Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Patent
1985-06-19
1986-10-07
McCarthy, Helen M.
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
361320, 501137, 501138, 501139, C04B 3546, H01G 412
Patent
active
046162895
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
TECHNICAL FIELD
The present invention relates to ceramic high dielectric composition to be used mainly as laminated ceramic capacitor.
BACKGROUND ART
Hitherto many proposals have been made on ceramic high dielectric compositions with barium titanate (BaTiO.sub.3) as host material, and they have been used specially for disc type ceramic capacitors.
The barium titanate is a material having ferrodielectric characteristic, and its Curie point lies around 120.degree. C. Demarcated by this 120.degree. C., in the lower temperature side thereof it becomes tetragonal, and in the upper temperature side thereof it becomes cubic. And it is well known that in the tetragonal region it shows ferrodielectric characteristics and in the cubic region it shows paraelectric characteristics.
Since a ceramic material consisting solely of barium titanate has a very large change of dielectric constant dependent on temperature and also has a large dielectric dissipation tan .delta. in a temperature range of about normal temperature, it is seldom used as capacitor by itself and hitherto devices have been made to shift the Curie point to around the normal temperature and to decrease the temperature dependency by adding various additives. CaTiO.sub.3, BaZrO.sub.3, SrTiO.sub.3, BaSnO.sub.3 and etc. are known as representative of the additives. By adding these appropriately and by adjusting with a small amount of composition, materials having characteristics of X7R, Y5T, Y5V, Z4V and etc. of EIA (Electric Industries Association) standard are offered. The fact is that these materials have been hitherto utilized generally as ceramic capacitors of the thick disc type, for instance having 0.5-1 mm thickness of element.
During these years, miniaturization of capacitors is progressing corresponding to miniaturization of various electronics-related components, and the most in laminated ceramic capacitors. The laminated layer ceramic capacitor is one in which ceramic dielectric body is made into thin film of around 25-100 .mu.m and is sandwiching comb type electrodes to form a multiple layer structure. And since the ratio of the electrodes area to the electrodes gap can be made very large, its capacitance per volume can be made as large as 100 times or larger in comparison with the ceramic disc type capacitor, and the same capacitance can be assured with a volume as small as 1/10 or less, and therefore much miniaturization is easy.
When such a ceramic dielectric thin film is used, however, it is the fact that conventional disc type ceramic composition can not be used as it is. That is, since a voltage per unit length is loaded 10 times or more than the conventional case, a material having small voltage-dependencies of ceramic dielectric constant and small dissipation factor have become to be needed. Besides, due to a recent adoption of direct bonding system onto printed circuit board, such a strong material as is not destroyed by bending of the printed circuit board is needed. Further, since in electronics tuner or the like using the laminated ceramic capacitors, the frequencies are shifting to higher band of high sensitivities, those having good high frequency characteristics become necessary also with regard to the laminated ceramic capacitors. Especially, those having the characteristic of YD in JIS (Japanese Industrial standard) or the characteristic of Y5T in EIA standard are requested by a large number of users in relation to an electronic tuner, and those which have a dielectric constant of 3000 or above and tan .delta. of 2.0% or lower and low equivalent series resistance at a frequency band of 1-100 MHz are requested.
DISCLOSURE OF THE INVENTION
Accordingly, the present invention is to provide ceramic high dielectric composition with good high frequency characteristics, having dielectric constant of 3000 or above, small voltage dependency, large bending strength and good high frequency characteristics, by containing as additive 1-5 weight parts of CaTiO.sub.3 and 2-3 weight parts of Ta.sub.2 O.sub.5 to 100 weight
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Itakura Gen
Kuroda Takayuki
Kusakabe Kenji
Ushijima Tadayoshi
Matsushita Electric - Industrial Co., Ltd.
McCarthy Helen M.
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