Abstract:
A touch panel is provided. The touch panel comprises a first substrate and a second substrate facing the first substrate. A black matrix is formed on the first substrate defining a plurality of sub-pixel areas, a plurality of color filters on the sub-pixel areas. A photosensitive sensitive element is formed on the second substrate. The color filters comprise a red color filter, a green color filter, a blue color filter and a white color filter over the photosensitive element.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a touch panel, and in particular to light sensitive touch panel having improved photosensitivity. 
   2. Description of the Related Art 
   Touch panels generally include a liquid crystal panel (LCD) with an additional sensitive film thereon. The additional sensitive film may increase cost and reduce the transmittance of the LCD about by 20%. Light sensitive touch panels include a photosensitive thin film transistor with photosensitive amorphous channel and a display element of LCD integrated and manufactured thus lowering cost and improving optical properties. 
     FIG. 1  is a circuit diagram of a conventional light sensitive touch panel. The light sensitive touch panel  10  comprises a first substrate (not shown) and a second substrate (not shown). A black matrix on the first substrate defining a plurality of sub-pixel areas (not shown); a plurality of color filter patterns on the sub-pixel areas (not shown). A plurality of horizontal scan lines  16  and a plurality of perpendicular data lines  18  are disposed on the second substrate. Each sub-pixel includes a pixel thin film transistor  20  having a gate electrically connected to one of the scan lines  16 , a source electrically connected to one of the data lines  18  and a drain electrically connected to a pixel electrode (not shown).  FIG. 2  is a schematic diagram showing the sub-pixels of the conventional light sensitive touch panel. A red color filter  24 , a green color filter  26  and a blue color filter  28  corresponding to the respective pixel electrodes  22  are formed on the upper substrate  12  to respectively display red light, green light and blue light. The pixel electrodes  22  are formed on the lower substrate  14 . Additionally, a black matrix  30  is formed among the red color filter  24 , the green color filter  26  and the blue color filter  28  to shield the pixel thin film transistor (not shown) and prevent light leakage from adjacent sub-pixels, thereby obtaining high contrast. 
   The Human eye has relatively low sensitivity to blue light, thus a photosensitive element comprising a photosensitive thin film transistor and a readout thin film transistor must be located under the blue color filter. As shown in  FIG. 1 , a photosensitive thin film transistor  32  comprises a gate electrode and a source electrode both electrically connected to a horizontal common line  34  and a drain electrode electrically connected to the readout thin film transistor  36 . The readout thin film transistor  36  comprises a gate electrode electrically connected to one of the scan lines  16 , a source electrically connected to a perpendicular readout line  38  and a drain electrically connected to the photosensitive thin film transistor  32 . Under the blue color filter, the gates of the pixel thin film transistor  20  and the readout thin film transistor  36  are respectively connected to the adjacent scan lines  16  surrounding the blue sub-pixel. When the photosensitive thin film transistor  32  is radiated by an ambient light, a photo current is produced. On the other hand, when the photosensitive thin film transistor  32  is shielded by a touch object, the photo current is not produced. The readout thin film transistor  36  reads out and periodically transfers the photo current to a processor (not shown) by a readout line  38 . The touched position can be detected by the processor according to photo current change when light sensitive touch panel  10  is touched by a touch object. Thus, the touch control function of the touch panel can be performed. 
   The photosensitive element is arranged under the blue color filter of the conventional light sensitive touch panel, the photosensitive thin film transistor is therefore radiated by the ambient light after passing through the blue color filter. The ambient light is partially absorbed by the blue color filter thus reducing the photosensitivity of the photosensitive element. 
   BRIEF SUMMARY OF THE INVENTION 
   Therefore, there is a need to provide a touch panel such as a light sensitive touch panel with improved photosensitivity. The touch panel includes a photosensitive element arranged under the white color filter to allow the ambient light to directly radiate from the photosensitive thin film transistor. 
   An exemplary embodiment of a touch panel comprises a first substrate, a second substrate. A black matrix on the first substrate defining a plurality of sub-pixel areas; a plurality of color filters on the sub-pixel areas, wherein said color filters comprise a red color filter, a green color filter, a blue color filter and a white color filter. A plurality of scan lines and a plurality of data lines vertically and horizontally arranged on the second substrate. Each sub-pixel comprises a pixel thin film transistor having a gate electrode electrically connected to one of the scan lines, a source electrically connected to one of the data lines and a drain electrode electrically connected to a pixel electrode. At least one photosensitive element is formed in the sub-pixel regions. Moreover, the white color filter is over the photosensitive element. 
   A detailed description is given in the following embodiments with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
       FIG. 1  is a circuit diagram of a conventional touch panel; 
       FIG. 2  is a schematic diagram showing a sub-pixel of the conventional touch panel; 
       FIG. 3  is a circuit diagram of an exemplary touch panel of the invention; 
       FIG. 4  is a schematic diagram of a touch panel of a first embodiment of the invention; 
       FIG. 5  is a schematic diagram of a touch panel of a second embodiment of the invention; and 
       FIG. 6  is schematic diagram showing curves of voltage difference versus luminance of red light, green light, blue light and white light respectively. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
   In order to increase resolution and brightness, liquid crystal displays having four color filters (red, green, blue and white) have been developed to replace the conventional touch panel having only three color filters (red, green, blue). The white color filter without color pigments, dye or colorants can directly display a white light from a backlight source. In some embodiments of the invention, a photosensitive element is integrated and manufactured under the white color filter of the liquid crystal display of the touch panel thereby improving photosensitivity of the photosensitive element. 
   As shown in  FIG. 3 , a plurality of horizontal scan lines  102  and a plurality of vertical data lines  104  are disposed on the second substrate (not shown). Color filters are regularly arranged in red sub-pixel  116 , green sub-pixel  118 , blue sub-pixel  120  and white sub-pixel  122 . A red color filter, a green color filter and a blue color filter respectively corresponding to red sub-pixel  116 , green sub-pixel  118 , and blue sub-pixel  120  are disposed on the first substrate (not shown). There is a no colored layer (no pigments or dye or colorants) corresponding to the white sub-pixel  122 . The white sub-pixel  122  may comprises a transparent organic resin layer. 
   The red sub-pixel  116 , the green sub-pixel  118 , the blue sub-pixel  120 , and the white sub-pixel  122 , serving as display elements, respectively comprise a pixel thin film transistor  106 . The pixel thin film transistor  106  has a gate electrode electrically connected to one of the scan lines  102 , a source electrode electrically connected to one of the data lines  104  and a drain electrode electrically connected to a pixel electrode (not shown). The white color filter in the white sub-pixel  122  is over the photosensitive element comprising a photosensitive thin film transistor  108  and a readout thin film transistor  110 . The photosensitive thin film transistor  108  may comprise a gate electrode and a source electrode both electrically connected to a common line  112  and a drain electrically connected to the readout thin film transistor  110 . The readout thin film transistor  110  may comprise a gate electrode electrically connected to one of the scan lines  102 , a source electrode electrically connected to a vertical readout line  114  and a drain electrode electrically connected to the photosensitive thin film transistor  108 . In the white sub-pixel  122 , the gate electrodes of the pixel thin film transistor  106  and the readout thin film transistor  110  are respectively connected to the adjacent scan lines  102  surrounding the sub-pixel region which is covered by the white color filter of the white sub-pixel  122 . 
     FIG. 4  and  FIG. 5  are schematic diagrams of the touch panels of the first and second embodiments of the invention. As shown in  FIG. 4 , red sub-pixel  116 , green sub-pixel  118 , blue sub-pixel  120  and white sub-pixel  122  are regularly arranged in the touch panel  100  of a first embodiment. A photosensitive element comprising a photosensitive thin film transistor (not shown) and a readout thin film transistor  110  is formed under the white color filter of the white sub-pixel  122 . The readout line  114  arranged along the vertical direction is connected to the readout thin film transistor  110 . Similarly, as shown in  FIG. 5 , red sub-pixel  116 , green sub-pixel  118 , blue sub-pixel  120  and white sub-pixel  122  are regularly arranged in the touch panel  100  of a second embodiment. A photosensitive element comprising a photosensitive thin film transistor (not shown) and a readout thin film transistor  110  is formed under the white color filter of the white sub-pixel  122 . The readout line  114  arranged along the horizontal direction is connected to the readout thin film transistor  110 . 
     FIG. 6  is schematic diagram showing curves of voltage difference versus luminance of red light, green light, blue light and white light respectively. A photosensitive thin film transistor  108  is respectively radiated by different luminance of red, green, blue and white light. The voltage difference is a voltage drop of a photo current through a fixed resistor. Thus, the greater the measured voltage difference, the greater produced photo current. Among the range of 1 to 1000 cd/cm 2  of the ambient light, white light and green light can produce a greater voltage difference. If the photosensitive thin film transistor  108  is disposed under the green color filter (green sub-pixel  118 ), the image color of the light sensitive touch panel may be changed. On the other hand, the white color filter (white sub-pixel  122 ) is over a photosensitive thin film transistor  108  and a pixel thin film transistor, wherein the pixel thin film transistor is not completely turned on while displaying a color image. Therefore, the image color of the light sensitive touch panel may not be changed. 
   As compared with the poor photosensitivity of conventional touch panels, the photosensitive thin film transistor of the photosensitive element formed under the white color filter can be directly radiated by the ambient light without passing through a colored layer. Thus, greater photo current can be produced and photosensitivity of the touch panel can be improved. 
   While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.