Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2000-12-06
2002-07-02
Koslow, C. Melissa (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S134000
Reexamination Certificate
active
06413896
ABSTRACT:
TECHNICAL FIELD
The present invention relates to improvements in methods of manufacturing dielectric ceramic compositions for electronic devices, and in particular, to a method of manufacturing dielectric ceramic compositions for electronic devices comprising composite perovskite type compounds utilized in the SHF band whereby a ceramic is obtained of internally uniform properties, in particular of excellent temperature coefficient and sintering ability, by controlling the coupling conditions of metallic ions and oxygen ions in the composition by using a specific content of the oxygen concentration in the sintering atmosphere.
BACKGROUND ART
Dielectric ceramic compositions for electronic devices of various types are utilized on account of their low loss characteristics and excellent temperature characteristics. There are various types of such dielectric ceramic compositions, which are used in particular for temperature compensating capacitors and in dielectric resonators or strip line cards for microwave device etc for satellite broadcasting and reception and for down-conversion, utilizing their low loss in the SHF band.
In general, as dielectric ceramic compositions employed for the SHF band, conventional perovskite compounds which were widely employed included composite perovskite compounds in particular Ba(B
⅓
.A
⅔
)O
3
compositions (where A is Ta and B is a divalent metallic ion (Zn or Ni, Co, Mn)), specifically Ba(Zn
⅓
.Ta
⅔
)O
3
materials.
The characteristics such as high &egr;r, high Q and &tgr;f=0 that are required for the dielectric ceramic compositions used in this SHF band are tightly specified and composition control in order to match such characteristics that are needed by materials capable of f control is extremely important; for this purpose, prolonged sintering and complex adjustment of constiutents was necessary.
In conventional dielectric ceramic compositions, composition control, in particular, since the Zn contained in the aforesaid composition easily evaporates, control of Zn, is extremely important. Also, on sintering, the Zn diffuses to the outer surface of the ceramics and is volatilized, tending to form a so-called “skin” due to the formation of Zn-deficient constituents, such as Ba
5
Ta
4
O
15
. Thus, it was difficult to obtain internally uniform ceramics in stable fashion, so it was difficult to obtain ceramics of stable characteristics.
Also, depending on the application, it was necessary to adjust to a prescribed resonance frequency temperature coefficient &tgr;f; however, it was known that the Ba(Zn
⅓
.Ta
⅔
)O
3
material has a if in the vicinity of zero.
Previously, as a result of various investigations of the aforesaid Ba(Zn
⅓
.Ta
⅔
)O
3
etc composition aimed at eliminating the drawbacks of the aforesaid composite perovskite compounds and controlling the Zn in the dielectric ceramic composition, by controlling the Zn to a prescribed value in the composition by the inclusion of specific trivalent metallic ions, as ceramics of internal uniformity with excellent characteristics and excellent sintering capability,
XBa(Zn
⅓
.Ta
⅔
)O
3
—YSr(Ga
½
.Ta
½
)O
3
solid solutions and XBa(Zn
⅓
.Ta
⅔
)O
3
—Y(Ba
Z
.Sr
1-Z
)(Ga
½
.Ta
½
)O
3
solid solutions have been proposed (Laid-open Japanese Patent Application No. H. 2-285616, Laid-open Japanese Patent Publication No. H. 3-232751).
In recent years, with miniaturization of electronic devices and the shift of frequency bands in the communications field to high frequency bands, the drawback has been experienced that it has been necessary to make dielectric elements of large size, owing to the low dielectric constant of conventional dielectric ceramic compositions.
DISCLOSURE OF THE INVENTION
In view of the foregoing situation regarding conventional composite perovskite compounds, an object of the present invention is to provide a method of manufacturing a dielectric ceramic composition for electronic devices whereby an internally uniform ceramic composition of excellent relative permittivity can be obtained in a stable fashion by controlling the temperature coefficient of the resonance frequency, by adjusting the oxygen concentration of the sintering atmosphere to a specific content, without adjusting the composition, by suppressing evaporation of Zn contained in the ceramic composition.
Aiming at solving the above problems of the prior art, the present inventors discovered that the dielectric constant of a system in which some of the Ta in the foregoing Ba(Zn
⅓
.Ta
⅔
)O
3
solid solution system was substituted by Nb, i.e. an XBa(Zn
⅓
.(Ta
M
.Nb
1-M
)
⅔
)O
3
—Y(Ba
Z
.Sr
1-Z
)(Ga
½
.Ta
½
)O
3
solid solution system was increased, and the Ga in a YSr(Ga
½
.Ta
½
)O
3
solid solution system was effective in improving sintering facility.
However, although the molding was cooled with a cooling rate of 250° C./Hr to room temperature after holding for 30 minutes to 96 hours at 1400° C. to 1550° C. after heating to 1400° C. to 1550° C. with a rate of temperature rise of 250° C./Hr in an atmosphere of O
2
concentration of 70% or higher, the drawback was experienced of a considerable fall in relative permittivity when the temperature coefficient of resonance frequency was controlled to a low value by adjustment of the composition of this solid solution ceramic composition.
However, as a result of various investigations aimed at preventing this drop in relative permittivity of the solid solution system, the inventors discovered that the temperature coefficient of resonance frequency could be controlled and the drop in relative permittivity restricted to a minimum by, instead of adjusting the composition of the solid solution system, adjusting the oxygen concentration in the sintering atmosphere to a specific content, and in this way perfected the present invention.
Specifically, when manufacturing a dielectric ceramic composition for electronic devices consisting of a composition expressed by the basic composition X(Ba
Z
.Sr
1-Z
)(Zn
⅓
(Ta
M
Nb
1-M
)
⅔
)O
3
—Y(Ba
Z′
.Sr
1-Z′
)(Ga
½
.Ta
½
)O
3
wherein X, Y, Z, Z′ and M that define the composition ranges satisfy the following values, the present invention consists in a method of manufacturing a dielectric ceramic composition for electronic devices wherein sintering is performed at 1400° C. to 1550° C. or sintering is performed at 1400° C. to 1550° C. after pre-sintering at 900° C. to 1300° C. in an N
2
atmosphere containing an oxygen concentration of 6% to 40%:
X+Y
=1,
0.3
≦X
≦1,
0.7
≧Y
≧0,
0
≦Z
≦1,
0
≦Z
′≦1,
0.2
≦M
≦0.8.
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, BaCO
3
, SrCO
3
, ZnO, Ta
2
O
5
, Nb
2
O
5
, Ga
2
O
3
powder of grain size of 1 &mgr;m or less are blended and mixed so as to form a composition X(Ba
Z
.Sr
1-Z
)(Zn
⅓
(Ta
M
.Nb
1-M
)
⅔
)O
3
—Y(Ba
Z′.Sr
1-Z′
)(Ga
½
.Ta
½
)O
3
(X+Y=1, 0.3≦X≦1, 0.7≧Y≧0, 0≦Z≦1, 0≦Z′≦1, 02≦M≦0.8), then dried and calcined in air or an oxygen or N
2
atmosphere at 1000° C. to 1200° C., then pulverized and granulated, uniaxially pressure-molded, or molded under hydrostatic pressure, then subjected to removal of binder, and heated with a rate of rise of temperature of 50° C./hour to 300° C./hour in an N
2
atmosphere of oxygen concentration adjusted to 6% to 40%, and sintered by holding for 30 minutes to 96 hours at 1400° C. to 1550° C., then cooled with a cooling rate of 50° C./hour to 300° C./hour to room temperature.
In the present invention, pre-sintering for 30 minutes to 96 hours at 900° C. to 1300° C. allows O
2
gas in the sintering atmosphere to penetrate into pores of the molding and so is effective in promoting fineness of the sintered body.
Reasons for the restrictions in the composition
The reasons for the restrictions of X, Y in
Nishikawa Kazuhiro
Shimada Takeshi
Toji Kazuya
Dykema Gossett PLLC
Koslow C. Melissa
Sumitomo Special Metals Co. Ltd.
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