JP3318952B2 - Dielectric ceramic composition and multilayer ceramic capacitor using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric ceramic composition and a multilayer ceramic capacitor using the same, and more particularly, to a dielectric ceramic composition used for a multilayer ceramic capacitor including internal electrodes made of, for example, Ni or a Ni alloy, and the like. The present invention relates to a multilayer ceramic capacitor using the same.

[0002]

2. Description of the Related Art Generally, in a manufacturing process of a multilayer ceramic capacitor, first, a sheet-shaped dielectric material having an electrode material to be an internal electrode applied to the surface thereof is prepared. As the dielectric material, for example, a material mainly containing BaTiO ₃ is used. The dielectric material in the form of a sheet having internal electrodes is obtained by laminating the sheet-shaped dielectric material coated with the electrode material, thermocompression bonding, and firing the integrated material at 1250 to 1350 ° C. in a natural atmosphere. Then, an external electrode conducting to the internal electrode is baked on the end face of the dielectric ceramic to obtain a multilayer ceramic capacitor. Further, with the recent development of electronics, miniaturization of electronic components has rapidly progressed, and the tendency of miniaturization of multilayer ceramic capacitors has also become remarkable.

[0003]

The materials of the internal electrodes used in such a multilayer ceramic capacitor include:
The following conditions must be satisfied.

(A) Since the dielectric porcelain and the internal electrodes are fired at the same time, the dielectric porcelain has a melting point higher than the temperature at which the dielectric porcelain is fired.

(B) It is not oxidized even in an oxidizing high-temperature atmosphere and does not react with a dielectric.

As an electrode material satisfying such conditions, noble metals such as platinum, gold, palladium and alloys thereof have been used.

However, these electrode materials have excellent characteristics, but are expensive. Therefore, the ratio of the electrode material cost to the multilayer ceramic capacitor is 30 to 7%.
It reached 0%, which was the biggest factor in increasing the manufacturing cost.

[0008] In addition to the noble metals, N
There are base metals such as i, Fe, Co, W, and Mo. However, these base metals are easily oxidized in a high-temperature oxidizing atmosphere, and do not serve as an electrode. Therefore, in order to use these base metals as internal electrodes of a multilayer ceramic capacitor, it is necessary to fire them together with dielectric ceramics in a neutral or reducing atmosphere. However, the conventional dielectric porcelain material has a drawback that when it is fired in such a reducing atmosphere, it is significantly reduced and becomes a semiconductor.

As a method for reducing the size of the multilayer ceramic capacitor, it is generally known to use a material having a large dielectric constant or to reduce the thickness of the dielectric layer. However, a material having a large dielectric constant has a large crystal grain, and when the material is formed into a thin film having a thickness of 10 μm or less, the number of crystal grains existing in one layer is reduced, and reliability is reduced.

On the other hand, JP-A-58-135507 discloses
JP-A-58-223669, JP-A-59-861
As disclosed in Japanese Patent Publication No. 03-203, there is known a dielectric porcelain having a small crystal grain size obtained by adding cerium oxide or neodymium oxide to a barium titanate solid solution. By reducing the crystal grain size in this way, the number of crystal grains existing in one layer can be increased, and a decrease in reliability can be prevented.

However, the material to which the rare earth oxide is added is reduced when fired in a reducing atmosphere, and it has not been possible to manufacture a multilayer ceramic capacitor using a base metal such as Ni as an internal electrode.

Therefore, a main object of the present invention is to provide a dielectric porcelain composition which does not turn into a semiconductor even when fired in a reducing atmosphere and has a large dielectric constant despite its small crystal grain size. An object of the present invention is to provide a low-cost and highly reliable small-sized large-capacity multilayer ceramic capacitor.

[0013]

Means for Solving the Problems The first invention is based on Ba, S
r, Mg, Ti, Co and Re (Re is Tb, Dy,
(At least one selected from Ho and Er), and has the following general formula: (Ba _1-xyz Sr _x
Re _y Mg _z ) _m (Ti _{1-o Coo} ) O ₃ ,
x, y, z, o and m are 0.05 ≦ x ≦ 0.35,
0.0005 ≦ y ≦ 0.03, 0.0005 ≦ z ≦ 0.
05, 0.0005 ≦ o ≦ 0.03, 1.00 ≦ m ≦
For 100 moles of the main component satisfying the relationship of 1.04,
When the respective oxides of Mn and Ni are represented as MnO ₂ and NiO as subcomponents, at least one of the respective oxides of Mn and Ni is used in an amount of 0.02 to 2.
0 mol added and contained, with the main component being 100 parts by weight,
The oxide glass containing _{BaO-SrO-Li 2 O-} SiO 2 as a main component containing 0.05 part by weight to 5.0 parts by weight, a dielectric ceramic composition.

A second invention is a multilayer ceramic capacitor including a dielectric layer made of the dielectric ceramic composition and an internal electrode made of one of Ni and a Ni alloy.

[0015]

[Function] Ba, Sr, Mg, Ti, Co and Re (R
e adjusts the composition ratio of each oxide of at least one kind of rare earth element selected from Tb, Dy, Ho and Er), and oxides of Mn and Ni and BaO—SrO—Li
By adding an oxide glass containing ₂ O—SiO ₂ as a main component, firing can be performed in a reducing atmosphere without deteriorating its characteristics. Furthermore, T
Rare earth oxides and Co oxides of b ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ and Er ₂ O ₃ have an effect of suppressing the grain growth of the dielectric. Since the crystal grain size is small, 1
Since the number of crystal grains existing in one dielectric layer can be increased, a decrease in reliability can be prevented even if the thickness of the dielectric layer is reduced.

[0016]

According to the present invention, it is possible to obtain a dielectric ceramic composition which is not reduced even when fired in a reducing atmosphere and does not turn into a semiconductor. Therefore, when a multilayer ceramic capacitor is manufactured using this dielectric ceramic composition, a base metal can be used as an electrode material and can be fired at a relatively low temperature of 1270 ° C. or less, so that the cost of the multilayer ceramic capacitor can be reduced. Can be planned.

Further, in the multilayer ceramic capacitor using this dielectric ceramic composition, the dielectric constant is 10,000 or more, and although it has such a high dielectric constant,
The crystal grains are as small as 3 μm or less. Therefore, even if the dielectric layer is made thinner, the amount of crystal grains present in the layer does not decrease unlike the conventional multilayer ceramic capacitor. Therefore, a highly reliable, small-sized, large-capacity multilayer ceramic capacitor can be obtained.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments.

[0019]

EXAMPLE First, as a raw material, B having a purity of 99.8% or more was used.
_{aCO 3, SrCO 3, MgCO 3} , Tb 2 O 3, Dy
₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , TiO ₂ , CoO,
MnO ₂ and NiO were prepared. (Ba)
_1-xyz Sr _x Re _y Mg _z ) _m (Ti _{1-o Coo} ) O
_It was represented by the composition formula of ₃ , and was blended so that x, y, z, o, and m had the ratios shown in Table 1, to obtain a blended raw material. here,
Re is at least one selected from Tb, Dy, Ho, and Er. The raw materials were wet-mixed in a ball mill, pulverized, dried, and calcined in air at 1100 ° C. for 2 hours to obtain a calcined product. The calcined product was pulverized by a dry pulverizer to obtain a pulverized product having a particle size of 1 μm or less. BaO-S having a particle diameter of 1 μm or less prepared in advance is added to the pulverized material.
The rO-Li ₂ O-SiO ₂ were weighed oxide glass mainly, by adding an organic solvent such as polyvinyl butyral binder and ethanol were wet mixed by a ball mill to prepare a ceramic slurry. Thereafter, the ceramic slurry was formed into a sheet by a doctor blade method to obtain a rectangular green sheet having a thickness of 26 μm.

[0020]

[Table 1]

Next, a conductive paste mainly composed of Ni was printed on the ceramic green sheet to form a conductive paste layer for forming internal electrodes. A plurality of ceramic green sheets on which the conductive paste layer was formed were stacked such that the side from which the conductive paste was drawn out was alternated to obtain a laminate. The obtained laminated body is heated to a temperature of 350 ° C. in an N ₂ atmosphere to burn the binder, and then the oxygen partial pressure is set to 10 ^-9 to 10 ^-12 MPa.
₂ -N ₂ - calcined for 2 hours at a temperature shown in Table 2 in a reducing atmosphere consisting of air gas, to obtain a ceramic sintered body. The surface of the obtained ceramic sintered body was observed with a scanning electron microscope at a magnification of 1500 times, and the grain size was measured. Table 2 shows the results.

[0022]

[Table 2]

After firing, an Ag paste was applied to both end surfaces of the obtained sintered body and baked at a temperature of 600 ° C. in an N ₂ atmosphere to form external electrodes electrically connected to the internal electrodes. The external dimensions of the multilayer ceramic capacitor thus obtained are 1.6 mm in width, 3.2 mm in length,
The thickness is 1.2 mm, and the thickness of the dielectric ceramic layer interposed between the internal electrodes is 16 μm. The total number of effective dielectric ceramic layers is 19, and the area of the counter electrode per layer is 2.1 mm ² .

The capacitance (C) and the dielectric loss (tan)
δ) is measured at a frequency of 1 kHz using an automatic bridge type measuring instrument.
The measurement was performed at z, 1 V _rms and a temperature of 25 ° C., and the dielectric constant (ε) was calculated from the capacitance. Next, in order to measure the insulation resistance (R), a DC voltage of 25 V was applied for 2 minutes using an insulation resistance meter, and the insulation resistance (R) at 25 ° C. and 85 ° C. was measured. The product of (C) and the insulation resistance (R), that is, the CR product was determined. Further, the rate of change of the capacitance with respect to the temperature change was measured. The rate of change of the capacitance with respect to the temperature change was −2 based on the capacitance at 20 ° C.
Rate of change (ΔC / C ₂₀ ) at 5 ° C. and 85 ° C. and −25 ° C.
A value (│ΔC / C _{20 │max} ) having the maximum change rate as an absolute value in the range of ℃ to 85 ° C. was shown. Table 2 shows the results.

Next, the reasons for limiting each composition will be described.

(Ba _{1 -xyz} Sr _x Re _y Mg _z ) _m (
Ti _{1-o Coo} ) O ₃ , as shown in sample number 1,
When the Sr amount x is less than 0.05, the dielectric constant ε is 10,000
And the dielectric loss tan δ exceeds 5.0%, which is not preferable. Further, as shown in sample No. 17, the amount of Sr x
Exceeds 0.35, the sinterability of the porcelain deteriorates, the dielectric loss tan δ exceeds 5.0%, and the CR product becomes 10% at 25 ° C.
It is less than 00 MΩ · μF and less than 100 MΩ · μF at 85 ° C., which is not preferable because the insulation resistance is lowered.

Further, when the Re amount y is less than 0.0005 as in Sample No. 2, the dielectric loss tan δ is 5.0.
%, And the crystal grain size is larger than 3 μm, which is not preferable because the dielectric layer cannot be made thin. On the other hand, if the amount of Re y exceeds 0.03 as in Sample No. 18, the porcelain is reduced when baked in a reducing atmosphere, becomes semiconductor, and the insulation resistance is greatly reduced, which is not preferable.

If the Mg content z is less than 0.0005 as in sample No. 3, the CR products at 25 ° C. and 85 ° C. are undesirably reduced. On the other hand, like sample number 19,
When the Mg amount z exceeds 0.05, the dielectric constant ε is 10,000
In addition to this, the insulating property also decreases, which is not preferable.

As shown in sample No. 4, the amount of Co is 0.00
When the value is less than 05, the dielectric loss tan δ exceeds 5.0%,
Further, since the crystal grain size is larger than 3 μm, the dielectric layer cannot be made thinner, which is not preferable. On the other hand, as shown in Sample No. 20, when the Co amount o exceeds 0.03, the dielectric loss tan
δ increases beyond 5.0%, and CR product becomes 1 at 25 ° C.
It is less than 000 MΩ · μF and less than 100 MΩ · μF at 85 ° C., which undesirably lowers the insulation resistance.

As shown in sample No. 5, (Ba _1-xyz Sr
_{x Re y Mg z) m (} Ti 1-o Co o) the molar ratio of O ₃ m
If it is less than 1.000, the porcelain is reduced when fired in a reducing atmosphere, becomes semiconductor, and the insulation resistance is undesirably reduced. On the other hand, when the molar ratio m exceeds 1.04 as in Sample No. 21, the sinterability becomes extremely poor, which is not preferable.

Further, as shown in Sample No. 6, MnO ₂ ,
When the added amount of NiO is less than 0.02 mol, the CR product at 85 ° C. becomes low, and the reliability of long-time use at high temperatures is undesirably reduced. On the other hand, as in sample number 22,
If the amounts of MnO ₂ and NiO exceed 2.0 mol, the dielectric loss tan δ will increase to more than 5.0%, and the insulation resistance will also decrease, which is not preferable.

Further, as shown in Sample No. 7, BaO-Sr
When the amount of oxide glass for the O-Li ₂ O-SiO ₂ as the main component is less than 0.05 part by weight, the sintering property is deteriorated, the dielectric loss tanδ undesirably exceed 5.0%. On the other hand, as in Sample No. 23, BaO-SrO-L
If the amount of the oxide glass containing i ₂ O—SiO ₂ as a main component exceeds 5.0 parts by weight, the dielectric constant is reduced to less than 10,000 and the crystal grain size is larger than 3 μm.

On the other hand, a multilayer ceramic capacitor using the dielectric ceramic composition of the present invention has a dielectric constant of 10
000 or more, the dielectric loss tan δ is 5.0% or less, and the rate of change of the capacitance with respect to temperature is −25 ° C. to 85 ° C.
It is possible to obtain a dielectric porcelain satisfying the F characteristic standard defined in the JIS standard in the range of ° C. Moreover, in this multilayer ceramic capacitor, the insulation resistance at 25 ° C. and 85 ° C. is 1000 MΩ ·
It shows a high value of not less than μF and not less than 100 MΩ · μF. Further, the dielectric ceramic composition of the present invention has a firing temperature of 127.
Sintering can be performed at a relatively low temperature of 0 ° C. or less, and the particle size is as small as 3 μm or less.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-296313 (JP, A) JP-A-3-222311 (JP, A) JP-A-5-9066 (JP, A) JP-A-5-906 17212 (JP, A) JP-A-5-70221 (JP, A) JP-A-5-78167 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 3/12 303 C04B 35/46 H01G 4/12 358

Claims (2)

(57) [Claims] 1. Ba, Sr, Mg, Ti, Co and R
e (Re is at least one kind of rare earth element selected from Tb, Dy, Ho and Er), and comprises the following general formula (Ba _{1 -xyz} Sr _x Re _y Mg _z ) _m (Ti _{1 -o} Co _o) is represented by _{O 3, x, y, z} , o and m, 0.05 ≦ x ≦ 0.35 0.0005 ≦ y ≦ 0.03 0.0005 ≦ z ≦ 0.05 0 0.0005 ≦ o ≦ 0.03 1.00 ≦ m ≦ 1.04 With respect to 100 moles of the main component satisfying the relationship of, Mn and Ni oxides were added as sub-components to MnO ₂ and Ni
When represented by O, at least one kind of each oxide of Mn and Ni is added and contained in a total amount of 0.02 to 2.0 mol of each oxide, and the main component is defined as 100 parts by weight, and BaO—
_{SrO-Li 2 O-SiO 2} 0.05 parts by weight of oxide glass mainly comprising 5.0 containing parts, the dielectric ceramic composition. 2. A multilayer ceramic capacitor comprising a dielectric layer made of the dielectric ceramic composition of claim 1 and an internal electrode made of one of Ni and a Ni alloy.