PATENT DOCUMENT

Publication Number: US-7522236-B2
Application Number: US-23478905-A
Country: US
Kind Code: B2

Title: Cosmetically uniform reflective border area in a transflective display

Abstract:
One embodiment of the present invention provides a transflective display in which a border area adjacent to an active area has a reflectivity that is substantially the same as the active area when the display is turned off. This display includes a polarizer layer, a color filter glass (CFG) layer, a liquid crystal layer, and a reflector layer. The CFG layer contains color filters in the active area, while the border area of the CFG layer is designed to have a reflectivity that is substantially the same as the active area when the display is turned off.

Claims:
1. A transfective display in which a border area adjacent to an active area has a reflectivity substantially similar to the active area when the display is turned off, comprising:
 a polarizer layer; 
 a color filter glass (CFG) layer which contains color filters in the active area; 
 a liquid crystal layer; and 
 a reflector layer 
 wherein the border area of the CFG layer is fabricated to have a reflectivity that is substantially the same as the active area, thereby making the border area visually indistinguishable from the active area when the display is turned off. 
 
     
     
       2. The transflective display of  claim 1 ,
 wherein a given active pixel in the active area of the CFG layer includes a transmissive hole for transmitting color via a backlight; and 
 wherein a given border pixel in the border area of the CFG layer includes a black mask area whose size and location within the given border pixel are substantially the same as those of the transmissive hole for a pixel in the active area. 
 
     
     
       3. The transflective display of  claim 2 , wherein the size and location of the black mask area within the given border pixel is adjusted to match the reflectivity of a pixel in the active area when the display is turned off. 
     
     
       4. The transflective display of  claim 1 ,
 wherein a given pixel in the CFG layer includes a clear hole that allows ambient light to reflect directly off of the reflector layer; 
 wherein the clear hole can be adjusted in size to tune the color point of the given pixel; and 
 wherein the size of a clear hole in the border area varies from the size of a clear hole in the active area in order to adjust the reflectivity in the border area to be substantially the same as in the active area when the display is turned off. 
 
     
     
       5. The transflective display of  claim 1 ,
 wherein the pixel size in the border area is different from the pixel size in the active area; and 
 wherein varying the pixel size can adjust the pixel&#39;s light aperture ratio and can thereby change the pixel&#39;s reflectivity. 
 
     
     
       6. The transflective display of  claim 5 , wherein the size of pixels in the border area can vary. 
     
     
       7. The transflective display of  claim 1 ,
 wherein the cell gap is the distance between the CFG layer and the reflector layer; and 
 wherein the cell gap in the border area varies from the cell gap in the active area; and 
 wherein changing the cell gap in the border area changes the reflectivity of the border area. 
 
     
     
       8. The transflective display of  claim 1 , wherein the surface roughness of the reflector layer in the border area varies from the surface roughness of the reflector layer in the active area in order to modify the reflectivity of the border area. 
     
     
       9. A method for manufacturing a transflective display in which a border area adjacent to an active area has a reflectivity substantially similar to the active area when the display is turned off, the method comprising:
 forming a polarizing layer; 
 forming a color filter glass (CFG) layer which contains color filters in the active area; 
 forming a liquid crystal layer; and 
 forming a reflector layer; 
 wherein the border area of the CFG layer is fabricated to have a reflectivity that is substantially the same as the active area, thereby making the border area visually indistinguishable from the active area when the display is turned off. 
 
     
     
       10. The method of  claim 9 ,
 wherein a given active pixel in the active area of the CFG layer includes a transmissive hole for transmitting color via a backlight; and 
 wherein a given border pixel in the border area of the CFG layer includes a black mask area whose size and location within the given border pixel are substantially the same as those of the transmissive hole for a pixel in the active area. 
 
     
     
       11. The method of  claim 10 , wherein the size and location of the black mask area within the given border pixel is adjusted to match the reflectivity of a pixel in the active area when the display is turned off. 
     
     
       12. A computing device that includes:
 a computational engine; 
 a memory-based storage system; and 
 a transflective display used to present information; 
 wherein the transflective display includes a border area adjacent to an active area; 
 wherein the border area is fabricated to have a reflectivity that is substantially the same as the active area, thereby making the border area visually indistinguishable from the active area when the display is turned off. 
 
     
     
       13. The computing device of  claim 12 , wherein the transflective display includes:
 a polarizer layer; 
 a color filter glass (CFG) layer which contains color filters in the active area; 
 a liquid crystal layer; and 
 a reflector layer; 
 wherein the border area of the CFG layer is fabricated to have a reflectivity that is substantially the same as the active area. 
 
     
     
       14. The computing device of  claim 13 ,
 wherein a given active pixel in the active area of the CFG layer includes a transmissive hole for transmitting color via a backlight; and 
 wherein a given border pixel in the border area of the CFG layer includes a black mask area whose size and location within the given border pixel are substantially the same as those of the transmissive hole for a pixel in the active area. 
 
     
     
       15. The computing device of  claim 14 , wherein the size and location of the black mask area within the given border pixel is adjusted to match the reflectivity of a pixel in the active area when the display is turned off. 
     
     
       16. The computing device of  claim 13 ,
 wherein a given pixel in the CFG layer includes a clear hole that allows ambient light to reflect directly off of the reflector layer; 
 wherein the clear hole can be adjusted in size to tune the color point of the given pixel; and 
 wherein the size of a clear hole in the border area varies from the size of a clear hole in the active area in order to adjust the reflectivity of the border area to be substantially the same as in the active area when the display is turned off. 
 
     
     
       17. The computing device of  claim 13 ,
 wherein the pixel size in the border area is different from the pixel size in the active area; and 
 wherein varying the pixel size can adjust the pixel&#39;s light aperture ratio and can thereby change the pixels reflectivity. 
 
     
     
       18. The computing device of  claim 17 , wherein the size of pixels in the border area can vary. 
     
     
       19. The computing device of  claim 13 ,
 wherein the cell gap is the distance between the CFG layer and the reflector layer; and 
 wherein the cell gap in the border area varies from the cell gap in the active area; and 
 wherein changing the cell gap in the border area changes the reflectivity of the border area. 
 
     
     
       20. The computing device of  claim 13 , wherein the surface roughness of the reflector layer in the border area varies from the surface roughness of the reflector layer in the active area in order to modify the reflectivity of the border area.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention generally relates to transflective liquid crystal displays. More specifically, the present invention relates to a reflective border area in a transflective display which is cosmetically similar to an active area of the display when the display is turned off. 
     2. Related Art 
     Explosive growth in the popularity of mobile communication and computing devices has created a burgeoning demand for low-power displays. Recently-developed transflective color displays provide the ability to display information in a low-power, reflective mode as well as through a transmissive mode which uses a backlight. Transflective displays offer a compromise between purely transmissive or reflective displays, since they can function reflectively in bright sunlight, but can also be backlit when needed in low-light conditions. 
     Unfortunately, existing transflective color displays suffer from a cosmetic problem in some situations. Transflective color displays typically have a black mask bordering the active pixels. However, in a white transflective display, the active pixels are white when the display is turned off. This results in a cosmetically undesirable combination of a white active area bordered by the black mask, with the black mask in turn bordered by the color of the housing. Thus, when the display is turned off it has a non-uniform appearance that is cosmetically undesirable. 
     Hence, what is needed is an apparatus and a method for alleviating the above-described cosmetic problem with transflective displays. 
     SUMMARY 
     One embodiment of the present invention provides a transflective display in which a border area adjacent to an active area has a reflectivity that is substantially the same as the active area when the display is turned off. This display includes a polarizer layer, a color filter glass (CFG) layer, a liquid crystal layer, and a reflector layer. The CFG layer contains color filters in the active area, while the border area of the CFG layer is designed to have a reflectivity that is substantially the same as the active area when the display is turned off. 
     In a variation on this embodiment, a given pixel in the active area of the CFG layer includes a transmissive hole through which light from a backlight is transmitted. Instead of a transmissive hole, a given pixel in the border area of the CFG layer includes a black mask region whose size and location 
     within the pixel are substantially the same as for the transmissive hole for a pixel in the active area. 
     In a further variation on this embodiment, the size and location of the black mask areas within pixels in the border area are adjusted to match the reflectivity of pixels in the active area when the display is turned off. 
     In a variation on this embodiment, a given pixel in the CFG layer additionally includes a clear hole that allows ambient light to reflect more directly off of the reflector layer and can be adjusted in size to tune the color point of the pixel. The size of the clear hole in the border area can differ from the size of the clear hole in the active area to adjust the reflectivity of the border area to be substantially the same as for the active area. 
     In a variation on this embodiment, the pixel size in the border area is different from the pixel size in the active area. Note that varying a pixel&#39;s size can adjust the pixel&#39;s light aperture ratio, and can thereby change the pixel&#39;s reflectivity. 
     In a further variation on this embodiment, the size of pixels in the border area can vary. 
     In a variation on this embodiment, the distance between the CFG layer and the reflector layer, known as the cell gap, can vary between the border area and the active area, wherein changing the cell gap in the border area changes the reflectivity of the border area. 
     In a variation on this embodiment, the surface roughness of the reflector layer in the border area varies from the surface roughness of the reflector layer in the active area, thereby modifying the reflectivity of the border area. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates a device with a transflective display in accordance with an embodiment of the present invention. 
         FIG. 2  illustrates a cross-sectional view of the components of a transflective color display in accordance with an embodiment of the present invention. 
         FIG. 3  illustrates a frontal view of border pixels with black masks in contrast to active area pixels with transmissive areas in accordance with an embodiment of the present invention. 
         FIG. 4  illustrates border pixels having different sizes in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
     Transflective Displays 
     In an ideal manufacturing process, the device housing precisely borders the edge of a display&#39;s active area on all sides. However, since such precision is beyond achievable tolerances of existing cost-effective manufacturing technologies, transflective displays typically include a visible border region between the active area of the display and the device housing. This border region can compensate for some amount of misalignment between the display and the housing. A ‘border’ is used to denote any area immediately or mediately adjacent to the active area of a display. It need not completely encircle the active area. 
     For example,  FIG. 1  illustrates a device  100  with a transflective display  102 . The transflective display  102  includes an active area  104  and a border area  106 . The border area  106  does not include addressable pixels nor backlighting capabilities, and has different reflective properties than the active area. The difference in reflectivity, due in part to the presence of a black mask in the border area, results in a darker color that gives the appearance of a black line between the active area  104  and the device housing  108 . Note that the border area can be larger, smaller, or more irregular than shown in  FIG. 1 . 
     A common practice in display design is to copy the features of either the reflective or the transmissive portions of the active area into the border area. However, because the active and non-active areas have different optical properties, this approach still results in differing reflectivities in the different regions. The present invention minimizes the visibility of the border area when the device is powered off by minimizing the optical difference between the active and border areas in transflective displays. 
       FIG. 2  illustrates a cross-sectional view of the components of a transflective color display. More specifically,  FIG. 2  illustrates a portion of the display&#39;s border area  204  and active area  206 , as well as a portion of the area covered by the device housing  202 . The transflective display is composed of layers of material that include:
         a polarizer  210 ;   a layer of color filter glass (CFG)  212  coated with a combination of a black mask and red, green, and blue color filters  214 ;   a layer of liquid crystal  216  bordered by an edge seal  218 , that has a width specified by the cell gap  220 ;   a reflector layer  222  that is opaque in the border area but has transmissive holes in the active area that allow light from the backlight  232  to pass through;   a circuitry layer  224  that includes gate lines and edge circuits  226  in the border area and pixel circuits  228  in the active area;   a layer of thin-film transistor (TFT) glass  230 ; and   a backlight  232  that spans the active area and may overlap into the border area.       
     Transflective color displays offer the ability to convey information in both a reflective mode as well as via a transmissive mode that operates by using the backlight  232 . Note that no information is conveyed in the non-addressable pixels of the border area. In transmissive mode  240 , light from the backlight  232  shines through the holes in the reflector layer, and is modified by the liquid crystal layer  216 , which is controlled by the pixel circuits  228 . The modified light then passes through a transmissive area  242  in the color filters ( 212 - 214 ) and through the polarizer  210 . The system converts the white backlight into specific colors by controlling the intensity of light that passes through the liquid crystal display and which is directed into the red, green, and blue filters of the transmissive area. 
     In reflective mode  244 , ambient light passes through the polarizer and color filter layers ( 210 - 214 ) and is modified in intensity by the liquid crystal layer  216 . The modified light then reflects off of the reflector layer  222  to exit through the display by passing back through the above-mentioned layers a second time. The reflected light enters through the reflective area  246  in the color filters ( 212 - 214 ), which is distinct and offset from the transmissive area  242 . 
     While both the reflective and transmissive areas are present in the active area of the display, within the border area the transmissive areas are instead replaced by a black mask  248 . Note that the reflective areas are present in both the active and border areas, but are only actually used to convey information in the active area. 
     Matching Reflectivity in Transflective Displays 
       FIG. 3  illustrates a frontal view of border pixels that contain a color filter and reflector pattern that are substantially the same as that of the active area, with a black mask  248  placed in the transmissive areas. Within a given border pixel  302 , a black mask area  248  whose size and location within the pixel are substantially the same as those of a corresponding transmissive area in a pixel of the active area  304  reduces the reflectivity of the border pixel. Since the black mask often reflects less light than a transmissive area of substantially the same size, due to some limited amount of reflectivity from the backlight in the transmissive area, the size of the black mask is typically adjusted (reduced) to match the reflectivity of the transmissive area. Thus, the size and location of the black mask areas in pixels of the border region can be tuned to increase or decrease the reflectivity of the border area as desired. 
     In reflective mode, some amount of light is lost as the ambient light passes through the layers of the screen, reflects against the reflector layer, and then passed out through the screen again. Less light is lost in transmissive mode, since the light only passes through the screen once. An additional area can be provided in each sub-pixel to improve the brightness of the display in reflective mode. For example, “clear holes”  306  in each sub-pixel contain no filters or masks, and allow ambient light to pass through and reflect unimpeded from the reflector layer. These clear holes, which may be of different size for each type (red, green, or blue) of sub-pixel, provide an adjustment mechanism that allows the color purity of the reflective mode to match the color purity of the transmissive mode more closely. As a secondary effect, the use of clear holes also results in additional reflection through the color filters as well. 
     In general, clear holes improve reflectivity, resulting in a brighter display and white point, higher contrast, and better color mixing. Furthermore, the size and location of the clear holes within each given pixel of the border area can additionally be modified to further match the reflectivity of pixels in the border area with pixels of the active area. 
     The size of pixels in the border area can also be used to adjust the reflectivity of the region. For example,  FIG. 4  illustrates edge pixels whose sizes are modified  402  to fit the display area. Resizing options include scaling the edge pixels to fit, as shown in  FIG. 4 , or uniformly resizing the border pixels so that a discrete number of same-size pixels fill the border region. Since changing the size of a pixel changes the size and pitch of the reflective area, clear holes, and black mask, and thus changes the aperture ratio of the pixel, this technique provides an additional mechanism for changing the reflectivity of the border region to match the active area. 
     A further set of mechanisms for adjusting the reflectivity of the border area involves modifying the cell gap and the surface roughness of the reflector layer in the border area. For the former case, the cell gap, or the distance between the CFG layer and the reflector layer, can be varied in the border area from the cell gap in the active area. 
     The foregoing descriptions of embodiments of the present invention have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims.

Metadata:
Filing Date: 20050923
Publication Date: 20090421
Grant Date: 20090421
Priority Date: 20050923
Inventors: GETTEMY SHAWN R.
ZHONG JOHN Z.
FRASER SHERRIDYTHE ANNE
CHEN WEI
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133555", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133555", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133388", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133509", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133388", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133509", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 37893392