RU2391442C1 - Method of anode foil obtainment - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to electronics, particularly to methods of manufacturing of anode foil applicable in solid-state electrolytic condensers with conductive polymer electrolyte. Method involves application of porous layer of valve metal nitride onto both sides of aluminium foil in vacuum chamber, and further oxidation of obtained layer in vacuum chamber with continuous movement of aluminium foil. Valve metal nitride layer is applied by electron-beam evaporation of metal in nitrogen atmosphere or in nitrogen mix with inert gases. Further oxidation of obtained layer is performed in steady-state or impulse magnetron discharge plasma and/or high-frequency discharge plasma of 10⁹ - 10¹⁵ cm^-3 density.

EFFECT: environmentally safe and simple method of obtaining anode foil with high specific capacity.

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Description

The invention relates to the field of electrical engineering, in particular to the manufacture of anode foil, which can be used in solid electrolytic capacitors with an electrolyte from a conductive polymer.

A known method of creating an anode foil by resistive evaporation of aluminum in a vacuum, followed by applying it to a moving aluminum tape. After receiving the porous coating, it is anodized in the appropriate electrolyte to obtain aluminum oxide of the required thickness (GB 2056503, 03/18/1981, patent holder Standard Telephones and Cables Ltd). This method does not allow to obtain anode foils based on oxides of refractory materials, while the dielectric constant of such oxides, for example TiO ₂ , can be 5 or more times greater than Al ₂ O ₃ , which can significantly increase the specific anode capacity. In addition, electrolytic anodizing is an environmentally harmful process.

The closest analogue is the technical solution disclosed in patent US 7391604 B2, publ. 06/24/2008, patent holders of Sanyo Electric Co., Ltd (JP); Saga Sanyo Industries Co., Ltd., (JP); Japan Capacitor Industrial Co., Ltd., (JP). A method of manufacturing an anode foil of a solid electrolytic capacitor is as follows. To increase the surface of aluminum foil, electrochemical etching is performed. As a result of etching, the surface roughness increases significantly, which ultimately leads to an increase in the specific capacity of the anode foil. Using electron beam evaporation in vacuum, a titanium nitride (TiN) film is formed on the surface of the etched aluminum foil. Other methods can be used to create a titanium nitride film, since the porosity and density of the coating are not of particular importance. Next, an aluminum foil with a titanium nitride film formed on it is immersed in a chemical solution, where it is oxidized to form titanium dioxide (TiO ₂ ), both on the surface and in the bulk of the deposited TiN film. The resulting TiO ₂ film has stable properties compared to pure titanium films oxidized in the electrolyte. The relative permittivity of such a film reaches 100, which leads to a significant increase in the capacity of the anode foil.

However, this method includes several electrochemical processes that are environmentally unsafe. In addition, this method provides for preliminary imparting to the aluminum base the properties of the bearing surface, which makes the process of manufacturing the anode foil more long and laborious.

The technical problem to which the present invention is directed is the creation of an environmentally friendly, simpler method for the production of anode foil with a high specific capacity for solid electrolytic capacitors.

The problem is solved in that the method of producing the anode foil will include applying in a vacuum chamber on both sides of the aluminum base a porous layer of valve metal nitride. The deposition of a valve metal nitride layer is carried out on a continuously moving aluminum base by electron beam evaporation of the metal in a vacuum chamber in a nitrogen atmosphere or in a mixture of nitrogen with inert gases. Next, the resulting layer is oxidized in a stationary or pulsed magnetron discharge plasma and / or in a high-frequency discharge plasma with a plasma density of 10 ⁹ to 10 ¹⁵ cm ^-3 to form an oxide layer with a thickness of not more than 10 μm.

The method can be implemented in an installation where the step of applying a porous layer of valve metal nitride on an aluminum base and the step of forming an anode coating on an aluminum base (oxidation in plasma) is carried out in separately installed devices or in an installation where both steps are carried out in one device.

Figure 1 shows a diagram of a coating installation in which it is possible to combine the processes of applying a porous layer of valve metal nitride on an aluminum base and oxidation in plasma.

Stage 1.

The aluminum base (foil) 1 in the vacuum chamber (not shown in the figure) from the feeding device 2 passes through a system of guide and tension rollers 3 and enters the cooled drums 4, on which a porous layer of valve metal nitride, for example titanium nitride, is deposited on it electron beam evaporation of titanium from evaporators 5 in an atmosphere of nitrogen or a mixture of nitrogen and inert gases, and enters the receiving device 6.

The precipitation of titanium nitride occurs simultaneously on both sides of the aluminum base.

In this case, the RF plasma generator 7, the dual magnetron system 8, including stationary and pulsed magnetrons, are turned off.

The aluminum base may be pre-purified and activated by means of an ion source 9.

At the same time, at the first stage, the curtains 10 are open.

After the stage of applying the porous titanium nitride is completed, the aluminum base is stopped moving from the feeding device 2 to the receiving device 6, the evaporation of titanium from the evaporators 5 (6) is stopped and the ion sources 9 are turned off.

2 stage.

At the second stage, the installation environment is changed: the supply to the vacuum chamber of nitrogen is turned off and the supply of oxygen or carbon dioxide is turned on.

During the second stage, an anodic coating based on aluminum is formed.

The evaporation of titanium from evaporators 5 is not performed. An aluminum base 1 with a titanium nitride coating deposited on it during stage 1 from a receiving device 6 passes through a system of guide and tension rollers 3 and cooled drums 4 and enters the receiving device 2.

To form an anode coating of titanium dioxide, the titanium nitride coating is oxidized by means of a reactive plasma formed by a dual magnetron system (stationary or pulsed magnetrons) 8 and / or an RF plasma generator 7.

In this case, the system of dual magnetrons (stationary and pulsed magnetrons) 8 and the RF plasma generator 7 can operate both individually and simultaneously.

In the second stage, the curtain 10 is closed.

The step of applying a porous layer of valve metal nitride on an aluminum base and the step of forming an anode coating on an aluminum base (oxidation in plasma) is performed on one device, in the same volume of the vacuum chamber, of the same coating unit, which greatly simplifies the method of obtaining anode foil, making the process of obtaining it less time consuming.

To create the oxide layer of TiO ₂ using:

a) Stationary magnetron discharge

Operating voltage range: 250-600 V

The discharge current density: 1-100 mA / cm ²

Plasma Density: 10 ⁹ -10 ¹¹ cm ^-3

Dose (ion flux): 10 ¹⁷ -10 ¹⁹ 1 / cm ²

b) Pulsed magnetron discharge

Operating voltage range: 500-2000 V

The discharge current density: 1-25 A / cm ²

Plasma Density: 10 ¹¹ -10 ¹³ cm ^-3

Dose (ion flux): 10 ¹⁷ -10 ²⁰ 1 / cm ²

c) High-frequency (radio-frequency) induction discharge

Plasma Density: 10 ⁹ -10 ¹³ cm ^-3

Dose (ion flux): 10 ¹⁷ -10 ¹⁹ 1 / cm ²

As a result of plasma exposure, a complete volumetric oxidation of the titanium nitride layer occurs, and the pores inside the layer become denser, while the film surface remains highly developed with a high degree of roughness.

The anode foil obtained in this way has a high specific capacity due to the large specific surface and can withstand large breakdown stresses due to compaction of the internal structure of the film.

In this case, the aluminum base may have a surface that does not have the properties of a bearing surface.

The anode foil may have a specific titanium content on the surface of the aluminum base of 2.0 ÷ 5.0 g / m ² .

Comparative example.

Figure 2 shows the structure of the anode foil, which was obtained by oxidation of a porous titanium nitride coating deposited on an aluminum base. The oxide layer of TiO ₂ was formed during a stationary magnetron discharge in an atmosphere of an oxygen-containing gas with an electric bias applied to the sample. Figure 2 shows two sides of the foil, as well as a top view for both sides. It can be seen that the foil consists of several layers. The lower layer is a titanium nitride coating layer, and the upper layer is titanium oxide. Oxygen in the discharge actively reacts with titanium, oxidizing it. Due to the porosity of the titanium nitride layer, oxygen penetrates to a greater depth, leading to changes in the depth of the film, which in the drawing corresponds to a lighter middle layer. The upper, lightest layer is pure titanium oxide. The thickness of the upper layer deposited in an oxygen-containing gas atmosphere is less than 100 nm. Moreover, the upper layer is very dense and there are no visible traces of porosity, which is significant.

Figure 3 shows the structure of the anode foil obtained by applying titanium oxide to an aluminum base in a magnetron in a mixture of inert gas and oxygen-containing gas.

Figure 3 shows four coatings obtained in various application modes. As can be seen from Figure 3, the coatings have different thicknesses, which is reflected in the color of the coatings. In all cases, coatings on aluminum have a globular structure. Moreover, globules have a very elongated shape and not all of them have adhesion to the surface of the aluminum substrate. The apparent porosity of the coating is also great. The surface relief of oxide films deposited on an aluminum base has a finer structure than the relief of oxide films deposited on a titanium nitride coated aluminum base. This is due to the fact that titanium oxide films on aluminum foil actually grow on a thin layer of aluminum oxide, where there are a large number of condensation and nucleation centers. Films on the initial cathode foil already grow on the formed globular structure of the titanium nitride coating.

Claims (2)

1. A method of producing an anode foil, comprising applying in a vacuum chamber on both sides of an aluminum foil a porous layer of valve metal nitride and subsequent oxidation of the obtained layer, characterized in that the layer of valve metal nitride and the subsequent oxidation of the resulting layer are carried out in a vacuum chamber with continuous movement of aluminum foil, while the deposition of a layer of valve metal nitride is carried out by electron beam evaporation of the metal in a nitrogen atmosphere or in a mixture of nitrogen with inert gases, and the subsequent oxidation of the obtained layer is carried out in a plasma with a density of 10 ⁹ to 10 ¹⁵ cm ^-3 stationary or pulsed magnetron discharge, and / or high-frequency discharge. 2. The method according to claim 1, characterized in that the deposition of a valve metal nitride layer and its oxidation is carried out until an oxide layer is formed with a thickness of not more than 10 μm.

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