JPH11109356A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve brightness, a visual angle characteristic, and an aperture ratio. SOLUTION: This device is a vertical orientation type liquid crystal display device which is provided with liquid crystal layers 40 having vertically oriented liquid crystal molecules 41 between plurally formed display electrodes 19 and counter electrodes 31, and controls the orientation of the liquid molecules 41 by an electric field. And, transparent auxiliary electrodes 50 for controlling the orientation of the liquid crystal molecules 41 are formed vertically or horizontally via an insulating layer 15 riding across the adjacent display electrodes 19, and further, orientation control windows 32 are formed in the horizontal or vertical direction on the side of the counter electrode 31 so as to be positioned at the center of the display electrode 19.

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 which has improved luminance, viewing angle characteristics, and aperture ratio.

[0002]

2. Description of the Related Art LCDs have advantages of small size, thin shape, low power consumption, and the like, 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

A 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 on. Is done. The display electrode and the TFT are formed on the same substrate, and the counter electrode, which forms the other side of the pixel capacitance, is formed entirely on another substrate facing the liquid crystal layer. That is, the liquid crystal and the counter 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 or one frame period until the next turn on of the TFT. The liquid crystal has electro-optical anisotropy, and the transmittance is controlled according to the voltage applied to the pixel capacitance. By controlling the transmittance for each display pixel, these light and dark areas are visually recognized as a display image.

The initial alignment state of the liquid crystal is further determined 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. Usually, a polarizing plate is provided outside both substrates, and in the TN system, the polarization axis of each polarizing plate coincides with the alignment direction on the respective substrate side. Therefore, when no voltage is applied, the linearly polarized light that has passed through one of the polarizing plates is in a form that follows the twisted orientation of the liquid crystal,
It turns in the liquid crystal layer and is emitted from the other polarizing plate, and the display is recognized as white. Then, by applying a voltage to the pixel capacitance 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 reduced, and the display is temporarily turned black. As described above, a system in which white is displayed after no voltage is applied and then black is applied in response to voltage application is called a normally white mode, which is the mainstream of TN cells.

FIGS. 5 and 6 show the structure of a unit pixel portion of a conventional liquid crystal display device. FIG. 5 is a plan view, and FIG.
It is sectional drawing which followed the G line. On the substrate (100), C
gate electrode (10) made of metal such as r, Ta, Mo, etc.
1) is formed, over which SiNx or / and S
A gate insulating film (102) made of iO2 or the like is formed. On the gate insulating film (102), p-Si (10
3) is formed. The p-Si (103) has S patterned thereon in the shape of the gate electrode (101).
Using an injection stopper (104) such as iO2, phosphorus,
(N-) low concentration (L-) containing low concentration of impurities such as arsenic
D (Lightly doped) region (LD), and (N +) source and drain regions (S, D) containing the same high concentration of impurities are formed outside the region (LD). Immediately below the injection stopper (104) is an intrinsic layer containing substantially no impurities, and serves as a channel region (CH).
An interlayer insulating film (105) made of SiNx or the like is formed to cover the p-Si (13), and the interlayer insulating film (10) is formed.
5) On the source electrode (10) made of Al, Mo, etc.
6) and a drain electrode (107) are formed and connected to the source region (S) and the drain region (D) via contact holes formed in the interlayer insulating film (105), respectively. On the entire surface covering this TFT, SOG (SPIN O
N GLASS), BPSG (BORO-PH-OSPHO SILICATE GLAS
S), a flattening insulating film (108) such as an acrylic resin is formed. ITO on the flattening insulating film (108)
A display electrode (109) for driving a liquid crystal made of a transparent conductive film such as (indium tin oxide) is formed.
08) is connected to the source electrode (106) through the contact hole opened.

An alignment film (120) made of a polymer film such as polyimide is formed on the entire surface covering all of them, and the initial alignment of the liquid crystal is controlled by a predetermined rubbing treatment.
On the other hand, on another glass substrate (130) placed at a position facing the substrate (100) with the liquid crystal layer interposed, a counter electrode (131) formed entirely of ITO is provided. 131), an alignment film (133) of polyimide or the like is formed thereon and subjected to a rubbing treatment.

Here, a nematic phase having a negative dielectric anisotropy is used for the liquid crystal (140), and the alignment film (120, 1) is used.
33) DAP (deformation) using a vertical alignment film
of vertically aligned phase) type. The DAP type is a voltage controlled birefringence (ECB).
This is one of the d birefringence systems in which the transmittance is controlled by utilizing the difference in the refractive index between the major axis and the minor axis of the liquid crystal molecules, that is, birefringence. In the DAP 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, and the retardation amount according to the electric field intensity of the liquid crystal layer, that is, the ordinary light component in the liquid crystal By controlling the difference between the phase velocities of the light beam and the extraordinary light component, light is emitted from the other polarizing plate at a desired transmittance. In this case, the display changes from black to white by increasing the applied voltage from the state where no voltage is applied, so that the normally black mode is set.

[0008]

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,
In the TN system, the transmitted light intensity can be adjusted, and E
In the CB method, the hue can be separated by controlling the spectral intensity depending on the wavelength. The amount of retardation depends on the angle between the major 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 so-called viewing angle dependency problem.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and a liquid crystal layer having vertically aligned liquid crystal molecules is provided between a plurality of display electrodes and a counter electrode. A liquid crystal display device of a vertical alignment method for controlling the alignment of the liquid crystal molecules by an electric field, wherein an alignment control window is formed in the counter electrode, and a voltage is applied between the display electrodes via a display electrode and an insulating layer. In this configuration, an auxiliary electrode that is not formed is formed.

Further, a liquid crystal layer having vertically aligned liquid crystal molecules is provided between a plurality of display electrodes and a counter electrode, and a vertical alignment type liquid crystal display device in which the alignment of the liquid crystal molecules is controlled by an electric field. Auxiliary electrodes are formed between the display electrodes in one of the horizontal and vertical directions with a display electrode and an insulating layer interposed therebetween. In this configuration, an orientation control window that is continuous in one of the horizontal directions is formed.

According to this, luminance and viewing angle characteristics can be improved by preventing poor alignment. Further, the auxiliary electrode is a transparent electrode, and according to this, the aperture ratio can be improved.

[0012]

1 and 2 show the structure of a part of a liquid crystal display device according to a first embodiment of the present invention. FIG.
2A is a plan view, FIG. 2A is a cross-sectional view along the line HH in FIG. 1, and FIG. 2B is a cross-sectional view along the line II in FIG. Substrate (1
0) The TFT formed on top is the p-SiT shown in the conventional example.
Although the configuration is the same as that of the FT, it is simplified here.

A gate electrode (11) made of a metal such as Cr, Ta, or Mo is formed on a substrate (10), and a gate insulating film (12) made of SiNx or / and SiO2 is formed to cover the gate electrode (11). ing. Gate insulating film (1
2) p-Si (16) is formed thereon, and the center is an intrinsic layer channel region, and impurities are implanted outside the channel region to form a source region and a drain region. p-Si (1
6), an interlayer insulating film (15) is formed so as to cover this, and a drain electrode (17) is connected to the drain region. Further, a display electrode (19) made of a transparent conductive film such as ITO (indium tin oxide) is provided on the interlayer insulating film (1).
It is connected to the source region via the contact hole opened in 5).

An alignment film (not shown) made of a polymer film such as polyimide is formed on the entire surface covering all of them. On the other hand, on another glass substrate (30) placed at a position facing the substrate (10) with the liquid crystal layer interposed, a counter electrode (31) entirely formed of ITO is provided,
On the counter electrode (31), an alignment film (not shown) such as polyimide is formed. In the present invention, the alignment film (not shown) and the liquid crystal (40) are selected so that the liquid crystal molecules (41) are vertical.

As shown in FIGS. 1 and 2B, the feature of the present invention is that it is located on the side of the counter electrode (31), substantially at the center of the display electrode (19), and straddles all the display electrodes in the horizontal direction. Is provided with an orientation control window (32) continuously in the horizontal direction. The alignment control window (32) is provided with the counter electrode (3).
This is the part where 1) does not exist. Further, as shown in FIGS. 2A and 2B, the display electrode (1) is formed on the gate insulating film (12).
An auxiliary electrode (50) is provided via the insulating layer (15) and the insulating layer (15). The auxiliary electrode is formed continuously between the display electrodes in the vertical direction, as shown by hatching in FIG. 1, and is formed so as to straddle adjacent display electrodes.

No voltage is applied to the auxiliary electrode (50), so that it is in a floating state. Therefore, as shown by the broken line in FIG.
Are capacitively coupled to the adjacent display electrodes (19). Therefore,
When a horizontal line inversion drive for inverting and driving the liquid crystal panel for each horizontal line or a field inversion drive for inversion for each field is performed, the auxiliary electrode (50) is capacitively coupled with the display on both sides in the horizontal direction. A voltage approximately intermediate to the voltage of the electrode (19) will be applied. That is, the display electrodes are formed as if they were continuously formed in the horizontal direction.

Here, as shown in FIG. 2B, the liquid crystal molecules (4) are located between the alignment control window (32) and the display electrode (60).
Since no electric field is applied so as to incline 1), the liquid crystal molecules are vertically aligned there as shown. However, an electric field is generated in the periphery of the liquid crystal, as shown by the dotted line in the figure. In the regions R1, R2, R3, and R4 sandwiched between the alignment control window (32) and the display electrodes (60), the alignment directions of the liquid crystal are alternately viewed from the vertical direction as shown in FIG. 2B. In the opposite direction.

On the other hand, when viewed from the horizontal direction as shown in FIG. 2A, all the liquid crystal molecules are inclined from the edge of the display electrode toward the alignment control window (32). Looks like. As described above, in this example, since the display electrodes are formed continuously in the horizontal direction, this uniform orientation occurs over one horizontal line. That is, R1, R
The alignment of the liquid crystal becomes uniform over the entire area of the lines 2, R3, and R4. Accordingly, there is no defective orientation, and the luminance and viewing angle characteristics are significantly improved.

In this case, the auxiliary electrode (50) is connected to the IT
Since it is made of a transparent electrode such as O, one horizontal line is all continuous, and the aperture ratio is greatly improved. 3 and 4 show a partial structure of a liquid crystal display according to a second embodiment of the present invention. FIG. 3 is a plan view, and FIG.
FIG. 4B is a cross-sectional view taken along the line KK of FIG. 3.

This embodiment is different from the first embodiment in that the directions of forming the auxiliary electrode (50) and the orientation control window (32) are opposite to those in the previous example. That is, as shown in FIG.
On the side, an alignment control window (32) is provided substantially at the center of the display electrode (19) and continuously in the vertical direction so as to straddle all the display electrodes in the vertical direction. Further, as shown in FIGS. 4A and 4B, the auxiliary electrode (5) is provided on the substrate (10) via the display electrode (19), the insulating film (12) and the insulating layer (15).
0) is provided. The auxiliary electrode is formed continuously between the display electrodes in the horizontal direction, as shown by oblique lines in FIG. 3, and is formed so as to straddle adjacent display electrodes.

Since no voltage is applied to the auxiliary electrode (50) as in the previous example and the auxiliary electrode (50) is in a floating state, as shown by a dotted line in FIG.
0) is capacitively coupled to the adjacent display electrodes (19). Therefore, if the vertical line inversion drive for inverting and driving this liquid crystal panel for every vertical line or the field inversion drive for inversion for each field is performed, the auxiliary electrode (50)
The display electrodes (19) on both sides in the vertical direction that are capacitively coupled
A voltage that is approximately the middle of the above voltage is applied. That is,
It is as if the display electrodes are formed continuously in the vertical direction.

As shown in FIG. 4A, the liquid crystal molecules (4) are located between the alignment control window (32) and the display electrode (60).
Since an electrode is not applied so as to incline 1), the liquid crystal molecules are vertically aligned there as shown in the figure. However, an electric field is generated in the periphery of the liquid crystal, as shown by the dotted line in the figure. In the regions C1, C2, C3, and C4 sandwiched between the alignment control window (32) and the display electrode (60), the alignment directions of the liquid crystal alternate when viewed from the horizontal direction as shown in FIG. 4A. In the opposite direction.

On the other hand, when viewed from the vertical direction as shown in FIG. 4B, all the liquid crystal molecules are inclined from the edge of the display electrode to the direction of the alignment control window (32). Looks like. As described above, in this example, since the display electrodes are formed as if they were continuously formed in the vertical direction, this uniform alignment occurs over one line in the vertical direction. That is, C1, C
The alignment of the liquid crystal is uniform over the entire vertical line of C2, C3 and C4. Accordingly, there is no defective orientation, and the luminance and viewing angle characteristics are significantly improved.

Also in this case, the auxiliary electrode (50) is
Since it is formed of a transparent electrode such as O, one vertical line is all continuous, and the aperture ratio is greatly improved.

[0025]

As is clear from the above description, it is possible to improve the luminance and the viewing angle characteristics by preventing the alignment defect, and to improve the aperture ratio because the auxiliary electrode is a transparent electrode. Can be.

[Brief description of the drawings]

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

FIG. 2 is a sectional view taken along lines HH and II in FIG. 1;

FIG. 3 is a plan view of a pixel portion of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is a sectional view taken along lines JJ and KK of FIG. 1;

FIG. 5 is a plan view of a unit pixel portion of a conventional liquid crystal display device.

FIG. 6 is a sectional view taken along line GG of FIG. 3;

DESCRIPTION OF SYMBOLS 10 Substrate 11 Gate electrode 12 Gate insulating film 15 Interlayer insulating film 16 Source electrode 17 Drain electrode 19 Display electrode 20 Alignment film 30 Glass substrate 31 Counter electrode 32 Alignment control window 40 Liquid crystal 41 Liquid crystal molecule 50 Auxiliary electrode

Claims (5)

[Claims] A vertical alignment type liquid crystal display device in which a liquid crystal layer having liquid crystal molecules vertically aligned is provided between a plurality of display electrodes and a counter electrode, and the alignment of the liquid crystal molecules is controlled by an electric field. A liquid crystal display device, wherein an orientation control window is formed in the counter electrode, and an auxiliary electrode to which no voltage is applied is formed between the display electrode via a display electrode and an insulating layer. 2. A vertical alignment type liquid crystal display device wherein a liquid crystal layer having liquid crystal molecules vertically aligned is provided between a plurality of display electrodes and a counter electrode, and the alignment of the liquid crystal molecules is controlled by an electric field. An auxiliary electrode is formed between the display electrodes in one of the horizontal and vertical directions via a display electrode and an insulating layer, and is positioned on the side of the counter electrode, substantially in the center of the display electrode, and A liquid crystal display device, wherein an alignment control window continuous in one of horizontal directions is formed. 3. The liquid crystal display device according to claim 1, wherein the auxiliary electrode is a transparent electrode. 4. The liquid crystal display device according to claim 2, wherein no voltage is applied to the auxiliary electrode. 5. The liquid crystal display device according to claim 1, wherein the auxiliary electrode is formed so as to straddle an adjacent display electrode.