Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2001-12-13
2004-06-08
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S138000, C501S139000
Reexamination Certificate
active
06746980
ABSTRACT:
BACKGROUND THE INVENTION
The present invention relates to a dielectric ceramic composition suitable for a nickel electrode multilayer ceramic capacitor in which low temperature sintering can be carried out, and in particular, relates to a dielectric ceramic composition and to a multilayer ceramic capacitor using the same, which satisfy X7R characteristics as a temperature characteristic of capacitance and which have reduction resistance in which there is little dielectric loss at or above room temperature.
Hitherto, compositions consisting of barium titanate are widely used as dielectric materials for multilayer ceramic capacitors, since the dielectric constant is high, the temperature characteristic is superior, the bias dependence is small, and the withstand voltage is superior.
Generally, a multilayer ceramic capacitor is produced by the following method. That is, dielectric powder such as barium titanate is mixed with an organic binder; then, the mixture is suspended and is formed in the shape of a sheet by the doctor blade method, and a dielectric ceramic layer is thereby produced. Furthermore, metal powder for an internal electrode is mixed with organic compounds such as organic solvent, plasticizer, and organic binder, to form a metal powder paste, and the paste is printed on the above dielectric ceramic layer by screen printing. Next, the dielectric ceramic layers are dried and are then alternatingly laminated and adhered; organic components are then removed by a heating treatment at about 300° C. in air and are sintered at 1000° C. or more. Subsequently, external electrodes are bonded by heating at both ends of the dielectric ceramic layer, and a multilayer ceramic capacitor is thereby produced. Although the sintering temperature is generally about 1000° C. when lead is used in the dielectric ceramic composition, it is necessary to carry out sintering at about 1300° C. or more when barium titanate is used therein because sintering characteristics are different. Thus, in the production method for a multilayer ceramic capacitor, the dielectric layers and the internal electrode metal layers are sintered at the same time.
As metals used in the internal electrode of the multilayer ceramic capacitor, heretofore, noble metals such as silver, palladium, platinum, gold, etc., in powder form, or base metals such as nickel, cobalt, iron, molybdenum, tungsten, etc., in powder form have been used, but since less expensive electronic materials are recently required, development of a multilayer ceramic capacitor using the latter base metal powder, in particular, metallic nickel powder, is widely employed. A sintering process in the above production method for the multilayer ceramic capacitor can also be carried out in an oxygen atmosphere when a noble metal powder is used in the internal electrode. However, when a base metal such as nickel is used therein, an insulation oxide is formed in an oxidizing atmosphere at high temperatures. Therefore, it is necessary to carry out the sintering in a reducing atmosphere such as hydrogen gas in this case.
In the production method for the multilayer ceramic capacitor, in order to remove organic constituents, an oxidation-reduction reaction is generated by carrying out heat treatment in air, or by carrying out the sintering in a reducing atmosphere in the case of the nickel electrode, as described above, and a volume change due to expansion and shrinkage is generated in the metal powder. In addition, a volume change is also generated in the dielectric by sintering; however, sintering characteristics such as volume changes due to expansion and shrinkage of each material in sintering, etc., are different, since different materials such as the dielectric and the metal powder are sintered at the same time. Warp is thereby generated in a metal paste layer, and as a result, there is a problem in that structural defects in which the layered structure is destroyed by a so-called “delamination” such as crack or peeling. Therefore, as a dielectric material, materials which can be sintered at as low a temperature as possible are required.
In addition, as a dielectric material, heretofore, materials which maintain an equilibrium state with oxygen in air were used, since they form oxides. However, in dielectrics used therefor, reduction resistance (or non-reducibility) is required, in which the characteristics are not affected by oxygen partial pressure, that is, in which it is reduced, does not turn into semiconductor, and is stable, even if the oxygen partial pressure is low, since the multilayer ceramic capacitor in the nickel electrode is sintered in the reducing atmosphere described above.
Therefore, in order to solve the above problem, various research has been conducted with regard to non-reducing dielectric ceramic compositions. Specifically, a multilayer ceramic chip capacitor comprising a dielectric layer containing BaTiO
3
as a main component, and containing MgO, Y
2
O
3
, at least one of BaO and CaO, SiO
2
, MnO, and at least one of V
2
O
5
, and MoO
3
, as a subcomponent, wherein the subcomponent comprises 0.1 to 3 mol of MgO, 5 mol or less of Y
2
O
3
, 2 to 12 mol of BaO and CaO, 2 to 12 mol of SiO
2
, 0.5 or less mol of MnO, 0 to 0.3 mol of V
2
O
5
, 0 to 0.3 mol of MoO
3
, and more than 0 mol of V
2
O
5
and MoO
3
, when BaTiO
3
is 100 mol, is disclosed in Japanese Unexamined Patent Publication No. 8-124785.
In addition, a dielectric ceramic composition comprising a main component in which x and y satisfy 0.01≦x≦0.1 and 0.1<y<0.26, respectively, when the chemical formula of the main component is represented by (Ba
1−x
Ca
x
)(Ti
1−y
Zr
y
)O
3
, and comprising 0.2 to 1 weight parts of Y
2
O
3
, 0.06 to 0.6 weight parts of MnO
2
, 0.1 to 1 weight parts of Al
2
O
3
, 0.1 to 1 weight parts of NiO and 0.1 to 1 weight parts of (1−&agr;)Li
2
O−&agr;SiO
2
(0.3<&agr;(mole ratio)<0.7), to 100 parts of the main component, is disclosed in Japanese Unexamined Patent Publication No. 10-139538.
Furthermore, a dielectric ceramic composition comprising a barium titanate solid solution and additional components and comprising a sintering promoter as a subcomponent, wherein a main component is within an range of 0.950≦A/B (mole ratio)≦1.050, 0.12<a≦0.30, and 0.04≦b≦0.30, when the chemical formula of the dielectric ceramic composition is represented by ABO3 +aR+bM (ABO3 is a barium titanate solid solution; R is an oxide of metal elements selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb, and Lu; M is oxide of metal elements selected from Ni, Mg, Fe, Al, Cr, and Zn; and a and b are the mole ratio converted into the chemical formula including one metal element of each oxide).
The above conventional technologies improve reduction resistance and low temperature sintering of the dielectric material, and in addition, satisfy X7R characteristics, and they have moderate effects in reliability, bias characteristics, etc. However, with recent demands such as for rapid miniaturization of portable telephones, personal computers, etc., or increase in capacitance, a dielectric layer of the multilayer ceramic capacitor is required to be thin, and the thickness thereof is required at present to be 10 &mgr;m or less. In this case, there is a problem in that the withstand voltage between a pair of internal electrodes is reduced when the dielectric layer is thinned. In addition, since it is required to have low electric power consumption form the viewpoint of energy conservation, dielectric materials which have low dielectric loss at or above room temperature and are exothermic, are desired.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a dielectric ceramic composition suitable for a multilayer ceramic capacitor in which an internal electrode is made of nickel, and to provide a multilayer ceramic capacitor using the same. Specifically, it is an object thereof to provide a dielectric ceramic composition in which the dielectric constant is high; low temperature s
Aisawa Shuuji
Horiguchi Tadahiko
Sakai Hideki
Tokita Kouji
Group Karl
Toho Titanium Co., Ltd.
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