Capacitor comprising a BCZT dielectric

Details Capacitor comprising a BCZT dielectric Capacitor comprising a BCZT dielectric

2001-06-27

2002-08-20

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Fixed capacitor

C361S321100, C361S321500, C361S306300, C501S134000, C501S139000

Reexamination Certificate

active

06437970

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a capacitor, particularly a multi-layer capacitor with inner electrodes of a base metal and with a ceramic dielectric which essentially comprises a dielectric composition of a barium-calcium-manganese-zirconium-titanate as a basic material.
Multi-layer capacitors are used, inter alia, for decoupling and buffering the power supply of processors, particularly high-power microprocessors. During operation in the high-power mode, these active electronic components generate much heat, and even with an intensive cooling the temperature of a high-power processor in permanent operation is between 70° C. and 80° C. Conventional multi-layer capacitors of the specification Y5V have only 20% of their rating (&Dgr;C≈80%) at an operating temperature of 80° C. For manufacturing microprocessors, capacitors of the specification X7R are therefore preferably used, because they still have 85% of their rating (&Dgr;C<±15%) at a temperature of 125° C. The specific capacitance of an X7R capacitor is, however, approximately 5 times lower at room temperature than that of a capacitor of the specification Y5V, so that an X7R capacitor must have larger dimensions, for example, the dimensions of a 1 &mgr;F X7R capacitor must be at least of the size 1206 (length 0.12 nominal, width 0.06 nominal). For capacitances of >5 &mgr;F, the more expensive tantalum capacitors can therefore only be used until now.
A ceramic multi-layer capacitor having a plurality of ceramic layers on the basis of doped BaTiO
3
and a plurality of electrode layers mainly comprising nickel is already known from WO 98/54737, in which capacitor the ceramic layers and the electrode layers are alternately stacked so that they constitute a multi-layer structure and are implemented on both side faces with electric connections contacting the electrode layers, and in which the main components of the doped BaTiO
3
are defined by the general formula
(Ba
1−a−b
Ca
a
Dy
b
)(Ti
1−c−d−e−f
Zr
c
Mn
d
Nb
e
)
f
O
3+∂
. This capacitor is suitable for DC applications at high temperatures.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a capacitor having a ceramic dielectric and at least two electrodes, in which the dielectric essentially comprises a dielectric ceramic composition of a barium-calcium-manganese-zirconium-titanate as a basic material, which capacitor is suitable for DC applications at high temperatures and has smaller dimensions than the prior-art capacitor.
According to the invention, the object is solved by a capacitor having a ceramic dielectric and at least two electrodes, in which the dielectric essentially comprises a dielectric ceramic composition of a barium-calcium-manganese-zirconium-titanate as a basic material having the composition (Ba
1−x
Ca
x
)
y
[Ti
1−a−b−c−d
Zr
a
Mn
b
Nb
c
Dy
d
]O
3
with 0<a≦0.25, 0<b≦0.015, 0.001≦c≦0.01, 0.005≦d≦0.02, 0<x≦0.20, 1.001≦y≦1.014, 0.0005≦z≦0.03.
Within the scope of the present invention, it is preferred that the general formula is (Ba
1−x
Ca
x
)
y
[Ti
1−a−b−c−d
Zr
a
Mn
b
Nb
c
Dy
d
]O
3
with 0<a≦0.25, c−0.5d≦b≦0.015, 0.001≦c≦0.01, 0.005≦d≦0.02, 0<x≦0.20, 1.001≦y≦1.014, 0.0005≦z≦0.03.
It is also preferred that the dielectric ceramic composition comprises, as a further additive, SiO2 in a quantity z with 0.0005≦z≦0.03 mol/unit.
Furthermore, it is preferred that the electrodes consist of nickel or a nickel-containing alloy.
The invention also relates to a dielectric ceramic composition of a barium-calcium-manganese-zirconium-titanate as a basic material having the general formula (Ba
1−x
Ca
x
)
y
[Ti
1−a−b−c−d
Zr
a
Mn
b
Nb
c
Dy
d
]O
3
with 0<a≦0.25, 0<b≦0.015, 0.001≦c≦0.01, 0.005≦d≦0.02, 0<x≦0.20, 1.001≦y≦1.014,0.0005≦z≦0.03.
It is preferred that the general formula is (Ba
1−x
Ca
x
)
y
[Ti
1−a−b−c−d
Zr
a
Mn
b
Nb
c
Dy
d
]O
3
with 0<a≦0.25, c−0.5d≦b≦0.015, 0.001≦c≦0.01,0.005≦d≦0.02,0<x≦0.20, 1.001≦y≦1.014, 0.0005≦z≦0.03.
It is also preferred that the composition comprises, as a further additive, SiO2 in a quantity z with 0.0005≦z≦0.03 mol/unit.
Such a dielectric ceramic composition is characterized by a low sintering temperature of 1200° C. Due to its fine grain structure it is suitable for very thin dielectric layers. Capacitors with a dielectric comprising this material have an extraordinarily high breakdown voltage <100 V/&mgr;m and are resistant to aging when they are DC operated. With this dielectric ceramic composition, capacitors having a high capacitance and small dimensions can be manufactured, while they simultaneously have a long lifetime.
Within the scope of the present invention it is preferable that the electrodes comprise nickel or a nickel-containing alloy.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.


REFERENCES:
patent: 5790367 (1998-08-01), Mateika et al.
patent: 5889647 (1999-03-01), Hansen et al.
patent: 6043974 (2000-03-01), Chen et al.
patent: 6072688 (2000-06-01), Hennings et al.
patent: 6078494 (2000-06-01), Hansen
patent: 6195250 (2001-02-01), Matoba et al.
patent: 6243254 (2001-06-01), Wada et al.
patent: 6310761 (2001-10-01), Hori et al.

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