JPH0345485B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a transparent conductive film for use in transparent electrodes for liquid crystals, in which a conductive film mainly containing indium is provided on a polymer. Conventionally, transparent conductive films are mainly based on polyester films, and are used in transparent electrodes of electroluminescent displays and electrochromic displays, surface heating elements such as day frosters and transparent heaters, surface switches such as touch panels, infrared reflective films, and Although it is widely used in transparent flexible circuit boards, etc., its application to liquid crystal display elements has recently been considered. Application to liquid crystal display elements is that by using film-shaped electrodes, the element can be made thinner, it is easy to handle in the production process, and punching processing is possible, and continuous production is possible if it is a film-shaped material. It has the following characteristics. The required performance of normal transparent conductive film is as follows:
It has good transparency and good conductivity. Furthermore, in order to use it as a transparent electrode for liquid crystal, it is necessary that conductivity defects or disconnections do not occur during processing. Also, in the processing process,
The causes of such defects are thought to be mainly abrasions caused during handling and dissolution in an alkaline aqueous solution during the etching process. Therefore, it is required to have excellent scratch resistance and alkali resistance. Another necessary characteristic is the absence of optical anisotropy. For example, in the case of a uniaxially stretched polyester film having optical anisotropy, the axis of optical anisotropy must be precisely aligned with the axis of a polarizing plate used in a liquid crystal element, resulting in very poor workability. Furthermore, heat resistance is also an important characteristic from the viewpoint of processability. A transparent conductive film that satisfies all of the above-mentioned properties has not only not been seen in the past, but also no consideration has been given to such characteristics. The present inventors used polyether sulfon film as a base material because it does not have optical anisotropy and has heat resistance, and as a result of intensive research to satisfy all of the above properties, we found that it can be used as a transparent electrode for liquid crystals. We have successfully developed a transparent conductive film with unprecedented performance. The manufacturing method will be described in detail below. As mentioned above, polyether sulfon film does not have optical anisotropy and is heat resistant, so it is suitable as a base material for transparent conductive films. However, because it is hygroscopic, it can only be obtained with poor conductivity and processability under the same conditions as conventional polyester films. Conventionally used polyester films and glass absorb little moisture, so they do not require any special pretreatment, and can be used as transparent conductors by reducing the vacuum level to about 2 x 10 ^-3 Torr, which is the standard sputtering range. was completed. On the other hand, in the case of polyether sulfonate film that easily absorbs moisture, as a result of various studies conducted by the present inventors,
It was found that it is necessary to dehumidify for 5 minutes or more under a high vacuum of 10 ^-4 Torr or less. It has been found that if this condition is not met, only an unstable transparent conductive film with poor conductivity can be obtained. It is known that a transparent conductive film can be formed on a plastic substrate by, for example, a vacuum evaporation method or a sputtering method. In particular, the sputtering method has attracted attention because it can form a low-resistance film with excellent adhesion on a substrate with relatively low heat resistance without post-treatment, but conventional sputtering equipment has It was not used much because the speed was very slow and the temperature of the substrate rose rapidly. Recently, a magnetron type sputtering apparatus has appeared as an improved version of the sputtering apparatus which has various drawbacks as described above. This magnetron-type sputtering device applies a magnetic field to the target as an evaporation source, confines electrons in the magnetic field, increases the ionization effect, and increases the plasma density, thereby preventing the temperature of the substrate from rising and achieving a high deposition rate. It also has the advantage of being able to reduce working pressure. In general, a high deposition rate is preferable from the viewpoint of productivity, but in the present invention, if the deposition rate of the conductive film is set to 300 Å/min or more, the crystal lattice of the conductive film will be disturbed, internal stress will increase, and the resistance will increase. It was found that only an unstable film was formed due to deterioration of scratch resistance. Further, an oxide containing indium as a main component was used for the conductive film. When forming a conductive film as in the present invention, conductivity,
Substrate heating is often used as a means of improving transparency. For example, when using glass as a base material, the base material is usually heated to about 350℃ to lower the resistance and
We are aiming for high transparency. This is to remove water adhering to the surface of the base material, stabilize the oxidation and crystallization of the conductive film, and form a well-ordered crystal lattice.
This is not preferable because it not only reduces the adhesion between the conductive film and the base material, but also increases the internal stress of the conductive film and increases the resistance. In this case, it has also been found that when the dimensional change of the base material is 0.5% or more, the above phenomenon occurs in the case of a conductive film of an oxide containing indium as a main component. For example, polyester film, which is said to be relatively heat resistant, has a
This range is exceeded when heated to ℃. On the other hand, in the case of polyether sulfonate film, the dimensional change is less than 0.5% even when heated to 100℃, so it is possible to heat the base material, but low resistance and high transparency can be obtained.
It has also been found that when used as an electrode for liquid crystal, the temperature range for heating the substrate without causing deterioration of various properties is 70 to 100°C. For example, sufficient transparency and conductivity cannot be obtained at temperatures below 70°C, and conductive films formed at temperatures above 100°C may suffer from poor adhesion due to heat shrinkage or increased internal stress, as seen with polyester films. etc., instability and deterioration of various characteristics were observed. In general, in the case of sputtering, it is possible to form a thin film on a substrate using the target substance as it is, but when a compound is used as a target, decomposition of the compound occurs and decomposition products are contained in the thin film. There is a possibility that Also in the present invention,
Lower oxides produced by decomposition of the target substance are contained in the conductive film, causing poor conductivity and transparency. In order to prevent this, we have found that it is effective to include oxygen in argon, which is a sputter gas. If the amount of oxygen is too small, the formation of lower oxides cannot be prevented, resulting in poor conductivity and transparency. Furthermore, since the crystalline state is not adjusted, it also leads to deterioration of scratch resistance and alkali resistance. On the other hand, when oxygen is excessive, the transparency does not change, but the conductivity becomes poor. Scratch resistance and alkali resistance are better when oxygen is slightly excessive, but since the present invention is aimed at transparent electrodes for liquid crystals, even if the conductivity is slightly deteriorated, other scratch resistance and alkali resistance can be improved. As a result of careful consideration from this point of view, we found that the amount of oxygen in the spatter gas is
It has been found that introducing 2 vol% is a suitable condition for a transparent electrode for liquid crystals. Even under the conditions described above, a transparent conductive film with relatively good properties and excellent transparency and conductivity can be produced, but it is necessary to further improve processability in order to use it as a transparent electrode for liquid crystals. . Regarding processability, no study has been made regarding conventional transparent conductive films. However, now that transparent conductive films are being used not only as electrodes for liquid crystals as in the present invention, but also in various other applications, the demands for processability are increasing among users. In the present invention, two performances are required for workability. It has abrasion resistance that can withstand abrasion during handling, and alkali resistance that makes it difficult to dissolve in alkaline aqueous solutions used in the etching process. These two problems can be improved to some extent by improving the conditions for producing the conductive film, but as a result of further investigation, it was found that the conductive film can be strengthened by increasing the film thickness. This is because when the membrane is thin, it resembles an island-like structure, so it is easily destroyed and disconnected by a slight external force, and when immersed in an alkaline aqueous solution,
Even if the film is etched by a small amount, the rate of increase in resistance is extremely large and wires are easily broken. However, if the film is too thick, not only will transparency be poor, but flexibility will also be lost. As a result of extensive research, we discovered that a stable continuous film with good properties could be formed by increasing the film thickness to 400 Å or more.
If the film thickness is increased to 550 Å or more, it will no longer satisfy the condition of visible light transmittance of 80% or more for use in liquid crystals, so the thickness of the conductive film should be 400 to 550 Å.
is the most suitable. Examples of the present invention will be described below. Example 1x 100μm polyether sulfon
It was dehumidified for 5 minutes under a high vacuum of 10 ^-4 Torr. Thereafter, the substrate temperature was raised to 80°C, and argon containing 1 vol% oxygen was introduced into the system. The conductive film is deposited at a deposition rate of 200 Å/min using a DC magnetron sputtering device.
It was formed in The film thickness was 500 Å. The transparent conductive film thus obtained has a sheet resistance of
The transmittance of visible light was 80% at 300Ω/mouth. Abrasion resistance was evaluated by rubbing several times with gauze under load. Alkali resistance was evaluated by immersing it in 10% sodium hydroxide for 5 minutes. No matter which test was conducted, there was almost no change in resistance value and the results were good.
The following study was conducted as a comparative example. Comparative Example 1 The same substrate was dehumidified at 5×10 ⁻⁴ Torr for 5 minutes.
Thereafter, a conductive film was formed under the same conditions as in the example. In this case, the resistance value is 700Ω/mouth, and the scratch resistance and
Alkali resistance was poor. Comparative Example 2 The same substrate was dehumidified for 5 minutes under a high vacuum of 1×10 ⁻⁴ Torr. Thereafter, the substrate was heated to a temperature of 50°C. A conductive film was formed under the same conditions as in the example. In this case, the resistance value was as high as 400Ω/mouth. Comparative Example 3 The same substrate was dehumidified at 1×10 ⁻⁴ Torr for 5 minutes.
Thereafter, the substrate temperature was set to 150°C. A conductive film was formed under the same conditions as in the example. In this case, the scratch resistance and alkali resistance were poor. Comparative Example 4 The same substrate was dehumidified at 1×10 ⁻⁴ Torr for 5 minutes.
Thereafter, the substrate temperature was raised to 80°C and oxygen-free argon was introduced into the system. A conductive film was formed under the same conditions as in the example. In this case, the resistance value is 500Ω/
The transparency was also poor, with a transmittance of 75%. Scratch resistance and alkali resistance were also poor. Comparative Example 5 The same substrate was dehumidified at 1×10 ⁻⁴ Torr for 5 minutes.
Thereafter, the substrate temperature was raised to 80°C, and argon containing 3 vol% oxygen was introduced into the system. A conductive film was formed under the same conditions as in the example. In this case the resistance value is 700
Ω/ My mouth was high. Comparative Example 6 The same substrate was dehumidified at 1×10 ⁻⁴ Torr for 5 minutes.
Thereafter, the substrate temperature was raised to 80°C, and argon containing 1 vol% oxygen was introduced into the system. Deposition speed 500Å/min
A conductive film was formed. The film thickness was 500 Å. In this case, the sheet resistance was 400Ω/mouth, and the scratch resistance and alkali resistance were also poor. Comparative Example 7 The same substrate was dehumidified at 1×10 ⁻⁴ Torr for 5 minutes.
Thereafter, the substrate temperature was raised to 80°C and argon containing 1 vol% oxygen was introduced into the system. Deposition speed of conductive film
It was formed at 200 Å/min. The film thickness was 300 Å.
In this case, the resistance value will be 500Ω/mouth and scratch resistance.
Alkali resistance became poor. Comparative Example 8 The same substrate was dehumidified at 1×10 ⁻⁴ Torr for 5 minutes.
Thereafter, the substrate temperature was raised to 80°C, and argon containing 1 vol% oxygen was introduced into the system. Deposition speed of conductive film 200
Formed at Å/min. The film thickness was 600 Å. In this case, the transmittance was 75%, which was poor. The results of the above Examples and Comparative Examples 1 to 8 are shown in Table 1. 【table】

Claims (1)

[Claims] 1 After removing moisture from polyether sulfon film in a high vacuum of 2×10 ^-4 Torr or less using a magnetron type sputtering device for more than 5 minutes,
While heating to 100℃, the deposition rate is 300Å/min or less in argon gas containing 1 to 2 Vol% oxygen.
A method for producing a transparent conductive film, which comprises sputtering an oxide containing indium as a main component to a thickness of 400 to 550 Å to form a transparent conductive film.