KR20000009053A - Liquid crystal display elements with composite electric field type - Google Patents

Abstract

PURPOSE: This is for the optical visual field angle for controlling initial opposite directing and the better luminance with low driving voltage by solving the crosstalk and persistence in the liquid crystal display using the conventional transverse electric field. CONSTITUTION: This is composed of two parts; clear board(104) which has a pair of electrodes with liquid crystal field(140) between them and facing direction board(115) which has electrode applicable to the inclined and longitudinal electric fields. In the clear board(104) common electrodes(120) applicable to transverse and data electrode(130) are on the same or another field, and the first opposite direction layer(125a) are on the top of the board. Also facing direction electrode(108) which has the inclined or longitudinal electric field among data electrodes(130) is on the face of the facing direction board(115), Color filter and optical cut-off filter are on the upper part of the board and the first opposite direction layer(125b) is on the top of it. So opposite direction improves after applying additional longitudinal or inclined electric fields on the liquid crystal layer and realizing the better luminance and optical visual field angle with using the first, second opposite direction layer(125a,125b).

Description

Complex field type liquid crystal display device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device. In particular, a composite field type liquid crystal driving a liquid crystal layer by applying a transverse electric field by two electrodes formed on a transparent substrate, and applying a gradient electric field and a longitudinal electric field by forming a counter electrode on a counter substrate. It relates to a display element.

Recently, in order to solve the problem that the contrast ratio is lowered and the color is changed according to the viewing angle in the liquid crystal display, an in-plane switching mode is a liquid crystal display device that drives a liquid crystal layer by forming a plurality of electrode pairs on a transparent substrate. LCDs have been disclosed by a number of papers and patents.

FIG. 1 is a view showing a liquid crystal driving electrode of a transverse electric field type liquid crystal display device, and FIG. 2 is a cross-sectional view taken along the line AA ′ of FIG.

The common electrode 20 and the data electrode 30 are formed on the transparent substrate 5 with the insulating layer 7 interposed therebetween. The first alignment layer 25a is formed over the entire pixel region, and the second alignment layer 25b is formed on the counter substrate 15.

When no voltage is applied to the common electrode 20 and the data electrode 30, the liquid crystal molecules 10 remain aligned along the initial alignment direction (R direction). In the drawing, angle θ represents an angle (hereinafter referred to as an orientation angle) between the common electrode 20 and / or the data electrode 30 and the major axis of the liquid crystal molecule 10.

When voltage is applied to the two electrodes 20 and 30 to form an electric field in the dotted arrow direction of FIG. 2, the liquid crystal molecules 10 in the liquid crystal layer 40 rotate in the direction of the arrow of FIG. 1 along the direction of the electric field. .

However, in the above-described liquid crystal display device, the distance between the common electrode 20 and the data electrode 30 should be maintained within a certain range in which the electric field strength is not weakened in order to obtain desirable driving characteristics of the liquid crystal molecules 10. The biased electrode structure causes crosstalk, afterimages, and the like.

Also, in the liquid crystal display device as shown in FIGS. 1 and 2, when the 45 ° alignment is performed with respect to the data electrode and the common electrode, the liquid crystal molecules are arranged in parallel along the direction of the pre-formed electric field when voltage is applied, so that the viewing angle and There is a problem that it is difficult to expect an improvement effect of color-shift.

The present invention is to solve the above problems of the prior art, by forming a counter electrode on a substrate facing the substrate on which at least one pair of electrodes for applying a transverse electric field is applied by applying a gradient electric field and a longitudinal electric field between the two substrates An object of the present invention is to provide a composite field type liquid crystal display device having improved luminance by low liquid crystal driving voltage.

Another object of the present invention is to reduce the driving voltage of the liquid crystal layer by forming an alignment film having a low alignment control force on the transparent substrate.

Still another object of the present invention is to adjust the initial alignment state of the liquid crystal to realize a wide viewing angle and at the same time reduce the color conversion.

In order to achieve the above object, a composite field type liquid crystal display device according to the present invention has a transparent substrate and a counter substrate, a liquid crystal layer interposed therebetween, and a common formed on the transparent substrate and applying a transverse electric field to the liquid crystal layer. An electrode and a data electrode, a first alignment film formed on the common electrode and the data electrode, a counter electrode formed on the counter substrate and applying a gradient electric field and a longitudinal field together with the data electrode, and a second alignment film formed on the counter electrode. Is done.

The common electrode and the data electrode are formed on the same layer or different layers by patterning the same material or different materials. The counter electrode is formed over the entire counter substrate.

The common electrode and the data electrode of the present invention form a complex electric field together with the electrode formed on the counter substrate to lower the driving voltage of the liquid crystal layer, thereby making the distance between the common electrode and the data electrode wider than before, which improves the aperture ratio. To increase the brightness.

In addition, according to the present invention, by applying an alignment layer having a small alignment control force on the transparent substrate without applying the same alignment layer to the above two substrates, it is possible to further reduce the driving voltage of the liquid crystal layer, ideally by adjusting the initial alignment state of the liquid crystal It is possible to provide a wide viewing angle liquid crystal display element.

1 is a view showing a liquid crystal driving electrode of a conventional transverse electric field type liquid crystal display device.

2 is a cross-sectional view taken along line AA ′ of FIG. 1.

3 is a view showing a liquid crystal driving electrode of the composite field type liquid crystal display device of the present invention.

4 is a view showing an initial alignment state of the liquid crystal according to the present invention.

<Explanation of symbols for the main parts of the drawings>

105: transparent substrate 108: counter electrode

110: liquid crystal molecules 115: opposing substrate

120: common electrode 125a, 125b: alignment layer

130: data electrode 140: liquid crystal layer

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

3 is a cross-sectional view of a unit pixel area of a composite field type liquid crystal display device according to an exemplary embodiment of the present invention, and a gate electrode (not shown) connected to a gate wiring (not shown) on the transparent substrate 104 and a gate electrode on the gate electrode. Data made of a stacked gate insulating film 105 made of a material such as SiNx or SiOx, and Cr, Al, or Al alloy electrically connected to a data wiring (not shown) when voltage is applied on the gate insulating film 105. Cr, Al, or Al alloy, which is electrically connected to the electrode 130 and a common wiring (not shown) in the same plane as the data electrode 130 to apply a transverse electric field together with the data electrode 130. A first alignment layer 125a is formed on the common electrode 120 and the common electrode 120 and the data electrode 130 to impart a specific alignment state to the liquid crystal molecules of the liquid crystal layer 140. In this case, the common electrode 120 and the data electrode 130 may be formed of a transparent metal such as indium tin oxide (ITO). In this case, the aperture ratio may be increased by maximizing the efficiency of transmitted light. In addition, forming the two electrodes 120 and 130 on the same layer may reduce the driving voltage by eliminating the storage capacitance such as an insulating film that may be present therebetween. In addition, the two electrodes 120 and 130 may be formed in different layers through an insulating film.

On the opposing substrate 115, an opposing electrode 108 made of a transparent metal such as ITO forming an inclined electric field and a terminating electric field together with the data electrode 130 is formed over the entire substrate, and, although not shown in the drawings, Although not shown, a light blocking layer (not shown) for preventing light leakage near the thin film transistor, gate wiring, data wiring, and common wiring, and a color filter layer (not shown) including R, G, and B color filter elements are provided. It is also possible to form an overcoat layer thereon for the purpose of planarization thereon. Subsequently, a second alignment layer 125b is formed above the counter electrode 108 to hold the liquid crystal molecules in the liquid crystal layer 140 together with the first alignment layer 125a in a specific alignment state.

As shown in the drawing, when voltage is applied to the common electrode 120, the data electrode 130, and the counter electrode 108, a solid line near the first alignment layer 125a between the common electrode 120 and the data electrode 130. An electric field (lateral electric field) as indicated by an arrow is formed, and an electric field (inclined and terminal electric field) as indicated by a dotted arrow is formed in the liquid crystal layer 140 between the counter electrode 108 and the data electrode 130. The liquid crystal molecules rotate by an electric field from the initial alignment state of the first alignment layer 125a and the second alignment layer 125b by a predetermined size, for example, a change in the alignment angle. In this case, when the liquid crystal used is positive-type, the long axis of the liquid crystal molecules follows the direction of the electric field, and when the liquid crystal molecule is negative-type, the long axis of the liquid crystal molecules follows the direction opposite to the direction of the electric field.

In order to reduce the driving voltage of the liquid crystal, in the present invention, the first alignment layer 125a of FIG. 3 is formed by photoalignment treatment of an alignment layer having a small anchoring energy (10 ⁻³ _{erg / cm 2} or less). Specifically, a photoalignment material such as polysiloxanecinnamate, polyvinylcinnamate or cellulosecinnamate is applied to the alignment layer 125a, and then polarized on the alignment layer 125a. In this case, the unpolarized light is irradiated to the alignment layer one or more times, wherein the light is preferably ultraviolet rays.

The alignment process for the second alignment layer 125b is obtained by coating a material such as polyimide, polyamide, polyvinylalcohol, polyamic acid, or SiO ₂ on the alignment layer 125b. This is done by rubbing after. Specifically, after applying the above-described alignment film material, rubbing is performed in the R1 (or R2) direction to determine the orientation direction, and then rubbing is performed in the R2 (or R1) direction while the region I is blocked with a mask.

Table 1 below is for explaining the driving voltage relationship between the conventional transverse electric field method and the composite electric field method according to the present invention, as can be seen from the table, the composite electric field method according to the present invention is compared with the conventional transverse electric field method. A decrease (about 1.5 Volt) is shown.

Pre-twist angle (。) Vth (Volt) Vmax (Volt) IPS method 70 1.23 4.40 Complex electric field method 70 0.87 2.90

4 is a view showing an initial alignment state of the liquid crystal according to the present invention, wherein the liquid crystal molecules 110 having an alignment angle of R ₁ and R ₂ and having an alignment angle of θ are randomly free between two electrodes 120 and 130. It is oriented with the tilt. The pixel region is divided into regions I and II by dividing lines (dotted and dashed lines) across the two electrodes 120 and 130, and the liquid crystal molecules in each region are in an symmetrical alignment state with respect to the dividing lines. .

Table 2 shows the change in contrast ratio (C / R) when the polarization axis direction (the extension direction of the common electrode and / or the data electrode) of the polarizing plate maintains the angle between the major axis direction of the liquid crystal and θ. .

θ (。) 0 One 2 3 4 5 C / R 300 280 250 200 180 100

As can be seen from Table 2, the applicable θ value is 0 ° ≤θ≤5 ° and the black luminance does not change when θ is 0 to 2 °, but when θ is 0 to 1 °, the direction of rotation of the liquid crystal is shifted to the foreground. (disclination) may occur, so the most preferable θ value is 2 ° ≦ θ ≦ 3 °.

The above-described orientation division method may be applied to the second alignment layer 125b as well as the first alignment layer 125a, and may be simultaneously implemented for the two alignment layers 125a and 125b.

In the composite field liquid crystal display device according to the present invention, a composite electric field is formed by a pair of electrodes applying a transverse electric field and a counter electrode applying a gradient electric field and a longitudinal electric field together with at least one of them, and a top plate and / or The driving voltage of the liquid crystal layer can be lowered by forming an alignment film having a small anchoring energy on the lower plate.

In addition, by dividing the pixel region, the liquid crystal exhibits opposing driving characteristics in each region, thereby making it possible to enlarge the viewing angle and prevent color change.

Furthermore, it is possible to secure a sufficient distance between the electrodes biased to the substrate to increase the light transmittance along with the reduction of crosstalk and afterimage.

Claims (21)

A pair of first and second substrates facing each other, A liquid crystal layer formed between the two substrates; A pair of electrodes formed on the first substrate and applying a transverse electric field to the liquid crystal layer; A composite field type liquid crystal display device which is integrally formed over a second substrate and includes a counter electrode which applies a gradient electric field and a longitudinal electric field to the liquid crystal layer together with the pair of electrodes. The method of claim 1, A gate wiring and a data wiring arranged vertically and horizontally on the first substrate to define a pixel region; Common wiring arranged in the pixel region; A thin film transistor formed at the intersection of the gate wiring and the data wiring, The liquid crystal display device of claim 1, further comprising a first alignment layer formed on the first substrate. 2. The liquid crystal display of claim 1, wherein the pair of electrodes is a common electrode and a data electrode. The liquid crystal display of claim 1 or 3, wherein the common electrode and the data electrode are formed on the same layer. The method according to claim 1 or 2, A light blocking layer formed on the second substrate to prevent leakage of light in the vicinity of the gate wiring, the data wiring, and the thin film transistor; A color filter layer formed on the light shielding layer, The liquid crystal display device of claim 1, further comprising a second alignment layer formed on the second substrate. The composite field type liquid crystal display of claim 1, wherein the counter electrode is indium tin oxide (ITO). The composite field type liquid crystal display device according to claim 2 or 5, wherein any one of the first alignment layer and the second alignment layer is an alignment layer having a small anchoring energy. 8. The composite field type liquid crystal display device according to claim 7, wherein the alignment layer having a small anchoring energy is an optical alignment layer. The complex electric field method according to claim 8, wherein the material constituting the photoalignment layer is selected from the group consisting of polysiloxanecinnamate, polyvinylcinnamate, and cellulosecinnamate. Liquid crystal display device. According to claim 2 or 5, wherein the material constituting any one of the first alignment film and the second alignment film is polyimide (polyimide), polyamide (polyamide), polyvinyl alcohol (polyvinylalcohol), polyamic acid (polyamic acid) And SiO ₂ . A pair of first and second substrates facing each other, A liquid crystal layer formed between the two substrates and divided into a plurality of regions; A pair of electrodes formed on the first substrate and applying a transverse electric field to the liquid crystal layer; A counter electrode formed over the entire second substrate and applying a gradient electric field and a longitudinal electric field to the liquid crystal layer together with the pair of electrodes; And the angle θ of the long axis of the liquid crystal present in the unit region in the liquid crystal layer and the adjacent region in the extending direction of the pair of electrodes is 0 ° ≦ θ ≦ 5 °. 12. A liquid crystal display device according to claim 11, wherein θ is 2 ° ≦ θ ≦ 3 °. The method of claim 11, A gate wiring and a data wiring arranged vertically and horizontally on the first substrate to define a pixel region; Common wiring arranged in the pixel region; A thin film transistor formed at the intersection of the gate wiring and the data wiring, The liquid crystal display device of claim 1, further comprising a first alignment layer formed on the first substrate. 12. The liquid crystal display of claim 11, wherein the pair of electrodes is a common electrode and a data electrode. 15. The liquid crystal display of claim 11 or 14, wherein the common electrode and the data electrode are formed on the same layer. The method according to claim 11 or 12, wherein A light blocking layer formed on the second substrate to prevent leakage of light in the vicinity of the gate wiring, the data wiring, and the thin film transistor; A color filter layer formed on the light shielding layer, The liquid crystal display device of claim 1, further comprising a second alignment layer formed on the second substrate. 12. The liquid crystal display of claim 11, wherein the counter electrode is indium tin oxide (ITO). 17. The liquid crystal display of claim 13 or 16, wherein any one of the first alignment layer and the second alignment layer is an alignment layer having a small anchoring energy. 20. The liquid crystal display of claim 18, wherein the alignment layer having the small anchoring energy is an optical alignment layer. 20. The complex electric field method according to claim 19, wherein the material constituting the optical alignment layer is selected from the group consisting of polysiloxanecinnamate, polyvinylcinnamate, and cellulosecinnamate. Liquid crystal display device. The method of claim 13 or 16, wherein the material constituting any one of the first alignment layer and the second alignment layer is a polyimide (polyimide), polyamide (polyamide), polyvinyl alcohol (polyvinylalcohol), polyamic acid (polyamic acid) And SiO ₂ .