JPH07230097A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the display screen of the liquid crystal display device which has a vertical orientation ECB mode from becoming rough owing to the appearance of discrenation by specifying the orientation vector of a liquid crystal director. CONSTITUTION:On a display electrode 11, an orientation control electrode 19 which is united with a gate line 18 and along a diagonal is provided, and the potential difference between the orientation control electrode 19 and a common electrode is set larger than the potential difference between the display electrode 11 and common electrode. Consequently, the electric field in a cell is controlled to determine the vectorial angle of the orientation vector, thereby preventing discrenation. Further, an axis of polarization is set at right angles or in parallel to a substrate side and then a priority visual angle direction is set to the up- down and right-left directions of the screen.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an ECB (Electrically
The present invention relates to a liquid crystal display device of the Controlled Birefringence (voltage controlled birefringence) system, and particularly to a liquid crystal display device that achieves good viewing angle characteristics and high display quality by controlling the orientation of the liquid crystal director.

[0002]

2. Description of the Related Art Liquid crystal display devices 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 liquid crystal display device using a thin film transistor (hereinafter abbreviated as TFT) as a switching element is capable of displaying a fine moving image and is used for a TV display or the like.

A liquid crystal display device includes a TFT substrate in which a predetermined electrode pattern is provided on a transparent substrate such as glass,
A counter substrate having a common electrode is laminated with a liquid crystal layer having a thickness of several μm sandwiched therebetween, and further sandwiched between two polarizing plates whose polarization axes are orthogonal to each other. In particular, by forming a polymer film such as polyimide as a vertical alignment treatment on both substrate surfaces and performing rubbing, and by using a nematic liquid crystal having a negative dielectric anisotropy as the liquid crystal layer, the initial alignment of the liquid crystal director VAN (Vertically aligned nematic) with a pretilt angle within 10 ° to the substrate normal direction and a color filter added at a predetermined position on the optical path for colorization.
Called type.

In the TFT substrate, TFTs are formed at intersections where a plurality of gate lines and drain lines are arranged so as to cross each other.
It has a structure connected to display electrodes arranged in a matrix. The gate lines are line-sequentially scanned and selected,
All the TFTs on the same scanning line are turned on, and a data signal synchronized with this is supplied to each display electrode via the drain line. The potential of the common electrode is also set in synchronization with the scanning of the gate line, and the liquid crystal is driven by the potential difference between the display electrodes facing each other to form the pixel capacitance. For example, white light incident from the TFT substrate side is changed into linearly polarized light by the first polarizing plate. When no voltage is applied, this incident linearly polarized light does not undergo birefringence in the liquid crystal layer, is blocked by the second polarizing plate, and the display becomes black (normally black mode). Then, when a predetermined voltage is applied to the liquid crystal layer, the liquid crystal director having a negative dielectric anisotropy changes so that the angle formed by the orientation vector and the electric field direction approaches a right angle. The liquid crystal is also
Since the refractive index has anisotropy, the incident linearly polarized light undergoes birefringence to become elliptically polarized light, and the light passes through the polarizing plate. Since the transmitted light intensity depends on the applied voltage, gradation display is possible by adjusting the applied voltage for each pixel, and the brightness (black and white) of each pixel is visually recognized in the display image as a whole.

[0005]

In the nematic liquid crystal director, the orientation vector when a voltage is applied is restricted only by the angle with respect to the electric field direction, and the azimuth angle about the electric field direction is released. Therefore, the TFT substrate has irregularities on the surface due to the unevenness of the surface alignment treatment, and the horizontal direction electric field due to the potential difference between the electrodes in the liquid crystal cell causes the alignment vector. Regions different from each other occur. That is, if the orientation vector is partially abnormal, the continuity of the liquid crystal causes the orientation vector having the azimuth angle to follow the continuity to spread over a certain region. If such a phenomenon occurs at a plurality of locations in the cell, a plurality of regions having orientation vectors having different azimuth angles while having the same angle with the electric field direction are generated. The boundary line between these regions has a different transmittance from others, and is called disclination. If many disclinations with different shapes occur for each pixel, problems such as graininess on the screen and failure to obtain the expected color display may occur.

Further, if the orientation vector of each area becomes irregular in the display area, there is a problem that the viewing angle dependency increases. Further, there is a problem that the threshold value and mutual conductance of the TFT change due to static electricity generated during rubbing, which causes so-called electrostatic breakdown.

[0007]

The present invention has been made in view of the above problems, and a thin film transistor substrate having a predetermined conductor pattern on the opposite surface side and an opposite substrate having a common electrode on the opposite surface side are made of liquid crystal. In a liquid crystal display device in which a polarizing plate is provided such that the two substrates are sandwiched and bonded to each other, and the polarizing plates are provided so that the polarization axis directions thereof are orthogonal to each other, the thin film transistor substrate is a transparent substrate laminated on a transparent substrate. Display electrodes arranged in a matrix by etching a conductive film, a plurality of drain lines arranged between rows of the display electrodes, and semiconductor layers sequentially covering the display electrodes and the drain lines. The thin film transistor is obtained by etching a laminated body including an insulating film and a metal film, and is partially overlapped with the vicinity of the display electrode and the drain line. And a plurality of gate lines forming a transistor, and an alignment control electrode disposed at a position along a diagonal line on each of the display electrodes, extending from an adjacent gate line different from the gate line for driving the display electrode. It is a configuration having and.

[0008]

By providing an alignment control electrode having a potential different from that of the display electrode on the display electrode, the electric field in the cell is controlled by the potential difference between the alignment control electrode, the display electrode and the common electrode.
The azimuth of the orientation vector is specified. That is, the electric field in the cell is obliquely inclined to have a predetermined angle with respect to the normal direction of the substrate, and the orientation vector and the electric field direction when no voltage is applied,
By setting a predetermined angle in advance, the liquid crystal director tilts in the direction of increasing this angle at the shortest because of elasticity due to continuity of liquid crystal.

By arranging the alignment control electrodes on the diagonal line of the pixel, in each zone partitioned by the alignment control electrodes, the liquid crystal directors are tilted as shown by the alignment vectors symmetrical to each other and are planar. , Its projection vector is in a direction orthogonal to the orientation control electrode.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is an enlarged plan view of the pixel portion. Display electrodes (11) made of a transparent conductive material such as ITO are arranged in a matrix on the substrate. A drain line (13) is arranged between columns and a gate line (18) is arranged between rows between the respective display electrodes (11), and they are orthogonal to each other. A TFT is formed at each intersection and is connected to the display electrode (11). A gate line (18) is formed on the display electrode (11).
An alignment control electrode (19) is integrally formed with the display electrode (11) and is arranged along one diagonal line of the display electrode (11). The alignment control electrode (19) is connected to the gate line (18) on the side different from the gate line of the TFT that drives the display electrode (11) on which the alignment control electrode (19) is superimposed.

A detailed description will be given below with reference to FIG. 2 showing a cross section taken along the line AA of FIG. A display electrode (11) and a drain line (13) are patterned on a transparent substrate (10) such as glass by sputtering ITO and photo-etching, and a part thereof is a source electrode (12) and a drain electrode (14). ) Are close to each other.

Here, in the sputtering of ITO, the source and drain wirings (11, 12, 13, 14) are made to contain phosphorus by using a group 5 element such as phosphorus added to ITO as a target. Keep it.
On the source electrode (12) and the drain electrode (14),
a-Si (15), insulating film (16), gate electrode (1
7) are sequentially laminated to form a TFT. The insulating film (16) is, for example, SiN _x , and the gate electrode (17)
Is made of Al or the like integrated with the gate line (18) and the orientation control electrode (19). These, a-Si, Si
N _X, Al is deposited by successive gate lines (17, 18,
Patterning is performed with the same mask of 19). In addition, a-
Si is formed by plasma CVD. At this time, phosphorus in ITO diffuses to the a-Si side to form a high concentration N-type thin film at the interface, and ohmic contact between ITO and a-Si is obtained. To be

Further, the entire surface is covered with a vertical alignment film (20) obtained by subjecting a polymer film of polyimide or the like to vertical alignment treatment, and then T
It becomes an FT substrate. Then, a transparent substrate such as glass (3
0), a common electrode (31) made of ITO and a vertical alignment film (32) made of polyid are formed on the opposite substrate, and the nematic liquid crystal having negative dielectric anisotropy in the gap is attached to the TFT substrate. Encapsulate. Furthermore, by sandwiching the polarization axes orthogonal to each other on the outside of both substrates (10, 30) with two polarizing plates so that they are all at an angle of 45 ° with respect to the alignment control electrode (19), A liquid crystal display device, which is an embodiment of the present invention, is completed.

The orientation control electrode (19) is connected to the gate line (1
8), which is a so-called additional capacitance type, which is integrated with the display electrode (11) sandwiching the insulating film (16) to form a capacitance. As shown in FIG. 3, the gate signal (V
_G ) sets its OFF level so that it has the same frequency and amplitude as the common electrode signal (V _C ) and has a constant potential difference (V _CD ). As a result, the effective potential difference (V _CD ) between the alignment control electrode (19) and the common electrode (31) is irrespective of whether the potential difference (V _LC ±) between the display electrode (11) and the common electrode (31) is inverted. , The display electrode (11) and the common electrode (3
It is made larger than the effective potential difference (V _LC ) from 1).

In this case, as shown in FIG. 4, the liquid crystal directors (41) in each zone partitioned by the alignment control electrodes (19) are controlled so that the alignment vectors are symmetrical to each other. FIG. 4 is a schematic cross-sectional view showing the positional relationship between the display electrode (11), the alignment control electrode (19) and the common electrode (31). Since the electric field (40) between the alignment control electrode (19) and the common electrode (31) expands strongly to both outsides, the electric field (40) near the edge of the alignment control electrode (19) causes the display electrode (11). ) To the common electrode (31) in an oblique direction away from the alignment control electrode (19). Further, at the edge of the display electrode (11), the electric field (40) flows from the display electrode (11) to the common electrode (3).
It occurs obliquely from inside the area of the display electrode (11) to outside the area of the display electrode (11) toward 1). Due to these two actions and the elasticity based on the continuity of the liquid crystal, the liquid crystal director (41) tilts in the direction in which the angle formed by the alignment vector and the electric field direction increases at the shortest when a voltage is applied. In the two zones of the display section partitioned by the alignment control electrode (19), the plane projection of the alignment vector is controlled so as to be perpendicular to the alignment control electrode (19) and line-symmetric. .

Therefore, the pixel is divided into two by the orientation control electrode (19).
Since the orientation vector can be controlled in each of the divided areas, disclination is prevented. Further, as shown in FIG. 5, each orientation control electrode is 45 ° with respect to the side of the substrate.
The liquid crystal director is inclined at a right angle to the alignment control electrode. Therefore, by arranging the two polarizing plates so that the polarization axis is at an angle of 45 ° with respect to the tilt direction of the liquid crystal director, that is, at a right angle or parallel to the side of the substrate, The preferential viewing angle direction can be the vertical and horizontal directions.

[0017]

As is clear from the above description, the alignment control electrodes formed in the diagonal direction of the pixel can constrain the alignment vector in the display pixel symmetrically with respect to the alignment control electrode. The appearance of nations is prevented. Further, by setting the polarization axis at a right angle or parallel to the substrate side, a liquid crystal display device having a preferential viewing angle direction in the vertical and horizontal directions of the display screen can be obtained.

Further, since the surface alignment treatment by rubbing is unnecessary, the manufacturing cost is reduced and the deterioration of the TFT characteristics due to static electricity is prevented.

[Brief description of drawings]

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

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

FIG. 3 is a waveform diagram illustrating a driving method of the liquid crystal display device of the present invention.

FIG. 4 is a cross-sectional view illustrating the function and effect of the present invention.

FIG. 5 is a plan view illustrating the effects of the present invention.

[Explanation of symbols]

 10, 30 transparent substrate 11 display electrode 12 source electrode 13 drain line 14 drain electrode 15 a-Si 16 insulating film 17 gate electrode 18 gate line 19 alignment control electrode 20, 32 vertical alignment film 31 common electrode 40 electric field 41 liquid crystal director

Claims (3)

[Claims] 1. A thin film transistor substrate having a predetermined conductor pattern on the opposite surface side and an opposite substrate having a common electrode on the opposite surface side are bonded together with a liquid crystal sandwiched therebetween, and the opposite back surface sides of the two substrates are adhered to each other. In a liquid crystal display device in which polarizing plates are provided so that polarization axis directions are orthogonal to each other, the thin film transistor substrate is a display electrode arranged and formed in a matrix by etching a transparent conductive film laminated on a transparent substrate. And a plurality of drain lines arranged between the rows of the display electrodes, and a stacked body including a semiconductor layer, an insulating film, and a metal film, which are sequentially stacked to cover the display electrodes and the drain lines. A plurality of gate lines that partially overlap the display electrode and the drain line to form a thin film transistor, and Wherein the position along the diagonal of the display electrodes, a liquid crystal display device characterized by having an extending arranged alignment control electrode from the gate lines of adjacent different said gate lines according to the driving of the display electrodes. 2. The liquid crystal display device according to claim 1, wherein the effective potential difference between the alignment control electrode and the common electrode is set to be larger than the effective potential difference between the display electrode and the common electrode. 3. The polarizing plate according to claim 1, wherein the two polarizing plates are provided such that the polarization axis directions thereof both form an angle of 45 ° with the alignment control electrode. 2. The liquid crystal display device according to item 2.