RU2322722C1 - Method for producing oxide layer on anodes of oxide-semiconductor and electrolytic capacitors - Google Patents

Abstract

FIELD: producing oxide layer on anodes of oxide-semiconductor and electrolytic capacitors.

SUBSTANCE: proposed method depending on electrochemical treatment of anodes disposed in electrolyte filled bath includes molding of anodes under electrostatic condition, evaluation of electrolyte resistance at beginning of electrostatic condition continued until voltage across bath rises by voltage drop across electrolyte resistance, this being followed by transfer to voltage regulation in electrolyte filled bath while maintaining anode voltage at value equal to oxidation voltage; in the process electrolyte resistance in Ohm is found from formula R_e = U₀/I_d, where U₀ is voltage across electrolyte filled bath at beginning of electrostatic condition, V; I_d is process-desired current, A; voltage across electrolyte filled bath is regulated using formula U_b = U_ox + I_a x R_e, where U_b is voltage across electrolyte filled bath, V; U_ox is oxidation voltage, V; I_a is actual value of anode current, A; R_e is electrolyte resistance, Ohm.

EFFECT: reduced time taken to produce oxide layer on anodes of oxide-semiconductor and electrolytic capacitors.

3 cl, 3 dwg

Description

The invention relates to methods for manufacturing electronic products, namely capacitors, mainly oxide semiconductor and electrolytic, and relates to a method for producing an oxide layer on volume-porous anodes.

A known method of producing an oxide film on anodes, which can be used in the manufacture of electrolytic and oxide semiconductor capacitors, described in A.S. No. 577573, M. Cl. НСС 9/24, published on 10/25/1977, including forming anodes in a flowing electrolyte at a constant current density and molding at a constant voltage lower than the final voltage value at a constant current density, molding at a constant voltage is carried out in an electrolyte, temperature which is 40-250 ° C higher than the temperature of the electrolyte during molding at a constant current density.

The process of forming anodes, as a result of which an oxide layer forms, which serves as a dielectric, on which the characteristics of the capacitor depend, is determined by the following factors:

- composition and temperature of the electrolyte;

- current density at the anode;

- the duration of the molding.

With increasing temperature of the electrolyte, its resistance decreases, the conditions for diffusion of ions improve, the uniformity of the molding of the anodes increases, but the resistance of the electrolyte is not taken into account in this method, therefore, considerable time is required to obtain an oxide layer.

Closest to the technical nature of the claimed method is a method of producing an oxide layer on the anodes of electrical and oxide-semiconductor capacitors (Mirzoev R.A. Electrochemical processing of metals. Anode processes, 1988. Textbook LPI named after M.I. Kalinin, p. 45), in which the method is carried out in two stages: first in the galvanostatic mode, i.e. at a constant current density 0.5-50 mA / cm ^2, the sintered metal value determined at the anode (defined process I _REF in Figure 3), then at a constant voltage in a bath of electrolyte. Depending on the required thickness of the oxide layer δ _OX , the oxidation voltage U _{OX is} selected (FIG. 3). The voltage U _O in the prototype (figure 3) is due to the voltage drop on the resistance of the electrolyte, therefore, the galvanostatic mode almost starts with U _O.

In the galvanostatic mode, the anode potential, and with it the voltage on the bath, grow linearly with time. When the voltage on the bath reaches U _OX , go into constant voltage maintenance mode. Due to the thickening of the anodic oxide film (AOP), the field strength in it decreases, which leads to a gradual decrease in current. Under constant voltage conditions, the process is conducted until the current drops to a certain level or a predetermined time. It is necessary that the duration of forming the anodes at constant voltage is sufficient to even out the thickness of the oxide layer inside the anode and on its outer surface.

At the same time, it has been observed in practice that when the anodes are molded too long, the leakage currents begin to increase, which is associated with the onset of AOP crystallization.

The above prototype method does not take into account the voltage drop across the electrolyte, which leads to a significant slowdown in the formation of the oxide layer and, as a result, to an increase in the leakage currents of capacitors.

The objective of the invention is to reduce the time of obtaining the oxide layer by compensating for the voltage drop across the resistance of the electrolyte by increasing the voltage on the bath by this value.

This problem is solved in the proposed method for producing an oxide layer on the anodes of oxide semiconductor and electrolytic capacitors, based on the electrochemical treatment of anodes placed on a bath with an electrolyte, including forming the anodes in the galvanostatic mode, determine the resistance of the electrolyte at the beginning of the galvanostatic mode, which continues until the voltage is reached on the bath, increased by the magnitude of the voltage drop on the resistance of the electrolyte, then go into voltage control mode I am in a bath with an electrolyte, maintaining the voltage at the anodes equal to the oxidation voltage, while the resistance of the electrolyte R _E in Ohms is determined by the formula:

where U _O is the voltage on the bath with electrolyte at the beginning of the galvanostatic mode in B,

I _ZAD - current, which is set by the technological process in A;

voltage regulation on the bath with the electrolyte is carried out according to the formula: U _B = U _OX + I _a · R _E , where U _OX is the oxidation voltage in V, I _a is the current value of the anode current in A, R _E is the electrolyte resistance in Ohms.

A distinctive feature of the claimed method for producing an oxide layer on the anodes of oxide semiconductor and electrolytic capacitors in comparison with methods known from the prior art is:

- determination of the resistance of the electrolyte at the beginning of the galvanostatic mode is as follows.

, где U_В=U_О, где U_О - напряжение на ванне в начале гальваностатического режима;When you turn on the programmable source of direct current 4 (figure 1) there is a voltage drop on the bath with electrolyte U _In , which is the sum of the voltage drop on the anode U _a and in the electrolyte U _E. Therefore, U _B = U _anode + U _electrolyte . But at the beginning of the galvanostatic mode, the oxide layer on the anode has not yet formed, therefore, its resistance R _a = 0. Therefore, U _B = U _electrolyte . Anode current I _REF. is set by the technological process from a programmable direct current source 4, then

where U _B = U _O , where U _O is the voltage on the bath at the beginning of the galvanostatic mode;

- determination of the resistance of the electrolyte, the value of which is considered constant throughout the entire process, because the temperature and concentration of the electrolyte are kept almost constant throughout the process, which allows increasing the voltage on the bath by the voltage drop on the resistance of the electrolyte I _a · R _E and then switching to the voltage control mode on the bath with the electrolyte and thereby reduce the rise time of the oxidation voltage U _OX and as a result, reduce the time of the oxidation process.

Thus, the identified distinguishing features, as well as their relationship in the proposed method are not known from the prior art, therefore, the proposed solution meets the criterion of "inventive step" and has novelty.

Figure 1 presents a block diagram that implements the proposed method.

Figure 2, 3 presents the dependence of voltage and current on time during oxidation of the anodes, respectively, according to the claimed method and the method prototype.

The block diagram (figure 1) contains a bath 1 with an electrolyte, in which a grid with anodes 2 of capacitors is placed, the cathode 3 is installed at the bottom of the bath. The grating with the anodes 2 of the capacitors and the cathode 3 are connected to a programmable direct current source 4, including, for example, a processor connected to power keys and a digital indicator, the processor, in turn, connected to the control panel and an analog-to-digital converter, to which connected current and voltage meter. The programmable direct current source provides galvanostatic mode, voltage regulation mode according to a given formula in the proposed method.

Consider the method of producing an oxide layer on the anodes of oxide semiconductor capacitors by the example of K53-16-16V - 33 microfarads produced by OJSC "Plant" Mezon ".

As an electrolyte, a 1% solution of phosphoric acid H ₃ PO _{4 is used} , the temperature of which is 60 ° C during the entire technological process.

Include programmable DC source 4 in the mode of stabilization of the current, providing galvanostatic mode. In this case, a current flows through the anodes 2 and the electrolyte, which is determined by the required current density in the technological process, i.e. I _REF. = 12 A. At the beginning of the galvanostatic mode, an oxide film on the anode has not yet formed and the voltage drop on it is 0. In this case, the voltage drop on the electrolyte in our case is 32 V, i.e. U _O = 32 V.

, которое считаем постоянным в течение всего технологического процесса.

, which we consider constant throughout the entire process.

As the formation of the oxide film on the anodes 2 of the capacitors, the resistance of the anodes 2 R _a increases linearly with time, while the voltage on the bath 1 also increases.

For a given rating of capacitors K53-16-16 V-33 μF, the oxidation voltage U _OX is 60 V (specified by the process). However, when the voltage on the bath reaches 160 V, the voltage at the anodes 2 will be equal to U _a = U _OX -U _E = 60-32 = 28 V.

Therefore, in the proposed method, the programmable direct current source 4 continues to operate in galvanostatic mode until the voltage on the bath is increased by an increase in the voltage drop across the electrolyte resistance, i.e. U _V = U _OX + U _O = 60 + 32 = 92 V (the voltage at the anodes 2 reaches 60 V).

Then they switch to the control mode on the bath 1 with U _B electrolyte according to the formula: U _B = U _OX + I _a · R _E , where U _OX is the oxidation voltage in V; I _a - current value of current in A; R _E is the resistance of the electrolyte in Ohms, maintaining the voltage at the anodes equal to the oxidation voltage.

In the proposed method, the oxidation voltage U _OX = 60 V at the anodes is achieved much faster than in the prototype method; and at the same time in the prototype method, the voltage only on the bath U _B = 60 V (figures 2 and 3). Therefore, the time for producing the oxide layer on the anodes of the capacitors is reduced.

Claims (3)

1. A method of producing an oxide layer on the anodes of oxide semiconductor and electrolytic capacitors, based on the electrochemical processing of anodes placed in a bath with an electrolyte, including forming the anodes in the galvanostatic mode, characterized in that they determine the resistance of the electrolyte at the beginning of the galvanostatic mode, which continues until the voltage on the bath, increased by the magnitude of the voltage drop across the resistance of the electrolyte, then go into the voltage control mode on the bath with electric electrolyte, maintaining the voltage at the anodes equal to the oxidation voltage. 2. The method according to claim 1, characterized in that the electrolyte resistance R _e is determined by the formula:

where U _o is the voltage on the bath with electrolyte at the beginning of the galvanostatic mode, B; I _REF. - current, which is set by the technological process, A. 3. The method according to claim 1, characterized in that the voltage control mode on the bath with the electrolyte is carried out according to the formula: U _in = U _ox + I _a · R _e , where U _in - voltage on the bath with electrolyte, B; U _ox is the oxidation voltage, B, I _a - the current value of the anode current, A, R _e - resistance of the electrolyte, Ohm.

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