Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reissue Patent
2000-03-15
2004-04-06
Wood, Elizabeth D. (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S032000, C501S138000
Reissue Patent
active
RE038491
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention is directed to a composition for producing a ceramic dielectric and a method of making a ceramic dielectric from such a composition, wherein the composition can be sintered at a low temperature, has a high nonloaded Q value (hereinafter referred to as Q value) in a microwave bandwidth region, and is capable of being sintered simultaneously with a high conductivity conductor, such as silver or copper. The composition sintered at a lower temperature according to the present invention can be used, for example, in the production of ceramic dielectrics used in the construction of multilayer microwave resonators and filters.
Description of the Prior Art
The increase in the magnitude of communication information transmitted in recent years has promoted the rapid development of various communication system utilizing microwave bandwidth regions, such as cellular telephones, satellite communication and satellite broadcasting, as well as the development of various microwave dielectric materials to accommodate the industry's needs. The ceramic dielectrics used in the microwave bandwidth region exhibit characteristics that the Q value tends to reduce as the working frequency is increased. They are, furthermore, required to have the following characteristics:
(1) a high Q value in the microwave bandwidth region,
(2) a high specific dielectric constant (er), and
(3) a small absolute value for the temperature coefficient (&tgr;f) of the resonancy frequency.
Various kinds of compositions having the foregoing characteristics have been developed. Known compositions having a high Q value include, for example, Ba(Mg
1/3
Ta
2/3
)O
3
and Ba (Zn
1/3
Ta
2/3
)O
3
. Known compositions having a high specific dielectric constant include, for example, a BaO.TiO
2
.RE
2
O
3
(in which RE represents a rare earth element), each of which is used as a resonator, a filter, or the like.
It has been recently proposed to employ a multilayer type dielectric resonator or filter using a conductor as an internal electrode to create multilayer ceramic materials utilized in a high frequency bandwidth region, such as a microwave, since it is necessary to form a high conductivity metallic conductor onto the surface of the composition. This is accomplished by sintering the conductor between ceramic layers. Noble metals, such as platinum or palladium, which are expensive but resistant to high temperature, are employed in the production of existing ceramic dielectrics in which the sintering temperature exceeds 1000° C., thus resulting in increased production costs. It is extremely advantageous if a composition is sinterable at a low temperature, for example, about, 900° C. This reduces the production costs since an inexpensive metal material, such as silver or copper, can be used as the conductor. Accordingly, the industry has demanded the development of a ceramic dielectric produced by a composition that can be sintered at a temperature of about 900° C.
Generally, sintering compositions at low temperatures involves such methods as: (a) adding glass frit as a sintering aid; (b) utilizing finely atomized submicron size starting materials; or (c) utilizing a chemical process, such as the sol-gel method. However, since the usual compositions have low reactivity with glass, they suffer from the added difficulty of forming compositions at high densities creating the additional problem of drastically reducing the Q value.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the foregoing problems and provide a ceramic dielectric created by sintering a composition at a low temperature of about 900° C. Therefore, the compositions can be simultaneously sintered with a high conductivity conductor, such as silver or copper, to produce a ceramic dielectric having a high Q value in the microwave bandwidth and a small temperature coefficient of resonance frequency. A reduction in production costs is realized.
The foregoing object can be attained in accordance with the first aspect of the present invention by providing a ceramic dielectric by sintering a composition at a low temperature, when the composition comprises of a calcined powder, which contains from 0.1 to 20 parts by weight of ZaO, from 0.1 to 10 parts by weight of Ta
2
O
5
and from 0.1 to 1 parts by weight of MnO
2
, based on 100 parts by weight of a composition represented by: BaO.xTiO
2
(in which 3.0≦×≦5.7). 0.1 to 20 parts by weight of a glass powder (based on 100 parts by weight of the calcined powder), having a transition point of lower than 450° C., are added to the calcined powder and then sintered.
In accordance with a second aspect of the present invention the calcined powder comprises of at least one of the following: less than 1 part by weight of WO
3
, not more than 15 parts by weight of SnO
2
, not more than 15 parts by weight of MgO, not more than 10 parts by weight of SrO, and not more than 5 parts by weight of ZrO
2
in combination with BaO.xTiO
2
based on 100 parts by weight of the composition represented by BaO.xTiO
2
(in which 3.0≦×≦5.7).
Furthermore, according to the present invention, the product of the Q value and the resonance frequency of the composition may not be less than 2000 GHz.
Also, a ceramic dielectric can be obtained in accordance with a third aspect of the present invention by a process comprising the steps of combining starting materials to form a composition containing from 0.1 to 20 parts by weight of ZnO from 0.1 to 10 parts by weight of Ta
2
O
5
and from 0.1 to 1 parts by weight of MnO
2
, based on 100 parts by weight of a composition represented by: BaO.xTiO
2
(in which 3.0≦×≦5.7), calcining the composition of a temperature from 900° to 1200° C. to prepare the calcination product, then pulverizing the calcination product, admixing 0.1 to 20 parts by weight of a glass powder having a transition point of not higher then 450° C., to 100 parts by weight of the resultant calcinated powder, molding the mixture into a predetermined shape and then sintering the same at a temperature from 850° C. to 1000° C.
Moreover, a ceramic dielectric can be attained in accordance with a fourth aspect of the present invention by a process, wherein the composition is further blended with at least one of the following: less than 1 part by weight of WO
3
, not more than 15 parts by weight of SuO
2
, not more than 15 parts by weight of MgO, not more than 10 parts by weight of SrO and not more than 5 parts by weight of ZrO
2
as the starting material(s), based on 100 parts by weight of a composition represented by: BaO.xTiO
2
(in which 3.0≦×≦5.7).
The composition according to the present invention has a high Q value in a microwave bandwidth region, a small temperature coefficient of resonance frequency, and as extremely high density (low water absorption). According to the process steps for producing the ceramic dielectric according to the present invention, a composition having both excellent density and dielectric characteristics can also be produced. This is accomplished by adding a specified amount of glass, having a predetermined transition point, to a specific ceramic raw material composition, formulated to effectuate sintering at a relatively low temperature. Therefore, a composition excellent both in density and dielectric characteristics can be obtained, thereby promoting sintering at a lower temperature without being problematic, even in the case where the total amount of the glass powder used is small, by using a glass powder containing a predetermined total amount of PbO or a predetermined amount of PbO and R
2
O (R represents an alkali metal element) and further using a calcined powder and a glass powder each of a predetermined average grain size.
DETAILED DESCRIPTION OF THE INVENTION
Applicants have made various studies of BaO.xTIO
2
compositions capable of being sintered at a low temperature to obtain a composition having a high Q value while maintaining &tgr;f within a practical characteristi
Katagiri Hiroshi
Mizutani Hidetoshi
Okuyama Masahiko
Ozeki Hirofumi
Yoshida Noritaka
Morgan & Lewis & Bockius, LLP
NGK Spark Plug Co. Ltd.
Wood Elizabeth D.
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