JPH0120428B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical Field> The present invention relates to a color liquid crystal display device having matrix-type electrodes, and particularly to an electrode structure for color display. <Prior art> As a color liquid crystal display device with a relatively simple liquid crystal panel structure, capable of full color display, and with good display quality, there is almost no color shift in the display due to the thickness of the glass substrate used in the panel. A liquid crystal display device in which a multicolor filter layer is formed inside a liquid crystal panel has already been announced. Among these, the panel structure of a typical color liquid crystal display device is shown in FIG. A signal-side transparent electrode 2 and a scanning-side transparent electrode 2' constituting a matrix electrode are formed on opposing surfaces of two opposing glass substrates 1, and an alignment layer 3 is coated thereon. Red, green, and blue color filter layers 4, 4', and 4'' are superimposed on the signal side transparent electrode 2, and a twisted nematic liquid crystal 5 is interposed between the alignment layers 3 to apply an electric field. A color display is performed in response to the change in the orientation of the liquid crystal molecules.A polarizing plate 6 for visualizing the orientation change of liquid crystal molecules is disposed outside the glass substrate 1 so that the polarization direction is perpendicular to the polarization direction.7 is the polarization direction; denotes a power source connected to the electrodes 2 and 2', 9 denotes a light source such as an incandescent lamp, fluorescent lamp, or EL lamp installed on the back side, and 10 denotes an observer.In the panel structure shown in Fig. 1, transparent electrodes Color filter layers 4, 4', 4'' are formed on the color filter layers 4, 4', 4'' in this structure, as shown in FIG _.
There are two problems: the threshold voltage V _th fluctuates due to variations in the film thickness of the color filter layers 4, 4', 4'' themselves as shown in FIG. 3. In the diagram, l ₁ is When there is no color filter layer, l ₂ is the applied voltage vs. light transmittance characteristic curve when there is a color filter layer. In this case, not only the signal-side electrodes but also the scanning-side electrodes increase.As a result, the operating period allocated to one scanning-side electrode within a certain frame frequency decreases, and the display contrast decreases. The following two driving methods can be considered to drive an XY matrix liquid crystal panel that can display large amounts of information up to (2) Voltage averaging method that optimizes the bias voltage to maximize the ratio of effective voltage applied to the liquid crystal (operating margin) when the voltage is turned on and off. (1) This method enables virtually static drive and can apply sufficient voltage when turned on, resulting in good display contrast. On the other hand, since a thin film transistor is formed as a switching element at the intersection of the XY electrodes, it is less effective than a conventional liquid crystal panel. However, in method (2), as the number of scanning electrodes N increases, the voltage applied to the liquid crystal during on/off increases. Ratio of effective voltage

There is a problem in that as the equation approaches 1, the operating margin becomes small and sufficient display contrast cannot be obtained. Furthermore, when this operating margin becomes smaller, and a color filter layer is provided on a transparent electrode, the threshold voltage V _th changes as shown in Figures 2 and 3, resulting in a clear display contrast. I can't. Good display contrast can be obtained by reducing the thickness of the color filter layer and at the same time reducing variations in the thickness to improve the fluctuations in threshold voltage V _th as shown in Figures 2 and 3. It is. However, if the color filter layer is made too thin, a predetermined color density cannot be obtained, and only color display with poor color purity can be achieved. It is also difficult to uniformly apply the color filter material to the underlayer. Therefore, in order to enable color liquid crystal display with a liquid crystal display device in which a color filter layer is provided inside a liquid crystal panel, a structure in which a color filter layer is provided below a transparent electrode is considered to be effective. FIG. 4 is a block diagram showing an electrode structure in which a color filter layer is provided below a transparent electrode. With the structure shown in Figure 4, the voltage applied to the liquid crystal will not drop at the color filter layers 4, 4', 4'', nor will it be affected by the thickness of the color filter layer, and the voltage applied to the liquid crystal will be directly connected to the transparent electrode. 2, the voltage is applied to the liquid crystal.Next, we will discuss the method of forming a transparent electrode on the color filter layer.When forming a transparent electrode on the color filter layer, the transmittance and sheet resistance of the transparent electrode are If the substrate temperature is increased from a certain point, the color filter will change color, so normal electron beam evaporation cannot be used, and transparent electrodes must be formed by low-temperature sputtering, ion plating, etc. This will be explained with reference to Figures A and 5B.First, red, green, and blue color filters are formed at predetermined positions on a glass substrate, and transparent electrodes are formed thereon by low-temperature sputtering or the like. After patterning the photoresist along the color filter pattern, the transparent electrode is etched.This photoetching method has a problem in that the etching solution gets to the bottom of the color filter layer and peels off the color filter layer and the transparent electrode. There are also the above,
In addition to the photoetching method, there is a method of forming the upper transparent electrode by a lift-off method. In this method, a photoresist is used and patterned on the color filter layer, a transparent electrode is formed on the entire surface by low-temperature sputtering, etc., and the lower photoresist is removed. At the same time, unnecessary portions of the transparent electrode are also peeled off and patterned. In the lift-off method, peeling of the color filter layer is not observed as in the photo-etching method described above, but when patterning a transparent electrode by the lift-off method, there is a problem that lift-off is difficult if the transparent conductive film is made too thick. . A similar problem also occurs when the substrate temperature is raised to lower the sheet resistance. Therefore, in the case of the lift-off method, the resistance value of the transparent electrode becomes relatively high, and sufficient voltage is not applied to the liquid crystal, making it impossible to obtain good display contrast. <Objective of the Invention> The present invention provides a liquid crystal display device capable of displaying full color by providing a transparent electrode in the upper layer of a color filter layer to eliminate fluctuations in the threshold voltage V _th and at the same time reduce the resistance value provided in the lower layer. It is an object of the present invention to provide a new and useful color liquid crystal display device in which display contrast is improved by contacting a transparent electrode with a low opacity and an upper layer transparent electrode. <Example> FIG. 6 shows an electrode structure of a color liquid crystal display device for explaining an example of the present invention. A transparent electrode 2 with relatively low resistance is provided below the color filter layers 4, 4', 4'', that is, on the top surface of the glass substrate 1, and after forming the color filter layers 4, 4', 4'' thereon,
Furthermore, a transparent electrode 2'' is placed on top of this by lift-off method.
By forming the electrode structure of the color liquid crystal display device. The manufacturing process will be explained in detail below. Example 1 As shown in FIG. 7A, a transparent electrical film having a relatively low resistance value is deposited on a glass substrate 1 by electron beam evaporation. At this time, by heating the glass substrate 1 to 350°C, a transparent conductive film with a transparency of 80% or more and a sheet resistance of 20Ω/cm ^{2 or} less was obtained. This transparent conductive film is etched into a predetermined pattern using a FeCl ₃ -HCl based etching solution to form a transparent electrode 2 . A photosensitive water-soluble polymer film 11 is coated on the transparent electrode 2, as shown in FIG. 7B.
As the water-soluble polymer membrane 11, casein G-90
(manufactured by Tokyo Ohka) to which ammonium dichromate was added at a ratio of 10 wt% as a photosensitive material was used and applied onto the glass substrate 1 using a spinner.
At this time, set the spinner rotation speed to 3000 RPM,
The thickness of the water-soluble polymer membrane 11 is approximately 0.5 μm. Next, it is patterned into a predetermined pattern by exposure and phenomenon, and the water-soluble polymer film 11 is selectively dyed using red, green, and blue dyes. The specific staining method is to use photoresist AZ on the areas other than those to be dyed red.
-1350J. (manufactured by Shipprey), and then dye the opening. Red staining conditions are shown below. Kayanol Milling GRA (manufactured by Nippon Kayaku) Acetic acid Pure water 10g 10ml 100ml Immerse the glass substrate in the above dye. The liquid temperature and immersion time at this time are 60°C for 5 minutes. Next, after peeling off the photoresist, a new photoresist is patterned and the openings are dyed green. In the case of green dyeing, green spectral characteristics can be obtained by dyeing with an anionic cyan dye and then dyeing with a cationic yellow dye. The dyeing conditions for the first and second colors when dyeing green are shown below. Kayakryl Piure Blue FGA (manufactured by Nippon Kayaku) The glass substrate was immersed in a solution consisting of acetic acid, pure water, 10 g, 10 ml, and 1000 ml at 60°C for 5 minutes to perform the first color staining. Subsequently, it was immersed in a solution of Kayacryl Yellow 3RL (manufactured by Nippon Kayaku) consisting of 5 g and 1000 ml of pure water at 60°C for 3 minutes, and a second color was dyed to obtain green spectral characteristics. Next, after peeling off the photoresist, a new photoresist is applied and patterned again, and the openings are dyed blue. The blue staining conditions are shown below. Kayakryl Milling Turkey Blue (manufactured by Nippon Kayaku) Immerse in a solution consisting of acetic acid, pure water 10g 10ml 1000ml at 60°C for 5 minutes. After forming a color filter layer by dyeing the water-soluble polymer film 11 with each dye, color filter layers 4, 4',
The portions 14 other than the color filter layers 4, 4', and 4'' are covered with a photoresist 13 as shown in FIG. 7C, and a second transparent conductive film is deposited thereon. Photoresist for lift-off 1
3, AZ-1350J (manufactured by Shippray Co., Ltd.) is used, and the film thickness is set to about 1 μm by applying with a spinner. The second transparent conductive film is formed by ion plating. Since proteins such as casein and organic dyes are used as color filter materials, the filter itself has poor heat resistance, so the substrate heating temperature during ion plating is set at about 100 to 150°C. Under these conditions, the color filter does not change color or fade. In this example, ion plating was performed at a substrate temperature of 150°C. Other conditions for forming a transparent conductive film using the ion plating method are as follows. Effective output of radio frequency (RF) Vacuum degree Film thickness plating speed 200W Reduce pressure to 1×10 ^-5 Torr, then leak _O2 and set to 5×10 ^-4 Torr, 1000Å 10Å/sec or more, Figure 7 As shown in D, transmittance is about 70
%, and a sheet resistance of about 700 to 1000 Ω/cm ² was obtained. Thereafter, the glass substrate was immersed in acetone and left in an ultrasonic bath for about 5 minutes, so that the photoresist under the transparent conductive film was dissolved in the acetone, and the transparent conductive film was patterned as shown in Figure 7E. . As a result, color filter layers 4, 4',
A second layer of transparent electrode 2'' is obtained on 4''. 6 is a sectional view of the electrode substrate in the scanning direction, that is, the X direction of FIG. 8, and FIG. 9 is a sectional view of the electrode substrate in the Y direction perpendicular to this. The first layer and the second layer transparent electrodes 2, 2'' are electrically contacted in the areas where the color filter layers 4, 4', 4'' are not provided on the first layer transparent electrode 2 to establish a conductive state. I am getting . Next, SiO ₂ is deposited on the glass substrate 1 on which the color filter layers 4, 4', 4'' are formed by electron beam evaporation, and then treated with a silane-based alignment agent, and then polished. Rub with a cloth.Also, the other glass substrate placed opposite to each other is similarly coated with SiO ₂ on the patterned transparent electrode.
is vapor-deposited, and treated with a silane-based alignment agent and rubbed. After bonding the peripheries of both glass substrates with epoxy resin, the epoxy resin is heated and hardened.
A twisted nematic field effect type color liquid crystal display panel is manufactured by injecting and sealing nematic liquid crystal into the gap between the substrates. Example 2 In Example 1, the width of the first layer transparent electrode 2 and
Although the widths of the color filter layers 4, 4', and 4'' are the same, in this embodiment the widths of the color filter layers are changed as shown in FIG. The width of the transparent electrode in the second layer is the same as the width of the transparent electrode in the first layer, but it may also be made larger like the color filter layer.Figure 11 shows the width of the transparent electrode in the Y direction. is a cross-sectional view of the first layer transparent electrode 2, where the color filter layers 4, 4', 4'' are not provided, and there is electrical contact between the first and second layer transparent electrodes 2, 2''. Example 3 In Example 1, the ion plating method was used to form the second transparent conductive film 2'', but in this example, the transparent conductive film is formed by a low temperature sputtering method. In FIG. 8, a transparent conductive film is formed by a low-temperature sputtering method on a glass substrate on which a portion of the first layer of transparent electrode 2 on which the color filter layer is not provided and a portion other than the transparent electrode 2 is coated with photoresist. form. As in Example 1, the substrate heating temperature was
The temperature is set at 150 to 200°C and controlled to prevent discoloration and fading of the color filter layer. In this example, the substrate temperature was 200°C. Other conditions for forming a transparent conductive film using the low temperature sputtering method are as follows. Effective output vacuum level of radio frequency (RF) Film thickness sputtering speed 850W Initial ultimate vacuum level 7 × 10 ^-7 Torr After that, Ar + O ₂ mixed gas (mixing ratio 10:4) was set to a leakage rate of 4 × 10 ^-3 Torr to 1000Å 2 Å/sec Formed with a transparent conductive film under the above conditions, transmittance approximately 70
%, and a sheet resistance of about 800 to 1200 Ω/cm ² is obtained. Note that the color filter material and lift-off photoresist are the same as in Example 1. <Effects of the Invention> According to the present invention, in a color liquid crystal display device having matrix-type electrodes, a transparent electrode with relatively low resistance is provided below the color filter layer,
Furthermore, by providing a second transparent electrode on the top of the color filter layer, which has a higher resistance value than the transparent electrode on the bottom, the voltage drop in the color filter layer itself can be improved and the voltage drop caused by the unevenness of the layer thickness of the color filter layer can be improved. Variations in threshold voltage V _th can also be improved. In addition, the above second transparent electrode is formed by the lift-off method, and for the above reasons, it can be used even if the resistance value is relatively high, and the second transparent electrode can be formed without causing the problem of peeling of the color filter layer and the lower transparent electrode. Can form electrodes. With such a color display electrode, a voltage can be efficiently applied to the liquid crystal layer, and a uniform full color display with excellent display contrast can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional color liquid crystal display device. FIG. 2 is a transmittance-voltage characteristic diagram showing that the threshold voltage is increased by providing a color filter layer. FIG. 3 is a transmittance-voltage characteristic diagram showing that the threshold voltage varies depending on the layer thickness of the color filter layer. FIG. 4 is a detailed configuration diagram of a color filter side substrate of a conventional color liquid crystal display device.
FIGS. 5A and 5B are process explanatory diagrams of the photoetching method and the lift-off method. FIG. 6 is an explanatory cross-sectional view of a color filter side substrate of a color liquid crystal display device showing one embodiment of the present invention. Figure 7 A, B, C, D,
E is a manufacturing process diagram of the color filter side substrate shown in FIG. 6. FIG. 8 is a perspective view of FIG. 7C. FIG. 9 is an explanatory cross-sectional view of the color filter side substrate shown in FIG. 6 in the orthogonal direction. FIGS. 10 and 11 are explanatory cross-sectional views of the color filter side showing other embodiments of the present invention. 1...Glass substrate, 2...1st layer transparent electrode,
2'... Scanning side transparent electrode, 2''... Second layer transparent electrode, 3... Alignment layer, 4, 4', 4''... Color filter layer (red, green, blue), 5... Liquid crystal, , 6...Polarizing plate.

Claims (1)

[Scope of Claims] 1. Forming intersecting matrix-like transparent electrodes on opposing surfaces of two light-transmitting substrates facing each other, and layering a color filter layer on the transparent electrodes on one of the substrates. In the color liquid crystal display device, a resistor is provided on the upper and lower surfaces of the color filter layer corresponding to at least each intersection of the matrix-like transparent electrodes, from a first transparent electrode on the substrate side and a first transparent electrode on the color filter layer. For color display, a two-layer transparent electrode consisting of a second transparent electrode with a high value and a lift-off method is formed, and the first transparent electrode and the second transparent electrode on each color filter layer are electrically conductive. A color liquid crystal display device characterized by having an electrode structure.