Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
1999-08-06
2001-06-05
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S321200, C361S321500, C501S134000
Reexamination Certificate
active
06243254
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric ceramic composition and a laminated ceramic capacitor using the same, especially to a ceramic capacitor having inner electrodes made of Ni.
2. Description of the Related Art
Ceramic layers and inner electrode metal layers are alternately stacked in the laminated ceramic capacitor. A cheap base metal such as Ni has been recently used for the inner electrodes in place of expensive noble metals such as Ag and Pd for reducing the production cost. When Ni is used for the electrodes, the capacitor should be fired in a reducing atmosphere where Ni is not oxidized. However, ceramics comprising barium titanate as a principal component may be endowed with semiconductive properties when the ceramics are fired in a reducing atmosphere. Accordingly, as disclosed for example in Japanese Examined Patent Publication No. 57-42588, a dielectric material in which the ratio between the barium site and titanium site in the barium titanate solid solution is adjusted to be larger than the stoichiometric ratio has been developed. This allows the laminated ceramic capacitor using Ni as electrodes to be practically used, thereby expanding its production scale.
Since electronic parts have been rapidly miniaturized with the recent advance of electronics, small size ceramic capacitors with large capacitance as well as temperature stability of electrostatic capacitance are required. The ceramic capacitors having the Ni electrodes are also under the same circumstances.
For complying with the requirements of large capacitance and small size, the dielectric ceramics should be made to be thinner and multi-layered. However, much higher voltage is impressed on the dielectric material when the dielectric ceramic layer is thinned, often causing troubles such as decrease of dielectric constant, increase of temperature dependency of the electrostatic capacitance and deteriorated stability of other characteristics when conventional dielectric materials are used. Especially, when the thickness of the dielectric layer is reduced to 5 &mgr;m or less, 10 or less ceramic particles are contained between the inner electrodes, making it difficult to assure a stable quality.
Making the dielectric layer thin is accompanied by other problems. Solder plating layers as external electrodes are usually formed on the baked electrodes of a conductive metal powder in order to comply with automatic packaging of the laminated ceramic capacitor. Therefore, the plating layer is generally formed by electroplating. Oxides containing boron or a glass is added, on the other hand, into some dielectric ceramics as a sintering aid. However, the dielectric ceramic using these additives has so poor resistance against plating that characteristics of the laminated ceramic capacitor may be deteriorated by dipping it into a plating solution. It has been a problem that reliability is markedly decreased in the ceramic capacitor having thin dielectric ceramic layers.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a laminated ceramic capacitor with high reliability and large capacitance especially using Ni for inner electrodes, wherein dielectric constant is not decreased exhibiting a stable electrostatic capacitance even when the dielectric ceramic layers are thinned, and temperature characteristics of the electrostatic capacitance satisfy the B-grade characteristics prescribed in the JIS standard and the X7R-grade characteristics prescribed in the EIA standard.
The present invention also provides a highly reliable laminated ceramic capacitor with large capacitance made of thin dielectric ceramic layers having an excellent plating solution resistance.
In one aspect, the present invention provides a laminated ceramic capacitor provided with a plurality of dielectric ceramic layers, inner electrodes formed between the dielectric ceramic layers and external electrodes being in electrical continuity with the inner electrodes, the dielectric ceramic layer being represented by the following formula:
(Ba
1−x
Ca
x
O)
m
TiO
2
+&agr;Re
2
O
3
+&bgr;MgO+&ggr;MnO
(Re
2
O
3
is at least one or more of the compounds selected from Y
2
O
3
, Gd
2
O
3
, Tb
2
O
3
, Dy
2
O
3
, Ho
2
O
3
, Er
2
O
3
and Yb
2
O
3
, &agr;,&bgr; &ggr;, m and x representing molar ratio in the range of 0.001≦&agr;≦0.10, 0.001≦&bgr;≦0.12, 0.001<&ggr;≦0.12, 1.000<m ≦1.035 and 0.005<x≦0.22), and containing about 0.2 to 5.0 parts by weight of either a first sub-component or a second sub-component relative to 100 parts by weight of a principal component containing about 0.02% by weight or less of alkali-metal oxides in (Ba
1−x
Ca
x
O)
m
TiO
2
as a starting material to be used for the dielectric ceramic layer, wherein the first sub-component is a Li
2
O—(Si,Ti)O
2
—MO based oxide (MO is at least one of the compound selected from Al
2
O
3
and ZrO
2
) and the second sub-component is a SiO
2
—TiO
2
—XO based oxide (XO is at least one of the compound selected from BaO, CaO, SrO, MgO, ZnO and MnO). The inner electrodes are preferably composed of nickel or a nickel alloy.
The material (Ba
1−x
Ca
x
O)
m
TiO
2
to be used for the dielectric ceramic layer preferably has a mean particle size of about 0.1 to 0.7 &mgr;m.
The first sub-component represented by xLiO
2
—y(Si
w
Ti
1−w
)Q
2
—zMO (x, y and z are represented by molar percentage (mol %) and w is in the range of 0.30≦w≦1.0) may be within the area surrounded by the straight lines connecting between the succeeding two points represented by A (x=20, y=80, z=0), B (x=10, y=80, z=10), C (x=10, y=70, z=20), D (x=35, y=45, z=20), E (x=45, y=45, z=10) and F (x=45, y=55, z=0) or on the lines in a ternary composition diagram having apexes represented by each component LiO
2
, (Si
w
Ti
1−w
)O
2
and MO provided that when the component is on the line A-F, w is in the range of 0.3≦w≦1.0.
The second sub-component represented by xSiO
2
—yTiO
2
—zXO (x, y and z are represented by mol %) may be within the area surrounded by the straight lines connecting between the succeeding two points represented by A (x=85, y=1, z=14), B (x=35, y=51, z=14), C (x=30, y=20, z=50) and D (x=39, y=1, z=60) or on the lines in a ternary composition diagram having apexes represented by each component SiO
2
, TiO
2
and XO.
At least one of the compounds Al
2
O
3
and ZrO
2
are contained with a combined amount of about 15 parts by weight (ZrO
2
is about 5 parts by weight or less) in the second sub-component relative to 100 parts by weight of the SiO
2
—TiO
2
—XO based oxide.
The external electrodes are composed of sintered layers of a conductive metal powder or a conductive metal powder supplemented with a glass frit.
Alternately, the external electrodes are composed of sintered layers of a conductive metal powder or a conductive metal powder supplemented with a glass frit, and plating layers formed thereon.
It is preferable to use the ceramic having the composition to be described hereinafter in order to improve the plating resistance. The dielectric ceramic layer in the laminated ceramic capacitor is represented by the following formula:
(Ba
1−x
Ca
x
O)
m
TiO
2
+&agr;Re
2
O
3
+&bgr;MgO+&ggr;MnO
(Re
2
O
3
is at least one or more of the compounds selected from Y
2
O
3
, Gd
2
O
3
, Tb
2
O
3
, Dy
2
O
3
, Ho
2
O
3
, Er
2
O
3
and Yb
2
O
3
, &agr;, &bgr; &ggr;, m and x representing molar ratio in the range of 0.001&agr;≦0.10, 0.001≦&bgr;0.12, 0.001<&ggr;≦0.12, 1.000<m≦1.035 and 0.005<x≦0.22), and contains about 0.2 to 5.0 parts by weight of the compound selected from either a first sub-component, a second sub-component or a third sub-component relative to 100 parts by weight of a principal component containing about 0.02%
Hamaji Yukio
Hiramatsu Takashi
Shibata Masamitsu
Wada Nobuyuki
Dinkins Anthony
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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