JPH1096926A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a reflection type liquid crystal display device to reduce visual angle dependency maintaining a high numerical aperture and increase in an angle of visibility. SOLUTION: An orientation control electrode 13 is distributed between every two columns of display electrodes, and also an orientation control window 22 is distributed between every two columns and every line. In a side which the orientation control electrode 13 and an orientation control window 22 are lining, a diagonal electric field is formed inclining in the same direction of the opposing side, and an orientation of a liquid crystal is controlled with respect to its picture elements in a same direction. Since each picture element is different in preferred visual angle direction, macroscopic visual recognition of them averages luminous intensities and contrast ratios, reducing a visual angle dependency, and increasing an angle of visibility.

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 (LCD) for performing display utilizing the electro-optical anisotropy of liquid crystal.
In particular, the present invention relates to a liquid crystal display device having a high aperture ratio and a wide viewing angle.

[0002]

2. Description of the Related Art LCDs have advantages such as small size, thin shape, and low power consumption, and are being put to practical use in fields such as OA equipment and AV equipment. In particular, an active matrix type using a thin film transistor (hereinafter abbreviated as TFT) as a switching element can perform static driving with a duty ratio of 100% in principle in a multiplex manner, and has a large screen and a high-definition moving image display. Used in

The TFT is a field-effect transistor, is arranged in a matrix on a substrate, and is connected to a display electrode forming one of pixel capacitances using a liquid crystal as a dielectric layer. The TFTs are simultaneously turned on / off for the same row by a gate line, and a pixel signal voltage is supplied from a drain line, and a display voltage specified in a matrix is charged to a pixel capacitance with the TFT turned off. Is done. Display electrode and TFT
Are formed on the same substrate, and the common electrode that constitutes the other of the pixel capacitors is formed entirely on another substrate that is opposed to the liquid crystal layer. That is, the liquid crystal and the common electrode are partitioned by the display electrode to form a display pixel. The voltage charged in the pixel capacitance is insulated by the off resistance of the TFT for one field period until the next turn on of the TFT. The liquid crystal has electro-optical anisotropy, and the optical characteristics are controlled according to the voltage applied to the pixel capacitance. By controlling the transmitted light intensity for each display pixel, these light and dark areas are visually recognized as a display image.

[0004] The initial alignment state of the liquid crystal is elastically fixed by an alignment film provided at the interface between the two substrates. For example, there is a twisted nematic (TN) system in which a nematic phase having a positive dielectric anisotropy is used as a liquid crystal and an orientation vector is twisted at 90 ° between both substrates. Normal,
Polarizing plates are provided outside the two substrates, and in the TN method, the polarization axes of the respective polarizing plates coincide with the orientation directions of the respective substrates. Therefore, when no voltage is applied, the linearly polarized light that has passed through one of the polarizing plates rotates in the liquid crystal layer along the twisted orientation of the liquid crystal, and is emitted from the other polarizing plate.
The display is recognized as white. Then, by applying a voltage to the pixel capacitor to form an electric field in the liquid crystal layer, the liquid crystal changes its orientation so as to be parallel to the electric field due to its dielectric anisotropy, and the twist arrangement is broken. As a result, the incident linearly polarized light is no longer rotated in the liquid crystal layer, the amount of light emitted from the other polarizing plate is narrowed down, and the display gradually becomes black. As described above, a system in which white is displayed when no voltage is applied and becomes black in response to voltage application is called a normally white mode, and is a mainstream of TN cells.

A type using a nematic phase having a negative dielectric anisotropy as a liquid crystal is a VAN (vertic).
There is a type that uses a vertical alignment film as an alignment film called “ally-aligned nematic”. The VAN type is one of voltage controlled birefringence (ECB) systems, and controls transmittance by utilizing a difference in refractive index between a long axis and a short axis of liquid crystal molecules, that is, birefringence. . V
In the AN type, when a voltage is applied, incident linearly polarized light transmitted through one of the orthogonally arranged polarizing plates is converted into elliptically polarized light by birefringence in the liquid crystal layer. By controlling the difference between the phase velocities of the light components, a desired transmittance can be emitted from the other polarizing plate. In this case, the display changes from black to white by increasing the applied voltage from the voltage non-applied state, and the normally black mode is set.

[0006]

As described above, in a liquid crystal display device, by applying a desired voltage to a liquid crystal loaded between a pair of substrates on which predetermined electrodes are formed, the light in the liquid crystal layer is reduced. The desired transmittance or hue is obtained by controlling the rotation or birefringence of the image, and a display image is created. That is,
By controlling the amount of retardation by changing the orientation of the liquid crystal, the intensity of transmitted light can be adjusted in the TN method, and the hue can be separated by controlling the wavelength-dependent spectral intensity in the ECB method. The amount of retardation is
It depends on the angle between the long axis of the liquid crystal molecules and the direction of the electric field. Therefore, even if the angle between the electric field and the long axis of the liquid crystal molecules is primarily controlled by adjusting the electric field strength, the retardation is relatively dependent on the angle that the observer visually recognizes, that is, depending on the viewing angle. When the amount changes and the viewing angle changes, the transmitted light intensity or the hue also changes, which has been a problem of so-called viewing angle dependency.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problem, and has a plurality of gate lines and drain lines arranged on a substrate so as to intersect each other, and an intersection of the plurality of gate lines and drain lines. A liquid crystal display comprising a thin film transistor formed in a portion, a liquid crystal driving display electrode connected to these thin film transistors, and a liquid crystal driving common electrode provided on another substrate opposed to and sandwiching the liquid crystal. In the device, the display electrode is formed on an interlayer insulating film that covers the thin film transistor, and an alignment control electrode that is electrically insulated from the display electrode is disposed in a partial region between the display electrodes. In the common electrode corresponding to a part of the region between the display electrodes, an alignment control window formed by the absence of the electrode is provided, and the alignment of the liquid crystal is controlled by a predetermined direction. Is a control and configuration to.

Thus, the oblique electric field is prevented from being generated at the display electrode edge by the alignment control electrode, and the oblique electric field is formed by the alignment control window provided correspondingly. The orientation of the liquid crystal is specified by the joint action with the oblique electric field generated along the side where neither the alignment control electrode nor the alignment control window is provided. Also, for the side provided with only the orientation control window,
The oblique electric field does not occur and does not affect the orientation of the liquid crystal whose direction is controlled.

In particular, the orientation control electrode is arranged below the interlayer insulating film. As a result, the display electrode is enlarged to a region on the thin film transistor, and the aperture ratio is increased. In particular, the display electrode is a reflective electrode.
Thereby, the liquid crystal display device can obtain an extremely high aperture ratio as a reflection type.

[0010] In particular, the alignment control electrode is provided along one side of the display electrode, and the alignment control window is provided along a side of the display electrode where the alignment control electrode is provided and a side adjacent thereto. This is the configuration provided. This prevents the generation of an oblique electric field along the edge of the display electrode in order to give the liquid crystal the same effect as the display electrode on the side where the alignment control electrode is provided. An oblique electric field is generated along the edge of the alignment control window, and is in the same direction as the oblique electric field along the side where neither the alignment control electrode nor the alignment control window is provided. Also,
With respect to the two sides provided with only the alignment control window, the edge of the display electrode and the edge of the alignment control window are aligned, so that an oblique electric field does not occur along the edge of the display electrode. Therefore, the same oblique electric field is generated only on the two opposite sides of the display electrode, so that the orientation of the liquid crystal is controlled in a uniform direction in the pixel.

In particular, one alignment control electrode is provided in common with respect to two adjacent rows of the display electrodes, and is arranged along alternately left and right sides of the display electrode every other row. This is a configuration commonly provided for two adjacent rows of display electrodes. As a result, the orientation of the liquid crystal is controlled in a bilaterally symmetrical direction every two columns, so that the preferred viewing angle direction changes left and right for each column, and a liquid crystal display device having a wide viewing angle can be formed by the combined light. can get.

In particular, the effective potential difference between the alignment control electrode and the display electrode is smaller than the effective potential difference between the display electrode and the common electrode. Accordingly, the orientation control electrode exerts an effect similar to that of the display electrode on the liquid crystal between the display electrodes, thereby preventing an oblique electric field from being generated along the edge of the display electrode. In particular, the display electrodes in the end row are:
One side is provided in a triangular shape that shares the display electrode in the next column with the alignment control electrode and the alignment control window, and the other side shares the display electrode in the next row with the alignment control window. Configuration.

As a result, sufficient orientation control of the alignment direction by the oblique electric field is performed on the long oblique side of the display electrode, so that the alignment control is satisfactorily performed continuously in the center of the display pixel group.

[0014]

FIG. 1 is a partial plan view of a liquid crystal display according to an embodiment of the present invention. FIG. 2 shows the A-
FIG. 3 is a cross-sectional view taken along line A-B of FIG. Here, the VAN type is shown. Substrate (1
0), Al, Ta, Mo, Cr, ITO (indium
A drain line (11) and a source electrode (12) formed of a low-resistance metal such as tin oxide) are provided. An orientation control electrode (13) is also formed of a low-resistance metal in parallel with the drain line (11). The alignment control electrode (13), the drain line (11) and the source electrode (12) may be formed of the same material and in the same process. In a direction intersecting the drain line (11) and the orientation control electrode (13), a semiconductor layer (14), an insulating layer (15), and a gate line (1) made of a low-resistance metal are provided.
6) are formed in the same shape, and a part of the drain line (1) is formed.
1) and TF disposed in a region extending from the source electrode (12).
T. SOG (spin on glass) and BPSG (boro-phospho
o A flattening insulating film (17) such as silicate glass is entirely formed. On this planarizing insulating film (17),
A display electrode (18) made of a low-resistance light reflecting material such as Al is formed, and is connected to the source electrode (12) through a contact hole opened in the planarizing insulating film (17). Further, on the display electrode (18), an alignment film (19) made of polyimide or the like for controlling the initial alignment of the liquid crystal is formed.

At a position facing the substrate (10), another substrate (20) is fixed with a liquid crystal (30) interposed therebetween.
On the opposing surface, a transparent conductive ITO is formed over the entire surface to form a common electrode (21). Common electrode (21)
Inside, an electrode absent portion is formed corresponding to the gap between the display electrodes (18), and serves as an alignment control window (22). An alignment film (23) is also provided on the common electrode (21).

The liquid crystal (30) is a nematic phase having negative dielectric anisotropy, and its initial orientation is perpendicular to the substrate (10, 22) due to the interaction with the orientation films (19, 23). It is fixed elastically to be. Although not shown, two polarizing plates are arranged outside the substrates (10, 20) so that the polarization axes are orthogonal to each other. The liquid crystal (30) has a display electrode (18) and a common electrode (2).
The orientation of the liquid crystal molecules (31) is oriented in a direction perpendicular to the electric field as the orientation is changed by the electric field formed by the voltage applied in 1) and the electric field intensity is increased.

The orientation control electrode (13) is in parallel with the drain line (11) and is connected to the drain line (11).
One line is provided for each line, and extends along those sides in common with the two rows of the display electrodes (18). The alignment control window (22) extends in common with the two columns of the display electrodes (18) as well as the alignment control electrode (13), and is also provided between all rows. That is, the display electrode (18)
With respect to the one side, the alignment control electrode (18) and the alignment control window (22) are in planar contact with each other, and only the alignment control window (22) is in planar contact with this side and two sides sandwiching this side. ing. The side where the alignment control electrode (13) and the alignment control window (22) are in contact is alternately left and right every other row of the display electrodes (18).

A voltage having the same polarity as the voltage applied to the display electrode (18) is applied to the alignment control electrode (13). For example, in line inversion driving in which the polarity of an applied voltage is inverted for each line, the output of each stage of a shift register for controlling on / off of an analog switch for sampling an original image signal of a driver on the drain side and the inverted output thereof are set to one. Switching is performed for each line, and a voltage having the same polarity as the voltage applied to the display electrode (18) with respect to the line is applied to each alignment control electrode (13). At this time, it is desirable that the output voltage of each stage taken out of the shift register be an optimal voltage value via a level shifter or the like. Further, since the number of output stages of the shift register and the number of the orientation control electrodes (13) are different, it is necessary to connect to the orientation control electrode (13) every several stages appropriately. Thereby, the orientation control electrode (1)
To 3), a voltage having the same polarity as that of the display electrode (18) and having a potential difference between the display electrode (18) smaller than the potential difference between the display electrode (18) and the common electrode (21) is applied. Is done.

When the present liquid crystal display device having the above configuration is driven and a voltage is applied, as shown in FIG.
On the side of the side corresponding to the alignment control electrode (13) and the alignment control window (22), from the outside to the inside of the display electrode (18),
The electric field (3) inclined obliquely toward the common electrode (21)
2) is formed. This is because the voltage applied to the display electrode (18) and the voltage applied to the alignment control voltage (13) are close to each other, and the alignment control electrode (13) exerts an effect similar to that of the display electrode (18) on the liquid crystal layer (30). In the vicinity of the surface of the substrate (10), the shape of equipotential lines becomes relatively flat, and on the corresponding substrate (20) side, an orientation control window (22) is formed. It is because. Therefore, the electric field (32) is applied to the orientation control electrode (1).
From 3), the common electrodes (2) on both sides of the orientation control window (22)
It is formed diagonally toward 1).

On the other hand, on the side of the display electrode (18) opposed to the display electrode (18), at the display electrode (18) edge, from the inside to the outside of the display electrode (18), diagonally toward the common electrode (21). An inclined electric field (32) is created. The oblique electric fields (32) generated on the opposite sides of the display electrodes (18) are inclined in the same direction as shown in FIG. Therefore, the liquid crystal molecules (31) are inclined from left to right in the figure with respect to the oblique electric field (32) on both sides of the display electrode (18) so as to minimize the angle formed by the major axis. ,
Due to the continuity of the liquid crystal, it becomes uniform over the entire area of the pixel.

Since the polarity of the voltage applied to the display electrode (18) is inverted for each line, the polarity of the voltage applied to the alignment control electrode (13) is also inverted. The polarity of the voltage held by the display electrode (18) and the polarity of the voltage of the orientation control electrode (13) are reversed in the line, so that the potential difference between the display electrode (18) and the orientation control electrode (13) increases, and the substrate (10) The equipotential lines on the side of ()) are greatly deformed from flat. However, the orientation control of the orientation control electrode (13) acts when the TFT is turned on, that is, when the voltage of the display electrode (18) is applied. Therefore, even if the polarity of the alignment control electrode (13) changes during the voltage holding period when the TFT is off, the tilt direction of the liquid crystal molecules (31) does not change.

As shown in FIG. 3, the display electrode (18)
Are provided only with the alignment control window (22). Therefore, an electric field does not occur in the oblique direction toward the common electrode (21) at the edge of the display electrode (18), and the liquid crystal molecules (31) are controlled in the oblique direction on these sides. Absent. Therefore, as shown by the arrow in FIG. 1, the alignment of the liquid crystal molecules (31) is inclined only in the left-right direction, and the left direction and the right direction are alternately arranged for each column. That is, in one set of two rows, the left inclination and the right inclination are bilaterally symmetric. For this reason, by combining the priority viewing angle direction of the left tilt pixel and the priority viewing angle direction of the right tilt pixel, the priority viewing angle direction is macroscopically widened, and a liquid crystal display device with a wide viewing angle is obtained.

In particular, in the present embodiment, as shown in FIG. 1, the shape of the display electrode (18) for the pixel at the end row is changed to the display electrode (18) whose one side is adjacent to the left and right and the alignment control electrode ( 13) and the orientation control window (22) are in common, and the other side is a triangle so that the display electrode (18) vertically adjacent to and the orientation control window (22) are in common contact. Thereby, an oblique electric field is generated on the oblique side of the display electrode (18), and more effective alignment control is performed. Therefore,
In the central part of the pixel group, the separation distance between the display electrodes (18) is small, and in particular, on the side opposite to the side on which the alignment control electrode (13) is provided, sufficient orientation control is performed by the oblique electric field (32). Even in the case where the pixel group cannot be received, strong alignment control is performed at the pixels in the end row as shown by the arrow in FIG. Orientation control is performed.

When the present invention is applied to the TN system, the sectional structures along the line AA and the line BB in FIG. 1 are as shown in FIGS. 4 and 5, respectively. The liquid crystal (40) is a nematic phase having a positive dielectric anisotropy, and has an alignment film (19, 2).
3) is a parallel alignment film which has been rubbed in a predetermined direction. The liquid crystal molecules (41) are elastically fixed by interaction with the alignment films (19, 23) such that the initial alignment is in a direction parallel to the substrates (10, 20). The rubbing direction of the alignment films (19, 23) is the direction shown by the thick solid line arrow (50) and the thick broken line arrow (51) below in FIG. Although not shown, both substrates (10, 20)
, Two polarizing plates are arranged so that the polarization axis directions are orthogonal to each other. The liquid crystal (40) has a display electrode (1).
8) and the electric field formed by the voltage applied to the common electrode (21), the orientation is changed, and as the electric field strength is increased, the major axis direction of the liquid crystal molecules (41) is directed to the electric field direction.

When the liquid crystal display device having this configuration is driven and a desired voltage is applied between the display electrode (18) and the common electrode (21), as shown in FIG. At the edge, the oblique electric field (3
2) occurs. The liquid crystal molecules (41) are directed along the oblique electric field (32) in the shortest axis direction at the shortest.
The display electrodes (18) are started up in the same direction. Therefore, the direction in which the liquid crystal molecules (41) rise from the parallel direction and tilt is opposite to the direction in which the liquid crystal molecules (31) tilt from the vertical direction in the VAN type, as shown in FIG. In addition, as shown in FIG.
In the upper and lower sides of 8), the direction in which the orientation is inclined is not controlled.
That is, in FIG. 1, the tilt direction of the liquid crystal molecules (41) is
In the direction opposite to the thick arrow, the right and left alternate alternately for each row.

[0026]

As is clear from the above description, by controlling the direction of the liquid crystal alignment for each pixel, pixels having different preferential viewing angles are macroscopically viewed, and their luminance and contrast ratio are averaged. Therefore, the viewing angle dependency is reduced and the viewing angle is widened. In addition, since the direction of orientation is uniformly aligned in the entire area of each pixel and the orientation is changed for each pixel, the pixel is suitable for miniaturization and high definition, and the area between display electrodes is reduced due to the reflection type, In addition, since the boundaries having different orientations are aligned with the region between the display electrodes, the loss of the effective display region due to the alignment division is eliminated, and the aperture ratio is significantly increased.

[Brief description of the drawings]

FIG. 1 is a partial plan view of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

FIG. 4 is a sectional view taken along line AA of FIG.

FIG. 5 is a sectional view taken along line BB of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 20 Substrate 11 Drain line 12 Source electrode 13 Alignment control electrode 14 Semiconductor layer 15 Insulating layer 16 Gate line 17 Planarization insulating film 18 Display electrode 19, 23 Alignment film 21 Common electrode 22 Alignment control window 30, 40 Liquid crystal layer 31, 41 Liquid crystal molecules 32 Electric field

Claims (7)

[Claims] A plurality of gate lines and a plurality of drain lines arranged on a substrate so as to intersect with each other; a thin film transistor formed at an intersection of the plurality of gate lines and the drain line; and a liquid crystal connected to the thin film transistors In a liquid crystal display device including a display electrode for driving and a common electrode for driving liquid crystal provided on another substrate opposed to the liquid crystal, the display electrode is formed on an interlayer insulating film covering the thin film transistor. And an alignment control electrode that is electrically insulated from the display electrode is disposed in a part of the region corresponding to between the display electrodes, and corresponds to a part of the region between the display electrodes. A liquid crystal display device, wherein an alignment control window formed by the absence of the electrode is provided in the common electrode, and the alignment of the liquid crystal is controlled in a predetermined direction. 2. The liquid crystal display device according to claim 1, wherein the alignment control electrode is disposed below the interlayer insulating film. 3. The liquid crystal display device according to claim 1, wherein the display electrode is a reflective electrode. 4. The alignment control electrode is provided along one side of the display electrode, and the alignment control window is formed along a side of the display electrode where the alignment control electrode is provided and a side adjacent thereto. 2. The device according to claim 1, wherein
The liquid crystal display device according to any one of claims 1 to 3. 5. The alignment control electrode is provided in common for two adjacent rows of display electrodes, and is arranged along alternately left and right sides of the display electrode every other row, and the alignment control window is provided with the display electrode. 5. The liquid crystal display device according to claim 4, wherein the liquid crystal display device is provided in common for two adjacent rows. 6. The method according to claim 1, wherein an effective potential difference between the alignment control electrode and the display electrode is smaller than an effective potential difference between the display electrode and the common electrode.
The liquid crystal display device as described in the above. 7. The display electrodes in the end row share one side with the display electrodes in the adjacent column, the alignment control electrode and the alignment control window, and the other side with the display electrodes in the adjacent row. The liquid crystal display device according to claim 5, wherein the liquid crystal display device is provided in a triangular shape having the common alignment control window.