Patent Publication Number: US-11029570-B2

Title: Reflective LCD panel by disposing a white sub-pixel unit in the pixel unit and using the while sub-pixel unit in collaboration with the pixel electrode to increase brightness of the pixel unit

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a divisional application of co-pending U.S. patent application Ser. No. 16/671,174, filed on Nov. 1, 2019, which is a divisional application of U.S. patent application Ser. No. 15/579,946, filed on Dec. 6, 2017 and now U.S. Pat. No. 10,509,282, which is a national stage of PCT Application No. PCT/CN2017/113016, filed on Nov. 27, 2017, claiming foreign priority of Chinese Patent Application No. 201710814427.9, filed on Sep. 11, 2017. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of display techniques, and in particular to a reflective liquid crystal display (LCD) panel. 
     2. The Related Arts 
     The liquid crystal display (LCD) panel provides the advantages of thinness, low power consumption, without radiation, and is widely used in mobile phones, PDA, digital camera, PC screens or notebook PC screens. 
     Most LCD devices on the market are backlight-typed, which includes a backlight module, an LCD panel engaged to the backlight module, and a front frame fastening the LCD panel and the backlight module. The operation principle of the LCD panel is to place the liquid crystal (LC) molecules in two parallel glass substrates. A plurality of vertical and horizontal small wires is disposed between the two glass substrates. The LC molecules are controlled to change direction by powering on or off, and the light of the backlight module is refracted to produce an image. 
     At present, the LCD device is categorized, based on the type of light source, transmissive type LCD, reflective LCD, and transflective LCD. 
     With the rise of mobile devices and wearable applications, the demand for thinness and power saving of display devices is also growing. Therefore, the development of low power consumption display device becomes increasingly important. The traditional transmissive LCD has been massively produced, and the color, quality, resolution of the products are able to meet most of the needs. However, the LCD is relatively high power consumption when the display is used in mobile and wearable devices, which restricts usage time. 
     Because reflective LCD can display with ambient light without the need for energy-consuming backlights, the reflective LCD shows great potential in mobile devices and wearable display applications. 
       FIG. 1  shows a schematic view of a known reflective LCD panel. As shown in  FIG. 1 , the reflective LCD panel comprises: an upper substrate  100  and a lower substrate  200  disposed opposite to each other, and a liquid crystal layer  400  sandwiched between the upper substrate  100  and the lower substrates  200 ; the upper substrate  100  comprising: a first base substrate  110 , a color filter (CF) layer  240  and a black matrix (BM) disposed on the first base substrate  110 , a common electrode  120  disposed on the CF layer  240  and the BM  250 ; the lower substrate  200  comprising: a second base substrate  210 , a thin film transistor (TFT) device layer  220  disposed on the second base substrate  210 , and a pixel electrode  230  disposed on the TFT device layer  220 ; wherein the CF layer  240  comprising a transmissive red sub-pixel unit  310 , a transmissive green sub-pixel unit  320  and a transmissive blue sub-pixel unit  330  separated by the BM  250 ; the pixel electrode  230  is a reflective electrode. The operation principle of the reflective LCD panel is that the ambient light passes through the CF layer  240  and the LC layer  400  to reach the pixel electrode  230 . Then, the pixel electrode  230  reflects the light and the reflected light passes again through the LC layer  400  and the CF layer  240 , and is emitted from the surface of the upper substrate  100  to realize image display. During the operation of the reflective LCD panel, ambient light passes back and forth through the CF layer  240  and the LC layer  400 , resulting in relatively large loss of ambient light and low utilization, leading to insufficient brightness of the display screen of the LCD panel. 
     To improve the utilization of the ambient light by the reflective LCD panel, a reflective LCD panel as shown in  FIG. 2  is proposed. As shown in  FIG. 2 , the reflective LCD panel comprises: an upper substrate  100  and a lower substrate  200  disposed opposite to each other, and a liquid crystal layer  400  sandwiched between the upper substrate  100  and the lower substrates  200 ; the upper substrate  100  comprising: a first base substrate  110  and a common electrode  120  disposed the first base substrate  110 ; the lower substrate  200  comprising: a second base substrate  210 , a thin film transistor (TFT) device layer  220  disposed on the second base substrate  210 , a pixel electrode  230  disposed on the TFT device layer  220 , and a CF layer  240  and a BM  250  disposed on the pixel electrode  230 ; wherein the CF layer  240  comprising a reflective red sub-pixel unit  310 ′, a reflective green sub-pixel unit  320 ′ and a reflective blue sub-pixel unit  330 ′ separated by the BM  250 ; the pixel electrode  230  is a transparent electrode. Specifically, the reflective red sub-pixel unit  310 ′ can reflect red light and absorb green light and blue light, the reflective green sub-pixel unit  320 ′ can reflect green light and absorbs red light and blue light, and the blue reflective sub-pixel unit  330 ′ can reflect blue light and absorb red light and green light. The operation principle of the reflective LCD panel is that the ambient light passes through the LC layer  400  to reach the CF layer  240 , and then the CF layer  240  selectively absorbs and reflects the light, and the reflected light passes through the LC layer  400  again and emits from the surface of the upper substrate  100  to realize image display. During the operation of the reflective LCD panel, the ambient light passes through the CF layer  240  only once, which reduces the loss of ambient light in the CF layer  240 . However, since the CF layer  240  absorbs most of the spectrum and the ambient light needs to go through the structural layers such as the LC layer  400 , the upper and lower alignment films (not shown) and the first base substrate  110  twice, the loss of ambient light is still large. Therefore, the brightness of the display screen of the LCD panel still needs improvement. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a reflective LCD panel, by disposing a white sub-pixel unit in the pixel unit and using the white sub-pixel in collaboration with the pixel electrode to increase the brightness of the pixel unit, leading to improving the emission brightness of the reflective LCD panel. 
     To achieve the above object, the present invention provides a reflective LCD panel, which comprises: an upper substrate and a lower substrate disposed opposite to each other, and a liquid crystal (LC) layer sandwiched between the upper substrate and the lower substrate; the upper substrate comprising: a first base substrate, a common electrode disposed on the first base substrate; the lower substrate comprising: a second base substrate, a thin film transistor (TFT) device layer disposed on the second base substrate, a pixel electrode disposed on the TFT device layer, and a color filter (CF) layer and a black matrix (BM) disposed on the pixel electrode; 
     wherein the CF layer comprising a plurality of pixel units arranged in an array, with each pixel unit comprising: a red sub-pixel unit, a green sub-pixel unit, a blue sub-pixel unit, and a white sub-pixel unit separated by the BM; the red sub-pixel unit able to reflect red light and absorb green light and blue light; the green sub-pixel unit able to reflect green light and absorb red light and blue light; the blue sub-pixel unit able to reflect blue light and absorb red light and green light; 
     when the white sub-pixel unit being a transparent film, the pixel electrode being a reflective electrode; when the white sub-pixel unit being a reflective film, the pixel electrode being a transparent electrode or non-transparent electrode; 
     when the white sub-pixel unit being a transparent film, the red light, green light and blue light able to pass through the white sub-pixel unit; when the white sub-pixel unit being a reflective film, the red light, green light and blue light able to be reflected by the white sub-pixel unit. 
     According to a preferred embodiment of the present invention, the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit of the pixel unit are arranged in one of the following three arrangements: 
     the first arrangement: the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit being arranged in a row from left to right; 
     the second arrangement: the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit being arranged in a column from top to bottom; 
     the third arrangement: the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit being arranged in an upper row and a lower row; the upper row comprising: from left to right, the red sub-pixel unit and the green sub-pixel unit; the lower row comprising: from left to right, the blue sub-pixel unit and the white sub-pixel unit; wherein the red sub-pixel unit and the blue sub-pixel unit forming a column, and the green sub-pixel unit and the white sub-pixel unit forming a column. 
     According to a preferred embodiment of the present invention, the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit have the same thickness; 
     when the pixel electrode is a reflective electrode, the pixel electrode is made of metal; when the pixel electrode is a transparent electrode, the pixel electrode is made of a transparent conductive metal oxide; and when the pixel electrode is a non-transparent electrode, the pixel electrode is made of metal. 
     According to a preferred embodiment of the present invention, the reflective LCD panel further comprises: a first alignment film disposed at a side of the upper substrate facing the LC layer; a second alignment film disposed at a side of the lower substrate facing the LC layer, an upper polarizer disposed at a side of the upper substrate facing away from the LC layer; and a lower polarizer disposed at a side of the lower substrate facing away from the LC layer; wherein the upper polarizer and the lower polarizer have absorbing axes mutually perpendicular to each other. 
     According to a preferred embodiment of the present invention, the reflective LCD panel further comprises: a spacer disposed between the BM and the second alignment film, the spacer and the BM are made of the same material and formed monolithically. 
     The present invention also provides a reflective LCD panel, which comprises: an upper substrate and a lower substrate disposed opposite to each other, and a liquid crystal (LC) layer sandwiched between the upper substrate and the lower substrate; the upper substrate comprising: a first base substrate, a common electrode disposed on the first base substrate; the lower substrate comprising: a second base substrate, a thin film transistor (TFT) device layer disposed on the second base substrate, a color filter (CF) layer and a black matrix (BM) disposed on the TFT device layer, and a pixel electrode disposed on the CF layer and the BM; 
     wherein the CF layer comprising a plurality of pixel units arranged in an array, with each pixel unit comprising: a red sub-pixel unit, a green sub-pixel unit, a blue sub-pixel unit, and a white sub-pixel unit separated by the BM; the red sub-pixel unit able to reflect red light and absorb green light and blue light; the green sub-pixel unit able to reflect green light and absorb red light and blue light; the blue sub-pixel unit able to reflect blue light and absorb red light and green light; 
     the white sub-pixel unit being a reflective film, and the pixel electrode being a transparent electrode or non-transparent electrode; 
     the white sub-pixel unit being a reflective film, and the red light, green light and blue light able to be reflected by the white sub-pixel unit. 
     According to a preferred embodiment of the present invention, the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit of the pixel unit are arranged in one of the following three arrangements: 
     the first arrangement: the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit being arranged in a row from left to right; 
     the second arrangement: the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit being arranged in a column from top to bottom; 
     the third arrangement: the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit being arranged in an upper row and a lower row; the upper row comprising: from left to right, the red sub-pixel unit and the green sub-pixel unit; the lower row comprising: from left to right, the blue sub-pixel unit and the white sub-pixel unit; wherein the red sub-pixel unit and the blue sub-pixel unit forming a column, and the green sub-pixel unit and the white sub-pixel unit forming a column. 
     According to a preferred embodiment of the present invention, the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit have the same thickness; the pixel electrode is made of metal; the pixel electrode is made of a transparent conductive metal oxide. 
     According to a preferred embodiment of the present invention, the reflective LCD panel further comprises: a first alignment film disposed at a side of the upper substrate facing the LC layer; a second alignment film disposed at a side of the lower substrate facing the LC layer, an upper polarizer disposed at a side of the upper substrate facing away from the LC layer; and a lower polarizer disposed at a side of the lower substrate facing away from the LC layer; wherein the upper polarizer and the lower polarizer have absorbing axes mutually perpendicular to each other. 
     According to a preferred embodiment of the present invention, the reflective LCD panel further comprises: a spacer disposed between the BM and the pixel electrode, the spacer and the BM are made of the same material and formed monolithically. 
     The present invention also provides a reflective LCD panel, which comprises: an upper substrate and a lower substrate disposed opposite to each other, and a liquid crystal (LC) layer sandwiched between the upper substrate and the lower substrate; the upper substrate comprising: a first base substrate, a common electrode disposed on the first base substrate; the lower substrate comprising: a second base substrate, a thin film transistor (TFT) device layer disposed on the second base substrate, a pixel electrode disposed on the TFT device layer, and a color filter (CF) layer and a black matrix (BM) disposed on the pixel electrode; 
     wherein the CF layer comprising a plurality of pixel units arranged in an array, with each pixel unit comprising: a red sub-pixel unit, a green sub-pixel unit, a blue sub-pixel unit, and a white sub-pixel unit separated by the BM; the red sub-pixel unit able to reflect red light and absorb green light and blue light; the green sub-pixel unit able to reflect green light and absorb red light and blue light; the blue sub-pixel unit able to reflect blue light and absorb red light and green light; 
     when the white sub-pixel unit being a transparent film, the pixel electrode being a reflective electrode; when the white sub-pixel unit being a reflective film, the pixel electrode being a transparent electrode or non-transparent electrode; 
     when the white sub-pixel unit being a transparent film, the red light, green light and blue light able to pass through the white sub-pixel unit; when the white sub-pixel unit being a reflective film, the red light, green light and blue light able to be reflected by the white sub-pixel unit. 
     wherein the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit of the pixel unit being arranged in one of the following three arrangements: 
     the first arrangement: the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit being arranged in a row from left to right; 
     the second arrangement: the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit being arranged in a column from top to bottom; 
     the third arrangement: the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit being arranged in an upper row and a lower row; the upper row comprising: from left to right, the red sub-pixel unit and the green sub-pixel unit; the lower row comprising: from left to right, the blue sub-pixel unit and the white sub-pixel unit; wherein the red sub-pixel unit and the blue sub-pixel unit forming a column, and the green sub-pixel unit and the white sub-pixel unit forming a column; 
     wherein the red sub-pixel unit, the green sub-pixel unit, the blue sub-pixel unit, and the white sub-pixel unit having the same thickness; 
     when the pixel electrode being a reflective electrode, the pixel electrode being made of metal; when the pixel electrode beings a transparent electrode, the pixel electrode being made of a transparent conductive metal oxide; and when the pixel electrode being a non-transparent electrode, the pixel electrode being made of metal. 
     further comprising: a first alignment film disposed at a side of the upper substrate facing the LC layer; a second alignment film disposed at a side of the lower substrate facing the LC layer, an upper polarizer disposed at a side of the upper substrate facing away from the LC layer; and a lower polarizer disposed at a side of the lower substrate facing away from the LC layer; wherein the upper polarizer and the lower polarizer having absorbing axes mutually perpendicular to each other; 
     further comprising: a spacer disposed between the BM and the second alignment film, the spacer and the BM being made of the same material and formed monolithically. 
     The present invention provides the following advantages. The reflective LCD panel of the present invention is disposed with white sub-pixel unit in the pixel unit. When the pixel electrode is disposed below the CF layer, the white sub-pixel unit is a transparent film layer and the pixel electrode is a reflective electrode, or when the white sub-pixel unit is a reflective film layer, the pixel electrode is a transparent electrode or a non-transparent electrode; when the pixel electrode is disposed above the CF layer, the white sub-pixel unit is a reflection film layer and the pixel electrode is a transparent electrode. The reflective LCD panel of the present invention utilizes the combination of the white sub-pixel unit and the pixel electrode to improve the utilization of the ambient light, so as to enhance the brightness of the pixel unit and further enhance the brightness of the reflective LCD panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To make the technical solution of the embodiments according to the present invention, a brief description of the drawings that are necessary for the illustration of the embodiments will be given as follows. Apparently, the drawings described below show only example embodiments of the present invention and for those having ordinary skills in the art, other drawings may be easily obtained from these drawings without paying any creative effort. In the drawings: 
         FIG. 1  is a schematic view showing the structure of a conventional reflective LCD panel; 
         FIG. 2  is a schematic view showing the structure of another conventional reflective LCD panel; 
         FIG. 3  is a schematic view showing the structure of a reflective LCD panel provided by a first embodiment of the present invention; 
         FIG. 4  is a schematic view showing the structure of a reflective LCD panel provided by a second embodiment of the present invention; 
         FIG. 5  is a schematic view showing the first arrangement of the pixel unit in the reflective LCD panel provided by the first and second embodiments of the present invention; 
         FIG. 6  is a schematic view showing the second arrangement of the pixel unit in the reflective LCD panel provided by the first and second embodiments of the present invention; 
         FIG. 7  is a schematic view showing the third arrangement of the pixel unit in the reflective LCD panel provided by the first and second embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     To further explain the technique means and effect of the present invention, the following uses preferred embodiments and drawings for detailed description. 
     Refer to  FIG. 3 . The present invention provides a reflective LCD panel, which comprises: an upper substrate  10  and a lower substrate  20  disposed opposite to each other, and a liquid crystal (LC) layer  40  sandwiched between the upper substrate  10  and the lower substrate  20 ; the upper substrate  10  comprising: a first base substrate  11 , a common electrode  12  disposed on the first base substrate  11 ; the lower substrate  20  comprising: a second base substrate  21 , a thin film transistor (TFT) device layer  22  disposed on the second base substrate  21 , a pixel electrode  23  disposed on the TFT device layer  22 , and a color filter (CF) layer  24  and a black matrix (BM)  25  disposed on the pixel electrode  23 ; 
     wherein the CF layer  24  comprising a plurality of pixel units  30  arranged in an array, with each pixel unit comprising: a red sub-pixel unit  31 , a green sub-pixel unit  32 , a blue sub-pixel unit  33 , and a white sub-pixel unit  34  separated by the BM  25 ; the red sub-pixel unit  31  able to reflect red light and absorb green light and blue light; the green sub-pixel unit  32  able to reflect green light and absorb red light and blue light; the blue sub-pixel unit  33  able to reflect blue light and absorb red light and green light; 
     when the white sub-pixel unit  34  being a transparent film, the pixel electrode  23  being a reflective electrode; when the white sub-pixel unit  34  being a reflective film, the pixel electrode  23  being a transparent electrode or non-transparent electrode. 
     Specifically, when the white sub-pixel unit  34  is a transparent film, the red light, green light and blue light are able to pass through the white sub-pixel unit  34 ; when the white sub-pixel unit  34  is a reflective film, the red light, green light and blue light are able to be reflected by the white sub-pixel unit  34 . 
     When the white sub-pixel unit  34  is a transparent film layer, the pixel electrode  23  is a reflective electrode. The operation principle of the reflective LCD panel is: the white ambient light passes through the LC layer  40  to reach the red sub-pixel unit  31 , the green sub-pixel unit  32 , and the blue sub-pixel unit  33  of the CF layer  24 ; the red sub-pixel unit  31 , the green sub-pixel unit  32 , and the blue sub-pixel unit  33  of the CF layer  24  perform selective absorption and reflects red light, green light, blue light, respectively; the reflected red, green and blue light passes through the LC layer  40  again and emits from the surface of the upper substrate  10 ; the white ambient light passes through the LC layer  40  to reach the white sub-pixel  34  of the CF layer  24 ; the white ambient light passes through the white sub-pixel unit  34  of the CF layer  24  and is reflected by the pixel electrode  23 ; the reflected white light passes through the LC layer  40  again and emits from the surface of the upper substrate  10 . 
     When the white sub-pixel unit  34  is a reflective film layer, the pixel electrode  23  is a transparent electrode or a non-transparent electrode. The operation principle of the reflective LCD panel is: the white ambient light passes through the LC layer  40  to reach the red sub-pixel unit  31 , the green sub-pixel unit  32 , and the blue sub-pixel unit  33  of the CF layer  24 ; the red sub-pixel unit  31 , the green sub-pixel unit  32 , and the blue sub-pixel unit  33  of the CF layer  24  perform selective absorption and reflects red light, green light, blue light, respectively; the reflected red, green and blue light passes through the LC layer  40  again and emits from the surface of the upper substrate  10 ; the white ambient light passes through the LC layer  40  to reach the white sub-pixel  34  of the CF layer  24 ; the white ambient light is reflected by the white sub-pixel unit  34 ; the reflected white light passes through the LC layer  40  again and emits from the surface of the upper substrate  10 . 
     Compared to the conventional reflective LCD panel shown in  FIG. 2 , the present invention disposes a white sub-pixel unit  34  in the pixel unit  30  and uses the white sub-pixel unit  34  in collaboration with the pixel electrode  23  to add a beam of white light in the light emitted from the pixel unit  30  so as to increase the brightness of the pixel unit  30  and the emission brightness of the reflective LCD panel. 
     Specifically, the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  of the pixel unit  30  can be arranged in the same row or in different rows, but all must be in the same layer. 
     Specifically, the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  of the pixel unit  30  are arranged in one of the following three arrangements: 
     As shown in  FIG. 5 , the first arrangement: the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  are arranged in a row from left to right. 
     As shown in  FIG. 6 , the second arrangement: the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  are arranged in a column from top to bottom. 
     As shown in  FIG. 7 , the third arrangement: the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  are arranged in an upper row and a lower row; the upper row comprises: from left to right, the red sub-pixel unit  31  and the green sub-pixel unit  32 ; the lower row comprises: from left to right, the blue sub-pixel unit  33  and the white sub-pixel unit  34 ; wherein the red sub-pixel unit  31  and the blue sub-pixel unit  33  form a column, and the green sub-pixel unit  32  and the white sub-pixel unit  34  form a column. 
     Specifically, the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  have the same thickness, or slightly different. 
     Specifically, when the pixel electrode  23  is a reflective electrode, the pixel electrode  23  is made of metal, preferably, aluminum (Al); when the pixel electrode  23  is a transparent electrode, the pixel electrode  23  is made of a transparent conductive metal oxide, preferably ITO; and when the pixel electrode  23  is a non-transparent electrode, the pixel electrode  23  is made of metal, preferably, aluminum (Al). 
     Specifically, the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  are all made of organic material. 
     Specifically, the BM  25  is to prevent the light from the adjacent sub-pixel units among the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  from mixing, and to improve purity of the light color emitted from a single sub-pixel unit. 
     Specifically, the reflective LCD panel further comprises: a first alignment film  51  disposed at a side of the upper substrate  10  facing the LC layer  40 ; a second alignment film  52  disposed at a side of the lower substrate  20  facing the LC layer  40 , an upper polarizer  61  disposed at a side of the upper substrate  10  facing away from the LC layer  40 ; and a lower polarizer  62  disposed at a side of the lower substrate  20  facing away from the LC layer  40 ; wherein the upper polarizer  61  and the lower polarizer  62  have absorbing axes mutually perpendicular to each other. 
     Moreover, the reflective LCD panel further comprises: a spacer  70  disposed between the BM  25  and the pixel electrode  23 , the spacer  70  is to maintain the thickness of LC box so as to prevent the thickness of LC layer  40  from changing when the LCD panel is pressed. The disposition of the spacer  70  will not affect the aperture ratio of the pixel unit  30 , which facilitates the aperture ratio of the LCD panel. 
     Preferably, the spacer  70  and the BM  25  are made of the same material and formed monolithically to save production time and cost. 
     The above reflective LCD panel adds a white sub-pixel unit  34  to the pixel unit  30  and disposes the pixel electrode  23  beneath the CF layer  24 . The white sub-pixel unit  34  is a transparent film layer and the pixel electrode  23  is a reflective electrode. Alternatively, the white sub-pixel unit  34  is a reflective film layer and the pixel electrode  23  is a transparent electrode or non-transparent electrode. The present invention uses the white sub-pixel unit  34  in collaboration with the pixel electrode  23  to increase the brightness of the pixel unit  30  and the emission brightness of the reflective LCD panel. 
     Refer to  FIG. 4 . The present invention also provides a reflective LCD panel, which comprises: an upper substrate  10  and a lower substrate  20  disposed opposite to each other, and a liquid crystal (LC) layer  40  sandwiched between the upper substrate  10  and the lower substrate  20 ; the upper substrate  10  comprising: a first base substrate  11 , a common electrode  12  disposed on the first base substrate  11 ; the lower substrate  20  comprising: a second base substrate  21 , a thin film transistor (TFT) device layer  22  disposed on the second base substrate  21 , a color filter (CF) layer  24  and a black matrix (BM)  25  disposed on the TFT device layer  22 , and a pixel electrode  23  disposed on the CF layer  24  and the BM  25 ; 
     wherein the CF layer  24  comprising a plurality of pixel units  30  arranged in an array, with each pixel unit comprising: a red sub-pixel unit  31 , a green sub-pixel unit  32 , a blue sub-pixel unit  33 , and a white sub-pixel unit  34  separated by the BM  25 ; the red sub-pixel unit  31  able to reflect red light and absorb green light and blue light; the green sub-pixel unit  32  able to reflect green light and absorb red light and blue light; the blue sub-pixel unit  33  able to reflect blue light and absorb red light and green light; 
     the white sub-pixel unit  34  being a reflective film, the pixel electrode  23  being a transparent electrode. 
     Specifically, when the white sub-pixel unit  34  is a reflective film, the red light, green light and blue light are able to be reflected by the white sub-pixel unit  34 . 
     The operation principle of the reflective LCD panel is: the white ambient light passes through the LC layer  40  and the pixel electrode  23  to reach the red sub-pixel unit  31 , the green sub-pixel unit  32 , and the blue sub-pixel unit  33  of the CF layer  24 ; the red sub-pixel unit  31 , the green sub-pixel unit  32 , and the blue sub-pixel unit  33  of the CF layer  24  perform selective absorption and reflects red light, green light, blue light, respectively; the reflected red, green and blue light passes through the LC layer  40  again and emits from the surface of the upper substrate  10 ; the white ambient light passes through the LC layer  40  and the pixel electrode  23  to reach the white sub-pixel  34  of the CF layer  24 ; the white ambient light is reflected by the white sub-pixel unit  34 ; the reflected white light passes through the pixel electrode  23  and the LC layer  40  again and emits from the surface of the upper substrate  10 . 
     Compared to the conventional reflective LCD panel shown in  FIG. 2 , the present invention disposes a white sub-pixel unit  34  in the pixel unit  30  and uses the white sub-pixel unit  34  in collaboration with the pixel electrode  23  to add a beam of white light in the light emitted from the pixel unit  30  so as to increase the brightness of the pixel unit  30  and the emission brightness of the reflective LCD panel. 
     Specifically, the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  of the pixel unit  30  can be arranged in the same row or in different rows, but all must be in the same layer. 
     Specifically, the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  of the pixel unit  30  are arranged in one of the following three arrangements: 
     As shown in  FIG. 5 , the first arrangement: the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  are arranged in a row from left to right. 
     As shown in  FIG. 6 , the second arrangement: the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  are arranged in a column from top to bottom. 
     As shown in  FIG. 7 , the third arrangement: the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  are arranged in an upper row and a lower row; the upper row comprises: from left to right, the red sub-pixel unit  31  and the green sub-pixel unit  32 ; the lower row comprises: from left to right, the blue sub-pixel unit  33  and the white sub-pixel unit  34 ; wherein the red sub-pixel unit  31  and the blue sub-pixel unit  33  form a column, and the green sub-pixel unit  32  and the white sub-pixel unit  34  form a column. 
     Specifically, the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  have the same thickness, or slightly different. 
     Specifically, the pixel electrode  23  is made of a transparent conductive metal oxide, preferably ITO. 
     Specifically, the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  are all made of organic material. 
     Specifically, the BM  25  is to prevent the light from the adjacent sub-pixel units among the red sub-pixel unit  31 , the green sub-pixel unit  32 , the blue sub-pixel unit  33 , and the white sub-pixel unit  34  from mixing, and to improve purity of the light color emitted from a single sub-pixel unit. 
     Specifically, the reflective LCD panel further comprises: a first alignment film  51  disposed at a side of the upper substrate  10  facing the LC layer  40 ; a second alignment film  52  disposed at a side of the lower substrate  20  facing the LC layer  40 , an upper polarizer  61  disposed at a side of the upper substrate  10  facing away from the LC layer  40 ; and a lower polarizer  62  disposed at a side of the lower substrate  20  facing away from the LC layer  40 ; wherein the upper polarizer  61  and the lower polarizer  62  have absorbing axes mutually perpendicular to each other. 
     Moreover, the reflective LCD panel further comprises: a spacer  70  disposed between the BM  25  and the second alignment film  52 , the spacer  70  is to maintain the thickness of LC box so as to prevent the thickness of LC layer  40  from changing when the LCD panel is pressed. The disposition of the spacer  70  will not affect the aperture ratio of the pixel unit  30 , which facilitates the aperture ratio of the LCD panel. 
     Preferably, the spacer  70  and the BM  25  are made of the same material and formed monolithically to save production time and cost. 
     The above reflective LCD panel adds a white sub-pixel unit  34  to the pixel unit  30  and disposes the pixel electrode  23  above the CF layer  24 . The white sub-pixel unit  34  is a reflective film layer and the pixel electrode  23  is a transparent electrode. The present invention uses the white sub-pixel unit  34  in collaboration with the pixel electrode  23  to increase the brightness of the pixel unit  30  and the emission brightness of the reflective LCD panel. 
     In summary, the present invention provides a reflective LCD panel. The reflective LCD panel of the present invention is disposed with white sub-pixel unit in the pixel unit. When the pixel electrode is disposed below the CF layer, the white sub-pixel unit is a transparent film layer and the pixel electrode is a reflective electrode, or when the white sub-pixel unit is a reflective film layer, the pixel electrode is a transparent electrode or a non-transparent electrode; when the pixel electrode is disposed above the CF layer, the white sub-pixel unit is a reflection film layer and the pixel electrode is a transparent electrode. The reflective LCD panel of the present invention utilizes the combination of the white sub-pixel unit and the pixel electrode to improve the utilization of the ambient light, so as to enhance the brightness of the pixel unit and further enhance the brightness of the reflective LCD panel. 
     It should be noted that in the present disclosure the terms, such as, first, second are only for distinguishing an entity or operation from another entity or operation, and does not imply any specific relation or order between the entities or operations. Also, the terms “comprises”, “include”, and other similar variations, do not exclude the inclusion of other non-listed elements. Without further restrictions, the expression “comprises a . . . ” does not exclude other identical elements from presence besides the listed elements. 
     Embodiments of the present invention have been described, but not intending to impose any unduly constraint to the appended claims. Any modification of equivalent structure or equivalent process made according to the disclosure and drawings of the present invention, or any application thereof, directly or indirectly, to other related fields of technique, is considered encompassed in the scope of protection defined by the claims of the present invention.