KR100289652B1 - Reflective Liquid Crystal Display - Google Patents

Abstract

The present invention discloses a reflective liquid crystal display device for improving hysteresis and improving response speed. The present invention discloses an upper and lower substrates opposed to each other at a predetermined distance and provided with electrodes on respective inner surfaces thereof; A liquid crystal layer including several liquid crystal molecules interposed between the upper and lower substrates; A vertical alignment layer interposed between the liquid crystal layer and a surface of the substrate provided with an electrode; A polarizer disposed on an outer surface of the upper substrate; A quarter-wave plate disposed between the upper substrate and the single orphan plate; And a reflecting plate disposed on an outer surface of the daily substrate, wherein the phase retardation value (refraction of the liquid crystal molecules by the product of the anisotropy and the thickness of the liquid crystal layer) of the liquid crystal layer is λ / 4 (λ is the wavelength of the light source), The liquid crystal molecules in the liquid crystal layer are characterized by negative dielectric anisotropy.

Description

Reflective Liquid Crystal Display

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display, and more particularly, to a reflective liquid crystal display capable of improving response speed while preventing hysteresis of the liquid crystal display.

In general, the reflective liquid crystal display does not require a separate light source, and uses natural light.

In the reflective liquid crystal display, when natural light is incident from the upper substrate, light is reflected again through the pixel electrode. At this time, light is absorbed or passed according to the arrangement state of the liquid crystal molecules.

In the conventional reflective liquid crystal display, as shown in FIG. 1, the lower substrates 1 and 5 are disposed to face each other. The thin film transistor TFT formed by a well-known technique is provided in the upper part of the lower substrate 1, and the organic insulating film 2 is formed on the lower substrate 1 provided with the thin film transistor TFT. In the organic insulating layer 2, a contact hole is formed to expose a predetermined portion of the thin film transistor TFT, that is, a source electrode, and is formed on the organic insulating layer 2 so as to contact the exposed thin film transistor TFT through the contact hole. The pixel electrode 3 is formed.

In this case, in the reflective liquid crystal display, the pixel electrode 3 is made of an aluminum metal film having excellent interface reflection characteristics. Even if the pixel electrode 3 is formed of an opaque metal film, it only serves as a reflection, and thus has no relation to the aperture ratio of the liquid crystal display.

The black matrix 6 is formed on the inner surface of the upper substrate 5 and corresponding to the thin film transistor TFT, and the color pixels 7 are formed on both sides of the black matrix 6. The common electrode 8 is formed on the surfaces of the black matrix 6 and the color pixels 7.

Although not shown in the drawings, horizontal alignment films are provided on the inner surface of the upper and lower substrates 1 and 5, respectively, and the vertical alignment films are rubbed in a direction crossing each other.

The liquid crystal layer 9 is interposed between the upper and lower substrates 1 and 5. Here, the liquid crystal layer 9 includes a nematic liquid crystal molecule 9a containing a chiral dopant and a dye 9b for selectively absorbing and blocking incident light. At this time, as the dye 9b is known, light is absorbed when the light passes the long axis of the dye 9b, and light passes through the short axis.

Here, in the conventional reflective liquid crystal display device, in order to improve the reflection angle of light, a topology is artificially formed on the surface of the organic insulating film 2.

However, the conventional reflective liquid crystal display device is a hysteresis phenomenon in which the transmittance in the rising atmosphere is different from the transmittance in the falling atmosphere even with the same voltage by inserting a dye material that selectively transmits or blocks light in the liquid crystal. Is generated. This affects the image quality.

In addition, in the conventional reflective liquid crystal display device, since the dyeing material must be injected into the liquid crystal, the process is complicated.

In addition, since a conventional reflective liquid crystal display device generally has a twisted nematic (TN) structure, the response time is not excellent.

Accordingly, an object of the present invention has been made to solve the above-mentioned conventional problems, and aims to prevent the hysteresis phenomenon by excluding the dye injection, and to simplify the manufacturing and improve the response time.

1 is a cross-sectional view of a conventional reflective liquid crystal display device.

2 is a cross-sectional view of a reflective liquid crystal display device according to an exemplary embodiment of the present invention.

3A to 3F illustrate polarization states when no electric field is formed in the reflective liquid crystal display of the present invention.

4A to 4D are diagrams showing polarization states when an electric field is formed in the reflective liquid crystal display of the present invention.

(Explanation of symbols for the main parts of the drawing)

10 lower substrate 12 gate insulating film

13: thin film transistor 14: organic insulating film

15 contact hole 16 pixel electrode

17: first vertical alignment layer 20: upper substrate

22 counter electrode 24 second vertical alignment layer

26: polarizer 28: quarter-wave plate

30: liquid crystal layer 30a: liquid crystal molecules

In order to achieve the above object of the present invention, according to an embodiment of the present invention, opposed to each other at a predetermined distance, the upper and lower substrates provided with electrodes on each inner surface; A liquid crystal layer including several liquid crystal molecules interposed between the upper and lower substrates; A vertical alignment layer interposed between the liquid crystal layer and a surface of the substrate provided with an electrode; A polarizer disposed on an outer surface of the upper substrate;

A quarter-wave plate disposed between the upper substrate and the polarizer; And a reflector disposed on an outer surface of the lower substrate.

The phase retardation value (the product of the refractive index anisotropy of the liquid crystal molecules and the thickness of the liquid crystal layer) of the liquid crystal layer is λ / 4 (λ is the wavelength of the light source), and the liquid crystal molecules in the liquid crystal layer are characterized in that the dielectric anisotropy is negative.

(Example)

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

2 is a cross-sectional view of a reflective liquid crystal display device according to an exemplary embodiment of the present invention, and FIGS. 3A to 3F are views illustrating polarization states when no electric field is formed in the reflective liquid crystal display device of the present invention. 4A to 4D illustrate polarization states when an electric field is formed in the reflective liquid crystal display of the present invention.

Referring to FIG. 2, the lower substrate 10 and the upper substrate 20 face each other with the liquid crystal layer 30 including several liquid crystal molecules 30a interposed therebetween. The lower substrate 10 and the upper substrate 20 are transparent insulating substrates. The liquid crystal 30 is one in which the product of the distance between the upper and lower substrates (hereinafter, referred to as a cell gap: d) and the refractive index anisotropy (Δn) of the liquid crystal can be λ / 4. That is, in the present embodiment, the liquid crystal 30 serves to delay the phase of incident light by 90 °. In addition, the liquid crystal 30 in the present embodiment does not include a dyeing material as in the prior art, and a material having negative dielectric anisotropy is used.

On the inner side of the lower substrate 10, one thin film transistor 13 including the gate insulating layer 12 is formed for each unit pixel. The organic insulating layer 14 is formed on the thin film transistor 13. In this case, irregularities are formed on the surface of the organic insulating layer 14 to improve the reflectance of the liquid crystal display, and the organic insulating layer 14 is used to expose the drain electrode (or source electrode) portion of the thin film transistor 13. The contact hole 15 is provided. The pixel electrode 16 is formed on the organic insulating layer 14 and is contacted with the drain electrode (or source electrode) of the thin film transistor through the contact hole 15. At this time, the pixel electrode 16 is formed on the surface of the organic insulating layer 14. Under the influence of the unevenness, the surface thereof also has unevenness, thereby increasing the reflection efficiency of light A first vertical alignment layer 17 is formed on the pixel electrode 16.

The outer surface of the lower substrate 10 is provided with a reflector 18 for reflecting light incident from the upper substrate 20 again.

On the other hand, the counter electrode 22 is disposed on the inner surface of the upper substrate 20 facing the lower substrate 10, and the second vertical alignment layer 24 is formed on the surface of the counter electrode 22. At this time, a color pixel (not shown) is interposed between the inner surface of the upper substrate 20 and the counter electrode 22, as is known.

A polarizer 26 for linearly polarizing natural light is disposed on the outer surface of the upper substrate 20, and a phase difference (phase retardation) of λ / 4 is generated between the polarizer 26 and the outer surface of the upper substrate 20. Half-wave plate 28 is interposed.

In the liquid crystal display, when an electric field is formed between the pixel electrode 16 and the counter electrode 22, as shown in the “ON” state of FIG. 2, the liquid crystal molecules 30a of the dielectric anisotropy have a long axis perpendicular to the electric field. It is tufted.

Natural light is then linearly polarized by the polarizer 26, as shown in FIG. 3A. Here, in FIG. 3A, the light passing through the polarizer 26 has the same horizontal component as the vertical component, the traveling direction of the polarized light is called the Z-axis, and the light passing through the polarizer 26 is called right linearly polarized light. The state of X component and Y component show the same phase.

When an electric field is applied, the light polarized linearly by the polarizer 26 changes its polarization state while passing through the quarter-wave plate 28. That is, the quarter-wave plate 75 generates a phase difference of 90 °, that is, one quarter of the period (for example, 360 °) in the normal path and the abnormal path. Accordingly, the linearly polarized light passes through the quarter wave plate 28 and is left circularly polarized as shown in FIG. 3B.

The light passing through the quarter-wave plate 28 passes through the liquid crystal layer 30, and the phase retardation occurs by 90 ° again. At this time, since the liquid crystal layer 30 demonstrates the phase by λ / 4, as described above, the circularly polarized light is linearly polarized on the left side as shown in FIG. 3C. At this time, the light passing through the liquid crystal layer 30 (see FIG. 3C) has a 90 ° phase difference from the linearly polarized light passing through the initial polarizer 26 (see FIG. 3A).

The light passing through the liquid crystal 30 passes through the reflecting plate 18 and becomes left linearly polarized light, as shown in FIG. 3D.

Thereafter, the light passing through the liquid crystal layer 30 is reflected by the reflecting plate 18 by 180 degrees to become left linearly polarized light, as shown in FIG. 3D. After that, the left linearly polarized light reflected by the reflector 18 is again passed through the liquid crystal layer 30, and the phase delay is generated again, and as shown in FIG. 3E, the right circularly polarized light. Subsequently, the light passing through the liquid crystal layer 30 passes through the quarter-wave plate 28 again, whereby a phase difference is generated by λ / 4 again, and as shown in FIG. 3, right linearly polarized light. Accordingly, the light passing through the quarter-wave plate 28 coincides with the polarization axis of the polarizer 26, so that the screen passes through the polarizer 28 to become white.

Subsequently, light passing through the liquid crystal 30 passes through the quarter wave plate 28 again, and a 90 ° phase difference is generated. As shown in FIG. 3F, the linearly polarized light is right-polarized, and the right linearly polarized light is polarizer 26. ) Is reached. At this time, since the polarization axis of the polarizer 28 and the right linearly polarized light (FIG. 3F) are parallel, the light passes through the polarizer 28 and the screen becomes white.

On the other hand, if no electric field is formed between the pixel electrode 16 and the counter electrode 22, the molecules 30a in the liquid crystal 30 are vertically aligned films 17 and 24, as shown in " OFF " The long axis and the substrate surface are arranged vertically under the influence of Accordingly, natural light is linearly polarized right through the polarizer 26, as shown in FIG. 4A, and circularly polarized to the left, as shown in FIG. 4B while passing through the half-wave plate 28. FIG.

Then, the left circularly polarized light through the quarter-wave plate 28 passes through the liquid crystal 30, in which the polarization state is not changed. That is, the polarization state does not change while the light passes through the long axis of the liquid crystal molecule 30a so that the liquid crystal molecules 30a uniformly form a long axis with the surface of the substrate. Therefore, the circularly polarized state of FIG. 4B is maintained.

Thereafter, the left circularly polarized reflected light passes through the liquid crystal layer 30 again, and the polarization state is not changed. The left circularly polarized reflected light passing through the liquid crystal layer 30 passes through the quarter reflection wavelength plate 28 and generates a phase difference of λ / 4, resulting in left linearly polarized light, as shown in FIG. 4D. Accordingly, the screen becomes dark by being perpendicular to the polarization axis of the polarizer 26.

Accordingly, by adjusting the phase delay value of the liquid crystal layer 30, the display can be realized without a chromosome. In addition, since only one type of liquid crystal molecules are present in the liquid crystal layer 30, a uniform transmittance may be obtained in an atmosphere of increasing and decreasing transmittance. Therefore, problems such as hysteresis can be solved.

As described in detail above, according to the present invention, in the reflection type liquid crystal display device, the phase retardation value of the liquid crystal layer is set to be λ / 4 so that display can be performed without using a dye. In addition, since only a single liquid crystal molecule in the liquid crystal layer is provided, hysteresis can be prevented. Therefore, the image quality is improved.

In addition, by adopting a vertical alignment mode having excellent response characteristics, the response speed of the reflective liquid crystal display device is further improved.

In addition, this invention can be implemented in various changes within the range which does not deviate from the summary.

Claims (2)

An upper and lower substrates facing each other at a predetermined distance and provided with electrodes on respective inner surfaces thereof; A liquid crystal layer including several liquid crystal molecules interposed between the upper and lower substrates; A vertical alignment layer interposed between the liquid crystal layer and a surface of the substrate provided with an electrode; A polarizer disposed on an outer surface of the upper substrate; A quarter-wave plate disposed between the upper substrate and the polarizer; And A reflection plate disposed on an outer surface of the lower substrate, The phase retardation value (the refraction of the liquid crystal molecules by the product of the anisotropy and the thickness of the liquid crystal layer) of the liquid crystal layer is λ / 4 (λ is the wavelength of the light source), The liquid crystal molecule of the liquid crystal layer is a reflection type liquid crystal display, characterized in that the dielectric anisotropy is negative. The reflective liquid crystal display device according to claim 1, wherein an electrode surface formed on the lower substrate has irregularities.