JP2000068160A - Ta SOLID ELECTROLYTIC CAPACITOR AND ITS MANUFACTURE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve largely the withstanding voltage of a Ta solid electrolytic capacitor without reducing its electrostatic capacity, by providing in it as its dielectric layer a composite oxide layer of a Ta oxide and a BaTa oxide. SOLUTION: Creating a granulating powder by mixing a binder with a Ta metal powder, a pressing constructive method is applied to the granulating powder to create a compressively molded body having a buried anode lead 2 (made of a Ta metal). Sintering this molded body at a high temperature in a vacuum or an inert gas atmosphere, an anode body 4 is obtained. Then, subjecting the surface of the anode body 4 to an anodic oxidation, a first dielectric layer 6 is formed on the surface of the anode body 4 to obtain a formation body 5. At this time, the first dielectric layer 6 is made of Ta2O5. Then, dipping this formation body 5 into the aqueous solution of Ba(OH)2 and holding it in the saturated water-vapor atmosphere of a high temperature and a high pressure, the vicinity of the surface of the first dielectric layer 6 is changed into a dielectric layer 7 (BaTa2O6 layer) to obtain the formation body 5 having as its dielectric layer a composite oxide layer of Ta2O5 and BaTa2O6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Ta solid electrolytic capacitor and a method of manufacturing the same, and more particularly to a Ta solid electrolytic capacitor capable of suppressing a decrease in capacitance and increasing a dielectric breakdown voltage, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Normally, a solid electrolytic capacitor has an anode body,
It is roughly composed of a dielectric layer (oxide layer), a conductive material layer (solid electrolyte layer), and a cathode layer. Hereinafter, an example of a conventional method for manufacturing a solid electrolytic capacitor will be described.
First, a method for manufacturing the anode body will be described. A binder for improving the moldability is mixed with the Ta metal powder to produce a granulated powder for press molding. Using the granulated powder, a compression molded body having an anode lead (using Ta metal) embedded therein is formed by a press method. This molded body is 1300-160
By sintering at a high temperature of about 0 ° C. and a high vacuum of about 10 ⁻⁶ Torr, an anode body for a solid electrolytic capacitor is obtained.

[0003] In theory, a group of metallic materials called "valve-action metals" could be used as the material of the anode body, but only Ta and Al among them have been put to practical use. Moreover, in the case of Al, the anode body is rarely manufactured by sintering as described above, and an etching foil is generally used. Therefore, when the anode body is manufactured by the above method, at present, the material is almost limited to Ta only.

Next, formation of a dielectric layer (oxide layer) will be described. In order to form a dielectric layer on the surface of the above-mentioned anode body, an oxide layer as a dielectric layer is formed by a technique called anodic oxidation. Anodization involves immersing the anode body and a counter electrode for energization in an electrolyte solution,
This is a method in which an oxide layer is formed on the surface of the anode body by applying a current while keeping the counter electrode at a potential lower than that. The potential difference between the anode body and the counter electrode at this time is called a formation voltage, and the feature of this method is that the thickness of the oxide layer can be easily determined by controlling the formation voltage. Also,
The anode body that has undergone this anodization is called a conversion body.

Next, the formation of the solid electrolyte layer will be described. Forming a conductive material layer as a counter electrode surface corresponding to the anode body metal outside the oxide layer of the above-mentioned chemical conversion,
The basic structure as a capacitor is obtained. This conductive material layer is called a solid electrolyte layer. As the solid electrolyte layer, manganese dioxide obtained by thermally decomposing manganese nitrate is generally used, but recently, a conductive organic polymer such as polypyrrole has been formed into a layer by chemical polymerization, electrolytic polymerization, etc. Things are also used.

Next, the formation of the cathode layer will be described. A conductive material layer is further formed on the outer side of the chemical formed after the formation of the solid electrolyte layer, and this layer is referred to as a cathode layer. The cathode layer connects the solid electrolyte layer and the external terminal (cathode) for mounting,
It also has the effect of reducing the connection resistance and reducing stress during the exterior and mounting of the capacitor. In general, a graphite paste and a silver paste are used together to form the cathode layer. Finally, an external terminal and an exterior are formed. A metal external terminal for mounting is attached to the element after the formation of the cathode by welding, bonding, or the like, and is further packaged with a resin or the like for the purpose of improving moisture resistance and handling properties to obtain a solid electrolytic capacitor.

[0007]

As described above, the metals that can be used as the anode body material of the solid electrolytic capacitor are a group called "valve action metals", but only Ta and Al are practically used. is there. The reason is that the film formed by anodic oxidation of other valve action metals is not insulating, or even if it has an insulating property, it is at a low level that cannot be used as a solid electrolytic capacitor.

[0008] Al and Ta also differ in the method of forming the anodic oxide film. In the case of Al, the properties of the film are controlled by reacting with various substances in the anodic oxidation step. In the case of Ta, however, the reactivity is very high. Due to the low temperature, the composition of the oxide film is not changed in the anodic oxidation step. However, since anions in the chemical conversion solution may be taken into the film during anodization,
Various chemical conversion liquids are used to improve the properties of the film. However, the change in the characteristics of the film due to this is limited (for example, a reduction in leakage current due to a reduction in defects).
Characteristics such as dielectric constant and dielectric breakdown voltage are basically the same as Ta ₂ O ₅ .

Therefore, when Ta is used, doping of the Ta powder with another substance (reacting with the Ta powder at the time of sintering the anode body) for the purpose of changing the composition of the oxide film,
The use of alloy powder of a with other substances has been attempted,
It has not been put to practical use yet. Generally, to improve the withstand voltage of a solid electrolytic capacitor, the thickness of the anodic oxide film is increased, but the withstand voltage and the capacitance of the capacitor are inversely proportional. Is reduced.

BaTa ₂ O ₆ used as an insulating material of an electroluminescent (EL) display is made of Ta.
_{Although the} dielectric constant is almost the same as that of ₂ O ₅ , it is known that it has a withstand voltage twice or more. If this BaTa ₂ O ₆ can be used as an oxide film, it is considered that the withstand voltage can be greatly improved without lowering the capacitance. However, as described above, it is very difficult to obtain an anodic oxide film having such a composition in a Ta solid electrolytic capacitor.
In addition, a method of performing a reaction by heating after sputtering, such as that used in EL, has a drawback that a film cannot be formed inside an anode body which is a porous body, and thus cannot be used.

[0011] The reason for producing such a defect is that Ta
Low reactivity of itself. Normally, when forming an anodic oxide film for a Ta solid electrolytic capacitor, 1 at
m and room temperature to about 90 ° C. are selected. Under these conditions, even though anions of the chemical conversion solution may be incorporated into the Ta ₂ O ₅ film during anodic oxidation, they may be Ta or T 2.
It does not react with a ₂ O ₅ . Therefore, a Ba compound cannot be obtained as an anodized film even if an aqueous solution of a Ba salt or the like is used as a chemical conversion solution under the above-described anodic oxidation conditions. In view of the above, an object of the present invention is to provide a Ta solid electrolytic capacitor having improved characteristics by changing the film composition after or during anodic oxidation of a Ta anode body and a method of manufacturing the same. .

[0012]

According to the present invention, there is provided a Ta solid-state device according to the present invention.
The capacitor is made of Ta as a dielectric layer._TwoO_FiveAnd BaTa _Two
O₆Characterized by having a composite oxide layer of Also,
The Ta solid electrolytic capacitor according to the present invention has a dielectric layer
BaTa_TwoO₆Characterized by having only an oxide layer
You. That is, the dielectric layer of the Ta solid electrolytic capacitor
Ta_TwoO_FiveAnd BaTa_TwoO₆Or a composite oxide layer of
aTa_TwoO₆By using only the oxide layer, the anodized skin
Withstand voltage of Ta solid electrolytic capacitor without thick film
Can be improved, and the Ta solid
A decrease in the capacitance of the electrolytic capacitor can be suppressed.

The method for manufacturing a Ta solid electrolytic capacitor according to the present invention is characterized in that an anode body obtained by mixing a Ta powder and a binder and sintering a pressed compact is anodized,
The anode body surface to form a Ta ₂ O ₅ oxide layer, then by changing the BaTa ₂ O ₆ layers a portion of the Ta ₂ O ₅ layer using hydrothermal synthesis method, Ta ₂ O ₅ layer and BaTa An anode body having a ₂ O ₆ composite oxide layer as a dielectric layer is obtained. That is, the Ta ₂ O ₅ layer on the surface of the anode body is treated by a hydrothermal synthesis method, and a part of the Ta ₂ O ₅ layer is changed to a BaTa ₂ O ₆ layer. An improved Ta solid electrolytic capacitor can be obtained.

Further, according to the present invention, there is provided a Ta solid electrolytic condenser.
The manufacturing method of the solder is to mix Ta powder and binder
Anodic acid is added to the anode body obtained by sintering
BaTa_TwoO₆layer
Characterized by obtaining an anode body having only a dielectric layer
I do. In other words, simultaneous anodic oxidation and hydrothermal synthesis are applied to the anode body.
By doing so, the surface layer of the anode body is made of BaTa._TwoO₆Layer only
Can be formed as a dielectric layer,
Ta solid electrolytic capacitor with improved withstand voltage of dielectric layer while suppressing
Capacitor can be obtained. In addition, the hydrothermal synthesis method
In general, special reactions are promoted using solutions under high temperature and high pressure.
In the present invention, it is a method under normal formation conditions.
Does not generate BaTa _TwoO₆Important hand to generate
Has become the law.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited to only these embodiments. As a first embodiment, T
A method for manufacturing a solid electrolytic capacitor having a composite oxide layer of an a ₂ O ₅ layer and a BaTa ₂ O ₆ layer as a dielectric layer will be described. First, a method for manufacturing the anode body will be described. T used for the anode body of the solid electrolytic capacitor of the first embodiment
As the powder a, the raw materials conventionally used can be used as they are. A binder for improving the formability is mixed with the Ta metal powder in an amount of 1 to 5% by weight to produce a granulated powder 1 for press molding. Using this granulated powder 1, a compression molded body 3 having an anode lead 2 (made of Ta metal) embedded therein is produced by a press method as shown in FIG. This molded body 3 is 10 ^-6
By sintering at a high temperature in a vacuum of Torr or less or in an inert gas atmosphere, an anode body 4 for a Ta solid electrolytic capacitor as shown in FIG. 2 is obtained.

Next, a dielectric layer (Ta ₂ ) is formed on the surface of the anode body 4.
O ₅ layer). In order to form a dielectric layer on the surface of the anode body 4, the anode body 4 and a counter electrode for energization are immersed in an electrolyte solution, and the anode body 4 is maintained at a positive potential, and the counter electrode is maintained at a potential lower than that and energized. Anodization is performed by
Is formed on the surface of the anode body to obtain a chemical conversion body 5 as shown in FIG. At this time, the first dielectric layer 6 is made of Ta.
Consists of ₂ O ₅ .

Next, a second dielectric layer 7 (BaTa ₂ O ₆ layer) is formed on the surface of the first dielectric layer 6. Chemical conversion 5 is Ba
The first dielectric layer 6 (Ta ₂ O ₅ ) is immersed in an aqueous solution of (OH) ₂ and maintained in a high-temperature, high-pressure saturated steam atmosphere.
Layer) is near the surface of the second dielectric layer 7 (BaTa ₂ O ₆ layer)
, And as shown in FIG. 4, Ta ₂ O ₅
And a chemical conversion product 5 having a BaTa ₂ O ₆ composite oxide layer.

Next, a solid electrolyte layer is formed. When a solid electrolyte layer is formed outside the dielectric layers 6 and 7 of the above-mentioned chemical conversion 5 as a counter electrode surface corresponding to the anode body metal, a basic structure as a capacitor is obtained. As the solid electrolyte layer, here, manganese dioxide obtained by thermally decomposing manganese nitrate was used, but it is also possible to use a conductive organic polymer such as polypyrrole formed in a layer by chemical polymerization, electrolytic polymerization, or the like. it can.

Next, a cathode layer is formed. A graphite paste, on the outside of the chemical conversion body 5 after the formation of the solid electrolyte layer,
A cathode layer made of a silver paste is formed. Finally, an external terminal and an exterior are formed. A metal external terminal for mounting is mounted on the element after the formation of the cathode by welding, and is further packaged with a resin to obtain the solid electrolytic capacitor of the first embodiment.

As described above, in the solid electrolytic capacitor of the first embodiment, Ta ₂ is used as the dielectric layer.
By using the composite oxide layer of O ₅ and BaTa ₂ O ₆ , the withstand voltage of the solid electrolytic capacitor can be improved without increasing the thickness of the anodic oxide film, and the capacitance of the solid electrolytic capacitor due to the improvement of the withstand voltage can be improved. Reduction can be suppressed.

The technical scope of the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention. For example, in the first embodiment, Ta is used as the dielectric layer.
_Although a composite oxide layer of 2O ₅ and BaTa ₂ O ₆ was used, BaT
It may have only the a ₂ O ₆ layer as the dielectric layer.

Hereinafter, as a second embodiment, BaTa
_A method for manufacturing a solid electrolytic capacitor having only a ₂ O ₆ layer as a dielectric layer will be described. The steps in which the second embodiment differs from the first embodiment are only the portions where the dielectric layer is formed, and the description of the other steps is omitted with reference to the first embodiment. Anodization is performed to form a dielectric layer on the surface of the anode body 4. At this time, the chemical conversion solution is an aqueous solution of Ba (OH) ₂ , and anodization is performed in a saturated steam atmosphere of high temperature and high pressure, so that only the BaTa ₂ O ₆ layer is formed as the dielectric layer.

As described above, in the solid electrolytic capacitor of the second embodiment, BaT is used as the dielectric layer.
By using the oxide layer of a ₂ O ₆ , the withstand voltage of the solid electrolytic capacitor can be improved without increasing the thickness of the anodic oxide film, and a decrease in the capacitance of the solid electrolytic capacitor due to the improvement in the withstand voltage can be suppressed. Can be.

[0024]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. (Example 1) 1-5 wt% of a binder was mixed with Ta metal powder having an average particle diameter of 10 µm to prepare a granulated powder for press molding. Using this granulated powder, a compression molded body having an anode lead (made of Ta metal) embedded therein was produced by a press method. The molded body was sintered at 1600 ° C. for 30 minutes in a vacuum of 10 ⁻⁶ Torr or less or in an inert gas atmosphere to obtain an anode body for a Ta solid electrolytic capacitor.

By anodizing this anode body, Ta ₂
An O ₅ dielectric layer was formed to obtain a chemical conversion product. This chemical conversion product is immersed in a 0.2N Ba (OH) ₂ aqueous solution, and is placed in a saturated steam atmosphere at a temperature of 120 ° C. and a pressure of 2 atm for about 3 hours.
Left for 0 minutes. Thus, a BaTa ₂ O ₆ dielectric layer was formed near the surface of the Ta ₂ O ₅ dielectric layer of the anode body.

A manganese dioxide layer obtained by thermally decomposing manganese nitrate was formed as a solid electrolyte layer as a counter electrode surface corresponding to the anode metal on the outside of the dielectric layer of the above-mentioned chemical conversion body. A cathode layer composed of a graphite paste and a silver paste was further formed on the outside of the formed body after the formation of the solid electrolyte layer. A metal external terminal for mounting is welded to the element after the formation of the cathode, and is further covered with resin to form a Ta.
A solid electrolytic capacitor was obtained.

(Comparative Example 1) A method similar to that of Example 1 except that the step of forming a BaTa ₂ O ₆ dielectric layer was not performed was performed.
a Solid electrolytic capacitor was obtained. Example 1 and Comparative Example 1
In each case, the conditions (a powder particle size, a powder amount, a sintering condition, a formation voltage) under which a capacitance and a dielectric breakdown voltage of about 30 μF-50 to 80 V were obtained were set.

As a means for comparing the embodiment and the comparative example, two characteristics of capacitance and breakdown voltage were used. The measurement conditions are shown below. Measurement frequency: 12 for capacitance measurement
0 Hz, effective value: 1.0 Vrms, bias voltage: 1.
The condition of 5V was used. The breakdown voltage measurement was performed under the conditions of a voltage boosting rate: 10 V / min and a breakdown determination current: 10 mA.

FIG. 5 shows the results. FIG. 5A shows a change in dielectric breakdown voltage of Example 1 and Comparative Example 1, and FIG. 5B shows a change in capacitance. From FIG. 5A, it can be seen that the capacitor of Example 1 has a breakdown voltage about 1.5 times higher than the capacitor of Comparative Example 1. FIG. 5B shows that although the capacitance of the capacitor of Example 1 is lower than that of the capacitor of Comparative Example 1, the decrease is only about 3%.

FIG. 6A shows the change in the breakdown voltage when the same chemical breakdown film as in Example 1 is obtained by increasing the thickness of the chemical conversion film, and FIG. 6B shows the change in the capacitance. The only way to increase the dielectric breakdown voltage by the conventional method is to increase the thickness of the chemical conversion film as the dielectric layer. Therefore, when the breakdown voltage is designed to be about 1.5 times as shown in FIG.
As shown in the figure, the capacitance is reduced by about 33%.

As shown in the graph of FIG. 5, the Ta solid electrolytic capacitor of Example 1 can increase the breakdown voltage to about 1.5 times that of Comparative Example 1. Furthermore, the capacitance, which conventionally decreased in inverse proportion to the increase in the breakdown voltage, also increased to about 3%.
%. The reason for obtaining such an effect is that the dielectric breakdown voltage of Ta ₂ O ₅ is 1.5
(MV / cm), whereas the dielectric breakdown voltage of BaTa ₂ O ₆ is 3.5 (MV / cm), which is about 2.3 that of Ta ₂ O ₅ .
That the dielectric breakdown voltage is twice as high,
BaTa ₂ O ₆ is 22 compared to 23 of a ₂ O ₅ , which is attributable to a decrease of only about 4%.

The breakdown voltage of the capacitor of Example 1 is improved only about 1.5 times, because only a part of the Ta ₂ O ₅ layer is changed to BaTa ₂ O ₆ . In general, a method of promoting a special reaction by using a solution under a high temperature and a high pressure is called a hydrothermal synthesis method, and in the present invention, BaTa ₂ O ₆ which is not generated under normal formation conditions is formed. Has become an important technique.

As another embodiment, a different example of a method for manufacturing a dielectric layer will be described. (Example 2) When forming a dielectric layer on the surface of the above-mentioned anode body by anodic oxidation, a chemical conversion solution was made of 0.2N Ba (OH) _2.
By performing anodic oxidation in an aqueous solution and in a saturated steam atmosphere at a temperature of 120 ° C. and a pressure of 2 atm, only BaTa ₂ O ₆ is formed as a dielectric layer.

In the second embodiment, the dielectric layer is made of BaTa.
_Since there is only ₂ O ₆ , the dielectric breakdown voltage is slightly higher than in the first embodiment. However, in the method of the second embodiment, it is necessary to conduct electricity for anodic oxidation in a high-temperature, high-pressure saturated steam atmosphere, so that it is necessary to maintain electrical insulation of the wiring.

Example 3 In order to form a dielectric layer on the surface of the above-mentioned anode body, Ta was anodic oxidized in the same manner as in Example 1.
After the formation of the ₂ O ₅ layer, a part of the layer was
Change to Ta ₂ O ₆ . At this time, Ba (O
H) 0.1 N concentration of ₂ aqueous solution, the ambient temperature 200 ° C.
And

In the third embodiment, the concentration of the Ba (OH) ₂ aqueous solution is reduced, so that a higher temperature saturated steam atmosphere is required. In practice, the aqueous solution concentration is 0.1N
It is desirable that this is the case. The same can be said for the Ba (OH) ₂ concentration used in the second embodiment.

(Embodiment 4) A dielectric layer was formed on the surface of the anode body.
Is formed by anodic oxidation in the same manner as in Example 1 to form Ta.
_TwoO_FiveTo form Then, Ta_TwoO_FiveHydrothermal synthesis of part of the layer
BaTa by the method _TwoO₆For immersion used when changing to
BaO or B having a concentration of 0.1 N or more as an aqueous solution
aO_TwoUsing an aqueous solution of

BaO or BaO ₂ used in Example 4
Reacts with water to form Ba (OH) _2, and these aqueous solutions are the same as Ba (OH) ₂ . In addition, it is more convenient to use Ba (OH) ₂ because it generates heat during melting.

Example 5 A dielectric layer was formed on the surface of the anode body.
Is formed by anodic oxidation in the same manner as in Example 1 to form Ta.
_TwoO_FiveTo form Then, Ta_TwoO_FiveHydrothermal synthesis of part of the layer
BaTa by the method _TwoO₆For immersion used when changing to
As an aqueous solution, 0.1 N or more of Ba (NO _Three)_TwoOr
BaHPO_FourIs used. This way
In this case, the same effect as in the first embodiment can be obtained.

[0040]

As described in detail above, the Ta of the present invention
Solid electrolytic capacitors are made of Ta ₂ O ₅ and Ba as dielectric layers.
By using a composite oxide layer of Ta ₂ O ₆ or an oxide layer of only BaTa ₂ O ₆ , the withstand voltage of the solid electrolytic capacitor can be improved without increasing the thickness of the anodic oxide film, and the withstand voltage can be improved. Therefore, a decrease in the capacitance of the solid electrolytic capacitor due to the above can be suppressed.

In the method for manufacturing a Ta solid electrolytic capacitor of the present invention, the Ta ₂ O ₅ layer on the surface of the anode body is treated by a hydrothermal synthesis method, and a part thereof can be changed to a BaTa ₂ O ₆ layer. Thereby, the T with improved withstand voltage of the dielectric layer is improved.
a A solid electrolytic capacitor can be obtained. In the method for manufacturing a Ta solid electrolytic capacitor of the present invention, it is possible to form only the BaTa ₂ O ₆ layer as a dielectric layer on the surface layer of the anode body by simultaneously performing anodic oxidation and hydrothermal synthesis on the anode body. it can. Thereby, a Ta solid electrolytic capacitor in which the withstand voltage of the dielectric layer is improved can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a compression molded body 3. FIG.

FIG. 2 is a schematic view showing an anode body 4 for a Ta solid electrolytic capacitor.

FIG. 3 is a schematic view showing a chemical conversion body 5 having a Ta ₂ O ₅ oxide layer as a dielectric layer.

FIG. 4 is a schematic view showing a chemical conversion body 5 having a composite oxide layer of Ta ₂ O ₅ and BaTa ₂ O ₆ as a dielectric layer.

FIG. 5A is a graph showing a change in dielectric breakdown voltage of Example 1 and Comparative Example 1, and FIG. 5B is a graph showing a change in capacitance.

FIG. 6A is a graph showing a change in a dielectric breakdown voltage when a chemical conversion film is made thick to obtain a breakdown voltage similar to that of Example 1, and FIG. 6B is a graph showing a change in a capacitance.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 Granulated powder 2 Anode lead 3 Compression molded body 4 Anode body 5 Chemical compound 6 First dielectric layer (Ta ₂ O ₅ layer) 7 Second dielectric layer (BaTa ₂ O ₆ layer)

Claims (4)

[Claims] 1. A dielectric layer comprising Ta ₂ O ₅ and BaTa ₂ O ₆
A Ta solid electrolytic capacitor having a composite oxide layer of 2. A Ta solid electrolytic capacitor having an oxide layer of only BaTa ₂ O ₆ as a dielectric layer. 3. An anode body obtained by mixing a Ta powder and a binder and sintering a press-formed compact is anodized to form a Ta ₂ O ₅ oxide layer on a surface layer of the anode body. Next, a part of the Ta ₂ O ₅ layer was converted to BaTa ₂ O ₆
A method for producing a Ta solid electrolytic capacitor, characterized in that an anode body having a composite oxide layer of a Ta ₂ O ₅ layer and a BaTa ₂ O ₆ layer as a dielectric layer is obtained by changing into a layer. 4. An anode body obtained by mixing a Ta powder and a binder and sintering a press-formed compact is subjected to anodic oxidation and hydrothermal synthesis simultaneously to form only a BaTa ₂ O ₆ layer. A method for producing a Ta solid electrolytic capacitor, characterized in that an anode body having a dielectric layer is obtained.