JPH0816758B2 - Liquid crystal image display device and method of manufacturing the same - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal panel having an image display function, and more particularly to an active type liquid crystal image display device having a switching element for each picture element and a manufacturing method thereof.

2. Description of the Related Art Due to recent advances in microfabrication technology, liquid crystal materials, packaging technology, etc., it has become possible to obtain television images on a commercial basis that are small in size of about 2-6 inches, but are practically unproblematic for liquid crystal panels. It was A so-called active liquid crystal panel in which a color display is easily realized by forming an RGB colored layer on one of the two glass plates constituting the liquid crystal panel, and a switching element is built in for each picture element. Guarantees images with low crosstalk and a high contrast ratio. Such a liquid crystal panel has 120-240 scanning lines and 240 signal lines.
-A matrix structure of about 720 is standard, for example, the 6th
As shown in the figure, the semiconductor integrated circuit chip 3 for supplying a drive signal is directly connected to the electrode terminal group 6 of the scanning line formed on one of the translucent insulating substrates constituting the liquid crystal panel 1, for example, the glass substrate 2. (COG (Chip-On-Glass) method,
For example, a connection film 4 based on a polyimide resin thin film and having a gold-plated copper foil terminal group (not shown)
An electric signal is supplied to the image display unit by a mounting means such as a method of fixing the signal line to the electrode terminal group 5 of the signal line while pressing it with an adhesive. Here, two mounting methods are shown simultaneously for convenience, but it goes without saying that one of the mounting methods is actually selected. Reference numerals 7 and 8 denote image display portions at the center of the liquid crystal panel 1 and electrode terminal groups 5 and 6 for signal lines and scanning lines.
The wiring path connecting between the electrode terminal group and the electrode terminal group does not necessarily have to be made of the same conductive material as the electrode terminal group.

Reference numeral 9 is another glass plate which is a transparent insulating substrate having a transparent conductive counter electrode common to all the picture elements, and two glass plates 2 and 9 are spacers such as quartz fibers and plastic beads. Is formed with a predetermined distance, and the gap is a closed space sealed with a sealing material and a sealing material, and the closed space is filled with liquid crystal. In many cases,
The glass substrate 9 is called a color filter because an organic thin film containing one or both of a dye and a pigment called a coloring layer is applied to the closed side of the glass plate to provide a color display function. Depending on the properties of the liquid crystal material, a polarizing plate is attached to either the upper surface of the glass plate 9 or the lower surface of the glass plate 2 or both surfaces thereof, and the liquid crystal panel 1 functions as an electro-optical element.

FIG. 7 is an equivalent circuit diagram of an active liquid crystal panel in which an insulated gate transistor 10 is arranged as a switching element for each picture element, and FIG. 8 is a cross-sectional view of a main part of the panel. The element drawn by the solid line is on one glass substrate 2,
The element drawn by the broken line is formed on the other glass substrate 9. Scan line 11 (8) and signal line 12 (7)
Is a thin film transistor 1 using, for example, amorphous silicon as a semiconductor layer and a silicon nitride film (Si ₃ N ₄ ) as a gate insulating film.
Simultaneously with the formation of 0, it is formed on the glass substrate 2. The liquid crystal cell 13 includes a transparent conductive picture element electrode 14 formed on the glass substrate 2, a transparent conductive counter electrode 15 formed on the color filter 9, and a closed It is composed of a liquid crystal 16 that fills the space, and is electrically treated the same as a capacitor.

As described above, the colored layer 17 made of colored photosensitive gelatin, colored photosensitive resin, or the like is arranged in the three primary colors of RGB in a predetermined arrangement corresponding to the pixel electrodes 14 on the closed space side of the color filter 9. There is. The counter electrode 15 common to all the pixel electrodes 14 is formed on the coloring layer 17 as shown in order to avoid voltage distribution loss due to the presence of the coloring layer 17.
For example, if it is attached to two glass plates in contact with the liquid crystal 16,
The polyimide resin thin film layer 18 having a film thickness of about 0.1 μm is an alignment film for aligning liquid crystal molecules in a predetermined direction. In addition, when a twisted nematic (TN) type liquid crystal 16 is used, two polarizing plates 19 are required above and below.

By arranging the low-reflectivity opaque film 20 on the boundary of the RGB colored layer 17, it is possible to prevent the reflected light from the wiring layer such as the signal line on the glass substrate 2 and improve the contrast ratio, and the outside of the switching element 10. The increase in leak current due to light irradiation can be prevented, and it is possible to operate even under strong external light, which has been put to practical use as a black matrix. There are many possible configurations of black matrix material, but considering the occurrence of steps at the boundaries of the colored layers and the light transmittance, it is costly but a Cr thin film with a thickness of about 0.1 μm is simple. .

In FIG. 7, the storage capacitor 21 is not always an essential component for an active liquid crystal panel, but it improves the utilization efficiency of the driving signal source, suppresses the stray parasitic capacitance failure, and operates at high temperature. Image flicker
It is effective for prevention and is appropriately adopted. Further, in order to facilitate understanding, main factors such as a light source and a spacer in addition to the thin film transistor, the scanning line 11 and the storage capacitor 21 are omitted in FIG. Reference numeral 22 is a conductive thin film for connecting the pixel electrode 14 and the drain of the insulated gate transistor 10, and is generally formed of the same material as the signal line 12 at the same time.

However, in the active type liquid crystal panel, it is difficult to drive all the liquid crystal cells 13 under the same conditions because the device structure is complicated, and therefore, a phenomenon in which a displayed image flickers and is visible easily occurs. . It is a well-known fact that image flickering is also called flickering and occurs when a liquid crystal panel having a simple matrix organization is observed obliquely or when a drive signal contains a large amount of DC components. In order to reduce the flicker, all liquid crystal cells should be in the same driving state so that the liquid crystal cell 13 and the insulated gate transistor 10 are constituent elements.
Also, there is a method of manufacturing the storage capacitor 21 with high accuracy, and a method of driving adjacent liquid crystal cells 13 in opposite phases and visually escaping so that the liquid crystal panel is not observed as a whole. In the former case, not only the manufacturing conditions for active board and panel assembly become stricter, but also large defects are required due to the large storage capacity required, and defects such as lower aperture ratio are highlighted. In the latter case, flicker apparently decreases. However, since the counter electrode 15 is held at a constant voltage and is driven by an alternating current, the signal voltage becomes high, and therefore a minute variation DC voltage component between the liquid crystal cells, which is a cause of flicker, is also increased. However, there is a drawback that the liquid crystal deteriorates and browns when used, and the image quality is impaired.

Originally, as shown in FIG. 8, if the organic thin film alignment film 18 exerts an insulating function to insulate the surface of the signal line 12, the drain wiring 22, and the conductive electrodes such as the pixel electrodes 14, Liquid-phase cell 13 including element electrode 14, counter electrode 15 and liquid crystal layer 16
No direct current will flow into the liquid phase layer 16 and no deterioration of the liquid phase layer 16 should occur. However, as described above, the alignment film 18 has a thickness of 0.
It is as thin as about 1 μm, and it is easy to have pin holes inside because the general alignment film coating method is offset printing.
In order to prevent the active element from being thermally destroyed, the alignment film 18 alone is used for the signal line 12, because the alignment film is cured (heat cured) at a relatively low temperature of 300 ° C. or lower.
The surfaces of the drain wiring 22 and the pixel electrodes 14 and the like can be insulated only incompletely, and it is difficult to prevent the deterioration of the liquid crystal layer 16 to some extent. In particular, since the signal voltage is continuously supplied to the signal line 12 from the outside, a DC component easily flows between the signal line 12 and the counter electrode 15. Therefore, instead of the thin alignment film, as shown in FIG. 9, the liquid crystal layer 16 is formed by coating the entire surface of the active substrate 2 with a transparent insulating film 23, for example, Si ₃ N ₄ in a film thickness of about 0.5 μm. It will be easily understood that the deterioration of can be avoided.

However, it is preferable to form a thick passivation layer 23 over the entire surface in the sense that the manufacturing process becomes long and the voltage applied to the liquid crystal layer 16 is lowered due to the presence of the insulating layer on the pixel electrode 14. It is a situation that cannot be said. Regarding the latter, it is possible to selectively remove the passivation layer 23 on the pixel electrode 14, but if there is a high step of the passivation layer on or in the vicinity of the pixel electrode 14, the alignment film 18 The rubbing treatment with the dry cloth was not regularly performed, and the side effect was generated in which the alignment of the liquid crystal was disturbed and the reverse domain was generated to deteriorate the display image quality.

The present invention aims to solve such problems of the conventional technology.

Means for Solving the Problems The present invention introduces an anodic oxidation step in order to selectively insulate only a signal line made of Al and a drain wiring, and Al ₂ O
_{A 3} (alumina) film is selectively formed on the signal line and the drain wiring.

Since the alumina thin film, which is an insulator, is selectively formed only on the signal line and drain line, there is no drop in the voltage applied to the liquid crystal layer, and the passivation layer deposition process is not required. The shortening of the process is promoted.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5. FIG. 1 shows a pattern on an active substrate 2 which constitutes a liquid crystal image display device according to a first embodiment of the present invention. In anodic oxidation, it is necessary to electrically connect all the wirings on which the oxide film is to be grown.
Are connected to a common connection line 23 via the terminal electrode 5, and the connection line 23 is connected to a connection part 24, which is a solid pattern, in the peripheral part of the glass substrate 2. (Here, the solid pattern is a wide Al pattern selectively left so as to be electrically connected by being sandwiched by a clip or the like as described later.) The connection line 23 and the connection portion 24 Is formed of the same Al as the signal line 12. The active substrate 2 shown in FIG. 1 is a container filled with the chemical conversion liquid 25 as shown in FIG.
The positive (+) terminal 28, which is installed in the DC power supply 27, is connected to the connecting portion 24 of the active substrate 2 by using a jig such as a clip, and the negative (-) terminal 29 is gold or platinum. Etc. is connected to the electrode plate 30. Upon anodic oxidation of Al, porous alumina oxide (alumina, Al ₂ O ₃ ) grows in the chemical conversion liquid containing oxalic acid or sulfuric acid as the main component, and non-porous dense aluminum oxide conversion liquid containing boric acid. Although it is known that alumina grows, details of anodic oxidation of Al are disclosed in Japanese Patent Publication No. 59-34798, which is a prior application example. In any case, in anodic oxidation, when the concentration and temperature of the chemical conversion solution are constant, the film thickness of the growing oxide film is determined by the chemical conversion voltage. Therefore, if appropriate conditions are selected, as shown in FIG. For example, it is extremely easy to form the alumina film 31 of about 0.1-0.3 μm on the Al signal line 12 having a film thickness of 1 μm. Since some current flows through the drain wiring 22 through the channel resistance of the insulated gate transistor, if strong external light is applied to the active substrate 2 during anodization, the channel resistance will decrease and
The oxide film 32 easily grows on the surface of 22, but the channel resistance is an order of magnitude higher than that of Al.
It would be inefficient to continue the anodic oxidation for a long time until the alumina film having the same film thickness as the signal line 12 grows on 22 as well.
After completion of the anodic oxidation, as shown in FIG. 1, if the active substrate 2 is cut along the cutting line 33, the connection terminal 23 is cut and the electrode terminals 5 are independently formed to complete the active substrate 2.

If the electrode terminals are COG-compatible and small, it is difficult to separate the electrode terminals by cutting the active substrate 2. In such a case, for example, a photosensitive resin pattern is selectively formed on the connection line 23, the photosensitive resin pattern is first removed after completion of anodization, and then the alumina film is used as an etching mask for Al. If selectively removed, the electrode terminals can be made independent.

In the first embodiment, since the surface of the active substrate 2 is exposed and the purity control of the chemical conversion liquid is insufficient, ionic impurities in the chemical conversion liquid mix into the insulated gate type transistor, resulting in poor transistor characteristics. Countermeasures are easy if there is a margin in the pattern layout that connects both ends of the signal line to the connection line, but if the signal line has a disconnection, the anodic oxide film may be removed. There is a drawback that some regions do not grow.

In the second embodiment, as shown in FIG. 4, the photosensitive resin layer 35 is formed by a well-known photolithography method in the reverse pattern of the above pattern after the Al layer 34 serving as the signal line (source wiring) and the drain wiring is deposited. The surface of the Al layer 34 is selectively anodized using the reverse pattern 35 as a mask for the anodization to form 36 and 37. After the anodic oxidation is completed, the photosensitive resin pattern 35 is removed, and the anodic oxide films 36 and 37 are used as masks for Al.
The active substrate 2 shown in FIG. 5 is formed by selectively etching the layer 34.
Is completed. Impurities in the chemical conversion liquid are taken into the anodic oxide film, which avoids the risk of unstable electrical characteristics of the insulated gate transistor.

In FIG. 3, the entire surfaces of the signal line 12 and the drain wiring 22 are coated with alumina films 31 and 32, but in FIG. 5, the signal line 12 and the drain wiring 22 are covered with alumina films 36 and 37. The side surfaces of the signal line 12 and the drain wiring 22 which are coated are different in that Al is exposed. The pattern width of the signal line 12 and the drain wiring 22 is generally 10 μm.
Since it is about m, if impurities of the liquid crystal material and the alignment film, especially ionic impurities can be excluded so that the purity of the liquid crystal 16 layer can be maintained sufficiently high, ionic impurities are also used in the second embodiment. It can be understood that the DC current component due to is reduced to about 1/5 of that of the conventional example, so that the deterioration of the liquid crystal is significantly improved.

With respect to the structure of the active substrate, the position where the pixel electrode is formed in the thickness direction largely depends on the structure of the insulated gate transistor and the manufacturing method thereof, and is therefore omitted in the above description. Since the picture element electrode is insulated only from the signal line by the insulated gate transistor, it is not necessary to insulate the surface of the drain wiring connecting the picture element electrode and the insulated gate transistor. If there is a defect that the transistor is always turned on, there is a high possibility that the liquid crystal will be deteriorated in the vicinity of the defect, and it is preferable that the drain wiring is also insulated as in the present invention. For the same reason, the pixel electrodes are not located on the top layer of the active substrate, but instead of transparent insulating SiO ₂ or Si ₃ N.
A more reliable liquid crystal image display device can be obtained when ₄ is deposited on the pixel electrodes. In addition, if the signal line does not also serve as the source wiring of the insulated gate transistor and is not covered with an insulating film, it is not necessary to explain that the same treatment as the signal line is necessary for the source wiring. Ah

As described above, according to the present invention, in order to prevent or significantly reduce the direct current component that flows into the liquid crystal cell and deteriorates the liquid crystal, the surfaces of the signal line and drain wiring made of Al are made of insulating alumina. It is coated with a film. Therefore, even if a high signal voltage is applied by adopting flickerless driving, the liquid crystal layer is deteriorated and the display image is colored brown and the quality problem is solved. In addition, since the surface of the signal line and the drain wiring can be insulated without increasing the film thickness, it is possible to prevent a decrease in the voltage effectively supplied to the liquid crystal cell as compared with the conventional overall passivation using a transparent insulating thin film. It was possible, and there was no possibility that the displayed image would be dark, and the excellent effect of maintaining the alignment state of the alignment film was obtained.

[Brief description of drawings]

FIG. 1 is a pattern diagram on an active substrate constituting a liquid crystal image display device according to a first embodiment of the present invention, FIG. 2 is a conceptual sectional view showing an anodizing method in the device, and FIG.
FIG. 4 is a cross-sectional view of a main part of a substrate of the same device, and FIGS. 4 and 5 are cross-sectional views of a main part in a manufacturing process of an active substrate which constitutes a liquid crystal image display device according to a second embodiment of the present invention. FIG. 7 is a perspective view showing a mounting means on a liquid crystal panel, FIG. 7 is an equivalent circuit diagram of an active type liquid crystal panel, FIG. 8 is a cross-sectional view of a main part of the panel, and FIG. 9 is carried out to prevent deterioration of liquid crystal. It is sectional drawing which shows the passivation on the active substrate of the conventional example. DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel, 2 ... Glass plate, 9 ... Color filter, 10 ... Insulated gate transistor, 11 ... Scanning line, 12 ... Signal line, 13 ... Liquid crystal cell, 14 ... Picture electrode ,
15 …… Counter electrode, 16 …… Liquid crystal, 18 …… Alignment film, 22 …… Drain wiring, 23 …… Connecting wire, 24 …… Solid pattern, 25…
… Chemical solution, 26 …… Container, 27 …… DC power supply, 28 …… + (plus) terminal, 29 …… – (minus) terminal, 30 …… electrode plate, 31, 36 …… Alumina film on signal line, 32, 37 …… Alumina film on drain wiring, 33 …… Cutting line, 34 …… Al layer,
35: Photosensitive resin pattern.

Claims (4)

[Claims] 1. A first light-transmissive insulating substrate having a plurality of scanning lines and signal lines, and having an insulated gate transistor and a pixel electrode for each unit pixel, and a transparent conductive counter substrate. A liquid crystal image display device in which liquid crystal is filled between a second translucent insulating substrate having an electrode, wherein the liquid crystal image display device is located on the uppermost layer on the first translucent insulating substrate and is in contact with the liquid crystal. A liquid crystal image display device, wherein the signal line is made of aluminum whose surface is anodized, and is electrically insulated from the liquid crystal. 2. A first translucent insulating substrate having a plurality of scanning lines and signal lines, and having an insulated gate transistor and a pixel electrode for each unit pixel, and a transparent conductive counter substrate. A liquid crystal image display device in which liquid crystal is filled between a second translucent insulating substrate having an electrode, wherein the liquid crystal image display device is located on the uppermost layer on the first translucent insulating substrate and is in contact with the liquid crystal. A liquid crystal image display device, characterized in that the signal line and the drain wiring of the insulated gate transistor are made of anodized aluminum whose surfaces are not equal in thickness, and are electrically insulated from the liquid crystal. 3. A first light-transmissive insulating substrate having a plurality of scanning lines and signal lines, and having an insulated gate transistor and a pixel electrode for each unit pixel, and a transparent conductive counter substrate. A liquid crystal image display device in which liquid crystal is filled between a second translucent insulating substrate having an electrode, wherein the liquid crystal image display device is located on the uppermost layer on the first translucent insulating substrate and is in contact with the liquid crystal. A liquid crystal image display characterized in that the signal line and the drain wiring of the insulated gate transistor are made of anodized aluminum with the same thickness on the surface except the side surface thereof, and are electrically insulated from the liquid crystal. apparatus. 4. A first translucent insulating substrate having a plurality of scanning lines and signal lines, and having an insulated gate transistor and a pixel electrode for each unit pixel, and a transparent conductive counter substrate. A method for manufacturing a liquid crystal image display device, comprising filling a liquid crystal between a second transparent insulating substrate having an electrode, wherein the liquid crystal is located on the uppermost layer on the first transparent insulating substrate. In forming the signal line in contact with the drain wiring of the insulated gate transistor, a photosensitive resin pattern having a reverse pattern of the signal line and the drain wiring is selectively formed on the aluminum after deposition of aluminum. Then, after selectively anodizing the aluminum, the photosensitive resin pattern is removed, and the aluminum is removed using the anodized portion as an etching mask, thereby manufacturing the liquid crystal image display device. .