Transflective LCD panel and pixel structure with first and second overlapping common electrodes disposed in one direction both overlapping data line disposed in a second direction

A pixel structure of a transflective LCD panel includes a substrate, a data line and a scan, a thin film transistor containing an extending electrode, a first common electrode and a second common electrode, a transmissive pixel electrode, and a reflective pixel electrode forming a first coupling capacitor with the extending electrode and a second coupling capacitor with the second common electrode. The first and second common electrodes and the data line overlap with each other in an overlapping area, wherein the first common electrode is disposed between the second common electrode and the data line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transflective liquid crystal display (LCD) panel and a pixel structure thereof, and more particularly, to a transflective LCD panel with a single gap and a pixel structure thereof.

2. Description of the Prior Art

Most LCDs can be categorized into three kinds: the transmissive type, the reflective type, and the transflective type according to their light source. The transmissive LCD uses backlight as a source for emitting light. The light emitted by the backlight will pass through the LCD panel to let an user see the image displayed on the LCD panel. The reflective LCD has a reflective pixel electrode. When displaying the image, the ambient light will enter the LCD from the user side and then be reflected by the reflective pixel electrode. The reflected light will pass through the reflective LCD panel again, and finally the user can see the image displayed on the LCD. The transflective LCD panel has the LCD both of transmissive type and reflective type. In other words, each pixel area of the transflective LCD panel comprises a transmission region and a reflection region.

Generally, a traditionally transflective LCD panel has an array substrate, a color filter substrate, and a liquid crystal layer disposed between the two substrates. The transflective LCD panel further includes pluralities of pixel areas, and each of the pixel areas comprises a reflection region and a transmission region, while each reflection region and each transmission region has a reflective pixel electrode and a transmission pixel electrode respectively. Because the transmission region of the transflective LCD panel uses a backlight as its light source, the light will pass through the liquid crystal layer only once. However, the reflection region uses the ambient light as a light source, so that the light will pass through the liquid crystal layer twice. In such a case, the optical path-length difference in the reflection region is twice as much as that in the transmission region, such that the relation of reflectance versus voltage mismatches the relation of transmittance versus voltage (i.e. gamma curve) while driving the liquid crystal (LC) molecules.

For this reason, manufacturers have designed a transflective LCD panel having a dual cell gap to solve the problem of mismatching driving voltage. More specifically, in this kind of transflective LCD panel, a dielectric layer is disposed under the reflective pixel electrode so as to adjust a cell gap of the reflection region. By disposing the dielectric layer, the cell gap of the liquid crystal layer in the reflection region is smaller than the cell gap in the transmission region, so that the optical path-length difference of light passing through the reflection region is the same as that of light passing through the transmission region. However, although the problem of mismatching driving voltage may be solved through the above-mentioned design of dual gap by adjusting the optical path-length difference in the transflective LCD panel, an obvious height difference of the border between the reflection region and the transmission region will make the LC molecules difficult to align, thereby resulting in light leakage and lowering the quality of displayed images. Furthermore, the step of fabricating the dielectric layer in the reflection region increases the fabrication cost and decreases yield.

On the other hand, in order to solve the mismatching problem of gamma curves of the transmission mode and the reflection mode of the transflective LCD panel, manufacturers have also develop an adjusted capacitance coupling (ACC) technique, by the way of disposing a first common electrode, a second common electrode, a first coupling capacitor (CC), and a second coupling capacitor (C2) in the transflective LCD panel to change the voltage difference of the reflection region through the coupling of the first coupling capacitor and the second coupling capacitor, so as to adjust the gamma curve of the reflection type to match the gamma curve of the transmission type. However, in the device arrangement of the current ACC technique design, the additional second common electrode crosses the data line on the array substrate such that the voltage of the second common electrode will be affected when a signal is transferred through the data line to the pixels of the display panel, resulting in serious cross-talk problem, which cannot meet the requirement of product standard that the cross-talk has to be less than 2%. As a result, the current ACC transflective LCD panel with a single gap still has an apparent disadvantage of serious cross-talk and cannot display high-quality images for meeting the product standards.

SUMMARY OF THE INVENTION

It is one of the objectives of the present invention to provide a single-gap transflective LCD panel that has a special arrangement of the first common electrode and the second common electrode to solve the above-mentioned problem of serious cross-talk resulted from the effect between the overlapping second common electrode and data line of the prior-art transflective LCD panel.

The present invention provides a pixel structure for applying to a transflective LCD panel. The pixel structure is adapted to a substrate having a pixel area comprising a reflection region and a transmission region. The pixel structure comprises a data line disposed on the substrate along a first direction; a scan line disposed on the substrate along a second direction, wherein the second direction intersects the first direction; a TFT electrically connected to the scan line and the data line, comprising an extending electrode; and a first common electrode and a second common electrode disposed on the substrate substantially along the second direction, the first common electrode and the second common electrode intersecting the data line in an overlapping area where the first common electrode, the second common electrode, and the data line overlap with each other, the first common electrode in the overlapping area being disposed between the second common electrode and the data line; a transmission pixel electrode electrically connected to the TFT; and a reflective pixel electrode forming a first coupling capacitor by coupling with the extending electrode and a second coupling capacitor by coupling with the second common electrode.

The present invention further provides a transflective LCD panel comprising: a first substrate having a pixel area comprising a reflection region and a transmission region; a data line disposed on the first substrate along a first direction; a scan line disposed on the first substrate along a second direction, the second direction and the first direction intersecting with each other; a first common electrode and a second common electrode disposed on the first substrate, wherein the first common electrode and the second common electrode are arranged substantially along the second direction and intersect the data line in an overlapping area, and the first common electrode, the second common electrode, and the data line overlap with each other in the overlapping are while the first common electrode in the overlapping area is disposed between the second common electrode and the data line; a transmission pixel electrode electrically connected to the TFT; a reflective pixel electrode, forming a first coupling capacitor by coupling with the extending electrode and a second coupling capacitor by coupling with the second common electrode; a second substrate disposed oppositely to the first substrate; and a liquid crystal layer disposed between the first substrate and the second substrate.

It is an advantage of the pixel structure of the present invention that the first common electrode, the second common electrode, and the data line overlap with each other in the overlapping area while the first common electrode is disposed between the data line and the second common electrode within their overlapping part. Therefore, the first common electrode substantially shields the affection to the second common electrode from the data line. Accordingly, the voltage of the second common electrode will not be affect when a signal is inputted in the data line, and the cross-talk effect is reduced.

DETAILED DESCRIPTION

FIG. 1is a schematic diagram of a transflective LCD panel10according to the present invention. The transflective LCD panel10comprises a first substrate12, a second substrate14disposed parallel with and oppositely to the first substrate12, and a liquid crystal layer16disposed between the first substrate12and second substrate14. Generally, the first substrate12may be called as an array substrate or a pixel substrate, having a plurality of pixel areas18(shown inFIG. 2) defined thereon and arranged as an array in the display area of the transflective LCD panel10. The second substrate14may be called as a color filter (CF) substrate because CFs and black matrix layers are disposed on the surface of the second substrate14and each pixel area18may produce corresponding colorful lights. In addition, the present invention transflective LCD panel10uses an adjusted capacitance coupling (ACC) technique for adjusting the gamma curve of the reflection mode, and therefore preferably has only a single gap G.

FIG. 2is an equivalent circuit model of a pixel structure86of the transflective LCD panel10, wherein the pixel structure86corresponds to one pixel area18of the first substrate12. The pixel area18comprises at least a data line20and a scan line22. The pixel area18further comprises a TFT24, whose gate24G and source24S are electrically connected to the scan line22and the data line20respectively, while the drain24D of the TFT24is electrically connected to the top electrode plates of the transmission LC capacitor CLCt, the storage capacitor Cst, and the first coupling capacitor CC. The bottom electrode plate26of the first coupling capacitor CCis electrically connected to the reflection LC capacitor CLCrand the second coupling capacitor C2, wherein both the transmission LC capacitor CLCtand the reflection LC capacitor CLCrtake the transparent electrode disposed on the surface of the second substrate14as their bottom electrode plate, and the storage capacitor Csttakes the first common electrode COM1on the surface of the first substrate12as its bottom electrode plate. In addition, the pixel area18further comprises a second common electrode (COM2)28coupling to a periphery circuit on the first substrate12, which serves as the bottom electrode plate of the second coupling capacitor C2.

With reference toFIGS. 3-6,FIG. 3is a schematic diagram of top view of the device arrangement of the pixel structure86according to a first embodiment of the present invention, andFIGS. 4-6are sectional views along line4-4′,5-5′,6-6′ of the pixel structure86inFIG. 3. In order to simplify the figure, only the devices on the first substrate12are illustrated inFIGS. 3-6. As shown inFIG. 3, the pixel area18are broadly defined by two data lines20and two scan lines22, wherein the data lines20and scan lines22are disposed on the first substrate12along a first direction (such as direction Y) and a second direction (such as direction X) respectively. The first direction intersects and is perpendicular to the second direction. Further, the pixel area18further comprises a transmission region30and a reflection region32. The TFT24is positioned in the reflection region32of another adjacent pixel area18, and near the intersection part of the data line20and scan line22. The TFT24has an extending electrode34electrically connected to the drain24D. However, the extending electrode34may be considered as a portion of the drain24D. Referring toFIG. 4, the TFT24is a top-gate type TFT, having a source24S, a drain24D, and a channel region24C formed in the first patterned conductive layer62. In this embodiment, the first patterned conductive layer62comprises polysilicon materials. The source24S and drain24D are formed at two side parts of the first patterned conductive layer62through an ion implantation process of these parts of the first patterned conductive layer62, while the middle part without doping of ions serves as the channel region24C of the TFT24. Above the first patterned conductive layer62, a gate insulating layer36, a gate24G, an inter-layer dielectric (ILD) layer38, and a planarization layer40are disposed on the first substrate12in order. The gate24G is composed of a second patterned conductive layer42. In addition, the data line20is electrically connected to the source24S through the via hole44disposed in the gate insulating layer36and the ILD layer38.

Referring toFIG. 3, the material composing the extending electrode34may comprise the first patterned conductive layer62and the second patterned conductive layer42, extending form the drain24D up through the transmission region30and the storage capacitor region68into the reflection region32of the pixel area18. In the transmission region30, the extending electrode34is electrically connected to the transmission pixel electrode66, so that the transmission pixel electrode66and the transparent electrode COMCF(not shown, disposed on the lower surface of the second substrate14) on another side of the liquid crystal layer16forms an transmission LC capacitor CLCt, wherein the liquid crystal layer16serves as the dielectric layer of the transmission LC capacitor CLCt.

Referring toFIG. 5,FIG. 5is a schematic diagram of the sectional view along line5-5′ of the storage capacitor region68ofFIG. 3. With comparison ofFIG. 5andFIG. 3, the storage capacitor region68comprises the first common electrode50, which is composed of the third patterned conductive layer52. The extending electrode34positioned in the storage capacitor region68is considered as the top electrode plate of the storage capacitor Cst, the first common electrode50is considered as the bottom electrode plate of the storage capacitor Cst, and the dielectric layer56positioned between the second patterned conductive layer42and the third patterned conductive layer52serves as the dielectric layer between the top and bottom electrode plates of the storage capacitor Cst. In addition, the material of the data line20comprises the fourth patterned conductive layer54, which is disposed above the second patterned conductive layer42and the third patterned conductive layer52.

With reference toFIG. 6andFIG. 3at the same time, after the extending electrode34lines through the storage capacitor region68, it continuously extends up to the reflection region32. The reflection region32comprises a reflective pixel electrode58composed of the third patterned conductive layer52. In the reflection region32, the extending electrode34and reflective pixel electrode58are coupled to form a first coupling capacitor70, wherein the dielectric layer56disposed vertically between the third patterned conductive layer52and second patterned conductive layer42serves as the dielectric layer of the first coupling capacitor70. In addition, on the surface of the planarization layer40an adjusting layer46with a rough surface is disposed in the reflection region32, which forms pluralities of bumps. A reflection layer48is disposed on the adjusting layer46and has a rough and uneven surface for reflection light out of the transflective LCD panel10. The reflection layer48is preferably formed with conductive metal materials, such as aluminum. The reflection layer48is electrically connected to the reflective pixel electrode58through a contact plug (not shown), and may be considered as a portion of the reflective pixel electrode58. As a result, in the reflection region62, the reflection layer48(or the reflective pixel electrode58) and the transparent electrode positioned on the other side of the liquid crystal layer16forms the reflection LC capacitor CLCr. Furthermore, the second common electrode28in the reflection region32is substantially arranged along the second direction and formed with the second patterned conductive layer42, wherein the second common electrode28and the first common electrode50are electrically insulated by the dielectric layer56. In addition, the fourth patterned conductive layer54further forms a second common electrode branch60, serving as a portion of the second common electrode28because the second common electrode branch60is electrically connected to the second common electrode28comprising the second patterned conductive layer42through the via hole64. As shown inFIG. 6, the second common electrode28and the reflective pixel electrode58are coupled to form the second coupling capacitor72.

With comparison toFIG. 3andFIG. 6, the first common electrode50is arranged on the first substrate12substantially along the second direction, similar to the second common electrode28, and parallel to the scan line22. However, in order to avoid the problem of cross-talk caused by the intersection of the second common electrode28and the data line20in the prior-art structure, a portion of the first common electrode50of the present invention pixel structure86is specially designed to shift upwardly from the storage capacitor region68and to pass through the intersection portion of the second common electrode28and the data line20. Furthermore, the first common electrode50is disposed between the second common electrode28and the data line20vertically so as to shield the affect to the second common electrode28from the data line20. In other words, the first and second common electrodes50,28arranged along the second direction intersect the data line20arranged along the first direction in an overlapping area74. Besides, the first and second common electrodes50,28and the data line20overlap with each other in the overlapping area74, while the first common electrode50in the overlapping area74is disposed between the second common electrode28and data line20vertically. As shown inFIG. 6, in the overlapping area74, the data line20is disposed above both of the first and second common electrodes50,28, and the first common electrode50in the overlapping area74is disposed above the second common electrode28, such that the first common electrode50can effectively shield the influence of the data line20to the second common electrode28and reduce cross-talk effect.

In this embodiment, the second patterned conductive layer42forms the second common electrode28, the scan line22and a portion of the extending electrode34, the third patterned conductive layer52forms the first common electrode50and the reflective pixel electrode58, and the fourth patterned conductive layer54forms the data line20and the second common electrode branch54. As a result, the materials of the second, the third, and the fourth patterned conductive layers42,52,54preferably comprise metal materials with good conductivity, such as copper (Cu), chromium (Cr), and molybdenum (Mo). In addition, the second, the third, and the fourth patterned conductive layers42,52,54may be considered as a first metal layer, a second metal layer, and a third metal layer. In this situation, in order to reduce the total amounts of photomask and photolithography process applied in the whole fabrication process, two ion implantation processes and the photolithography process for defining the pattern of the second patterned conductive layer42may be integrated into one process when fabrication the TFT24according to the present invention.

FIG. 7toFIG. 9are schematic diagrams of the fabrication process of the TFT24according to the first embodiment of the present invention. First, as shown inFIG. 7, the first substrate12is provided, and then a first patterned conductive layer62is formed on the first substrate12, comprising the predetermined areas for forming source, drain, and channel region. The formation method of the first patterned conductive layer62includes sequentially forming a low-temperature polysilicon material and a photoresist layer on the first substrate12, performing a photolithography process to use a photomask with patterns of the source, drain, channel region, and a portion of the extending electrode34to pattern the photoresist layer, and taking the patterned photoresist layer as a mask to etch the low-temperature polysilicon material to form the first patterned conductive layer62. Thereafter, a gate insulating layer36and a first metal layer76are sequentially formed on the first substrate12, covering the first patterned conductive layer62.

Then, referring toFIG. 8, a photoresist layer is formed on the first substrate12, preferably comprising negative-type photoresist materials, and a photolithography process is performed to the photoresist layer so as to form a patterned photoresist layer78with a pattern a little larger than a predetermined pattern of the gate. Thereafter, the patterned photoresist layer78is taken as an etching mask to perform a dry-etching process and a wet-etching process to the first metal layer76in order. After these etching processes, the bottom of the patterned photoresist layer78and the first metal layer76are under-cut, such that the bottom surface of the patterned photoresist layer78is smaller than the top surface of the patterned photoresist layer78. Accordingly, the patterned first metal layer76forms the second patterned conductive layer42containing the gate24G. Wherein, the pattern of the gate24G is approximately smaller than the patterned photoresist layer78. Sequentially, an upright ion implantation process80with high concentration ions, such as a P+ type ion implantation process, is performed to form the source24S and drain24D near two sides of the gate24G on the first patterned conductive layer62. As shown inFIG. 8, the top surface of the patterned photoresist layer78is larger than the gate24G, and therefore the spacing of the source24S and the drain24D is larger than the width of the gate24G.

With reference toFIG. 9, the patterned photoresist layer78is removed, and the gate24G is taken as a mask to perform an upright ion implantation process82with low concentration ions, such as P− type ions, to form lightly doped drains (LDDs)24L in the first patterned conductive layer62, between the two sides of the gate24G to the source24S and drain24D. The portion of the first patterned conductive layer62without doping right below the gate24G serves as the channel region24C of the TFT24. As mentioned above, according to the fabrication process of the TFT24of the present invention, only a photolithography process and a patterned photoresist layer78are needed for defining the patterns of the gate24G, source24S, drain24D, and LDDs24L. As a result, the TFT24can be fabricated by using only two photomasks, effectively reducing the amount of photomasks and saving the fabrication cost. Accordingly, although three metal layers are applied for forming the devices of the pixel structure86of the present invention, the total amounts of photomask and photolithography process used in the fabrication process may be the same as that of the traditional fabrication method. Therefore, the fabrication process and cost of the present invention can meet the current process and cost standard.

FIGS. 10-12is a schematic diagram of a pixel structure according to a second embodiment of the present invention, whereinFIG. 10is a top-view of the pixel area, andFIGS. 11-12are sectional views along line11-11′ and line12-12′ of the pixel structure shown inFIG. 10respectively. Noted that similar elements and devices are represented by the same numerals in the first and second embodiments. The first and second common electrodes50,28in this second embodiment are formed with different patterned conductive layers from those in the first embodiment. Clearly speaking, the first and second common electrodes50,28are formed with the second patterned conductive layer42and the first patterned conductive layer62respectively. Therefore, the formation of the third patterned conductive layer52in the first embodiment is omitted, such that the amount of photomask and cost of the fabrication process may be further lowered.

The detailed design of the pixel structure86according to the second embodiment of the present invention pixel is described in the following. First, with reference toFIG. 10, the pixel area18is surrounded by two data lines20and two scan lines22, comprising a transmission region30and a reflection region32. The data lines20and the scan lines22are formed with the third patterned conductive layer84(corresponding to the fourth patterned conductive layer54in the first embodiment) and the second patterned conductive layer42respectively. The TFT24of the pixel area18is positioned in the reflection region32of an adjacent pixel area18, electrically connected to the transmission pixel electrode66in the transmission region30through the extending electrode34. The transmission pixel electrode66couples with the transparent electrode disposed on the surface of the first substrate12to form a transmission LC capacitor CLCt.

Referring toFIG. 11, in the storage capacitor region68, the extending electrode34is formed with the third patterned conductive layer84and the first patterned conductive layer62, forming the storage capacitor Cstwith the first common electrode50. In addition, the extending electrode34further forms a first coupling capacitor70by coupling with the reflective pixel electrode58in the reflection region32, as shown inFIG. 10.

With reference toFIG. 12, the reflective pixel electrode58is electrically connected to a reflection layer48on the surface of the planarization layer40, and forms a reflection LC capacitor CLCrby coupling with the transparent electrode (not shown) on the second substrate14, wherein the reflection LC capacitor CLCris electrically connected to the first coupling capacitor70in series. In addition, the reflective pixel electrode58further forms a second coupling capacitor72by coupling with the second common electrode28, parallel to the reflection LC capacitor CLCr.

Similar to the first embodiment of the present invention, the first common electrode50of this embodiment is formed with the second patterned conductive layer42, and is substantially parallel with the second common electrode28composed of the first patterned conductive layer62. The first common electrode50and the second common electrode28intersect the data line20in an overlapping area74. In the overlapping area74, the first common electrode50is disposed between the second common electrode28and the data line20along vertical axis so as to shield the influence from the data line20to the second common electrode28and to improve cross-talk problem. In addition, the first common electrode50only lines and bends downward near the two sides of the second coupling capacitor72into the storage capacitor region68, forming the storage capacitor Cstwith the extending electrode34.

In addition, in this embodiment, since the first patterned conductive layer62is used for forming the source24S, drain24D, a portion of the extending electrode34of the TFT24and the second common electrode28, it preferably comprises polysilicon materials, and may be doped with high concentration ions through an ion implantation process to form a heavily-doped polysilicon layer. On the other hand, the first common electrode50, the reflective pixel electrode58, and the scan line22are composed of the second patterned conductive layer42, and the data line20, a portion of the extending electrode34, and the second common electrode branch60are formed with the third patterned conductive layer84. Therefore, the second patterned conductive layer42and the third patterned conductive layer84preferably comprise metal materials and may be considered as a first metal layer and a second metal layer. It should be noted that the advantage of the pixel structure86in this embodiment is that all the electric devices of the pixel area18are formed only with the first, second, and the third patterned conductive layers62,42,84. Especially, the second common electrode28may be formed with the doped polysilicon material layer the same as the source24S and drain24D. Therefore, the amount of photomask, process materials and cost can be reduced.

In contrast to the prior art, since the first common electrode of the present invention pixel structure is disposed in the overlapping area between the second common electrode and data line vertically, it can effectively lower the influence of signal or voltage among the second common electrode and data line even though the second common electrode and data line overlap with each other. Therefore, the cross-talk problem is obviously improved. As a result, the pixel structure of the present invention may apply the ACC technique to match the reflection gamma curve with the transmission gamma curve for providing a single-gap transflective LCD panel, wherein the cross-talk effect of the transflective LCD panel can also be improved at the same time.