Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2000-10-13
2002-06-11
Brunsman, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S139000, C361S321300, C361S321400, C361S321500
Reexamination Certificate
active
06403513
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric ceramic composition having a resistance to reduction and to a multi-layer ceramic capacitor or other electronic device using the same.
2. Description of the Related Art
A multi-layer ceramic capacitor, one type of electronic device, is broadly used as a compact, large capacity, high reliability electronic device. The number used in each piece of electronic equipment has also increased. In recent years, along with increasing miniaturization and improved equipment performance, there has been increasingly stronger demand for further reductions in size, increases in capacity, reductions in price and improvements in reliability in multi-layer ceramic capacitors.
Multi-layer ceramic capacitors are normally produced by stacking a paste for forming the internal electrode layers and a paste for forming the dielectric layers using the sheet method or printing method, etc. and then co-firing the internal electrode layers and dielectric layers in the stack together.
As the electroconductive material for the internal electrode layers, generally Pd or a Pd alloy is used, but since Pd is high in price, relatively inexpensive Ni, Ni alloys, and other base metals have come into use. When using a base metal as the electroconductive material of the internal electrode layers, firing in the atmosphere ends up oxidizing the internal electrode layers and therefore the co-firing of the dielectric layers and internal electrode layers has to be done in a reducing atmosphere. When being fired in a reducing atmosphere, however, the dielectric layers end up being reduced and becoming lower in specific resistance. Therefore, non-reducing type dielectric materials are being developed.
In multi-layer ceramic capacitors using a dielectric ceramic composition, insulation resistence (IR) remarkably deteriorates when an electric field is applied, more specifically, there is a disadvantage in that an IR lifetime is short and the credibility is low.
There also arises a disadvantage that when the dielectric composition is exposed to a direct-current electric field, a permittivity ∈r declines over time. Also, a superimposed direct-current voltage is used for a capacitor in some cases and there is a disadvantage that when a direct-current voltage is applied to a capacitor having a dielectric composition wherein a strong dielectric composition is a main composition, a capacitor value generally declines (DC bias characteristics). When a dielectric composition layer is made thinner in order to make a chip capacitor more compact and larger in capacity, an electric field affecting the dielectric composition layer at the time of applying a direct-current voltage becomes strong, so the permittivity ∈r is liable to change over time, that is, the capacitor change over time becomes remarkably large and DC bias characteristics declines.
Further, a capacitor is also required to have excellent temperature characteristics. In particular, in some applications, it is desired that the temperature characteristics be smooth under harsh conditions. In recent years, multi-layer ceramic capacitors have come into use for various types of electronic equipments such as the engine electronic control units (ECU) mounted in engine compartments of automobiles, crank angle sensors, antilock brake system (ABS) modules, etc. These types of electronic equipment are used for stabilizing engine control, drive control, and brake control, and therefore are required to have excellent circuit temperature stability.
The environment in which these types of electronic equipment are used is envisioned to be one in which the temperature falls to as low as −20° C. or so in the winter in cold areas or the temperature rises to as high as +130° C. or so in the summer right after engine startup. Recently, there has been a trend toward reduction of the number of wire harnesses used for connecting electronic apparatuses and the equipment they control. Electronic apparatuses are also being mounted outside of the vehicles in some cases. Therefore, the environment is becoming increasingly severe for electronic apparatuses. Accordingly, capacitors used for these electronic apparatuses have to have smooth temperature characteristics over a broad temperature range.
Temperature-compensating capacitor materials superior in temperature characteristics such as, (Sr, Ca)(Ti, Zr)O
3
based, Ca(Ti, Zr)O
3
based, Nd
2
O
3
—2TiO
2
based, La
2
O
3
—2TiO
2
based, and other materials are generally known, but these compositions have extremely low permittivitys (generally less than 100), so it is substantially impossible to produce a capacitor having a large capacity.
To create dielectric ceramic compositions having a high dielectric constant and a smooth capacity-temperature characteristics, compositions comprised of BaTiO
3
as a main component plus Nb
2
O
5
—Co
3
O
4
, MgO—Y, rare earth elements (Dy, Ho, etc.), Bi
2
O
3
—TiO
2
, etc. are known. Looking at the temperature characteristics of a dielectric ceramic composition comprising BaTiO
3
as a main component, where the Curie temperature of pure BaTiO
3
is close to about 130° C., it is extremely difficult to satisfy the R characteristic of the capacity-temperature characteristic (&Dgr;C=+15% or less) in the region higher in temperature than that. Therefore, a BaTiO
3
based high dielectric constant material can only satisfy the X7R characteristic of the EIA standard (−55 to 125° C., &Dgr;C=+15% or less). By only satisfying the X7R characteristic, the material is not good enough to be used in an electronic apparatus of an automobile which is used in the above-mentioned harsh environments. The above electronic apparatus requires a dielectric ceramic composition satisfying the X8R characteristic of the EIA standard (−55 to 150° C., &Dgr;C=±15% or less).
To satisfy the X8R characteristic in a dielectric ceramic composition comprised of BaTiO
3
as a main component, it has been proposed to shift the Curie temperature to the high temperature side by replacing the Ba in the BaTiO
3
with Bi, Pb, etc. (Japanese Unexamined Patent Publication (Kokai) No. 1998-25157 and No. 1997-40465). Further, it has also been proposed to satisfy the X8R characteristic by selecting a BaTiO
3
+CaZrO
3
+ZnO+Nb
2
O
5
based composition (Japanese Unexamined Patent Publication (Kokai) No. 1992-295048, No. 1992-292458, No. 1992-292459, No. 1993-109319, and No. 1994-243721).
In each of these compositions, however, Pb, Bi, and Zn are easily vaporized and scattered making, firing in air or another oxidizing atmosphere a prerequisite. Therefore, there are the problems that it is not possible to use an inexpensive base metal such as Ni for the internal electrodes of the capacitor and it is necessary to use Pd, Au, Ag, or another high priced precious metals.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a dielectric ceramic composition having a high permittivity, having a capacity-temperature characteristic satisfying the X8R characteristic of the EIA standard (−55 to 150° C., &Dgr;C=+15% or less), able to be fired in a reducing atmosphere, and further, to provide a multi-layer ceramic capacitor or other electronic device using this dielectric ceramic composition.
To attain the above object, a dielectric ceramic composition according to the first aspect of the present invention comprises:
a main component composed mainly of barium titanate,
a first subcomponent including at least one compound selected from MgO, CaO, BaO, SrO and Cr
2
O
3
,
a second subcomponent containing silicone oxide as a main composition,
a third subcomponent including at least one compound selected from V
2
O, MoO
3
, and WO
3
,
a fourth subcomponent including an oxide of R1 (where R1 is at least one element selected from Sc, Er, Tm, Yb, and Lu), and
a fifth subcomponent including CaZrO
3
or CaO+ZrO
2
,
wherein the ratios of the subcomponents to 100 moles of
Fujikawa Yoshinori
Sato Shigeki
Terada Yoshihiro
Brunsman David
TDK Corporation
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