DE1111738B - Process for the production of a capacitor from a film-forming metal with a formed dielectric cover layer - Google Patents

Description

INTERNAT.KL. H 01 g

GERMAN

PATENT OFFICE

W 28467 VIIIc / 21g

REGISTRATION DATE: AUGUST 29 T 1960

NOTICE
THE REGISTRATION
ANDOUTPUTE
EDITORIAL: JULY 27, 1961

The invention is concerned with an improved method for manufacturing capacitors, which use an electrode made of an oxide film-forming metal, and capacitors made in this way. The improvement is particularly evident in a reduction in the residual or leakage current the capacitors.

There are a group of metals, such as tantalum, aluminum, niobium, hafnium, and zirconium, that are used as film-forming metals and their oxides are known to be excellent form dielectric material that is well suited for use in capacitors. A peculiar advantage of using one of these oxides as a dielectric layer in a capacitor is the ease with which it is generated. So it becomes a tightly adherent, impermeable one and uniform oxide skin on the surface of a body of film-forming metal by the usual generated electrolytic anodic treatment. The insulated metal body is then used as an electrode of the capacitor to be built is used.

Anodically treated electrodes made of a film-forming metal are used in the manufacture of three general capacitor types are used. The wet electrolytic capacitor is the prototype of this group and simply consists of an anodized electrode immersed in a suitable liquid electrolyte is immersed. The container that contains the anodized electrode and the electrolyte, is usually used as the second electrode of the capacitor. Where the anodized electrode consists of a foil tape, the counter electrode and the spacer are wound together with the anode.

The second type of capacitor developed after the wet electrolyte type is the solid electrolytic capacitor, which often takes the form of an anodized porous body, one after the other covered with a layer of manganese dioxide and a layer of an electrically conductive metal with the latter serving as the second electrode. The manganese dioxide serves the same purpose as the liquid electrolyte in the wet electrolytic capacitor and facilitates the healing of defects or the rebuilding of voids in the dielectric oxide film.

The newest capacitor, referred to here as a printed capacitor, is made by means of deposition a layer of film-forming metal on a substrate, for example by sputtering or vacuum evaporation, then a method of manufacture

a capacitor

made of a film-forming metal

with a formed dielectric

Top layer

Applicant:

Western Electric Company Incorporated, New York, N.Y. (V. St. A.)

Representative: Dipl.-Ing. H. Fecht, patent attorney, Wiesbaden, Hohenlohestr. 21

Claimed priority: V. St. v. America September 21, 1959

David Alexander McLean, Chatham, N.J. (V. St. Α.), Has been named as the inventor

the deposited layer anodized to form an oxide film, and finally one Opposite electrode deposited in direct contact with the anodized film.

The development of the printed capacitor was closely related to problems related to dielectric Approach the oxide film directly. The wet electrolyte has the benefit of healing all imperfections in the dielectric film, which are either present from the beginning or subsequently with Operation of the capacitor occur. However, this capacitor suffers from some general drawbacks based on the fact that the condenser has a relatively large volume of liquid Electrolytes used. The solid electrolytic capacitor with a thin layer of manganese dioxide Replacing the liquid electrolyte is in many respects of the wet electrolyte type think.

The printed capacitor represents the ultimate goal in capacitor design, the one Use an electrode made of a film-forming metal. The way in which the film-forming electrode was made apparently diminishes the presence of

109 649/313

3 4

Defects or imperfections in the anodically treated expediently made of platinum, and the electrolyte 6 in

dielectric film, as that of the other two complements the shape shown in the figure. Of the

Types of capacitors used electrolytes alone Electrolyte 6 is a non-aqueous liquid that

serve to compensate for undesirable effects that a low ion concentration of one or more

due to the imperfection of the dielectric 5 contains halogens.

Film caused bypasses the high quality. The etching process according to the invention begins with the

of the dielectric with printed capacitors the closing of switch 3, whereby the electrode 1

Need to get an electrolytic positive at all. Would be the dielectric oxide film that

Medium to use. Accordingly, this anode 1 is completely covered, so it would be practical

Capacitor type because of its simplicity and ease of use, no current can flow through the circuit. Any-

The ability of the fabrication is excellent for the use of which defects or defects that occur in the dielectric

suitable for use in printed circuits. Film may be present, but serve as a guide

The present invention is directed to a useful avenue for electricity. At these points, to improve the quality of the dielectric ren, the halogen ions react with the film-forming metal, oxide layer of film-forming electrodes, which at the 15 of which the anode 1 consists. The main set manufacture of capacitors are used. of the dielectric film and the underlying. It has been found that the undesirable imperfect metal electrode remains affected by this treatment, imperfections and defects in the anodized. The electrolytic etching process is continued for a short time by a treatment according to the present invention and practically eliminated by opening the formwork. The final score 20 ter 3 interrupted. The treated electrode is treated with such a treatment is a decrease in the leakage current again anodically in a conventional electrolyte and a corresponding increase in the proportion treated in order to oxidize the exposed surfaces of the electrolytic capacitors, which the required regulation electrode,
have moderately low leakage current. To understand the various variations of the process

According to the present invention, to be able to evaluate the anodic rens, it is necessary to analyze the effect of the treated first electrode with a non-aqueous etching process of the film electrolyte according to the invention, which is a behavior-forming electrode. The moderately low concentration of one or more subsequent discussions refers specifically to containing more halogen ions; the electrode becomes film-forming electrodes which are then used in a printed capacitor for a short period of time. It is to be noted, however, during which negatively charged halogens note that the principles to be developed are attracted to ions from the anode and are applicable to all types of film-forming electrodes, certain parts of the underlying film-forming wherever they are used.
Metal react, etch it; Thereupon the first It appears that the various defects or electrodes are anodically oxidized again and with a non-uniformity in the dielectric film, the second electrode converges to form a capacitor - as current-carrying centers built during the invention. The anodic etching triggers the fihnbildende, according to the etching process, proving that, depending on the voltage, metal is only present at defects in the anodized metal. That is, the voids and defects kei film on. If the anodically treated film had completely collapsed and allowed current to pass through, in the sense that it was free of defects 4 ° until a certain potential is reached, so that there would be interruptions, there would be practically no group of defects with relatively small ones Current would flow, and there would be no reaction at the voltage collapse, a second would occur with a higher electrode surface. Voltage and a third no current during the

Following this etching process, the film etching process lets through until the potential at which The electrode forming the electrode is in turn customary in one of the 45 the electrode has previously been anodized anodic treatment of aqueous electrolytes is sufficient. Once a breakthrough has occurred, it is verum to oxidize the parts of the electrode surface causes an autocatalytic effect to increase exposed by the etching process. Current flow, which is a corresponding amplification of the

The etching process according to the invention can result in the reaction of the halogen with the underlying halogen Manufacturing process causes wet electrolytic condensate 50 metal, creating the exposed surface Ren, solid electrolytic capacitors and printed enlarged and a stronger current for flowing ge capacitors be inserted, and it results is brought. Because of this nature of the etching process in any case a general decrease in leakage- effective measures must be taken to Current of capacitors produced in this way. The invention caused excessive erosion in the neighborhood of the 55 55 particular imperfections must be prevented for printed capacitors. The problem is special Value, because with this construction the healing of serious at the flaws of a stress through defect and voids that break in the dielectric as these are etched first. If you let them Oxide skin may be present, not pre-erosion in these places in an uncontrolled manner is seen. continue, so practically all of the current flow

The understanding of the invention is directed by the ab- 60 through these points, whereby each effective

education facilitated, which the schematic drawing treatment of the electrode points of higher

represents voltage of an electrode, which is prevented according to the existing breakthrough savings,

of the invention is etched. Two special etching methods are suggested

In the drawing is an anodized gene in order to avoid the differences in

Electrode 1, for example made of tantalum, is shown, which links 65 to the breakdown voltage of the imperfections.

with the positive pole of a controllable direct current- th to reduce problems. The first of these methods

source 2 is connected. The electrical circuit has the merit of simplicity in that

is through switch 3, ammeter 4, cathode 5, only one etching step is required.

This procedure is performed at a relatively high voltage and is usage based a low conductivity electrolyte. The voltage used in this etching process is ordinary of the order of magnitude of the working voltage or higher, so that the whole group of imperfections, which have breakdown voltages equal to or less than the working voltage during the Process are eroded. An excessive attack at points of lower breakdown voltage will by using electrolytes of low conductivity, which reduces the etching effect because of the high electrical resistance makes it more uniform. The etching process consists of dipping the anodic treated electrode in a non-aqueous electrolyte containing halogen ions. The electrode is then connected anodically at a potential that is at least the working voltage of the capacitor corresponds, and preferably at a potential equal to twice the working voltage. Man allows the etching to proceed for a period of time, preferably 1 to 4 minutes. The etched electrode is then anodized again in a conventional electrolyte.

It is important to keep the etching current density below 10 mA / cm ² and preferably in the range of 1 to 3 mA / cm ² ; the current density is conveniently kept within appropriate limits by controlling the concentration of halogen ions in electrolytes. It has been found that the desired current densities are obtained using an electrolyte which has a specific resistance in the range from 10 ² to 10 ⁴ ohm / cm. Treatment at current densities higher than the determined value is very likely to have a detrimental effect on the oxide dielectric film because of the excessive heat generated at the voids.

The duration of the etching process is not a critical variable and the limits mentioned above can be be crossed, be exceeded, be passed. However, longer etching times tend to increase the effective resistance and a reduction in capacitance, with the loss of electrode material for both Effects is responsible. The use of etching times below one minute reduces the dated Advantages obtained according to the invention. The second of the two proposed methods consists of a sequence of etching steps with increasing voltage, each step being the usual anodic Treatment follows to the parts of the electrode exposed in the previous etching step to heal. This method gives the same results as the one described above, but in different ways Art. By using a sequence of etching steps, the imperfections are grouped group by group treated with the tension at which they collapse. So can the first etching step with a voltage carried out, which corresponds to approximately 20% of the working voltage, for a period of time from 1 to 4 minutes. This etching step causes erosion of those places where the Breakdown voltage is 20% or less of the working voltage. The anodic treatment that Following this step, a dielectric oxide skin is created over the eroded parts of the electrode, so that these parts do not let any current through in the subsequent etching steps. This procedure will repeatedly until the desired maximum tension is reached.

Since the lower voltage imperfections are not subjected to an excessively high etching potential in this process, the conductivity of the electrolyte is not a critical factor. However, the limits set out above with regard to the etching current density also apply in this case. The maximum etch current density is therefore approximately 10 mA / cm ² , and the preferred range is between 1 and 3 mA / cm ² . In this process, the current density is conveniently controlled by a suitable choice of the etching time and voltage.

Regardless of the particular technique, a voltage should be reached during the etching process that is at least equal to the operating voltage. In this way, imperfections can be treated effectively otherwise the breakthrough in operation and thus a considerable increase in leakage current would cause. It is recommended that the applied voltage be reduced for increased reliability corresponds to at least twice the working voltage.

The etching electrolyte suitable for use according to the invention can be made from any non-aqueous Solvents that contain halogen ions. The requirement that the electrolyte is non-aqueous is based on the need to keep the etching solution free of all ions that form oxygen at the anode. The presence of oxygen would lead to the formation of the usual dielectric Promote oxide layer and counteract the desired etching process accordingly. Therefore For example, methyl alcohol, ethyl alcohol, acetone, nitrobenzene, phenol and aniline can be used as solvents be used. As salts form aluminum chloride, lithium chloride, ammonium bromide, potassium fluoride, Sodium iodide and sodium fluoride halogen ions for the stated purpose.

The advantages of the present invention are best demonstrated by comparing capacitors honored that are produced with and without the etching process according to the invention. Six capacitors were made according to the following procedure:

A tantalum layer approximately 5000 Å thick was placed on a glass substrate in the desired shape Education (cathodic) dusted. The tantalum film was then at a potential of 100 volts in anodically treated with an electrolyte, which is composed of 1 part by weight of oxalic acid and 2 parts by weight of water and 3 parts by weight of ethylene glycol. The electrolyte was kept at 105 ° C. After that it was a gold counter electrode is deposited in contact with the anodized surface. The leakage current of these capacitors measured at 75 volts is listed in Table I below.

Table I.

Leakage current in amps
3.0 x 10-8
2.2 x 10-8
3.2 · ΙΟ- »

Short circuit
9.8 x 10-9
10-6

A set of four capacitors, Examples 1 through 4, were made in the following manner:

The process used for the capacitors having the characteristics shown in Table I was retained in the anodizing process. At this point in the procedure, each capacitor, after washing and drying, was immersed in an etching solution consisting of 0.01 weight percent lithium chloride in methyl alcohol. The capacitor was then anodically brought to a potential of 90VoIt, which corresponds to about 180% of the operating voltage of 50 volts. The etching process was continued for a time of 2 to 3 minutes, the etching current density corresponding to approximately 1 mA / cm ² .

After the etching step, the capacitor was washed and dried and then again at one Potential of 100 volts under the aforementioned conditions anodized for a period of about 3 minutes. The leakage currents of the Capacitors are listed in Table II for a voltage of 75 volts.

Table IV

Leakage current in
Microamps

Fixed electrolytic capacitor

normal

execution

40

Etched

execution

Wet electrolytic capacitor

Normal etched

from from

leadership. guide

20th

It is to be understood that the examples presented above are merely illustrative for the practice the invention are intended. The treatment according to the invention can be film-forming with electrodes of any one Metal and in the manufacture of every type of capacitor. Furthermore is the principle of the etching technique described can be applied to any device that has a dielectric Oxide film produced by anodic treatment on an electrode made of film-forming metal.

Table II
Leakage current in amps

Example 1 2,3 · ΙΟ " ⁹

Example 2 2.4 x 10 " ⁹

Example 3 2.8 · ΙΟ " ⁹

Example 4 3.0 x 10 ^ ⁹

30th

Two more sets of four capacitors each (Example 5 through 8 and 9 through 12) were made according to the above for example 1 to 4 described procedure, with the change that example 5 to 8 in a solution of 0.05 percent by weight ammonium bromide in acetone and example 9 to 12 in one Electrolytes made from 0.02 weight percent aluminum chloride in methyl alcohol were etched. The leakage currents these capacitors are included in Table III.

Table III
Leakage current in amps

Example 5 2.8 · ΙΟ " ⁹

Example 6 2.8 · ΙΟ " ⁹

Example 7 3.8 x 10 ~ ⁹

Example 8 2.3 · ΙΟ " ⁹

Example 9 3.4 × 10 ^-9

Example 10 3.4 · IO- ⁹

Example 11 2.8 x 10 ~ ⁹

Example 12 3.4 x 10 ~ ⁹

The comparison of the leakage currents listed in Tables II and III with those in Table I clearly shows the advantages that are gained by using the etching technique according to the invention.

Table IV lists the values that demonstrate the benefits of the present invention for wet electrolytic capacitors and solid electrolytic capacitors. The solid electrolytic capacitors included Niobium anodes, and the wet electrolytic capacitors were with sintered porous aluminum anodes manufactured. The use of an etched electrode is found to result in a decrease the leakage current for both capacitor types.

Claims (7)

PATENT CLAIMS: A method of manufacturing a capacitor having a formed dielectric cover layer, in which a first electrode consisting essentially of a film-forming metal is anodized to form a dielectric oxide film thereon, characterized in that the anodized electrode is converted into a non-aqueous ion at least one halogen-containing electrolyte is immersed and anodically connected so that an electric current flows between the first electrode and the electrolyte and etches the electrode and that the first electrode is then anodically oxidized again and assembled with a second electrode to form the capacitor. 2. The method according to claim 1, characterized in that the electrode consists of a a layer of deposited layer of a film-forming metal and that the second Electrode is in direct contact with the dielectric oxide film. 3. The method according to claim 1, characterized in that the first electrode has an im essentially consists of film-forming metal porous body and that a solid Electrolyte is placed between the oxide dielectric film and the second electrode. 4. The method according to claim 1, characterized in that a liquid electrolyte between the oxide dielectric film and the second electrode. 5. The method according to any one of the preceding claims, characterized in that the current density for etching is in the range from 1 to 10 mA / cm ² for the surface of the first electrode. 6. The method according to claim 5, characterized in that the current density is 1 to 3 mA / cm ^{2 of} the surface of the first electrode. 7. The method according to any one of the preceding claims, characterized in that the resistance of the non-aqueous electrolyte is in the range from 1 · 10 ² to 1 · 10 ⁴ ohm / cm . 1 sheet of drawings © 103 649/313 7.