KR101117988B1 - Trans-flective Type Liquid Crystal Display Device - Google Patents

Abstract

The present invention relates to a semi-transmissive liquid crystal display device which is intended to reduce the cost by eliminating the compensation film to improve optical performance such as contrast, viewing angle, etc. in the transmission part, and to use no compensation film. A gate wiring and a data wiring defining a pixel region composed of a reflecting portion and a transmitting portion vertically intersecting on a substrate, a thin film transistor formed at an intersection thereof, an organic insulating film formed at a reflecting portion of the pixel region, and the organic A reflective electrode formed on the insulating film and connected to the thin film transistor, a pixel electrode formed on the transmissive part of the pixel region, an insulating layer formed to cover the reflective electrode and the pixel electrode, and the insulating layer interposed between the insulating layer. The reflective layer is formed on the reflective electrode, and the insulating layer is interposed between the insulating layers. A common electrode parallel to the pixel electrode, a first alignment layer formed on the first substrate including the common electrode, and having a different orientation direction of the reflecting portion and an orientation direction of the transmission portion, and oppositely bonded to the first substrate. And a second substrate having a second alignment film having the same alignment direction with respect to the entire surface, and a first transverse electric field formed between the first electrode and the second substrate, and formed between the pixel electrode and the common electrode in the transmission part. Driven by a second transverse electric field formed between the reflective electrode and the common electrode, and the first and second polarizations respectively attached to outer surfaces of the first and second substrates. It includes a film.

Transflective, transverse electric field, compensation film

Description

Transflective Type Liquid Crystal Display Device

1 is a cross-sectional view of a transflective liquid crystal display device according to the prior art.

2 is a cross-sectional view of a transflective liquid crystal display device according to the present invention;

Figure 3 is a graph showing the reflectance with respect to the wavelength of the transflective liquid crystal display device according to the present invention.

4A to 4C are cross-sectional views of an alignment film processing process according to the first embodiment of the present invention.

5A to 5C are cross-sectional views of an alignment film processing process according to a second embodiment of the present invention.

* Explanation of symbols on the main parts of the drawings

111 TFT array substrate 116 insulating layer

117: pixel electrode 118: organic insulating film

120: reflective electrode 121: color filter array substrate

124: common electrode 131: liquid crystal layer

150, 151: first and second polarizing films 160, 161: first and second alignment films

180: rubbing roll

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a semi-transmissive liquid crystal display device which is intended to reduce the cost by removing the compensation film to improve the performance of contrast, viewing angle, etc. in the transmission part, and to reduce the cost by not using the compensation film. It is about.

Recently, the liquid crystal display device, one of the flat panel display devices that are attracting attention, is an element that changes the optical anisotropy by applying an electric field to a liquid crystal that combines the liquidity and the optical properties of the crystal, which is applied to a conventional cathode ray tube. Compared with its low power consumption, small volume, large size, and high definition, it is widely used.

The liquid crystal display device has a structure in which a color filter array substrate as an upper substrate and a thin film transistor (TFT) array substrate as a lower substrate are disposed to face each other, and a liquid crystal having dielectric anisotropy is formed therebetween. Is driven by switching a TFT added to hundreds of thousands of pixels through a pixel selection address wiring to apply a voltage to the pixel.

The liquid crystal display device has a variety of different modes depending on the nature of the liquid crystal and the structure of the pattern.

Specifically, the TN mode (Twisted Nematic Mode) for arranging the liquid crystal directors to be twisted by 90 ° and then applying a voltage to the liquid crystal directors, and dividing one pixel into several domains to change the viewing angle of each domain to change the wide viewing angle. Multi-domain mode to implement, OCB mode (Optically Compensated Birefringence Mode) to compensate the phase change of light according to the direction of light by attaching a compensation film to the substrate, and two on one substrate In various embodiments, an electrode may be formed so that the director of the liquid crystal is twisted in a parallel plane of the alignment layer, such as an in-plane switching mode.

Meanwhile, the liquid crystal display device includes a transmissive liquid crystal display device using a backlight as a light source, a reflective liquid crystal display device using external natural light without using the backlight as a light source, and a transmissive liquid crystal display device with high power consumption due to the backlight. It can be classified into a semi-transmissive liquid crystal display device for overcoming the disadvantages and disadvantages of the reflective liquid crystal display device that cannot be used when the external natural light is dark.

Since the transflective liquid crystal display device has a reflective part and a transmissive part at the same time inside the unit pixel, both the transmissive type and the transmissive type can be used as necessary.

Here, the transmissive part of the transmissive and transflective liquid crystal display elements emits light from the backlight incident through the lower substrate into the liquid crystal layer to brighten the brightness, and the reflector of the reflective and transflective liquid crystal display devices is upper when the external natural light is bright. The luminance is brightened by reflecting external light incident through the substrate.

Hereinafter, a transflective liquid crystal display device will be described with reference to the accompanying drawings.

1 is a plan view of a transflective liquid crystal display device according to the prior art.

A semi-transmissive liquid crystal display device in which one pixel region is divided into a reflecting portion R and a transmitting portion T includes a thin film transistor array substrate having a plurality of wirings and a thin film transistor, and a color opposing the thin film transistor array substrate. As shown in FIG. 1, a liquid crystal layer is formed between the thin film transistor array substrate and the color filter array substrate, and the reflector R is disposed on the lower surface of the liquid crystal layer. The reflective electrode 590 is formed to reflect external natural light to the outside.

Specifically, natural light incident from the outside to the reflective part R reaches the screen surface by reciprocating the liquid crystal layer 531 from the top, and light incident to the transmissive part T from the backlight passes through the liquid crystal layer to the screen surface. To reach.

For reference, an alignment layer for arranging molecules of the liquid crystal layer 531 in a predetermined direction is further provided on inner surfaces of the thin film transistor array substrate and the color filter array substrate, and on the outer surface of the substrate for adjusting the optical axis of light. Polarizing films 550 and 551 are further provided.

Further, QWP (Quarter Wave Plate) films 562 and 563 are further provided between the liquid crystal layer 531 and the polarizing films 550 and 551 to delay the phase difference.

However, when only the QWP film is used, as shown in ② of FIG. 3, it can be seen that the reflectance is changed with respect to the wavelength. When the colors of R, G, and B are reflected, the reflectances are different from each other, resulting in poor image quality. Means that.

In order to prevent this, there is further provided a half wave plate (HWP) film (561,564) between the polarizing film (550,551) and the QWP film (562,563) to have the effect arranged by the wideband QWP, thereby uniformizing the entire wavelength of visible light It shows a reflectance. As described above, in the case of the transflective liquid crystal display device, a polarizing film, a compensation film (QWP, HWP), a liquid crystal layer, a compensation film (HWP, QWP), it is generally composed of a laminated structure of the polarizing film.

However, the transflective liquid crystal display device according to the prior art has the following problems.

That is, in the case of a semi-transmissive liquid crystal display device having a laminated structure of a polarizing film, a compensation film (QWP, HWP), a liquid crystal layer, a compensation film (HWP, QWP), and a polarizing film, the light of the transmissive part T is compensated for. Since passing through the sheet, the image quality deterioration occurs in the contrast, viewing angle, etc. Another problem occurs that the price increases and the thickness of the device increases with the use of the compensation film.

Accordingly, the present invention has been made in order to solve the above problems, by eliminating the compensation film to improve the performance of the contrast, viewing angle, etc. in the transmission portion, and to reduce the cost by using a compensation film without a transflective liquid crystal display device The purpose is to provide.

A semi-transmissive liquid crystal display device of the present invention for achieving the above object is a gate wiring and data wiring defining a pixel region consisting of a reflecting portion and a transmissive portion vertically intersecting on the first substrate, and a thin film formed at the intersection thereof A transistor, an organic insulating film and a reflective electrode formed in the reflective portion of the pixel region, a first electrode formed in the transmissive portion of the pixel region, and insulated from the reflective electrode and the first electrode, and the upper portion of the reflective electrode in the reflective portion A second electrode formed in the transmissive portion and parallel to the first electrode, a first alignment film formed on the first substrate and having a different orientation direction of the reflecting portion and an orientation direction of the transmissive portion, and oppositely bonded to the first substrate; A second substrate having a second orientation having the same orientation with respect to the entire surface, a liquid crystal layer formed between the first and second substrates, And first and second polarizing films attached to the first and second substrate outer surfaces, respectively.

The transflective liquid crystal display device according to the present invention is characterized in that the alignment direction of the reflecting portion R and the transmitting portion T of the lower substrate is different, and the liquid crystal molecules are twisted in the horizontal direction by a transverse electric field. .

Hereinafter, the transflective liquid crystal display device according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a cross-sectional view of a transflective liquid crystal display device according to the present invention, and FIG. 3 is a graph showing reflectance with respect to the wavelength of the transflective liquid crystal display device according to the present invention. 4A to 4C are cross-sectional views of the alignment film processing process according to the first embodiment of the present invention, and FIGS. 5A to 5C are cross-sectional views of the alignment film processing process according to the second embodiment of the present invention.

As shown in FIG. 2, the transflective liquid crystal display device according to the present invention includes a TFT array substrate 111 having a first alignment layer 160 having different alignment directions between the reflection portion and the transmission portion, and the reflection portion and the transmission portion. The color filter array substrate 121 having the second alignment layer 161 having the same alignment direction is formed to be opposed to each other, and the liquid crystal layer 131 is provided between the two substrates 111 and 121, and the first substrate is disposed on the outer surfaces of the two substrates. Second polarizing films 150 and 151 are attached, respectively.

At this time, the compensation film is not provided between the substrate and the polarizing film, the alignment direction of the second alignment layer 161 is to be parallel or perpendicular to the transmission axis of the second polarizing film 151, the first alignment layer The transmissive part alignment direction of 160 may be the same as that of the second alignment layer 161, and the reflector alignment direction of the first alignment layer 160 may be twisted 60 to 80 °. In this case, a black condition is established in the Voff state, thereby entering a normally black mode.

That is, when the transmission axis of the second polarizing film 151 is configured in the 0 ° direction, the transmission axis of the first polarizing film 150 is configured in the 90 ° direction to be perpendicular to the transmission axis of the upper polarizing film, 2 The liquid crystal molecules 130 on the alignment layer 161 and the surface of the first alignment layer 160 of the transmissive portion are aligned in the 0 ° direction, and the liquid crystal molecules 130 on the surface of the first alignment layer 160 of the reflecting portion are in the 60 to 80 ° direction. Is oriented. A small amount of dopant may be added to the liquid crystal layer to determine the twist direction of the liquid crystal molecules.

In the liquid crystal display device having such a configuration, the retardation value of the reflecting portion is 150 to 250 nm and the retardation value of the transmitting portion is 260 to 360 nm. In order to adjust the retardation value, the cell gap of the liquid crystal layer or the physical properties of the liquid crystal Can change. However, it is easy to change the liquid crystal cell gaps d1 and d2 in order to change the retardation value of the reflecting part and the transmitting part. The organic insulating film 118 is further provided in the reflecting part to adjust the liquid crystal cell gap of the reflecting part.

Specifically, as illustrated in FIG. 2, the TFT array substrate 111 includes a gate wiring (not shown) and a data wiring 115 that vertically cross a unit pixel region, and the gate wiring and the data wiring. A thin film transistor (TFT) (not shown) formed at an intersection point, an organic insulating film 118 formed to be limited to the reflecting portion R to influence the cell gap d2 of the reflecting portion, and the organic material of the reflecting portion R A reflective electrode 120 formed on the insulating film 118 and contacting the drain electrode of the thin film transistor TFT, a pixel electrode 117 formed in the transmission part T and contacting the drain electrode of the thin film transistor; A plurality of common electrodes 124 are formed in a predetermined area above the reflective electrode in the reflector R and are formed in parallel to the pixel electrode in the transmissive part T, and are common from the reflective electrode 120 and the pixel electrode 117. Insulating layer 1 for insulating electrode 124 16) and a first alignment layer 160 which is subjected to an alignment process so that the alignment direction of the reflecting portion and the alignment direction of the transmitting portion are different from each other.

In this case, the pixel electrode 117 is integrally formed on the same layer as the reflective electrode 120 to receive the same voltage. As described above, the pixel electrode is applied to the reflective electrode 120 and the pixel electrode 117. And a Vcom voltage is applied to the common electrode. Of course, by changing the positions of the pixel electrode and the common electrode and providing the pixel electrode on the reflective electrode, the Vcom voltage may be applied to the reflective electrode and the common electrode and the pixel voltage may be applied to the pixel electrode.

Here, the common electrode 124 is disposed to be parallel to the pixel electrode 117 in the transmission portion T of the pixel region to form a first transverse electric field, and the reflection electrode 120 in the reflection portion R of the pixel region. ) To form a second transverse electric field. The liquid crystal molecules of the transmissive portion are rearranged by the first transverse electric field to control the degree of light transmission of the transmissive portion, and the liquid crystal molecules of the reflective portion are rearranged by the second transverse electric field to control the degree of light transmission of the reflective portion.

That is, the transverse electric field type liquid crystal display device of the present invention operates in a transflective mode. When no external light source exists, the transverse electric field type liquid crystal display device is driven in the transmissive mode by a first transverse electric field between the pixel electrode of the transmissive part T and the common electrode. When an external light source is present, the light source is driven in the reflection mode by the second transverse electric field between the reflective electrode and the common electrode of the reflector R.

The color filter array substrate 121 facing and bonding to the TFT array substrate 111 is provided with a color filter layer (not shown) and a second alignment layer 161 oriented in one direction with respect to the entire surface.

The transflective property of the transflective liquid crystal display device configured as described above increases the transmittance while the liquid crystal molecules rotate horizontally, and the twist angle of the first alignment layer is 66 degrees and the retardation value is 200 nm. As a result of confirming ①), as shown in FIG. 3, the reflectance was uniform for all wavelengths compared to the case of using only the compensation film of QWP (②).

Therefore, the transflective liquid crystal display device to which the technical idea of the present invention is applied can exhibit the same effect as that of a wideband QWP without using a compensation film, and has the same all-optical characteristics as a transmissive IPS by not using a separate compensation film. do.

On the other hand, the present invention is characterized in that the orientation direction of the reflecting portion and the transmission portion is different with respect to the first alignment layer, the alignment process will be described in detail as follows. The alignment treatment is possible by light irradiation or rubbing. In the case of the first alignment layer, two alignment treatments are performed in order to change the alignment directions of the reflecting portion and the transmitting portion.

First, referring to the alignment of the first alignment layer using light irradiation, as shown in FIG. 4A, the photo-alignment polymer material is spin-coated on the upper surface of the TFT array substrate 111 on which the reflective electrode 120 is formed. (spin-coating) and roll-coating (coating) to form a first alignment layer 160, and as shown in Figure 4b, ultraviolet (UV: Ultra-Violet Ray) to the entire surface of the substrate Is irradiated and subjected to the first alignment treatment.

Thereafter, as shown in FIG. 4C, the substrate is exposed under the substrate 111 to perform a second alignment treatment with respect to the transmission part. During back exposure, the reflecting electrode of the reflecting portion shields light so that the alignment film of the reflecting portion is not irradiated with light. As light used for light irradiation, linearly polarized light, non-polarized light, partial polarized light, unpolarized light, deep UV, mid UV, or the like may be used.

As a result, the alignment directions of the first alignment film of the reflecting portion and the first alignment film of the transmissive portion are different from each other. Here, the first direction is a direction perpendicular or parallel to the transmission axis of the first polarizing film and the second direction is a direction twisted 60 to 80 ° with respect to the transmission axis of the first polarizing film.

On the other hand, the orientation treatment using the rubbing roll is as follows.

First, as shown in FIG. 5A, the alignment layer raw material solution is printed on the upper surface of the TFT array substrate 111 on which the reflective electrode 120 is formed to form the first alignment layer 160, and then the rubbing roll 180 is used. To rub in the first direction.

As shown in FIG. 5B, the photoresist 190 is coated on the entire surface of the first alignment layer 160 which is rubbed in the first direction, and is exposed under the substrate 111 to develop the exposed photoresist. Pattern. At this time, since the reflective electrode 120 shields the UV light, the photoresist of the reflecting portion not irradiated with light is removed and only the photoresist of the transmissive portion remains.

Thereafter, as illustrated in FIG. 5C, a rubbing process is performed on the first alignment layer 160 of the reflector in the second direction. As a result, the alignment directions of the first alignment film of the reflecting portion and the first alignment film of the transmissive portion are different from each other. Here, the first direction is a direction perpendicular or parallel to the transmission axis of the first polarizing film and the second direction is a direction twisted 60 to 80 ° with respect to the transmission axis of the first polarizing film. Of course, depending on the nature of the photoresist, the photoresist of the portion to which light is irradiated may remain. In this case, the first rubbing direction is twisted 60 to 80 ° and the second rubbing direction is perpendicular to the transmission axis of the first polarizing film. It may be parallel.

As described above, in the present invention, the liquid crystal alignment direction of the upper substrate is made constant and the reflection and transmissive portions of the lower substrate are different, and the liquid crystal molecules are horizontally twisted by an electric field so that the compensation film is not provided separately. It is characterized by forming an element that satisfies the conditions of the wideband QWP. At this time, the initial liquid crystal alignment direction of the reflector is 60 to 80 degrees twisted and the retardation value of the reflector is 150 to 250nm as described above.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

The transflective liquid crystal display device according to the present invention as described above has the following effects.

First, since the transflective liquid crystal display device according to the present invention does not use a separate compensation film, it is possible to prevent the optical performance of the transmissive part from being degraded by the compensation film, and thus have the same all-optical characteristics as the transmissive IPS.

Second, the transflective liquid crystal display device according to the present invention can exhibit the same effect as the wide band QWP without using the compensation film, compared to the conventional four compensation films used to satisfy the wide band QWP condition. The process cost can be reduced, and the problem of thickening of the device by the compensation film can be solved.

Claims (14)

A gate wiring and a data wiring defining a pixel region composed of a reflecting portion and a transmitting portion vertically crossing the first substrate, a thin film transistor formed at an intersection thereof; An organic insulating film formed on the reflecting portion of the pixel region; A reflective electrode formed on the organic insulating film and connected to the thin film transistor; A pixel electrode formed in the transmissive portion of the pixel region; An insulating layer formed to cover the reflective electrode and the pixel electrode; A common electrode formed on the reflective electrode with the insulating layer interposed therebetween in the reflective part and parallel to the pixel electrode with the insulating layer interposed therebetween; A first alignment layer formed on the first substrate including the common electrode and different from each other in an alignment direction of the reflection unit and an alignment direction of the transmission unit; A second substrate opposite to the first substrate and provided with a second alignment film having the same alignment direction with respect to the front surface; A second formed between the first and second substrates and driven by a first transverse electric field formed between the pixel electrode and the common electrode in the transmissive part, and formed between the reflective electrode and the common electrode in the reflective part; A liquid crystal layer driven by a transverse electric field, And a first polarizing film and a second polarizing film respectively attached to the outer surfaces of the first and second substrates. The method of claim 1, A semi-transmissive liquid crystal display device, characterized in that the retardation value of the reflecting portion and the transmitting portion is adjusted by the step of the organic insulating film. The method of claim 2, The liquid crystal layer retardation value of the said reflection part is 150-250 nm, The liquid crystal layer retardation value of the transmissive part is 260-360 nm, The transflective liquid crystal display element characterized by the above-mentioned. delete The method of claim 1, And a pixel voltage is applied to the reflective electrode and the pixel electrode, and a Vcom voltage is applied to the common electrode. delete The method of claim 1, A transflective liquid crystal display device, characterized in that the transmission axis of the first polarizing film and the second polarizing film are perpendicular to each other. The method of claim 1, The transmissive part orientation direction of the first alignment layer and the orientation direction of the second alignment layer are configured to be parallel or perpendicular to the transmission axis of the second polarizing film, and the reflector alignment direction of the first alignment layer is configured to be twisted 60 to 80 °. A transflective liquid crystal display device characterized by the above-mentioned. The method of claim 1, The polarization axis of the first polarizing film is disposed to be 90 °, The polarization axis of the second polarizing film is disposed to be 0 °, The second alignment layer and the first alignment layer of the transmission portion are aligned in the 0 ° direction, A semi-transmissive liquid crystal display device, wherein the surface of the first alignment layer of the reflector is aligned in a 60 to 80 ° direction. The method of claim 1, The polarization axis of the first polarizing film is disposed to be 90 °, The polarization axis of the second polarizing film is disposed to be 0 °, The second alignment layer and the first alignment layer of the transmission portion are aligned in a 90 ° direction, A semi-transmissive liquid crystal display device, wherein the surface of the first alignment layer of the reflector is aligned in a 60 to 80 ° direction. The method of claim 1, The transflective liquid crystal display device is a transflective liquid crystal display device, characterized in that the normally black mode (Normally Black Mode). The method of claim 1, And the first alignment layer is aligned in two directions by light irradiation or rubbing. 13. The method of claim 12, And the first alignment layer is photo-aligned by back light irradiation using the reflective electrode as a mask after front light irradiation. 13. The method of claim 12, And the first alignment layer is aligned by a partial rubbing treatment using a photoresist pattern as a mask after the entire surface rubbing treatment.

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