JPH035725B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to a liquid crystal display device, and in particular to electrodes of a liquid crystal display device in which a thin film transistor (hereinafter abbreviated as TFT) is added to each display pixel in a matrix type liquid crystal display. It concerns the formation method.

<Prior art> A matrix type liquid crystal display device using TFT is
It was released in 1973 by Westinghouse Company in the United States. This is a method that enables high-contrast display even when performing multiplex driving with a small duty ratio, ie, multiple lines, by incorporating thin-film transistors and capacitors into a liquid crystal display panel. For detailed information, refer to “IEEE on Electron Devices.ED−20.P955.
(1973); TPB rody et al; “A6″×6″ 20lines/in Liquid Crystal
The equivalent circuit diagram of this liquid crystal display panel (Figure 1) is reported below.
This will be briefly explained using a schematic block diagram (FIG. 2).

As shown in FIG. 1, each picture element 10 of the matrix type liquid crystal display device includes a thin film transistor 1.
1 and a thin film capacitor 12 are added, and the capacitance 1 of the thin film capacitor 12 and the liquid crystal
3 are connected in parallel, and the thin film transistor 11 and thin film capacitor 12 are connected in series. The display of each picture element 10 is performed by applying a scanning signal to the row electrode 14 connected to the gate electrode of the thin film transistor 11 and by applying a data signal to the column electrode 15 connected to the source electrode of the thin film transistor 11. This is done by controlling charging and discharging, that is, controlling the voltage applied to the liquid crystal.

As a matrix type liquid crystal display device having the above-mentioned operating principle, the one shown in FIG. 2 is generally known. In Figure 2, 2
1 is a thin film transistor, 22 is a thin film capacitor 1
2, and also serves as the drain electrode and display electrode of the thin film transistor 21. 27
is the other electrode of the thin film capacitor 12, 24 is a row electrode connected to the gate electrode of the thin film transistor 21, 25 is a column electrode connected to the source electrode of the thin film transistor, and 26 is an electrode for insulating the row electrode 24 and the row electrode 25. It is an insulating film. These row electrodes 24 and column electrodes 25 are formed between each picture element 10.

In the above report, the semiconductor materials for TFT are:
CdSe is used, but other materials such as
CdS.Te.PbTe.Amorphous silicon (a-Si).
Using materials such as polycrystalline silicon (p-Si)
Research and development of TFT is currently progressing. By the way, TFTs using a-Si as a semiconductor film among these have an ON-OFF ratio of 10 or more and a resistance of 10 ¹⁰ Ω or more (however, channel dimensions: width (W) - 1000 μm, length (L)
_-40μm ). This R _OFF value is two to three orders of magnitude higher than other materials. This means that to obtain the memory time (Tmemory) determined by R _OFF (Cs + C _LC ), the value of (Cs + C _LC ) must be reduced by 1/10.
0 to 1/1000, and the memory capacitor Cs connected in parallel with the liquid crystal cell reported by Westinghouse and others can be omitted. This means that the panel manufacturing process can be reduced and the cost can be reduced. Moreover, in the above report, the row electrode 24, the column electrode 25
Metal materials such as Al and Au are used as electrode materials. Since these metal electrodes do not transmit light, it is necessary to narrow the electrode width in order to produce a bright display, but there are certain limits due to restrictions such as edging accuracy and yield. As a solution to this problem, it is effective to use a transparent conductive film (ITO) instead of metal materials such as Au and Al as the electrode material for the row electrodes 24 and column electrodes 25.
No. 9189 has been filed. TFT of this patent application
is a 1000Å film formed by vapor deposition on the gate insulating film.
SiO or SiO ₂ film is used. However, considering the operating principle of TFTs, it is desirable for the gate insulating film to be as thin as possible from the viewpoint of low-voltage driving. However, such insulating films cannot be fabricated by vapor deposition or
It is extremely difficult to form a pinhole-free thin film using the CVD method. On the other hand, if anodic oxidation is used, it is possible to form a pinhole-free insulating film considering its formation principle, and this insulating film will be extremely effective if applied to the gate insulating film of a TFT. For details, please refer to JP-A-54-
It is explained in Publication No. 99576. Special application 1989-9189
The issue describes the structure of an XY matrix type liquid crystal display panel in which a TFT with a gate insulating film formed using an anodizing method is added to each pixel of the display, and row and column electrodes are formed with a transparent conductive film. but,
It has not been made clear how to form gate/row electrodes having an electrode structure in which gate electrodes whose surfaces are anodized are connected using row electrodes made of transparent conductive films. To carry out the anodizing treatment, as shown in FIGS. 3A and 3B, a vapor deposition substrate 32 on which a metal thin film 31 to be anodized is formed is prepared.
is immersed in an ammonium tartrate electrolyte 33 having a concentration of about 4%, and a DC voltage is applied in the order of constant current formation and constant voltage formation, thereby oxidizing the metal surface and forming an anodic oxide film 36. This is used as a gate insulating film. However, a conductive film that cannot be anodized on the surface of the metal to be anodized, for example,
If Ni, Au, In ₂ O ₃ , etc. are attached and the conductive film is in direct contact with the electrolyte, the anodization process will not proceed even if anodized, and the conductive film that cannot be anodized will not be able to be anodized in the electrolyte. Since the metal is melted and corroded, causing disconnection, it becomes impossible to form an anodic oxide film on the target metal surface. Therefore, conventionally, except for the metal to be anodized, the other conductive films were coated with an insulating film such as resist or SiO ₂ and then anodized. However, it is extremely difficult to form a pinhole-free film with this resist or SiO ₂ , and it is difficult to form a gate/row electrode with an electrode structure in which anodized gate electrodes are connected with a transparent conductive film. , there was a negative effect on production yield. Therefore, it has not been possible to complete an XY matrix type liquid crystal display device having the above-mentioned features with a high yield.

<Object of the invention> The present invention provides a liquid crystal display in which a TFT using an anodic oxide film as a gate insulating film as described above is added to each picture element of a liquid crystal display, and row and column direction electrodes are formed with a transparent conductive film. It is an object of the present invention to provide a method for forming a gate electrode, gate insulating film, and row/column electrodes in a display device with a high yield.

<Embodiment> FIG. 4 is a structural diagram of an XY matrix type liquid crystal display device to which an embodiment of the present invention is applied. FIG. 5 shows a pattern diagram of each electrode, etc. formed in each step of manufacturing the XY matrix type liquid crystal display device shown in FIG. 4. Hereinafter, one embodiment of the present invention will be described with reference to this pattern diagram.

Step 1: Gate electrode formation On the main surface of a substrate made of glass, quartz, ceramic, etc., a material that can be used as a gate electrode and can be anodized, such as Ta, is vapor-deposited.
Etching is performed using an etching solution (HF.HNO ₃ ) in the pattern shown in FIG. 5A to form an island-shaped gate electrode 41.

Step 2: Formation of gate connection electrode An electrode material for gate electrode connection is deposited on the entire surface,
Thereafter, etching is performed in the pattern shown in FIG. 5B to connect the gate electrodes 41. At the same time, the gate connection electrode material on the gate electrode 41 to be anodized is removed. The gate connecting electrode material should be capable of anodic oxidation, have selective etching properties with the gate electrode material, and be able to remove the gate connecting electrode without damaging the gate electrode 41 and the film on which the gate electrode 41 is anodized. Any material may be used as long as it satisfies the conditions described above, and when Ta is used as the gate electrode, Al, for example, is used as the gate connection electrode. As the etching solution, there is a NaOH aqueous solution.

Step 3: Anodizing treatment In this step, when anodizing, the gate electrode 4
A chemical conversion treatment is performed not only on the gate connection electrode 1 but also on the gate connection electrode. At this time, since there is no metal that cannot be anodized as in the conventional case, there is no need to cover it with resist, and therefore problems caused by pinholes etc. occurring in the resist are also solved.

Step 4: Removal of gate connection electrode The gate connection electrode is removed by the method described in Step 2. As a result of this treatment, only the gate electrode pattern that has been anodized remains. The gate electrode part where the gate connection electrode overlapped was not anodized and the metal surface was exposed, and by overlapping and interconnecting the row electrode 42 formed with a transparent conductive film that was later deposited on this part. Gate/row electrodes 46 are formed.

Step 5: Formation of row electrodes, column electrodes, and pixel electrodes After depositing a transparent conductive film (ITO) on the entire surface, the fifth
Etching is performed in the pattern shown in Figure C to form row electrodes 42, column electrodes 43, and picture element electrodes 10.

Step 6: Semiconductor film formation TFT semiconductor film 4 in the pattern shown in Figure 5D.
form 4. As the semiconductor film 44, CdSe,
Various materials can be used, such as CdS, Te, PbTe, amorphous silicon, or polycrystalline silicon, but amorphous silicon is used in this embodiment. The semiconductor film 44 is deposited on one end of the gate electrode 41 at the cutout corner of the picture element electrode 10 .

Step 7: Formation of Source/Drain Electrodes A source electrode that connects the column electrode 43 and the semiconductor film 44 and a drain electrode that connects the semiconductor film 44 and the picture element electrode 10 are formed in the pattern shown in FIG. 5E. The source/drain electrode 45, gate electrode 41, and semiconductor film 44 constitute a TFT.

Through each of the above steps, a TFT substrate is manufactured in which TFTs using an anodic oxide film as a gate insulating film are arranged corresponding to each picture element, and row and column electrodes are formed of transparent conductive films. This TFT substrate and a counter substrate formed with a counter electrode facing the picture element electrode constitute a liquid crystal cell, and by sealing a liquid crystal layer in the liquid crystal cell, display is performed using the picture element electrode 10 as a unit picture element. A matrix type liquid crystal display device is manufactured. By driving the TFTs through matrix electrodes, a dot matrix type display pattern can be formed arbitrarily.

<Effects of the Invention> By manufacturing the TFT substrate as explained above, problems during anodization can be solved,
The use of transparent conductive films for the row and column electrodes provides a bright display, and the use of an anodic oxide film for the gate insulating film of the TFT allows for low voltage drive and good TFT characteristics. It is possible to manufacture liquid crystal display devices such as an XY matrix type liquid crystal display device with a high yield.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram of a conventional XY matrix type liquid crystal display device. Figure 2 is the TFT of Figure 1.
It is a pattern diagram. FIGS. 3A and 3B are explanatory diagrams for explaining a method of anodizing. FIG. 4 is a TFT pattern diagram of a liquid crystal display device obtained according to one embodiment of the present invention. FIGS. 5A to 5E are diagrams of patterned electrodes used in each manufacturing process to explain one embodiment of the present invention. 41... Gate electrode, 42... Row electrode, 43... Column electrode, 44... Semiconductor film, 45... Source/drain electrode.

Claims (1)

[Claims] 1. A step of forming a gate electrode of a thin film transistor on a substrate, connecting the gate electrodes with a different anodizable metal from the gate electrode, and then forming a gate insulating film on the gate electrode through anodic oxidation treatment. a step of removing the metal and reconnecting the gate electrodes with a transparent conductive film; forming a thin film transistor on each of the gate electrodes;
A method for manufacturing a liquid crystal display device, comprising the step of using the substrate as a cell substrate to encapsulate liquid crystal.