JPH11265155A - Substrate for plane type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for plane type display device equipped with an undercoat film, which is hardly released during a preparation process by providing metal oxide coating or the like formed by the oxidizing treatment of metal coating on the surface of the substrate exposing plastics at least. SOLUTION: A plastics substrate 11, for which an Al film 12 is deposited, is immersed in an electrolytic bath 14, in which a non-erosion type electrolyte 13 not to dissolve Al2 O3 is stored, while facing a counter electrode 15, a positive voltage is applied to the Al film 12 in respect to the counter electrode 15, and the Al film 12 is anodized. As a result, the Al film 12 on the plastics substrate 11 is modified into Al2 O3 film by anodizing, and the plastics substrate 11 coating its surface with an Al2 O3 film 16 can be provided. The Al2 O3 film 16 of this plastics substrate 11 is transparent to visible light, is improved in insulation property, has satisfactory blocking ability to the dispersion of impurity such as sodium and is functioned as the satisfactory undercoat film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a liquid crystal cell and an EL device.
(Electroluminescence) The present invention relates to a substrate used for a flat display device such as a cell.

[0002]

2. Description of the Related Art Conventionally, a flat display device has two
A liquid crystal material, an EL material, and the like are sandwiched in a space formed by a single glass substrate, and an electric field is applied to these materials from electrodes formed on each substrate to change the optical characteristics of the portion. Alternatively, characters or images are displayed by emitting light.

For example, a liquid crystal display device using a liquid crystal material is:
A liquid crystal material having dielectric anisotropy is sandwiched in a gap between a glass substrate having two upper and lower electrodes, and a voltage is applied between the electrodes to form an electric field to control the orientation direction of liquid crystal molecules. Characters and images are displayed by changing optical characteristics such as the refractive index and optical rotation of the light in that portion.

In a display device using an EL material, the EL material is held in a gap between a glass substrate having two upper and lower electrodes, and a voltage is applied between the electrodes to apply an electric field to the EL material. Characters and images are displayed by utilizing the phenomenon that energy is emitted as light when carriers excited in the conduction band from the emission center fall back into the emission center.

As described above, in a conventional flat display device, a liquid crystal material or an EL material is held between gaps formed by a glass substrate having two upper and lower electrodes, and a voltage is applied between electric fields. Display.

A glass substrate is used as two flat substrates for a conventional flat display device in order to ensure transparency with respect to visible light. However, glass has a large specific gravity.
This glass substrate was the main cause of making the flat panel display heavy.

In order to avoid such a problem, a substrate made of a plastic material such as acrylic resin, polyester or allyl resin having a lower specific gravity than glass is used as a plane substrate, and amorphous silicon or polycrystalline silicon is formed thereon. Forming a switching element such as a thin film transistor (TFT) using a matrix array substrate;
Attempts have been made to produce a display device using this substrate.

However, since the plastic material generally contains impurities such as sodium that adversely affect the TFT, when a TFT matrix array is formed directly on a plastic substrate, these impurities diffuse into the TFT portion. Then, for example, there is a problem that an unstable factor such as a change in the threshold voltage of the TFT is caused.

Therefore, when a display device is manufactured using a plastic substrate, a so-called undercoat film is formed on the plastic substrate to form a
It is necessary to insulate between the FT portions and prevent diffusion of these impurities into the TFT portion. Such an undercoat film is used when the substrate is used for a flat display device.
Naturally, it is necessary to have transparency to visible light, and it is necessary to electrically separate the elements of the matrix array formed thereon from each other. (SiO ₂ ) was used.

However, sputtering or CVD
Method, silicon oxide films directly deposited on plastic substrates often peeled off from the plastic substrate during the matrix array fabrication process including subsequent heat treatment, which was a major cause of reduced product yield. .

This is because the bonding force at the interface between the plastic substrate and the undercoat film made of oxide is weak, and a large difference in thermal expansion coefficient exists between the plastic substrate and the undercoat film. It is considered that a large deformation difference occurs between the plastic substrate and the undercoat film at the time of the process, and exfoliation occurs at the interface.

[0012]

As described above, since the conventional flat display device uses a glass substrate,
There is a problem that the weight of the flat panel display increases.

Although the use of a lightweight plastic substrate has been considered, there is a problem in that impurities such as sodium in the plastic material adversely affect the TFT. In order to block such impurities, it has been considered to form an undercoat film such as a silicon oxide film that transmits visible light for preventing diffusion of impurities on a plastic substrate. In the case of the oxide film, there is a problem that the oxide film is easily separated from the plastic substrate and the product yield is reduced.

The present invention has been made to solve such a conventional problem. When a display device is manufactured using a lightweight plastic substrate, the bonding force at the interface with the plastic substrate is strong, and the manufacturing process is difficult. It is an object of the present invention to provide a substrate for a flat panel display device provided with an undercoat film in which peeling does not easily occur.

[0015]

According to a first aspect of the present invention, there is provided a substrate for a flat panel display device, wherein at least a surface of the substrate is made of a plastic, and a metal coating applied to at least the surface of the substrate where the plastic is exposed. And a metal oxide film formed by the method described above. Examples of the plastic used in the present invention include acrylic resin, polyester, and allyl resin having a specific gravity smaller than that of glass. Examples of the metal oxide film that is not deposited on the plastic substrate include oxides of metal films such as Al, Ti, and Ta. The thickness of these metal oxide films is usually about 50 nm to 2 μm.

According to a second aspect of the present invention, there is provided a substrate for a flat display device,
At least a surface of a plastic substrate, a metal oxide film formed by oxidizing a metal film formed on at least the surface of the substrate where the plastic is exposed, and selectively remaining in the metal oxide film. And a metal coating pattern.

Examples of the metal film pattern include, for example, wirings and electrodes formed in the metal oxide film. The thickness of the metal oxide coating in this case is usually 50
The thickness of the metal film remaining in the oxide film is usually about 50 nm to 500 nm.

According to a third aspect of the present invention, there is provided a substrate for a flat display device,
A substrate having at least a plastic surface, a transparent conductive film adhered to at least the surface of the substrate at which the plastic is exposed, and a metal oxide formed by oxidizing the metal film formed on the transparent conductive film. And an object coating.

Examples of the transparent conductive film include ITO and tin oxide. The thickness of the transparent conductive coating is usually
It is about 100 nm to 1 μm.

According to a fourth aspect of the present invention, there is provided a substrate for a flat display device,
A substrate having at least a plastic surface, a metal oxide film formed by oxidizing a metal film applied to at least the surface of the substrate where the plastic is exposed, and a matrix formed on the metal oxide film. It includes a scanning line, a signal line, and a switching element.

[0021]

[Operation] As described above, when a flat-panel display device is manufactured using a plastic substrate, it is necessary to form a so-called undercoat film, which separates the plastic substrate from the TFT portion and prevents diffusion of impurities into the TFT portion. There is
When insulating material films such as silicon oxide are directly deposited as an undercoat film, these insulating material films often peel off from the plastic substrate during the subsequent matrix array forming process.

This is because silicon oxide or the like is in a state in which the electron orbits of the respective constituent atoms are already filled by chemical bonds, and few bonds contributing to new bonds are left, so that the plastic substrate and It is considered that the bonding force at the interface is weak, and separation at the interface easily occurs when a large deformation difference occurs between the plastic substrate and the undercoat film.

On the other hand, Al, Ti,
When coated with a metal film such as Ta, it is experimentally confirmed that the plastic substrate does not peel off even when subjected to a heat treatment at about 200 ° C. or less, after which the plastic substrate is not adversely affected by softening or the like. Was confirmed. This is because the metal atoms have many dangling bonds, so the metal atoms covering the plastic substrate also incorporate the atoms on the surface of the plastic substrate to form metal bonds, and are strong at the interface between the plastic substrate and the metal film. It is considered that a binding force is generated.

According to the first aspect of the present invention, a plastic substrate is coated with a metal film of Al, Ta or the like by sputtering or other methods, and then these metal films are coated with an oxide film by a known method such as anodic oxidation. By doing so, it is possible to obtain an undercoat film that is transparent to visible light and has good electrical insulation while maintaining a strong bonding force at the interface with the plastic substrate.

According to the second aspect of the present invention, a plastic substrate is coated with a metal film of Al, Ta or the like by sputtering or other methods, and then these metal films are oxidized by an anodic oxidation method or another known oxidation treatment method. When forming an oxide film by using a mask, a region where the entire metal thin film is oxidized and a region where only the upper portion of the metal thin film is oxidized and the metal thin film remains at the lower portion are formed using a mask. The metal film adhered to the plastic substrate is selectively left in the film. This metal film is used as a wiring or an electrode.

Further, according to the invention of claim 3, tin oxide,
A metal oxide film is formed on a transparent conductive film such as an ITO film. Al, Ti, T are available for tin oxide and ITO.
Since there are many dangling bonds as in the case of the metal coating such as a, the coating is formed in a manner that also incorporates atoms on the surface of the plastic substrate,
Strong bonding force is obtained at the interface with the plastic substrate. The transparent conductive film can be used as an electrode when a metal film formed thereon is oxidized by anodic oxidation. That is, when an electrode is directly connected to the metal film when the metal thin film is anodized, there is a problem that the metal film in a portion deviated from the current path is not oxidized and the transparency of the undercoat film is reduced. However, when a transparent conductive film is coated on a plastic substrate and then a metal film is formed on the plastic substrate and then anodized, the transparent conductive film serves as a conductive path and can be uniformly anodized. it can.

The transparent conductive film can also be used as an electric conductor for removing charges from the plastic insulator. That is, since a plastic substrate is generally a good insulator having an electrical resistivity that is about two to three orders of magnitude larger than glass, a display device made using a plastic substrate is subject to friction during handling and the like. When local charging occurs, it is not easy to remove the charged charges compared to a display device made using a glass substrate, and the display state in the vicinity becomes unstable due to the influence of the charged charges. However, in the invention of claim 3, the transparent conductive film can be used as an electrode for static elimination.

A fourth aspect of the present invention is a matrix substrate used for an active matrix type liquid crystal display device. This substrate is also an insulating film in which an undercoat film is formed by coating a metal film on a plastic substrate and then converting it to an oxide.Therefore, while maintaining a strong bonding force at the interface with the plastic substrate, the substrate is exposed to visible light. On the other hand, it is transparent and has good electrical insulation. Therefore, I
A light-weight and highly reliable liquid crystal display device can be formed by holding a liquid crystal composition between substrates by arranging a counter substrate on which a common electrode is formed by TO or the like in parallel with the electrode surface facing each other.

The substrate for a flat-panel display device according to the present invention is an undercoat film formed on a plastic substrate, which is formed by forming a metal film of Al, Ti, Ta or other metal on a plastic substrate, and oxidizing the metal film. Since the oxide coating is used, an undercoat film that is transparent to visible light and has good insulating properties can be obtained while maintaining a strong bonding force at the interface with the plastic substrate.

Therefore, a TFT can be formed by depositing amorphous silicon or polycrystalline silicon thereon, thereby forming a matrix array. Also, by providing an electrode extraction window in a part of the transparent insulating film, and setting the transparent conductive film to an arbitrary potential through the electrode extraction window,
Even when local charging occurs in the plastic substrate, the charging state is TF due to the shielding effect of the transparent conductive film.
The effect of T on the threshold voltage and the effect on liquid crystal materials, EL materials, and the like can be prevented, and instability of the display state can be suppressed.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, portions common to the drawings are denoted by the same reference numerals, and redundant description will be omitted.

(Embodiment 1) FIGS. 1A to 1C are process cross-sectional views for explaining a process for obtaining a structure according to an embodiment of the present invention.

First, a plastic substrate 11 having a predetermined thickness
Was prepared, and an Al film 12 having a thickness of 50 nm was deposited on the surface of the plastic substrate 11 by using a sputtering method (FIG. 1A).

Next, the plastic substrate 11 on which the Al film 12 is deposited is immersed in an electrolytic bath 14 containing a non-erodable electrolytic solution 13 in which AI ₂ O ₃ is not dissolved, facing the counter electrode 15. Anodization was performed on the Al film 12 by applying a positive voltage to the Al film 12 with respect to the counter electrode 15 (FIG. 1B).

As a result, Al on the plastic substrate 11
The film 12 was transformed into an Al ₂ O ₃ film by anodization, and a plastic substrate whose surface was covered with an Al ₂ O ₃ film 16 was obtained (FIG. 1C).

In the thus obtained plastic substrate shown in FIG. 1C, the Al ₂ O ₃ film 16 is transparent to visible light, has excellent insulating properties, and has an impurity such as sodium. Had excellent stopping power against the diffusion of

Therefore, when an amorphous silicon or polycrystalline silicon was deposited on the plastic substrate 11 to form a matrix array, it functioned as an excellent undercoat film.

Further, the AI ₂ O ₃ prepared in this embodiment was used.
The film 16 forms a metal bond with the Al film covering the plastic substrate 11 taking in the atoms on the surface of the plastic substrate 11 and then forms Al ₂ O ₃ while maintaining the state.
Since the film has changed, the plastic substrate is not subjected to a fatal influence such as softening after that, that is, 200 ° C.
Even if the heat treatment is performed to the following degree, the plastic substrate 1
No peeling occurred between the sample and No. 1.

(Embodiment 2) FIG. 2 shows a substrate for a flat display device in which an Al ₂ O ₃ film 16 is formed on both the front and back surfaces of a plastic substrate 11.

As described above, the flat display device substrate having the Al ₂ O ₃ films 16 on both surfaces is obtained by forming the Al film 12 on the surface of the plastic substrate 11 in the step of FIG.
And an Al film 12 is similarly deposited on the back surface of the plastic substrate 11, and a positive voltage is applied to both the front and back Al films 12 in the step of FIG.
It is obtained by transforming into an Al ₂ O ₃ film by anodization.

In the flat display device substrate of this embodiment, since the Al ₂ O ₃ film 16 is formed on both the front surface and the rear surface of the plastic substrate 11, the symmetry with respect to the thermal expansion and contraction of the substrate is increased, and the process is improved. This has the effect of preventing the occurrence of wafer deformation such as warpage due to the difference in the coefficient of thermal expansion between the plastic substrate 11 and the undercoat film 16 during a middle heating step or the like.

(Embodiment 3) FIGS. 3A to 3E are process diagrams for explaining a process for obtaining a substrate for a flat display device according to another embodiment of the present invention.

First, a plastic substrate 11 is prepared, and the surface of the plastic substrate 11 is
An Al film 12 having a thickness of 00 nm was deposited (FIG. 3A).

Next, the plastic substrate 11 on which the Al film 12 has been deposited is immersed in a non-erodable electrolytic solution (not shown).
Anodization is performed on the Al film 12 by applying a positive voltage to a counter electrode (not shown) in the electrolyte, and the Al film 12 having a thickness of 50 nm from the surface is transformed into an Al ₂ O ₃ film 16. (FIG. 3B).

Further, A
A mask pattern 17 of a photoresist film is formed on the l ₂ O ₃ film 16 (FIG. 3C), immersed again in a non-erodable electrolyte (not shown), and a counter electrode (not shown) in the electrolyte. was anodized by applying a positive voltage to not), the Al film 12 of a portion which is not covered by the mask pattern 17 Al ₂ O
_It was denatured into _three films 16 (FIG. 3D).

At this time, in the portion of the Al film 12 covered by the mask pattern 17, anodization does not proceed and
The film remained. Next, by removing the mask pattern 17, a plastic substrate partially covered with the Al ₂ O ₃ film 16 including the Al film pattern 12 was obtained (FIG. 3E).

In the plastic substrate shown in FIG. 3 (e), the Al ₂ O ₃ film 16 can be used as an excellent undercoat film as in the case of FIG. 1 (c). A matrix array could be formed by depositing crystalline silicon or polycrystalline silicon.

At this time, A which was left without being partially anodized
The l-film pattern portion is formed by removing a portion of the Al ₂ O ₃ film 16 thereon by etching to form a wiring layer connected to a drain region or the like of a TFT made of amorphous silicon or polycrystalline silicon. By leaving this Al film pattern at the boundary between adjacent pixels by utilizing the fact that light is not transmitted, it can be used as a so-called black matrix layer.

(Embodiment 4) FIGS. 4 (a) to 4 (d) are process diagrams for explaining a process for obtaining a substrate for a flat panel display according to still another embodiment of the present invention.

First, a plastic substrate 11 is prepared, and 150 n is formed on the surface of the acrylic substrate 11 by a sputtering method.
An m-thick ITO film 18 was deposited, and then a 100-nm thick Al film 12 was deposited on the ITO film 18 by a sputtering method (FIG. 3A). Next, a part of the Al film 12 was removed by etching using a normal PEP method to expose the ITO film 18 in that part, and an electrode extraction window 14 for the ITO film 18 was formed (FIG. 3B).

In this state, the whole is immersed in a non-erodible electrolytic solution 13 in which Al ₂ O ₃ is not dissolved, and a positive voltage is applied to the counter electrode 15 in the electrolytic solution through the electrode take-out window 19 to the ITO film 18. Anodization is performed on the Al film 12 by applying the voltage (FIG. 3C), and the Al film 12 is transformed into an Al ₂ O ₃ film 16, whereby the surfaces of the ITO film 18 and the Al film are formed.
A plastic substrate covered with the ₂ O ₃ film 16 was obtained (FIG. 3D).

In the above method, a positive voltage with respect to the counter electrode 15 is applied to the ITO
Since the anodization is performed, the current path is secured even after the most of the Al film 12 is transformed into the Al ₂ O ₃ film 16 by the anodization, and the Al film 12 is completely converted to the Al ₂ O _3. It can be transformed into a membrane 16.

In the plastic substrate shown in FIG. 3D, the ITO film 18 and the Al ₂ O ₃ film 16 are transparent to visible light, and the Al ₂ O ₃ film 16 has excellent insulating properties. A TFT can be formed by depositing amorphous silicon or polycrystalline silicon on this structure to form a matrix array. In addition, the ITO film 18 has excellent conductivity of about 10 to 50 Ωcm, and even when charging occurs in the plastic substrate due to its shielding effect, the charging state is determined by the threshold voltage of the TFT, the liquid crystal material, and the EL material. The influence on the electric field and the like can be removed to prevent the display state from becoming unstable.

In the above process, when performing anodization,
If an electrode for applying a positive voltage is taken out from the end face of the ITO film 18, it is not always necessary to form the electrode take-out window 19, and the step of FIG. 3B can be omitted. However, by creating the electrode extraction window 19, the electrode extraction window will be used in the future,
The ITO film 18 can be fixed at an arbitrary potential. In this way, even when a large amount of charge is generated in the plastic substrate, the influence of this charge causes the IT
The potential of the O film 18 itself is not changed, and it is possible to effectively prevent the charging state in the plastic substrate from making the display state unstable.

(Embodiment 5) FIG. 5 is a sectional view schematically showing one application example of this embodiment.

FIG. 5 shows that a gate electrode 21 is formed on an ITO film 18 and an Al ₂ O ₃ film 16 which cover the surface of a plastic substrate 11, and an amorphous silicon TFT 23 as a switching element is interposed via a gate insulating film 22. And a matrix array formed by forming pixel electrodes 24 using an ITO film. Where TFT
23 and a part of the pixel electrode 24 are made of metal wiring 26.
Are electrically connected to each other.

In the embodiment shown in FIG. 5, the electrode take-out window 14 is formed by partially removing the Al ₂ O ₃ film 16 by etching.
The wiring 26 for the ITO film 18 is taken out from the device, and the tip of the wiring 26 is connected to the reference potential (earth potential) of the matrix array formed on the Al ₂ O ₃ film 16.
In this structure, the ITO film 18 is used as a shield for preventing the display state from becoming unstable when charge is generated in the plastic substrate, and is used as an additional capacitance with respect to the pixel electrode 24. 24 is used to stabilize the potential.

[0058] Incidentally, the process of anodization in the above embodiment, Al was performed with a non-erodible electrolytic solution which does not dissolve the Al ₂ O _3, is created in such a way ₂
Since the O ₃ film thickness is proportional to the applied voltage, the film thickness to be formed is limited. When a thicker Al ₂ O ₃ film thickness is required, anodization is performed once in an erosive electrolyte having a property of slightly dissolving Al ₂ O ₃ , and then in a non-erodible electrolyte. It can be obtained by performing anodization again. In the above embodiment, Al is used as the metal deposited on the plastic substrate to form the undercoat film. However, the present invention is not limited to this, and other metals such as Ti, Ta, and Zr can be used. As a means for forming the undercoat film, a plasma oxidation method or the like can be used in addition to anodization.

[0059]

As described above, the substrate for a flat-panel display device of the present invention has a plastic substrate on which Al, Ti, T
After being coated with a metal coating such as a, the film obtained by converting these metal coatings to an oxide by anodic oxidation or the like is used as an undercoat film, so that a strong bonding force at the interface with the plastic substrate is maintained. In addition, it is possible to obtain an undercoat film which is transparent to visible light, has good insulation properties, and can effectively suppress diffusion of impurities.

When a transparent conductive film is formed on a plastic substrate and then the undercoat film is formed thereon, a transparent conductive film and a metal film are deposited on the plastic substrate, and the transparent conductive film and the metal film are opposed to each other in an electrolytic solution. Since a positive voltage to the electrode is applied to the transparent conductive film to perform anodization of the metal film, a current path is secured even after most of the metal film is transformed into an insulating film by anodization, and the metal film is formed. It can be completely transformed into an insulating film. In addition, by using such a structure, even if charge is generated in the plastic substrate due to the shielding effect of the transparent conductive film, the charge state is TF.
The influence on the threshold voltage of T, the electric field inside the liquid crystal material and the EL material, and the like can be eliminated to prevent the display state from becoming unstable.

[Brief description of the drawings]

FIG. 1 is a process chart showing a process of manufacturing a substrate for a flat panel display according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a flat panel display device substrate according to a second embodiment of the present invention.

FIG. 3 is a process chart showing a process of manufacturing a substrate for a flat panel display according to a third embodiment of the present invention.

FIG. 4 is a process plan view showing a process of manufacturing a substrate for a flat panel display according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view showing a flat panel display device substrate according to a fifth embodiment of the present invention.

[Explanation of symbols]

11 ... Plastic substrate, 12 ... Al film, 13 ...
Electrolyte, 14 ... Electrolyzer, 15 ... Counter electrode, 16 ...
Al ₂ O ₃ film, 17 resist pattern, 18 I
TO film, 19 ... Electrode extraction window, 21 ... Gate electrode, 22 ... Gate insulating film, 23 ... TFT, 24 ...
Pixel electrode, 25, 26 ... Metal wiring

Claims (4)

[Claims] 1. A semiconductor device comprising: a substrate having at least a surface made of plastic; and a metal oxide film formed by oxidizing a metal film applied to at least the surface of the substrate where the plastic is exposed. Substrate for flat panel display. 2. A metal oxide film formed by oxidizing a metal film formed on at least the surface of the substrate where the plastic is exposed, and a metal oxide film formed by oxidizing a metal film formed on at least the surface of the substrate where the plastic is exposed. A substrate for a flat-panel display device, comprising: a metal film pattern that is left as is. 3. A substrate having at least a plastic surface, a transparent conductive film applied to at least a surface of the substrate where the plastic is exposed, and an oxidation treatment of a metal film formed on the transparent conductive film. A flat display device substrate, comprising: a formed metal oxide film. 4. A substrate having at least a surface of a plastic, a metal oxide film formed by oxidizing a metal film applied to at least a surface of the substrate where the plastic is exposed, and a matrix on the metal oxide film. A substrate for a flat display device, comprising: a scanning line, a signal line, and a switching element formed in a shape.