DE2036101A1 - Method of depositing a retaining layer of lead oxide on a "support" - Google Patents

Description

WESTERN ELECTRIC COMPANY Incorporated- At least 1/2 -. a / 3

New York, N.Y., 10007, VStA

Process for depositing an adhesive lead dioxide layer on a substrate

The invention relates to a method of deposition an adhesive lead dioxide layer on a substrate, and in particular on the never-lying layers of such layers for use than the solid electrolyte in the manufacture of solid electrolytic capacitors.

Although the theoretical possibility has long been recognized It was found that the high capacitance per unit area of the dielectric, as occurs in wet electrolytic capacitors, also could be achieved in capacitors using similarly produced metal oxide dielectrics, but the inconvenient ones omitting ionic electrolytes, the first commercially successful capacitors of this type were based on the U.S. - Patents 3,093,883 and 3,166. 693 described method. After that, a semiconducting manganese dioxide layer is created often referred to as solid electrolyte, on an anodically generated dielectric oxide film on a capacitor plate

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from a film-forming metal, usually tantalum, on, ·. brought; the counter-facing is then covered by a metal layer formed on the manganese dioxide layer, usually with the interposition of a graphite layer. >

Earlier attempts to make a capacitor of a similar construction using lead dioxide as the solid electrolyte was used in place of manganese dioxide on the oxide dielectric film (see U.S. Patents 1,906,691 and 3,066,247), did not lead to commercially viable products.

It was later shown (see U.S. Patent 2. 993, 266) that Capacitors could be successfully made by anodizing a tantai capacitor sheet to obtain a tantalum oxide dielectric film, followed by deposition of the metallic counter-layer directly on the tantalum oxide - without a manganese dioxide intermediate layer - if used as the initial tantalum, Capacitor coating a tantalum film sputtered onto a dielectric substrate is used. Even with such capacitors often referred to as thin film capacitors are, better yields can be obtained, especially in the case of capacitors with a larger area, if a

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Manganese dioxide layer is interposed. The capacitors with the manganese dioxide layer, however, show a much higher loss factor because of the specific Resistance of manganese dioxide introduced series resistance, a circumstance * which limits their application in certain cases.

Because of the significantly higher electrical conductivity of lead dioxide, this series resistance problem could be circumvented 'if a useful method of depositing a lead dioxide layer with adequate physical properties to replace the manganese dioxide layer in the capacitors, regardless of whether they were DunnscMcht capacitors, were developed or capacitors with solid metal coatings. Previous attempts to manufacture capacitors in this way have not been successful _S; because of the difficulty of depositing lead dioxide, firstly in adherent layers, secondly in film form, or thirdly in uniform and continuous layers.

According to the invention, lead dioxide films are deposited on a substrate with mechanical properties so that the

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Production of capacitors is made possible in which the lead dioxide layers can be used as the solid electrolyte on the metal oxide dielectric. Such capacitors have a lower series resistance than similar capacitors that use manganese dioxide. Thin film capacitors, made with these lead dioxide layers are in higher yield than similar capacitors available with the metallic counter-facing directly on the dielectric oxide is deposited.

The lead dioxide is produced by oxidation of a divalent lead compound generated in solution with the help of a persulfate. When this reaction is carried out in the presence of a backing surface the lead dioxide will precipitate in the bulk of the solution without a reasonable precipitate the surface would get. It has been found, however, that when silver ions are present when the surface of the support such a solution, which has a slightly acidic pH, is exposed to an initial adherent lead dioxide precipitate is generated on the surface. The lead dioxide precipitate can then be built up by the

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initially coated base surface of a second Solution that is identical to the one previously used. Alternatively, the lead dioxide can be built up by Exposing the initially coated substrate surface such a solution (like the one previously used) which has a somewhat alkaline pH. In this procedure, if once the initial coating has been carried out,

the second precipitation step even without the presence of \

Silver ions progress satisfactorily in the solution.

For purposes of illustration, the invention is presented largely described using printed capacitors. It is clear, however, that the method described can also be used for the Manufacture of solid electrolytic capacitors can be used in which, for example, foils, wound

Wires or porous bodies made of the film-forming metal as λ

a capacitor plate can be used.

The inventive method and its application in the manufacture of a solid electrolytic capacitor is in the Claims indicated and below with reference to the drawing

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explained in detail.
Show it:

Fig. 1 is a plan view of a base with a layer of a film-forming layer deposited thereon Metal,

Fig. 2 is a plan view of the body of Fig. 1 according to Anodizing,

3 shows a plan view of the body according to FIG. 2 after a lead dioxide layer has been deposited,

Fig. 4 is a plan view of the body of Fig. 3 according to the knocking down of an opposing layer,

FIG. 5 shows a sectional view of the arrangement according to FIG. 4 and

6 shows a diagram to illustrate the loss factor depending on the frequency.

In Fig. 1, a base 11 is shown on which a metal pattern is to be generated according to the invention. That used Backing material can be rough in nature and have sharp changes in contour, or it can be any

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the usual smooth-surfaced underlay materials that normally used in the manufacture of capacitors. Preferred base materials are glasses and ceramic materials etc.

The first step in making a thin film capacitor is the cleaning of the pad 11 according to the usual methods. A layer of a film-forming metal 12 is then applied the substrate 11 is deposited by conventional methods, e.g. by cathodic sputtering, vacuum vapor deposition etc., as described by L. Holland in "Vacuum Deposition of Thin Films," John Wiley & Sons, 1956.

The film-forming metals of interest here are those whose oxides are known to be excellent dielectrics and include tantalum, aluminum, niobium, and titanium Zircon.

For the purposes of the present invention, the minimum thickness depends the layer deposited on the substrate depends on two factors. The first factor is the thickness of the metal, which are converted into the oxide during the subsequent anodization

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is converted. The second factor is the minimum thickness of the metal that has remained unoxidized after anodizing, which just shows the resistance that is allowed as a maximum in the case of the film-forming capacitor coating can. It has been determined that the preferred minimum thickness of the metal coating is approximately 3,000 Å.

Subsequently, the film-forming metal layer 12 in one suitable anodizing bath, for example citric acid., Phosphoric acid and the like, anodized to form an oxide film 13 (Fig. 2).

Then, as the next production step, a layer of lead dioxide 14 is deposited on the anodically produced oxide layer 13 (Fig. 3).

As indicated above, the lead dioxide can precipitate in a series of repetitive treatments in acidic solutions containing a divalent lead compound, a persulfate and silver ions, or alternatively in one two-step process, initially the substrate is exposed to the specified acidic solution and then one

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alkaline solution with a divalent lead compound and a persulfate.

In both cases, a lead dioxide film is produced on the oxide layer 13 in the first step. This is achieved by reacting a solution containing ammonium acetate in a molar concentration of 1-8, lead acetate in a *

molar concentration of 0.1-1 and a soluble silver salt

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in a molar concentration of 5x10 to 5x10 contains and a pH value in the range of 5, 0 - 6, 9 (optimum * 6, 0) shows, with a 1-2 molar solution of a material that consists of the sulfates of sodium, potassium and per Ammonium existing group is selected. It should be noted here that the upper concentration limit for the lead acetate corresponds to the upper limit for ammonium acetate. The reaction is allowed to proceed long enough to produce a film to produce, the thickness of which is in the range of 200-800 Å. Deviations from the specified concentration or pH ranges result in the desired film not being produced can be generated.

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The next stage of lead dioxide precipitation is this Growing a lead dioxide layer on the previously formed film. This can be achieved either by that the substrate carrying the film is exposed to a solution of the type previously used and the procedure is repeated until a lead dioxide layer of the desired thickness is obtained, or by adding the previously used solution without silver salt and with the pH value raised to 10-12 - optimum at pH 10.3 - is used. The most convenient way to do this is to add ammonium hydroxide to the reaction mixture described above until the desired pH is reached will. Lead dioxide then grows on the lead dioxide film initially produced by way of a crystal growth mechanism and not by precipitation, which is initially responsible for this Phenomenon, on. The growth is continued until a lead dioxide layer 14 (Fig. 3) of the desired thickness is obtained will. For the purposes of the present invention it is

It is desirable to grow a layer in the range of 4000-6000 Å in thickness. Layers with less than 4000 A are ineffective in the capacitor for the intended purpose, while, as has been found, layers above 6000 K in thickness do not adhere sufficiently to the substrate.

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Another alternative method can end this can be achieved by adding a saturated aqueous ■

Solution of potassium persulphate to a saturated solution of lead oxide in an o, 1 -2, ο molar potassium hydroxide solution.

After receiving the lead dioxide layer 14 in the required Thickness, the metallic counter-facing 15 (Fig. 4) is deposited on and in intimate contact with the lead dioxide layer. The sectional view of the resulting arrangement is shown in FIG.

An example is given below in detail.

A 2, 5 χ 7/6 cm glass substrate having a 800 A thick tantalum pentoxide base layer was purified by conventional methods using ultrasound and wetting agents washes. The substrate was then placed in a sputtering apparatus and a 5000 Å thick layer of tantalum was deposited. Thereafter, a pattern with 15 capacitors was made in the tantalum layer according to the usual photolithographic

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Methods etched in. The tantalum pattern was then anodized in a 0.01% strength aqueous citric acid solution, with a constant current of one milliamp per square inch was used until a voltage of 130 volts was reached. At this point the arrangement of the further Leave anodizing at constant voltage for 30 minutes. Subsequently, a lead dioxide film was anodized on top of the Layer created by reacting 250 milliliters of a solution of 0.3 molar lead oxide in concentrated Ammonium acetate (made by mixing 9 parts by volume of 30% ammonium hydroxide with 7 parts by volume Glacial acetic acid) was dissolved, with one liter of a saturated

-5 aqueous solution of ammonium persulfate and 8x10 molar silver nitrate at room temperature for 60 minutes; this resulted in a lead dioxide coating with a thickness of 400 K.

The assembly was then removed from the plating bath and rinsed in distilled water for two minutes. as next, the assembly was immersed in a solution containing 2 parts by volume of 2 molar ammonium persulfate, furthermore

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4 parts by volume of 30% ammonium hydroxide and 6 parts by volume of the 0.3 molar lead oxide solution described above. A growth of a lead dioxide layer with a thickness of 5000 A was then achieved within 40 minutes. The assembly was then rinsed in distilled water for 2 minutes

and dried in air at 100 ° C. for 1 hour. A review the resulting lead dioxide layer was found to adhere well to the backing member. Eventually it was the counter-coating onto the lead dioxide layer by evaporating a 250 A thick nickel-chromium alloy (80% nickel and 20% chromium) and a 5000 Å thick gold layer. The finished capacitors showed an average dissipation factor of approximately 0.004 at 1 kilohertz.

For comparison purposes, the procedure described above was repeated with the exception that one 5000 Å thick manganese oxide layer according to the usual pyrolytic Methods instead of the lead dioxide layer was deposited. The completed capacitors had an average Loss factor of approximately 0.04 at 1 kilohertz. Accordingly, it can be seen that the method described

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leads to a considerable improvement in the loss factor.

To improve the adhesion of the described layers compared to those deposited by customary methods To demonstrate lead dioxide layers, a lead peroxide layer was used on an anodic oxide layer of 5000 A thick tantalum produced by dipping the anodic oxide layer into a solution of lead tetraacetate in acetic anhydride, then pulling the layer out of the solution and Hydrolyze the resulting film by exposing moist air was blown against. The experiment was repeated twenty times, and it was found that the adhesiveness such layers are significantly worse than the adhesiveness of those produced by the present process Layers, and that these layers were also quite irregular was.

6 is a diagram showing the frequency dependency of the dissipation factor for capacitors shown once according to the present method

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and on the other hand instead of the lead dioxide layer had a manganese oxide layer. The capacitors compared with one another had the same dimensions and Manganese oxide or lead dioxide layers of the same thickness. It can be seen that the dissipation factor of the lead dioxide film capacitors significantly lower than that of the earlier manganese dioxide layer capacitors in the frequency range from 0.1 to 1000 kilohertz is.

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Claims (5)

PATENT CLAIMS 1. Method of depositing an adherent lead dioxide layer on a base made of a solution containing a divalent lead compound and a persulfate for oxidation of the lead in lead peroxide, characterized in that the surface of the base with the solution at Presence of silver ions is brought into contact with an initial lead dioxide precipitate on the Surface, keeping the pH of the solution is set in the range of 0, 5 to 6, 9, and that subsequently the initial precipitate is brought into contact with a solution containing a divalent lead compound and contains a persulfate and has a pH of 5, 0 to 6, 9 or 10 to 12 to an additional Generate lead dioxide precipitate on top of the initial precipitate. 2. The method according to claim 1, characterized in that the solution Ammo nium az et at, lead acetate and a persulfate contains that from the persulphates of sodium, 009886 / 7O16 Potassium and ammonium existing group selected
will. 3. The method according to claim 2, characterized in that
the molar concentration of the solution components is kept within the following ranges: Ammonium acetate 1-8 i Lead acetate 0.1-1 Persulfate 1-2 where the upper concentration limit of the lead acetate ,, the upper limit of the concentration of ammonium acetate is equivalent to. 4. The method according to claim 1, 2 or 3, characterized in that that the silver ions are added to the solution in the form of a soluble silver salt, the molar concentration of which -5 -4 ■ tion is in the range from 5x10 to 5 χ 10. 5.) Application of the method according to one of claims 1
to 4 in the manufacture of a solid electrolytic capacitor, wherein a film-forming metal is partially anodized to produce a dielectric oxide layer thereon, 00988 6/2016 - 18 - and depositing a backing on the dielectric layer in intimate contact, characterized in that a lead dioxide layer is deposited between the dielectric oxide layer and the backing by first forming a thin film of lead dioxide on the dielectric oxide layer by reacting an acidic one first solution of ammonium acetate, lead acetate and a soluble silver salt with a compound selected from the group consisting of persulfates of sodium, potassium and ammonium group _a and in that a lead dioxide layer in a thickness in the range of 4000 - 6000 a on the generated film grown is by reacting a second solution of ammonium acetate, lead acetate and a persulfate selected from the group consisting of the persulfates of sodium, potassium and ammonium. 009886/2016 Blank page