JPH0432213A - Ceramic capacitor - Google Patents

Abstract

PURPOSE:To obtain a highly reliable ceramic capacitor which has excellent electric characteristics including a capacity and is hardly susceptible to defects by locating a conductive barrier layer between a ceramic dielectric and an electrode for preventing the diffusion of the material of the dielectric into the material of the conductor. CONSTITUTION:This laminated ceramic capacitor is made by laminating a ceramic dielectric 1, a barrier layer 2 and an electric 3 in order some times and then forming a pair of external electrodes 4 as terminals on both ends of the laminated body. For the material of the barrier layer, it is desired that the material has a low reactivity with low melting-point metal such as Pb or Bi and is hardly oxidized even if it is burned in the air or under the hypoxia partial pressure. More specifically, high melting- point metal such as Pd or Au or a conductive inorganic compound such as SnO2 or ITO is desirable for the material of the barrier layer. Because of such a structure of the capacitor, the material of the dielectric is prevented from being diffused into the electrode at the time of burning or heat treatment. The diffusion of the material of the dielectric into the electrode causes the deterioration of characteristics of the ceramic capacitor. The deterioration of characteristics of the ceramic capacitor is prevented by keeping the diffusion of the material of the dielectric from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a ceramic capacitor using a perovskite composition as a dielectric material.

(Prior Art) Dielectric materials are naturally required to have a large dielectric constant, but are also required to satisfy electrical properties such as temperature coefficient of dielectric constant, dielectric loss, and insulation resistance. As a dielectric material satisfying such electrical characteristics, perovskite compositions have been reported for a long time, and ceramic capacitors using perovskite compositions as dielectric materials are widely known.

On the other hand, when a dielectric material is applied to a ceramic capacitor in this way, in addition to the above-mentioned electrical properties being required, it is also desired that the dielectric material has excellent properties as a ceramic material.

Specifically, the characteristics required for a ceramic material include a relatively low firing temperature. That is, when considering a multilayer ceramic capacitor, since the electrodes and the dielectric are fired integrally, the conductive material used for the electrodes is required to be stable even at the firing temperature of the dielectric material. Therefore, if the firing temperature of the dielectric material is high, expensive materials such as Pt and Pd must be used as the conductor material, but it is possible to fire at a low temperature to the extent that inexpensive materials such as Ag can be used. That is what is required.

For the reasons mentioned above, in recent years, ceramics using perovskite-type compositions containing low-melting point metals such as Pb and Bi, which can be fired at relatively low temperatures, and Ag-Pd alloys as dielectric materials and conductive materials, respectively, have been developed. Capacitors are becoming mainstream. However, in such ceramic capacitors, there is a risk that the dielectric material will diffuse into the electrodes during firing, increasing the electrical resistance of the electrodes and impairing the electrical characteristics. In addition, especially PbO contained in dielectric materials
, B15on, etc., partially volatilizes during firing and reacts with the conductive material in the electrode, resulting in a problem in that the capacitance of the ceramic capacitor is reduced and the reliability is lowered.

(Problems to be Solved by the Invention) As electronic devices have become smaller and faster in recent years, there has been an increasing demand for higher density ceramic capacitors. In order to meet such demands, attempts are currently being made to reduce the thickness of ceramic dielectrics and electrodes of ceramic capacitors.

However, when ceramic dielectrics and electrodes are thinned in this way, the diffusion of the dielectric material into the electrodes as described above becomes even more serious, and there is even a risk that the electrodes may break and cause insufficient capacity defects. . Furthermore, there is also the possibility that the conductive material in the electrodes will diffuse into the ceramic dielectric, causing a short circuit between the opposing electrodes of the ceramic capacitor.

It is an object of the present invention to solve these problems and provide a highly reliable ceramic capacitor that has excellent electrical characteristics including capacitance, is less likely to cause defects, and is highly reliable.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a ceramic dielectric material using a perovskite type composition as a dielectric material, and a ceramic dielectric material having Ag, Ag-Pd, The present invention is a ceramic capacitor comprising an electrode using at least one of Cu and Ni as a conductive material, the ceramic capacitor having a conductive barrier layer between the ceramic dielectric and the electrode. That is, the ceramic capacitor of the present invention is characterized in that a barrier layer is provided between the ceramic dielectric and the electrode to prevent diffusion of the dielectric material and the conductive material.

In the ceramic capacitor of the present invention, the barrier layer as described above is required to exhibit electrical conductivity. This is because if such a barrier layer is insulating, the capacitance of the resulting ceramic capacitor will be significantly reduced.

Furthermore, the materials used for the barrier layer include Pb,
It is desired that it has low reactivity with low melting point metals such as Bi, and that it is not easily oxidized even when fired in the air or under low oxygen partial pressure. Specifically, such materials include high melting point metals such as Pd, Au, Pt, Rh, SnO*,
ITO, MnO, Cub, Ru5t.

LaCo0. , TiN, graphite, carbon, and other conductive inorganic compounds. Among these, the high melting point metal has a particularly low electrical resistance, and the ESR (equivalent series resistance) of the resulting ceramic capacitor does not increase.
More suitable. Further, in the present invention, it is also possible to use a perovskite-type oxide superconductor as the material for the barrier layer.

On the other hand, the dielectric material used in the present invention is Pb
(Mg+/s Nbxis) Os, P b
(Zn+/sNb*zs)ol, PbTiOs, PbZ
rOs.

Pb (Fe172 Nb)72 ) O3, Pb (
FexzsWsys) Os, Pb (Mg
+zt Wxyx ) Os.

Lead-containing perovskite type compositions having Pb(Nfx/sNb5ys)Os as a basic component, BaTtO, 5rTiOs, CaTi0. .

Examples include perovskite type compositions such as substituted products of MgT i O.

Furthermore, in the ceramic capacitor of the present invention, a protective layer containing at least one of ZrO and MgO as a main component can be provided on the uppermost layer and the lowermost layer. At this time, in order to lower the firing temperature of the protective layer and enable simultaneous firing with the perovskite composition, ZrO□ and MgO
2 to 5% by weight of a glass component with respect to at least one of
More preferably B 10 @ S l 01
It is desired that an A L x OsB a O-M g O type glass component be added. The reason why the above-mentioned Z r O* and MgO were selected as the materials for the protective layer is that these oxides are components that have low reactivity with pb and si.

Further, the present invention can be suitably applied to a multilayer ceramic capacitor in which ceramic dielectrics as described above are formed in multiple layers. A vertical cross-sectional view of such a multilayer ceramic capacitor is shown in FIG. In other words, in such a multilayer ceramic capacitor, a ceramic dielectric (
1), a barrier layer (2) and an electrode (3) are sequentially laminated, and then a pair of external electrodes (4) serving as terminals are formed at both ends. Furthermore, in the multilayer ceramic capacitor shown in FIG. 1, the protective layer (5) according to the present invention is provided on the uppermost layer and the lowermost layer. In addition, in such a multilayer ceramic capacitor, the external electrode is formed by baking at a temperature of about 900°C or less for a short time after the ceramic dielectric is fired, so it is necessary to provide a barrier layer between the external electrode and the ceramic capacitor. There's no need.

(Function) In the ceramic capacitor of the present invention, by having the structure as described above, diffusion of the dielectric material into the electrode during firing or heat treatment is suppressed. As mentioned above, diffusion of the dielectric material into the electrodes causes deterioration of various characteristics of the ceramic capacitor, so the present invention prevents such deterioration of various characteristics by suppressing the diffusion of the dielectric material. be done. In particular, when a conductive inorganic compound as described above is used as a material for the barrier layer, diffusion of the conductive inorganic compound and the conductive material in the electrode may occur depending on the conditions during firing or heat treatment. However, such diffusion does not pose a particular problem in the ceramic capacitor of the present invention. Furthermore, in the ceramic capacitor of the present invention, if the above-mentioned protective layers are provided on the uppermost layer and the lowermost layer, the mechanical strength of the ceramic capacitor will of course be improved.
When using a perovskite composition containing Bi etc.,
Evaporation of low melting point components during firing or heat treatment is suppressed. Therefore, it is possible to reduce the possibility that the electrical characteristics of the ceramic capacitor will be insufficient due to insufficient firing due to evaporation of low melting point components. Furthermore, for this reason, careful control of the vapor pressure of the low melting point component during firing (heat treatment), which was performed in the conventional manufacturing process of ceramic capacitors, is no longer necessary. It goes without saying that the effects of forming such a protective layer can be obtained regardless of the presence or absence of the barrier layer according to the present invention.

(Example) Examples of the present invention are shown below.

Example 1 First, lead isopropoxide, metallic magnesium, niobium isopropoxide, and titanium isopropoxide were mixed as starting materials in a molar ratio of 1+0.31:0.62:0.07, and the mixture was mixed with ethyl cellosolve as a solvent. After adding it to the solution, it was heated and stirred in a nitrogen stream to uniformly dissolve it. Ethyl alcohol containing distilled water was added to this solution to perform hydrolysis, and the hydroxides of each metal were precipitated. Next, the obtained precipitate was filtered and washed twice with distilled water, followed by ball mill mixing using a resin-coated ball and a resin pot. After drying the obtained powder, it was calcined at 800°C for 2 hours, and the calcined powder was re-pulverized to give the general formula 0.
93Pb (MgtzsNb*/s)On 0.
A dielectric powder represented by 07PbTi03 was obtained. The obtained dielectric powder had an average particle size of 0.3 μm and little agglomeration, and when a veneer firing experiment was conducted, the firing temperature was 10.
It was densely fired at 00°C and had a relative dielectric constant of 16,000.

Next, 6% by weight of polyvinyl butyral, 2% by weight of butyl phthalate.
After adding 31% by weight of the dielectric powder to a solution consisting of 25% by weight of ethyl alcohol and 36% by weight of toluene and stirring, the mixture was placed in a polyethylene bottle and subjected to a ball mill with zirconia beads for 24 hours. A uniformly dispersed dielectric slurry was obtained. Next, using a reverse roll coater device, the dielectric slurry was applied onto a base film (polyethylene terephthalate film) whose surface had been previously treated with silicone to improve releasability, and then dried to a thickness of i2 μm.
A dielectric green sheet was created.

On the other hand, apart from the above-mentioned process, a glass plate whose surface has been previously treated with boron nitride to improve releasability is used as a substrate, and a barrier layer with a thickness of 0.5 μm is coated on the entire surface of the substrate. After sequentially laminating an 8 μm electrode and a 0.5 μm thick barrier layer using the ion blating method, etching was performed to form a 7.5 mm x 7.5 mm electrode with a 5 mm interval.
It was processed to a size of 2.5 mm. As shown in Table 1, the barrier layer is SnO* (containing Sb).
, MnO, Cub, TiN, and carbon were formed, each using Sn (containing 8 wt% sb) as an evaporation source.

A film was formed using Mn, Cu, Ti, and carbon by a reactive ion blasting method. In addition, 70 layer g-30Pd was used as the conductive material for the electrodes in all cases.

Next, the barrier layer and electrodes formed on the glass substrate were transferred onto a dielectric green sheet separately prepared by the method described above. FIG. 2 is a longitudinal sectional view schematically showing such a transfer process. That is, as shown in FIG. 2, a dielectric green sheet (7) formed on a base film (6), a barrier layer (2) and an electrode (3) formed on a glass substrate (8), After the base film (6) is brought into contact with
Heat and pressurize. After this, by separating the glass substrate (8), the barrier layer (2) and the electrode (3) are peeled off from the boron nitride layer (11) on the glass substrate (8) and transferred onto the dielectric green sheet (7). Ru.

Next, the dielectric green sheet on which the barrier layer and electrodes have been formed in this way is brought into contact with a dielectric green sheet on which no barrier layer and electrodes have been formed, which has been fixed in advance on a jig, and the above-mentioned process is carried out. Transfer was performed in the same manner. FIG. 3 is a longitudinal sectional view schematically showing this process. Thereafter, the transfer process shown in FIG. 3 is repeated to form a barrier layer (2) and an electrode (3) on the dielectric green sheet (7) fixed on the jig (12)'. The dielectric green sheets (7) are stacked one after another,
Finally, up to 40 layers were laminated. Next, the obtained laminate was pressed with a rubber press at 300 kg 1 a at 1165°C for 1
Perform isostatic pressing for 4 minutes, then use a diamond cutter to
．． 0mmx3. After cutting into 1 mm chips, they were sealed in a magnesia crucible and fired at 1000° C. for 1 hour.

After firing, electrodes were cut out from both ends of the laminate using sandpaper, and after applying Ag paste thereon, they were baked at 800° C. in a belt furnace to form external electrodes.

Table 1 shows the results of measuring the capacitance of the multilayer ceramic capacitor according to the present invention thus obtained. 8 again
Under the conditions of 0℃ and 95%RH, 10μ of DC current is applied to 500
Table 1 shows the results of a reliability test with time applied.2 Furthermore, Table 1 shows a multilayer ceramic capacitor that is exactly the same as the multilayer ceramic capacitor according to the present invention except that it does not have a barrier layer. The results of similar capacity measurements and reliability tests are also shown as a comparative example.

As shown in Table 1, all of the multilayer ceramic capacitors according to the present invention have a sufficient capacitance of 5.0 μF or more, and this value is equal to This value was close to the theoretical value of 5.3 μF determined from the measured value. In addition, its characteristics do not deteriorate even under high temperature and high humidity conditions, and it has excellent reliability. On the other hand, in the multilayer ceramic capacitor according to the comparative example, the capacitance was small, and short-circuiting of the opposing electrodes occurred after the reliability test, resulting in defects. When we analyzed the cause of this, we found that
In the multilayer ceramic capacitor according to the comparative example, the conductive material in the internal electrode partially reacted with lead oxide vapor during firing, causing the internal electrode to break. It was confirmed that this was due to migration into the body.

Table 1 Example 2 First, a dielectric green sheet was prepared in the same manner as in Example 1, and then film thicknesses of 0.15 μm and 0.6 μm were deposited on predetermined positions on the dielectric green sheet, respectively.

A 0.15 μm barrier layer, an electrode, and a barrier layer were sequentially laminated by sputtering. However, in this example, as shown in Table 2, the barrier layers are P4. Pt
Four different types of barrier layers consisting of , Au, and Rh were formed, and the conductive material of the electrodes was all Ag. Thereafter, the dielectric green sheets on which barrier layers and electrodes have been formed are laminated and crimped by a conventional method, and then cut into chips and fired.
Next, by baking external electrodes onto both ends, a multilayer ceramic capacitor according to this example was obtained.

Example 1 Regarding the obtained multilayer ceramic capacitor
The results of the same capacitance measurement and reliability test as in the second
Shown in the table. As is clear from Table 2, a multilayer ceramic capacitor with large capacity and high reliability was obtained in this example as well.

The following is a margin.Table 2 Example 3 First, a Pt thin film having a thickness of 0.2 μm was formed on an MgO substrate by RF magnetron sputtering to form a barrier layer according to the present invention. However, as a target, a PT plate with a diameter of 5 inches bonded to a water-cooled Cu plate was used, and the distance between the substrate and target was approximately 1
00mm, and 0.5Pa Ar and 0.00mm. High frequency power with an energy of 500 W was applied in an atmosphere. This p
When the t-thin film was analyzed by X-ray diffraction, it was confirmed that it was oriented in the <111> direction.

Furthermore, a film with a thickness of 1 μm was coated on this PT thin film by the same method.
An Ag thin film with a thickness of 0.2 μm and a PT thin film with a thickness of 0.2 μm were sequentially formed. Thereafter, the obtained Pt thin film and Ag thin film were patterned by ion milling to form a barrier layer and an electrode according to the present invention.

Next, on the substrate on which the barrier layer and electrodes were formed, the same R
A 1 μm thick zirconate titanate film was formed by F magnetron sputtering. However, as targets, P b O, T i O@,
Z r 02 , L a x Os are used as starting materials, and these are Pb6. myLao, +5 (Zro,
5sTio4t)ol + 10mo 1% PbO was mixed and calcined at 800 to 900°C, and the calcined powder was ground in a ball mill, a binder was added, molded, and then sintered at 1200 to 1250°C. A ceramic plate obtained by After film formation, a resist pattern is formed on the thin film of the zirconate titanate carrier by photolithography, and the thin film is selectively etched using this resist pattern as a mask to form the ceramic dielectric according to the present invention. I fell asleep. Further, a barrier layer and electrodes were formed on this ceramic dielectric by the same method as in the case of forming the barrier layer and electrodes previously, and then heat treatment was performed at 1000° C. for 30 minutes to obtain a ceramic capacitor of the present invention. .

At the same time, a ceramic capacitor without the barrier layer according to the present invention and having an 80Ag-20Pt thin film with a thickness of 1.4 μm as an electrode was prepared in the same manner as a comparative example.

Table 3 shows the results of capacitance measurements and reliability tests conducted on such ceramic capacitors in the same manner as in Example 1. As is clear from Table 3, a ceramic capacitor with sufficient capacity and higher reliability than the comparative example was obtained in this example. A sheet was prepared, and a barrier layer with a thickness of 0.3 μm, an electrode with a thickness of 0 μm, and a barrier layer with a thickness of 0.3 μm were placed on a glass plate that had been subjected to the same surface treatment as in Example 1. They were sequentially formed by applying a solution containing metal ions and then firing. However, MnO was used as the material for the barrier layer, and 70Ag-30Pd was used as the conductor material for the electrode. Next, Example 1
A barrier layer and an electrode were transferred onto a dielectric green sheet in the same manner as in . Thereafter, the dielectric green sheets were laminated in the same manner as in Example 1, but in this example, the uppermost and lowermost green sheets were made of the same material as the green sheets on which the barrier layer and electrodes were formed. thing,
Three types were prepared: one consisting of ZrO and a glass component, and one consisting of MgO and a glass component. Note that the green sheet made of ZrO* or MgO and glass components as described above is first made of ZrO or MgO powder and 30% by weight of B! 01.30% by weight Sl 0 *
, 10% by weight Al! Using a glass component consisting of 01.20% by weight of BaO and 10% by weight of MgO as a starting material, a dielectric slurry represented by the general formula 0.07PbTiO was prepared in Example 1. After preparing a slurry using the method described above, a green sheet was created using a doctor blade method. At this time, the glass component was added in an amount of 5% by weight based on ZrO or MgO, and the thickness of the green sheet was 200 μm.
It was set as m. Next, the three types of laminates obtained were crimped and cut into chips, then sealed in a magnesium crucible and fired.
Alternatively, in the case of a laminate using a green sheet made of MgO and glass components, a protective layer mainly composed of ZrO or MgO was formed on the upper and lower surfaces. Further, in this example, each laminate was fired while changing the filling rate into the magnesium crucible. However, the filling rate was calculated using the formula (*) below. Thereafter, external electrodes were baked on both ends to obtain a multilayer ceramic capacitor according to the present invention.

Volume filling rate of entire sample = (*) Magnesium crucible volume Regarding the obtained multilayer ceramic capacitor, Example 1
．． Table 4 shows the results of the same capacitance measurement and reliability test. As is clear from Table 4, in the multilayer ceramic capacitor with no protective layer formed, sufficient characteristics were obtained when firing was performed at a filling rate of 8Qvo 1%, but when the filling rate was 40vo 1%, sufficient characteristics were obtained. %, the capacity is insufficient and the filling rate is 40vo 1%
In the case of 60vo1%, defects occurred after the reliability test. On the other hand, in a multilayer ceramic capacitor having a protective layer mainly composed of ZrO or MgO, the filling rate is 40vo 1% + 60vo 1%.

Sufficient capacity was obtained in all cases of 8Qvo1%, and no defects were observed even after the reliability test, indicating high reliability. Furthermore, there were no cracks or chips that occurred during baking of the external electrodes, and there was no damage due to thermal stress generated during mounting, and the mechanical strength was excellent. That is, in the present invention, it has been confirmed that the above-mentioned protective layer is effective in improving the characteristics of a ceramic capacitor, and that by providing such a protective layer, careful control of the vapor pressure of the lead component during firing becomes unnecessary. Ta.

[Advantageous Effects of the Invention] As described above, according to the present invention, it is possible to provide a ceramic capacitor that has excellent electrical characteristics such as capacitance and is highly reliable.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a multilayer ceramic capacitor according to the present invention, FIG. 2 is a vertical cross-sectional view schematically showing transfer of barrier layers and electrodes in the manufacturing process of the multilayer ceramic capacitor according to the present invention, and FIG. FIG. 2 is a vertical cross-sectional view schematically showing an example of a lamination step in the manufacturing process of a multilayer ceramic capacitor according to the present invention. 1... Ceramic dielectric 2... Barrier layer 3...
・Electrode 4...External electrode 5...Protective layer

Claims (5)

[Claims] (1) A ceramic dielectric using a perovskite composition as a dielectric material, and a pair formed facing each other with the ceramic dielectric interposed therebetween and using at least one of Ag, Ag-Pd, Cu, and Ni as a conductive material. What is claimed is: 1. A ceramic capacitor comprising: an electrode; further comprising a conductive barrier layer between the ceramic dielectric and the electrode to prevent diffusion of the dielectric material. (2) The ceramic capacitor according to claim 1, wherein the barrier layer is made of at least one metal selected from Pd, Au, Pt, and Rh. (3) Barrier layer is SnO_2, ITO, MnO, CuO
2. The ceramic capacitor according to claim 1, comprising at least one inorganic compound selected from , RuO, LaCoO_3, TiN, graphite, and carbon. (4) The ceramic capacitor according to claim 2 or 3, wherein the perovskite composition is a lead-containing perovskite composition. (5) The ceramic capacitor according to claim 4, wherein the uppermost layer and the lowermost layer are provided with a protective layer containing at least one of ZrO_2 and MgO as a main component.