| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | May 26, 1998 |
| PATENT TITLE |
Dielectric ceramic composition |
| PATENT ABSTRACT |
A dielectric ceramic composition for microwave applications consists essentially of the compound having a formula B'B.sub.2 "O.sub.6, wherein B' is at least one metal selected from the group of Mg, Ca, Co, Mn,Ni and Zn, and wherein B" is one of Nb or Ta, and additionally includes at least one compound selected from the group of CuO, V.sub.2 O.sub.5, La.sub.2 O.sub.3, Sb.sub.2 O.sub.5, WO.sub.3, MnCO.sub.3, MgO, SrCO.sub.3, ZNO, and Bi.sub.2 O.sub.3 as an additive, wherein the amount of the additive is 0.05% to 2.0% by weight of the total weight of the composition. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | February 4, 1997 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A dielectric ceramic composition for microwave applications consisting essentially of the compound having the formula B'B.sub.2 "O.sub.6, wherein the B' is at least one metal selected from the group of Mg, Co, Mn, Ni and Zn, and the B" is selected from the group of Nb and Ta, and an additive wherein the amount of additive is 0.05% to 2.0 by weight of the total weight of the composition. 2. The dielectric ceramic composition defined as in claim 1, wherein said additive consists of at least one compound selected from the group of CuO, V.sub.2 O.sub.5, La.sub.2 O.sub.3, Sb.sub.2 O.sub.5, WO.sub.3, MgO, SrCO.sub.3, ZnO, and Bi.sub.2 O.sub.3 . 3. A dielectric ceramic composition for microwave frequency consisting essentially of a solid solution which is a mixture of B'Nb.sub.2 O.sub.6 and B'Ta.sub.2 O.sub.6 in a mole fraction, wherein B' is at least one metal selected from the group of Mg, Co, Mn, Ni and Zn, and an additive in an amount of 0.05% to 2.0% by weight of the composition. 4. The dielectric ceramic composition defined as in claim 3, wherein said additive consists of at least one compound selected from the group of CuO, V.sub.2 O.sub.5, La.sub.2 O.sub.3, Sb.sub.2 O.sub.5, WO.sub.3, MgO, SrCO.sub.3, ZnO, and Bi.sub.2 O.sub.3. 5. A dielectric ceramic composition for microwave frequency consisting essentially of a solid solution which is a mixture of B'Nb.sub.2 O.sub.6 and B'T.sub.2 O.sub.6 in a mole fraction, wherein B' is Zn, and an additive in an amount of 0.05% to 2.0% by weight of the composition. 6. The dielectric ceramic composition defined as in claim 5, wherein the mole fractionof ZnNb.sub.2 O.sub.6 is 0.2 to 0.5. 7. A dielectric ceramic composition for microwave frequency consisting essentially of a solid solution which is a mixture of B'Nb.sub.2 O.sub.6 and B'Ta.sub.2 O.sub.6 in a mole fraction, wherein B' is Mg, and an additive in an amount of 0.05% to 2.0% by weight of the composition. 8. The dielectric ceramic composition defined as in claim 7, wherein the mole fraction of MgNb.sub.2 O.sub.6 is less than 0.1. 9. A dielectric ceramic composition for microwave frequency consisting essentially of a solid solution which is a mixture of B'Nb.sub.2 O.sub.6 and B'Ta.sub.2 O.sub.6 in a mole fraction, wherein B' is at least one of Zn and Mg, and an additive in an amount of 0.05 to 2.0% by weight of the composition. 10. The dielectric ceramic composition defined as in claim 5, wherein the additive is at least one compound selected from the group of CuO, V.sub.2 O.sub.5, La.sub.2 O.sub.3, Sb.sub.2 O.sub.5, WO.sub.3, MgO, SrCO.sub.3, ZnO, and Bi.sub.2 O.sub.3. 11. The dielectric ceramic composition defined as in claim 6, wherein the additive is at least one compound selected from the group of CuO, V.sub.2 O.sub.5, La.sub.2 O.sub.3, Sb.sub.2 O.sub.5, WO.sub.3, MgO, SrCO.sub.3, ZnO, and Bi.sub.2 O.sub.3. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
TECHNICAL FIELD The present invention relates to dielectric ceramic compositions for microwave application and, more particularly, to dielectric ceramic compositions for microwave devices such as, for example, those having a dielectric resonator designed to operate in a microwave frequency range. BACKGROUND ART Recently, telecommunications such as mobile communication and satellite communication have focused a growing interest in dielectric ceramic devices for microwave application. In particular, mobile communication arrangements which include automobile telephones, a cellular phones, pagers and GPS (Global Positioning Systems) employ microwave dielectric materials which are required to posses various electrical and physical properties such as, for example, high permittivity (.epsilon.), high quality factor(Q), small temperature coefficient of resonance frequency (.tau..sub.f), and good sintering characteristics. Studies pertaining to dielectric compositions for microwave applications have been directed to dielectric compositions of the TiO.sub.2 type. As the result, it has been determined that TiO.sub.2 based dielectric compositions including Ba.sub.2 Ti.sub.9 O.sub.2 O (Zr,Sn) TiO.sub.4, BaO-Re.sub.2 O.sub.3 -TiO.sub.2 (Re:Rare earth) and BaO-Nd.sub.2 O.sub.3 -TiO.sub.2 (BNT type) along with dielectrics having a complex perovskite structure such as Ba (Mg.sub.1/3 Ta.sub.2/3 ) O.sub.3 'Ba (Zn.sub.1/3 Ta.sub.2/3 ) O.sub.3 and Ba (Mg.sub.1/3 Nb.sub.2/3 )O.sub.3 are suitable for the above type of application. Further, efforts are being actively directed to the development of new dielectric materials which are formed using solid solutions of two or more ceramic compositions having perovskite structures. The dielectrics of the BNT type, however, present problems in that they have Q factor smaller than other dielectrics with respect to high frequency and exhibit a limited resonance frequency below 1 GHz. Further, Nd.sub.2 O.sub.3 is a rare-earth metal which is a costly compared with other elements. With regard to dielectrics of (Zr,Sn)TiO.sub.4 type, which are widely used due to their high Q factor and stable temperature characteristics, permittivity is in the range of 30 to 40, Q factor is about 8000 at 4 GHz and temperature coefficient of resonance frequency (Ef) is in the range of -30 to +30 ppm/.degree. C. This composition which is manufactured by a general solid phase reaction, is, however, sintered at a sintering temperature above 1600.degree. C., and is difficult to sintered at low temperatures without the addition of sintering agent such as CuO, CO.sub.2 O.sub.3, ZnO, and the like. However, the addition of the sintering agent deteriorates the physical properties of the ceramic composition. Although various liquid phase methods are used for powder syntheses (e.g. Sol-Gel, alkoxide and coprecipitation methods), these methods are too complex to carry out econmically and result in the rise of a production costs. Dielectrics of complex perovskite type ceramic compositions, for example, Ba(Zn.sub.1/3 Ta.sub.2/3 )O.sub.3, are also difficult to sinter because of a sintering temperature above 1550.degree. C. Furthermore, it is difficult to control the numerous process factors in case that agents such as BaZrO.sub.3 and Mn are added to decrease the sintering temperature. As the size of electronic equipment such as dielectric filters becomes smaller, multilayer devices has been considered in connection with the necessary miniaturization. However, the production of such arrangements requires that the dielectric material and the electrodes be co-fired. In order to use low-priced Ag or Cu electrodes, the dielectric material must exhibit a low sintering temperature. For this reason, it still remains necessary to develop new dielectric ceramic compositions which have good sintering characteristics and simple compositions as well as at least still having the characteristics of conventional dielectric ceramic compositions necessary for microwave applications. DISCLOSURE OF THE INVENTION Studies have focused on materials having a binary system of the ABO.sub.3 type which exhibit a cubic complex perovskite structure with an ion at the B site. As a result, it was discovered that the dielectric ceramic compositions of the present invention exhibits dielectric characteristics such as a permittivity and a Q factor, which are similar to those of ceramic compositions having complex perovskite structures, but which can be sintered at lower temperatures than the conventional complex perovskite structures. It is therefore an object of the present invention to provide dielectric ceramic compositions for microwave applications with desired electrical and physical properties, which overcome the above-mentioned limitations and disadvantages of the related art. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof. To achieve the foregoing object and advantages, there is provided a dielectric ceramic composition for microwave applications consisting essentially of the general formula B'B.sub.2 "O.sub.6, wherein the B' is, at least one element selected from the group of Mg, Ca, Co, Mn, Ni and Zn, and wherein B" is at least one of Nb and Ta. From the experimental results of the B'B".sub.2 O.sub.6 dielectric ceramic composition shown in Tables. 1 and 2, it was established that the temperature coefficient of resonant frequency is positive for B'Ta.sub.2 O.sub.6 type, but negative for B'Nb.sub.2 O.sub.6 type. This, therefore, rendered it possible to regulate the resonant frequency temperature coefficient to have a positive or negative value that approximates zero, by forming a solid solution designed with proper mole fractions of dielectrics of B'Nb.sub.2 O.sub.6 type and B'Ta.sub.2 O.sub.6 type. In general, various additives are added to the dielectric ceramic compositions in order to improve the dielectric characteristics and to reduce the sintering temperature. For example, additives such as MnCO.sub.3, MgO, SrCO.sub.3 or ZnO improve the dielectric characteristics and other substances of low melting points such as glass, or oxides of Pb, Bi or V decrease the sintering temperature and to cause the composition to be sintered to have a liquid phase. An additive oxide amount of less than 0.05% by weight of the total weight of the composition, is not effective. However, an oxide content of more than 2.0% by weight may deteriorate the dielectric characteristics of the composition due to the possibility of the formation of a second phase. For this reason, the content of the additive is, preferably, 0.05% to 2.0% by weight of the total weight of the dielectric composition in the present invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. |
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