JP2001155969A - Capacitor and manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitor with one electrode with a low-LC value, a small variation in LC value without decreasing the capacity, or high heat resistance, and provide its manufacturing method. SOLUTION: In this manufacturing method, a dielectric made of niobium oxide is formed on an electrode of a capacitor. When electrolytic oxidation is carried out with on electrode as an anode in an electrolytic solution, the electrolytic oxidation is started with a constant current which is initially not less than 200 mA per weight of the electrode, and continued with constant voltage to form the dielectric.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor and a method for manufacturing the same, and more particularly to a capacitor having a low leakage current (hereinafter abbreviated as "LC") value or a small variation thereof without lowering the capacity, or having a good heat resistance. And a method of manufacturing the same.

[0002]

2. Description of the Related Art Capacitors used in electronic devices such as cellular phones and personal computers are desired to be small in size and large in capacity. Among such capacitors, a tantalum electrolytic capacitor is preferably used because of its large capacity and good performance for its size. Normally, tantalum oxide is used as a dielectric of a tantalum electrolytic capacitor, but in order to further increase the capacity, a niobium electrolytic capacitor using a niobium oxide having a larger dielectric constant as a dielectric has been studied.

[0003]

The capacity of a niobium electrolytic capacitor using a niobium dielectric obtained by a conventional method in which electrolytic oxidation is performed in an electrolytic solution using one electrode made of niobium as an anode is large. In some cases, the value may be large, or the variation may be large, or the heat resistance may be insufficient, and further improvement in reliability is required.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a capacitor having a low LC value or a small variation without lowering the capacity or having a good heat resistance and a method of manufacturing the same. To provide.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the present inventors have found that the use of a unique electrolytic oxidation method as a manufacturing method for forming a niobium oxide dielectric material allows the above-mentioned problems to be solved. The inventors have found that the problem can be solved, and have completed the present invention. 1) According to a first aspect of the present invention, there is provided an electrode comprising two electrodes and at least a dielectric interposed therebetween, wherein one of the electrodes is made of niobium and the dielectric is made of the niobium. In the method of manufacturing a capacitor made of niobium oxide formed above, when performing electrolytic oxidation in an electrolytic solution using one electrode made of niobium as an anode, an initial current value is set to 2 per weight of one electrode made of niobium.
A method for manufacturing a capacitor, characterized in that electrolytic oxidation is started in a constant current state of not less than 00 [mA], and then electrolytic oxidation is continued at a constant voltage to produce the dielectric. 2) A second invention for solving the above-mentioned problem is the method for producing a capacitor as described in 1) above, wherein niobium of one electrode is partially nitrided. 3) A third invention for solving the above-mentioned problems is the method for producing a capacitor according to the above 2), wherein the nitrogen content of niobium of one electrode is 50 to 150,000 ppm by weight. 4) A fourth invention for solving the above-mentioned problems is characterized in that the electrolytic solution is an aqueous solution comprising phosphoric acid, the concentration of which is 0.01% by weight or more and 5% by weight or less. A method for manufacturing a capacitor according to any one of the preceding claims. 5) The fifth invention for solving the above-mentioned problems is characterized in that the temperature at the time of electrolytic oxidation is 60 ° C. or more, 1) to 4) above.
A method for manufacturing a capacitor according to any one of the preceding claims. 6) A sixth aspect of the present invention for solving the above-mentioned problems is that the structure of one of the electrodes is a sintered body and the CV value is at least 50,000.
[CV / g] or more;
It is a manufacturing method of the capacitor given in any one of 5). 7) A seventh aspect of the present invention for solving the above-mentioned problems is that an electrode is composed of two electrodes and at least a dielectric interposed therebetween, and one of the electrodes is made of niobium, and the dielectric is made of the niobium. In the niobium oxide capacitor formed above, when performing electrolytic oxidation in an electrolytic solution using one niobium electrode as an anode, an initial current value is set to 200 [m / m2] per weight of the one niobium electrode.
A] This is a capacitor having the dielectric formed by starting electrolytic oxidation in the constant current state described above and then continuing electrolytic oxidation at a constant voltage. 8) An eighth invention for solving the above-mentioned problems is the capacitor as described in 7) above, wherein niobium of one of the electrodes is partially nitrided. 9) A ninth invention for solving the above-mentioned problems is that the structure of one of the electrodes is a sintered body and the CV value is at least 50,000.
The capacitor according to the above item 7) or 8), which is not less than [CV / g]. [Operation] The operation of the present invention is not necessarily clear, but can be estimated as follows. Normally, niobium has a higher oxygen affinity than tantalum, so oxygen in the dielectric couple is pulled out to the internal electrode side during the fabrication of the dielectric, but a stable dielectric can be formed by fabricating the dielectric faster than this phenomenon Can be estimated. In other words, it is presumed that a more stable dielectric is formed by a method of forming a dielectric quickly under a constant current state at a value much higher than a current value at which a good dielectric is generally considered to be formed. Furthermore, it is estimated that a high-capacity and more stable dielectric is formed by adjusting the concentration of the electrolytic solution at the time of electrolytic oxidation forming the dielectric and the temperature at the time of electrolytic oxidation forming the dielectric. I have.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment for obtaining a capacitor of the present invention will be described. The niobium forming one electrode used in the method for manufacturing a capacitor of the present invention contains an alloy of niobium, and its shape can be plate-like, foil-like, rod-like, sintered, or the like. The size can be arbitrarily determined in consideration of the capacity of the capacitor to be manufactured. In the case of a foil shape or a rod shape, the surface area per unit volume may be increased by bending, winding, or etching the surface to increase the capacity. 10 ⁰ × After compression molding the, for example a powder of the above-mentioned material the case of producing a sintered body
500 to 2 under conditions of 133 to 10 ^-6 × 133 [Pa]
A method of leaving at 000 ° C. for several minutes to several hours can be used.

A dielectric made of niobium oxide is formed on the surface of the electrode by electrolytic oxidation. In the present invention, the dielectric is formed on the niobium electrode by applying a voltage between the niobium electrode as an anode and a counter electrode separately prepared in an electrolytic solution. Here, a method of electrolytic oxidation for forming a dielectric is as follows. Initially, electrolytic oxidation is started in a constant current state having a much higher value (for example, 10 times or more) than a current value at which a good dielectric is generally considered to be formed. Thereafter, when the voltage reaches a predetermined voltage, electrolytic oxidation is continuously performed in a constant voltage state in which the predetermined voltage is maintained. By performing electrolytic oxidation in this manner, a predetermined voltage is reached in a short time. When an electrode having a dielectric film formed in this manner is used, a leakage current value (hereinafter referred to as “L
C value ". ) Is low or its variation is small,
Alternatively, a capacitor having good heat resistance can be obtained. For example, the constant current value is set to 200 [mA] or more, preferably 400 [m], per one niobium electrode.
A] If the constant current value is less than 200 [mA], it is difficult to obtain a capacitor having a low leakage current value or a small variation thereof, or having good heat resistance.

Conventionally known metals such as tantalum, niobium, platinum and iron nickel alloy can be used as the counter electrode. The above-mentioned predetermined voltage value to be applied can be arbitrarily determined in consideration of the operating voltage and the capacitance value of the capacitor to be manufactured. For example, a capacitor having an operating voltage of 10 V uses an applied voltage of 40 V, and a capacitor having an operating voltage of 6.3 V uses an applied voltage of 20 to 22 V.

As the type of the electrolytic solution, a mineral acid, an organic acid, an aqueous solution using one or more salts of these acids, and a non-aqueous solution using one or more salts of these acids can be used. Particularly, from the viewpoint of practicality such as easiness of work and safety, an aqueous solution containing phosphoric acid is used and its concentration is adjusted to 0.01% by weight or more.
% By weight, more preferably 0.1% by weight or more and 4% by weight or less. 0.01% by weight
If it is less than this, it takes a long time to reach the predetermined voltage,
The effect of the present invention is not likely to be obtained, and it is disadvantageous in terms of production efficiency. If it exceeds 5% by weight, the capacity of the produced capacitor may decrease.

[0010] The electrolysis temperature is preferably at least 60 ° C, more preferably at least 80 ° C. When the temperature is lower than 60 ° C., not only the effect of the operation of the present invention may not be easily obtained, but also the LC value of the manufactured capacitor may vary greatly.

Niobium, one of the electrodes of the present invention, may be partially nitrogenated. From the viewpoint of further lowering the LC value, the amount of nitrogen is 50 to 150,000 weight pp.
m, preferably 100 to 7000 ppm by weight, more preferably 500 to 7000 ppm by weight. As the nitriding method, any one of gas nitriding, liquid nitriding, ion nitriding, gas nitriding, and the like, or a combination thereof can be used.

The gas nitriding treatment by leaving in a nitrogen gas atmosphere is preferable because the apparatus is simple and the operation is easy.
Nitrogenation is performed at a temperature of 2,000 ° C. or less and the time is several tens of hours. Niobium, which is partially nitrided with a desired amount of nitrogen, can be obtained. In general, the higher the temperature, the shorter the required amount of nitrogen can be obtained. If niobium is left in a nitrogen atmosphere for several tens of hours even at room temperature, niobium partially nitrided with a nitrogen content of several hundred ppm by weight can be obtained. In addition, it is possible to shorten the nitriding time by introducing nitrogen under pressure. Conversely, if nitrogen is introduced under reduced pressure, the nitridation time is delayed. For example, even if the niobium is allowed to stand under an extremely reduced pressure such as 0.01 × 133 [Pa], nitriding hardly occurs within an industrial range of several tens of hours.

Furthermore, when the structure of the electrode is a sintered body,
A sintered body is manufactured using niobium, a niobium alloy, or a powder partially nitrided thereof, and has a CV value (a value obtained by dividing a product of a capacity and an applied voltage during electrolytic oxidation by an electrode weight) of at least 50,000. [CV / g] or more is preferable because a large-capacity capacitor can be obtained. For example, the CV value can be obtained by using powder having an average particle diameter of 3 to 5 [μm]. Furthermore, a larger CV value can be obtained by reducing the average particle size of the powder shape for producing the sintered body. In order to obtain 100000 [CV / g] or more, for example, 0.3 to 2 [μm], and to obtain 600,000 [CV / g] or more, for example, 0.2 [μm] or less. Accordingly, a sintered body having a larger CV value required for obtaining a capacitor having a larger capacity can be obtained.

The niobium powder having such an average particle size is as follows:
For example, it can be obtained by a method of pulverizing sodium reduced product of potassium fluoroniobate, a method of pulverizing and dehydrogenating a hydride of niobium ingot, a method of reducing niobium oxide by carbon, and the like. For example, in the case of a method obtained by pulverizing and dehydrogenating a hydride of a niobium ingot, a niobium powder having a desired average particle size can be obtained by preparing a hydrogenation amount and a pulverization time of the niobium ingot, a pulverizer, and the like. .

A partially nitrided electrode can be obtained by using a method in which a sintered body is manufactured and then nitrided. For example, after molding and sintering niobium powder, the sintered body can be nitrided using the above-described nitriding treatment method.

Here, in this specification, the amount of nitrogen in niobium and niobium powder is not the state adsorbed on these materials, but the one which is surely bonded and nitrided.

On the other hand, the other electrode of the capacitor of the present invention is not particularly limited, and examples thereof include at least one compound selected from an electrolytic solution, an organic semiconductor and an inorganic semiconductor known in the aluminum electrolytic capacitor industry. Can be Specific examples of the electrolyte include a mixed solution of dimethylformamide and ethylene glycol in which 5% by weight of isobutyltripropylammonium borotetrafluoride electrolyte is dissolved, and a mixture of propylene carbonate and ethylene glycol in which 7% by weight of tetraethylammonium borotetrafluoride is dissolved. Solution and the like. Specific examples of the organic semiconductor include an organic semiconductor composed of benzopyrroline tetramer and chloranil, an organic semiconductor composed mainly of tetrathiotetracene, an organic semiconductor composed mainly of tetracyanoquinodimethane, and the following general formula (1) Alternatively, an organic semiconductor mainly composed of a conductive polymer obtained by doping the polymer represented by (2) with a dopant may be used. Specific examples of the inorganic semiconductor include an inorganic semiconductor containing lead dioxide or manganese dioxide as a main component and an inorganic semiconductor made of triiron tetroxide. Such semiconductors may be used alone or in combination of two or more.

[0018]

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[0019]

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In the formulas (1) and (2), R1 to R
4 is hydrogen, an alkyl group having 1 to 6 carbon atoms or 1 to carbon atoms.
6, which may be the same or different, X represents an oxygen, sulfur or nitrogen atom, and R5 is present only when X is a nitrogen atom, And R1 and R2 and R3 and R4 may be bonded to each other to form a ring.
Examples of the polymer represented by the formula (1) or (2) include polyaniline, polyoxyphenylene, polyphenylene sulfide, polythiophene, polyfuran, polypyrrole, polymethylpyrrole, and derivatives of these polymers.

When an organic semiconductor and an inorganic semiconductor having an electric conductivity in the range of 10 ⁻² S · cm ⁻¹ to 10 ³ S · cm ⁻¹ are used, the impedance value of the produced capacitor becomes smaller, and Can be further increased.

When the other electrode is solid, for example, a carbon paste and a silver paste are sequentially laminated on the other electrode and sealed with a material such as an epoxy resin to form a capacitor. The capacitor may have niobium or tantalum leads molded integrally with niobium or later welded to the electrodes. When the other electrode is a liquid, the capacitor formed of the two electrodes and the dielectric is housed in, for example, a can electrically connected to the other electrode to form a capacitor. In this case, the electrode side of niobium is designed to be led out to the outside through the niobium or tantalum lead wire, and at the same time, to be insulated from the can by insulating rubber or the like.

By manufacturing a capacitor according to the present invention described above, it is possible to manufacture a capacitor having a low LC value or a small variation without lowering the capacity, or having good heat resistance.

[Examples] Specific examples of the present invention will be described below in more detail. The nitriding amount of the powder was measured as follows. The amount of nitrogen in the powder was determined using an oxygen-nitrogen measuring device manufactured by LECO, which determines the amount of nitrogen from the thermal conductivity, and the ratio to the separately measured mass of the powder was defined as the amount of nitriding.

The capacity of the sintered body was measured as follows. At room temperature, the capacity at 120 Hz measured by connecting an HP LCR measuring instrument between a sintered body immersed in 30% sulfuric acid and an electrode of a tantalum material immersed in a sulfuric acid solution is defined as the capacity of the sintered body. did.

The leakage current value (LC value) of the sintered body was measured as follows. At room temperature, a DC voltage of 70% of the formation voltage at the time of forming the dielectric was continuously applied for 3 minutes between the sintered body immersed in the 20% phosphoric acid aqueous solution and the electrode placed in the phosphoric acid aqueous solution. The current value measured later was defined as the leakage current value of the sintered body. In the present invention, a voltage of 14 [V] was applied.

The capacitance of the capacitor processed into a chip was measured as follows. At room temperature, 120 Hz was measured by connecting an HP LCR measuring instrument between the terminals of the fabricated chip.
The capacitance at was taken as the capacitance of the capacitor processed into a chip.

The leakage current of the capacitor processed into a chip was measured as follows. Rated voltage value (2.5 [V], 4
[V], 6.3 [V], 10 [V], 16 [V], 25
[V] etc.) of about 1/3 of the formation voltage during dielectric production
A DC voltage close to about 1/4 was continuously applied between the terminals of the manufactured chip at room temperature for one minute, and the current value measured was taken as the leakage current value of the capacitor processed into the chip.
In the present invention, a voltage of 6.3 [V] was applied.

The heat resistance of the capacitor was measured as follows. The produced capacitors were mounted together with solder on a laminated substrate having a thickness of 1.5 mm and passed through a reflow furnace three times, and the number of capacitors having an LC value of 500 μA or more was counted. Here, the condenser is about 230 ° C x 30 seconds x when passing through the reflow furnace.
Since heating is performed three times, a practical thermal history (for example, soldering of a component mounted on the front surface of the board, soldering of a component mounted on the back surface, and soldering of a post-installed component are performed three times) Of the soldering heat history).

Test Examples 1 to 23 Niobium powder consisting of partially nitrided niobium powder having an average particle size of 1 μm (obtained by leaving the niobium powder at 300 ° C. for 2 hours in a nitrogen gas atmosphere. 0.1 g of 2,500 ppm by weight of nitrogen), and a size of about 1.8 ×
A molded body of 3.5 × 4.5 mm was prepared, and the temperature was 1150 ° C.
Sintered. The obtained partially nitrided niobium sintered body is
It was immersed in the electrolytic solution shown in Table 1 and subjected to a chemical conversion treatment by applying a formation voltage of 20 V for 600 minutes under the conditions shown in Table 1 using the tantalum plate as a counter electrode. Here, the application time is an elapsed time after the applied voltage is stabilized at a constant voltage of 20 V. Table 1 shows the CV value of this electrode.

Next, the above-mentioned sintered body on which the dielectric was formed was immersed in an aqueous solution of manganese nitrate,
Repeat the process of heating and reacting for 0 minutes multiple times,
A manganese dioxide layer was formed on the dielectric oxide film as the other electrode layer. Subsequently, a carbon layer and a silver paste layer are sequentially laminated thereon, and then placed on a lead frame, and the whole is sealed with an epoxy resin to have a size of 7.3 ×
A chip capacitor of 4.3 × 2.8 mm was manufactured.

Table 1 shows the capacitance, average value and variation of LC values (2σ: twice the standard deviation value), and heat resistance of the produced capacitors. In addition, the average value and standard deviation value obtained by preparing and measuring 20 samples for each test example are shown.
Prepared.

[0033]

[Table 1]

Test Examples 24-29 Next, niobium powder composed of partially nitrided niobium powder having an average particle size of 0.7 μm (niobium powder was dried at 300 ° C. for 9 hours)
Obtained by leaving in a nitrogen gas atmosphere for 0 minutes. 1800 ppm by weight of combined nitrogen. ) To obtain a sintered body in the same manner as in Test Examples 1 to 6. Further, a capacitor was produced in the same manner as in Test Examples 1 to 6, except that the other electrode was made of polypyrrole prepared from pyrrole, ansoraquinonesulfonic acid and an aqueous solution of ammonium persulfate. Table 2 shows various performances of the manufactured capacitor.

[0035]

[Table 2]

[0036]

According to the method of manufacturing a capacitor of the present invention, when performing electrolytic oxidation in an electrolytic solution using one electrode made of niobium as an anode, an initial current value is set to 200 per weight of one electrode made of niobium. Since the dielectric is manufactured by starting electrolytic oxidation in a constant current state of [mA] or more and then continuing electrolytic oxidation at a constant voltage, the LC value is low without lowering the capacity or the variation thereof is reduced. It is possible to manufacture a capacitor that is small or has good heat resistance.

Claims (9)

[Claims] 1. An electrode comprising two electrodes and at least a dielectric interposed therebetween, wherein one of the electrodes is made of niobium, and the dielectric is made of niobium oxide formed on the electrode made of niobium. In the method for manufacturing a capacitor, when performing electrolytic oxidation in an electrolytic solution using one electrode made of niobium as an anode, the current value is initially set to 200 [mA] or more per weight of one electrode made of niobium. Wherein the electrolytic oxidation is started, and then the electrolytic oxidation is continued at a constant voltage to produce the dielectric. 2. The method according to claim 1, wherein niobium of one of the electrodes is partially nitrided. 3. The nitrogen content of niobium of one electrode is 50 to 15
The method according to claim 2, wherein the amount is 0000 ppm by weight. 4. The capacitor according to claim 1, wherein the electrolytic solution is an aqueous solution comprising phosphoric acid, the concentration of which is not less than 0.01% by weight and not more than 5% by weight. Manufacturing method. 5. The method for producing a capacitor according to claim 1, wherein the temperature of the electrolytic solution during electrolytic oxidation is 60 ° C. or higher. 6. The structure of one of the electrodes is a sintered body,
The method according to any one of claims 1 to 5, wherein the value is at least 50,000 [CV / g] or more. 7. An electrode comprising two electrodes and at least a dielectric material interposed therebetween, wherein one of the electrodes is made of niobium, and the dielectric material is made of niobium oxide formed on the electrode made of niobium. When performing electrolytic oxidation in an electrolytic solution using one of the niobium electrodes as the anode, the electrolytic oxidation is performed in a constant current state in which the current value is initially 200 mA or more per weight of the one of the niobium electrodes. And a capacitor having the dielectric formed by continuing electrolytic oxidation at a constant voltage thereafter. 8. The capacitor according to claim 7, wherein the niobium of one of the electrodes is partially nitrided. 9. The structure of one of the electrodes is a sintered body,
The capacitor according to claim 7, wherein the value is at least 50,000 [CV / g] or more.