KR100304916B1 - Transverse electric field liquid crystal display device - Google Patents

Abstract

The transverse electric field type liquid crystal display device according to the present invention includes a transparent substrate and an opposite substrate facing each other with a liquid crystal layer interposed therebetween, gate wiring and data wiring arranged vertically and horizontally on the transparent substrate, and the data wiring and gate wiring. A thin film transistor formed at an intersection of the at least two transistors, a common wiring formed in parallel with the gate wiring, at least one pair of common and data electrodes formed alternately in parallel with the data wiring to apply a transverse electric field, and a plurality of common electrodes on the transparent substrate. And a first alignment layer having a small alignment control force and a second alignment layer formed on the counter substrate.

Description

Transverse electric field liquid crystal display device

The present invention relates to a liquid crystal display device, and more particularly, to a transverse electric field type liquid crystal display device for driving a liquid crystal layer by applying a transverse electric field by two electrodes formed on a transparent substrate.

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). The angle θ in the figure represents an angle formed by the long axis of the common electrode 20 and / or the data electrode 30 and the liquid crystal molecule 10 (hereinafter referred to as an orientation angle).

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 liquid crystal display device, in order to obtain desirable driving characteristics of the liquid crystal molecules 10, the distance between the common electrode 20 and the data electrode 30 must be maintained within a narrow range in which the electric field strength is not weakened. As a result, the biased electrode structure causes crosstalk and afterimages.

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 an alignment film having a low alignment control force on a substrate formed with at least a pair of electrodes for applying a transverse electric field, a transverse electric field system exhibiting improved luminance by a low liquid crystal drive voltage It is an object to provide a liquid crystal display device.

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 transverse electric 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, 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, and a second alignment film formed on the counter substrate.

The common electrode and the data electrode are formed on the same layer or different layers by patterning the same material or different materials.

According to the present invention, by applying an alignment layer having a small alignment control force to at least one of the above two substrates, it is possible to further reduce the driving voltage of the liquid crystal layer, and to adjust the initial alignment state of the liquid crystal to provide an ideal wide viewing angle liquid crystal display device. Makes it possible to provide.

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 cross-sectional view of a unit pixel area of a transverse electric field type liquid crystal display device according to an exemplary embodiment 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 110: liquid crystal molecules

115: counter substrate 120: common electrode

125a and 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 transverse electric field type liquid crystal display device according to an exemplary embodiment of the present invention, and FIG. 4 is a plan view of a unit pixel showing an initial alignment state of a liquid crystal device according to an exemplary embodiment of the present invention. A gate electrode (not shown) connected to a gate electrode (not shown), a gate insulating film 105 made of a material such as SiNx or SiOx stacked on the gate electrode, and data wiring (when voltage is applied on the gate insulating film 105). Data electrode 130 made of Cr, Al, or Al alloy, and the like, and electrically connected to a common wiring (not shown) on the same plane as the data electrode 130. The liquid crystal powder of the liquid crystal layer 140 on the common electrode 120 made of Cr, Al, or Al alloy, etc. to apply a transverse electric field together with the electrode 130 and the common electrode 120 and the data electrode 130. There is a first alignment film (125a) for imparting a particular orientation state is formed against. 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 counter substrate 115, although not shown, a light shielding layer (not shown) and a color filter of R, G, and B to prevent light leakage near thin film transistors, gate wirings, data wirings, and common wirings. A color filter layer (not shown) made of elements is formed, and it is also possible to form an overcoat layer thereon for the purpose of planarization. Subsequently, the second alignment layer 125b is formed 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 a voltage is applied to the common electrode 120 and the data electrode 130, an electric field is formed between the common electrode 120 and the data electrode 130 in the direction of the arrow near the first alignment layer 125a. 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 negative type is negative, the long axis of the liquid crystal molecules follows the direction perpendicular to the direction of the electric field.

In order to reduce the driving voltage of the liquid crystal, in the present invention, an alignment layer having a small anchoring energy (10 ⁻³ erg / cm ² or less) is used to photoalign the first alignment layer 125a or the second alignment layer 125b of FIG. 3. Formed by treatment. Specifically, a photoalignment material such as polysiloxanecinnamate, polyvinylcinnamate, or cellulosecinnamate is applied to the alignment layer 125a or 125b, and then the alignment layer 125a or 125b. ) Or after irradiating the polarized or non-polarized light once or more to determine the alignment direction of the liquid crystal in the region I in the R1 (or R2) direction, and then the polarized or unpolarized state in the state in which the region I is blocked with a mask. Light is irradiated once or more to the region II to determine the alignment direction of the liquid crystal in the region II in the R2 (or R1) direction. At this time, the light is preferably ultraviolet light.

It is also possible to carry out the above method continuously for each area and apply it to a multi-domain.

In the rubbing orientation treatment, a material such as polyimide, polyamide, polyvinylalcohol, polyamic acid or SiO ₂ is applied to the alignment layer 125a or 125b and then rubbed. Is performed. 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 in the R2 (or R1) direction while the region I is blocked with a mask is performed. Determine different orientations in the area. Even in this case, it is also possible to carry out the above method for each region continuously and apply it to the multidomain.

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 1 shows the change in the contrast ratio (C / R) when the polarization axis direction (the extension direction of the common electrode and / or 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 1, the applicable θ value is 0 ° ≤θ≤5 ° and the black luminance is unchanged when θ is 0 to 2 °, but when θ is 0 to 1 °, the rotation direction of the liquid crystal is out of shift. (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.

The transverse electric field liquid crystal display device according to the present invention forms an alignment film having a small anchoring energy on a substrate on which a pair of electrodes applying a transverse electric field is formed, thereby securing a sufficient distance between the electrodes biased to the substrate, thereby preventing crosstalk and residual image. It is possible to increase the light transmittance along with the decrease, and to lower the driving voltage of the liquid crystal layer.

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.

Claims (11)

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 alignment regions; A pair of electrodes formed on the first substrate and applying a transverse electric field to the liquid crystal layer, And the angle θ of the long axis of the liquid crystal present in the unit alignment region and the adjacent alignment region in the liquid crystal layer and the extending direction of the pair of electrodes is 0 ° ≦ θ ≦ 5 °. The transverse electric field liquid crystal display device according to claim 1, wherein θ is 2 ° ≦ θ ≦ 3 °. 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 transverse electric field liquid crystal display device further comprising a first alignment layer formed on the first substrate. The transverse electric field liquid crystal display device according to claim 1, wherein the pair of electrodes are a common electrode and a data electrode. The transverse electric field liquid crystal display device according to claim 1 or 4, 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, A transverse electric field liquid crystal display device further comprising a second alignment film formed on the second substrate. The transverse electric field liquid crystal display device according to claim 3 or 6, wherein at least one of the first alignment layer and the second alignment layer is an alignment layer having a small anchoring energy. The transverse electric field liquid crystal display device according to claim 7, wherein the anchoring energy is 10 ⁻³ erg / cm ² or less. 8. The transverse electric field liquid crystal display device according to claim 7, wherein the alignment film having a small anchoring energy is an optical alignment film. 10. The transverse electric field method according to claim 9, wherein the material constituting the optical alignment layer is selected from the group consisting of polysiloxanecinnamate, polyvinylcinnamate, and cellulosecinnamate. Liquid crystal display device. According to claim 3 or 6, wherein the material constituting at least 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 selected from the group consisting of a transverse electric field type liquid crystal display device.