Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2001-04-17
2003-04-15
Brunsman, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S137000
Reexamination Certificate
active
06548437
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to dielectric ceramics containing barium titanate as a main component and an electronic component comprising a dielectric layer containing the dielectric ceramics.
2. Description of the Related Art
In recent years, electronic equipment has rapidly advanced in size reduction because of sophistication of ICs (integrated circuits), LSIs (large scale integrated circuits) and so on. With the advance in size reduction, a capacitor that is an electronic component is also advancing in size reduction, and thus demand for a multilayer capacitor is growing sharply. For example, known is a multilayer capacitor comprising a capacitor element having dielectric layers interleaved with inner electrodes and terminal electrodes formed in the capacitor element. For example, the multilayer capacitor requires flatness in temperature coefficient of capacitance in a wide range of temperatures between −55° C. and 125° C. or 150° C., prevention of deterioration in insulation resistance (IR) resulting from the use of the capacitor at high temperature, and so on.
Characteristics of the multilayer capacitor depend greatly on characteristics of dielectric ceramics constituting the dielectric layer. For example, dielectric ceramics containing barium titanate as a main component have been heretofore known as dielectric ceramics having a high dielectric constant, but dielectric ceramics whose temperature coefficient of capacitance have been flattened by adding various auxiliary components to barium titanate have been recently developed. As the above-mentioned dielectric ceramics, reported are, for example, dielectric ceramics having a nonuniform structure in which additives are partly diffused in crystal particles of barium titanate (see Key Engineering Materials Vols. 157-158 (1999), pp. 17-24), dielectric ceramics having a double particle structure generally called a core shell structure in which a diffusion region of additives is formed on the outer periphery of crystal particles of barium titanate (see Key Engineering Materials Vols. 157-158 (1999), pp. 9-16), and the like.
Methods of synthesizing barium titanate powders constituting the dielectric ceramics include, for example, solid phase method, oxalate process, coprecipitation method, alkoxide process, hydrothermal synthesis, and so on. However, barium titanate powders having a smaller particle diameter have been recently sought so as to make a multilayer capacitor increasingly thinner and more multilayered for a smaller size and a larger capacity. Therefore, barium titanate powders synthesized by hydrothermal synthesis capable of obtaining powders having a smaller particle diameter have been heretofore used.
However, it is reported that, when barium titanate powders are synthesized by hydrothermal synthesis, the entry of hydrogen ions (H+) during synthesis causes vacancies of barium (Ba) or titanium (Ti) (see Journal of the Korean Physical Society Vol. 32, February 1998, pp. S260-264, and Journal of the European Ceramic Society 9 (1992), pp. 41-46). Furthermore, these literatures teach that the use of barium titanate powders synthesized by hydrothermal synthesis causes migration of defects during heat treatment and during sintering and thus causes creation of voids, which have an influence upon crystallizability and dielectric properties of barium titanate of dielectric ceramics. By performing experiments, the inventor obtained the result that, when barium titanate powders synthesized by hydrothermal synthesis were used, the longevity of insulation resistance under load at high temperature, i.e., the so-called lifetime of IR degradation was short.
SUMMARY OF THE INVENTION
The invention is designed to overcome the foregoing problems. It is an object of the invention to provide dielectric ceramics capable of enhancing the lifetime of IR degradation, and an electronic component using the dielectric ceramics.
Dielectric ceramics of the invention contain: barium titanate for acting as a main component; a first auxiliary component containing at least one element in a group consisting of magnesium (Mg), calcium (Ca), barium, strontium (Sr) and chromium (Cr); a second auxiliary component containing silicon oxide; a third auxiliary component containing at least one element in a group consisting of vanadium (V), molybdenum (Mo) and tungsten (W); and a fourth auxiliary component containing at least one element in a group consisting of erbium (Er), thulium (Tm), ytterbium (Yb), yttrium (Y), dysprosium (Dy) and holmium (Ho), wherein the rate of existence of crystal particles having voids is 10% or lower in terms of the count rate.
In the dielectric ceramics of the invention, the rate of existence of crystal particles having voids is 10% or lower in terms of the count rate, and, thus, little deterioration in insulation resistance occurs at high temperature.
Preferably, in the dielectric ceramics of the invention, an average crystal particle diameter is more than 0.1 &mgr;m and not more than 0.7 &mgr;m. This more effectively prevents deterioration in insulation resistance at high temperature.
Preferably, the second auxiliary component further contains at least one oxide in a group consisting of barium, calcium, strontium, magnesium, lithium (Li) and boron (B), and the second auxiliary component functions as a sintering assistant, for example.
Preferably, the dielectric ceramics of the invention are made by using, as a raw material, barium titanate powders synthesized by oxalate process or solid phase method. This facilitates reducing the rate of existence of crystal particles having voids to 10% or lower in terms of the count rate and thus facilitates preventing deterioration in insulation resistance at high temperature.
Preferably, the dielectric ceramics of the invention are made by using, as a raw material, barium titanate powders having an average particle diameter of not less than 0.1 &mgr;m and less than 0.7 &mgr;m or barium titanate powders having a barium-to-titanium compositional ratio (Ba/Ti) of more than 1 and less than 1.007. This allows the dielectric ceramics to have an average crystal particle diameter of a predetermined size and thus more effectively prevents deterioration in insulation resistance at high temperature.
An electronic component of the invention comprises a dielectric layer containing the dielectric ceramics of the invention.
Other and further objects, features and advantages of the invention will appear more fully from the following description.
REFERENCES:
patent: 6226172 (2001-05-01), Sato et al.
patent: 6335302 (2002-01-01), Satoh et al.
patent: 6403513 (2002-06-01), Sato et al.
patent: 6407024 (2002-06-01), Satoh et al.
patent: A 60-81023 (1985-05-01), None
patent: 05-109318 (1993-04-01), None
patent: 06-333780 (1994-12-01), None
patent: 11-154620 (1999-06-01), None
patent: A 11-255560 (1999-09-01), None
patent: 2000026160 (2000-01-01), None
patent: 2000034166 (2000-02-01), None
patent: 2000154055 (2000-06-01), None
patent: 2000154057 (2000-06-01), None
patent: 2000169226 (2000-06-01), None
patent: 2000185969 (2000-07-01), None
patent: 2001031467 (2001-02-01), None
Effects of the Microstructure on Dielectric Properties for BaTiO3-Based MLC with Ni Electrode by Y. Okino et al of Taiyo Yuden Co., Ltd., Key Engineering Materials vols. 157-158 (1999) no month provided. pp. 9-16.
A Study on Capacitance Aging in Ni-Electrode, BaTiO3-Based MLCCs with X7R Characteristics by S. Sato et al of TDK Corporation, Key Engineering Materials vols. 157-158 (1999) no month provided. pp. 17-24.
Grain Size Effects on Dielectric Properties and Crystal Structure of Fine-grained BaTiO3Ceramics by Y. Sakabe et al. of Murata Mfg. Co. Ltd., Journal of the Korean Physical Society, vol. 32, (Feb. 1998), pp. S260-264.
Characterization of Hydrothermal Barium Titanate by Detlev Hennings & Seriyati Schreinemacher, Journal of the European Ceramic Society 9 (1992) no month provided. 41-16.
Method and process for producing barium titanate and its composite particle by Kyoichi S
Fujikawa Yoshinori
Sato Shigeki
Terada Yoshihiro
Brunsman David
Oliff & Berridg,e PLC
TDK Corporation
LandOfFree
Dielectric ceramics and electronic component does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dielectric ceramics and electronic component, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dielectric ceramics and electronic component will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3088276