JPH06187833A - Transparent conductive film - Google Patents

Abstract

PURPOSE:To provide a transparent conductive film with low resistance and high transmissivity, even when manufactured at a high speed, and high grade and low cost without marring electric property, even after given high- temperature heat treatment in an oxidizing atmosphere such as an air atmosphere, by controlling the concentration of potassium and crystallinity to preset values. CONSTITUTION:A transparent conductive film contains 0.1atom% or more and 15atom% or less potassium with respect to zinc, and in a X-ray diffraction pattern it has a diffraction peak on the plane (002) and the half value width of a diffraction line being 1.2 degrees or less on the plane (002). Otherwise, it contains 0.5atom% or more and 12atom% or less potassium with respect to zinc, and in a X-ray diffraction pattern it has a diffraction peak on the plane (002) and the half value of a diffraction line being 0.6 degree or less on the plane (002). The specific resistance is 10<-2>OMEGA.cm or less and the thickness 100Angstrom or more and 5mu or less. The film with the concentration of potassium being 0.5atom% or more and 12atom% or less at an atomic ratio shows high conductivity, when formed, and high grade and low cost without marring electric property even after given heat treatment in the air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent conductive film having a high performance, particularly a transparent electrode for display such as a liquid crystal display device and a plasma light emitting device, a transparent electrode for a solar cell, a heat ray reflecting film and a transparent heating element. The present invention relates to a useful transparent conductive film and a transparent heating element having the transparent conductive film.

[0002]

2. Description of the Related Art A transparent conductive film has both high transmittance and high conductivity in the visible light range, and is used for a transparent electrode for a display element such as a liquid crystal display element, a plasma light emitting element, an EL (electro luminescence) element, or the like. , Solar cells, TFTs, and other transparent electrodes of various light receiving elements. In addition, heat-reflecting films for automobiles and buildings, antistatic films for photomasks and other applications, various anti-fog windows such as freezer showcases, glass with melting ice and anti-fog function for automobile windshields (Electrically Heated) Window, EHW
It is widely used for transparent heating elements such as. Furthermore, it is also used as a substrate for electrochromic devices as light control glass.

Conventionally, as a transparent conductive film, tin oxide (SnO ₂ ) containing antimony or fluorine as a dopant, indium oxide (In ₂ O ₃ ) containing zinc as a dopant, zinc oxide, etc., is deposited on a glass substrate. Known indium tin oxide film (hereinafter referred to as IT
The O film) is widely used mainly as an electrode for a display element such as a liquid crystal because a low resistance film can be easily obtained.

The conductive glass for reach indoors is formed by spraying a raw material liquid onto a substrate heated to several hundreds of degrees by a spraying method and causing a thermal decomposition reaction on the substrate surface to form a tin oxide film. Fluorine and antimony are often used as the dopant for imparting conductivity to the film. However, in the spray method, for a large substrate of about 1 m × 2 m used in reach indoor or EHW, a film having a uniform film quality can be stably produced with a uniform film thickness over the entire processing area. Is very difficult.

If the film thickness is not uniform, the reflectance and the reflected color become uneven, resulting in an unsightly appearance. Also, if the sheet resistance is not uniform in the film surface, abnormal heating or local abnormal heating may occur when electricity is applied. However, there is a portion that is not heated, which is not preferable in terms of function or safety. In addition, when the film is formed, it is easy for the film to wrap around the back surface of the substrate, and it is difficult to effectively mask the peripheral portion and the area around the electrode lead-out portion where the film is not desired. However, there is a problem in that the process becomes complicated and the cost increases.

Further, a film system using a metal thin film having a film thickness of several hundred liters by a sputtering method is used for EHW. The metal film has a high transmittance in the visible region in order to secure the transparency required as a window material for vehicles in the visible region (400 to 700 nm), and it can be driven by an electric system (12 to 24 V) of an automobile. It is necessary to simultaneously satisfy the two points of low resistance, and silver is used because it is most suitable among various metal materials.

Usually, for the purpose of increasing the transparency in the visible region and preventing a staggered appearance, both sides of the silver layer are sandwiched by transparent dielectric films to reduce the reflectance in the visible region. It is used in a three-layer structure in which optical conditions are adjusted, or in a five-layer film structure in which both sides and two layers of silver are sandwiched by a transparent dielectric film. However, the so-called electromigration phenomenon is known in the metal thin film, and if current is continued,
Metal atoms in the film easily diffuse at the grain boundaries and within the grains to form hillocks and voids, which easily causes film breakage.

Further, since the silver film originally has low durability to the environment, it is easily susceptible to chemical attack due to moisture, etc., and is suitable as a transparent heating element which replaces the silver laminated film system from the viewpoint of demand for improvement in reliability. A new membrane system was desired.

As a transparent conductor film capable of imparting electric conductivity to a transparent substrate to give a function as a transparent heating element, a doped tin oxide film formed by a vapor deposition method or an ion plating method, Similarly, there are ITO and doped zinc oxide films formed by vapor deposition, ion plating and sputtering. However, for the tin oxide film, it is difficult to form a low-resistance transparent conductive film suitable for a transparent heating element by such a so-called physical vapor deposition method.

Regarding the ITO film, a low resistance film can be easily obtained, and a transparent electric film having uniform characteristics and film thickness even on a large area substrate suitable for EHW and reach indoors, especially by the sputtering method. It is possible to form
Since indium is a rare metal, it is expensive, and there is a limit to lowering the cost of the treated substrate, which hinders the expansion of the application of the transparent heating element to a wide range of fields. In addition, the resource reserve of indium is particularly small compared to other elements, and since it is extracted as a by-product during refining of zinc ore, its production amount also depends on the zinc production amount. Have difficulty.

In the future, when the demand for a transparent conductive film including other uses such as display devices is increased, in the case of ITO, there is a problem in stable supply of indium as a raw material. On the other hand, it is known that in a transparent conductive film containing zinc oxide (ZnO) as a main component, when aluminum is used as a dopant, a low resistivity of the order of 10 ⁻⁴ Ω · cm, which is comparable to that of an ITO film, can be obtained. At the time of film formation, in order to avoid damage to the film due to high energy particle bombardment, it is necessary to arrange the substrate vertically with respect to the target, apply an external magnetic field, or use a non-oxidizing atmosphere after film formation. Heat treatment was required.

Further, it is difficult to manufacture the low resistance film with good reproducibility because it is easily affected by the change of the target property with time, and the film forming rate of the low resistance film is extremely small, about 5 Å / sec or less. In actual industrial production, there is a fatal problem that the production speed is slow, and it has not been widely used.

On the other hand, when a transparent conductive film is applied to an electrode of a display element or the like, the temperature is from 300 ° C.
The heat treatment is performed at a high temperature of about 00 ° C. In this case, heat treatment in an inert gas is also possible, but equipment for holding the atmosphere is required, which causes an increase in cost. Therefore, industrially, heat treatment in the atmosphere is required.
When the transparent conductive film is used as a heating element, the conductive film is used while being electrically heated in the atmosphere. Therefore, it is required that the change in resistance value due to heat generation is small, that is, heat resistance in an oxidizing atmosphere.

Also, when a transparent conductive film is applied as the heat ray reflective glass, high temperature heat treatment of 600 ° C. or higher is performed in the atmosphere when performing bending or strengthening, so that similar heat resistance is required. As described above, when the transparent conductive film is applied to the industrial field, not only heat resistance in a non-oxidizing atmosphere but high heat resistance in the air is required.

In this respect, the ITO film is not sufficient but has heat resistance in the atmosphere. For this reason, ITO is mainly used for liquid crystal display devices and the like, because it is required only to have heat resistance at a relatively low temperature around 300 ° C. On the other hand, the conventional ZnO film (without an additive) is significantly inferior to ITO in heat resistance in an oxidizing atmosphere, and improvement in heat resistance in an oxidizing atmosphere has been a problem in practical use.

Therefore, in order to improve the heat resistance of this ZnO film, as disclosed in Japanese Patent Publication No. 3-72011, ZnO is conventionally doped with an impurity of Group 3 of the periodic table so that argon can be added. It has been shown that the heat resistance is improved in a non-oxidizing atmosphere such as an air stream or a vacuum.

However, when impurities of Group 3 are added,
Although the heat resistance in an inert gas atmosphere or a reducing gas atmosphere is improved, a high temperature heat treatment at 400 ° C. in an air atmosphere may increase the electrical resistance by four digits or more, so that it cannot be used as a conductive film. It is also known (Technical Report of IEICE, CPM84-8,55 (1984)). Due to this lack of heat resistance in the atmosphere, the ZnO film is delayed in practical use as a transparent conductive film.

When the transparent conductive film is applied as the display element substrate, the transparent heating element, and the heat ray reflective glass as described above, the transparent conductive film undergoes high temperature heating in the atmosphere, and therefore the electrical and optical characteristics of the conductive film are improved. Having properties that are not compromised becomes extremely important. However, conventionally, a transparent conductive film containing ZnO as a main component has been expected as a low-cost material to replace ITO, but its heat resistance in an oxidizing atmosphere is insufficient, and thus its widespread practical application and industrialization have been delayed. Zn improves the heat resistance of
It has been regarded as the biggest problem of the O film.

[0019]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art, obtains a conductive film having a low resistance and a high transmittance even when it is manufactured at a high speed, and has an atmosphere or the like. High-quality and low-cost transparent conductive film having properties that do not impair electrical properties even in high-temperature heat treatment in an oxidizing atmosphere, particularly display element electrodes, transparent heating elements for construction and automobiles,
An object is to provide a transparent conductive film industrially useful as a heat ray reflective glass.

[0020]

The present invention has been made to solve the above-mentioned problems, and is a transparent conductive film containing zinc oxide as a main component, the transparent conductive film containing gallium against zinc. Content of 0.1 atom% or more and 15 atom% or less, the X-ray diffraction pattern thereof has a diffraction peak of the (002) plane, and the full width at half maximum of the diffraction line of the (002) plane is 1.2.
And a transparent heating film characterized by having the transparent conductive film on a substrate.

The transparent conductive film in the present invention contains gallium in an amount of 0.5 atom% or more and 12 atom% or less with respect to zinc.
It is preferable that the X-ray diffraction pattern has a diffraction peak due to the (002) plane and the half width of the diffraction line due to the (002) plane is 0.6 degrees or less.

The transparent conductive film in the present invention preferably has a specific resistance of 10 ^-2 Ω · cm or less and a film thickness of 100 Å or more and 5 μ or less. If the film thickness is 100 Å or less, there is a problem that a discontinuous film is liable to be formed and the film is likely to be broken in coating the step portion.
Further, if the film thickness is 5 μm or more, the film formation time becomes long, which causes an increase in cost. On the other hand, when the specific resistance is 10 ⁻² Ω · cm or less, the sheet resistance required as a transparent heating element can be satisfied in the above-mentioned film thickness range.

The transparent conductive film of the present invention (hereinafter, also simply referred to as a conductive film) may contain a metal element other than Zn and Ga in a range that does not impair the purpose of the present invention, but it is not a problem and the amount thereof is as small as possible. It is desirable to keep it.

Further, glass, plastic or the like can be used for the substrate forming the transparent conductive film of the present invention. When the substrate contains an alkali metal as its component, such as soda lime glass, in order to prevent the diffusion of the alkali metal from the substrate to the conductive film during film formation, heat treatment or long-term use, It is more preferable to form a base layer containing an oxide of a metal such as Si, Al, or Zr as a main component between the conductive films.

The method for forming the conductive film of the present invention is not particularly limited, and a physical vapor deposition method such as a sputtering method or a vacuum vapor deposition method or a chemical vapor deposition method such as a CVD method is used, and a good electrical conductivity is obtained at a lower substrate temperature. A physical vapor deposition method that can obtain film characteristics is preferable. Among them, a sputtering method using a high-density plasma effective as a activating means for promoting crystallinity, a low-voltage sputtering method using a high magnetic field, and
The plasma activated vacuum deposition method is more preferable for obtaining a film having low resistance and excellent heat resistance. When forming the transparent conductive film of the present invention by the sputtering method, the target is not only added with a predetermined amount of gallium oxide in zinc oxide and then sintered, but preferably at a temperature of 1400 ° C. or higher for 2 hours or more. It is preferable to use a material that has been subjected to a treatment for holding it so that gallium oxide is sufficiently dissolved in zinc oxide to form a solid solution. In the examples, the direct current method is shown as the sputtering method, but it goes without saying that this may be performed by a high frequency method.

In the conductive film according to the present invention, for example, when the conductive film is formed by the magnetron DC sputtering method,
Since low resistance and high heat resistance in the atmosphere are secured even when a film is formed at a high speed of up to 40 Å / sec, it is possible to grow the film at a practical film formation rate.

In the transparent heating element of the present invention, for the purpose of adjusting the appearance, one or more undercoat films are provided between the transparent conductive film layer and the substrate, or one or more overcoats are formed on the transparent conductive film layer. By providing a coat film, it is possible to adjust the transmission / reflection color tone and the visible light reflectance by utilizing the light interference phenomenon and the film absorption.

The film material of at least one layer of the undercoat film or at least one layer of the overcoat film is, for example, silicon oxide, titanium oxide, zirconium oxide, tin oxide, tantalum oxide, chromium oxide, niobium oxide or boron oxide. , At least one selected from the group consisting of indium oxide, zinc oxide, and cerium oxide, or a metal of titanium, zirconium, hafnium, chromium, or niobium, a nitride of the metal, and an oxynitride of the metal. At least one selected from the group can be exemplified.

The above-mentioned undercoat film and overcoat film can be effectively used for the purpose other than adjusting the optical characteristics. For example, it is effective for the purpose of imparting durability in order to improve the handleability of the coated product before the combination. In addition, with other bases, in a combined structure,
Alternatively, when using a multi-layer structure or when attaching the lead-out part of the electrode lead, the purpose is to adjust the adhesiveness with the interlayer film, spacer, other parts to be assembled in the mating structure, or after forming the transparent heating element. , For the purpose of imparting heat resistance to withstand high temperature processes such as laminated glass formation, bus bar and electrode formation, strengthening and bending of glass substrates, and increasing reliability for use at high temperatures. But still effective.

The transparent heating element of the present invention can of course be used as a substrate alone having a transparent conductive film formed thereon, but it is subjected to a strengthening treatment or a pair of transparent substrates to satisfy safety standards for automobiles, for example. It is possible to carry out an adhesive treatment via the resin film or only with the resin film.

In the transparent heating element according to the present invention, at least two or more electrode lead-out portions for energization are provided, and the electrode lead-out portions have direct current, alternating current, or a voltage in which direct current and alternating current are superposed. The transparent substrate is heated by its Joule heat by being applied continuously or in a pulsed manner by duty driving for turning it on and off.

In the transparent heating element of the present invention, if necessary, a detecting means may be provided for the purpose of temperature control during electric heating, abnormal heating, and abnormality detection such as cracking of the transparent heating element.

FIG. 3 is a sectional view of the transparent heating element of the present invention, and FIG. 4 is a plan view of an EHW using the transparent conductive film of the present invention. In the figure, 1 is an overcoat layer, 2
Is a gallium-doped zinc oxide layer, 3 is an undercoat layer,
Reference numeral 4 is a substrate, 5 is an upper bus bar, 6 is a transparent heating film coating portion, 7 is a lower bus bar, and 8 is a substrate.

[0034]

The present inventors controlled the Ga concentration in the ZnO transparent conductive film to be 0.5% or more and 12% or less in atomic ratio, and the half-width of the (002) X-ray diffraction line of the film was 0.6. By controlling the crystallinity of the film so that
It has been found that a material as low as 10 ⁻⁴ Ω · cm, which is as low as ITO, can be easily obtained even when it is manufactured at high speed with a normal substrate arrangement. Further, they have found that these films do not deteriorate in conductivity after heat treatment in air at 500 ° C. or higher, and have extremely excellent heat resistance in an oxidizing atmosphere.

The simple addition of Ga to ZnO has already been reported (J. Electrochem. Soc, 127, 1636 (198).
0), Jpn.J.Appl.Phys, 24, L781 (1985)). The former is Zn
Is an example in which 1 atomic% of Ga is added, and the latter is Z
This is an example of a sputtering method in which 1 atomic% to 4 atomic% of Ga is added to n. However, in each case, it is a report example in which the addition film and the non-addition film were compared and examined in terms of electrical and optical characteristics, and no examination or description regarding heat resistance was found. Moreover, the conductivity of these films is inferior to that of the conventional Al-added film.

On the other hand, the present invention makes it possible to significantly improve the electrical characteristics and the heat resistance in the atmosphere by controlling the Ga addition amount and the crystallinity of the film. That is, the heat resistance does not appear only by including Ga,
It was found that Ga appears only when the content of Ga is within a specific range and the value of the half width of X-ray diffraction is less than or equal to the specific value.

It is generally well known that when ZnO is added with a metal of Group 3 of the periodic table, the electron density increases and the conductivity increases. It is considered that this is because the group 3 or trivalent metal substitutes at the position of divalent Zn to form a shallow electric donor and generate a free electron. At the same time, it is possible to explain the increase in electron density due to donor formation due to excess Zn being generated at interstitial sites and oxygen defects. It is presumed that these are mixed in the actual film. Group 3 elements and Z
Since the ionic radii of n are not the same, it is conceivable that crystal lattice distortion will occur even if they are replaced.

It is considered that not all the Group 3 elements can be replaced, but some of them are precipitated between crystal lattices or at grain boundaries. This is because the amount of the Group 3 element detected in the film is larger by about one digit than the amount theoretically calculated from the electron density. Since these excess elements cause lattice distortion, it is expected that oxygen vacancies will be generated. Defects such as oxygen vacancies are reduced by heat treatment in a high-temperature oxygen atmosphere, and at the same time, the electron density generated by the vacancies is also reduced, which leads to an increase in resistance.

Actually, the ZnO film to which a group 3 element of Al, In, and B other than Ga is added has excellent heat resistance in a non-oxidizing atmosphere, but has extremely poor heat resistance in an oxidizing atmosphere such as the air. As a result of detailed examination of the relationship between the composition and crystallinity of the film and the thermal stability in the atmosphere by X-ray diffraction, the present inventors have found that the additive element is Ga, not simply the Group 3 element,
Moreover, it has been found that a film having a high heat resistance in the atmosphere can be obtained only when the added amount is within a specific range and in addition, the half width of the X-ray diffraction of the film is less than a certain value.

The difference in ionic radius can be considered as the cause of the difference in heat resistance in the atmosphere when the additive element is Al, B, In and Ga. That is, the ionic radii of Al and B are too small compared with Zn, respectively, and conversely In is too large. Since the ionic radius of Ga is the closest to that of Zn, it is considered that the lattice strain in the case of substitution is the smallest. In order to obtain a low resistance film, it is necessary to add a large amount of Al, B and In. In this case, it is considered that the strain increases and oxygen vacancies are generated. It is considered that this defect is easily reduced by high-temperature heat treatment in an oxidizing atmosphere, and at the same time, the number of free electrons generated by the defect is also reduced, so that the resistance is increased.

On the other hand, in the case of a Ga-added film, it is considered that even if a large amount of Ga is added, lattice strain and oxygen defects are less likely to occur, so that the heat resistance in an oxidizing atmosphere is also improved. It was found that the heat resistance also strongly depends on the crystallinity of the film even when Ga is added, and when the film has good crystallinity, that is, when the half width of the X-ray diffraction line is less than a certain value, the heat resistance in an oxidizing atmosphere is remarkably high. It turned out to improve.

[0042]

【Example】

[Examples 1 to 6 and Comparative Examples 1 to 9] Examples of the present invention will be described in detail below with reference to the drawings. Prepare a glass substrate (5 cm × 5 cm × 1 mm) on which a silica film having a thickness of about 500 Å is formed as an alkali barrier coat, and gallium oxide (ZnO G
A ZnO transparent conductive film having a film thickness of 3000 Å to 10000 Å was formed in an Ar atmosphere by using various targets (Ga / Zn ratio of 0.3 to 15 atom%) to which a ₂ 0 ₃ ) was added. The target used at this time is a target in which gallium oxide is added to ZnO and then held at a temperature of 1400 ° C. or higher for 2 hours or more to sufficiently dissolve gallium oxide in ZnO.

The vacuum apparatus was evacuated to 10 ^-6 Torr or less in advance, and then Ar gas was introduced at 0.01 Torr for sputtering. The substrate temperature was set in the range of room temperature to 300 ° C. The sputtering power was set to 50 W as a standard condition, but was changed to 400 W as an example of high-speed film formation.

ZnO containing no impurities for comparison
Aluminum oxide (Al
₂ O ₃ ), indium oxide (In ₂ O ₃ ), boron oxide (B ₂ O ₃ ) added to various targets (Al / Zn
A ratio of 4 atomic%, an In / Zn ratio of 5 atomic%, and a B / Zn ratio of 4.5 atomic%) were prepared by a sintering method, and a sample of a comparative example was prepared by using this.

The Ga content in the produced film was quantitatively analyzed by ICP emission spectrometry after the ZnO film was dissolved in a 2N solution of hydrochloric acid. Ga content is atomic% based on zinc
Expressed as The specific resistance was calculated from the sheet resistance obtained by the 4-probe method and the film thickness measured by a stylus type film thickness meter.

The X-ray diffraction of the conductive film was measured by using a Kα ray of Cu with a rate meter using a proportional coefficient tube.
An example of X-ray diffraction measurement is shown in FIGS. This is an enlargement of the (002) X-ray diffraction peak for Example 3 and Comparative Example 4 of the ZnO film to which Ga was added, as described later.
As shown in the figure, 1/2 of the maximum intensity of the (002) peak
The line width (expressed in degrees) of the diffraction line having the intensity of is called a half-value width (half-value width), but in the case of Example 3 in FIG. 1, the half-value width is 0.28.
And 0.82 degrees in the case of Comparative Example 4 in FIG.

The visible light transmittance was measured by a spectroscope using an integrating sphere, and the transmittance was evaluated by an average value of wavelengths of 400 nm to 700 nm. These conductive films were subjected to a heat treatment test in air under the conditions shown in Table 1. Tables 2 and 3 show the results of measurement of changes in properties before and after heat treatment.

[0048]

[Table 1]

Examples 1, 2, 3, 4, 5, 6 shown in Table 2
Is the heat resistance test result for the film when the Ga addition amount is 0.5 atom% or more and 12 atom% or less and the half width of the (002) X-ray diffraction line is 0.6 degree or less. Example 3
The full width at half maximum of the X-ray diffraction line of the film is 0.28 as shown in FIG.
It was degree. These films have a film thickness of 10 ^-3 Ω · c
In addition to exhibiting a high conductivity of m to 10 ⁻⁴ Ω · cm,
Even after the heat treatment in the air at 500 ° C. for 10 minutes, the conductivity does not decrease, and the conductivity is equal or, conversely, improved.

No change in transmittance was observed, and it was found that the film was stable against heat treatment in the atmosphere. Especially noteworthy is the example of the high-speed film formation shown in Example 4, but even when the film is formed at a high speed of 40 Å / sec, a film having a small half-value width of 0.45 ° is 2 immediately after the film formation. It was found that the resistance was as low as × 10 ⁻⁴ Ω · cm and was stable even after the heat treatment in the air.

[0051]

[Table 2]

On the other hand, comparative examples 1 and 2 in Table 3 show examples in which the amount of Ga was too small even though it was added. Comparative Example 1 was undoped ZnO, and no heat resistance was observed, as is conventionally known. When Ga was added in an amount of 0.3 atomic%, the half-value width was good as shown in Comparative Example 2, but practically only insufficient heat resistance was obtained.

In Comparative Examples 3 and 4, the amount of Ga added is 0.5 atom%.
The above is an example in which the half width is as large as 0.6 or more.
In this case, although the resistance after film formation was low, the resistance was significantly increased by the heat treatment in the atmosphere. Comparative Example 5 is an example in which the added amount of Ga is 0.5 atomic% or more and the added amount is particularly increased.
An increase in resistance was observed due to heat treatment in air even though the half-width was 0.6 or less. The transmittance also changes (increases) with the above resistance change. This is considered to reflect the effect of oxidation due to heat treatment in the atmosphere.

Al, In, B which are Group 3 elements other than Ga
6 to 9 show comparative examples in which was added. In each case, it was revealed that the heat resistance in the atmosphere was not observed at all and the transmittance was changed although the half width was 0.6 degrees or less. In the case of adding Al in Comparative Example 7, high-speed film formation was attempted by increasing the sputtering power, but the resistance after film formation increased and the heat resistance deteriorated as compared with the case of low-speed film formation shown in Comparative Example 6. did. Thus, in the case of adding a Group 3 element other than Ga, no improvement in heat resistance was found even if the half width of X-ray diffraction was small.

[0055]

[Table 3]

[Example 7] A bus bar was formed on two opposite sides by screen printing and firing on a sufficiently washed soda lime silica glass (10 cm x 10 cm x 2 mm thick) substrate. The length of the bus bar was 8 cm, and the distance between the bus bars was 8 cm. On this substrate, by DC sputtering, a target of 7.5% gallium oxide in zinc oxide was used and the pressure was 0.01 T.
A zinc oxide transparent conductive film having a film thickness of 2000 Å was formed in an argon atmosphere of orr. The target used at this time was 1400 ° C. after adding gallium oxide to ZnO.
Hold gallium oxide at the above temperature for 2 hours or more to remove gallium oxide.
The target is a solid solution in O. The substrate was not particularly heated during the film formation.

The substrate on which the film was formed and another soda lime glass (10 cm ×
8.5 cm x 2 mm thick) and polyvinyl butyral (P
After performing the matching process using the VB) film, the resistance between the bus bar electrodes was measured and found to be 50.4Ω. When a voltage of 22 V was applied between the electrodes and a heat generation amount per unit area was 1,500 W / m ² , an energization test was conducted. After 6 weeks, both resistance and appearance did not change and were constant.

[Comparative Example 10] ZnO / Ag / ZnO was prepared by using an in-line type sputtering apparatus equipped with a bus bar-equipped substrate similar to that of Example 7 and a target of metallic zinc and Ag.
A high-transmittance conductive film having three layers was formed. The ZnO layer was formed by reactive sputtering in a mixed gas atmosphere of argon and oxygen with metallic zinc as a target. Ag
The layer was formed in a pure argon atmosphere with silver as a target. The film thickness of each layer is 450Å, 100 from the substrate side.
Å and 450Å. This laminated film had a terminal resistance of 7.1Ω measured between the bus bars.

In the same manner as in Example 7, the above-mentioned substrate and another soda lime glass (1
(0 cm × 8.5 cm × 2 mm thickness) with a PVB film, and then a voltage of 8.2 V is applied between the bus bars.
And the amount of heat generated per unit area is 1500 W / m ²
When a current-carrying test was carried out at, the appearance did not change, but the resistance between terminals increased to 12.9Ω after 3 weeks. When a current-carrying test was conducted subsequently, it exceeded 100 Ω in the 6th week.

[Comparative Example 11] An ITO target (In ₂ O ₃ -7.5w) was formed on the same substrate with a bus bar as in Example 7.
t% SnO ₂ ) was used to form an ITO layer having a film thickness of 2400 Å by an in-line DC sputtering apparatus. Argon and a mixed gas containing 2% of oxygen relative to the amount of argon were used as the sputtering gas, and the mixture was introduced by a mass flow meter so that the pressure in the film forming chamber during the sputtering was 0.01 Torr. The substrate was not particularly heated during the film formation. When the sheet resistance distribution in the 30 cm square substrate surface was measured, it was found that there was a variation of ± 30%. When a voltage of 22 V was applied between the bus bar electrodes, almost no heat was generated in the high resistance portion, and it was found that there was a problem in function as an electrothermal glass.

[Embodiment 8] When a glass substrate having a transparent heating element layer on which a gallium-doped zinc oxide film was formed was prepared in the same manner as in Embodiment 7, a zirconium-silicon alloy ( The composition is atomic ratio Zr / Si =
1/2) Using a target, an overcoat and an undercoat of a zirconia-silica film were continuously formed on a glass substrate without breaking vacuum by reactive sputtering in argon-oxygen plasma. That is, the overall film structure is, from the glass substrate side, a zirconia-silica film having a film thickness of 300Å, a gallium-doped zinc oxide film having a film thickness of 1200Å, and a zirconia-silica film having a film thickness of 300Å.

A bus bar and an electrode lead-out portion were printed on this by a screen printing method, and after baking at 300 ° C.,
A lead wire was soldered to the electrode extraction portion. After that, a glass having the same size and a spacer were sandwiched and sealed with a sealant to form a pair of glasses, and an electrically heated glass was obtained. When the resistance between the bus bar electrodes was measured with a lead wire penetrating the sealant and taken out to the outside, it was 108Ω. When a voltage of 32.2V was applied between the bus bars and an energization test was performed, no change was observed in the resistance value and the appearance even after 6 weeks,
It was constant.

[Comparative Example 12] Soda-lime silica glass (10 cm x 10 cm) that was thoroughly washed as in Example 7.
A bus bar was formed on two opposite sides by screen printing and firing on a substrate (× 2 mm thick). The length of the busbar is 8 cm, and the distance between the busbars is 8 cm.
Met. A zinc oxide transparent conductive film having a film thickness of 2000 Å was formed on this substrate by a DC sputtering method using a target in which 7.5% of gallium oxide was added to zinc oxide in an argon atmosphere at a pressure of 0.01 Torr. The target used at this time was one in which gallium oxide was added to ZnO and then held at a temperature of 1100 ° C. for 2 hours.
The substrate was not particularly heated during the film formation.

The substrate on which the film was formed and another soda lime glass (10 cm ×
8.5 cm x 2 mm thick) and polyvinyl butyral (P
After performing a matching process using the VB) film, the resistance between the bus bar electrodes was measured and found to be 65.2Ω. When a voltage of 25 V was applied between electrodes and a heat generation amount per unit area was 1500 W / m ² , an energization test was conducted, the resistance between terminals increased to 80.0 Ω after 3 weeks, and 92.5 Ω after 6 weeks. Increased to. Thus, the stability of the resistance value was poor.

[0065]

As is clear from Table 2, a film having a Ga concentration of 0.5 atomic% or more and 12 atomic% or less in atomic ratio is
The film exhibits high conductivity of the order of 10 ⁻³ Ω · cm to 10 ⁻⁴ Ω · cm at the time of film formation, and the conductivity does not decrease even after the heat treatment in the air, and the conductivity is equal or inversely improved. It can be seen that there is no change in transmittance and the film is stable in high temperature atmosphere.

On the other hand, as shown in Comparative Examples 1 and 2 in Table 3, even if the half-width of the X-ray diffraction line is 0.6 degree or less in the film having a Ga content of 0.5 atomic% or less, A large increase in resistance is seen after heat treatment in air. At the same time, the transmittance changes due to the heat treatment. Further, as shown in Comparative Examples 3 and 4, even when the Ga amount is 5 atomic%, when the half width is 0.6 degree or more, the resistance increase is observed by the heat treatment in the air.

Further, as shown in Comparative Example 5, in a film having a Ga concentration of 12 atomic% or more, a large increase in resistance is similarly observed after the heat treatment. Comparative examples 6 to 9 in the case where the additive is a Group 3 element other than Ga are shown. In all cases, the half-value width is 0.6 degrees or less, but no heat resistance in the atmosphere is observed. Obviously not.

The transparent heating element using the gallium-doped zinc oxide layer according to the present invention as a heating element layer has a long-term reliability against electric current as compared with a film system for a transparent heating element using a thin metal layer such as a thin silver layer. It excels in stability and stability against attacks from the environment.

Further, since it is possible to form a film on a large-area substrate with a uniform film thickness and film quality distribution by the DC sputtering method, a large area of, for example, 1 m width or more is required. It can be applied to cloudy applications, etc., and it is also excellent in terms of production efficiency because it is possible to arrange a plurality of small-sized substrates side by side and simultaneously form a plurality of films.

As described above, by controlling the Ga concentration and the half-value width of the X-ray diffraction line within a specific range, it is possible to realize a transparent conductive film having high conductivity and transmittance. The conductivity is not lost at all,
It is possible to obtain an oxidation resistant transparent conductive film. Therefore, these substrates have high transparency, low resistance, heat resistance in air,
Since it provides low-cost elements, various display elements, transparent electrodes such as solar cells and light-receiving elements, heat ray reflective films for construction and automobiles, selective transmission films, and electromagnetic wave shielding films, as well as anti-fog for automobiles, It is most suitable as a transparent heating element for waterproofing, freezing showcases, and other constructions, or as an antistatic film for photomasks and constructions, and can be applied to an extremely wide range of fields.

[Brief description of drawings]

FIG. 1 is a graph showing the full width at half maximum of a (002) X-ray diffraction line of a transparent conductive film of Example 3.

FIG. 2 is a graph showing the full width at half maximum of (002) X-ray diffraction line of the transparent conductive film of Comparative Example 4.

FIG. 3 is a sectional configuration diagram of the transparent heating element of the present invention.

FIG. 4 is a plan view of an EHW using the transparent conductive film of the present invention.

[Explanation of symbols]

 1: Overcoat layer 2: Gallium-doped zinc oxide layer 3: Undercoat layer 4: Substrate 5: Upper side bus bar 6: Transparent heating film coating part 7: Lower side bus bar 8: Substrate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H01L 31/04 (72) Inventor Kunihiko Adachi 1150 Hazawa-machi, Kanagawa-ku, Yokohama-shi, Kanagawa Asahi Glass Co., Ltd. Chuo In the laboratory

Claims (10)

[Claims] 1. A transparent conductive film containing zinc oxide as a main component, wherein the transparent conductive film contains gallium in an amount of 0.1 atom% or more and 15 atom% or less with respect to zinc. Has a diffraction peak due to the (002) plane,
2) A transparent conductive film having a half-value width of a diffraction line by a plane of 1.2 degrees or less. 2. The transparent conductive film contains gallium in an amount of 0.5 atomic% or more and 12 atomic% or less with respect to zinc, and has a diffraction peak due to a (002) plane in an X-ray diffraction pattern thereof, (002) 2. The transparent conductive film according to claim 1, wherein the half-width of the diffraction line by the surface is 0.6 degree or less. 3. The specific resistance of the transparent conductive film is 10 ⁻² Ω · cm.
The transparent conductive film according to claim 1 or 2, wherein the film thickness is in the range of 100 Å or more and 5 µ or less. 4. A transparent heating element comprising the transparent conductive film according to claim 1 on a substrate. 5. The one or more undercoat film between the substrate and the transparent conductive film, and / or the one or more overcoat film on the transparent conductive film. Transparent heating element. 6. The film material of at least one layer of the undercoat film or at least one layer of the overcoat film is silicon oxide, titanium oxide, zirconium oxide, tin oxide, tantalum oxide, chromium oxide, niobium oxide, boron oxide. The transparent heating element according to claim 5, comprising at least one selected from the group consisting of, indium oxide, zinc oxide, and cerium oxide. 7. The film material of at least one layer of the undercoat film or at least one layer of the overcoat film is a metal of titanium, zirconium, hafnium, chromium, niobium, a nitride of the metal, and an acid of the metal. The transparent heating element according to claim 5, wherein the transparent heating element comprises at least one selected from the group consisting of nitrides. 8. The transparent heating element according to claim 4, wherein the transparent heating element is provided with at least two electrode lead-out portions. 9. A detection means for the purpose of temperature control during heating and detection of abnormal heat generation.
The transparent heating element according to any one of items. 10. A laminated structure or a multilayer structure comprising the transparent heating element according to any one of claims 4 to 9.