KR20040093514A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: An LCD(Liquid Crystal Display) is provided to improve display characteristic. CONSTITUTION: An LCD includes the first and second substrates(100,200), a liquid crystal layer(300) formed between the first and second substrates, and an insulating thin film(240). The first substrate includes a transmission electrode(140) and a reflection electrode(150) having a window(151) exposing a part of the transmission electrode to define a reflection area(RA) and a transmission area(TA). The second substrate includes a color filter layer(220) and a common electrode(230) coated on the color filter layer in a uniform thickness. The color filter layer has the first thickness in the reflection area and the second thickness thicker than the first thickness in the transmission area. The first and second substrates are combined with each other. The insulating thin film is interposed between the first and second substrates in the reflection area and has dielectric index different from the dielectric index of the liquid crystal layer.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of improving display characteristics.

The transflective liquid crystal display displays an image in a reflection mode using the first light where the external light amount is abundant, and in the transmissive mode using the second light generated by consuming the electric energy charged therein when the external light amount is insufficient. Display the image.

The transflective liquid crystal display device includes a liquid crystal display panel including a thin film transistor (hereinafter, referred to as a thin film transistor), a color filter substrate facing the TFT substrate, and a liquid crystal layer interposed between the TFT substrate and the color filter substrate.

The TFT substrate has a TFT, a transparent electrode connected to the drain electrode of the TFT, and a reflective electrode. Here, the region in which the reflective electrode is formed on the transparent electrode is a reflection region, and the region in which the reflective electrode is not formed on the transparent electrode is a transmission region.

An organic insulating film in which a contact hole for exposing a drain electrode is formed between the TFT and the transparent electrode. Therefore, the transparent electrode is electrically connected to the transparent electrode and the drain electrode through the contact hole.

In general, the transflective liquid crystal display device drives a cell gap in the reflection region and a cell gap in the transmission region differently in order to improve light efficiency in the reflection mode and the transmission mode. In other words, the cell gap of the reflection area is made half of the cell gap of the transmission area. Such a transflective liquid crystal display device having a double cell gap is implemented by controlling the thickness of the organic insulating film provided in the TFT substrate.

However, since the thickness of the organic insulating layer is adjusted to form a double cell gap, it is difficult to secure the uniformity of the cell gap because the thickness of the organic insulating layer cannot be precisely controlled due to the process characteristics. Therefore, productivity of the transflective liquid crystal display device falls.

It is therefore an object of the present invention to provide a liquid crystal display device for improving display characteristics.

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

2 is a graph illustrating changes in transmittance and reflectance according to voltages applied to the transmission electrode and the reflection electrode.

3A to 3C are views illustrating a manufacturing process of the color filter substrate shown in FIG. 1 in detail.

4 is a cross-sectional view of a transflective liquid crystal display according to another exemplary embodiment of the present invention.

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

100 TFT substrate 120 TFT

130: organic insulating film 140: transmission electrode

150: reflective electrode 200: color filter substrate

220: color filter layer 230: common electrode

240, 160: insulating thin film 300: liquid crystal layer

400, 500: transflective liquid crystal display

The liquid crystal display according to the present invention for achieving the above object includes a first substrate, a second substrate, a liquid crystal layer of the first substrate and the second substrate and an insulating thin film.

The first substrate consists of a reflective electrode having a transmissive electrode and a transmissive window that opens a portion of the transmissive electrode to define a reflective region and a transmissive region.

The second substrate includes a color filter layer having a first thickness in the reflective region and having a second thickness greater than the first thickness in the transmissive region, and a common electrode provided on the color filter layer with a uniform thickness. Coupling against the first substrate.

The insulating thin film is interposed between the first substrate and the second substrate in the reflective region, and has a dielectric constant different from that of the liquid crystal layer.

According to the liquid crystal display device, the insulating thin film having a dielectric constant larger than that of the liquid crystal layer is provided only in the reflection region, thereby improving the reflection efficiency and the transmission efficiency of the liquid crystal display device, respectively.

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

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

Referring to FIG. 1, a transflective liquid crystal display device 400 according to an exemplary embodiment of the present invention may include a TFT substrate 100, a color filter substrate 200 and a TFT substrate 100 facing each other. The liquid crystal layer 300 is interposed between the 100 and the color filter substrate 200.

The TFT substrate 100 is a substrate having a plurality of TFTs 120, a transmission electrode 140, and a reflection electrode 150 on the first insulating substrate 110. The TFT 100 including the gate electrode 121, the source electrode 125, and the drain electrode 126 is formed on the first insulating substrate 110. An organic insulating layer 130 having a contact hole 131 for exposing the drain electrode 126 is formed on the TFT 120. The organic insulating layer 130 is made of a photosensitive insulating material made of acrylic resin.

Here, a plurality of irregularities 133 are provided on the surface of the organic insulating layer 130. That is, the convex portion 133a and the relatively thin concave portion 133b having a relatively thick thickness of the organic insulating layer 130 appear repeatedly to have the plurality of irregularities 133.

Thereafter, the transmission electrode 140, which is in electrical contact with the drain electrode 126 through the contact hole 131, is stacked on the organic insulating layer 30 with a uniform thickness. The transmissive electrode 140 is made of indium tin oxide (ITO) or indium zinc oxide (IZO), which is a transparent conductive material.

Thereafter, the reflective electrode 150 having the transmission window 151 for exposing a portion of the transmission electrode 140 is stacked on the transmission electrode 140 with a uniform thickness. The reflective electrode may have a single layer made of aluminum-neodymium (AlNd) or a double layer structure in which aluminum-neodymium (AlNd) and molybdenum tungsten (MoW) are sequentially stacked.

As described above, the transflective liquid crystal display device 400 includes a reflection area RA provided with the reflective electrode 150 and a transmission area TA provided with the transmission window 151.

In the reflective area RA, the image is reflected by the reflective electrode 150 which reflects the first light L1 incident through the color filter substrate 200 and emits the light to the outside through the color filter substrate 200 again. Is displayed. Meanwhile, in the transmission area TA, an image is displayed by emitting the second light L2 incident from a light source unit (not shown) disposed on the rear surface of the TFT substrate 110 through the transmission window 151.

The color filter substrate 200 is a substrate on which the color filter layer 220, the common electrode 230, and the insulating thin film 240 are disposed on the second insulating substrate 210.

The color filter layer 220 made of R (Red), G (Green), and B (Blue) is provided on the second insulating substrate 210. The color filter layer 220 has a first thickness t1 in the reflection area RA and a second thickness t2 greater than the first thickness t1 in the transmission area TA. In general, the color filter layer 220 has a step of about 0.6 μm between the reflective area RA and the transmission area TA.

The common electrode 230 is stacked on the color filter layer 220 in a uniform thickness. The common electrode 230 is made of ITO or IZO, which is a transparent conductive material.

The insulating thin film 240 having a dielectric constant greater than that of the liquid crystal layer 300 is provided on the common electrode 230. In particular, the insulating thin film 240 is provided only in the reflective region RA. In this case, the thickness t3 of the insulating thin film 240 is equal to the step of the color filter layer 220 formed between the reflective area RA and the transmission area TA. Therefore, the color filter substrate 200 may have a flat surface structure.

Therefore, the first cell gap d1 in the reflection area RA and the second cell gap d2 in the transmission area TA may be substantially the same. As a result, the transflective liquid crystal display 400 may have a uniform cell gap.

As described above, in the transflective liquid crystal display device 400, the reflective electrode 150 and the common electrode 230 are insulated by the liquid crystal layer 300 and the insulating thin film 240, and the transmission electrode ( 140 and the common electrode 230 are insulated by the liquid crystal layer 300. Therefore, the dielectric constant of the insulating film interposed between the reflective electrode 150 and the common electrode 230 and the dielectric constant of the insulating film interposed between the transmission electrode 140 and the common electrode 230 are different from each other. . Accordingly, the reflection voltage applied to the liquid crystal layer 300 in the reflection area RA and the transmission voltage applied to the liquid crystal layer 300 in the transmission area TA are also different.

2 is a graph showing changes in transmittance and reflectance according to the reflection voltage and the transmission voltage. However, in the graph shown in FIG. 2, the solid line represents the change in transmittance, and the dotted line represents the change in reflectance.

1 and 2, when about 4.2 V is applied to the liquid crystal layer 300 provided in the transmission area TA, the transflective liquid crystal display 400 exhibits a maximum transmittance (about 40%). . On the other hand, when about 2.6V is applied to the liquid crystal layer 300 provided in the reflective area RA, the transflective liquid crystal display 400 exhibits a maximum reflectance (about 38%). However, the voltage applied to the common electrode 230 is the same in the transmission area TA and the reflection area RA.

As described above, since the transmission voltage showing the maximum transmittance and the reflection voltage showing the maximum reflectance are different from each other, different voltages are applied to the liquid crystal layer 300 provided in the reflection area RA and the liquid crystal layer provided in the transmission area TA. It is preferable to apply. That is, about 4.2 V showing the maximum transmittance is applied to the liquid crystal layer provided in the transmission area TA, and 2.6 V smaller than 4.2 V is applied to the liquid crystal layer provided in the reflection area RA. Accordingly, the transmissivity and the reflectance of the transflective liquid crystal display device 400 can be ensured to the maximum.

In general, the capacitance C satisfies the following equation.

In Equation 1, 'ε' is a permittivity, 'd' is an interelectrode distance, and 'A' is an area of two electrodes.

As shown in Equation 1, the capacitance C is proportional to the permittivity epsilon. That is, when the distance d and the area A are constant, the capacitance C increases when the dielectric constant ε increases, and the capacitance C decreases in proportion to the decrease in the dielectric constant ε.

In addition, the capacitance satisfies the following equation (2).

In Equation 2, 'Q' is the amount of charge and 'V' is the voltage.

As shown in equation (2), the capacitance (C) is inversely proportional to the voltage (V). That is, as the capacitance C increases, the voltage V decreases in inverse proportion thereto. When the capacitance C decreases, the voltage V increases in inverse proportion thereto.

Referring back to FIG. 1, the insulating thin film 240 having a dielectric constant greater than that of the liquid crystal layer 300 is disposed between the TFT substrate 100 and the color filter substrate 200 in the reflective region RA. More is formed.

Therefore, the reflection voltage applied to the liquid crystal layer 300 in the reflection region RA is reduced in proportion to the dielectric constant of the liquid crystal layer 300 in the transmission region TA.

3A to 3C are views illustrating a manufacturing process of the color filter substrate shown in FIG. 1 in detail.

Referring to FIG. 3A, the color filter layer 220 formed of R (Red), G (Green), and B (Blue) is provided on the second insulating substrate 210. The color filter layer 220 has a first thickness t1 in the reflective region RA and a second thickness t2 greater than the first thickness t1 in the transmission region TA.

As shown in FIG. 3B, the common electrode 230 is stacked on the color filter layer 220 in a uniform thickness. The common electrode 230 is made of ITO or IZO, which is a transparent conductive material.

3C, the insulating thin film 240 having a dielectric constant greater than that of the liquid crystal layer 300 is provided on the common electrode 230. In particular, the insulating thin film 240 is provided only in the reflective region RA. In this case, the thickness t3 of the insulating thin film 240 is equal to the step of the color filter layer 220 formed between the reflective area RA and the transmission area TA. Therefore, the color filter substrate 200 may have a flat surface structure.

4 is a cross-sectional view of a transflective liquid crystal display according to another exemplary embodiment of the present invention. However, the same reference numerals are given to the same components as those shown in FIG. 1, and description thereof will be omitted.

Referring to FIG. 4, the transflective liquid crystal display device 500 according to another exemplary embodiment of the present invention includes a TFT substrate 100, a color filter substrate 200, and the TFT substrate facing the TFT substrate 100. The liquid crystal layer 300 is interposed between the 100 and the color filter substrate 200.

The TFT substrate 100 is a substrate having a TFT 120, an organic insulating layer, a transparent electrode 140, a reflective electrode 150, and an insulating thin film 160 on the first insulating substrate 110. First, the TFT including the gate electrode 121, the source electrode 125, and the drain electrode 126 is formed on the first insulating substrate 110. The organic insulating layer 130 having a contact hole 131 for exposing the drain electrode 126 is stacked thereon.

Subsequently, the transmission electrode 140, which is in electrical contact with the drain electrode 126 through the contact hole 131, is stacked on the organic insulating layer 30 to have a uniform thickness. The reflective electrode 150 having the transmission window 151 for exposing a portion of the transmission electrode 140 is stacked on the transmission electrode 140 with a uniform thickness.

Next, the insulating thin film 160 having a dielectric constant greater than that of the liquid crystal layer 300 is stacked on the reflective electrode 150. That is, the insulating thin film 160 is provided only in the reflective region RA.

The color filter substrate 200 is a substrate on which the color filter layer 220 and the common electrode 230 are disposed on the second insulating substrate 210.

The color filter layer 220 made of R (Red), G (Green), and B (Blue) is provided on the second insulating substrate 210. The color filter layer 220 has a first thickness t1 in the reflective region RA and a second thickness t2 greater than the first thickness t1 in the transmission region TA.

Thereafter, the common electrode 230 is stacked on the color filter layer 220 with a uniform thickness.

In this case, the third thickness t3 of the insulating thin film 160 included in the TFT substrate 100 is equal to the value obtained by subtracting the first thickness t1 from the second thickness t2. Therefore, the first cell gap d1 in the reflection area RA and the second cell gap d2 in the transmission area TA may be substantially the same. As a result, the transflective liquid crystal display 500 may have a uniform cell gap.

As described above, in the transflective liquid crystal display 500, the reflective electrode 150 and the common electrode 230 are insulated by the liquid crystal layer 300 and the insulating thin film 160, and the transmission electrode ( 140 and the common electrode 230 are insulated by the liquid crystal layer 300. Therefore, the reflective voltage applied to the liquid crystal layer 300 in the reflective region RA by the insulating thin film 160 is reduced than the transmission voltage applied to the liquid crystal layer 300 in the transmissive region TA.

According to the liquid crystal display, the first substrate includes a transmissive electrode and a reflective electrode defining a transmissive region and a reflective region, and the second substrate is provided with a color filter layer having different thicknesses in the reflective region and the transmissive region. The liquid crystal layer and the insulating thin film are interposed between the first substrate and the second substrate. The insulating thin film has a higher dielectric constant than the liquid crystal layer and is provided only in the reflective region.

Therefore, the reflection voltage applied to the liquid crystal layer in the reflection region is lower than the transmission voltage applied to the liquid crystal layer in the transmission region, thereby improving the reflection efficiency and the transmission efficiency of the liquid crystal display device, respectively. Therefore, the display quality of the liquid crystal display device can be improved.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims (7)

A first substrate having a transmissive electrode and a reflective electrode having a transmissive window for exposing a portion of the transmissive electrode, the reflecting region and the transmissive region being defined; A color filter layer having a first thickness in the reflective region and having a second thickness greater than the first thickness in the transmissive region, and having a common electrode provided on the color filter layer with a uniform thickness, A second substrate coupled toward; A liquid crystal layer interposed between the first substrate and the second substrate; And And an insulating thin film interposed between the first substrate and the second substrate in the reflective region and having a dielectric constant different from that of the liquid crystal layer. The liquid crystal display of claim 1, wherein the insulating thin film is an inorganic insulating film or an organic insulating film. The liquid crystal display device of claim 1, wherein the insulating thin film has a dielectric constant greater than that of the liquid crystal layer. The liquid crystal display device of claim 1, wherein the insulating thin film is provided on the common electrode. The liquid crystal display device of claim 4, wherein a thickness of the insulating thin film is equal to a value obtained by subtracting the first thickness from the second thickness. The liquid crystal display of claim 1, wherein the insulating thin film is provided on the reflective electrode. The thin film transistor of claim 1, wherein the first substrate further comprises a thin film transistor and an organic insulating layer formed on the thin film transistor and having contact holes for exposing a drain electrode of the thin film transistor. And the transparent electrode and the reflective electrode are electrically connected to the drain electrode through the contact hole.