Pixel structure and liquid crystal display panel

A pixel structure including an active device, a first pixel electrode, a second pixel electrode, a coupling line, a common electrode, and a liquid crystal layer is provided. The first pixel electrode and the second pixel electrode have a plurality of sets of stripped electrode patterns extending along different directions, respectively, and the first pixel electrode is electrically insulated from the second pixel electrode. The coupling line is disposed under the first and the second pixel electrode and electrically insulated from the second pixel electrode. The first pixel electrode is electrically connected to the active device through the coupling line. The common electrode is disposed over the first and the second pixel electrode. The liquid crystal layer is disposed between the common electrode and the first and second pixel electrodes. Moreover, the liquid crystal layer has two polymer layers and a liquid crystal molecule layer disposed between the polymer layers.

This application claims the benefit of Taiwan Patent Application Serial No. 95117813, filed on May 19, 2006. All disclosure of the Taiwan application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a pixel structure. More particularly, the present invention relates to a pixel structure using polymer-stabilized alignment.

2. Description of Related Art

In response to the increasing demand of displays, the industry put efforts in the development of the display. Among the displays, the cathode ray tube (CRT) has occupied the display market for many years, due to its high display quality and mature technology. However, the rising “environmental protection” awareness is against its power consumption and radiation disadvantage, and the limited flattening capability is against the market demands, and thus the cathode ray tube (CRT) cannot meet the market demands gradually. Therefore, the thin film transistor liquid crystal display (TFT-LCD), having superior properties such as high image quality, good space utilization, low power consumption, and no radiation, has become the mainstream display product of the market.

Currently, the market demands for the performance of LCDs includes high contrast ratio, no gray scale inversion, little color shift, high luminance, high color enrichment, high color saturation, fast response, and wide viewing angle. Technologies for achieving wide viewing angle comprises the twist nematic liquid crystal with wide viewing film, the in-plane switching (IPS) LCD, the fringe field switching LCD, and the multi-domain vertically alignment (MVA), etc.

FIG. 1Ais a schematic sectional view of a conventional MVA LCD panel, andFIG. 1Bis a top view of a TFT array substrate of the LCD panel as shown inFIG. 1A, wherein the schematic sectional view of the TFT array substrate inFIG. 1Ais taken along the section line A-A′ inFIG. 1B. Referring toFIGS. 1A and 1B, the conventional MVA LCD panel10comprises a TFT array substrate20, a color filter substrate30, and a liquid crystal layer40. The liquid crystal layer40is disposed between the TFT array substrate20and the color filter substrate30.

The color filter substrate30comprises a glass substrate31, a color filter layer32, a common electrode33, and a plurality of protrusions34. The color filter layer32is disposed over the glass substrate31. The common electrode33is disposed on the color filter layer32. The protrusions34are disposed on the common electrode33.

The TFT array substrate20comprises a glass substrate21, a plurality of scan lines22, a plurality of data lines23, a plurality of TFTs24, a plurality of transparent electrodes25, and a plurality of common lines26. The scan lines22and the data lines23are disposed on the glass substrate21. Each of the TFTs24is electrically connected to one of the scan lines22and one of the data lines23, respectively. Each of the transparent electrodes25is electrically connected to one of the TFTs24, respectively, and crosses one of the common lines26.

It should be noted that the transparent electrodes25have a plurality of slits25a. The slits25atogether with the protrusions34make liquid crystal molecules in the liquid crystal layer40being inclined in multiple directions, such that the scope of viewing angle of the MVA LCD panel10is increased. Therefore, the MVA LCD panel10meets the requirement of wide viewing angle.

Though the scope of viewing angle of the MVA LCD panel10can be increased by the slits25atogether with the protrusions34, when the MVA LCD panel10displays images, the color wash-out still occurs if the MVA LCD panel10is viewed at a large angle.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a pixel structure, suitable for eliminating the phenomenon of color wash-out of LCD panels, and increasing the aperture ratio of LCD panels to enhance the luminance of the LCD panels.

Another object of the present invention is to provide an LCD panel with preferable aperture ratio and high luminance.

In order to achieve the above-mentioned or other objects, the present invention provides a pixel structure, which comprises an active device, a first pixel electrode, a second pixel electrode, a coupling line, a common electrode, and a liquid crystal layer. The first pixel electrode and the second pixel electrode have a plurality of sets of first stripped electrode patterns and second stripped electrode patterns extending along different directions respectively, and the second pixel electrode is electrically insulated from the first pixel electrode. The coupling line is disposed under the first pixel electrode and the second pixel electrode, and is electrically insulated from the second pixel electrode. The first pixel electrode is electrically connected to the active device through the coupling line. The common electrode is disposed over the first pixel electrode and the second pixel electrode, and is formed without alignment patterns. The liquid crystal layer is disposed between the common electrode and the first pixel electrode and between the common electrode and the second pixel electrode. Moreover, the liquid crystal layer has a liquid crystal molecule layer and two polymer layers, and the liquid crystal molecule layer is disposed between the polymer layers.

According to the pixel structure as described in an embodiment of the present invention, the material of the polymer layers may be an acrylic polymer.

According to an embodiment of the present invention, the pixel structure further comprises a common line and a capacitor electrode, wherein the capacitor electrode is disposed over the common line and is electrically connected to the first pixel electrode. In addition, the common line is disposed under the first pixel electrode, and the first pixel electrode crosses the common line. In another embodiment, the first pixel electrode and the second pixel electrode can be disposed on two opposite sides of the common line, respectively. In an alternative embodiment, the pixel structure further comprises a dielectric layer disposed between the capacitor electrode and the common line. In another embodiment, the second pixel electrode comprises a first sub-pixel electrode and a second sub-pixel electrode. The first sub-pixel electrode and the second sub-pixel electrode are disposed on two opposite sides of the first pixel electrode, respectively.

According to the pixel structure as described in an embodiment of the present invention, the second pixel electrode comprises a first sub-pixel electrode and a second sub-pixel electrode. The first sub-pixel electrode and the second sub-pixel electrode are disposed on two opposite sides of the scan line, and are electrically connected, respectively.

According to the pixel structure as described in an embodiment of the present invention, four alignment regions are defined by the plurality of sets of first stripped electrode patterns of the first pixel electrode.

According to the pixel structure as described in an embodiment of the present invention, four alignment regions are defined by the plurality of sets of second stripped electrode patterns of the second pixel electrode.

The present invention further provides an LCD panel, which comprises a lower substrate, an upper substrate, a color filter array, and a plurality of pixel structures. The upper substrate is disposed over the lower substrate. The color filter array is disposed between the upper substrate and the lower substrate. The pixel structures are disposed between the color filter array and the lower substrate. Each of the pixel structures is electrically connected to a scan line and a data line. Each of the pixel structures comprises an active device, a first pixel electrode, a second pixel electrode, a coupling line, a common electrode, and a liquid crystal layer. The active device is electrically connected to the scan line and the data line. The first pixel electrode has a plurality of sets of first stripped electrode patterns extending along different directions. The second pixel electrode has a plurality of sets of second stripped electrode patterns extending along different directions, and is electrically insulated from the first pixel electrode. The coupling line is disposed under the first pixel electrode and the second pixel electrode, and is electrically insulated from the second pixel electrode. The first pixel electrode is electrically connected to the active device through the coupling line. The common electrode is disposed over the first pixel electrode and the second pixel electrode, and is formed without alignment patterns. The liquid crystal layer is disposed between the common electrode and the first pixel electrode and between the common electrode and the second pixel electrode. Moreover, the liquid crystal layer has a liquid crystal molecule layer and two polymer layers. The liquid crystal molecule layer is disposed between the polymer layers.

According to the LCD panel as described in an embodiment of the present invention, the polymer layers comprise an acrylic polymer.

According to the LCD panel as described in an embodiment of the present invention, each of the pixel structures further comprises a common line and a capacitor electrode. The capacitor electrode is disposed over the common line, and is electrically connected to the first pixel electrode.

According to the LCD panel as described in an embodiment of the present invention, the common line in each of the pixel structures is disposed under the first pixel electrode, and the first pixel electrode crosses the common line.

According to the LCD panel as described in an embodiment of the present invention, the first pixel electrode and the second pixel electrode in each of the pixel structures are disposed on two opposite sides of the common line, respectively.

According to the LCD panel as described in an embodiment of the present invention, each of the pixel structures further comprises a dielectric layer disposed between the capacitor electrode and the common line.

According to the LCD panel as described in an embodiment of the present invention, the second pixel electrode in each of the pixel structures comprises a first sub-pixel electrode and a second sub-pixel electrode, wherein the first sub-pixel electrode and the second sub-pixel electrode are disposed on two opposite sides of the first pixel electrode, respectively.

According to the LCD panel as described in an embodiment of the present invention, the second pixel electrode in each of the pixel structures comprises a first sub-pixel electrode and a second sub-pixel electrode. The first sub-pixel electrode and the second sub-pixel electrode are disposed on two opposite sides of the scan line, and are electrically connected, respectively.

According to the LCD panel as described in an embodiment of the present invention, four alignment regions are defined by the plurality of sets of first stripped electrode patterns of the first pixel electrode in each of the pixel structure.

According to the LCD panel as described in an embodiment of the present invention, four alignment regions are defined by the plurality of sets of second stripped electrode patterns of the second pixel electrode in each of the pixel structure.

In view of the above, in the LCD panel of the present invention, the liquid crystal molecule layer in the pixel structure is affected by the two polymer layers, such that the liquid crystal molecules present specific arrangements. In addition, the coupling line and the second pixel electrode constitute a coupling capacitor. If the capacitance value of the coupling capacitor is adjusted, the inclination degree of the liquid crystal molecules over the first pixel electrode and the second pixel electrode is changed. In this manner, the phenomenon of color wash-out of LCD panels can be eliminated. And LCD panels with the pixel structure will have high aperture ratio and high luminance.

In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.

DESCRIPTION OF EMBODIMENTS

The First Embodiment

FIG. 2Ais a partial schematic sectional view of an LCD panel according to the first embodiment of the present invention, andFIG. 2Bis a top view of an active device array substrate according to the first embodiment of the present invention, wherein the schematic sectional view of the active device array substrate ofFIG. 2Ais taken along the section line B-B′ inFIG. 2B. Referring toFIGS. 2A and 2B, the LCD panel600of the present embodiment comprises a lower substrate110, an upper substrate140, a color filter array150, and a plurality of pixel structures200. A plurality of scan lines120and a plurality of data lines130are formed on the lower substrate110. The color filter array150is disposed between the lower substrate110and the upper substrate140. The pixel structures200are disposed between the color filter array150and the lower substrate110. The detailed structure, arrangement position, connection relation, and material of various elements will be illustrated below.

Referring toFIGS. 2A and 2B, the pixel structure200is fabricated on the lower substrate110, and is electrically connected to one of the scan lines120and one of the data lines130on the lower substrate110. As shown inFIGS. 2A and 2B, the pixel structure200comprises an active device210, a first pixel electrode220, a second pixel electrode230, a coupling line240, a common electrode250, and a liquid crystal layer260.

The active device210is disposed on the lower substrate110, and is electrically connected to the corresponding scan line120and the corresponding data line130. The first pixel electrode220and the second pixel electrode230have first stripped electrode patterns222and second stripped electrode patterns232, respectively. The first stripped electrode patterns222and the second stripped electrode patterns232have a plurality of sets of extending directions respectively, and the second pixel electrode230is electrically insulated from the first pixel electrode220. The coupling line240is disposed under the first pixel electrode220and the second pixel electrode230, and is electrically insulated from the second pixel electrode230. The first pixel electrode220is electrically connected to the active device210through the coupling line240. The common electrode250is disposed over the first pixel electrode220and the second pixel electrode230, and is formed without alignment patterns. The liquid crystal layer260is disposed between the common electrode250and the first pixel electrode220, and between the common electrode250and the second pixel electrode230. The liquid crystal layer260has a liquid crystal molecule layer262and two polymer layers264, and the liquid crystal molecule layer262is disposed between the two polymer layers264.

As described above, the lower substrate110and the upper substrate140are glass substrates, quartz substrates, or substrates made of other appropriate materials. The scan lines120are, for example, aluminum alloy wires or wires made of other appropriate conductive materials. The data lines130and the coupling line240are chromium wires, aluminum alloy wires, or wires made of other appropriate conductive materials. The color filter array150comprises, for example, a plurality of red color filter patterns, green color filter patterns, and blue color filter patterns. The active device210is, for example, a TFT or other tri-polar switching devices. The first pixel electrode220and the second pixel electrode230are, for example, transmissive electrodes, reflective electrodes, or transflective electrodes, and the material of the first pixel electrode220and the second pixel electrode230is indium tin oxide (ITO), indium zinc oxide (IZO), metals, or other transparent or non-transparent conductive materials. In addition, the material of the common electrode250is ITO, IZO, or other transparent conductive materials. The material of the liquid crystal molecule layer262is, for example, negative liquid crystal molecules. The material of the polymer layers264is, for example, an acrylic polymer, and the polymer layers264is obtained through UV polymerization of monomer materials.

In the present embodiment, the pixel structure200further comprises a common line270and a capacitor electrode280, wherein the capacitor electrode280is disposed over the common line270and is electrically connected to the first pixel electrode220. In addition, the common line270is disposed under the first pixel electrode220, and the first pixel electrode220crosses the common line270.

As shown inFIG. 2A, the pixel electrode structure200further comprise a dielectric layer290disposed between the capacitor electrode280and the common line270. In other words, the capacitor electrode280, the common line270, and the dielectric layer290constitute a storage capacitor. More particularly, the lower substrate110, the scan line120, the data line130, the active device210, the first pixel electrode220, the second pixel electrode230, the coupling line240, the common line270, and the capacitor electrode280constitute the active device array substrate102. In addition, the material of the dielectric layer290is, for example, silicon nitride or other appropriate materials. The common line270is, for example, an aluminum alloy wire or a wire made of other appropriate conductive materials. The material of the capacitor electrode280is, for example, chromium, aluminum alloy, or other appropriate conductive materials. It should be noted that in the present embodiment, the capacitor electrode280and the coupling line240are connected together, and are formed simultaneously. However, in another embodiment, the capacitor electrode280and the coupling line240are not limited to be connected together, and are not limited to be formed simultaneously.

Referring toFIG. 2B, four alignment regions I, II, III, and IV are defined by the plurality of sets of the first stripped electrode patterns222of the first pixel electrode220, and two alignment regions I and II are defined by the plurality of sets of the second stripped electrode patterns232of the second pixel electrode230. When the pixel structure200is not driven, the liquid crystal molecules262ain the liquid crystal molecule layer262are affected by the alignment effect of the two polymer layers264, and are arranged vertically to the lower substrate110. When the pixel electrode200is driven, the liquid crystal molecules262ain the liquid crystal molecule layer262are inclined to the direction parallel to the lower substrate110. Particularly, the liquid crystal molecules262ahave substantially the same inclination direction in one of the alignment domains I, II, III, and IV, but the inclination directions of the liquid crystal molecules among the alignment domains I, II, III and IV are different. Through the arrangement of the liquid crystal molecules262ainclined in multiple directions, the LCD panel600fabricated with the pixel structures200will have a large viewing angle.

It should be noted that as shown inFIG. 2A, since the coupling line240is disposed under the second pixel electrode230, the coupling line240and the second pixel electrode230constitute a capacitor Ccp(as shown inFIG. 2C). Moreover, since the common electrode250is disposed over the first pixel electrode220and the second pixel electrode230which are electrically insulated from each other. The common electrode250together with the first pixel electrode220or the second pixel electrode230constitutes a capacitor C1Cor a capacitor C1C′ (as shown inFIG. 2C). The first pixel electrode220and the common line270constitute a capacitor Cst(as shown inFIG. 2C).

FIG. 2Cis an equivalent circuit diagram of the pixel structure ofFIG. 2A. Referring toFIG. 2C, the lower electrode plate and the upper electrode plate of the capacitor Ccpare the coupling line240and the second pixel electrode230respectively. The lower electrode plate and the upper electrode plate of the capacitor C1c′ are the second pixel electrode230and the common electrode250respectively. The lower electrode plate and the upper electrode plate of the capacitor C1care the first pixel electrode220and the common electrode250respectively. In addition, the lower electrode plate and the upper electrode plate of the capacitor Cstare the first pixel electrode220(or the capacitor electrode280) and the common electrode270respectively.

When the active device210is in the ON state, an external voltage Vais applied to the coupling line240, such that the voltage of the lower electrode plate (i.e., the first pixel electrode220or the capacitor electrode280) of the capacitor Cst, the lower electrode plate (i.e., the first pixel electrode220) of the capacitor C1c, and the lower electrode plate (i.e., the coupling line240) of the capacitor Ccpis Va. As the capacitor C1c′ and the capacitor Ccpare connected in series, the voltage difference (Va−Vcom) is distributed on the two capacitors C1c′ and Ccp. Thus, the voltage Vfof the lower electrode plate (i.e., the second pixel electrode230) of the capacitor C1c′ is different from the external voltage Va.

FIG. 2Dis a schematic view of the inclination of the liquid crystal molecules over the first pixel electrode and the second pixel electrode inFIG. 2A. Referring toFIG. 2D, if the overlapped area of the second pixel electrode230and the coupling line240is changed, the value of C1c′ can be adjusted, and the voltage Vfof the lower electrode plate (i.e., the second pixel electrode230) of the capacitor C1c′ is adjusted accordingly. Therefore, if the voltage Vfis changed, the inclination degree of the liquid crystal molecules262aover the second pixel electrode230is changed. By adjusting the inclination degree of the liquid crystal molecules262aover the first pixel electrode220and the second pixel electrode230, the phenomenon of color wash-out of the LCD panel600can be eliminated. In addition, since the LCD panel600fabricated with the pixel structures200is designed without protrusions, the LCD panel600will have high aperture ratio.

It should be noted that the direction and degree of inclination of the liquid crystal molecules262aas shown inFIG. 2Dis exemplary and is only to illustrate the efficacy of the pixel structures200. The direction and degree of inclination of the liquid crystal molecules262amay vary in practice.

The Second Embodiment

FIG. 3Ais a partial schematic sectional view of an LCD panel according to the second embodiment of the present invention, andFIG. 3Bis a top view of an active device array substrate according to the second embodiment of the present invention, wherein the schematic sectional view of the active device array substrate ofFIG. 3Ais taken along the section line C-C′ inFIG. 3B. Referring toFIGS. 3A and 3B, the LCD panel700of the present embodiment is a variation of the LCD panel600of the first embodiment, and wherein the first pixel electrode320and the second pixel electrode330of the pixel structure300are respectively disposed on two opposite sides of the common line270, and the coupling line340is not connected to the capacitor electrode280.

As the advantages of the LCD panel700and the pixel structure300are substantially the same as those described in the first embodiment, the details will not be described herein again.

The Third Embodiment

FIG. 4Ais a partial schematic sectional view of an LCD panel800according to the third embodiment of the present invention, andFIG. 4Bis a top view of an active device array substrate according to the third embodiment of the present invention, wherein the schematic sectional view of the active device array substrate ofFIG. 4Ais taken along the section line D-D′ inFIG. 4B. Referring toFIGS. 4A and 4B, the LCD panel800of the present embodiment is a variation of the LCD panel600of the first embodiment, and wherein the second pixel electrode430of the pixel structure400comprises a first sub-pixel electrode430aand a second sub-pixel electrode430b. And the first sub-pixel electrode430aand the second sub-pixel electrode430bare disposed respectively on two opposite sides of the first pixel electrode420.

As the advantages of the LCD panel800and the pixel structure400are substantially the same as those described in the first embodiment, the details will not be described herein again.

The Fourth Embodiment

In the aforementioned conventional art, the transparent electrodes25are confined between the adjacent scan lines22and the adjacent data lines23. However, this design does not effectively divide the pixel electrodes25. In order to make effective use of the pixel electrodes, the present embodiment provides a LCD panel and a pixel structure.

FIG. 5Ais a partial schematic sectional view of an LCD panel according to the fourth embodiment of the present invention, andFIG. 5Bis a top view of an active device array substrate according to the fourth embodiment of the present invention, wherein the schematic sectional view of the active device array substrate ofFIG. 5Ais taken along the section line E-E′ inFIG. 5B. Referring theFIGS. 5A and 5B, the LCD panel900is similar to the LCD panel600of the first embodiment, and wherein the second pixel electrode530of the pixel structure500is disposed on two opposite sides of the scan lines120, and is electrically connected. In addition, the pixel structure500comprises a coupling line540, and the coupling line540is electrically connected between the first pixel electrode520and the active device210, and is not connected to the capacitor electrode280.

Different from the conventional art that confines the transparent electrodes25between the adjacent scan lines22and the adjacent data lines23, in the present embodiment, the second pixel electrode530of the pixel structure500is disposed on two opposite sides of the scan lines120. Thus the pixel electrodes can be divided more flexibly, thereby making effective use of the pixel electrodes to improve the aperture ratio. Thus, if the LCD panel900is fabricated by the use of the pixel structure500, the LCD panel900will have higher aperture ratio and higher luminance. It should be noted that in the present embodiment, the coupling line540is not connected to the capacitor280. However, in other embodiments, the capacitor electrode280can be connected to the coupling line240, and they can be formed at the same time.

To sum up, the pixel structures of the present invention have at least the following advantages.

1. In the pixel structures of the present invention, the interaction between the liquid crystal molecule layer and the two polymer layers makes the liquid crystal molecules presenting specific arrangements. In other words, the pixel structures of the present invention can achieve the effect of alignment without adopting protrusions. Therefore, LCD panels fabricated with pixel structures of the present invention have higher aperture ratio and higher luminance.

2. In the LCD panel of one of the first to the third embodiments, the coupling line and the second pixel electrode of the pixel structure constitute a coupling capacitor. The capacitance value of the coupling capacitor can be adjusted to allow the liquid crystal molecules over the first pixel electrode and the second pixel electrode having different inclination degrees, thereby eliminating the phenomenon of color wash-out.

3. In the LCD panel of the fourth embodiment, the second pixel electrode of the pixel structure is disposed on two opposite sides of the scan line. Compared with the conventional art that confines the pixel electrode between two adjacent scan lines and two adjacent data lines, the pixel electrodes can be divided more flexibly, thereby making effective use of the pixel electrode and improving the aperture ratio and the luminance of the LCD panel.

4. The methods of fabricating the LCD panel and the pixel structures are compatible with existing processes. And additional processing equipment is not required.