Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Of electrical article or electrical component
Reexamination Certificate
2000-10-24
2002-11-26
Derrington, James (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Of electrical article or electrical component
C264S614000, C264S661000, C264S666000, C156S089160
Reexamination Certificate
active
06485672
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of manufacturing a dielectric ceramic composition, a multi-layer ceramic capacitor, and other electronic devices containing a dielectric layer.
BACKGROUND ART
A multi-layer ceramic capacitor is being broadly used as a compact, large capacity, high reliability electronic device. The number used in each piece of electrical equipment and electronic equipment has also become larger. In recent years, along with the increasing miniaturization and improved performance of equipment, there have been increasingly stronger demands 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 and firing a paste for formation of the internal electrodes and a slurry (paste) for formation of the dielectric using the sheet method or printing method etc. Generally Pd or a Pd alloy had been used for the internal electrodes, but Pd is high in price and therefore relatively inexpensive Ni or Ni alloys is now being used. When forming the internal electrodes by Ni or an Ni alloy, firing in the atmosphere ends up causing the electrodes to oxidize. Therefore, in general, after the binder is removed, the electrodes are fired at an oxygen partial pressure lower than the equilibrium oxygen partial pressure of Ni and NiO, then are heat treated to cause reoxidation of the dielectric layer (Japanese Unexamined Patent Publication (Kokai) No. 03-133116 and Japanese Patent No. 2787746).
If firing electrodes in a reducing atmosphere, however, the dielectric layer is reduced and the specific resistance ends up becoming smaller. Therefore, a reduction-resistant dielectric material which is not reduced even if fired in a reducing atmosphere has been proposed (I. Burn et al., “High Resistivity BaTiO
3
Ceramics Sintered in CO—CO
2
Atmospheres”,
J. Mater. Sci
., 10, 633 (1975); Y. Sakabe et al., “High-Permittivity Ceramics for Base Metal Monolithic Capacitors”, pn.,
J. Appl. Phys
., 20 Suppl. 20-4, 147 (1981)).
A multi-layer ceramic capacitor using these reduction-resistant dielectric materials, however, suffers from the problems of a short high temperature accelerated lifetime of the insulation resistance and a low reliability. Further, there is the problem that the relative permittivity of the dielectric falls along with time. This is particularly remarkable under a DC electric field. If the dielectric layer is made thinner to make the multi-layer ceramic capacitor smaller and larger in capacity, the field intensity applied to the dielectric layer for giving the DC voltage becomes larger. Therefore, the change in the relative permittivity along with time ends up becoming much greater.
In the standard established in the EIA standard and known as “X7R”, however, the rate of change of the capacity is set as within ±15% (reference temperature 25° C.) between −55° C. and 125° C. As a dielectric material satisfying the X7R characteristic, a BaTiO
3
+SrTiO
3
+MnO based composition shown in for example Japanese Unexamined Patent Publication (Kokai) No. 61-36170 is known. This composition, however, suffers from a large rate of change of the capacity under a DC electric field. For example, if a DC electric field of 50V is applied for 1000 hours at 40° C., the rate of change of the capacity ends up becoming from −10% to −30% and the X7R characteristic can no longer be satisfied.
Further, in the standard of the capacity-temperature characteristic known as the B characteristic (EIAJ standard), the rate of change is set to within ±10% (reference temperature 20° C.) between −25° C. to 85° C.
Further, in addition, as a reduction-resistant dielectric ceramic composition, mention may be made of the BaTiO
3
+MnO+MgO disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-71866, the (Ba
1−x
Sr
x
O)
a
Ti
1−y
Zr
y
O
2
+&agr;((1−z)MnO+zCoO)+&bgr;((1−t)A
2
O
5
+tL
2
O
3
)+wSiO
2
(where, A=Nb, Ta, V; L=Y or a rare earth element) disclosed in Japanese Unexamined Patent Publication (Kokai) No. 61-250905, barium titanate added with Ba
2
Ca
1−a
SiO
3
disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-83256, etc.
In all of these dielectric ceramic compositions, however, when the thickness of the dielectric layer is for example a super thin one of not more than 4 &mgr;m, it is extremely difficult to satisfy all of the characteristics of the capacity-temperature characteristic, the change in capacity under a DC electric field along with time, the accelerated lifetime of the insulation resistance, the drop in the capacity under a DC bias, etc. For example, in the disclosures of Japanese Unexamined Patent Publication (Kokai) No. 61-250905 and Japanese Unexamined Patent Publication (Kokai) No. 2-832, the problems arise of a short accelerated lifetime of the insulation resistance or a large drop in the capacity under a DC bias.
DISCLOSURE OF THE INVENTION
The present invention was made in view of these circumstances and has as its object to provide a method of manufacturing an electronic device containing a dielectric layer such as a multi-layer ceramic capacitor able to satisfy both of the capacity-temperature characteristics of the X7R characteristic (EIA standard) and the B characteristic (EIAJ standard), even when the dielectric layer is superthin, and having a small change in the capacity under a DC electric field along with time and further having a long accelerated lifetime of the insulation resistance and a small drop in capacity under a DC bias. Further, the present invention has as its object to provide a method of manufacturing a dielectric ceramic composition suitable for use as a dielectric layer of an electronic device containing a dielectric layer such as a multi-layer ceramic capacitor having such superior characteristics.
To achieve the above object, the present invention provides a method of manufacturing a dielectric ceramic composition comprising:
a main component expressed by the formula Ba
m
TiO
2+n
, wherein the “m” in the formula is 0.995≦m≦1.010, “n” is 0.995≦n≦1.010, and the ratio of Ba and Ti is 0.995≦Ba/Ti≦1.010,
a second subcomponent including a sintering aid containing silicon oxide as a main component, and other subcomponents,
comprising the steps of:
mixing the main component and at least part of the subcomponents except for the second subcomponent and to prepare a pre-calcination powder,
calcining the pre-calcination powder to prepare a calcined powder, and
mixing at least the second subcomponent in said calcined powder to obtain a dielectric ceramic composition having ratios of the subcomponents to the main component of predetermined molar ratios.
According to a first aspect of the present invention, said second subcomponent has a composition expressed by (Ba,Ca)
x
SiO
2+x
(where, x=0.8 to 1.2);
said other subcomponents include at least:
a first subcomponent including at least one type of compound selected from MgO, Cao, BaO, SrO, and Cr
2
O
3
a third subcomponent including at least one type of compound selected from V
2
O
5
, MoO
3
, and WO
3
, and
a fourth subcomponent including an oxide of R (where, R is at least one type of element selected from Y, Dy, Tb, Gd, and Ho); and
at least the second subcomponent is mixed in the calcined powder to obtain a dielectric ceramic composition having ratios of the subcomponents to 100 moles of the main component of:
the first subcomponent: 0.1 to 3 moles,
the second subcomponent: 2 to 12 moles,
the third subcomponent: 0.1 to 3 moles, and
the fourth subcomponent: 0.1 to 10.0 moles (where, the number of moles of the fourth subcomponent is the ratio of R by itself).
According to a second aspect of the invention,
said second subcomponent has a composition expressed by (Ba,Ca)
x
SiO
2+x
(where, x=0.8 to 1.2);
said other subcomponents include at least:
a first subcomponent incl
Nomura Takeshi
Sato Shigeki
Derrington James
TDK Corporation
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