JPH1039283A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bright and high-contact display by preventing the occurrence of the nonuniformity of a gap by a difference in level of transparent electrodes. SOLUTION: This liquid crystal display element has plural transparent electrodes 2A, 2B formed in parallel respectively on a pair of transparent substrates 1A, 1B, protective films 3A, 3B applied onto the transparent electrodes and oriented films 4A, 4B formed on these protective films, and is formed by interposing a liquid crystal layer 5 in the spacing where the respective oriented films 4A, 4B are disposed to face each other in such a manner that the respective transparent electrodes 2A, 2B of a pair of the transparent substrates 1A, 1B intersect each other. The thickness of the protective films 3A, 3B described above is set larger than the thickness of the transparent electrodes 1A, 1B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having improved display quality by reducing the occurrence of light leakage and alignment disorder caused by steps of electrodes formed on a transparent substrate. It relates to a display element.

[0002]

2. Description of the Related Art Among conventional liquid crystal display elements, a liquid crystal display element of a type called TN, that is, a twisted nematic type, is twisted 90 degrees by a nematic liquid crystal having a positive dielectric anisotropy between two electrode substrates. It has a helical structure, and a polarizing plate is disposed outside of both electrode substrates such that its polarization axis (or absorption axis) is orthogonal or parallel to liquid crystal molecules adjacent to the electrode substrate. See JP-B-51-13666).

[0003] Such a liquid crystal display element having a twist angle (α) of 90 degrees has problems in the steepness (γ) of the change in the transmittance of the liquid crystal layer with respect to the voltage applied to the liquid crystal layer and the viewing angle characteristics. ,
The number of time divisions (corresponding to the number of scanning electrodes) was 64, which was a practical limit.

However, in order to cope with recent demands for improving the image quality and increasing the amount of display information for the liquid crystal display device, the twist angle α of the liquid crystal molecules is made larger than 180 degrees, and the time-division driving characteristic is obtained by utilizing the birefringence effect. Applied Physics Letter 45, N
o.10,1021 1984 (Applied Physics Letter, TJScheffe
r, J.Nehring: "A new, highly multiplexable liquidcrys
tal display "), and a super twisted birefringence (SBE) liquid crystal display has been proposed.

A liquid crystal display device having a twisted structure capable of high time-division driving performs lighting by causing a state change of a liquid crystal layer between a non-selection voltage determined by a bias voltage and a duty ratio and a selection voltage. . However, when the twist angle is 180 degrees or more, coloring occurs due to the birefringence effect of the liquid crystal.

In order to avoid this coloring phenomenon, by providing a birefringent medium called a compensating element or a retardation plate in which the liquid crystal layer is twisted in the opposite direction to the liquid crystal layer, the phase difference is compensated and a black and white display is performed. Is known (Yoshino, Ozaki, "Liquid Crystal and Display Application and Basics", Corona Co., Ltd. 19
94). The halftone display is performed by applying a voltage between the non-selection voltage and the selection voltage.

In order to color this type of liquid crystal display device, at least three color filters are formed on one of a pair of substrates, and a voltage is selectively applied to a segment electrode provided for each color filter. By applying the voltage, a required color image can be displayed.

FIG. 9 is a schematic sectional view of an essential part for explaining a configuration example of a conventional liquid crystal display element. 1A1B is an upper electrode substrate and a lower electrode substrate made of a transparent substrate such as glass.
B is an upper electrode and a lower electrode which are transparent electrodes formed on the upper and lower electrode substrates, 3A and 3B are upper protective films and lower protective films,
A and 4B are an upper alignment film and a lower alignment film, and 5 is a liquid crystal layer.

In this figure, this liquid crystal display element comprises an upper electrode substrate 1A on which an upper electrode 2A and an upper protective film 3A and an upper alignment film 4A are formed in parallel, and a lower electrode 2B and a lower electrode 2B which are also formed in parallel. The lower electrode substrate 1B on which the protective film 3B and the lower alignment film 4B are formed is connected to the upper alignment film 3 so that the upper electrode 2A and the lower electrode 2B intersect (generally orthogonal).
A and the lower alignment film 3B are opposed to each other with a predetermined gap D1, a liquid crystal layer 5 is sealed in the gap between them, and both substrates 1A and 1 are sealed with a sealing material.
B is attached.

A liquid crystal display device having such a structure is generally called a simple matrix type liquid crystal display device, and the liquid crystal sealed to form a liquid crystal layer is super twisted using a birefringence effect to improve optical characteristics. Liquid crystal (STN),
A phase difference plate and a polarizing plate are laminated on the upper and lower electrode substrates.

[0011]

In this type of liquid crystal display device, a so-called pretilt angle .theta.1 for aligning the liquid crystal molecules constituting the liquid crystal layer 5 in a specific direction is set by rubbing treatment applied to the upper and lower alignment films. You.

The transparent electrodes (upper and lower electrodes) 2A and 2B formed on the upper and lower electrode substrates 1A and 1B are obtained by patterning an ITO film using a photolithographic etching technique or the like. There is a step at the edge due to the thickness of the transparent electrode.

This step is also mapped on the alignment films 3A and 3B. As a result, as shown in FIG. 9, a predetermined gap (so-called cell gap) D1 of the liquid crystal layer 5 is larger than a predetermined cell gap D2. Causes outbreaks.

The presence of the step results in a difference in the path length of the irradiation light of the backlight passing through the liquid crystal layer. In a portion where the optical path length is long, the display density is reduced, and in a color display, the color tone is shifted (whitish). .

The pretilt angle of the liquid crystal molecules at the step is a predetermined pretilt angle θ _{1 as} shown by θ ₂ in FIG.
Unlike this, the angle generally becomes large. In a portion where the pretilt angle is large, the liquid crystal molecules rise at a low voltage, so that the color tone becomes whitish, the black display becomes whitish, and the contrast decreases.

In order to prevent such light leakage, there has conventionally been a method of forming a light shielding film between transparent electrodes to make the cell gap uniform. However, there is a problem that the number of steps for that purpose increases and the display screen becomes dark due to a decrease in the light transmission area due to the formation of the light-shielding film so as to cover the edge of the transparent electrode.

It is an object of the present invention to provide a liquid crystal display device which solves the above-mentioned problems of the prior art and prevents bright and high-contrast display by preventing non-uniformity of a cell gap due to a step of a transparent electrode. Is to do.

[0018]

In order to make the configuration of the present invention for achieving the above object easier to understand, reference numerals are given to the embodiments.

That is, the first aspect of the present invention provides a plurality of transparent electrodes 2A and 2B formed in parallel on a pair of transparent substrates 1A and 1B, respectively, and protective films 3A and 3B covering the transparent electrodes. And alignment film 4 formed on protective film
A, 4B, and a liquid crystal layer 5 in a gap where the respective alignment films are opposed to each other so that the respective transparent electrodes of the pair of transparent substrates intersect.
In the liquid crystal display device having the protective film 3
The thickness of A, 3B is equal to or greater than the thickness of the transparent electrodes 1A, 1B.

In this configuration, the thickness of the protective films 3A and 3B is equal to or larger than the thickness of the transparent electrodes 1A and 1B.
For example, when the thickness of the transparent electrodes 1A and 1B is 0.5 μm, and the thickness of the protective films 3A and 3B is 0.5 to 2.0 μm, the steps existing at the edge portions of the transparent electrodes 1A and 1B are formed. Is reduced, and the surface smoothness of the alignment film formed to cover the protective films 3A and 3B is improved. As a result, the thickness of the liquid crystal layer 5 becomes substantially uniform, the difference in the length of the optical path passing therethrough is eliminated, the contrast becomes non-uniform, and the pretilt angle does not change, so that a high-quality display can be obtained.

According to a second aspect of the present invention, a plurality of color filters 11 divided by a light-shielding film 10 and a film covering the color filters are formed on one of the pair of transparent substrates 1A and 1B. It has a smoothing layer 12, a transparent electrode 2A formed on the smoothing layer 12, a protective film 3A covering the transparent electrode and an alignment film 4A formed on the protective film, while the other 1B has a transparent electrode 2B and a transparent electrode A liquid crystal layer 5 having a protective film 3B formed thereon and an alignment film 4B formed on the protective film, wherein the liquid crystal layer 5 is provided in a gap in which the respective alignment films 4A and 4B face each other such that the transparent electrodes of the pair of transparent substrates cross each other. , The thickness of the protective films 3A and 3B is equal to or greater than the thickness of the transparent electrodes 1A and 1B.

In this configuration, similarly to the above-mentioned invention, the thickness of the protective films 3A and 3B is equal to or larger than the thickness of the transparent electrodes 1A and 1B, for example, the thickness of the transparent electrodes 1A and 1B is 0.5 μm. At this time, the thickness of the protective films 3A and 3B is set to 0.5
By setting the thickness to 2.0 μm, the steps existing at the edge portions of the transparent electrodes 1A and 1B are reduced, and the surface smoothness of the alignment film formed to cover the protective films 3A and 3B is improved. Therefore, the thickness of the liquid crystal layer 5 becomes substantially uniform, the difference in the length of the light passing therethrough is eliminated, the contrast and color tone are not uneven, and the pretilt angle does not change, so that a high-quality color display can be obtained.

[0023] Further, the third invention according to claim 3 provides:
According to the first or second aspect of the present invention, the protective film has a relative dielectric constant of 2 to 20 and a specific resistance of 10 ⁷ to 10 ⁸ Ω · cm.

The dielectric constant is 2 to 20, and the specific resistance is 10 ⁷ to 1
By using a protective film having a resistance of 0 ⁸ Ω · cm, the conventional protective film is restricted in its electro-optical characteristics, that is, a voltage is effectively applied to the liquid crystal layer by minimizing a voltage drop in the protective film. As described above, since it is necessary to prevent the contrast ratio from decreasing, it is possible to eliminate the disadvantage that the film thickness cannot be increased.

As a material of the protective film, for example, fine particles of antimony, zinc, tin, or titanium are mixed into an organic polymer resin, and the specific resistance after film formation is 10 ⁷ to 1.
It is possible to use a mixture prepared so as to have a resistivity of 0 ⁸ Ω · cm and a dielectric constant of 2 to 20.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the illustrated embodiments.

FIG. 1 is a schematic sectional view showing the structure of a first embodiment of a liquid crystal display device according to the present invention, wherein 1A is an upper electrode substrate made of a transparent substrate, 1B is a lower electrode substrate,
A is an upper electrode, 2B is a lower electrode, 3A is an upper protective film, 3B is a lower protective film, 4A is an upper alignment film, 4B is a lower alignment film, and 5 is a liquid crystal layer.

The upper electrode substrate 1A and the lower electrode substrate 1B are made of a glass plate, and the upper alignment film 4A and the lower alignment film 4B are made of an organic polymer resin such as a polyimide, and are oriented in a predetermined direction by rubbing. .

The upper electrode 2A and the lower electrode 2B formed on each of the upper electrode substrate 1A and the lower electrode substrate 1B are a plurality of parallel stripes (patterns) formed by patterning ITO.
When the substrate surface is viewed from a vertical direction, the upper alignment film 4A and the lower alignment film 4B are opposed to each other in a state where the upper electrode 2A and the lower electrode 2B are orthogonal to each other, and a liquid crystal phase 5 is sealed in a gap therebetween.

When manufacturing this liquid crystal display element, first,
A so-called photolithography technique is used in which an ITO film having a thickness of 0.1 to 0.5 μm is formed on the upper electrode substrate 1A, a photoresist is applied thereon, and then exposed through a predetermined mask and developed. A stripe-shaped upper electrode 2A is formed.

In this embodiment, a semiconductor material is used as the material of the protective films 3A and 3B which cover the upper and lower electrodes. The protective film 3 </ b> A made of this semiconductor material has a thickness of 0.5 to 2.
A film is formed so as to cover the upper electrode 2A with a thickness of 0 μm, an upper alignment film 4A is formed thereon, and rubbing is performed to perform an alignment process.

Similarly, a stripe-shaped lower electrode 2B orthogonal to the upper electrode 2A is formed on the lower electrode substrate 1B, and a protective film 3B made of a semiconductor is formed thereon with a thickness of 0.5 to 2.0 μm. A film is formed, a lower alignment film 4B is formed, and a rubbing process is performed.

As a semiconductor material constituting the upper protective film 3A and the lower protective film 3B, for example, fine particles of antimony, zinc, tin, or titanium are mixed into an organic polymer resin, and the specific resistance after film formation is 10 ^7. Formulate so as to be 810 ⁸ Ω · cm. The dielectric constant is 2 to 20.

The upper and lower alignment films 4A and 4B formed on the protective films 3A and 3B have a thickness of about 0.5. . 4-0.07 μm
It is.

Next, the upper alignment film 4A of the upper electrode substrate 1A and the lower alignment film 4B of the lower electrode substrate 1B are opposed to each other at a predetermined gap, liquid crystal is sealed in the gap, and the sealing opening is sealed.

In the liquid crystal display device thus constructed, as shown in the figure, a step at the edge portion of the electrode (in the figure, the lower electrode 2B is shown, but the upper electrode 2A is also protected). The above-mentioned gap, that is, the above-mentioned cell gap is substantially equalized in the electrode portion D1 and the non-electrode portion D3 in the non-electrode portion.

It is not possible to increase the thickness of the protective film if the conventional insulating film is formed thick, because the electro-optical characteristics deteriorate as described above. However, as shown in this embodiment, By using a suitable semiconductor material, it is possible to greatly increase the film thickness.

FIG. 2 is a diagram for explaining the change in the residual step on the surface of the protective film due to the step of the transparent electrode with respect to the ratio of the thickness of the protective film to the thickness of the transparent electrode. The horizontal axis represents the thickness t ₂ of the protective film. The ratio of the thickness t ₁ of the transparent electrode (t ₂ / t ₁ ), and the vertical axis indicates the size of the step on the protective film.

As shown, the horizontal axis represents the thickness t _{2 of the} protective film.
Protection If substantially 1.0 or higher ratio of the thickness t ₁ of the transparent electrode film 3A, the optical path length due to the step on 3B D3 is approximately D1
, And variations in contrast and color tone, and changes in pretilt angle are within acceptable ranges. Then, the above (t ₂ /
It is sufficient for t ₁ ) to be at most 2.0.

FIG. 3 is a schematic sectional view of a main part of a liquid crystal display device according to a second embodiment of the present invention, in which the present invention is applied to a color liquid crystal display device.

In this embodiment, a plurality of color filters 11 partitioned by a light-shielding film (black matrix) 10 are formed on the upper electrode substrate 1A side, a smoothing layer 12 is formed thereon, and then the upper transparent electrode 2A is formed. Is formed by patterning. The configuration of the lower electrode substrate 1B is the same as that of FIG.

The upper and lower electrode substrates 1A, 1B are
In FIG. 1, upper and lower retardation plates 13A and 13B, not shown, are shown.
And upper and lower polarizing plates 14A and 14B. Other configurations are the same as those in FIG.

Also in this embodiment, a semiconductor material is used as a material of the protective films 3A and 3B covering the upper and lower electrodes. The protective film 3 </ b> A made of this semiconductor material has a thickness of 0.5 to 2.
The film is formed so as to cover the upper electrode 2A with a thickness of 0 μm.

As a result, steps existing at the edge portions of the transparent electrodes 1A and 1B are reduced, and the surface smoothness of the alignment film formed to cover the protective films 3A and 3B is improved. Therefore, the thickness of the liquid crystal layer 5 becomes substantially uniform, the difference in the length of the light passing therethrough is eliminated, the contrast and color tone are not uneven, and the pretilt angle does not change, so that a high-quality color display can be obtained.

FIG. 4 is a schematic perspective view for explaining the mutual arrangement of the constituent members of the liquid crystal display element according to the present invention. The liquid crystal molecules are twisted between the two upper and lower electrode substrates 1A and 1B sandwiching the liquid crystal layer 5. Orient so as to form a spiral structure. This helical structure contacts the liquid crystal on the upper and lower electrodes 2A and 2B,
For example, it can be obtained by rubbing the surface of the upper and lower alignment films 4A and 4B made of an organic polymer resin made of polyimide in one direction with, for example, a cloth or so-called rubbing.

The rubbing directions of the upper and lower electrode substrates 1A and 1B, which have been subjected to the alignment treatment in this manner, are substantially equal to each other.
Facing each other so that they cross in the range of 80 degrees to 360 degrees,
When a nematic liquid crystal having a positive dielectric anisotropy and having a predetermined amount of an optical rotation substance added thereto is sealed in a gap therebetween by sealing with a frame-shaped sealing material 7 having a cutout portion 7A for injecting the liquid crystal, the liquid crystal molecules become A helical molecular arrangement having a twist angle is formed between the upper and lower electrode substrates 1A and 1B.

The upper electrode substrate 1A thus configured
Retardation plate 13 as a member for providing a birefringence effect above
A, and an upper polarizing plate 14A is further laminated thereon.

Similarly, the lower electrode substrate 1B also has a lower electrode 2
B, a lower alignment film 4B is disposed on the lower retardation plate 13B.
And a lower polarizing plate 14B. It should be noted that a color filter structure for a color liquid crystal display element is not shown in FIG.

FIG. 5 is a partially cutaway perspective view for explaining a configuration example of a lower electrode substrate of a liquid crystal display device according to a second embodiment of the present invention, and the same reference numerals correspond to the same portions.

In the same figure, color filters 11R, 11G, 11B are formed on the inner surface of an upper substrate 1A by being partitioned by a black matrix 10, and the effects of these color filters and the unevenness of the black matrix are reduced thereon. Layer 12 made of an insulating material is applied. The upper electrode 2A and the upper alignment film 4A are formed on the smooth layer 12.

FIG. 6 is an exploded perspective view for explaining a configuration example of a liquid crystal module configured using the liquid crystal display device according to the present invention.

This liquid crystal module comprises a frame 20 having a display window 21, an insulating sheet 22, a printed circuit board 23,
Spacer 24, liquid crystal display element 25, cushion material 26,
The backlight 27, the light guide 28, and the mold frame 29 are laminated in this order, and are fixed by scissors between the frame 20 and the mold frame 29. Reference numeral 30 denotes a power socket for supplying power to the backlight 27.

In this form, the liquid crystal display element 25 and the printed circuit board 23 are connected by a tape carrier package. Instead, a peripheral circuit including a driving IC or the like is directly provided on the periphery of the transparent substrate constituting the liquid crystal display element. May be implemented.

FIG. 7 is a perspective view of a laptop personal computer as an example of an electronic apparatus using a liquid crystal module incorporating a liquid crystal display element according to the present invention.

This laptop personal computer comprises a main body 36 and a monitor 32, and the monitor is equipped with a liquid crystal module 31 incorporating a liquid crystal display device according to the present invention. 33 is a brightness volume, 34 is a contrast volume, and 35 is a switch for inverting the display background and the image.

FIG. 8 is a schematic block diagram of a control circuit of the liquid crystal display device in the laptop personal computer shown in FIG.
The liquid crystal display module is driven by C39. Note that RO
A memory 38 such as an M or a RAM stores display procedures and display data.

According to the above-described embodiment, a laptop personal computer having a large contrast ratio and excellent halftone display can be provided.

[0058]

As described above, according to the present invention,
By making the protective film made of a semiconductor material equal to or larger than the thickness of the transparent electrode, the level difference of the alignment film caused by the edge of the transparent electrode can be reduced and flattened, and the cost can be reduced without changing the conventional manufacturing process. In addition, a liquid crystal display device having good optical characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an essential part for explaining the structure of a first embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is an explanatory diagram of a change in a residual step on the surface of a protective film due to a step of a transparent electrode with respect to a ratio of a thickness of a protective film to a thickness of a transparent electrode.

FIG. 3 is a schematic cross-sectional view of a principal part explaining the structure of a second embodiment of the liquid crystal display device according to the present invention.

FIG. 4 is a schematic perspective view illustrating the mutual arrangement of components of the liquid crystal display element according to the present invention.

FIG. 5 is a partially broken perspective view illustrating a configuration example of a lower electrode substrate of a liquid crystal display element according to a second embodiment of the present invention.

FIG. 6 is an exploded perspective view illustrating a configuration example of a liquid crystal module configured using the liquid crystal display element according to the present invention.

FIG. 7 is a perspective view of a laptop personal computer as an example of an electronic apparatus using a liquid crystal module incorporating a liquid crystal display element according to the present invention.

8 is a schematic block diagram of a control circuit of the liquid crystal display device in the laptop personal computer shown in FIG.

FIG. 9 is a schematic cross-sectional view of a main part illustrating a configuration example of a conventional liquid crystal display element.

[Explanation of symbols]

 Reference Signs List 1A Upper electrode substrate 1B Lower electrode substrate 2A Upper electrode 2B Lower electrode 3A Upper protective film 3B Lower protective film 4A Upper alignment film 4B Lower alignment film 5 Liquid crystal layer, 7 Sealing material 10 Light shielding film (black matrix) 11 Color filter 12 Smooth layer 13A Upper retardation plate 13B Lower retardation plate 14A Upper polarizing plate 14B Lower polarizing plate. Reference Signs List 20 frame 21 display window 22 insulating sheet 23 printed board 24 spacer 25 liquid crystal display element 26 cushion material 27 backlight 28 light guide 29 mold frame 30 power socket.

Claims (3)

[Claims] A plurality of transparent electrodes formed in parallel with each of the pair of transparent substrates; a protective film covering the transparent electrodes; and an alignment film formed on the protective film. In a liquid crystal display element in which a liquid crystal layer is sandwiched between gaps in which the respective alignment films face each other so that transparent electrodes intersect, the thickness of the protective film is set to be equal to or greater than the thickness of the transparent electrode. Liquid crystal display element. 2. A color filter of a plurality of colors partitioned by a light-shielding film on one of a pair of transparent substrates, a smooth layer formed to cover the color filter, a transparent electrode formed on the smooth layer, and a cover of the transparent electrode. A transparent electrode, a protective film formed on the transparent electrode and an alignment film formed on the protective film, and the pair of transparent substrates. In a color-compatible liquid crystal display device in which a liquid crystal layer is sandwiched in a gap in which respective alignment films are opposed to each other such that the transparent electrodes cross each other, the thickness of the protective film is set to be equal to or greater than the thickness of the transparent electrode. A liquid crystal display device characterized by the above-mentioned. 3. The protective film according to claim 1, wherein the protective film has a relative dielectric constant of 2 to 20 and a specific resistance of 10 ⁷ to 10 ⁸ Ω · cm.
A liquid crystal display device, characterized in that: