KR20100018862A - Method of forming transparent conducting film - Google Patents

Abstract

PURPOSE: A method for forming a transparent conducting film is provided to obtain a transparent conducting film with excellent adhesion, visible light transmittance and surface uniformity by successively coating two kinds of ITO sol. CONSTITUTION: A method for forming a transparent conducting film comprises the steps of: (i) coating a transparent substrate with a first conducting sol that has weak adhesive power even though crystals are formed at a relatively low temperature; (ii) forming a first transparent conducting film by heat-treating the transparent substrate coated with the first conducting sol; (iii) forming a mixed layer of the first transparent conducting film and a second transparent conductor by soaking a second transparent conducting sol into the first transparent conducting film, wherein the second transparent conducting sol has stronger adhesive power than the first transparent conducting sol and is crystallized at a relatively high temperature; and (iv) forming a polycrystalline transparent conducting film by heat-treating the first transparent conducting film and the second transparent conductor.

Description

Transparent conductive film formation method {METHOD OF FORMING TRANSPARENT CONDUCTING FILM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of manufacturing display devices, and more particularly, to a method for forming a transparent conductive film for a transparent electrode of a display device.

Transparent conductive films used as transparent electrodes of display devices such as touch panels, plasma display panels (PDPs), and liquid crystal displays (LCDs) are used for physical vapor deposition or chemical vapor deposition (CVD) in vacuum. It can be formed as. In particular, many physical properties such as sputtering, ion plating, and electron beam evaporation using indium tin oxide, aluminum zine oxide (AZO), or antimony tin oxide (ATO) targets There are methods, which are mainly used for the formation of a conductive film having a small sheet resistance of 20 Ω / □ or less, and the sputtering method is most commonly used.The difference in the conductivity, transparency and surface roughness of the transparent conductive film depends on the sputtering method. In general, direct current magnetron sputtering is preferred.

Currently, the transparent electrode used for the resistive touch screen is mainly a transparent conductive film having a sheet resistance of 400Ω / □ to 500Ω / □, which is manufactured by a sputtering method. In order to obtain a large sheet resistance of about 400 Ω / □, ITO should be at least 30 nm thick for the transparent conductive film and at least about 150 nm for AZO. In the case of ITO, in order to obtain 30 nm, it is difficult to obtain a good surface flatness without defects because 10 to 15 nm sized ITO particles should be formed in two to three layers. Therefore, a high-resistance ITO film of 500 Ω / □ or more should be thinner than 30 nm. Therefore, it is not easy to obtain an ITO film having a high sheet resistance by the sputtering method.

ITO is preferred to ATO, which is relatively poor in stability due to its excellent stability at high temperature and high humidity. According to the method of forming a high sheet resistance ITO film using a conventional ITO solution, ITO is applied on a glass substrate by a wet process and subjected to heat treatment. Spin coating or dip coating is used as a wet process. The heat treatment temperature for forming an ITO film having good crystallinity is preferably 600 ° C. or higher (Thin solid films, 411 (2002) 56-59, 515 (2007) 3797-3801). However, in general, considering that the softening temperature of the glass substrate is 530 ° C. or lower, the glass substrate is deformed during the heat treatment of ITO, so the heat treatment temperature should be lowered. In addition, it is also important to maintain the adhesion of the film formed on the glass substrate since a heat treatment process for removing organic matter in the film coated by the wet process is to be performed.

This invention provides the transparent conductive film formation method which can improve the adhesive force of a glass substrate and a transparent conductive film, without causing distortion of a glass substrate.

The method for forming a transparent conductive film according to the present invention comprises the steps of: coating a first transparent conductor sol, which is crystallized at a relatively low temperature but has weak adhesion, on a transparent substrate; Heat-treating the transparent substrate coated with the first transparent conductor sol to remove organic substances and to form a primary transparent conductive film; A mixed layer of the first transparent conductive film and the second transparent conductor is formed by infiltrating the second transparent conductor sol having stronger adhesion than the first transparent conductor sol and crystallizing at a relatively high temperature into the first transparent conductive film. Making; And heat treating the first transparent conductive film and the second transparent conductor to form a polycrystalline transparent conductive film.

According to the present invention, a transparent conductive film used as a transparent electrode of a display device is formed by coating two kinds of ITO sol one by one, thereby providing excellent adhesiveness, and having better visible light transmittance and surface flatness than the transparent conductive film formed by sputtering. A conductive film can be formed.

In addition, according to the present invention, it is possible to easily form a high sheet resistance ITO film, which is difficult to form by the sputtering method, and to form an ITO film having sheet resistance of tens to thousands of Ω by controlling the concentration, film thickness, and heat treatment conditions. There is this.

In addition, the present invention for forming a transparent conductive film by a simple and economic process using spin coating, immersion coating does not require expensive equipment such as sputtering, it is economical at a low production cost.

According to the present invention, in order to form a transparent conductive film used for a touch panel or the like, a first transparent conductor sol, which is easily crystallized at a relatively low temperature but has low adhesion, is coated on a glass substrate, and heat treatment is performed to form an organic material. It removes and forms a primary transparent conductive film. Subsequently, a second transparent conductor sol, which is stronger than the first transparent conductor and crystallized at a relatively high temperature, is coated to infiltrate into the primary transparent conductive film. Thereby, the mixed layer of a primary transparent conductive film and a 2nd transparent conductor is formed. The first transparent conductive film and the second transparent conductor are heat-treated to polycrystallize to form a transparent conductive film. In this heat treatment, seeding effects are induced, crystallization is promoted, and adhesion is maintained.

Hereinafter, the present invention will be described in more detail.

1. Formation of the First Transparent Conductor ITO-A Sol

0.0137 moles of In (CH ₃ COO) ₃ and 0.0015 moles of SnCl _{4 ·} 5H ₂ O are added to a mixed solution of propionic acid and butanol. A mixed solution of propionic acid and butanol added with In (CH ₃ COO) ₃ and SnCl _{4 ·} 5H ₂ O was stirred, followed by heating with dilute nitric acid to form a transparent colorless ITO-A sol of 2 wt% or less. Figure 1 (A) shows the change in phase with the heat treatment temperature of the powder obtained by drying the ITO-A sol. Referring to FIG. 1 (A), when the heat treatment is performed at 350 ° C. for 1 hour, only pure ITO phase is obtained, and the strength does not increase significantly even when the heat treatment temperature is increased to 400 ° C., 450 ° C., and 500 ° C. FIG. That is, it can be seen that complete crystallinity is already obtained at a temperature of about 350 ° C to 400 ° C.

In addition, the surface FESEM photograph (Fig. 2 (A)) of the ITO-A film obtained by spin coating 2 wt% of ITO-A sol at 200 rpm for 30 minutes at 550 ° C. is mainly composed of large grains. Although small sized microparticles of various sizes are shown, the FESEM photograph of the surface of the ITO-A film obtained by heat treatment at 400 ° C. for 10 minutes (FIG. 2B) shows a uniform microstructure of fine particles. Is showing. Any ITO-A film obtained by changing the heat treatment process could not be used as a coating film because of poor adhesion.

2. Formation of Second Transparent Conductor ITO-B Sol

0.0137 moles of In (CH ₃ COO) ₃ and 0.0015 moles of SnCl ₄ · 5H ₂ O are added to a mixed solvent of DMF (dimethylformide) and butanol, followed by stirring, addition of nitric acid, and heating. Form B sol. Figure 1 (B) When a change in the heat-treating the powder obtained by drying the ITO-B sol, such as ITO-A Unlike the development on the ITO slow, in addition to the ITO, even if one hour at 600 ℃ thermal treatment small amounts of SnO ₂ Phase is observed. However, FIG. 3 shows the FESEM of the ITO-B film obtained by heat-treating the ITO-B sol coated with spin coating at 550 ° C. for 30 minutes, and shows a uniform microstructure composed of fine grains unlike the ITO-A film. The ITO-B membrane also showed excellent adhesion.

3. Formation of polycrystalline ITO film

Referring to FIG. 4, an ITO-A sol is spin coated on a soda glass or borosilicate glass (pyrex) substrate 10 (FIG. 4A), and heat treated at 350 ° C. to 400 ° C. A primary ITO film (ITO-A coating film) is formed (FIG. 4B). At this time, in order to prevent scratching of the primary ITO film (ITO-A) by the adhesive force, the heat treatment is performed only to remove the organic matter present in the ITO-A sol to form the primary ITO film (ITO-A) do. For example, the ITO-A sol is heat-treated at 350 ° C. to 400 ° C. for 10 minutes so that the primary ITO film (ITO-A) has a crystal structure as shown in FIG. 2 (B).

Next, the ITO-B sol is coated on the primary ITO membrane (ITO-A) so that the ITO-B sol is permeated into the ITO membrane (ITO-A) by capillary action. As a result, a mixed layer of the primary ITO film ITO-A and ITO-B is formed (FIG. 4C).

Subsequently, the glass substrates of the first ITO film (ITO-A) and the ITO-B mixed layer are dried in an oven, and then heat-treated at 400 ° C. to 600 ° C. to form a polycrystalline ITO film (ITO coating film) having excellent adhesion ( (D) of FIG. 4).

In this heat treatment process, fine crystals of the primary ITO film (ITO-A) crystallized at a relatively low temperature act as seeding and thus penetrate into the primary ITO film (ITO-A). ITO-B, which promotes crystallization and has relatively good adhesion, is permeated between the primary ITO film (ITO-A) and the glass substrate, so that good adhesion between the ITO film and the glass substrate can be expected.

1 (C) is an XRD graph showing the phase development promoting effect of ITO-B sol by ITO-A sol, by adding ITO-A sol to 10 wt% of ITO-A sol. The mixed sols obtained are dried to show a phase change with the heat treatment temperature. From the comparison of (A), (B) and (C) of Fig. 1, the powder obtained from the mixed sol is almost changed to ITO phase by heat treatment at 350 ° C. for 1 hour, and heat treatment at 400 ° C. for 1 hour. It can be seen that only the ITO phase is generated. That is, it can be seen that the phase change of the ITO-B sol is greatly promoted by the ITO-A sol.

Hereinafter, various embodiments of the present invention will be described.

Example  One

The soda glass (110 x 160 x 1.1 mm) substrate was cleaned and dried in an oven, then placed on a spin coater and spun at 200 rpm, poured about 5 ml of ITO-A sol (2 wt% ITO) and spin for 40 seconds. Coating. The soda glass substrate spin-coated with ITO-A sol was placed in an oven at 100 ° C., sufficiently dried, and then heated to 10 ° C. per minute and heat-treated at 400 ° C. for 10 minutes to form a transparent ITO-A film (primary ITO film). Rotate the glass substrate at 150 rpm and pour about 5 ml of ITO-B sol (2 wt% ITO) onto the primary ITO film and coat for about 40 seconds. The soda glass substrate on which the spin coating of ITO-B sol was completed on the primary ITO film was dried in an oven at 100 ° C., and heat-treated at 550 ° C. for 30 minutes to form an excellent adhesive transparent ITO film. The sheet resistance was 760 Ω / square, and the film thickness was 92% at 150 nm and 550 nm. The transmittance was measured by UV-VIS spectra, and the sheet resistance was measured after coating a silver electrode.

Example  2 to 4

The properties of the ITO membrane formed using the sol diluted in Example 1 with 1/2, 1/4, and 1/6 of ITO-A sol are shown in Table 1 below.

ITO-A Sol ITO-B Sol Adhesive Thickness (nm) Sheet resistance (Ω / □) Resistivity (x10 ^-2 Ω? Cm) Transmittance (%) 550nm Example 1 One One Great 150 760 1.14 92 Example 2 1/2 One Great 120 950 1.14 92 Example 3 1/4 One Great 105 980 1.03 92 Example 4 1/6 One Great 90 1150 1.03 92 Comparative Example 1 One 0 Bad 90 Comparative Example 2 0 One Great 83 3100 92

In Comparative Example 1 of Table 1, the ITO-A sol was spin-coated at 200 rpm and then heat-treated at 550 ° C. for 30 minutes by the method described in Example 1 to form an ITO conductive film. Scratches occur, resulting in poor adhesion. In Comparative Example 2, the ITO-B sol was spin-coated at 150 rpm in Example 1, and then heat-treated at 530 ° C. for 1 hour to form a transparent conductive film having excellent adhesion and a sheet resistance of 3100 Ω / □.

Example  5, 6

Examples 5 and 6 vary the concentrations of ITO-A sol and ITO-B sol in Example 1 to form an ITO film. Table 2 shows the characteristics of the ITO membrane according to the concentration change of the ITO-A sol and ITO-B sol.

ITO-A Sol ITO-B Sol Adhesive Thickness (nm) Sheet resistance (Ω / □) Resistivity (x10 ^-2 Ω? Cm) Transmittance (%) 550nm Example 1 One One Great 150 760 1.14 91 Example 5 One 1/3 Great n.a. 1200 n.a. 92 Example 2 1/2 One Great 120 950 1.14 92 Example 6 1/2 1/3 Great 75 1630 1.22 92 Example 7 One One Great 185 390 0.72 92

Example  7

Except for using borosilicate glass (pyrex) instead of soda glass as a glass substrate, the ITO film prepared in the same manner as in Example 1 showed a low resistance.

5 is an SEM photograph of the ITO film formed by Example 1, and FIG. 6 is an ITO film formed by Example 6. FIG.

The transparent conductive film formed according to the present invention may be used for manufacturing a touch screen, a display, a solar cell, a heating glass, and an electromagnetic shielding film. The transparent conductive film thus formed is particularly applicable to the manufacture of transparent conductive panels for touch screens requiring high sheet resistance.

It is to be understood that the above described embodiments are merely illustrative of some of the various embodiments employing the principles of the present invention. It will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the invention.

1 is a graph showing the XRD pattern change with the heat treatment temperature of the powder obtained by drying the ITO sol: (A) ITO-A sol, (B) ITO-B sol, (C) 10 wt% A // B ( 10 wt% ITO-A sol + 90 wt% ITO-B sol).

Figure 2 (A) is a SEM image of the surface of the ITO film obtained by heat-treating the ITO-A sol coating film at 550 ℃ 30 minutes.

Figure 2 (B) is a SEM image of the surface of the ITO film obtained by heat-treating the ITO-A sol coating film at 400 ℃ 10 minutes.

Figure 3 is a SEM image of the surface of the ITO film obtained by heat-treating the ITO-B sol coating film 550 ℃ / 30 minutes.

4 is a schematic view of a transparent conductive film forming process according to an embodiment of the present invention.

5 is a SEM image of the surface of the ITO membrane prepared in Example 1. FIG.

6 is a SEM image of the surface of the ITO membrane prepared in Example 6. FIG.

Claims (6)

As a transparent conductive film formation method, Coating a first transparent conductor sol, which is crystallized at a relatively low temperature, but which has weak adhesion, on the transparent substrate; Heat treating the transparent substrate coated with the first transparent conductor sol to form a primary transparent conductive film; A mixed layer of the first transparent conductive film and the second transparent conductor is formed by infiltrating the second transparent conductor sol having stronger adhesion than the first transparent conductor sol and crystallizing at a relatively high temperature into the first transparent conductive film. Forming; And And heat treating the primary transparent conductive film and the second transparent conductor to form a polycrystalline transparent conductive film. The method of claim 1, The primary transparent conductive film and the polycrystalline transparent conductive film are both ITO films, Wherein the first and second transparent conductor sols are first and second ITO sols, respectively. The method of claim 2, The first ITO sol, In (CH ₃ COO) ₃ and SnCl _{4 ·} 5H ₂ O were added to a mixed solution of propionic acid and butanol, and propionic acid to which In (CH ₃ COO) ₃ and SnCl _{4 ·} 5H ₂ O was added. A method of forming a transparent conductive film formed by stirring a mixed solution of butanol and adding diluted nitric acid and then heating. The method of claim 3, The second ITO sol, A method of forming a transparent conductive film formed by adding In (CH ₃ COO) ₃ and SnCl ₄ · 5H ₂ O to a mixed solvent of DMF (dimethylformide) and butanol, stirring and adding nitric acid, followed by heating. The method of claim 1, And injecting the second transparent conductor sol into the primary transparent conductive film, allowing the second transparent conductor sol to soak between the transparent substrate and the primary transparent conductive film. 6. The method according to any one of claims 1 to 5, The primary transparent conductive film is formed by heat treatment at 350 ℃ to 400 ℃, the polycrystalline transparent conductive film is formed by heat treatment at 400 ℃ to 600 ℃, a transparent conductive film forming method.

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