} In the dielectric layer 10, there are also particles composed only of the core portion 100.

Furthermore, the particles 102 constituting the dielectric layer 10 have a non-uniform particle diameter, and the shell part 101 has a smaller thickness as the core part 100 composed of barium titanate having a high dielectric constant has a larger particle diameter. Things.

ば ら つ き The variation in the particles constituting the dielectric layer changes due to the variation in the barium titanate particles used or the pulverization process. When barium titanate having a uniform particle size is used and the particle size after pulverization is also uniform, the thickness of the shell phase in each particle becomes substantially uniform, and desired dielectric particles cannot be obtained. If the pulverization is too weak to suppress the variation of the particle size, it is difficult to obtain a desired sheet because the coagulated powder remains. Therefore, it is necessary to control the average diameter of the used barium titanate, and further, the average diameter and the maximum particle diameter after pulverization.

Note that the method for measuring the particle size in the present embodiment will be described.

Each sample was observed using a scanning electron microscope, 10 straight lines were randomly drawn on the observation surface, the length of each straight line and the number of particles contained therein were measured, and the average particle size in a straight line was calculated. Then, the average value of ten straight lines is calculated, and this is defined as the average particle size.

Next, the capacitance and dielectric loss of the obtained multilayer ceramic capacitor were measured by subjecting the sample to a heat treatment at a temperature of 150 ° C. for 1 hour, leaving it at room temperature for 48 hours, and then inputting a signal at a frequency of 1 kHz in a 20 ° C. thermostat. The measurement was performed at a level of 1.0 Vrms, and the relative permittivity was calculated from the capacitance. The rate of change of the capacitance with respect to the temperature was calculated using (Equation 1) by measuring the capacitance from −25 ° C. to 85 ° C. while increasing the temperature.

As a comparative example, one manufactured using a dielectric material having a uniform particle size is shown.

The test results are shown in (Table 1).

(Table 1) As is clear from Table 1, the relative dielectric constant is higher in Example 1 and the capacitance change rate at 85 ° C. is lower than in Comparative Example.

In addition, although the result of this time is a result of performing the thickness of the dielectric layer 10 at 2.0 μm, it has been confirmed that the relative dielectric constant hardly changes even if the thickness is changed.

Further, by varying the particle size in a range where the maximum particle size of the pulverized powder is 0.6 μm or less and the average particle size is 0.5 μm or less, the state of the particles after the sub-component diffusion becomes Many subcomponents diffuse on the surface of the small (large specific surface area) barium titanate, and the thickness of the shell portion 101 is increased, resulting in particles having excellent temperature characteristics. On the other hand, on the surface of barium titanate having a large particle diameter (having a small specific surface area) exhibiting a high dielectric constant, diffusion of subcomponents is reduced and the thickness of the shell portion 101 is reduced, resulting in particles having an excellent relative dielectric constant. Therefore, the particles having excellent temperature characteristics and the particles having excellent relative dielectric constant in the dielectric layer 10 are fused to form the dielectric layer 10 having a high relative dielectric constant and a small rate of change in capacitance with temperature. You can get it.

(Embodiment 2)
Hereinafter, the present invention, particularly, the inventions described in claims 5 and 6 will be described.

In the present embodiment, the starting materials of the dielectric layer 10 are 0.6 mol% of SiO ₂ and 0.05 mol% of Mn ₃ O ₄ with respect to 100 mol% of BaTiO ₃ having an average particle size of 0.5 μm or less. In addition, the amounts of MgO, Dy ₂ O _3, and Ho ₂ O ₃ were changed, and a multilayer ceramic capacitor was manufactured in the same manner as in Embodiment 1, and the characteristics were measured. The results are shown in (Table 2).

As shown in Table 2, the larger the added amount of MgO, Dy ₂ O ₃ and Ho ₂ O ₃ , the smaller the relative dielectric constant. In particular, it can be seen that samples 1 to 3 and 5 have a high relative dielectric constant but a large temperature change rate of capacitance. This is because if the added amount of MgO, Dy ₂ O ₃ and Ho ₂ O ₃ constituting the shell phase is too small, the particles of the dielectric layer cannot form the core-shell structure. On the other hand, in Sample 16, since the added amounts of MgO, Dy ₂ O _3, and Ho ₂ O ₃ were large, the shell phase was formed sufficiently thick, and a high dielectric constant could not be realized.

That is, the total added amount of MgO, Dy ₂ O ₃ and Ho ₂ O ₃ is at least 1.6 mol% to 3.0 mol% with respect to 100 mol% of barium titanate which is the core of the particles constituting the dielectric layer 10. The shell portion can be reduced in thickness by not more than 1.6 mol% and preferably not more than 1.6 mol% and not more than 2.5 mol% (excluding 0 mol%). There will be many particles that exist only in the part. Further, the sintering temperature of the dielectric layer 10 can be lowered by setting the total amount of addition of MgO, Dy ₂ O ₃ and Ho ₂ O ₃ as described above. When the sintering temperature of the dielectric layer 10 exceeds 1300 ° C., the large particles and the small particles react with each other and the small particles disappear, and as shown in FIG. 10 can no longer be obtained.

In each of the above embodiments, Dy ₂ O ₃ and Ho ₂ O ₃ are used as rare earth compounds, but other rare earth compounds may be used. In particular, it is preferable to use at least one compound of each of Dy, Ho, Er, and Yb. This is because these elements are atoms having a small ionic radius among the rare earth elements, and promote the formation of a shell layer of the particles 102 constituting the dielectric layer 10 in the firing step, and are more effective than when other rare earth compounds are used. Also, the temperature characteristics tend to be good.

{Circle around (4)} As the specific surface area of the calcined powder after pulverization increases, the relative dielectric constant of the dielectric layer 10 can be improved.

The multilayer ceramic capacitor and the method of manufacturing the same according to the present invention can also be applied to a multilayer ceramic capacitor that requires small capacitance and large-capacity characteristics and a method of manufacturing the same.

Partially enlarged sectional view of a dielectric layer according to the first and second embodiments of the present invention. Partially cutaway sectional perspective view of multilayer ceramic capacitor according to Embodiments 1 and 2 of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 10 Dielectric layer 11 Internal electrode 12 External electrode 100 Core part 101 Shell part 102 Particle

Claims (7)

A laminate in which dielectric layers and internal electrode layers are alternately laminated, and an external electrode provided on an outer peripheral surface of the laminate, wherein the dielectric layer has a core portion centered on barium titanate and a surface thereof. A multilayer ceramic capacitor comprising a core-shell structure particle having a shell portion at a portion thereof, wherein the thickness of the shell portion present on the particle surface portion varies depending on the particle size of the particle. 2. The multilayer ceramic capacitor according to claim 1, wherein the shell portion present on the surface of the particles constituting the dielectric layer has a smaller thickness as the particle size increases. 2. The multilayer ceramic capacitor according to claim 1, wherein the particles constituting the dielectric layer include particles in which a part of the shell portion is not formed. 2. The multilayer ceramic capacitor according to claim 1, wherein the particles constituting the dielectric layer include particles only in the core portion. As a sub-component for forming the dielectric layer, a Mg compound or a Mg compound and a rare earth compound are contained, and the total amount thereof is 1.6 mol% or more and 3.0 mol% or less based on barium titanate. The multilayer ceramic capacitor according to claim 1, wherein the content of the compound is 3.0 mol% or less (excluding 0 mol%), and the content of the rare earth compound is less than 3.0 mol%. The multilayer ceramic capacitor according to claim 5, wherein the rare earth compound is at least one selected from Dy, Ho, Er, and Yb compounds. A first step of mixing powders of barium titanate, a Mg compound, and a rare earth compound having a uniform particle size, and heat-treating the mixture at 800 ° C. to 1100 ° C .; and powder obtained by mixing the mixture in the first step. A second step of pulverizing to have a specific surface area larger than the specific surface area of the body, and a third step of producing a ceramic sheet using the pulverized powder and alternately laminating with the internal electrode to obtain a laminate, And b. Firing the laminate to form external electrodes.

Images