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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer ceramic capacitor.
2. Description of the Related Art
A multilayer ceramic capacitor is composed of an element body having the configuration that a plurality of dielectric layers and internal electrode layers are alternately stacked and a pair of external terminal electrodes formed on both and
portions of the element body. The multilayer ceramic capacitor is produced by producing a pre-firing element body by alternately stacking pre-firing dielectric layers and pre-firing internal electrode layers exactly by necessary numbers first, then,
after firing the same, forming a pair of external terminal electrodes on both end portions of the fired element body.
When producing a multilayer ceramic capacitor, since the pre-firing dielectric layers and the pre-firing internal electrode layers are fired at a time, a conductive material included in the pre-firing internal electrode layers is demanded to have
a higher melting point than a sintering temperature of dielectric material powder included in the pre-firing dielectric layers, not to react with the dielectric material powder, and not to be dispersed in the fired dielectric layers, etc.
In recent years, to respond to the demands, as a conductive material included in the pre-firing internal elect layers, instead of conventionally used Pt, Pd and other precious metals, an Ag--Pd alloy to used, or those using Ni, which can be fired
in a reducing atmosphere, and other inexpensive base metals by giving reduction-resistance to the dielectric material have been developed.
The case of using Ni as a conductive material included in the pre-firing internal electrode layers will be explained as an example. Ni has a lower melting point comparing with that of dielectric material powder included in the pre-firing
dielectric layer. Therefore, when pre-firing dielectric layers and pre-firing internal electrode layers including Ni as a conductive material are fired at a time, due to a difference of sintering start temperatures of the dielectric material powder and
Ni, Ni internal electrode tends to become thick to be eventually broken as sintering of the dielectric material powder proceeds. Thus, to suppress this kind of breaking due to firing and to suppress sintering, there is proposed a technique of adding an
additive dielectric material as a sintering retarder to an internal electrode layer paste for forming the internal electrode layers (refer to the patent articles 1 to 5). The additive dielectric material has a property of being dispersed from the
internal electrode layer side to the interlayer dielectric layer side at the time of firing pre-firing interlayer dielectric layers and pre-firing internal electrode layers at a time.
In recent years, as a result that a variety of electronic apparatuses became compact, a multilayer ceramic capacitor installed inside the electronic apparatuses has been demanded to realize a compact body with a larger capacity, a low price and
high reliability. To respond to the demands, a fired internal electrode layer, fired interlayer dielectric layer arranged between mutually facing fired internal electrode layers have been made thinner. Specifically, a thickness after firing per one
fired interlayer dielectric layer has become as thin as 1 .mu.m or so and, along therewith, a thickness before firing per one pre-firing interlayer dielectric layer has also become thinner.
As the pre-firing interlayer dielectric layer becomes thinner, a content of a dielectric material per one dielectric layer for forming it decreases.
For example, the case of preparing an internal electrode layer paste obtained by adding an additive dielectric material at a predetermined weight ratio to Ni as a conductive material and forming by applying the paste to be a predetermined
thickness to a plurality of pre-firing interlayer dielectric layers, wherein the pre-firing thickness is gradually made thinner, will be considered. At this time, the weight ratio of a content of the additive dielectric material in the internal
electrode layer with respect to a content of the dielectric material in the pre-firing interlayer dielectric layer (a content of the additive dielectric material in the internal electrode layer/a content of the dielectric material in the pre-firing
interlayer dielectric layer) gradually increases as the thickness of the pre-firing interlayer dielectric layer applied with the internal electrode layer paste becomes thinner. It is because a content of the dielectric material in the pre-firing
interlayer dielectric lawyer decreases as the thickness of the pre-firing interlayer dielectric layer becomes thinner, so that a denominator of a formula of the above weight ratio becomes smaller, consequently, a value of the weight ratio becomes larger.
When considering this from the pre-firing interlayer dielectric layer side, it means that the thinner the thickness becomes, the larger an amount of the additive dielectric material to be dispersed from the internal electrode layer side
relatively becomes. Namely, a relative dispersal amount from the internal electrode layer aide to the interlayer dielectric layer side increases.
Also, as the pre-firing interlayer dielectric layer becomes thinner as above, the pre-firing internal electrode layer is also demanded to be thinner, however, to make the pre-firing internal electrode layer thinner, the additive dielectric
material as well as a conductive material, such as Ni, in the internal electrode layer paste for forming the same are demanded to be finer.
However, when the additive dielectric material to be dispersed from the internal electrode layer side to the interlayer dielectric layer side at the time of firing is made finer, grain growth of dielectric particles composing the interlayer
dielectric layer may be accelerated to influence the fine structure of the interlayer dielectric layer in some cases. As explained above, the influence is furthermore enhanced when the dispersal amount of the additive dielectric material from the
internal electrode layer aide to the interlayer dielectric layer side becomes larger. The influence on the fine structure can be ignored when a thickness of the fired interlayer dieleatric layer is made to be 2.0 .mu.m or more, however, the influence on
the fine structure tends to become large when the thickness of the fired interlayer dielectric layer is made thin as less than 2.0 .mu.m. Along with the influence on the fine structure as such, it is liable that various characteristics, such as a bias
characteristic and reliability, of a multilayer ceramic capacitor to be obtained are deteriorated.
To solve the disadvantages, the patent article 6 proposes a technique of adjusting additive composition for an internal electrode layer paste and adjusting a ratio of an average particle diameter of dielectric particles contacting the internal
electrode layer after firing and that of not contacting dielectric particles, concentration ratio of additive components and a core-shell ratio. According to the technique described in the patent article 6, a dielectric layer can be made thinner without
deteriorating a temperature characteristic, tan.delta. and lifetime. However, bias characteristics were not sufficiently improved in the technique described in the patent article 6, go that a problem to be solved still remained.
The patent article 7 discloses a multilayer ceramic capacitor wherein an adage particle diameter of dielectric particles near an eternal electrode is the same as or smaller than an average particle diameter of dielectric particles in an effective
region.
However, the technique described in the patent article 7 is for a purpose of preventing cracks at the time of sintering the external electrode, and an improvement of the bias characteristics cannot be expected.
Patent Article 1: The Japanese Unexamined Patent Publication No. 5-62855
Patent Article 2: The Japanese Unexamined Patent Publication No. 2000-277369
Patent Article 3: The Japanese Unexamined Patent Publication No. 2001-307939
Patent Article 4: The Japanese Unexamined Patent Publication No. 2003-77761
Patent Article 5: The Japanese Unexamined Patent Publication No. 2003-100544
Patent Article 6: The Japanese Unexamined Patent Publication No. 2003-124049
Patent Article 7. The Japanese Unexamined Patent Publication No. 2003-133164
SUMMARY OF THE INVENTION
An object of the present invention is to provide a multilayer ceramic capacitor, by which an improvement of a TC bias characteristic can be expected while obtaining various electric characteristics, particularly a sufficient permittivity, even
when an interlayer dielectric layer is made thin.
To attain the above objects, according to the present invention, there is provided
a multilayer ceramic capacitor comprising an internal electrode layer and a dielectric layer having a thickness of less than 2 .mu.m, wherein
said dielectric layer contains a plurality of dielectric particles, and
when it is assumed that standard deviation of a particle distribution of the entire dielectric particles in said dielectric layer is .sigma. (no unit), the .sigma. satisfies .sigma.<0.130.
Preferably, when assuming that an average particle diameter of the entire dielectric particles in said dielectric layer is D50 (unit: .mu.m) and a rate that dielectric particles (coarse particles) having an average particle diameter of 2.25 times
of the D50 exist in said entire dielectric particles is p (unit: %), said p satisfies p<12%.
The multilayer ceramic capacitor according to the present invention can be produced, for example, by the method below. Note that a production method of the multilayer ceramic capacitor of the present invention is not limited to the method below.
Note that, in the method below, the case where the dielectric layer contains a main component composed of barium titanate (barium titanate, wherein particularly the mole ratio m of the so-called A site and the B site is 0.990 to 1.35, expressed
by a composition formula (BaO).sub.0.990 to 1.035.TiO.sub.2 will be explained as an example.
The method of producing a multilayer ceramic capacitor, comprising the steps of:
firing a stacked body formed by using a dielectric layer paste containing a dielectric material and an internal electrode layer paste containing an additive dielectric material;
wherein the dielectric material in the dielectric layer paste contains a main component material and a subcomponent material;
the main component material is barium titanate expressed by a composition formula (BaO).sub.m.TiO.sub.2, wherein the mole ratio m is 0.990 to 1.035;
the additive dielectric material in the internal electrode layer paste contains at least an additive main component material; and
the additive main component material is barium titanate expressed by a composition formula (BaO).sub.m'.TiO.sub.2, wherein the mole ratio m' is 0.993<m'<0.50.
In this method, A/B, that is the mole ratio m' of the A site (the "(BaO)" part in the above formula) and a B site (the "TiO.sub.2" part in the above formula), of the additive main component material contained in the additive dielectric material
in the internal electrode layer paste is adjusted. Due to this, an existing state of dielectric particles composing a fired dielectric layer can be easily controlled.
Note that a composition of a dielectric oxide composing the main component is not limited to the barium titanate expressed by the above composition formula (BaO).sub.0.990 to 1.035.TiO.sub.2, and dielectric oxides below can be generally applied.
The dielectric oxides are expressed by a composition formula (AO).sub.m.BO.sub.2, wherein the "A" is at least one element selected from Sr, Ca and Ba, "B" is at least one element of Ti and Zr, and the mole ratio m is 0.990 to 1.035.
Preferably, the additive main component material has an ignition loss of less than 10.00%, by controlling an ignition loss of the additive main component material as well as the mole ratio m' of the additive main component material, the existing
state of dielectric particles suing the fired dielectric layers can be furthermore preferably controlled.
In this method, it is sufficient if the additive dielectric material includes "at least an additive main component material", and an additive subcomponent material is also contained in some cases. A composition of the additive subcomponent
material in this case may be the same as or different from a composition of a subcomponent material included in the dielectric material in the dielectric layer paste.
A material composing the internal electrode layer of the multilayer ceramic capacitor is not particularly limited in the present invention and precious metals may be also used other than base metals. When composing the internal electrode layer
by a base metal, the dielectric layer may contain a subcomponent including at least one kind of oxides of Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb and R (R is at least one kind of rare earth elements, such as Y) and compounds to become these oxides due to
firing, etc. other than the main component, such as barium titanate. As a result of containing the subcomponent, it is not made semiconductive even when fired in a reducing atmosphere and characteristics as a capacitor can be maintained. As explained
above, when producing a multilayer ceramic capacitor having a dielectric layer containing a subcomponent other than the main component, the dielectric material contained in the dielectric layer paste contains a main component material and subcomponent
material to form the main cement and subcomponent after firing. In this case, as explained above, an additive dielectric material contained in the internal electrode layer paste also contains additive subcomponent material other than the additive main
component material.
Preferably, the dielectric layer contains barium titanate expressed by a composition formula of (BaO).sub.m.TiO.sub.2, wherein the mole ratio m is 0.990 to 1.035, as a main component, a magnesium oxide and an oxide of rare earth elements as a
subcomponent, furthermore, at least one kind selected from a barium oxide and a calcium oxide and at least one kind selected from silicon oxide, manganese oxide, vanadium oxide and molybdenum oxide as another subcomponent.
At this time, it in preferable that an additive dielectric material included in the internal electrode paste contains barium titanate expressed by a composition formula (BaO).sub.m'.TiO.sub.2, wherein the mole ratio m' is 0.993<m'<1.030, as
an additive main component material and magnesium oxide (including a compound to be magnesium oxide after firing) and oxides of rare earth elements as additive subcomponent materials, furthermore, at least one kind selected from a barium oxide (including
a compound to be a barium oxide after firing) and a calcium oxide (including a compound to be a calcium oxide after firing) and at least one kind of a silicon oxide, a manganese oxide (including a compound to be a manganese oxide after firing), a
vanadium oxide and a molybdenum oxide.
Note that a dielectric layer simply expressed by "dielectric layer" means one or both of an interlayer dielectric layer and external dielectric layer in the present invention.
The present inventors focused on an existence state of a plurality of dielectric particles in a dielectric layer, committed themselves to study to find that an effect of improving a TC bias characteristic can be obtained while obtaining various
electric characteristics, particularly a sufficient permittivity, even when a thickness of an interlayer dielectric layer is made thin to less than 2 .mu.m by decreasing unevenness of particles by making a particle size distribution of the entire
dielectric particles sharp In the dielectric layer, that is, to make a standard deviation .sigma. of the particle distribution of the entire dielectric particles in the dielectric layer small.
By making the standard deviation a small, a rate p of large dielectric particles (coarse particles) existing in the entire dielectric particles in the interlayer electrode layer becomes small, but it is preferable that p<12% is satisfied as
explained above. As a result, an effect of improving a TC bias characteristic is furthermore enhanced.
Namely, according to the present invention, it is possible to provide a multilayer ceramic capacitor, by which a TC bias characteristic can be expected to be improved while obtaining various electric characteristics, particularly a sufficient
permittivity, even when an interlayer dielectric layer is made thin.
BRIEF DESCRIPTION OF DRAWINGS
These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, in which:
FIG. 1 is a schematic sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention;
FIG. 2 is an enlarged sectional view of a key part of an interlayer dielectric layer 2 shown in FIG. 1;
FIG. 3 is a graph showing respective temperature changes of binder removal processing, firing and annealing in an embodiment;
FIG. 4 is a SEM image showing a section condition of a sintered body after performing thermal etching on a sample 9 as an example;
FIG. 5 is a SEM image showing a section condition of a sintered body after performing thermal etching on a sample 1 as a comparative example;
FIG. 6 is a graph of a relationship of a particle diameter and frequency of dielectric particles composing an interlayer dielectric layer in the sample 9 as an example; and
FIG. 7 is a graph of a relationship of a particle diameter and frequency of dielectric particles composing an interlayer dielectric layer in the sample 1 as a comparative example.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Below, the present invention will be explained based on embodiments shown in drawings.
In the present embodiment, as a multilayer ceramic capacitor having internal electrode layers and dielectric layers, a multilayer ceramic capacitor wherein a plurality of in internal electrode layers and interlayer dielectric layers are
alternately stacked and external dielectric layers are arranged on both external end portions in the stacking direction of the internal electrode layers and interlayer dielectric layers will be explained as an example.
Multilayer Ceramic Capacitor
As shown in FIG. 1, a multilayer ceramic capacitor 1 according to an embodiment of the present invention has a capacitor element body having the configuration that interlayer dielectric layers 2 and internal electrode layers 3 are alternately
stacked. On end portions on both sides of the capacitor element body 10, a pair of external electrodes 4 connected respectively to the internal electrode layers 3 arranged alternately inside the element body 10 are formed. The internal electrode layers
3 are stacked so that and surfaces on both sides are exposed alternately to surfaces of the mutually facing two end portions of the capacitor element body 10. The pair of external electrodes 4 are formed on both end portions of the capacitor element
body 10 and connected to the exposed end surfaces of the alternately arranged internal electrode layers 3, so that a capacitor circuit is configured.
A shape of the capacitor element body 10 is not particularly limited; but is normally a rectangular parallelepiped shape. Also, a size thereof is not particularly limited and may be a suitable size in accordance with the use object, but is
normally length (0.4 to 5.6 mm).times.width (0.2 to 5.0 mm).times.height (0.2 to 1.9 mm) or so.
In the capacitor element body 10, external dielectric layers 20 are arranged on both external end portions in the stacking direction of the internal electrode layers 3 and the interlayer dielectric layers 2 to protect inside the element body 10.
Interlayer-Dielectric Layer and External Dielectric Layer
Compositions of the interlayer dielectric layers 2 and external dielectric layers 20 are not particularly limited in the present invention and are composed, for example, of a dielectric ceramic position below.
A dielectric ceramic composition of the present invention contains as a main component barium titanate expressed by a composition formula (BaO).sub.m.TiO.sub.2, wherein a mole ration m is 0.990 to 1.035.
The dielectric ceramic composition of the present embodiment contains a subcomponent together with the above main component. As the subcomponent, those containing at least one kind of oxides of Mn, Cr, Ca, Ba, Mg, V, W, Ta, Nb and R (R is at
least one kind of rare earth elements, such as Y) and compounds which becomes oxides by firing may be mentioned. By adding the subcomponent, characteristics as a capacitor can be obtained even by firing in a reducing atmosphere. Note that as an
impurity, a, trace component of C, F, Li, Na, K, P, S and Cl, etc. may be contained by not more than 0.1 wt % or so. Note that, in the present invention, compositions of the interlayer dielectric layers 2 and the external dielectric layers 20 are not
limited to the above.
In the present embodiment, it is preferable that a composition below is used as the interlayer dielectric layers 2 and the external dielectric layers 20. The composition contains barium titanate expressed by a position formula
(BaO).sub.m.TiO.sub.2, wherein a mole ration m is 0.990 to 1.035, as a main component, a magnesium oxide and oxides of rare earth elements as a subcomponent and, as still another subcomponent, at least one kind selected from a barium oxide and a calcium
oxide and at least one kind selected from a silicon oxide, a manganese oxide, a vanadium oxide and a molybdenum oxide. When calculating barium titanate in terms of [(BaO).sub.0.990 to 1.035.TiO.sub.2], a magnesium oxide in terms of MgO, oxides of rare
earth elements in terms of R.sub.2O.sub.3, a barium oxide in terms of BaO, a calcium oxide in terms of CaO, a silicon oxide in terns of SiO.sub.2, a manganese oxide in terms of MnO, a vanadium in of V.sub.2O.sub.3 and a molybdanum oxide in terms of
MoO.sub.3, the respective ratios with respect to 100 moles of [(BaO).sub.0.990 to 1.035.TiO.sub.2] are MgO: 0.1 to 3 moles, R.sub.2O.sub.3: more than 0 but not more than 5 moles, BaO+CaO: 0.5 to 12 moles, SiO.sub.2: 0.5 to 12 moles, MnO: more than 0 mole
but not more than 0.5 mole, V.sub.2O.sub.5: 0 to 0.3 mole and MoO.sub.3: 0 to 0.3 mole.
Various conditions, such as the number layers to be stacked and the thickness, of the interlayer dielectric layers 2 may be suitably determined in accordance with the object and use and, in the present embodiment, a thickness of the interlayer
dielectric layers 2 is made thin as preferably less than 2 .mu.m, more preferably 1.5 .mu.m or less, and furthermore preferably 1 .mu.m or less. In the present embodiment, even when the thickness of the interlayer dielectric layer 2 is made thin as
such, the TC bias characteristic is improved while obtaining various electric characteristics, particularly a sufficient permittivity. A thickness of the external dielectric layer 20 is, for example, 30 .mu.m to several hundreds of .mu.m or so.
As shown in FIG. 2, the interlayer dielectric layer 2 includes a plurality of dielectric particles 2a and a grain boundary phase formed between adjacent dielectric particles 2a.
The plurality of dielectric particles 2a are composed of contact dielectric particles 22a contacting the internal electrode layers 3 and non-contact dielectric particles 24a not contacting the internal electrode layers 3. The contact dielectric
particles 22a contact one of a pair of internal electrode layers 3 sandwiching an interlayer dielectric layer 2 including the contact dielectric particles 22a and do not contact both of them.
Here, when assuming that standard deviation of a particle size distribution of the entire dielectric particles 2a in the interlayer dielectric layer (a part contributing to a capacitance) 2 is .sigma. (no unit) and an average particle diameter
of the entire dielectric particles 2a in the interlayer dielectric layer 2 is D50 (unit: .mu.m), the ratio that dielectric particles (coarse particles) having an average particle diameter of 2.25 times of the D50 exist in the entire dielectric particles
2a is assumed to be p (unit: %). Note that the average particle diameter D50 of the entire dielectric particles 2a means an average particle diameter of the contact dielectric particles 22a and the non-contact dielectric particles 24a. The average
particle diameter is an average particle diameter not including dielectric particles in the external dielectric layer 20 as a part not contributing to a capacitance. Note that the D50 here is a value obtained by cutting the capacitor element body 10 in
the stacking direction of the dielectric layers 2 and 20 and internal electrode layers 3, measuring an average area of 200 or more dielectric particles 2a on the section shown in FIG. 2, calculating the diameter as an equivalent circle diameter, and
multiplying the result by 1.5.
At this time, in the present embodiment, .sigma. satisfies .sigma.<0.130, preferably 0.125 or less, and more preferably 0.120 or less. When the a value .sigma. too large, disadvantages arise that bias characteristics and reliability
decline, etc. The smaller the lower limit of the .sigma. is, the better.
In the present embodiment, it is preferable that p satisfies p<12%, and more preferably 10% or less. When the standard deviation .sigma. is small, the ratio p is considered to become small being in proportional thereto. The smaller the
lower limit of p is, the better.
Components of the grain boundary phase are normally an oxide of a material opposing the dielectric material or the internal electrode material, an oxide of a separately added material and an mode of a material mixed as an impurity in the
procedure.
Internal Electrode Layer
The internal electrode layers 3 shown in FIG. 1 are composed of a conductive material of a base metal substantially serving as an electrode. As the base metal to be used as a conductive material, Ni or a Ni alloy is preferable. As a Ni alloy,
an allay of at least one kind selected from Mn, Cr, Co, Al, Ru, Rh, Ta, Re, Os, Ir, Pt and W, etc. with Ni is preferable, and a Ni content in the allay is preferably 95 wt % or more. Note that the Ni or Ni alloy may contain a variety of trace
components, such as P, C, Nb, Fe, Cl, B, Li, Na, K, F and S, by not more than 0.1 wt %.
In the present embodiment, a thickness of the internal electrode layers 3 is made thin as preferably less than 2 .mu.m, and more preferably 1.5 .mu.m or less.
External Electrode
An the external electrodes 4 shown in FIG. 1, at least one kind of Ni, Pd, Ag, Au, Cu, Pt, Rh, Ru and Ir, etc. or alloys of these may be normally used. Normally, Cu, a Cu alloy, Ni and a Ni alloy, etc., Ag, an Ag--Pd alloy and an In--Ga alloy,
etc. are used. The thickness of the external electrodes 4 may be suitably determined in accordance with the use, and 10 to 200 .mu.m or so is normally preferable.
Production Method of Multilayer Ceramic Capacitor
An example of a production method of the multilayer ceramic capacitor 1 according to the present embodiment will be explained next.
(1) First, a dielectric layer paste for composing the interlayer dielectric layers 2 and external dielectric layers 20 shown in FIG. 1 after firing and an internal electrode paste for composing the internal electrode layers 3 shown in FIG. 1
after firing are prepared.
Dielectric Layer Paste
The dielectric layer paste is fabricated kneading dielectric materials and an organic vehicle.
As the dielectric materials, main component materials and subcomponent materials for forming a main component and subcomponent for composing the dielectric layers 2 and 20 after firing are included. The respective component materials are
suitably selected from a variety of compounds to be composite oxides and oxides, for example, carbonate, nitrate, hydroxides and organic metal compounds, etc. and mixed to use.
The dielectric materials are normally used as powder having an average particle diameter of 0.4 .mu.m or less, an preferably 0.05 to 0.30 .mu.m or so. Note that the average particle diameter here is a value obtained by observing particles of the
materials by a SEM and calculated by an equivalent circle diameter.
The organic vehicle contains a binder and a solvent. As the binder, for example, ethyl cellulose, polyvinyl butyral, an acrylic resin, and other various normal binders may be used. Also, the solvent is not particularly limited and terpineol,
butyl carbitol, acetone, toluene, xylene, ethanol and other organic solvents are used.
The dielectric layer paste may be formed also by kneading dielectric materials and a vehicle obtained by dissolving a water-soluble binder in water. The water soluble binder is not particularly limited, and polyvinyl alcohol, methyl cellulose,
hydroxyethyl cellulose, a water-soluble acrylic resin and emulsion, etc. are used.
A content of the respective components of the dielectric layer paste in not particularly limited, and a dielectric layer paste may be fabricated, for example, to contain about 1 to 50 wt % of a solvent.
The dielectric layer paste may contain additives selected from various dispersants, plasticizers, dielectrics, subcomponent compounds, glass flits, and insulators, etc. in accordance with need. When adding these additives to the dielectric layer
paste, the total mount is preferably not more than 10 wt % or so.
Internal Electrode Layer Paste
In the present embodiment, the internal electrode layer paste is fabricated by kneading a conductive material, additive dielectric material and an organic vehicle.
As the conductive material, Ni, a Ni alloy, furthermore, a mixture of these are used. The conductive material may be a spherical shape, a scale shape, etc. and the shape is not particularly limited, and may be a combination of these shapes. In
the case of a spherical shape, an average particle diameter of the conductive material is normally 0.5 .mu.m or less, and preferably 0.01 to 0.4 .mu.m or so. It is to attain a highly thin layer. The conductive material is contained in the internal
electrode layer paste by preferably 35 to 60 wt %.
The additive dielectric materials function to suppress sintering of internal electrodes (conductive material) in the firing step. In the present embodiment, the additive dielectric materials contain an additive main component material and an
additive subcomponent material.
In the present embodiment, as an additive main component material, barium titanate expressed by a composition formula (BaO).sub.m'.TiO.sub.2, wherein the mole ratio m' is 0.993<m'<1.050, preferably. 0.995.ltoreq.m'.ltoreq.1.035, and more
preferably 1.000.ltoreq.m'.ltoreq.1.020, is used. By using barium titanate having an adjusted additive main component material value m', an existing state of dielectric particles 2a composing the dielectric layers 2 after firing is controlled and, even
when the layer is made thin, the TC bias characteristic is improved while obtaining various electric characteristics, particularly permittivity. When the m' becomes large, the .sigma. in the interlayer dielectric layers 2 of an obtained capacitor 1
tends to be small. When the m' becomes too large, it is liable that sintering become insufficient.
In the present embodiment, those having a specific ignition loss are used as an additive main component material. By using a main component material having a specific ignition loses as an additive, a particle configuration of the interlayer
dielectric layer can be effectively controlled, and a bias characteristic of the capacitor 1 can be furthermore effectively improved. The ignition loss of the additive main component material is less than 10.00%, preferably 8.10%, more preferably 5.50%
or less, and particularly preferably 3.85% or less. When the ignition loss becomes too large, it is liable that the bias characteristic cannot be improved. Note that the lower the lower limit of the ignition loss is, the more preferable. Ultimately,
0% is idealistic, but such an additive main component material is normally difficult to be produced.
Here, the "ignition loss" means a weight change rate when holding from 200.degree. C. to 1200.degree. C. for 10 minutes in thermal treatment (processing of heating from the room temperature to 1200.degree. C. at a temperature rising rate of
300.degree. C./hour in the air and maintaining at 1200.degree. C. for 10 minutes) on the additive main component material. It is considered that the ignition loss is generated as a result that adsorption components and an OH group normally contained
in the additive dielectric material are evaporated due to the thermal treatment.
An average particle diameter of the additive main component material may be the came as the particle diameter of a main component material contained in the dielectric material in the dielectric layer paste, but it is preferably smaller than that,
more preferably 0.01 to 0.2 .mu.m, and particularly preferably 0.01 to 0.15 .mu.m. Note that the average particle diameter value is known to correlate with a specific surface area (SSA).
The additive dielectric materials (Only Additive main component materials are included in some cases, and both of additive main component materials and additive subcomponent materials are included in other cases. Below, it will be the same
unless otherwise mentioned.) are not particularly limited but it is preferable to be produced, for example, by the oxalate method, hydrothermal synthesis method, sol-gel method, hydrolysis and alkoxide method, etc. By using these method, it is possible
to efficiently produce an additive dielectric material including an additive main component material having the above specific ignition loss and m' (that in, A/B).
The additive dielectric material is included in the internal electrode layer paste preferably 5 to 30 wt %, and more preferably 10 to 2.0 wt % with respect to the conductive material. When a content of the additive dielectric material in the
paste is too small, the effect of suppressing sintering of the conductive material declines, while when too large, continuity of the internal electrode declines. Namely, a disadvantage that a sufficient capacitance as a capacitor cannot be secured may
be caused when the content of the a additive dielectric material is too small or too large.
The organic vehicle contains a binder and a solvent.
As the binder, for example, ethyl cellulose, an acrylic resin, polyvinyl butyral, polyvinyl acetal, polyvinyl alcohol, polyolefin, polyurethane, polystyrene, and copolymers of these, may be mentioned. The binder is contained in the internal
electrode layer paste preferably by 1 to 5 wt % with respect to mixed powder of the conductive material and the additive dielectric material. When the binder is too scarce, the strength tends to decline, while when too much, metal filling density of an
electrode pattern before firing declines and smoothness of the internal electrode layer 3 may be hard to be maintained after firing.
As the solvent, any of well known solvents, for example, terpineol, dihydroterpineol, butyl carbitol and kerosene, etc. may be used. A content of the solvent is preferably 20 to 50 wt % or so with respect to the entire paste.
The internal electrode layer paste may contain a plasticizer. As a plasticizer, benzylbutyl phthalate (BBP) and other phthalate esters, adipic acid, phosphoric ester and glycols, etc. may be mentioned.
(2) Next, a green chip is produced by using the dielectric layer paste and the internal electrode layer paste. When using a printing method, the dielectric layer paste and the internal electrode layer paste in a predetermined pattern are stacked
by printing on a carrier sheet, cut to be a predetermined shape, and removed from the carrier sheet, so that a green chip is obtained. When using a sheet method, a green sheet is formed by forming the dielectric layer paste to be a predetermined
thickness on a carrier sheet, the internal electrode layer paste is printed to be a predetermined pattern thereon, then, they are stacked to obtain a green chip.
(3) Next, binder removal is performed on the obtained green chip. The binder removal is processing for, for example as shown in FIG. 3, raising atmosphere temperature T0 from the room temperature (25.degree. C.) to binder removal holding
temperature T1 at a predetermined temperature raising rate, holding at the T1 for predetermined time, then, lowering the temperature at a predetermined temperature lowering rate.
In the present embodiment, the temperature raising rate is preferably 5 to 300.degree. C./hour, and more preferably 10 to 100.degree. C. The binder removal holding temperature T1 is preferably 200 to 400.degree. C. and more preferably 220 to
380.degree. C., and the holding time at the T1 is preferably 0.5 to 24 hours, and more preferably 2 to 20 hours. The temperature lowering rate is preferably 5 to 300.degree. C./hour, and more preferably 10 to 100.degree. C./hour.
A processing atmosphere of the binder removal in preferably air or reducing atmosphere. As the reducing atmosphere, for example, a wet mixed gas of N.sub.2 and H.sub.2 is preferably used. An oxygen partial pressure in the processing atmosphere
is preferably 10.sup.-4.5 to 10.sup.5 Pa. when the oxygen partial pressure is too low, the binder removal effect tends to decline, while wh | | |
