JP5903989B2 - Dielectric ceramic composition and multilayer ceramic capacitor - Google Patents

Description

  The present invention relates to a dielectric ceramic composition having resistance to reduction and an electronic component having the dielectric ceramic composition in a dielectric layer. More specifically, the capacitance-temperature characteristic is an X8R characteristic (−55 ° C. to 150 ° C. The dielectric ceramic composition and the multilayer ceramic capacitor satisfying a change rate of -15% to + 15% with respect to a capacity of 25 ° C. which is a reference temperature in a temperature range of

  A multilayer ceramic capacitor, which is an example of an electronic component, includes, for example, a ceramic green sheet made of a predetermined dielectric ceramic composition and an internal electrode layer having a predetermined pattern alternately stacked, and then integrated into a green chip obtained simultaneously. Manufactured by firing. Since the internal electrode layer of the multilayer ceramic capacitor is integrated with the ceramic dielectric by firing, it is necessary to select a material that does not react with the ceramic dielectric. For this reason, as a material constituting the internal electrode layer, conventionally, an expensive noble metal such as platinum or palladium has been inevitably used.

  However, in recent years, dielectric ceramic compositions that can use inexpensive base metals such as nickel and copper have been developed, and a significant cost reduction has been realized.

  On the other hand, there is a high demand for miniaturization of electronic components accompanying the increase in density of electronic circuits, and miniaturization and large capacity of multilayer ceramic capacitors are rapidly progressing. Accordingly, the dielectric ceramic composition per layer in the multilayer ceramic capacitor has been reduced, and a dielectric ceramic composition capable of maintaining the capacitance-temperature characteristics even when the thickness is reduced is demanded. In particular, it is desired to develop an X8R product that has high reliability and has a change rate from a dielectric constant at room temperature in the range of −55 ° C. to 150 ° C., which is −15% to + 15%.

On the other hand, for example, in Patent Document 1, BaTiO ₃ and an M component (as a dielectric ceramic having an X7R characteristic in which the capacity change rate falls within the range of −15% to + 15% in the range of −55 ° C. to 125 ° C. M is a dielectric ceramic composition having a ferroelectric phase region, the main component being at least one component selected from the group consisting of manganese oxide, iron oxide, cobalt oxide and nickel oxide. A dielectric ceramic composition is disclosed in which the concentration of the M component in the ferroelectric phase region changes from the outside toward the center.

  In addition, in order to increase the size and capacity of the multilayer ceramic capacitor, it is necessary to reduce the thickness of the dielectric layer and increase the number of stacked dielectric layers. Along with this, the electric field strength per layer increases, and dielectric breakdown tends to occur between the internal electrodes. As a result, the life of the multilayer ceramic capacitor is shortened, and the reliability with respect to the electrical characteristics is lowered. On the other hand, in Patent Document 2, a plurality of dielectric layers and a plurality of internal electrodes are integrally laminated, and the dielectric layers are made of a sintered body of ceramic particles. And a multilayer ceramic capacitor comprising a shell portion surrounding the core portion, wherein the shell portion is one or more acceptor types selected from Mn, V, Cr, Co, Fe, Ni, Cu and Mo. Element, Mg and rare earth elements (Ho, Sc, Y, Gd, Dy, Er, Yb, Tb, Tm, Lu) are contained, and the concentration of the acceptor element contained in the shell portion is determined as a core-shell boundary. A multilayer ceramic capacitor is disclosed that is composed of a dielectric ceramic composition designed so as to become higher toward the grain boundary side.

  Further, the concentration distribution in the particles is described in Patent Document 3. Patent Document 3 aims to provide a dielectric ceramic for forming a dielectric ceramic layer, which can provide good bias characteristics even when the dielectric ceramic layer of the multilayer ceramic capacitor is thinned. , ABO3 (A is Ba or the like, B is Ti or the like) as a main component, and further includes a rare earth element as a subcomponent, and includes dielectric grains and crystal grains, and is a dielectric ceramic. 90% or more of the crystal grains have a surface layer portion with a rare earth element / Ti molar ratio of 0.03 to 0.10 and an interior with a rare earth element / Ti molar ratio of 0.01 or less, and an average of the surface layer portion It is disclosed that a dielectric ceramic composition having a thickness to crystal particle diameter of 0.01 to 0.10 achieves a relatively flat dielectric constant temperature dependency.

Publication 2001-247363 Publication 2001-230149 Publication 2001-057314

  However, Patent Document 1 can satisfy both the X7R characteristic (EIA standard) and the B characteristic (EIAJ standard) indicating the temperature characteristics of the capacitance, and the voltage dependency of the capacitance and the insulation resistance. An electronic component such as a multilayer ceramic capacitor that is small and excellent in dielectric breakdown strength and can use Ni or Ni alloy as an internal electrode layer, a dielectric ceramic composition suitable for use as a dielectric layer of the electronic component, and a method for producing the same The purpose is to provide. For this reason, the capacity change rate at 150 ° C. falls below −15%, and the X8R standard cannot be satisfied. Particularly in recent years, in-vehicle multilayer ceramic capacitors whose mounting locations are concentrating on the engine part tend to require a guarantee at 150 ° C.

Patent Document 2 describes the distribution of subcomponent concentration in BaTiO ₃ particles, and a dielectric ceramic composition adjusted so that the subcomponent concentration increases from the particle center toward the grain boundary. It has been adopted. However, even in this dielectric ceramic composition, the capacity-temperature characteristic does not satisfy the X8R characteristic, and improvement has been desired.

  Further, in Patent Document 3, a relatively flat dielectric characteristic is obtained. However, when the temperature is high at 150 degrees, a good temperature characteristic is not obtained and needs to be improved.

  The present invention has been made in view of such a situation, and includes a dielectric ceramic composition that satisfies the capacitance-temperature characteristic X8R and that can improve the accelerated lifetime, and an electronic component that includes this dielectric ceramic composition as a dielectric layer. The purpose is to provide.

In order to achieve the above object, according to the present invention,
The ceramic particles are made of a sintered body of ceramic particles.
A dielectric ceramic composition composed of a sintered body having a shell portion covering the core portion,
The core part is composed of BaTiO ₃ that is substantially the main component,
The shell part is BaTiO ₃ and at least one element selected from Mg, Ba, Ca and Sr as the first subcomponent, and Sc, Y, La, Ce, Pr, Nd, Pm and Sm as the second subcomponent. , Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and at least one element selected from Mn, V, Fe, Co, Ni, Cr as the third subcomponent An element, at least one element selected from Al, Si, B, and Ge as the fourth subcomponent, and at least one element selected from Zr, Hf, Nb, and Ta as the fifth subcomponent ,
The concentrations of subcomponents with respect to Ti in the dielectric ceramic composition are as follows: first subcomponent: CP1 (at%), second subcomponent: CP2 (at%), and third subcomponent: CP3 (at%). , The fourth subcomponent: CP4 (at%), the fifth subcomponent: CP5 (at%),
0 (at%) <CP1 <5 (at%),
0 (at%) <CP2 <15 (at%),
0 (at%) <CP3 <1 (at%),
2 (at%) <CP4 <5 (at%),
0 (at%) <CP5 <1.5 (at%),
When the concentration of the second subcomponent with respect to Ti in the shell portion is CS2 (at%),
CS2> 10 (at%), CS2 / CP2> 2.122
A dielectric ceramic composition characterized by satisfying the following relational expression is provided.
Here, “the core part is substantially composed of BaTiO ₃ as a main component” means that the core part may contain first to fifth subcomponents.

  The dielectric ceramic composition having such characteristics has a shell portion that is significantly higher in concentration than the conventional dielectric ceramic composition, and has a clearer core-shell structure. Therefore, the capacitance temperature change is small, and highly reliable electrical characteristics can be obtained.

Furthermore, the c / a value, which is the ratio of the c-axis length to the a-axis length of the crystal lattice in the BaTiO ₃ raw material used for the production of the dielectric ceramic composition, satisfies the relational expression c / a <1.007. It is desirable.

By using BaTiO ₃ satisfying this condition as a raw material, the shell portion is efficiently concentrated, and the capacity-temperature characteristics and the high temperature accelerated life are further improved.

  According to the present invention, there is provided an electronic component having a dielectric layer and an internal electrode layer, wherein the dielectric layer is composed of the dielectric ceramic composition. The electronic component according to the present invention is not particularly limited, and examples thereof include a multilayer ceramic capacitor, a piezoelectric element, a chip inductor, a chip varistor, a chip thermistor, a chip resistor, and other surface mount (SMD) chip type electronic components.

The dielectric ceramic composition of the present invention contains the above-mentioned specific first to fifth subcomponents with respect to the main component containing BaTiO ₃ , and the dielectric particles constituting the dielectric ceramic composition are the main components. Having a core portion substantially constituted by and a shell portion around the core portion, and when the concentration of the second subcomponent with respect to Ti in the shell portion is CS2 (at%),
CS2> 10 (at%), CS2 / CP2> 2.122
It is limited to satisfy the following relational expression.

  As a result, the rare earth concentration in the shell portion is significantly increased, and a clearer core / shell structure is formed. Therefore, the capacity-temperature characteristics and the high temperature accelerated life can be improved.

  Since the dielectric ceramic composition of the present invention has the above characteristics, by applying the dielectric ceramic composition of the present invention to a dielectric layer of an electronic component such as a multilayer ceramic capacitor, for example, dielectric Even when the body layer is thinned to about 3 μm and used under conditions of a high rated voltage (for example, 50 V or more), high reliability and capacity-temperature characteristics corresponding to X8R can be realized.

  That is, it is possible to provide an electronic component that is small and has a large capacity, and has high reliability and a capacity-temperature characteristic corresponding to X8R.

FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention. FIG. 2 is a conceptual diagram for explaining the intraparticle structure of dielectric particles. FIG. 3 is a TEM photograph for explaining a method of measuring each element contained in the dielectric particles in the example of the present invention. FIG. 4 is a schematic view of the TEM photograph of FIG. 3 for explaining the boundary line and the pore portion between the core portion and the shell portion. FIG. 5 is a diagram showing the claims of the present invention. The shaded area is the scope of claims of the present invention.

  DESCRIPTION OF EMBODIMENTS Embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

Multilayer Ceramic Capacitor As shown in FIG. 1, a multilayer ceramic capacitor 1 according to an embodiment of the present invention includes a capacitor element body 10 having a configuration in which dielectric layers 2 and internal electrode layers 3 are alternately stacked.
At both ends of the capacitor element body 10, a pair of external electrodes 4 are formed which are electrically connected to the internal electrode layers 3 arranged alternately in the element body 10. There is no particular limitation on the shape of the capacitor element body 10. Moreover, there is no restriction | limiting in particular also in the dimension, What is necessary is just to set it as a suitable dimension according to a use.

  The internal electrode layers 3 are laminated so that the end faces are alternately exposed on the surfaces of the two opposite ends of the capacitor element body 10. The pair of external electrodes 4 are formed at both ends of the capacitor element body 10 and connected to the exposed end surfaces of the alternately arranged internal electrode layers 3 to constitute a capacitor circuit.

The dielectric layer dielectric layer 2 contains the dielectric ceramic composition of the present embodiment. The dielectric ceramic composition of the present embodiment includes a main component containing BaTiO ₃ ,
At least one element selected from Mg, Ba, Ca, and Sr as the first subcomponent;
At least one element selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, which are the second subcomponents,
At least one element selected from Mn, V, Fe, Co, Ni, and Cr as the third subcomponent;
At least one element selected from Al, Si, B, and Ge as the fourth subcomponent;
And at least one element selected from Zr, Hf, Nb, and Ta as the fifth subcomponent.

The BaTiO ₃ contained as the main component is represented by, for example, the composition formula Ba _m TiO _{2 + m} , _m in the composition formula is 0.990 <m <1.010, and the ratio of Ba and Ti is Those having 0.990 <Ba / Ti <1.010 can be used.

The content of at least one element selected from Mg, Ba, Ca, and Sr as the first subcomponent is 0 to 5 mol in terms of element with respect to 100 mol of the main component, preferably 2.7 to 4.5 moles. The first subcomponent mainly has an effect of suppressing the ferroelectricity of BaTiO _{3 as} the main component. When the content of the first subcomponent is within this range, the accelerated life tends to be improved.

The content of at least one element selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, which are the second subcomponents, The amount is 0 to 15 mol, preferably 8 to 10 mol, in terms of element with respect to 100 mol of the main component. The second subcomponent mainly has an effect of suppressing the ferroelectricity of BaTiO _{3 as} the main component.
When the content of the second subcomponent is within this range, the insulation resistance, the accelerated life, and the temperature characteristics tend to be improved.

  In addition to the above, subcomponents are selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. , Tb are particularly preferred.

  The content of at least one element selected from Mn, V, Fe, Co, Ni, and Cr as the third subcomponent is 0 to 1 mol in terms of element with respect to 100 mol of the main component, preferably 0.12 to 0.32 mol. When the content of the third subcomponent is within this range, the insulation resistance, the accelerated life, and the relative dielectric constant tend to be improved.

  The content of at least one element selected from Al, Si, B, and Ge as the fourth subcomponent is 2 to 5 mol in terms of element with respect to 100 mol of the main component, preferably 3.2 to 4.0 moles. When the content of the fourth subcomponent is within this range, the insulation resistance and the accelerated life tend to be improved.

  As the fourth subcomponent, it is preferable to use an oxide of Si from the viewpoint that the effect of improving the characteristics is large among the above oxides.

The content of at least one element selected from Zr, Hf, Nb, and Ta as the fifth subcomponent is 0 to 1.5 mol in terms of element with respect to 100 mol of the main component.
When the content of the fifth subcomponent is within this range, the capacity-temperature characteristic and the relative dielectric constant tend to be improved.

  Note that Zr as the fifth subcomponent may be a part of Zr substituted with Hf.

  In addition, in this embodiment, you may add another subcomponent in addition to the said 1st-5th subcomponent as needed.

  The thickness of the dielectric layer 2 is not particularly limited, and may be appropriately determined according to the use of the multilayer ceramic capacitor 1.

As shown in FIG. 2, the dielectric layer is composed of a core part 11 substantially composed of BaTiO _{3 as} a main component, and a first subcomponent around the core part 11. At least one element selected from certain Mg, Ba, Ca, Sr, and Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, which are second subcomponents , Tm, Yb, Lu, at least one element selected from Mn, V, Fe, Co, Ni, Cr as the third subcomponent, and Al, Si as the fourth subcomponent , B, and Ge, and a shell portion 12 in which at least one element selected from Zr, Hf, Nb, and Ta as the fifth subcomponent is diffused.

  In the present invention, the concentration of the second subcomponent in the shell portion 12 is defined as CS2 (at%). CS2 (at%) is calculated by quantitative analysis at the EDS observation point 13 in FIG. The shell portion may be a single phase in which the diffusion component is diffused substantially uniformly, or may be a plurality of phases formed from different diffusion components. It may be an aspect that gradually changes toward the inside.

The boundary between the core portion and the shell portion in this embodiment is determined by a TEM photograph of dielectric particles as shown in FIG. For example, the determination is made based on the boundary between the bright portion 14 that is the shell portion and the dark portion 15 that is the core portion, as shown in FIGS. Further, black dots 16 in FIGS. 3 and 4 are pores existing in the BaTiO ₃ .

  In the present embodiment, the concentration CS2 (at%) of the second subcomponent with respect to Ti in the shell part of the dielectric particles, which is defined as the hatched part in FIG. 2, is controlled to exceed 10 (at%). Here, when the concentration CS2 (at%) of the second subcomponent is less than 10 (at%), the capacitance at room temperature increases excessively, and the capacity-temperature characteristics deteriorate. That is, the X8R characteristic is not satisfied.

The capacity-temperature characteristic is defined by the following equation.

Capacity-temperature characteristics =
{(Capacitance at target temperature−Capacitance at 25 ° C.) /
(Capacitance at 25 ° C.)}
× 100 (%)

  The concentration CP2 of the second subcomponent with respect to Ti in the dielectric ceramic composition and the concentration CS2 (at%) of the second subcomponent with respect to Ti in the shell portion of the dielectric particle are CS2 / CP2> 2. It is controlled to satisfy the relational expression 122. The region satisfying these relational expressions is a region exceeding the straight line CS2 = 2.122 × CP2 in FIG. Here, when CS2 and CP2 satisfy CS2 / CP2 ≦ 2.122, the difference between the shell portion and the core portion is reduced, and a clear core-shell structure is not formed. For this reason, the capacity-temperature characteristic or the high temperature accelerated life is deteriorated.

In this embodiment, it is preferable to use BaTiO ₃ having a c / a value lower than 1.007 as a raw material.

By using BaTiO ₃ as described above, the concentration of the rare earth shell is increased, and a clearer core / shell structure is formed.

  By forming a clear core / shell structure as described above, the capacity-temperature characteristics and the high temperature accelerated life tend to be improved.

The conductive material contained in the internal electrode layer 3 is not particularly limited, but a relatively inexpensive base metal can be used because the constituent material of the dielectric layer 2 has reduction resistance. As the base metal used as the conductive material, Ni or Ni alloy is preferable. The Ni alloy is preferably an alloy of Ni and one or more elements selected from Mn, Cr, Co and Al, and the Ni content in the alloy is preferably 95% by weight or more. In addition, in Ni or Ni alloy, various trace components, such as P, may be contained about 0.1 wt% or less. The internal electrode layer 3 may be formed using a commercially available electrode paste. What is necessary is just to determine the thickness of the internal electrode layer 3 suitably according to a use etc.

The conductive material contained in the external electrode external electrode 4 is not particularly limited, but in the present invention, inexpensive Ni, Cu, and alloys thereof can be used. What is necessary is just to determine the thickness of the external electrode 4 suitably according to a use etc.

Manufacturing Method of Multilayer Ceramic Capacitor The multilayer ceramic capacitor of the present embodiment is the same as the conventional multilayer ceramic capacitor. After producing a green chip by a normal printing method or sheet method using a paste and firing it, the external electrode It is manufactured by printing or transferring and baking. Hereinafter, the manufacturing method will be specifically described.

First, a dielectric material (dielectric ceramic composition powder) contained in the dielectric layer paste is prepared, and this is made into a paint to prepare a dielectric layer paste. BaTiO ₃ powders having c / a = 1.006, 1.002, 1.007, and 1.011 as the ratio of the c-axis length to the a-axis length of the crystal lattice are prepared as the main component raw materials. did.

In addition to the so-called solid phase method, BaTiO ₃ powder as a main component material for obtaining the effects of the present invention can be obtained by various liquid phase methods (for example, oxalate method, hydrothermal synthesis method, alkoxide method, sol-gel method, etc.) What was manufactured by various methods, such as what was manufactured by this, can be used, and it manufactures using the conditions from which each crystallinity becomes low.

After preparing the above BaTiO ₃ powder base material, MgO, Tb ₂ O _3.5 , Yb ₂ O ₃ , MnO, SiO ₂ , ZrO ₂ are used as auxiliary component raw materials. The mixture was mixed as shown in Table 2 to obtain a dielectric ceramic composition powder.

  Sample numbers 1, 5, 6, 12, 13, 16, 17, 20, 21, 24, 27, 28, 31, 32, 35, 36, 39, and 40 in Tables 1 and 2 are the present invention. Is out of range.

  The dielectric layer paste may be prepared using an organic paint obtained by kneading a dielectric material and an organic vehicle, or may be a water-based paint.

  An organic vehicle is obtained by dissolving a binder in an organic solvent. The binder used for the organic vehicle is not particularly limited, and may be appropriately selected from usual various binders such as ethyl cellulose and polyvinyl butyral. The organic solvent to be used is not particularly limited, and may be appropriately selected from various organic solvents such as terpineol, butyl carbitol, acetone, toluene, and the like according to a method to be used such as a printing method or a sheet method.

In the present embodiment, the dielectric layer paste is adjusted using an organic paint.
That is, the dielectric ceramic composition powder, 100 parts by weight of alcohol as a solvent, 10 parts by weight of polyvinyl butyral resin as a binder, and 5 parts by weight of dibutyl phthalate (DOP) as a plasticizer are mixed. Each obtained a dielectric paste.

A ceramic green sheet is formed on a PET film using the dielectric paste obtained above.
In this embodiment, green sheets were formed by the doctor blade method, and rectangular ceramic green sheets having a thickness of 4.0 μm after drying were obtained.

  Then, after printing the internal electrode layer paste on this, they are laminated and cut into a desired shape to obtain a green chip.

The internal electrode layer paste is a conductive material powder made of a conductive metal such as silver or nickel or an alloy containing them, or various oxides, organometallic compounds, resinates, etc. that become the conductive material described above after firing. Prepare by kneading with organic vehicle.
In this embodiment, a nickel conductive paste was used, and a conductive paste film was formed on the green sheet by a printing method.

Eleven ceramic green sheets on which the conductive paste film was printed were stacked so that the conductive paste films were alternately pulled out at the end after cutting, and pressure-bonded to produce a laminate having 10 layers. . The bonding conditions were a temperature of 100 ° C. and a pressure of 1 MPa.
The laminate was cut into a desired shape to obtain a green chip having a width of 1.4 mm, a length of 2.2 mm, and a thickness of 1.4 mm.

The obtained green chip is subjected to a binder removal treatment and then fired.
As binder removal conditions, the temperature rising rate is preferably 5 to 300 ° C./hour, the holding temperature is preferably 180 to 400 ° C., and the temperature holding time is preferably 0.5 to 24 hours.
As firing conditions, the temperature rising rate is preferably 50 to 500 ° C./hour, the temperature holding time is preferably 0.5 to 8 hours, and the cooling rate is preferably 50 to 500 ° C./hour. Further, the firing atmosphere is preferably a reducing atmosphere, and as the atmosphere gas, for example, a mixed gas of N ₂ and H ₂ can be used by humidification.

  After firing in a reducing atmosphere, the capacitor element body is preferably annealed. Annealing is a process for re-oxidizing the dielectric layer, and this can significantly increase the IR lifetime, thereby improving the reliability.

  The binder removal treatment, firing and annealing may be performed continuously or independently.

  In the present embodiment, the binder removal treatment conditions were a temperature rising rate: 25 ° C./hour, a holding temperature: 260 ° C., a temperature holding time: 8 hours, and an atmosphere: in the air.

Firing conditions are: temperature rising rate: 200 ° C./hour, holding temperature: 1200 to 1350 ° C., temperature holding time: 2 hours, cooling rate: 200 ° C./hour, atmospheric gas: N ₂ + H ₂ + H ₂ O mixed gas (oxygen) ( ^Partial pressure: 10 ⁻¹² MPa). Here, since the temperature at which the sintering is completed depends on the size of the base material to be used and the amount of subcomponents, the holding temperature was fired at each optimum temperature for each example.

The annealing conditions are: temperature rising rate: 200 ° C./hour, holding temperature: 1050 ° C., temperature holding time: 2 hours, cooling rate: 200 ° C./hour, atmospheric gas: N ₂ + H ₂ O mixed gas (oxygen partial pressure: 10 ⁻⁷ MPa). A wetter was used for humidifying the atmospheric gas during firing and annealing.

  The capacitor element main body obtained as described above is subjected to end face polishing, for example, by barrel polishing or sand blasting, and the external electrode paste is applied and fired to form the external electrode 4. Then, if necessary, a coating layer is formed on the surface of the external electrode 4 by plating or the like.

Evaluation Method In carrying out the present invention, an evaluation method of barium titanate powder as a main component, a dielectric ceramic composition obtained, and an evaluation method of a multilayer ceramic capacitor produced using the same will be described.

About each obtained multilayer ceramic capacitor sample, the presence or absence of the core part and the shell part of the dielectric particles, the concentration CS2 (at%) with respect to Ti of the second subcomponent in the shell part, the relative dielectric constant εs, the insulation resistance (IR) The capacity-temperature characteristics (TC) and the high temperature accelerated lifetime (HALT) were measured by the methods shown below.

Concentration of the second subcomponent (rare earth element) in the shell portion The concentration of the second subcomponent (rare earth element) in the shell portion was examined using a transmission scanning electron microscope (STEM) equipped with an elemental analysis instrument (EDS). . As a sample, a laminated ceramic capacitor was cut out in a plane perpendicular to the dielectric layer, and a thin piece produced by FIB processing was used as a TEM sample.

  Immediately before TEM observation, the amorphous layer on the surface of the TEM sample was removed using a low acceleration Ar ion polishing apparatus.

  STEM observation is performed on such a TEM sample, and the crystal particles mainly composed of barium titanate are particles that can be clearly observed without overlapping with other crystal particles, and when observed in the STEM dark field, Particles with a clearly distinguishable core contrast were selected. FIG. 3 shows an observation example. About 50 such crystal grains, EDS elemental analysis is performed at an intermediate point (EDS observation point 13) between the portion where the contrast between the core portion and the shell portion changes sharply and the crystal grain boundary, and this is 10 for each crystal particle. Measurements were made point by point. These results were averaged and used as the concentration CS2 of the second subcomponent (rare earth element) in the shell portion.

Dielectric constant εs
With respect to the multilayer ceramic capacitor sample, a signal with a frequency of 1 kHz and an input signal level (measurement voltage) of 1 Vrms was input with a digital LCR meter (4284A manufactured by YHP) at a reference temperature of 25 ° C., and the capacitance C was measured.
The relative dielectric constant εs (no unit) was calculated based on the thickness of the dielectric layer, the effective electrode area, and the capacitance C obtained as a result of the measurement.
In this example, the relative dielectric constant was 900 or more.

Insulation resistance (IR)
Measurement was performed after applying a measurement voltage of 50 V / μm for 30 seconds with an IR measuring instrument. Measurement was performed with 10 chips, and an average value was obtained. The insulation resistance was good at 5.0E + 9Ω or more.

Capacity temperature characteristics (TC)
The capacitance at −55 to 160 ° C. was measured for the multilayer ceramic capacitor sample, and the rate of change relative to the capacitance at the reference temperature (25 ° C.) was calculated.
In this example, a material satisfying a capacity change rate at 150 ° C. of + 15% to −15% (X8R characteristics) was considered good.

High temperature accelerated life (HALT)
The multilayer ceramic capacitor samples were evaluated for high temperature accelerated life (HALT) by maintaining a DC voltage application state at 200 ° C. under an electric field of 35 V / μm and measuring the life time.
In this example, the time from the start of application until the insulation resistance drops by an order of magnitude was defined as the lifetime.
Further, this high temperature accelerated life was performed for 20 multilayer ceramic capacitor samples.
The evaluation criteria were good for 80 hours or more.

Sample numbers 1-24
First, samples 1 to 24 using BaTiO ₃ having a c / a value of c / a = 1.006 as a ratio of the c-axis length to the a-axis length of the crystal lattice as a main component material will be described first.

For BaTiO _{3 as the} main component, Mg as the first subcomponent, Tb and Yb as the second subcomponent, Mn as the third subcomponent, Si as the fourth subcomponent, Zr as the fifth subcomponent, An oxide or a carbonate compound is selected.

The composition ratio of BaTiO ₃ and the first to fifth subcomponents in the final product is as follows: BaTiO ₃ is 100 (at%), the first subcomponent Mg is 3.7 (at%), and the second subcomponent is Tb. And Yb are 3.8 (at%) and 5.3 (at%), respectively, the third subcomponent Mn is 0.23 (at%), and the fourth subcomponent Si is 3.2 (at%). %), And the mixed powder was produced by a ball mill so that Zr as the fifth subcomponent was 1.2 (at%).

Here, the composition ratio between BaTiO ₃ and the first to fifth subcomponents in the final product is defined as the basic composition.

  An organic binder was added to the mixed powder prepared by the ball mill to form a slurry, which was then formed into a sheet. Dielectric sheets were alternately laminated with internal electrodes, formed into chips, and then fired to obtain a desired multilayer ceramic capacitor sample.

Sample numbers 1-5
In Samples 1 to 5 in Table 3, Mg was taken up as the first subcomponent, and the amount of Mg element added was changed as shown in Table 1 for investigation. In this study, other subcomponent concentrations were fixed to the basic composition. As a result, Samples 2 to 4 satisfying 0 (at%) <CP1 (Mg concentration in Tables 2 and 3) <5 (at%) show high values of high temperature accelerated lifetimes.
When the Mg concentration is 0 (at%), the generation of oxygen defects is not suppressed, and the high temperature accelerated life is reduced. On the other hand, when the Mg concentration is higher than 5 (at%), the voltage applied to the grain boundary portion becomes too high, and the high temperature accelerated life is reduced.

Sample number 6-12
In Samples 6 to 12 in Table 3, Tb and Yb were taken up as the second subcomponent, and the addition amount of Tb element and Yb element was changed as shown in Table 1 for investigation. In this study, other subcomponent concentrations were fixed to the basic composition. As a result, in Samples 7 to 11 satisfying 0 (at%) <CP2 (the sum of the Tb concentration and the Yb concentration in Tables 2 and 3) <15 (at%), the insulation resistance, the high temperature accelerated lifetime, and the capacity-temperature characteristic Indicates a good value.

  When the Tb or Yb concentration is low, the sintering proceeds excessively, and the capacity-temperature characteristics are deteriorated and the high temperature accelerated life is reduced. On the other hand, when the Tb or Yb concentration is high, the increase in donor ions causes a decrease in insulation resistance, and at the same time, a decrease in high-temperature accelerated lifetime due to an increase in oxygen defects.

Sample numbers 13-16
In Samples 13 to 16 in Table 3, Mn was taken up as the third subcomponent, and the amount of Mn element added was changed as shown in Table 1 for investigation. In this study, other subcomponent concentrations were fixed to the basic composition. As a result, samples 14 to 15 satisfying 0 (at%) <CP3 (Mn concentration in Tables 2 and 3) <1 (at%), and the dielectric constant, insulation resistance, and high-temperature accelerated life showed good values. ing.

  When the Mn concentration is low, the generation of oxygen defects is not suppressed, and the insulation resistance and the high temperature accelerated life are reduced. On the other hand, when the Mn concentration is high, the ratio of the shell portion is excessively increased and the relative dielectric constant is decreased. At the same time, since the voltage applied to the grain boundary increases, the high temperature accelerated lifetime also decreases.

Sample number 17-20
In Samples 17 to 20 in Table 3, Si was taken up as the fourth subcomponent, and the amount of Si element added was changed as shown in Table 1 for investigation. In this study, other subcomponent concentrations were fixed to the basic composition. As a result, in Samples 17 to 20 in Table 3, Samples 18 to 19 satisfying 2 (at%) <CP4 (Si concentration in Tables 2 and 3) <5 (at%). It shows a good value.

  When the Si concentration is low, a sufficient sintered state cannot be obtained, so that the insulation resistance decreases. On the other hand, when the Si concentration is high, the grain growth is excessively promoted and the high temperature accelerated life is deteriorated.

Sample numbers 21-24
In Samples 17 to 20 in Table 3, Zr was taken up as the fifth subcomponent, and the amount of Zr element added was changed as shown in Table 1 for investigation. In this study, other subcomponent concentrations were fixed to the basic composition. As a result, the samples 22 to 23 satisfying 0.0 (at%) <CP5 (Zr concentration in Tables 2 and 3) <1.5 (at%), and the high-temperature accelerated lifetime and capacity-temperature characteristics have good values. Show.

  When the Zr concentration is 0.0 (at%), the change in the valence of Ti to the trivalence is not suppressed, and the lattice constant changes. This causes a decrease in relative dielectric constant and a deterioration in capacitance temperature characteristics. On the other hand, when the Zr concentration exceeds 1.5 (at%), segregation of Zr occurs, resulting in a decrease in relative permittivity and a deterioration in capacitance-temperature characteristics.

Sample number 25-40
Next, BaTiO ₃ whose c / a value, which is the ratio of the c-axis length to the a-axis length of the crystal lattice, is c / a = 1.002, 1.006, 1.007, 1.011 is used as a main component material. The used samples 25 to 40 will be described.

Similar to Example 1, with respect to BaTiO ₃ as the main component, Mg as the first subcomponent, Tb and Yb as the second subcomponent, Mn as the third subcomponent, Si as the fourth subcomponent, fifth subcomponent An oxide or a carbonic acid compound is selected for each of Zr as a component.

The composition ratio of BaTiO ₃ and the first to fifth subcomponents in the final product is as follows: BaTiO ₃ is 100 (at%), the first subcomponent Mg is 3.7 (at%), and the second subcomponent is Tb. And Yb are 0.1 to 3.8 (at%) and 0.2 to 5.3 (at%), respectively, and the third subcomponent Mn is 0.23 (at%), and the fourth subcomponent is A mixed powder was prepared by a ball mill so that a certain Si was 3.2 (at%) and the fifth subcomponent Zr was 1.2 (at%).

The concentration of the second subcomponent is 0.1 (at%) for Tb in sample numbers 25 to 28, 0.2 (at%) for Yb, and 1.9 (Tb for sample numbers 29 to 32). at%), Yb is 2.9 (at%), sample numbers 33 to 36, Tb is 2.4 (at%), Yb is 3.7 (at%), and sample numbers 37 to 40, Tb is 3.8 (at%) and Yb are set to 5.3 (at%).

The c / a value, which is the ratio of the c-axis length to the a-axis length of BaTiO ₃ used, is c / a = 1.002 for sample numbers 25, 29, 33, and 37, and sample numbers 26, 30, and 34. , 38, c / a = 1.006, sample numbers 27, 31, 35, 39, c / a = 1.007, and sample numbers 28, 32, 36, 40, c / a = 1.010 To do.

An organic binder was added to the mixed powder prepared by the ball mill to form a slurry, which was then formed into a sheet. Dielectric sheets were alternately laminated with internal electrodes, formed into chips, and then fired to obtain a desired multilayer ceramic capacitor sample.

  From Table 4, although the dielectric ceramic composition was synthesized with the same composition ratio, a difference appeared in the second subcomponent concentration CS2 in the shell part and CS2 / CP2 which is the ratio of CS2 and CP2. . Here, the same composition ratio refers to a set of sample numbers “25 to 28”, a set of “29 to 32”, a set of “33 to 36”, and “37 to 40”, respectively.

As the c / a value of the raw material for BaTiO ₃ decreased, CS2 and CS2 / CP2 increased.

Sample numbers 25, 26, 29, 30, 33, 34, 37, and 38 using BaTiO ₃ satisfying c / a <1.007 as raw materials satisfy CS2> 10 (at%) and CS2 / CP2> 2.122. Since they were satisfied, the capacity-temperature characteristics and the high temperature accelerated life were good.

On the other hand, in sample numbers 27, 28, 31, 32, 35, 36, 39, and 40 using BaTiO ₃ satisfying c / a ≧ 1.007 as the raw material, CS2> 10 (at%), CS2 / CP2 > 2.122 was not satisfied, and the capacity-temperature characteristic or accelerated life did not reach the standard value (capacitance-temperature characteristic: + 15% to -15%, high-temperature accelerated life: 80 hours or more).

  As shown in Table 4, the samples of sample numbers 25 to 40 satisfy all the reference values for the relative dielectric constant and the insulation resistance.

  As described above, the dielectric ceramic composed of the sintered body in which the concentration of the rare earth in the shell portion is increased by using the low crystal base material has been described. As described above, the life characteristic and the temperature characteristic are improved by configuring the shell part in which the rare earth is highly concentrated.

  By using the dielectric ceramic according to the present invention, a multilayer ceramic capacitor having excellent life characteristics and temperature characteristics can be manufactured. The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  By using the dielectric ceramic composition according to the present invention, it is possible to manufacture a monolithic ceramic capacitor having smaller life characteristics and temperature characteristics. The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Multilayer ceramic capacitor 2 ... Dielectric layer 3 ... Internal electrode layer 4 ... External electrode 10 ... Capacitor element main body 11 ... Core part 12 ... Shell part 13 ... EDS observation point 14 ... Bright part (shell part)
15 ... Dark part (core part)
16 ... spot (pore in particle)

Claims (3)

The ceramic particles are made of a sintered body of ceramic particles.
A dielectric ceramic composition composed of a sintered body having a shell portion covering the core portion,
The core portion is composed of BaTiO _{3 as} a main component,
The shell portion is at least one element selected from BaTiO ₃ and the first subcomponent Mg, Ba, Ca, Sr and the second subcomponent. Elements containing Tb and Yb, and Mn as the third subcomponent Element and the fourth subcomponent Si Elements and the fifth subcomponent Zr And the concentrations of subcomponents with respect to Ti in the dielectric ceramic composition are as follows: first subcomponent: CP1 (at%), second subcomponent: CP2 (at%), third subcomponent When component: CP3 (at%), fourth subcomponent: CP4 (at%), fifth subcomponent: CP5 (at%),
0 (at%) <CP1 <5 (at%),
0 (at%) <CP2 <15 (at%),
0 (at%) <CP3 <1 (at%),
2 (at%) <CP4 <5 (at%),
0 (at%) <CP5 <1.5 (at%),
When the concentration of the second subcomponent with respect to Ti in the shell portion is CS2 (at%),
CS2> 10 (at%)
And CS2 / CP2> 2.122
A dielectric ceramic composition characterized by satisfying: 2. The dielectric ceramic composition according to claim 1, wherein a c / a value of BaTiO ₃ used as a raw material of the dielectric ceramic composition is c / a <1.007. A multilayer ceramic capacitor comprising the dielectric ceramic composition as defined in claim 1.