Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Patent
1997-03-14
1998-03-31
Jones, Deborah
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
501136, C04B 35495, C04B 3500
Patent
active
057338310
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns ceramic dielectrics for use in electronic components and, in particular, it relates to ceramic dielectrics having a large unloaded Q-value and high relative dielectric constant, and a small temperature coefficient of resonant frequency, as well as methods for forming them.
RELATED ART STATEMENT
Heretofore, ceramic dielectrics for high frequency have often been used as materials for antenna duplexers for radio communication equipment such as mobile phones, cellular phones and chordless telephones, resonators used, for example, in voltage-controlled oscillators, or filters used in tuners for CATV. Since the wavelength of electromagnetic waves can be shortened in ceramic dielectrics for high frequency, to .di-elect cons..sub.r.sup.-1/2 (.di-elect cons..sub.r : relative dielectric constant) of the wavelength in a vacuum, electronic components such as resonators can be miniaturized by using such ceramic dielectrics.
The following three characteristics are required for such ceramic dielectrics for high frequency.
(a) A relative dielectric constant is as high as possible. That is, since the wavelength of high frequency is shortened to .di-elect cons..sub.r.sup.-1/2 (.di-elect cons..sub.r : relative dielectric constant) in the dielectrics, the size of the resonators, etc. can be miniaturized more easily as the relative dielectric constant increases for an identical resonant frequency.
(b) Dielectric loss (1/Q) is small in a high frequencies. That is, the unloaded Q-value is large.
(c) The variation coefficient of resonant frequency is only slightly affected by temperature change. That is, the temperature dependence on the relative dielectric constant is small.
The ceramic dielectrics used until now, for example, in microwave dielectric resonators, have various kinds of compositions. They have been known to include BaO-TiO.sub.2 -base and ZrTiO.sub.4 -base ceramics. As ceramic dielectrics related to the present invention, Ba(Zn.sub.1/3, Ta.sub.2/3)O.sub.3 -base and Ba(Mg.sub.1/3, Ta.sub.2/3)O.sub.3 -base ceramics have been known. For instance, Japanese Patent Publication No. 59-48484 describe ceramics of a particularly high unloaded Q-value having ingredients BaO, ZnO and Ta.sub.2 O.sub.5. Furthermore, it has been reported that addition of a small amount of SiO.sub.2 to Ba(Zn.sub.1/3, Ta.sub.2/3)O.sub.3 -Ba(Zn.sub.1/3, Nb.sub.2/3)O.sub.3 -base ceramics is effective in facilitating sintering and enhancing the Q-value (refer to "Material", Vol. 43 (1994), No. 489, 629.about.634 pp).
For the ceramic dielectrics, it is required that the relative dielectric constant (.di-elect cons..sub.r) and the unloaded Q-value are large and the temperature coefficient of resonant frequency (.tau..sub.f) is nearly equal to zero. However, no ceramic dielectric capable of satisfying all of the characteristics has as yet been developed. Also, in the Ba(Zn.sub.1/3, Ta.sub.2/3)O.sub.3 -base or Ba(Mg.sub.1/3, Ta.sub.2/3)O.sub.3 -base ceramics, miniaturizing of components is difficult since the relative dielectric constant (.di-elect cons..sub.r) is as low as 27 or less yet the Q-value is large. Furthermore, a satisfactory sintering is obtained by a process, which is strictly controlled and follows certain conditions, for example, sintering a specimen while placing it on a platinum plate in a magnesia crucible. Other ceramics are also having problems involving poor sintererability at high temperatures. Stable characteristics can not be easily achieved due to the varying conditions of the sintering.
The present invention has been accomplished for overcoming the foregoing problems and providing easy sinterable ceramic dielectrics, capable of satisfying all the characteristics required for ceramic dielectrics for high frequency, as well as, methods of forming them. A specific object of the present invention is to provide ceramic dielectrics that have a high Q-value, relative dielectric constant (.di-elect cons..sub.r) as high as 25 or more which is not attainable in existent materials c
REFERENCES:
patent: 5484753 (1996-01-01), Kagata et al.
patent: 5525562 (1996-06-01), Kagata et al.
patent: 5629252 (1997-05-01), Nishimoto et al.
"Preparation and Dielectric Properties of Ba(Zn1/3 Ta2/3)03-Ba(Zn1/3 Nb2/3)03 Ceramics Modified with Certain Additives," Ohuchi et al., J. Soc. Mat. Sci., Japan, vol. 43, No. 489, pp. 629-634, Jun. 1994.
Koga Akihiro
Takada Takahiro
Jones Deborah
Sumitomo Metal Industries Ltd.
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