Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2000-01-13
2001-12-18
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S311000, C361S313000, C361S321100
Reexamination Certificate
active
06331932
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to monolithic ceramic capacitors suitable for miniaturization and achievement of large capacitance. In particular, the present invention relates to a monolithic ceramic capacitor comprising a ceramic sintered compact having a core-shell structure.
2. Description of the Related Art
Monolithic ceramic capacitors comprising sintered compacts having core-shell structures using barium-titanate-based ferroelectric materials are known. In a ceramic sintered compact having a core-shell structure, a core particle composed of barium-titanate-based ferroelectric ceramic is surrounded by a shell layer composed of a dielectric material having a dielectric constant which is lower than that of the barium titanate. In the production of the ceramic sintered compact having the core-shell structure, ceramic core materials such as TiO
3
and BaCO
3
in a given formulation are mixed and calcined. The calcined mixture is pulverized. The resulting powder is mixed with materials for forming a shell, e.g., an organic binder, a dispersant and water, to form a ceramic slurry. The ceramic slurry is shaped into a ceramic green sheet by, for example, a doctor blade process. On the ceramic green sheet, a conductive paste containing powdered metal, such as Ag, Ag—Pd, Ni or Cu is applied by printing to form internal electrodes.
Plural ceramic green sheets provided with internal electrodes are laminated together. The resulting laminate is pressed in the vertical direction (thickness direction) and is sintered. External electrodes are formed on the two ends of the resulting sintered compact to form a monolithic ceramic capacitor composed of a ceramic sintered compact having a core-shell structure.
The monolithic ceramic capacitor having such a core-shell structure is said to have satisfactory temperature characteristics.
Recently, monolithic ceramic capacitors are required to be further miniaturized and have higher capacitance. In barium-titanate-based monolithic ceramic capacitors having core-shell structures, however, dielectric constants have not been improved as expected. Thus, further miniaturization and higher capacitance in the barium-titanate-based monolithic ceramic capacitors pose significant problems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a monolithic ceramic capacitor of a ceramic sintered compact having a core-shell structure which can achieve further miniaturization and higher capacitance, in addition to superior temperature characteristics.
A monolithic ceramic capacitor in accordance with one aspect of the present invention comprises a sintered ceramic compact having a core-shell structure, comprising cores composed of particulate dielectric ceramic and shells formed on the cores and composed of a material having a dielectric constant lower than that of the dielectric ceramic, at least two internal electrodes arranged in and separated by the ceramic sintered compact so as to overlap in the thickness direction; and at least two external electrodes formed on the outermost faces of the ceramic sintered compact, wherein the area ratio of the cores to the shells lies in a range of 7:3 to 3:7 in a cross-section of the sintered ceramic compact in an arbitrary direction.
Preferably, the particulate dielectric ceramic comprises a particulate barium-titanate-based ceramic.
Preferably, the internal electrodes comprise Ni.
In accordance with another aspect, the invention comprises a sintered ceramic compact for use in forming a monolithic ceramic capacitor, the sintered ceramic comprising a core-shell structure having cores composed of a particulate dielectric ceramic and shells formed on the cores and composed of a material having a dielectric constant lower than that of the dielectric ceramic, the area ratio of the cores to the shells lying in a range of 7:3 to 3:7 in a cross-section of the sintered ceramic compact in an arbitrary direction.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
REFERENCES:
patent: 4652967 (1987-03-01), Sakabe et al.
patent: 5225960 (1993-07-01), Kishi et al.
patent: 5757610 (1998-05-01), Wada et al.
patent: 6058005 (2000-05-01), Matoba et al.
patent: 6233134 (2001-05-01), Sakamoto et al.
patent: 6243254 (2001-04-01), Wada et al.
Kawabata Kazuaki
Kobayashi Fumiyuki
Ueno Yasushi
Yoneda Yasunobu
Dinkins Anthony
Ha Nguyen Thuc
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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