The present invention relates to a capacitor and a method of manufacturing the capacitor, and specifically to a capacitor improved in capacitance and breakdown voltage resistance and a method of manufacturing the capacitor.
As a technique to make a capacitor high in ratings and capacitance, there is known, for example, the laminated ceramic capacitor described in Japanese Patent Laid-Open No. 7-263270 (Patent Literature 1). FIG. 4 illustrates a cross section of this laminated ceramic capacitor. As illustrated in the figure, a ceramic laminated body 900 includes a lead-out electrode 910 connected to an external electrode 920; and a lead-out electrode 912 formed in the same layer as the lead-out electrode 910 and connected to the external electrode 920. The same lead-out electrodes as the lead-out electrodes 910 and 912 are also formed in other layers.
A floating electrode 930 is formed between the layer in which the lead-out electrodes 910 and 912 are formed and a layer located below that layer. A unitary capacitor unit 940 is formed of this floating electrode 930 and the lead-out electrode 910, and a unitary capacitor unit 942 is formed of the floating electrode 930 and the lead-out electrode 912. As described above, the unitary capacitor units 940 and 942 are connected in series between the external electrode 920 and an external electrode 922. The same floating electrodes as the floating electrode 930 are also formed between other layers. As described above, in the ceramic laminated body 900, laminated capacitors formed of a plurality of lead-out electrodes and a plurality of floating electrodes are connected in series between the external electrodes. The ceramic laminated body 900 is said to be able to improve voltage resistance while suppressing the occurrence of surface leakage.
Patent Literature 1: Japanese Patent Laid-Open No. 7-263270
In the ceramic laminated body 900 described in Patent Literature 1, however, the number of laminated electrodes, when viewed in the laminating direction of the electrodes (latitudinal direction in
Al electrolytic capacitors and laminated ceramic capacitors have been in widespread use. An Al electrolytic capacitor uses an electrolytic solution, and therefore, has the problem of liquid leakage. A process for manufacturing a laminated ceramic capacitor requires calcination, and therefore, the capacitor has the problem that thermal contraction between an electrode and a dielectric material occurs in a calcination process. As a technology to cope with these problems, a capacitor based on porous Al2O3 has been proposed recently (see, for example, Japanese Patent Laid-Open No. 2009-88034). The present inventors have found that there is the possibility of being able to remedy such failures as the occurrence of cracks in the above-described capacitor of lamination type by utilizing the porous capacitor described above.
According to one embodiment of the present invention, there is provided a capacitor that can have an improved capacitance value without sacrificing a dielectric breakdown voltage and a method for manufacturing the capacitor, as well as a capacitor that can have an improved dielectric breakdown voltage without sacrificing the capacitance value and a method for manufacturing the capacitor.
A capacitor according to one embodiment of the present invention is provided with a dielectric layer including first and second principal surfaces formed substantially parallel to each other and a plurality of holes formed so as to be substantially orthogonal to the first and second principal surfaces; a plurality of columnar electrodes formed by filling a conductive material into the plurality of holes; a first external electrode formed on the first principal surface of the dielectric layer, so as to electrically conduct to some of the plurality of columnar electrodes; and a second external electrode formed on the second principal surface of the dielectric layer, so as to electrically conduct to the others of the plurality of columnar electrodes, the others of the plurality of columnar electrodesnot being electrically conductive to the first external electrode, wherein at least one of the first and second external electrodes is composed of a plurality of electrical conductor units electrically isolated from each other.
A capacitor manufacturing method according to one embodiment of the present invention includes the steps of: preparing a base material for valve metal including first and second principal surfaces formed substantially parallel to each other; anodizing the base material to form a dielectric layer in which a plurality of holes substantially orthogonal to the first and second principal surfaces is formed; filling a conductive material into the plurality of holes in the dielectric layer to form a plurality of columnar electrodes; forming, on the first principal surface, a first external electrode electrically conductive to some of the plurality of columnar electrodes; and forming, on the second principal surface, a second external electrode electrically conductive to the others of the plurality of columnar electrodes, the others of the plurality of columnar electrodes not being electrically conductive to the first external electrode, wherein at least one of the first and second external electrodes is formed so as to be electrically isolated from each other.
Objects, features, and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.
According to one embodiment of the present invention, there is provided a capacitor that can have an improved capacitance value while maintaining a required dielectric breakdown voltage and a method for manufacturing the capacitor, as well as a capacitor that can have an improved dielectric breakdown voltage while maintaining a required capacitance value and a method for manufacturing the capacitor.
This application claims the right of priority based on Japanese Patent Application No. 2010-150018, titled “Capacitor and Method for Manufacturing Same” and filed on Jun. 30, 2010, the content of which is incorporated herein by reference in its entirety. Hereinafter, a description will be given of modes for carrying out the present invention.
The structure of a capacitor according to one embodiment of the present invention will be described with reference to
Each columnar electrode 16 is formed so as to be substantially orthogonal to one principal surface 14A of the dielectric layer 14. A first external electrode 18 is formed on this principal surface 14A. The first external electrode 18 is electrically connected to some of the multitude of columnar electrodes 16. In one embodiment, columnar electrodes 16 electrically conductive to the first external electrode 18 function as negative electrodes. Second external electrodes 20A and 20B are formed on the other principal surface 14B of the dielectric layer 14. These second external electrodes 20A and 20B are electrically connected to the others of the columnar electrodes 16, which are not electrically conductive to the first external electrode 18. In one embodiment, columnar electrodes 16 electrically conductive to the second external electrodes 20A and 20B function as positive electrodes. Some of the columnar electrodes 16 (for example, columnar electrodes 16 to function as negative electrodes) and the second external electrodes 20A and 20B are insulated from each other by an insulating cap 24, and the remaining columnar electrodes 16 (for example, columnar electrodes 16 to function as positive electrodes) and the first external electrode 18 are insulated from each other by an insulating cap 22. The second external electrodes 20A and 20B are formed so as to be electrically isolated from each other on the principal surface 14B of the dielectric layer. Consequently, the capacitor 10 has a structure in which capacitance-generating portions of the capacitor are serially connected in two stages as equivalent circuits. The second external electrodes 20A and 20B are connected to external terminals 26 and 28, respectively. In addition, the first external electrode 18 is covered with a protective layer 30. Likewise, the second external electrodes 20A and 20B, except portions thereof on which the external terminals 26 and 28 are provided, are covered with a protective layer 32.
An oxide of valve metal (Al, Ta, Nb, Ti, Zr, Hf, Zn, W, Sb, or the like), for example, is used as the material of the dielectric layer 14. The external electrodes 18, 20A and 20B and the external terminals 26 and 28 are composed of, for example, metal such as Cu, Ni, Cr, Ag, Au, Pd, Fe, Sn, Pb, Pt, Ir, Rh, Ru or Al, solder made therefrom, and/or a material formed by laminating these types of metal or solder. Platable metal, such as Cu, Ni, Co, Cr, Ag, Au, Pd, Fe, Sn, Pb or Pt, and/or an alloy thereof, for example, is used as the material of the columnar electrodes 16. The insulating caps 22 and 24 are composed of, for example, an oxide of valve metal, such as Al, Ta, Nb, Ti, Zr, Hf, Zn, W or Sb, an air gap, electrodeposited resin, such as polyimide, epoxy or acrylic, electrodeposited TiO2, or electrodeposited SiO2. The protective layers 30 and 32 are composed of, for example, SiO2, SiN, resin, or metal oxide.
The distance between the first external electrode 18 and each of the second external electrodes 20A and 20B (i.e., the thickness of the dielectric layer 14) is, for example, several 100 nm to several 100 μm, and the thicknesses of the first external electrode 18 and the second external electrodes 20A and 20B are, for example, several 10 nm to several The columnar electrodes 16 are formed so that the diameter thereof is, for example, approximately several 10 nm to several 100 nm, the length thereof is, for example, approximately several 100 nm to several 100 μm, and the distance between adjacent columnar electrodes 16 is, for example, approximately several 10 nm to several 100 nm. The insulating caps 22 and 24 are formed so that the thickness thereof is, for example, several 10 nm to several 10 μm. The protective layers 30 and 32 are formed so that the thickness thereof is, for example, several 10 nm to several 10 μm.
Next, one example of a method for manufacturing the capacitor 10 according to one embodiment of the present invention will be described with reference to
In one embodiment, the first-stage anodization treatment illustrated in
Next, the bare metal portions of the metal base material 50 (portions not oxidized by anodization treatment) are removed as illustrated in
Next, the seed layer 58 is removed and the dielectric layer 14 is cut off at a position shown by a dotted line (near the upper end of each second hole 56), as illustrated in
Next, as illustrated in
If Al is used as the metal base material 50, Al is anodized and a porous dielectric layer 14 made of porous Al2O3 is obtained. This porous dielectric layer 14 includes a multitude of cells substantially hexagonal in cross-sectional view (a circular cell is shown by a dotted line, however, in
Next, a comparative example will be described with reference to
Next, a description will be given of the capacitance and dielectric breakdown voltage of a capacitor according to one embodiment of the present invention. As described above, in the capacitor according to one embodiment of the present invention, the thickness of the dielectric layer of a unit capacitor (configured into a columnar electrode-dielectric layer-columnar electrode structure) composing the capacitor varies according to the anodization voltage used in the first-stage anodization treatment. Accordingly, the capacitance and dielectric breakdown voltage of the capacitor depend on the anodization voltage used in the first-stage anodization treatment. For example, the dielectric thickness (the thickness of a portion of the dielectric layer 14 present between columnar electrodes 16) of the capacitor manufactured by performing the first-stage anodization treatment using an anodization voltage half the anodization voltage used in the manufacture of the capacitor 100 of the comparative example is half the dielectric thickness of the capacitor 100 of the comparative example. Accordingly, the capacitance of the capacitor is doubled and the dielectric breakdown voltage thereof is halved. In addition, since the cell size (refers to the size of a cell in plan view, and D1 in
Serially connecting capacitors (may in some cases be referred to as “element capacitors” in the present specification) manufactured using an anodization voltage half the anodization voltage used in the manufacture of the capacitor 100 of the comparative example in two stages causes the combined capacitance of the series-connected capacitors to be 4 times (8 times×½) the capacitance of the capacitor 100 of the comparative example and the total volume of the capacitors to be twice the volume of the capacitor 100 of the comparative example. In order to prevent volume increase due to series connection, the volume of element capacitors to be connected should be set to half the volume of the capacitor 100 of the comparative example. Since the capacitance of each element capacitor is proportional to the volume thereof, the capacitance of element capacitors obtained by serially connecting the capacitors each having a volume half the volume of the capacitor 100 of the comparative example in two stages is twice the capacitance of the capacitor 100 of the comparative example 2 (4 times×½). As described above, a capacitor the same in volume as the capacitor 100 of the comparative example but having capacitance twice the capacitance thereof can be obtained by serially connecting, in two stages, the element capacitors manufactured using an anodization voltage half the anodization voltage used in the manufacture of the capacitor 100 of the comparative example. In addition, since a voltage applied to each element capacitor of the series-connected capacitors is half the full voltage, each capacitor in which element capacitors are serially connected has the same dielectric breakdown resistance as the capacitor 100 of the comparative example. As described above, a capacitor having the same dielectric breakdown resistance as the capacitor 100 of the comparative example and capacitance twice the capacitance thereof can be obtained, while maintaining the same volume as that of the capacitor 100, by serially connecting, in two stages, the element capacitors manufactured using an anodization voltage half the anodization voltage used in the manufacture of the capacitor 100 of the comparative example.
Advantageous effects of the present invention were verified using the capacitor 100 of the comparative example as a reference. The capacitor 100 of the comparative example was formed by setting an anodization voltage used in the first-stage anodization treatment to 40 V, so that the size of the capacitor was 1 mm×0.5 mm×0.1 mm. The capacitance value of this capacitor 100 was 0.5 μF and the dielectric breakdown voltage thereof was 10 V. On the other hand, the capacitance value of the capacitor 10 according to one embodiment of the present invention configured by serially connecting element capacitors formed at the first-stage anodization voltage of 20 V in two stages was 1 μF, and the dielectric breakdown voltage of the capacitor was 10 V. As described above, it was confirmed that the capacitor 10 according to one embodiment of the present invention had capacitance twice as large as that of the capacitor 100 of the comparative example, while maintaining the same volume and the same dielectric breakdown resistance as those of the capacitor 100.
The capacitance value of the capacitor 10A according to another embodiment of the present invention configured by serially connecting element capacitors formed at a first-stage anodization voltage of 10 V in eight stages was 0.5 μF, and the dielectric breakdown voltage of the capacitor was 20 V. As described above, it was confirmed that the capacitor 10A according to another embodiment of the present invention had dielectric breakdown voltage twice as large as that of the capacitor 100 of the comparative example, while maintaining the same volume and the same capacitance as those of the capacitor 100.
By applying an even number of stages of series connection as in the capacitors 10 and 10A, the two external terminals 26 and 28 can be formed on the same surface. In addition, an element structure including one each of the external terminals 26 and 28 on the front and rear surfaces, respectively, can be easily attained by adopting a series-connected structure composed of an odd number of stages, though not illustrated, as in the capacitors 10 and 10A. As described above, an external terminal can be provided on a front or rear surface of an element in the case of the capacitors 10 and 10A. Consequently, a mounting area can be made smaller, compared with a laminated ceramic capacitor in which an external terminal has to be provided on a side surface thereof.
As described above, according to capacitors in accordance with various embodiments of the present invention, the capacitance value of a capacitor can be improved without sacrificing dielectric breakdown resistance or the dielectric breakdown resistance can be improved without sacrificing the capacitance value. In the capacitors in accordance with various embodiments of the present invention, a capacitance value and a rated voltage can be easily adjusted by adjusting the anodization voltage and/or the number of stages of series connection. For example, in the capacitors in accordance with various embodiments of the present invention, the capacitance value can be increased and the rated voltage can be decreased, or the capacitance value can be decreased and the rated voltage can be increased through the adjustment of the anodization voltage and/or the number of stages of series connection. In the capacitors in accordance with various embodiments of the present invention, both of two external terminals can be provided on the front surface, or one each of the external terminals can be respectively provided on the front and rear surfaces according to the embodiment of the capacitor in question. In the capacitors in accordance with various embodiments of the present invention, the occurrence of cracks can be prevented by a columnar electrode structure obtained by anodizing valve metal, when compared with such a planar electrode structure as that of a conventional laminated ceramic capacitor. In addition, the capacitors of the present invention are easy to manufacture.
Note that the present invention is not limited to the above-described embodiments, but may be modified in various other ways without departing from the gist of the invention. For example, the shapes and dimensions shown in the present specification are illustrative only and may be modified as appropriate. The materials shown in the present specification are also illustrative only, and various heretofore-known materials may be used instead. For example, various heretofore-known types of anodizable metal may be used, in addition to Al, as the metal base material 50 used to form the dielectric layer 14. The anodization voltages and the numbers of (numbers of stages of) element capacitors to be serially connected shown in the present specification are also illustrative only. Alternatively, an anodization voltage and the number of stages may be adjusted so as to satisfy capacitance and rated voltage requirements. The electrode lead-out structures shown in the present specification are also illustrative only, but may be design-changed as appropriate. The manufacturing processes shown in the present specification are also illustrative only, but may be modified as appropriate. For example, either the first external electrode 18 or the second external electrodes 20A and 20B may be formed first.
According to capacitors in accordance with various embodiments of the present invention, there are provided a capacitor that can have an improved capacitance value without sacrificing a dielectric breakdown voltage and a method for manufacturing the capacitor, or a capacitor that can have an improved the dielectric breakdown voltage without sacrificing the capacitance value and a method for manufacturing the capacitor.
10, 10A: Capacitor
12, 12A: Capacitor element
14: Dielectric layer
14A, 14B: Principal surface
16: Columnar electrode
16A, 16B: End
18, 18A to 18D: First external electrode
20, 20A to 20E: Second external electrode
22, 24: Insulating cap
26, 28: External terminal
30, 32: Protective layer
50: Metal base material
52: First hole
54: Oxide base material
56: Second hole
58: Seed layer
100: Capacitor
102: Capacitor element
104: Connection land
106: Connecting conductor
900: Ceramic laminated body
910, 912: Lead-out electrode
920, 922: External electrode
930: Floating electrode
940, 942: Unitary capacitor unit
Number | Date | Country | Kind |
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2010-150018 | Jun 2010 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2011/062048 | 5/26/2011 | WO | 00 | 2/28/2013 |