Abstract:
A display for virtual reality is discussed, which is capable of alleviating a screen-door effect, thereby improving its image quality. In the display for virtual reality, a light diffusion member, which diffuses light emitted from a light-transmitting area of a display panel to a light-blocking area of the display panel, is interposed between the display panel and an optical lens, whereby a user who views an image displayed on the display panel at a very close position does not perceive the light-blocking area, which improves the image quality of the display.

Description:
[0001]    This application claims the priority benefit of Korean Patent Application No. 10-2016-0029777, filed on Mar. 11, 2016 in Republic of Korea, which is hereby incorporated by reference as if fully set forth herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The present invention relates to a display for virtual reality, which may alleviate a screen-door effect, thereby improving the image quality of the display. 
         [0004]    Discussion of the Related Art 
         [0005]    A display for virtual reality is a visualization device that provides virtual reality (VR) or augmented reality by making a virtual image feel like reality through vivid images, sounds, and the like. Such a display for virtual reality realizes a large viewing area despite the small size thereof and has no limitation as to the viewing angle, and therefore, has been utilized in various fields including, for example, augmented-reality industry and education, virtual-reality experience appliances, wearable PC monitors, theme parks, movie viewing, and game display devices. 
         [0006]    However, because a display for virtual reality according to the related art forms an image at a position that is very close to the user&#39;s eyes, a light-blocking area between the sub-pixels of a display panel is clearly visible. Therefore, there occurs a screen-door effect, in which a lattice resembling a mosquito net is visible in an image realized in the display for virtual reality according to the related art, which is undesirable. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, the present invention is directed to a display for virtual reality that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
         [0008]    An object of the present invention is to provide a display for virtual reality, which may alleviate a screen-door effect, thereby improving image quality. 
         [0009]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the embodiments of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0010]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a display for virtual reality in which a light diffusion member, which diffuses light emitted from a light-transmitting area of a display panel to a light-blocking area of the display panel, is interposed between the display panel and an optical lens, whereby a user who views an image displayed on the display panel at a very close position does not perceive the light-blocking area, which may result in the improved image quality of the display panel. 
         [0011]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
           [0013]      FIG. 1  is a perspective view illustrating a display for virtual reality according to an embodiment of the present invention; 
           [0014]      FIG. 2  is a cross-sectional view illustrating the display for virtual reality illustrated in  FIG. 1 ; 
           [0015]      FIG. 3  is a plan view for explaining respective sub-pixels of a display panel illustrated in  FIG. 2 ; 
           [0016]      FIG. 4  is a cross-sectional view illustrating haze measurement equipment for measuring the haze ratio of a light diffusion member illustrated in  FIG. 2 ; 
           [0017]      FIG. 5A  is a view illustrating the sizes of the respective sub-pixels of the display panel illustrated in  FIG. 2 , and  FIG. 5B  is a view illustrating the sizes of enlarged sub-pixels, which are perceived by a user owing to the light diffusion member illustrated in  FIG. 2 ; 
           [0018]      FIGS. 6A to 6C  are cross-sectional views illustrating a first embodiment of the light diffusion member illustrated in  FIG. 2  according to the present invention; 
           [0019]      FIGS. 7A to 7C  are cross-sectional views illustrating a second embodiment of the light diffusion member illustrated in  FIG. 2  according to the present invention; 
           [0020]      FIGS. 8A to 8C  are cross-sectional views illustrating a third embodiment of the light diffusion member illustrated in  FIG. 2  according to the present invention; 
           [0021]      FIGS. 9A to 9C  are cross-sectional views illustrating a fourth embodiment of the light diffusion member illustrated in  FIG. 2  according to the present invention; 
           [0022]      FIG. 10  is a cross-sectional view illustrating a display for virtual reality, to which a liquid crystal display panel is applied as the display panel illustrated in  FIG. 2 , according to an embodiment of the present invention; 
           [0023]      FIG. 11  is a cross-sectional view illustrating a display for virtual reality, to which an organic light-emitting display panel having a light-emitting layer for white light is applied as the display panel illustrated in  FIG. 2 , according to an embodiment of the present invention; and 
           [0024]      FIG. 12  is a cross-sectional view illustrating a display for virtual reality, to which an organic light-emitting display panel having a light-emitting layer for red, green, and blue light is applied as the display panel illustrated in  FIG. 2 , according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Hereinafter, embodiments in accordance with the present invention will be described in detail with reference to the accompanying drawings. 
         [0026]      FIG. 1  is a perspective view illustrating a display for virtual reality according to an embodiment of the present invention, and  FIG. 2  is a cross-sectional view illustrating the display for virtual reality illustrated in  FIG. 1 . All the components of the display for virtual reality according to all embodiments of the present invention are operatively coupled and configured. 
         [0027]    The display for virtual reality illustrated in  FIGS. 1 and 2  includes a frame  100 , an optical lens  110 , a display panel  130 , and a light diffusion member  120 . 
         [0028]    The frame  100  has a user-wearable shape, such as, for example, the shape of a pair of glasses or a helmet. 
         [0029]    The optical lens  110  is disposed between the display panel  130  and a user to transfer an image, output from the display panel  130 , to the user&#39;s eyes. The optical lens  110  enlarges the image, formed by the display panel  130 , and refracts the enlarged image toward the user&#39;s eyeballs. Thus, the optical lens  110  serves to increase the viewing angle that the user can perceive, and to adjust the focal distance. Accordingly, the user may experience an effect in which the image formed by the display panel  130  looks like an image on a large screen at a certain distance. 
         [0030]    The display panel  130  includes a plurality of unit pixels, which are arranged in a matrix form. Each unit pixel may include red, green, and blue display sub-pixels R, G and B as illustrated in  FIG. 3 , or may include red, green, blue, and white sub-pixels R, G, B and W. Each sub-pixel is provided with a color filter or a light-emitting layer, which emits light of a predetermined color. A light-blocking area is disposed between the sub-pixels in order to prevent the mixing of color emitted from the color filter or the light-emitting layer. Note that the structure of the sub-pixels illustrated in  FIG. 3  is merely given by way of example, and the present invention is not limited to the structure illustrated in  FIG. 3 . 
         [0031]    The light diffusion member  120  is disposed between the display panel  130  and the optical lens  110 . The light diffusion member  120  diffuses the light emitted from the respective sub-pixels of the display panel  130  to the light-blocking area between the sub-pixels, thereby minimizing the perception of the light-blocking area between the sub-pixels. To this end, the light diffusion member  120  appropriately adjusts the haze ratio depending on at least one variable selected from among the resolution of the display panel  130 , the size of the display panel  130 , the pixel density (e.g., pixels per inch (PPI)), and the distance from the upper surface of the color filter or the light-emitting layer to the upper surface of the light diffusion member  120 . When the haze ratio is excessively low, the amount of light that is diffused to the light-blocking area is small and the user may perceive the light-blocking area. When the haze ratio is excessively high, the amount of light that is diffused to the light-blocking area is large, and an image is blurred. 
         [0032]    Here, the haze ratio indicates the degree of diffusion of incident light, and is the ratio of refracted light to all of the transmitted light that has passed through the light diffusion member  120 . This haze ratio is measured using a haze measurement device HD illustrated in  FIG. 4 . That is, light emitted from the display panel  130  passes through the light diffusion member  120  to thereby be introduced into the haze measurement device HD. At this time, the light that has passed through the light diffusion member  120  is subjected to, for example, refraction. The haze measurement device HD measures the light that proceeds within a predetermined angle (e.g., 2.5°) relative to a light incidence axis, by collecting the light at an exit. At this time, by measuring the amount Tt of the totality of light that has passed through the light diffusion member  120  at the entrance of the haze measurement device HD and the amount Td of light that has been refracted and has proceeded at a predetermined angle or more, calculation based on the haze ratio may be performed to obtain the value acquired by the following Equation 1. 
         [0000]      Haze= Td/Tt× 100%  Equation 1
 
         [0033]    As described, by appropriately adjusting the haze ratio via the light diffusion member  120 , the light emitted from the respective sub-pixels of the display panel  130  may be diffused to the light-blocking area between the sub-pixels. Thereby, the user may perceive that the width of the light-blocking area between the sub-pixels is smaller than the perception limit width, and therefore the user may perceive an increased aperture ratio. 
         [0034]    Here, the perception limit width of the user is the perception limit width RW of the light-blocking area between the sub-pixels, as perceived by the user who views the display for virtual reality, and may be calculated via the following Equation 2. 
         [0000]      FOV: PW =Resolution of Eyes: RW   Equation 1
 
         [0035]    As illustrated in Equation 2, the ratio of the maximum field of view (FOV) that the user can perceive to the maximum width PW of the display panel  130  is the same as the ratio of the minimum FOV that the user can perceive, i.e. the angular resolution of the eyes to the perception limit width RW. For example, when the user perceivable FOV of the display for virtual reality is 100°, the maximum width PW of the 5.5-inch display panel is 60.9 mm, and the angular resolution of the eyes is 1/60°, the perception limit width RW is 10.1 μm. 
         [0036]    Accordingly, when the width BW 1  of the light-blocking area between the sub-pixels of the display for virtual reality illustrated in  FIG. 5A  is equal to or larger than the perception limit width, the light emitted from the respective sub-pixels of the display panel may be diffused to the light-blocking area between the sub-pixels by appropriately adjusting the haze ratio using the light diffusion member  120 . In this way, as illustrated in  FIG. 5B , because the user perceives the sub-pixels as being enlarged, and the width BW 2  of the light-blocking area that the user perceives is smaller than the perception limit width of the user, the user may perceive an increased aperture ratio. 
         [0037]    The light diffusion member  120  has a film shape having any one of the structures illustrated in  FIGS. 6A to 9C . 
         [0038]    The light diffusion member  120  illustrated in  FIGS. 6A to 6C  is formed on a base film  126 , and is disposed on the display panel  130  or a polarizer POL with an adhesive layer  128 . 
         [0039]    Further, the light diffusion member  120  illustrated in  FIGS. 7A to 7C  is disposed on the polarizer POL of the display panel  130  to be integrated with the polarizer POL. The light diffusion member  120  illustrated in  FIGS. 7A to 7C  does not require, for example, the base film  126  or the adhesive layer  128 , unlike the structure illustrated in FIGS.  6 A to  6 C, thus realizing a reduction in the thickness and weight thereof. 
         [0040]    Furthermore, the light diffusion member  120  illustrated in  FIGS. 8A to 8C  is disposed on the uppermost layer of the display panel  130 , for example, on an upper substrate of the display panel or an encapsulation layer of an organic light-emitting diode display panel. Thus, the light diffusion member  120  illustrated in  FIGS. 8A to 8C  does not require, for example, the base film  126  or the adhesive layer  128 , unlike the structure illustrated in  FIGS. 6A to 6C , thus realizing a reduction in the thickness and weight thereof. 
         [0041]    The light diffusion member  120  illustrated in  FIGS. 9A to 9C  may be disposed between any one of the display panel  130  and the polarizer POL and the optical lens  110 , or may be disposed on the optical lens  110 . 
         [0042]    Meanwhile, the light diffusion member  120  may take the form of a film  122  containing beads  124 , as illustrated in  FIGS. 6A, 7A, 8A and 9A , may have irregular convex and concave portions formed on a photo-curable resin surface, as illustrated in  FIGS. 6B, 7B, 8B and 9B , or may have regular convex and concave portions formed on a photo-curable resin surface as illustrated in  FIGS. 6C, 7C, 8C and 9C . 
         [0043]      FIG. 10  is a cross-sectional view illustrating a display for virtual reality in which the display panel according to the present invention is applied to a liquid crystal display panel. 
         [0044]    In the display for virtual reality illustrated in  FIG. 10 , the light diffusion member  120  is disposed on the liquid crystal display panel  130 , which includes a color filter array  150  and a thin-film transistor array  160 , which face each other with a liquid crystal layer  188  interposed therebetween. 
         [0045]    The thin-film transistor array  160  includes a thin-film transistor  170 , a pixel electrode  156 , and a common electrode  186 , which are formed on a lower substrate  161 . 
         [0046]    The thin film transistor  170  supplies a data signal from a data line to the pixel electrode  156  upon receiving a gate signal from a gate line. To this end, the thin film transistor  170  includes a gate electrode  172 , a semiconductor layer  174  overlapping the gate electrode  172  with a gate insulation film  162  interposed therebetween, and source and drain electrodes  176  and  178 , which are formed on a first protective film  164  to come into contact with the semiconductor layer  174 . 
         [0047]    The common electrode  186  is connected to a common line, which supplies a common voltage. The common electrode  186  is formed parallel to the pixel electrode  156  and is formed alternately with the pixel electrode  156  in the case of a horizontal-field liquid-crystal display panel. The common electrode  186  is disposed on an upper substrate  151  in the case of a vertical-field liquid-crystal display panel, and has a plurality of slits in an organic protective film  158  in the case of a fringe-field liquid-crystal display panel. 
         [0048]    The pixel-electrode  156  is formed on a second protective film  166  and is connected to the drain electrode of the thin-film transistor. The pixel-electrode  156  forms an electric field along with the common electrode  186 , to which the common voltage is supplied, when a video signal is supplied to the pixel electrode  156  through the thin-film transistor  170 . Thereby, liquid-crystal molecules of the liquid crystal layer  188 , arranged between the color filter array  150  and the thin-film transistor array  160 , are rotated by dielectric anisotropy. In addition, the transmissivity of light that passes through a light-transmitting area is changed depending on the degree of rotation of the liquid crystal molecules, which realizes gradation. 
         [0049]    The color filter array  150  includes a black matrix  154  and color filters  152 , which are stacked one above another on the upper substrate  151 . The red, green, and blue color filters  152  are formed on the upper plate  151  in a light-transmitting area, which is defined by the black matrix  154 , to realize corresponding colors. The black matrix  154  is formed on the light-blocking area between the respective sub-pixels to enable discrimination from the light-transmitting area of each sub-pixel, and also serves to prevent light interference and leakage between the light-transmitting areas of the adjacent sub-pixels. Meanwhile, although  FIG. 10  illustrates an example in which the color filters  152  are disposed between the upper substrate  151  and the black matrix  154 , the black matrix  154  may be disposed between the upper substrate  151  and the color filters  152 . 
         [0050]    The light diffusion member  120  diffuses the light that has passed through the color filter  152 , which is disposed in the light-transmitting area of each sub-pixel of the liquid-crystal display panel  130 , to the light-blocking area to minimize the perception of the light-blocking area by the user. 
         [0051]      FIG. 11  is a cross-sectional view illustrating a display for virtual reality in which the display panel according to the present invention is applied to an organic light-emitting display panel having a color filter and a black matrix. 
         [0052]    In the display for virtual reality illustrated in  FIG. 11 , the light diffusion member  120  is disposed on the organic light-emitting display panel  130 , which includes the color filter array  150  and the thin-film transistor array  160 , which are bonded to each other with an adhesive layer  148  interposed therebetween. 
         [0053]    The color filter array  150  has the same (or similar) structure as the color filter array  150  illustrated in  FIG. 10 , and thus a detailed description thereof will be omitted or may be brief. 
         [0054]    The thin-film transistor array  160  includes the thin-film transistor  170  and a light-emitting device  180 , which are formed on the lower substrate  161 . 
         [0055]    The thin film transistor  170  includes the gate electrode  172 , the semiconductor layer  174  overlapping the gate electrode  172  with the gate insulation film  162  interposed therebetween, and the source and drain electrodes  176  and  178 , which are formed on the first protective film  164  to come into contact with the semiconductor layer  174 . 
         [0056]    The light-emitting device  180  includes an anode  182 , an organic light-emitting layer  184  formed on the anode  182 , and a cathode  186  formed over the organic light-emitting layer  184 . 
         [0057]    The anode  182  is electrically connected to the drain electrode  178  of the thin-film transistor  170 . The organic light-emitting layer  184  is formed on the anode  182  in the light-transmitting area, which is defined by a bank  168 , to overlap the color filter  152 , thereby emitting white light. The organic light-emitting layer  184  is formed on the anode  182  such that a hole-associated layer, a light-emitting layer, and an electron-associated layer are stacked one above another in that sequence or in the reverse sequence thereof. The cathode  186  is formed to face the anode  182  with the organic light-emitting layer  184  interposed therebetween. 
         [0058]    The light diffusion member  120  diffuses light emitted from the light-transmitting area of each sub-pixel of the organic light-emitting display panel  130  to the light-blocking area overlapping the black matrix  154 , thereby minimizing the perception of the light-blocking area by the user. To this end, the light diffusion member  120  appropriately adjusts the haze ratio depending on at least one variable selected from among the resolution of the display panel  130 , the size of the display panel  130 , the pixel density (e.g., pixels per inch (PPI)), and the distance from the upper surface of the color filter  152  to the upper surface of the light diffusion member  120 . 
         [0059]    For example, the haze ratio is set to be inversely proportional to at least one of the pixel density, the aperture ratio, and the distance from the upper surface of the color filter  152  to the upper surface of the light diffusion member  120 , and to be proportional to the width of the black matrix  154 . 
         [0060]    Specifically, because the lower the pixel density, the longer the distance between the sub-pixels, and consequently the wider the light-blocking area, a display panel having a relatively low pixel density is set to have a higher haze ratio of the light diffusion member  120  than a display panel having a relatively high pixel density. Because the lower the aperture ratio of the display panel, the longer the distance between the sub-pixels and the wider the light-blocking area, a display panel having a relatively low aperture ratio is set to have a higher haze ratio of the light diffusion member  120  than a display panel having a relatively high aperture ratio. Because the wider the black matrix  154  of the display panel, the longer the distance between the sub-pixels, and consequently the wider the light-blocking area, a display panel in which the black matrix  154  is relatively wide is set to have a higher haze ratio of the light diffusion member  120  than a display panel in which the black matrix  154  is relatively narrow. Because the shorter the distance from the upper surface of the color filter  152  to the upper surface of the light diffusion member  120  of the display panel, the greater the refraction angle of the light that has passed through the light diffusion member  120 , a display panel in which the distance from the upper surface of the color filter  152  to the upper surface of the light diffusion member  120  is relatively short is set to have a higher haze ratio of the light diffusion member  120  than a display panel in which the distance from the upper surface of the color filter  152  to the upper surface of the light diffusion member  120  is relatively long. 
         [0061]      FIG. 12  is a cross-sectional view illustrating a display for virtual reality in which the display panel according to the present invention is applied to an organic light-emitting display panel having no color filter and no black matrix. 
         [0062]    In the display for virtual reality illustrated in  FIG. 12 , the light diffusion member  120  is disposed on an encapsulation layer  138 , which is formed to cover the light-emitting device  180 . The light-emitting device  180  is formed in a light-emitting area provided by the black bank  168 , and includes a red light-emitting device  180 , a green light-emitting device  180 , and a blue light-emitting device  180 . The encapsulation layer  138  prevents the ingress of moisture or oxygen from the outside, thereby improving reliability. 
         [0063]    The light diffusion member  120  diffuses light that has passed through the light-emitting layer  184  for red, green, and blue light of each sub-pixel of the organic light-emitting display panel  130  to the light-blocking area overlapping the black bank  168 , thereby minimizing the perception of the light-blocking area by the user. To this end, in the case of an organic light-emitting display panel, which includes no color filter and emits light of the color of a corresponding pixel from a light-emitting layer, the light diffusion member appropriately adjusts the haze ratio depending on at least one variable selected from among the resolution of the display panel  130 , the size of the display panel  130 , the pixel density (e.g., pixels per inch (PPI)), and the distance from the upper surface of the organic light-emitting layer  184  to the upper surface of the light diffusion member  120 . 
         [0064]    For example, the haze ratio is set so as to be inversely proportional to at least one of the pixel density, the aperture ratio, and the distance from the upper surface of the organic light-emitting layer  184  to the upper surface of the light diffusion member  120 , and to be proportional to the width of the black back  168 . 
         [0065]    Specifically, because the lower the pixel density, the longer the distance between the sub-pixels, and consequently the wider the light-blocking area, an organic light-emitting display panel having a relatively low pixel density (aperture ratio) is set to have a higher haze ratio of the light diffusion member  120  than an organic light-emitting display panel having a relatively high pixel density. Because the wider the black bank  168  of the organic light-emitting display panel, the longer the distance between the sub-pixels, and consequently the wider the light-blocking area, an organic light-emitting display panel in which the black bank  168  is relatively wide is set to have a higher haze ratio of the light diffusion member  120  than an organic light-emitting display panel in which the black bank  168  is relatively narrow. Because the shorter the distance from the upper surface of the organic light-emitting layer  184  to the upper surface of the light diffusion member  120  of the organic light-emitting display panel, the greater the refraction angle of the light that has passed through the light diffusion member  120 , the organic light-emitting display panel in which the distance from the upper surface of the organic light-emitting layer  184  to the upper surface of the light diffusion member  120  is relatively short is set to have a higher haze ratio of the light diffusion member  120  than an organic light-emitting display panel in which the distance from the upper surface of the organic light-emitting layer  184  to the upper surface of the light diffusion member  120  is relatively long. 
         [0066]    Table 1 illustrates the results of simulating alleviation of a screen-door effect by adjusting the pixel density, the aperture ratio, and the distance between the light-emitting layer and the light diffusion member. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 No effect 
                 Effect 
                 Blurred Image 
               
               
                   
               
             
             
               
                 Panel 1 
                 20% haze 
                 50% haze 
                 80% haze 
               
               
                 Panel 2 
                 10% haze 
                 40% haze 
                 70% haze 
               
               
                 Panel 3 
                 10% haze 
                 60% haze 
                 90% haze 
               
               
                   
               
             
          
         
       
     
         [0067]    It can be seen that Panel 1 has a lower pixel density (ppi) than Panel 2, and shows alleviation of a screen-door effect at a haze ratio of about 50%, which is higher than that in Panel 2. It can be seen that Panel 2 has a higher aperture ratio than Panel 3, and shows alleviation of a screen-door effect at a haze ratio of about 40%, which is lower than that in Panel 3. It can be seen that Panel 3 has a shorter distance from the light-emitting layer to the light diffusion member than Panel 1, and shows alleviation of a screen-door effect at a haze ratio of about 60%, which is higher than that of Panel 1. 
         [0068]    Although in the embodiments of the present invention, the organic light-emitting display panel and the liquid crystal panel have been described by way of example, the present invention may be applied to all other display panels having a light-blocking area. 
         [0069]    In addition, although the embodiments of the present invention have been described only with reference to a top-emission-type organic light-emitting display panel, the present invention may also be applied to a bottom-emission-type organic light-emitting display panel or other types of organic light-emitting display panel. 
         [0070]    As is apparent from the above description, a light diffusion member is provided between a display panel and an optical lens according to one or more embodiments of the present invention. The light diffusion member may diffuse light emitted from a light-transmitting area of each sub-pixel in the display panel to a light-blocking area, which minimizes the perception of the light-blocking area by a user, resulting in the alleviation of a screen-door effect and the improved image quality. 
         [0071]    It will be apparent to those skilled in the art that the present invention described above is not limited to the embodiments described above and the accompanying drawings, and various substitutions, modifications, and alterations may be devised within the spirit and scope of the present invention.