Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2000-04-28
2001-12-18
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S308100, C361S309000, C361S303000
Reexamination Certificate
active
06331930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer capacitor, and more particularly, the present invention relates to a multilayer capacitor that can be advantageously used in a high frequency circuit. The invention also relates to an electronic device that is configured using the aforementioned multilayer capacitor.
2. Description of the Related Art
A multilayer capacitor that relates to the present invention is disclosed in, for example, Japanese Unexamined Utility Model Publication No. 49-127736. The multilayer capacitor disclosed therein has a structure that allows residual inductance to be reduced so as to be suitable for the use with high frequencies.
More specifically, the conventional multilayer capacitor has a rectangular capacitor body which has an overall dimension defined by a lengthwise dimension and a widthwise dimension that is smaller than the lengthwise dimension, and a heightwise dimension. End surface terminal electrodes are individually disposed on two end surfaces of the capacitor body. The end surfaces oppose each other and are individually defined by the widthwise dimension and the heightwise dimension of the capacitor body.
Also, a first inner electrode and a second inner electrode are provided in the capacitor body via dielectric layers. The first inner electrode extends so as to connect the two end surfaces of the capacitor body, thereby being electrically connected to the aforementioned end surface terminal electrodes at end sections thereof. On the other hand, the second inner electrode extends so as to connect two side surfaces, thereby being electrically connected to the aforementioned side surface terminal electrodes at end sections thereof.
Thus, the multilayer capacitor disclosed in the aforementioned publication has four terminal electrodes on two end surfaces and two side surfaces. Therefore, the residual inductance can be reduced to be less than the residual inductance in the case of a typical conventional multilayer capacitor that has only two terminal electrodes. However, electronic circuits that use the aforementioned multilayer capacitor having four terminal electrodes are still required to be used in higher frequency bands. To meet this requirement, the residual inductance, that is, equivalent serial inductance (ESL), must be reduced even more.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a multilayer capacitor that is constructed and arranged so as to minimize the ESL.
In addition, preferred embodiments of the present invention provide an electronic device and a high frequency circuit that include the multilayer capacitor described in the preceding paragraph.
According to one preferred embodiment of the present invention, a multilayer capacitor includes a capacitor body that has a shape defined by a lengthwise dimension, a widthwise dimension, and a heightwise dimension, first and second main surfaces that oppose each other and are individually defined by the lengthwise dimension and the widthwise dimension, first and second side surfaces that oppose each other and are individually defined by the lengthwise dimension and the heightwise dimension, and first and second end surfaces that oppose each other and are individually defined by the widthwise dimension and the heightwise dimension.
The capacitor body includes a plurality of dielectric layers extending toward the main surfaces, and at least one pair of first and second inner electrodes that oppose each other via the dielectric layers so that a capacitor unit is formed.
The first inner electrode extends so as to connect the first and second end surfaces, and the second inner electrode extends so as to connect the first and second side surfaces.
Also, first and second end surface terminal electrodes electrically connected to individual ends of the first inner electrode are provided on the first and second end surfaces, respectively, and first and second side surface terminal electrodes electrically connected to individual ends of the second inner electrode are provided on the first and second side surfaces, respectively.
In the multilayer capacitor configured as above, it was discovered that the ESL is minimized if the lengthwise dimension and the widthwise dimension are substantially the same.
Although it was discovered that the ESL can be minimized when the lengthwise dimension and the widthwise dimension are substantially the same, during manufacture of multilayer capacitors, it is relatively difficult to stably obtain capacitor bodies that have the lengthwise dimension and the widthwise dimension that are identical to each other without dimensional variations being produced.
Therefore, according to the present invention, an appropriate range of ratios of the lengthwise dimension and the widthwise dimension is provided. As a result, the ESL can be reliably minimized even when the lengthwise dimension and the widthwise dimension are not exactly the same. According to preferred embodiments of the present invention, the widthwise dimension of the capacitor body is preferably within a range of about 0.9 to about 1.1 times of the lengthwise dimension.
According to the unique structure and arrangement of preferred embodiments of the present invention, magnetic fluxes induced by current that flows in the multilayer capacitor effectively cancel each other, thereby minimizing the ESL. This allows resonant frequencies in the multilayer capacitor to be greatly increased. Therefore, a frequency range that functions in the multilayer capacitor is increased. Consequently, the multilayer capacitor is very well suited for use in high-frequency electronic circuits.
Also, according to preferred embodiments of the present invention, as a preferable ratio of the lengthwise dimension and the widthwise dimension, not only one specific value, but the range of values, that is, about 0.9 to about 1.1, is preferred. Therefore, during manufacture of the capacitor body of the multilayer capacitor, problems with dimensional variations are eliminated.
Also, in preferred embodiments of the present invention, it is preferable that individual widths of the first and second inner electrodes are substantially uniform. In this case, the lengthwise dimension and the widthwise dimension are arranged either to be the same or substantially to be the same. In addition, the terminal electrodes are individually provided on two end surfaces and two side surfaces, each of the individual terminal electrodes is connected to at least one of ends of the inner electrodes. Therefore, directional characteristics with respect to the length direction and the width direction can be substantially disregarded. This allows the multilayer capacitor to be easily handled and mounted since the component does not have any directionality can be picked up, moved and mounted without regard for positional orientation.
Also, when the individual widths of the first and second inner electrodes are substantially the same, the dimensions of four portions where the inner electrodes do not overlap with each other can be arranged substantially to be the same. Therefore, magnetic fluxes induced by current that flows in the portions where the inner electrodes do not overlap with each other can be set off, thereby allowing further reduction in the ESL to be implemented.
Also, as described above, when the individual widths of the inner electrodes are substantially the same, that is, when the inner electrodes do not form angles in peripheral edge portions, electric-field concentration does not occur easily. Therefore, the dielectric strength of the multilayer capacitor is greatly improved.
Also, it is preferable that the lengthwise dimension and the widthwise dimension of the capacitor body are determined to be within a range of about 1.5 to about 4.0 mm. In this case, it is more preferable that widths of the first and second inner electrodes are determined to be within a range of about 0.9 to about 2.5 mm. In this case, the
Asakura Kyoshin
Hori Haruo
Kondo Takanori
Kuroda Yoichi
Naito Yasuyuki
Dinkins Anthony
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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