JPH06194656A - Tn liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the TN liquid crystal display element of higher display quality which obtains nearly uniform visual angle characteristics in all directions by improving the visual angle characteristics. CONSTITUTION:This TN liquid crystal display element has a couple of substrates 1 and 2 which are arranged across from each other, a couple of transparent electrodes 3 and 4 which are provided on the couple of substrates 1 and 2 and put one over each other by holding a liquid crystal layer 5 between to form display areas, and slits 7 and 8 formed by removing parts of the transparent electrodes 3 and 4 in the respective display areas on the couple of display electrodes 3 and 4; and the slit of one of the couple of transparent electrodes 3 and 4 and the slit of the other transparent electrode are arranged alternately in the display areas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twisted nematic (abbreviated as TN) liquid crystal display device, and more particularly to a TN liquid crystal display device having improved viewing angle characteristics and improved display quality.

[0002]

2. Description of the Related Art A liquid crystal display element used in a liquid crystal display or the like, a so-called liquid crystal cell, changes a specific molecular arrangement of liquid crystal into another different molecular arrangement by an action from the outside such as an electric field, and transmits an optical signal between them. The change in the physical characteristics is used as a visual change for display. In order to bring the liquid crystal molecules into a specific alignment state, it is usual to perform an alignment treatment on the surface of a glass substrate provided with electrodes sandwiching the liquid crystal.

In the alignment treatment of a TN liquid crystal cell, a glass substrate on which a transparent electrode sandwiching a liquid crystal is formed is rubbed, and at that time, rubbing directions are perpendicular to each other so that the liquid crystal cell displays a negative image. In the case of, the polarizing plates of parallel polarizers that sandwich the cell are arranged so that their polarization axes are parallel to one of the rubbing directions, and in the case of positive display, the polarization axes of the polarizing plates of orthogonal polarizers. Are arranged so as to be parallel to the rubbing direction of the substrate.

[0004]

When the alignment treatment is carried out by such rubbing, the orientation of the liquid crystal molecules is uniform, so that the angle at which the image is easily seen by the observer is within a specific angle range. It has limited viewing angle characteristics.

For example, FIG. 5A is an example of an equal contrast curve representing the viewing angle characteristics of a TN liquid crystal cell. Figure 5
In (A), the center of the circle is the display point of the liquid crystal cell,
An angle from the perpendicular to the liquid crystal cell is taken concentrically around that point, and the observation position in the horizontal plane is indicated by the angle φ in a radial pattern.

The thick solid curve in FIG. 5A is an equal contrast line, and the contrast value is shown on each curve. As shown in FIG. 5A, it can be seen that the viewing angle region with high contrast is biased to a specific angle region. Therefore, such a liquid crystal cell has a viewing angle dependency that it is easy to see from one direction and hard to see from another direction.

When such a liquid crystal cell having a viewing angle dependency is used as a display device, the contrast becomes extremely sharp at a certain angle (around φ = 45 ° in the example of FIG. 5A) with respect to the display screen. When it is extremely low, the brightness of the display is reversed.

The view angle characteristic as shown in FIG.
This is because the pretilt as shown in FIG. 5B occurs during rubbing. The direction in which the liquid crystal has a pretilt is as shown in FIG.
The direction of the vector to be rubbed is indicated by the arrow in (B).

When a voltage is applied to the liquid crystal cell, the liquid crystal molecules rise in the pretilt direction.
When observed from that direction, the optical activity tends to be eliminated. Therefore, the direction in which the vector ends, that is, the direction in which the liquid crystal molecules rise (the direction in which the liquid crystal molecules are tilted up) is the easiest to see, and the opposite direction is the most difficult to see.

[0010]

According to the conventional technique described above, the TN liquid crystal display element has a viewing angle characteristic in which display quality deteriorates in a specific direction.

It is an object of the present invention to provide a TN liquid crystal display device having a higher display quality, in which the viewing angle characteristic is improved and a substantially uniform viewing angle characteristic is obtained in all directions. The TN liquid crystal in the present invention includes STN (super twist nematic) liquid crystal in a broad sense.

[0012]

A TN liquid crystal display device of the present invention comprises a pair of substrates which are arranged to face each other, and a pair of substrates which are provided on the pair of substrates and overlap each other with a liquid crystal layer interposed therebetween to form a display region. Transparent electrode and a slit in which a part of the transparent electrode in the display area of each of the pair of transparent electrodes is removed, the slit of one transparent electrode of the pair of transparent electrodes and the other transparent electrode And the slits are alternately arranged in the display area.

[0013]

By providing slits alternately arranged between a pair of transparent electrodes in the display area, small areas in which the rising directions of liquid crystal molecules are opposite to each other are simultaneously formed in the display area of the pair of electrodes when a voltage is applied. Therefore, the viewing angle dependence of the small areas of each other is complemented, and the viewing angle dependence of the entire display area is reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of a TN liquid crystal display device according to an embodiment of the present invention will be described below with reference to FIGS. First, FIG. 1 shows the basic concept of the present invention. FIG. 1A shows the liquid crystal molecule alignment in the state where no voltage is applied to the TN liquid crystal cell, and FIG. 1B shows the liquid crystal molecule alignment in the state where the voltage is applied. With reference to FIG. 1, the principle of reducing the viewing angle dependency in the present invention will be described.

The upper and lower transparent glass substrates 1 and 2 are opposed to each other, and transparent electrodes 3 and 4 are formed on the inner surfaces of the substrates. A display region is formed by sandwiching the TN liquid crystal layer 5 between the upper and lower transparent electrodes 3 and 4.

The liquid crystal molecules 6 in the liquid crystal layer 5 gradually rotate in the direction of the major axis of the molecule from one transparent electrode to the other transparent electrode due to the alignment treatment of the upper and lower substrates when there is no electric field in FIG. 1 (A). Thus, at the upper end and the lower end, the alignment directions of the liquid crystal molecules 6 are orthogonal to each other in the horizontal plane.

A characteristic structure of the present invention is that upper and lower transparent electrodes 3 and 4 are provided with slits 7 and 8 from which a part of the electrodes is removed. Moreover, the slits 7 of the upper transparent electrode 3 do not overlap the slits 8 of the lower transparent electrode 4 and are displaced from each other.

If a predetermined voltage is applied between the transparent electrodes 3 and 4 in the state shown in FIG. 1A, the edge portion of the slit is indicated by the broken arrow in FIG. Such lines of electric force 9 (so-called fringe electric field) are generated. That is, the lines of electric force in the slits 7 and 8 are not perpendicular to the electrode surface (substrate surface), and become an oblique electric field.

With respect to the oblique electric field 9, the liquid crystal molecules 6 rise in the direction of the solid arrow. This is the same as the rising direction of liquid crystal molecules when there is a pretilt angle. The alignment state of the liquid crystal molecules 6 in response to the electric field is shown in FIG. From FIG. 1B, it can be seen that the rising directions of the liquid crystal molecules 6 are different between the left and right with the vicinity of the central portions of the slits 7 and 8 as boundaries. Moreover, due to the arrangement in which the upper and lower slits 7 and 8 are provided alternately without overlapping, the rising directions of the liquid crystal molecules 6 are alternately reversed in the small regions partitioned by the slits 7 and 8.

That is, the liquid crystal molecules 6 in the central portion are tilted to the left (downward to the right) in the drawing in the small area a, conversely to the right (downward left) in the small area b, and again in the small area c. Lean to the left (downward to the right). Even if the slits are further increased alternately by the upper and lower electrodes, the reversal of the inclination appears alternately.

The best viewing direction is from the left side of the figure in the small areas a and c, and from the upper right side in the small area b. In addition, the worst state of visual recognition is in the opposite direction.

Therefore, in any viewing angle direction, the small area with the best visible state compensates for the small area with the worst visible state, so that the viewing angle dependence of the entire display area is reduced and the TN liquid crystal display element The display quality is improved. As for the visibility in other directions, as shown by the characteristics in FIG.
No problem.

Further, it is generally known that the threshold value for an oblique electric field is lower than that for an electric field in a direction perpendicular to liquid crystal molecules. This indicates that, in the present invention, the liquid crystal molecules near the slit respond to the electric field earlier than the other liquid crystal molecules, and it is guaranteed that the small regions of different arrangement are stably formed. is doing.

Next, the structure of the embodiment of the present invention using the basic structure shown in FIG. 1 is shown in FIGS. FIG. 2 is a plan view of an example of a simple segment type TN liquid crystal display element.
FIG. 3 is a perspective view of FIG. 2 and more clearly shows the relationship between the upper and lower electrodes and the slit.

The TN liquid crystal display element shown in FIG. 2 displays the numeral "1". As shown in FIG. 3, the inner region surrounded by the contour line of the character “1” has upper and lower transparent electrodes 10 and 20.
It is a display area sandwiched between and. The transparent electrode 10,
The glass substrate on which 20 is formed is similar to that of FIG.

The upper transparent electrode 10 has slits 11, 1
2, 13 are formed. In the lower transparent electrode 20, the slit 2 is provided at a position not overlapping the slits 11, 12, and 13.
1, 22, 23 are formed. When the upper and lower transparent electrodes 10 and 20 in which the slits are formed are stacked and viewed from above, a display region that looks like FIG. 2 is formed. In order to make the display characteristics as uniform as possible, it is preferable that the intervals between the slits be substantially constant.

In FIG. 2, arrows 30 and 40 respectively indicate the orientation directions of the upper and lower substrates (not shown) by rubbing. In this example, when a liquid crystal having a left-handed chiral property is used, the alignment direction of the liquid crystal molecules in the central portion of the liquid crystal layer when there is no electric field is the direction of arrow 50 in FIG.

Therefore, as described above in the basic principle, the longitudinal direction of the slits 11, 12, 13, 21, 22, 23 is the same as the alignment direction 5 of the liquid crystal molecules in the central part of the liquid crystal layer.
It is orthogonal to 0. Slits are 11 and 2 in the display area
1, 12, 22, 13, and 23 are alternately arranged between the upper and lower electrodes. Therefore, the rising directions of the liquid crystal molecules are alternately inverted. The cross section at II ′ of FIG. 2 corresponds to the cross sectional view of FIG.

With the configuration shown in FIGS. 2 and 3, the inclination of the liquid crystal molecules in the small area sandwiched by the slits in the display area of the character "1" when the electric field is applied is alternately reversed, so that the viewing angle characteristic as a whole is improved. Since it is complemented and the viewing angle dependence is reduced,
The visibility is improved from any direction.

Here, the effectiveness of making the longitudinal direction of the slit perpendicular to the alignment direction of the liquid crystal molecules in the central portion of the liquid crystal layer will be described. As described above, it is effective that the oblique electric field required in the present invention has an oblique component parallel to the alignment direction of the liquid crystal molecules in the central portion of the liquid crystal layer. For this reason, it is desirable that the longitudinal direction of the slit be orthogonal to the liquid crystal molecule alignment direction.

Further, when the width of the slit (the length in the direction orthogonal to the longitudinal direction) is wider than a certain amount, the electric field in the central portion of the slit becomes extremely weak, and the liquid crystal molecules do not react to the applied voltage. Occurs, and a display defect occurs in that area. The width of the slit is 2mm, depending on the applied voltage
The following are preferred.

On the contrary, if the width of the slit is too narrow, a sufficient oblique electric field will not be generated and the effect of the present invention will not be sufficiently exhibited. At least the width of the slit is preferably equal to or larger than the thickness of the liquid crystal layer 5, that is, the so-called cell gap.

Further, the gap between the adjacent slits between the upper and lower electrodes (in the example of FIG. 2, for example, slits 21 and 1)
The distance between the small areas sandwiched between 1 and 1 is preferably large in order to secure a sufficient display area, but it is not preferable in terms of display quality if the presence of slits is visually identified, so that is prevented. It is better to be as narrow as possible. Empirically,
It may be desirable for the spacing between the slits to be larger than the cell gap of the liquid crystal layer 5 and substantially smaller than 2 mm.

Next, the pretilt angle of the liquid crystal layer 5 will be described. In order to ensure the symmetry of the response of the liquid crystal molecules 6 to the oblique electric field 9, it is desirable that the pretilt angle, which is the angle formed by the substrate surface and the director direction of the liquid crystal molecules, is small. It is desirable that it is at least smaller than the inclination angle of the oblique electric field. For example, the pretilt angle is substantially 10
The angle is preferably less than 0 °, and ideally 0 °.
In order to realize this, the following method can be considered.

Usually, in order to give a certain tilt angle to the liquid crystal molecules 6 at the center of the liquid crystal layer 5, the arrow 30 in FIG.
And the rubbing direction as shown by the arrow 40 is selected. That is, the head of the liquid crystal molecule 6 is twisted by 90 ° while keeping the head slightly lifted, but if one of the rubbing directions is reversed (the opposite direction of 40), the liquid crystal layer 6 is tilted together with the thickness. It can be seen that the angle also has to be changed, and the tilt angle of the liquid crystal molecules in the central portion of the liquid crystal layer is 0 ° due to the symmetry of the liquid crystal molecule alignment in the liquid crystal.

Although the embodiments described with reference to FIGS. 2 and 3 have been described by taking the simple segment type liquid crystal display device as an example, the present invention is such that upper and lower electrodes alternately have slits as shown in the sectional structure of FIG. As long as it is arranged, it can be applied to an active matrix type liquid crystal display device using a TFT or the like and a dot matrix type liquid crystal display device.

FIG. 4 shows an embodiment in which the present invention is applied to a TFT active matrix liquid crystal display device. Figure 4 is T
FIG. 3 is a plan view of an area of several pixels of an FT active matrix liquid crystal display device. Since the active matrix type liquid crystal device is common nowadays, its structure will be briefly mentioned.

In FIG. 4, a plurality of TFT elements 60 made of amorphous silicon or the like, a transparent pixel electrode 61 made of ITO or the like, a source electrode S and a gate electrode G of the TFT element 60 are formed on a transparent glass substrate (not shown). A source line (signal line) 62 and a gate line (scanning line) 63 which are respectively connected to and are formed, and the TFT element 60 drives the pixel electrode 61 via the drain electrode D.
An alignment film (not shown) is formed on the pixel electrode 61.

Although it is difficult to illustrate in a plan view, it is omitted,
Another glass substrate is arranged on the glass substrate on which the pixel electrode is formed so as to face the substrate, with a TN liquid crystal layer interposed therebetween, and a common electrode is formed on the substrate. An alignment film that has been subjected to an alignment treatment is formed on the surface of the common electrode that is in contact with the liquid crystal layer.

The orientation of both substrates is shown on the left side of FIG. The orientation direction of the lower substrate is shown by the dotted line 70, and the orientation direction of the upper substrate orthogonal to it is shown by the solid arrow 80. The arrow 90 indicates the alignment direction of the liquid crystal molecules in the central part of the liquid crystal layer.

The pixel electrode 61 has a plurality of slits 64 formed by removing a part of the electrode and shown by solid lines. Further, the common electrode facing the pixel electrode 61 is also provided with a slit 65 in which a part of the electrode is removed as shown by a broken line. The slits 64 and 65 of the upper and lower substrates are arranged alternately.

The cross section taken along the line II-II 'of FIG. 4 is shown in FIG.
It basically corresponds to the sectional structure shown in. Due to the slits 64 and 65 alternately arranged between the upper and lower electrodes, the same operational effect as described with reference to FIG. 1 is produced.

Although the active matrix structure has another structure other than the above, the present invention can be applied to such another active matrix structure. The present invention is
It is needless to say that the person skilled in the art can make various modifications and improvements based on the above disclosure without being limited to the embodiments described with reference to the drawings.

[0044]

By providing slits alternately arranged between a pair of transparent electrodes in the display area, a small area in which the rising directions of the liquid crystal molecules are opposite to each other in the display area of the pair of electrodes when voltage is applied. Since they are formed at the same time, the viewing angle dependence of each small area is complemented, the viewing angle dependence of the entire display area is reduced, and the visibility is good when viewed from any direction, and the display quality is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a TN liquid crystal display device of the present invention.

FIG. 2 is a plan view of a simple segment type TN liquid crystal display device according to an embodiment of the present invention.

FIG. 3 is a perspective view of a simple segment type TN liquid crystal display device according to an embodiment of the present invention.

FIG. 4 is a plan view of an active matrix type liquid crystal display device according to an exemplary embodiment of the present invention.

FIG. 5 is a diagram for explaining viewing angle characteristics and pretilt of a TN liquid crystal display device according to a conventional technique.

[Simple explanation of symbols]

 1, 2 ... glass substrate 3, 4 ... transparent electrode 5 ... liquid crystal layer 6 ... liquid crystal molecule 7, 8 ... slit 9 ··· Electric force lines 10, 20 ··· Transparent electrodes 11, 12, 13, 21, 22, 23 ··· Slits 30, 40 · · Alignment direction 50 ··· Liquid crystal layer Alignment direction of liquid crystal molecules in the central portion 60 ... TFT element 61 ... Pixel electrode 62 ... Source line 63 ... Gate line 64, 65 ... Slits 70, 80 ... Alignment method 90 ... Alignment method of liquid crystal molecules in central part of liquid crystal layer

Claims (5)

[Claims] 1. A pair of substrates arranged to face each other, a pair of transparent electrodes provided on the pair of substrates and overlapping each other with a liquid crystal layer interposed therebetween to form a display region, and each of the pair of transparent electrodes. And a slit from which a part of the transparent electrode in the display area is removed, and the slit of one transparent electrode of the pair of transparent electrodes and the slit of the other transparent electrode are alternately arranged in the display area. A TN liquid crystal display device characterized in that 2. The slit has a shape whose longitudinal direction extends in a direction orthogonal to an alignment direction of liquid crystal molecules in a central portion of the liquid crystal layer when no electric field is applied.
The TN liquid crystal display element described. 3. The liquid crystal molecules of the liquid crystal layer are substantially 10 °.
The TN liquid crystal display device according to claim 1, which is provided with the following pretilt angles. 4. The TN liquid crystal display device according to claim 1, wherein the width of the slit in the direction orthogonal to the longitudinal direction is larger than the thickness between the electrodes of the liquid crystal layer. 5. In the alternately arranged slits, a distance between the adjacent slits is larger than a thickness between the electrodes of the liquid crystal layer and is substantially smaller than 2 mm. Item 10. A TN liquid crystal display device according to item 1.