Abstract:
A high color expression display device and a method for manufacturing the same are provided. The display device includes a backlight module and a display panel for receiving light from the backlight module. The display panel has a color filter layer which consists of a plurality of color resists above the backlight module. Lights from the backlight module pass through the color resists and out of the display panel to form an output light. A NTSC saturation of the output light may be greater or smaller than 60%, and a CIE standard illuminant C test result of the color resists may correspondingly fall into different predetermined scopes to prevent color shift and maintain brightness of the display device.

Description:
[0001]    This application claims the priority based on a Taiwanese Patent Application No. 098102981, filed on Jan. 23, 2009, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a display device and a method for manufacturing the same; more particularly, the present invention relates to a high color expression display device and a method for manufacturing the same. 
         [0004]    2. Description of the Prior Art 
         [0005]    Display panels and panel display devices using the display panels have become the mainstream display devices. For example, various panel displays, home flat televisions, panel monitors of personal computers and laptop computers, and display screens of mobile phones and cameras are products widely using display panels. Particularly, the market demand for liquid crystal display devices largely increases in recent years. In order to meet the function and appearance requirements of liquid crystal displays, the design of backlight modules used in liquid crystal display devices is also diverse. 
         [0006]    In conventional, the backlight module usually uses tube lamps as the backlight source. Light emitted from the tube lamp can achieve a certain level of color rendering and color saturation. However, since the tube lamp occupies a larger space, the backlight module equipped with the tube lamp accordingly has a larger volume. Additionally, the tube lamp consumes more power resulting in low usable time for the entire system. In order to address the above problems, some backlight modules use white light emitting diodes (LEDs) as the light source. The white LED is advantageous in environmental protection, low power consumption, and small volume. However, the color expression and color saturation of the white LED still cannot match up those of the tube lamp. For example, the white LED made of a blue LED chip with yellow green phosphors usually generates small energy in the red light range causing color shift in the generated white light. 
         [0007]    Additionally, due to material properties and production limitations of the white LED, the availability of white LEDs is restricted. As shown in  FIG. 1 , due to various limitations, the available or suitable white LEDs are those having coordinates fallen into the area  10  (for example, in the CIE 1931 coordinate system). However, in consideration of color saturation and expression of other colors, the practical white LEDs may be those having coordinates fallen into the area  30 . Since only half of white LEDs in the area  30  will meet the limitations defined in the area  10 , the other half of white LEDs are not applicable which inevitably increases the production cost. 
         [0008]    Furthermore, for the current white LED technology, when the NTSC saturation of the display module is greater than 60%, other than the difficulties in selecting or manufacturing white LEDs, the overall green color of the display module usually shifts to adversely affect the overall color expression. The “NTSC saturation” means a percentage expression of dividing the actual color area of primary colors of the display module by the standard color area of primary colors defined by the NTSC (National Television System Committee). As described above, the color shift problem occurred when the NTSC saturation is high is one of the major problems of using the white LED as the backlight source. 
       SUMMARY OF THE INVENTION 
       [0009]    An objective of the present invention is to provide a display device and a method for manufacturing the same to achieve a better color expression and maintain the overall brightness. 
         [0010]    Another objective of the present invention is to a provide display device and a method for manufacturing the same, which may use white light emitting diodes (LEDs) with different color expression as a backlight source. 
         [0011]    Another objective of the present invention is to provide a display device and a method for manufacturing the same to reduce the production cost. 
         [0012]    In one embodiment, the display device includes a backlight module and a display panel disposed on the backlight module for receiving lights from the backlight module so as to produce images on the display panel. The display panel includes a color filter layer which consists of a plurality of color resists above the backlight module. Lights from the backlight module pass through the color resists and out of the display panel to form an output light. When a NTSC saturation of the output light is less than 60%, a result of the color resists under a CIE standard illuminant C test may include: 
         [0000]      0.125&lt;By&lt;0.172; 
         [0000]      2.4( Bx− 0.151)+0.142 ≦By≦ 2.5( Bx− 0.139)+0.142; and 
         [0000]      0.36 &lt;RY/GY&lt; 0.40, 
         [0000]    wherein (Bx, By) are coordinates of blue light obtained from the CIE standard illuminant C test, RY and GY are transmittances of red light and green light, respectively. 
         [0013]    When the NTSC saturation of the output light is greater than 60%, the result of the color resists under the CIE standard illuminant C test may include: 
         [0000]      0.123&lt;By&lt;0.154; 
         [0000]      Gx&lt;0.275; 
         [0000]        0 . 594 &lt;Gy&lt;0.620; and 
         [0000]        RY/BY&gt; 1.06, 
         [0000]    wherein (Gx, Gy) are coordinates of green light obtained from the CIE standard illuminant C test, BY is a transmittance of blue light. 
         [0014]    With such an arrangement of the color resists, coordinates (Wx, Wy) of the output light can be maintained approximate to coordinates (0.313, 0.329) of the standard white light so that the entire module can achieve a better performance when outputting the white light and can also maintain the transmittance of light without affecting brightness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  illustrates a schematic chromaticity diagram of a conventional white LED; 
           [0016]      FIG. 2  illustrates a schematic cross-sectional view of a display device of the present invention; 
           [0017]      FIG. 3  is a schematic chromaticity diagram of a white LED in accordance with an embodiment of the present invention; 
           [0018]      FIG. 4  is a backlight source in accordance with an embodiment of the present invention; 
           [0019]      FIG. 5  is a schematic intensity spectrum of a backlight source in accordance with an embodiment of the present invention; and 
           [0020]      FIG. 6  is a flow diagram of a manufacture method of a display device in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    The present invention provides a display device and a method for manufacturing the same. In a preferred embodiment, the display device includes a liquid crystal display device, such as liquid crystal display televisions, liquid crystal display monitors of personal computers and laptop computers, and liquid crystal display screens of mobile phones and digital cameras. 
         [0022]    As shown in  FIG. 2 , the display device preferably includes a backlight module  100  and a display panel  200 . In this embodiment, the backlight module  100  can be a direct type backlight module; however, in a different embodiment, the backlight module  100  can include a light guide plate to form an edge type backlight module. The display panel  200  is disposed on the backlight module  100  and configured to receive lights from the backlight module  100 . The display panel  200  preferably includes a first substrate  210 , a second substrate  230 , and a liquid crystal layer  250 . The liquid crystal layer  250  is sandwiched between the first substrate  210  and the second substrate  230 , and the behavior of liquid crystal molecules thereof is controlled by the electrodes on the first substrate  210  and the second substrate  230 . By controlling the behavior of the liquid crystal molecules, the display panel  200  is capable of exhibiting different brightness at different pixels so that images to be viewed by users are formed. 
         [0023]    When the first substrate  210  is a color filter substrate, a color filter layer  215  including a plurality of color resists  300  is disposed on the inner surface of the first substrate  210 . However, in a different embodiment, the color filter layer  215  can be disposed on the second substrate  230  or other locations above the backlight source  103  of the backlight module  100 . In this embodiment, after light of the backlight module  100  passes though the liquid crystal layer  250 , the light then passes through the color resists  300  of the first substrate  210 . Different color resist is selective to light of different wavelength. That is, different color resist allows light having a wavelength within in a given range to pass therethrough and blocks light having other wavelengths so that the display panel  200  is enabled to display different images. In this embodiment, the color resists  300  of the color filter layer  215  preferably include red, green, and blue resists, and the thickness thereof is preferably between 1.4 μm and 2.5 μm to accommodate the requirements of manufacturing processes and other elements. Moreover, the color filter layer may include resists of other color, such yellow, magenta, etc. 
         [0024]    For the output light  301  emitted from the color resists  300 , the color expression thereof is determined by two parameters: the spectrum characteristics of the light generated by the backlight module  100  and the optical property of the color resists  300 . Since the spectrum characteristics of the light generated by the backlight module is constant and not easy to be changed under certain conditions, it is preferably to modify the optical property of the color resists  300  for a better color expression. However, in other embodiments, the employment of backlight module  100  having different spectrum characteristics in cooperation with the color resists having modified optical property can also achieve a better effect. 
         [0025]    The optical property of the color resists  300  is preferably represented in accordance with the standard illuminant C test defined by the International Commission on Illumination (CIE). Standard illuminant C is a CIE standard illuminant for filtered tungsten illumination that simulates average daylight with a correlated color temperature (CCT) of 6774 degrees K. Besides directly performing the CIE standard illuminant C test, a standard illuminant A test can be performed to measure the transmittance of the color resists  300 , and the spectrum of the CIE standard illuminant C can be then used to calculate the transmittance spectrum occurred when the illuminant C serves as the test light source. Thereafter, the chromatic value of the color resist  300  can be obtained. The standard illuminant A is a tungsten lamp with a color temperature 2856 degrees K. 
         [0026]    In a preferred embodiment, when a NTSC saturation of the output light  301  is less than 60%, the result of the color resist  300  under the CIE standard illuminant C test includes: 
         [0000]      0.125&lt;By&lt;0.172; 
         [0000]      2.4( Bx− 0.151)+0.142 ≦By≦ 2.5( Bx− 0.139)+0.142; and 
         [0000]      0.36 &lt;RY/GY&lt; 0.40, 
         [0000]    wherein (Bx, By) are coordinates of blue light obtained from the CIE standard illuminant C test, RY and GY are transmittances of red light and green light, respectively. With such an arrangement of the color resists  300 , the coordinates (Wx, Wy) of the output light can be maintained approximate to coordinates (0.313, 0.329) of the standard white light with a tolerance preferably between ±(0.010, 0.010). Therefore, the entire module can achieve a better performance when outputting the white light. Moreover, the overall color of the output light does not shift easily and the light transmittance is also maintained without affecting the brightness. 
         [0027]    Table 1 shows the test result on color characteristics of the color resists  300  when the NTSC saturation of the output light is less than 60%. 
         [0000]                                                      TABLE 1                   Test result on color characteristics            Rx   Ry   Gx   Gy   Bx   By   Wx   Wy               0.595   0.345   0.322   0.556   0.156   0.143   0.310   0.331                    
In this embodiment, the backlight source  103  in cooperation with the color resists  300  has the color output characteristics shown in  FIG. 3 . From Table 1, with the color resists  300 , the output result of (Wx, Wy) is relatively close to the position (0.313, 0.329) of the standard white light. The output results of (Rx, Ry), (Gx, Gy), and (Bx, By) respectively for red, green, and blue colors are also within a reasonable range without color shift.
 
         [0028]    Additionally, in a preferred embodiment, when the NTSC saturation of the output light  301  is less than 60%, the color resists  300  can be further controlled to obtain Gx&gt;0.282 under the CIE standard illuminant C test. With such a modification, the color resists  300  can have more options to incorporate with the backlight source  103 . That is, the color resists  300  can match more backlight sources  103  with a variety of color output characteristics. In a different embodiment, if the color resists  300  are controlled to obtain Ry&gt;0.316 under the CIE standard illuminant C test, a similar effect can be achieved. Ry is y coordinate of red light obtained from the CIE standard illuminant C test. 
         [0029]    In another embodiment, the color resists  300  can be further controlled to obtain, for example, 0.534&lt;Gy&lt;0.564 under the CIE standard illuminant C test, so that the color saturation or purity of the output light can be enhanced. With such a modification, the green color expression of the output light can be modified to improve the overall color saturation. Additionally, when the color resists  300  are controlled to obtain 0.575&lt;Rx&lt;0.605 under the CIE standard illuminant C test, a similar effect can be achieved. Rx is x coordinate of red light obtained from the CIE standard illuminant C test. 
         [0030]    The conditions when the NTSC saturation of the output light  301  is greater than 60% are discussed in the following descriptions. When the NTSC saturation of the output light  301  is greater than 60%, the result of the color resists under the CIE standard illuminant C test includes: 
         [0000]      0.123&lt;By&lt;0.154; 
         [0000]      Gx&lt;0.275; 
         [0000]      0.594&lt;Gy&lt;0.620; and 
         [0000]        RY/BY&gt; 1.06, 
         [0000]    wherein (Gx, Gy) are coordinates of green light obtained from the CIE standard illuminant C test, BY is a transmittance of blue light. With such an arrangement of the color resists  300 , the coordinates (Wx, Wy) of the output light can be maintained approximate to coordinates (0.313, 0.329) of the standard white light with a tolerance preferably between ±(0.010, 0.010). Therefore, the entire module can achieve a better performance when outputting the white light. Moreover, the overall color of the output light does not shift easily, for example, Gx is controlled to be less than 0.330 (i.e. Gx&lt;0.330). 
         [0031]    Table 2 shows the test result on color characteristics of the color resists  300  when the NTSC saturation of the output light is greater than 60%. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Measurements of color characteristics of output light 
               
             
          
           
               
                   
                 CIE standard illuminant C 
               
               
                 Output light of display panel 
                 test result of color resists 
               
             
          
           
               
                 Rx 
                 Ry 
                 Gx 
                 Gy 
                 Bx 
                 By 
                 Wx 
                 Wy 
                 NTSC 
                 RY/RB 
                 By 
                 Gx 
                 Gy 
               
               
                   
               
             
          
           
               
                 0.606 
                 0.352 
                 0.320 
                 0.623 
                 0.155 
                 0.106 
                 0.309 
                 0.331 
                 60.8% 
                 1.25 
                 0.140 
                 0.264 
                 0.598 
               
               
                 0.606 
                 0.352 
                 0.320 
                 0.623 
                 0.150 
                 0.106 
                 0.305 
                 0.329 
                 61.3% 
                 1.17 
                 0.144 
                 0.264 
                 0.598 
               
               
                 0.606 
                 0.352 
                 0.327 
                 0.618 
                 0.150 
                 0.106 
                 0.307 
                 0.332 
                 60.1% 
                 1.17 
                 0.144 
                 0.273 
                 0.595 
               
               
                 0.606 
                 0.352 
                 0.327 
                 0.618 
                 0.154 
                 0.102 
                 0.312 
                 0.334 
                 60.1% 
                 1.30 
                 0.135 
                 0.273 
                 0.595 
               
               
                   
               
             
          
         
       
     
         [0032]    In the test of Table 2, the backlight source  103  in cooperation with the color resists  300  has a color output defined in a color space to be 0.285&lt;Wx&lt;0.315, 0.260&lt;Wy&lt;0.310. However, the color output defined in the color space can have a different range. From Table 2, with the color resists  300 , the output result of (Wx, Wy) is relatively close to the position (0.313, 0.329) of the standard white light, wherein the tolerance is ±(0.010, 0.010) for each coordinate. The output results of (Rx, Ry), (Gx, Gy), and (Bx, By) respectively for red, green, and blue colors are also within a reasonable range without color shift. Particularly, the Gx is controlled to be less than 0.330 (i.e. Gx&lt;0.330). 
         [0033]    The backlight source  103  of the backlight module  100  preferably includes a light emitting diode (LED). In the embodiment of  FIG. 2 , the backlight module  100  further includes at least one optical film  101 , such as diffusion plate, diffusion sheet, brightness enhancement film, polarizing film, disposed above the backlight source  103 . The backlight module  100  can also include other optical elements such as reflective sheet to be disposed corresponding to the backlight source  103  so as to improve the brightness and uniformity of the backlight module  100 . As shown in  FIG. 4 , the white LED includes an active light source  110  and a passive light source  130 . The active light source  110  can emit light upon providing a signal, while the passive light source  130  is excited by the light of the active light source  110  to generate light in another color. In this embodiment, the active light source  110  is preferably a blue LED chip, and the passive light source  130  is a non-blue phosphor, particularly a phosphor with a wavelength greater than that of the blue LED chip. When the blue LED chip emits blue light incident onto the phosphor, the phosphor is excited to generate light in different color so as to form a white light. In a preferred embodiment, the blue LED chip is used with yellow green phosphor, such as yttrium aluminum garnet (YAG) phosphor or silicate phosphor. However, in a different embodiment, it can be used with other phosphors such as red and green phosphors. In this embodiment, the phosphors are doped within the transparent body  170  of the bowel  150  of the white LED. In a different embodiment, the phosphors can be disposed (e.g. coated or adhered) at least on a partial light exit surface of the blue LED chip. 
         [0034]      FIG. 5  schematically illustrates an intensity spectrum of the light source  103 . As shown in  FIG. 5 , when the light source  103  is made of blue LED chip with yellow green phosphors, the intensity spectrum preferably exhibits a first peak range  510  and a second peak range  520 , and each peak range has a peak value, which represents a local maximum. For clarity, the longitudinal axis in  FIG. 5  represents a relative light intensity. As shown in  FIG. 5 , the first peak range  510  is located on the left side near the blue light range, preferably on the area with wavelength less than 500 nm. The second peak range  520  is located on the right side near the range of green and red lights, preferably on the area with wavelength greater than 500 nm. As shown in  FIG. 5 , since this embodiment uses the blue LED chip as the active light source  110  to generate blue light, which is then used to excite the passive light source  130  formed by phosphors to generate red and green lights, the intensity value in the first peak range  510  is preferably greater than that in the second peak range  520 . 
         [0035]    As shown in  FIG. 5 , since the phosphor in the embodiment is yellow green phosphors, the intensity spectrum exhibits only two peak ranges. Additionally, the intensity in the red light range with wavelength greater than 580 nm is relatively smaller. In other words, in comparison with other colors of light, the red light has smaller energy. In cooperation with the color resists of the above embodiment, the difference in energy among different colors can be balanced and therefore, the chromatic difference can be reduced. 
         [0036]    In a preferred embodiment, when the NTSC saturation is greater than 60%, the color resists  300  can be further controlled to obtain Ry&lt;0.330 and Bx&gt;0.136 under the CIE standard illuminant C test, wherein Ry is the y coordinate of red light obtained from the CIE standard illuminant C test. With such a modification, it is possible to control the white light to fall on an appropriate position in the color coordinate system and to reduce the color shift of green light so as to provide an appropriate color expression. 
         [0037]    In another embodiment, the color resists  300  can be further controlled to improve the overall color expression of the entire module. As shown in  FIG. 5 , the second peak range  520  in the intensity spectrum of the backlight source  103  has a full width at half maximum (FWHM) W. The full width at half maximum is a distance between two extreme values of the wavelength at which the intensity is equal to half of its local maximum value within the second peak range  520 . In a preferred embodiment, when the full width at half maximum of the second peak range  520  is greater than 110 nm, the color resists  300  can be controlled to allow the result of the CIE standard illuminant C test to further include: 
         [0000]      Ry&gt;0.343; 
         [0000]      Gx&lt;0.317; and 
         [0000]      Bx&gt;0.145, 
         [0000]    wherein Ry is the y coordinate of red light obtained from the CIE standard illuminant C test. 
         [0038]    In this embodiment, the active light source  110  of the backlight source  103  is preferably a blue LED chip, and the passive light source  130  is a YAG phosphor. 
         [0039]    In another embodiment, when the full width at half maximum W of the second peak range  520  is less than 110 nm, the color resists  300  can be controlled to allow the result of the CIE standard illuminant C test to further include: 
         [0000]      Ry&gt;0.348; 
         [0000]      Gx&lt;0.330; and 
         [0000]      Bx&gt;0.148, 
         [0000]    wherein Ry is the y coordinate of red light obtained from the CIE standard illuminant C test. 
         [0040]    In this embodiment, the active light source  110  of the backlight source  103  is preferably a blue LED chip, and the passive light source  130  is a silicate phosphor. 
         [0041]    The present invention also provides a method for manufacturing the display device. As the flow diagram shown in  FIG. 6 , step  1010  includes determining the NTSC saturation of the output light of the display device. The determination can be performed by experiments, simulations, or calculations to project the NTSC saturation of the output light occurred when the display device is assembled. When the NTSC saturation is determined to be less than 60%, step  1030  includes enabling a result of the color resists under a CIE standard illuminant C test to include: 
         [0000]      0.125&lt;By&lt;0.172; 
         [0000]      2.4( Bx− 0.151)+0.142≦ By≦ 2.5( Bx− 0.139)+0.142; and 
         [0000]      0.36 &lt;RY/GY&lt; 0.40, 
         [0000]    wherein (Bx, By) are coordinates of blue light obtained from the CIE standard illuminant C test, RY and GY are transmittances of red light and green light, respectively. With such an arrangement of the color resists  300 , the coordinates (Wx, Wy) of the output light can be maintained approximate to coordinates (0.313, 0.329) of the standard white light with a tolerance preferably between ±(0.010, 0.010). Therefore, the entire module can achieve a better performance when outputting the white light. Moreover, the overall color of the output light does not shift easily and the light transmittance is also maintained without affecting the brightness. In a preferred embodiment, by modifying the component ratio of the color resists, changing the manufacturing process of the color resists, changing the structural size of the color resists, or other parameters, the CIE standard illuminant C test of the color resists can be fallen within the above described conditions. 
         [0042]    When the NTSC saturation is determined to be greater than 60%, step  1050  includes enabling a result of the color resists under a CIE standard illuminant C test to include: 
         [0000]      0.123&lt;By&lt;0.154; 
         [0000]      Gx&lt;0.275; 
         [0000]        0 . 594 &lt;Gy&lt;0.620; and 
         [0000]        RY/BY&gt; 1.06, 
         [0000]    wherein (Gx, Gy) are coordinates of green light obtained from the CIE standard illuminant C test, BY is a transmittance of blue light. With such an arrangement of the color resists  300 , the coordinates (Wx, Wy) of the output light can be maintained approximate to coordinates (0.313, 0.329) of the standard white light with a tolerance preferably between ±(0.010, 0.010). Therefore, the entire module can achieve a better performance when outputting the white light. As described above, by modifying the component ratio of the color resists, changing the manufacturing process of the color resists, changing the structural size of the color resists, or other parameters, the CIE standard illuminant C test of the color resists can be fallen within the above described conditions. 
         [0043]    The present invention has been described through the relevant embodiments above; however, the embodiments above are only exemplary. What needs to point out is that the embodiments disclosed are not intended to limit the scope of the present invention. Contrarily, the modifications and the equivalents included in the spirit and scope of the claims are all included in the scope of this invention.