Multilayer ceramic capacitor and manufacturing method thereof

Details Multilayer ceramic capacitor and manufacturing method thereof Multilayer ceramic capacitor and manufacturing method thereof

2002-03-04

2002-11-26

Dinkins, Anthony (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Fixed capacitor

C361S321400, C501S134000, C501S138000, C501S139000

Reexamination Certificate

active

06487065

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of manufacturing multilayer ceramic capacitors, and more particularly relates to a multilayer ceramic capacitor formed with a CaTiO
3
/CaZrO3 ceramic capable of being fired in a neutral or reducing atmosphere.
2. Description of the Related Art
Internal electrodes of ceramic electronic components, such as a multilayer ceramic capacitor, have been formed of base metals, such as Ni and Cu, to reduce the material cost. Since base metals are readily oxidized, ceramics used for multilayer ceramic capacitors including such base metallic internal electrodes need to be fired in a neutral or reducing atmosphere.
Japanese Unexamined Patent Application Publication No.63-126117 discloses a dielectric ceramic composition for temperature compensation capable of being fired in a neutral or reducing atmosphere. The major component of the composition is expressed by the formula (Ca
1-x
Sr
x
)
m
(Zr
1-y
Ti
y
)O
3
, wherein variables x, y and m satisfy 0≦×≦0.6, 0≦y≦0.6, and 0.85≦m≦1.30, respectively. In addition, relative to 100 parts by weight of the major component, 0.5 to 8 parts by weight of MnO2 and 0.5 to 8 parts by weight of glass components containing TiO
2
, SiO
2
and the like are present.
According to this publication, the temperature characteristics of multilayer ceramic capacitors can be extensively controlled by controlling the Ti/Zr ratio of the dielectric ceramic composition. The temperature characteristic of the multilayer ceramic capacitor means the rate of change in capacitance with temperature and generally refers to a temperature coefficient represented by ppm/° C. The temperature coefficient is defined by the following equation:
Temperature coefficient=(
C
i
−C
0
)×10
6
/(
T
i
=T
0
)
wherein C
i
and C
0
are capacitances at temperatures t
i
and T
0
, respectively.
The temperature characteristic of a temperature-compensating ceramic capacitor is expressed by a combination of two alphabetical characters, one representing the temperature coefficient and the other representing an allowable error of the temperature coefficient. The dielectric ceramic composition according to the foregoing publication achieves a multilayer ceramic capacitor having a desired temperature characteristic in the range of CG to SL.
CG represents a temperature coefficient of 0 ppm/° C. and a temperature-coefficient allowable error of ±30 ppm/° C., and SL represents a temperature coefficient in the range of +350 to −1000 ppm/° C., as shown in Tables 1 and 2.
TABLE 1
Character
C
L
P
R
S
T
U
SL
Temperature
0
−80
−150
−220
−330
−470
−750
−1000
coefficient
to
(ppm/° C.)
+350
TABLE 2
Character
K
J
H
G
allowable error
±250
±120
±60
±30
(ppm/° C.)
Also, the publication discloses that increasing the Ti content improves the temperature characteristic of the ceramic capacitor.
However, multilayer ceramic capacitors formed of CaTiO
3
/CaZrO
3
are likely to cause a short circuit and a degradation of the insulation resistance (IR) at elevated temperature, as shown in a high-temperature loading test.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a reliable multilayer CaTiO
3
/CaZrO
3
ceramic capacitor and a method of manufacturing the same. This multilayer ceramic capacitor rarely exhibits a short circuit or degradation of the insulation resistance in a high-temperature loading test, solving the problem described above.
To this end, according to one aspect of the present invention, there is provided a multilayer ceramic capacitor comprising a sintered ceramic compact comprising primary crystalline phases mainly containing CaTiO
3
and CaZrO
3
and secondary phases mainly containing Si and Ca. The amount of Ca in the secondary phase is about 30 mol % or less. The multilayer ceramic capacitor also comprises internal electrodes lying in the sintered ceramic compact.
The internal electrodes may comprise a base metal to reduce the material cost of the multilayer ceramic capacitor.
Another aspect of the present invention is directed to a method of manufacturing the multilayer ceramic capacitor. The method comprises preparing a green ceramic laminate comprising main components including CaTiO
3
and CaZrO
3
, sub-components including MnO
2
and SiO
2
, and a plurality of internal electrodes. The method also comprises a step of firing the green ceramic laminate at a heating rate of at least about 5° C./min up to a maximum temperature. Thus, a multilayer ceramic capacitor having high reliability in a high-temperature loading test can be achieved.


REFERENCES:
patent: 5258150 (1993-11-01), Merkel et al.
patent: 6301092 (2001-10-01), Hata et al.
patent: 63-126117 (1988-05-01), None
patent: 8-45343 (1996-02-01), None
patent: 2000-252156 (2000-09-01), None

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