JPH1144887A - Reflection electrode substrate for display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrode substrate of high performance and high reliability by forming an reflection electrode of a two-layer structure comprising a silver alloy thin film with addition of one or more kinds of metals selected from platinum palladium, gold, nickel and copper, and an adhesive layer formed between the silver alloy thin film and a substrate. SOLUTION: The reflection electrode substrate 14 is obtd. by successively depositing an SiO2 thin film 13, mixture oxide thin film 11 essentially comprising indium oxide, and silver alloy thin film 12 as the main component on a glass substrate 10. The reflection electrode 15 has a two-layer structure comprising a silver alloy thin film 12 with addition of one or more kinds of metals selected from platinum, palladium, gold, nickel and copper, and an adhesive layer 11 (mixture oxide thin film) formed between the silver alloy thin film 12 and the substrate 10. The mixture oxide thin film 11 is formed by adding cerium oxide, tin oxide, titanium oxide to indium oxide as the base material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an output display device such as a liquid crystal display or an EL (electroluminescence) display, an input / output display device for directly inputting from a display screen, or an electrode used for a solar cell or the like. The present invention relates to a substrate, and more particularly to a reflective electrode substrate for a reflective liquid crystal display device.

[0002]

2. Description of the Related Art As a liquid crystal display, a transmission type liquid crystal display device having a built-in backlight lamp is generally used. However, these transmissive liquid crystal display devices have a problem in that the power consumption by the backlight of the display surface is large and the use time is short when the battery is driven, so that the characteristics of the portable device cannot be fully utilized. For this reason, in recent years, the development of a reflective liquid crystal display device using external light (that is, not incorporating a backlight) has been actively developed.

As a conventional reflection type liquid crystal display device, for example, as shown in a schematic view of FIG. 4, a reflection electrode 41 made of an aluminum metal thin film is disposed on a surface of a rear substrate 40 made of glass, which is in contact with a liquid crystal 42. Many structures close to the structure have been proposed. FIG. 4 shows an example of a structure in which the liquid crystal 42 is of a TN type or STN type. When the liquid crystal 42 is of a guest-host type, the rear substrate 40 is called a TFT (thin film transistor). A liquid crystal driving element is formed, and the polarizing film 47 is omitted.

[0004]

As described above, the reflective electrode 41 shown in FIG. 4 conventionally uses an aluminum thin film in many cases. However, aluminum has a problem that it is easily corroded by moisture or a base, and as a reflective electrode, the light reflectance is reduced and the electrical disconnection is easily caused. Further, aluminum has a characteristic problem that light reflectance is lower than silver.

For this reason, it has been proposed to use silver as a material for the reflective electrode. Silver can be said to be superior to aluminum in the above respects, that is, in terms of corrosion resistance and light reflectance (for example, silver has a light reflectance of approximately 10% superior to aluminum. ).
However, silver has a disadvantage that adhesion to a transparent substrate such as glass or plastic is low, and when formed as a silver thin film on a transparent substrate, it is easily peeled off from the substrate. When a silver thin film is formed on a substrate with high-purity silver, the high-purity silver thin film is easily aggregated under the influence of heat or oxygen, and the heat treatment causes the silver thin film to become cloudy. There is also a problem that looks like.

The present inventors have proposed a technique for compensating for the disadvantage of silver in Japanese Patent Application No. 7-88798. This technology uses a three-layer structure electrode in which a silver alloy thin film is sandwiched between mixed oxide layers. Since the surface of the silver alloy thin film is covered with the mixed oxide, there is an advantage that the silver alloy thin film is protected. Have

[0007] However, the above-mentioned proposed technique has the following problems. That is, generally, wet etching is performed on a three-layer electrode formed on a substrate to obtain a desired pattern shape. However, when a silver alloy thin film is formed thicker (for example, 800 to 2000 mm),
The problem is that the upper oxide layer of the three-layered electrode is easily peeled off during wet etching. In addition, when an oxide layer is laminated on the silver alloy thin film, there is a problem that the light reflectance on the short wavelength side decreases and the reflected light takes on a yellow tint.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a reflective electrode substrate for a display device having high performance (high reflectivity) and high reliability.

[0009]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems. as a result,
The present invention has solved the above-mentioned problems by focusing on the work function and melting point of a metal added to silver. In addition, a means for improving the adhesion of the silver alloy to a substrate such as glass has been found, and specific means will be described below.

The use of a silver thin film or a silver alloy thin film as a surface layer as a reflective electrode for a display device can be said to be preferable in terms of light reflectance. However, as described above, the silver thin film is vulnerable to heat treatment, for example, agglomeration or recrystallization is caused by heat treatment at around 200 ° C. Therefore, the surface of the silver thin film becomes cloudy due to the generated large crystal grains.

In order to avoid this, the present inventors have studied various silver alloy thin films obtained by adding other metal elements to silver. As a result, the decrease in the light reflectance of the silver alloy thin film when added is small, and as an additive metal element having an effect of preventing aggregation of silver, for example, gold, a noble metal such as platinum and palladium other than silver, nickel, or It has been found that copper is effective. Indium, tin, etc., when added to silver, have less effect on light reflectance, but since the melting point of indium or tin is low, in the range of a small amount of addition that does not affect light reflectance, It was found that the silver alloy thin film to which indium or tin was added was agglomerated and became cloudy even at a heat treatment of about 200 ° C.

Further, in order to improve the adhesion of the silver alloy thin film to a transparent substrate such as glass, a metal thin film or a metal oxide thin film having an adhesive force to glass is formed before forming the silver alloy thin film. The present inventors have found that the adhesive layer may be formed on a transparent substrate.

That is, the invention according to claim 1 is at least a reflective electrode substrate for a display device in which a light-reflective metal thin film is disposed on the substrate as a reflective electrode, wherein the reflective electrode is made of platinum, palladium, gold, nickel or the like. , And a silver alloy thin film to which at least one metal selected from copper is added,
(2) an adhesive layer disposed between the silver alloy thin film and the substrate;
It is characterized by having a layer structure.

The adhesive layer may be formed of a metal thin film such as aluminum, aluminum alloy, chromium, nickel-chromium alloy, magnesium alloy, high melting point metal such as titanium or tantalum, or an alloy of these metals. Alternatively, the adhesive layer may be formed using a thin film of a metal oxide such as indium oxide, tin oxide, aluminum oxide, zinc oxide, and titanium oxide, or a mixed oxide obtained by mixing these oxides, or a metal nitride. It may be formed.

However, when a silver alloy thin film is patterned into a stripe pattern and used as a reflective electrode, the silver alloy thin film is relatively soft, so that there is a problem that the silver alloy thin film is easily damaged and broken. To make up for this, the present inventors have found that it is preferable to use a hard conductive ceramic (for example, a mixed oxide of indium oxide) as the adhesive layer.

However, in this configuration, the interface between the silver alloy thin film and the mixed oxide thin film becomes weak in long-term storage or in a wet test (under high temperature and high humidity conditions), and the silver alloy thin film and mixed oxide There is a problem that the material thin film is easily peeled off. The present inventors have found that in the contact between silver and an oxide, electrons move from silver to the oxide in the presence of moisture (and even alkali), so that the reaction between silver and the oxide is accompanied by a complicated reaction. The weakening of the interface was determined to be evident from some test results. Therefore, it is important to suppress the electron emission from silver to the oxide in order to improve the moisture resistance of the electrode, and from this viewpoint, the present inventors consider that a metal having a higher work function than silver is converted to silver. It has been found that the added silver alloy thin film should be used.

That is, in the invention according to claim 2, at least in a reflective electrode substrate for a display device in which a light-reflective metal thin film is disposed on the substrate as a reflective electrode, the reflective electrode has a higher work function than silver. It has a two-layer structure of a silver alloy thin film to which a metal is added and an adhesive layer disposed between the silver alloy thin film and the substrate.

AGNE PERIODIC TABLE
According to (the periodic table of elements), the work function of silver is 4.28 eV. Similarly, copper is 4.47 eV, gold is 4.58 eV, nickel is 4.84 eV, palladium is 4.82 eV, and platinum is 5.29 eV.
V and a metal having a higher work function than silver is preferably added to silver. However, when the total amount of these additional metals exceeds 5 at% (atomic percent), the light reflectance of the silver alloy thin film is greatly reduced. Therefore, the amount of the additional metals is preferably 5 at% (atomic percent) or less.

As described above, it is preferable to use a hard conductive ceramic as an underlayer for the silver alloy thin film that is easily damaged to prevent disconnection of the reflective electrode. That is, the invention according to claim 3 is characterized in that the adhesive layer is a conductive metal oxide or a conductive mixed oxide.

As the conductive oxide, indium oxide,
Examples include tin oxide, zinc oxide, and mixed oxides of these oxides, and these oxides can be used in the present invention. Since silver and alkali metal elements easily move on the crystal grain boundaries and the surface of the oxide, in the reflective electrode of the present invention, diffusion of the alkali metal elements from silver and the substrate (particularly, diffusion at the grain boundaries) should be avoided. It is desirable that these oxides are formed as microcrystalline or amorphous. Therefore, it is desirable to add a metal oxide other than the above-described oxide to form an amorphous mixed oxide thin film having no crystal grain boundaries.

In the present invention, when the reflective electrode is patterned into a desired shape, it is necessary that the underlying conductive oxide serving as the adhesive layer can be etched together with the silver alloy thin film. Therefore, the present inventors have studied conductive oxides that are easily etched by an oxygen etchant, and as a result, have found that mixed oxides based on indium oxide or zinc oxide are preferable. It is. That is, the invention according to claim 4 is characterized in that the adhesive layer is indium oxide or a mixed oxide based on zinc oxide.

Further, the present inventors have proposed that in a configuration in which a silver-based thin film is in contact with a metal oxide layer, water (moisture) and an alkali metal element (for example, Na (sodium), K (potassium))
Etc.) for a long period of time, the interface between the silver-based thin film and the metal oxide layer was found to be significantly weakened. When this phenomenon proceeds further, the metal oxide layer is destroyed along with the aggregation of silver, and the appearance is seen as unevenness or spots. Since this phenomenon is remarkable when the substrate on which the reflective electrode is formed is soda glass or the like, the diffusion of the alkali metal element from the glass substrate promotes this phenomenon, that is, the deterioration of the reflective electrode. it is conceivable that. From this, the present inventors have found that the use of a substrate containing no alkali metal element prevents deterioration of the reflective electrode and improves the reliability of the reflective electrode. That is, the invention according to claim 5 is characterized in that the surface of the substrate or the substrate itself is a substrate made of a material substantially not containing an alkali metal element.

Actually, the substrate that can be employed in the present invention is, for example, a non-alkali glass substrate such as 7059 or 1737 manufactured by Corning, or SiO ₂ (silicon dioxide).
Glass, a silicon substrate, a plastic substrate, or the like. Note that, in addition to the above-described SiO ₂ (silicon dioxide), an oxide such as tantalum oxide or chromium oxide is used for the alkali barrier film for preventing the diffusion of the alkali metal element from the substrate containing the alkali metal element to the reflection electrode. Alternatively, a film may be formed using a nitride such as titanium nitride or zirconium nitride. It should be noted that a SiO ₂ film called “SiO ₂ dip”, which is sold for liquid crystal, is formed by a sol-gel method.
Since it contains a small amount of alkali, it is insufficient for use in the present invention.
It is better to form _two layers or the like as a film for an alkali barrier and insert it between the substrate and the electrode.

Next, the substrate used for the reflective electrode substrate of the present invention does not need to be transparent, and may be a substrate colored white, black or other colors depending on the use of the reflective electrode substrate. Further, the substrate itself may be a substrate on which an electric circuit is formed or a substrate on which a solar cell is formed, and may be made of amorphous silicon, polysilicon, or MI.
A substrate on which a semiconductor element such as M (diode element) is formed may be used. Further, a polarizing element, a diffraction grating, a hologram, a light scattering film, a λ / 4 wavelength plate, a retardation film, a micro lens, a color filter, and the like may be formed directly or indirectly on the reflective electrode. In addition, since the reflective electrode of the present invention has low resistance, it can be used for signal lines and bus lines of elements such as TFTs and MIMs, and can be used simultaneously with these and pixel electrodes.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below. <Embodiment> As shown in FIG. 1, a reflective electrode substrate 14 according to the present embodiment is composed of a SiO ₂ thin film 13 (40 nm thick), which is sequentially laminated on a glass substrate 10 having a thickness of 0.7 mm. The main part is composed of a mixed oxide thin film 11 (thickness: 30 nm) and a silver alloy thin film 12 (thickness: 200 nm) based on indium oxide.

Here, in the mixed oxide thin film 11 of the present embodiment, cerium oxide,
It contains tin oxide and titanium oxide. The composition is as follows: in atomic percent in terms of metal element (oxygen element is no count), indium 88 at% (at%), cerium 8.5 at% (at%), tin 3 at
% (Atomic percent) and titanium 0.5 at% (atomic percent).

The silver alloy thin film 12 is made of silver, platinum,
It uses a silver alloy to which gold and copper are added. The composition is 97 at% (at.%) Of silver, 1 at% (at.%) Of platinum, 1 at% (at.%) Of gold, 1 at% of copper.
% (Atomic percent).

As the glass substrate 10, soda glass called "H-coated product" manufactured by Nippon Sheet Glass Co., Ltd. was used.

The reflective electrode 15 having a two-layer structure according to the present embodiment.
Is formed by the following manufacturing process. First, the washed glass substrate 10 was housed in a vacuum chamber (sputtering apparatus) and evacuated. Then, the glass substrate
Without removing the 10 from the vacuum chamber, a SiO ₂ thin film 13 is formed as a film for an alkali barrier on the surface of the glass substrate 10 by a sputtering method, and then a mixed oxide thin film 11 and a silver alloy thin film 12 are continuously formed. The film was formed into a two-layer conductive film. In addition,
During sputtering, no intentional substrate heating was performed.

Next, after forming a photoresist film on the conductive film having a two-layer structure, the photoresist film was subjected to pattern exposure through an exposure pattern mask having a predetermined pattern. Next, development was performed to obtain a photoresist film in which the conductive film was exposed in accordance with a predetermined pattern, that is, a photoresist film in which the conductive film portion other than the portion serving as the reflective electrode was exposed. Next, using a sulfuric acid-based etchant containing 1% by weight of ceric ammonium nitrate, portions of the conductive film exposed from the photoresist film were dissolved and removed. Next, after removing the photoresist film, an annealing treatment was performed at a temperature of 200 ° C. for 1 hour to obtain a reflective electrode 15 having a predetermined stripe pattern.

The reflective electrode obtained by the above-described manufacturing process
The sheet resistance of No. 15 was as low as about 0.2Ω / □, which was extremely good as a display electrode. Next, the light reflectance of the reflective electrode 15 is 94.9% at a light wavelength of 550 nm,
A light reflectance of 90.5% at 0 nm and about 5 to 10% higher than the case where the reflective electrode was formed of aluminum was obtained.

In order to confirm the reliability of the reflective electrode 15 according to the present embodiment, a storage test was performed. That is, the temperature 60
After leaving the reflective electrode substrate 14 in an atmosphere at a temperature of 95 ° C and a humidity of 95% for 1000 hours, a peel test using a cellophane tape is performed. Test). However, the reflection electrode 15 does not peel off from the glass substrate 10 at all, and the adhesion of the reflection electrode 15 according to the present embodiment can be said to be extremely good even after long-term storage.

Next, for comparison with the reflective electrode substrate of the present invention, the following comparative example was performed. Comparative Example 1 In Comparative Example 1, a reflective electrode substrate 24 shown in FIG. 2 was obtained. Here, in Comparative Example 1, the reflective electrode 25 sandwiched the silver alloy thin film 22 (thickness 200 nm) between the mixed oxide thin film 21 (thickness 20 nm) and the mixed oxide thin film 26 (thickness 70 nm). The reflective electrode 25 was formed on the glass substrate 20 via a SiO ₂ thin film 23 serving as a film for an alkali barrier. The material of the glass substrate 20 and the like used in Comparative Example 1 is the same as that in the above-described embodiment. For example, the material of the mixed oxide thin film 21 and the mixed oxide thin film 26 is the same as the material of the mixed oxide thin film 11 of the above embodiment, and the material of the silver alloy thin film 22 is also the same as the material of the silver alloy thin film 12. I assumed the same.

The reflective electrode 25 having a three-layer structure according to the first comparative example was the same as the reflective electrode 25 except that the annealing temperature was 250 ° C.
This is formed by the same manufacturing process as the above embodiment. That is, the cleaned glass substrate 20 is housed in a vacuum chamber (sputtering apparatus), and after evacuation, without removing the glass substrate 20 from the vacuum chamber, the SiO ₂ thin film 23 for an alkali barrier is formed by a sputtering method. , A mixed oxide thin film 21, a silver alloy thin film 22, and a mixed oxide thin film 26 were successively formed to form a three-layer conductive film. Next, in the same manner as in the above embodiment, the conductive film is formed into a predetermined stripe-shaped pattern by performing formation of a photoresist film, pattern exposure, development, etching, and stripping of the photoresist film. Process,
The reflection electrode 25 is obtained.

The reflective electrode 25 having a three-layer structure according to Comparative Example 1
The light reflectance was 92.6% at a light wavelength of 550 nm and 83.5% at a light wavelength of 430 nm, which was inferior to the reflective electrode 15 of the above embodiment.

In order to confirm the reliability, a storage test was performed on the reflective electrode 25 of Comparative Example 1. That is, at a temperature of 60 ° C,
After leaving the reflective electrode substrate 24 in an atmosphere of 95% humidity for 1000 hours, a peel test using a cellophane tape was performed. As a result, random peeling of several μm to several tens of μm occurred in the upper oxide (mixed oxide thin film 26) on the pattern edge portion of the reflective electrode 25 having the stripe-shaped pattern. That is, it can be said that the reflective electrode 25 of the first comparative example has lower reliability than the reflective electrode 15 of the above-described embodiment.

As shown in <Comparative Example 2> FIG 3, SiO ₂
Except for the formation of the thin film, a reflective electrode substrate 34 was obtained by the same manufacturing process as in the above example. That is, in Comparative Example 2, a mixed oxide thin film 31 (thickness: 30 nm) was directly formed on a soda glass substrate 30 (“H-coated product” manufactured by Nippon Sheet Glass Co., Ltd. with a thickness of 0.7 mm) by a sputtering method. The reflective electrode 35 is obtained by forming a silver alloy thin film 32 (thickness: 200 nm) in a laminated manner.

In Comparative Example 2, the silver alloy thin film was used.
The composition of Part 32 was replaced by tin with a low melting point (melting point: 232 ° C), and the composition was 97 at% silver (atomic percent), 1 at% gold (atomic percent), and 2 at% tin.
(Atomic percent). The composition of the mixed oxide thin film 31 was the same as that of the mixed oxide thin film 11 of the above embodiment.

In this comparative example 2, after the formation of a photoresist film, pattern exposure, development, etching, and stripping of the photoresist film, etc., as in the above embodiment,
In the same manner as in the above embodiment, the reflective electrode 35 having a predetermined stripe-shaped pattern was obtained by performing an annealing treatment at a temperature of 200 ° C. for one hour. However, the light reflectance of the reflective electrode 35 after the annealing treatment is 89.6% at a light wavelength of 550 nm,
77.4% at a wavelength of light of 430 nm, the reflective electrode 15 of the above embodiment.
In addition, the surface of the silver alloy thin film 32 became cloudy, and aggregation of silver was observed.

In order to confirm the reliability, a storage test was performed on the reflective electrode 35 of Comparative Example 2. That is, at a temperature of 60 ° C,
After leaving the reflective electrode substrate 34 in an atmosphere of 95% humidity for 500 hours, a peel test using a cellophane tape was performed. As a result, only the silver alloy thin film 32 was peeled off at a width of about several μm from the pattern edge portion of the reflective electrode 35 in the form of a stripe pattern, and the reflective electrode 35 of Comparative Example 2 was formed as described above. The reliability was inferior to the reflective electrode 15 of the example.

After the storage test of the reflective electrode 35 described above, S
When the interface between the silver alloy thin film 32 and the mixed oxide thin film 31 was examined by the IMS analysis, uneven distribution of alkali metal elements such as Na (sodium) and K (potassium) was confirmed. This indicates that the reliability of the reflective electrode becomes insufficient when the formation of an SiO ₂ thin film as a film for an alkali barrier that prevents the diffusion of an alkali metal element from the substrate to the reflective electrode is omitted.

[0042]

According to the present invention, a reflective electrode having a two-layer structure in which the upper oxide thin film is omitted from the reflective electrode having a three-layer structure proposed by the present inventors, and silver is alloyed And
Further, a film for an alkali barrier, such as a SiO ₂ thin film, serving as a base layer is formed. With the reflective electrode substrate having such a configuration, it is possible to provide a reflective electrode substrate having high performance (high reflectance) and higher reliability.

[0043]

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a reflective electrode substrate of the present invention.

FIG. 2 is an explanatory view showing an example of a reflective electrode substrate used for comparison with the reflective electrode substrate of the present invention.

FIG. 3 is an explanatory view showing another example of the reflective electrode substrate used for comparison with the reflective electrode substrate of the present invention.

FIG. 4 is an explanatory view schematically showing an example of a reflection type liquid crystal display device.

[Description of Signs] 10, 20, 30 Glass substrate 11, 21, 26, 31 Mixed oxide thin film 12, 22, 32 Silver alloy thin film 13, 23 SiO ₂ thin film 14, 24, 34 Reflective electrode substrate 15, 25, 35 , 41 reflective electrode 40 back substrate 42 liquid crystal 43 transparent electrode 44 color filter 45 observer side substrate 47 polarizing film 48 light control film

Claims (5)

[Claims] At least a reflective electrode substrate for a display device, wherein a reflective metal thin film is disposed on a substrate as a reflective electrode, wherein the reflective electrode is made of platinum, palladium, gold, nickel,
And a silver alloy thin film to which at least one metal selected from copper is added, and an adhesive layer disposed between the silver alloy thin film and the substrate. Reflective electrode substrate. 2. A reflective electrode substrate for a display device wherein at least a light-reflective metal thin film is disposed on a substrate as a reflective electrode, wherein the reflective electrode comprises a silver alloy thin film to which a metal having a work function higher than silver is added. A reflective electrode substrate for a display device, wherein the reflective electrode substrate has a two-layer structure of an adhesive layer provided between the silver alloy thin film and the substrate. 3. The method according to claim 1, wherein the adhesive layer comprises a conductive metal oxide or
The reflective electrode substrate for a display device according to claim 1, wherein the reflective electrode substrate is a conductive mixed oxide. 4. The reflective electrode substrate for a display device according to claim 1, wherein the adhesive layer is a mixed oxide based on indium oxide or zinc oxide. 5. The substrate according to claim 1, wherein the surface of the substrate or the substrate itself is made of a material substantially not containing an alkali metal element. Reflective electrode substrate for display devices.