Abstract:
The present invention provides an enhanced light out-coupling device for extraction of light radiation from a light source. The enhanced light out-coupling device comprises a grid having a plurality of channels, a reflective material layer coated on the grid, and a high refractive index fluid layer. In addition, the grid can be filled with phosphor particles for light converting. The device of the presently claimed invention is able to effectively avoid the scattering problem generated from the sapphire substrate and phosphor particles, as well as reduce light adsorption by the array of grid during the light extraction, leading to better image quality.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims benefits from the U.S. provisional patent application No. 61/957,167 filed Jun. 26, 2013, and the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to a light out-coupling device. More preferably, it relates to an enhanced light out-coupling device for extraction of light radiation from a light source. The present invention also relates to a method for fabricating said light out-coupling device. 
       BACKGROUND OF THE INVENTION 
       [0003]    Light scattering has been a problem during the development of light emitting diode on silicon (LEDoS) device. It is due to the fact that the high refractive index of sapphire substrate of the LED chip enhance scattering. In addition, the use of phosphor particles for light conversion from blue to green and from blue to red colors will further enhance the scattering. This problem leads to unclear images when the LED pointed-light source is used to project light onto a screen, and adversely affects the LEDoS to be used for projector application. 
         [0004]    Insertion of collimator or grid may help to reduce scattering, as demonstrated in U.S Patent Application Publication No. 2012/0223875, but the light intensity is also reduced since the grid/collimator absorbs a certain amount of light. Similarly, it is still not favorable when the light source is used for projector application. &#39;875 is also not suitable for LED array in relatively smaller size as their claimed device lowers the light intensity of the light travelling through the grid-like structure due to the size limitation. 
         [0005]    The problem becomes worse when the size of micro-display is getting smaller. For a collimator with channel size less than 100 μm, the light absorbed by the sidewall becomes significant and the intensity of emitted light is reduced dramatically. 
       SUMMARY OF THE INVENTION 
       [0006]    A first aspect of the present invention provides an enhanced light out-coupling device, such as a collimator, comprising a grid having channels and highly reflective surface. The highly reflective surface, being a mirror-like coating, is able to enhance light extraction from a light source. The enhanced light out-coupling device can be filled with the light converting phosphors, which convert the light from the light source to longer wavelength. The reflective surface of the enhanced light out-coupling device can further help to extract the light with longer wavelength from the light converting phosphors. The light out-coupling device can further comprise a high refractive index fluid layer filled in the space between the grid and the light source such that light scattering problem generated from a sapphire substrate is further minimized. 
         [0007]    A second aspect of the present invention provides a method for fabricating said light out-coupling device, comprising the steps of forming a grid, and coating a reflective material layer on the grid. The step of forming the grid includes lithography patterning followed with chemical wet or dry etching of silicon wafers or other substrates. The step of coating the reflective material layer on the grid can include depositing the reflective material by solution method, wet chemical method, vapor deposition or sputtering. The solution method includes spray coating, dipping, electroplating; the wet chemical method includes mixing glucose and silver nitrate solution; the vapor deposition includes physical vapor deposition, chemical vapor deposition and other vapor deposition processes. The reflective material can also be deposited by sputtering of silver, aluminum, platinum and/or other metals. 
         [0008]    A third aspect of the present invention provides a display or projector comprising the light out-coupling device of the presently claimed invention. 
         [0009]    The light out-coupling device of the presently claimed invention is able to effectively avoid the scattering problem generated from the sapphire substrate and phosphor particles, leading to better image quality. Additionally, due to the presence of the reflective material layer coated on the grid, light adsorption by the array of grid is largely reduced, thereby substantially reducing the loss of output light intensity after the light extra by the light out-coupling device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawings illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the invention. 
           [0011]      FIG. 1  is a schematic diagram depicting a light out-coupling device according to an embodiment of the presently claimed invention; 
           [0012]      FIG. 2  is a flow chart depicting the steps of a method for fabricating a light out-coupling device according to an embodiment of the presently claimed invention; 
           [0013]      FIG. 3  is a flow chart depicting the steps of forming a grid according to an embodiment of the presently claimed invention; 
           [0014]      FIG. 4  is a photo showing a light out-coupling device according to an embodiment of the presently claimed invention; 
           [0015]      FIG. 5  is a schematic diagram depicting a light out-coupling device according to another embodiment of the presently claimed invention; 
           [0016]      FIG. 6  is a photo showing a light out-coupling device according to another embodiment of the presently claimed invention; 
           [0017]      FIG. 7  is a schematic diagram depicting a LED display arrays with a light out-coupling device according to an embodiment of the presently claimed invention; 
           [0018]      FIG. 8A  is a photo showing a LED display filled with red phosphors but without grid installation; 
           [0019]      FIG. 8B  is a photo showing a LED display with a light out-coupling device filled with red phosphors according to an embodiment of the presently claimed invention; and 
           [0020]      FIG. 9  is a photo showing a LED display with a light out-coupling device filled with green phosphors according to an embodiment of the presently claimed invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0021]    The following examples are used to assist the illustration and understanding of the presently claimed invention, but are not intended to limit the scope of the presently claimed invention. 
         [0022]      FIG. 1  is a schematic diagram depicting a light out-coupling device according to an embodiment of the presently claimed invention. The light out-coupling device  11  is located along a path of the light from a light source to a display panel. The light out-coupling device  11  comprises a grid  12  having a plurality of channels  13 . The grid  12  is coated with a reflective material layer  14 . A plurality of light beams  15 , came from an array of pointed-light source and comprising an amount of scattered light, passes through the channels  14  of the grid  12 . After passing through the grid  12 , the light beams  15  are converted into a plurality of aligned light beams  16 . Since there is the reflective material layer  14  deposited on the grids, the light beams  15  are substantially reflected by the reflective material layer  13 , that avoids the light beams  15  being absorbed by the grid, ultimately reducing the loss of output light intensity, and enhancing the performance of light extraction. 
         [0023]    Preferably, the grid is made of silicon, and pitches of the grid are in the range of 50-300 μm. The thickness of the grid can be 100 to 300 μm. 
         [0024]    Preferably, the reflective material layer has reflectance more than 97%, The thickness of the reflective material layer is less than 1 μm. The reflective material layer is deposited on the sidewalls of the channels, and made of silver, aluminum or other highly reflective metals. The channels can be square, rectangular, circular or any other regular or irregular shape. 
         [0025]    Preferably, the pointed-light source can be, but not limited to LED, LEDoS, polymer light emitting diode (PLED), or organic light emitting diode (OLED). 
         [0026]      FIG. 2  is a flow chart depicting the steps of a method for fabricating a light out-coupling device according to an embodiment of the presently claimed invention. The method comprises the steps of forming a grid ( 201 ), and coating a reflective material layer on the grid ( 202 ). 
         [0027]      FIG. 3  is a flow chart depicting the steps of forming a grid according to an embodiment of the presently claimed invention. The method comprises the steps of providing a silicon wafer ( 301 ), coating with photoresist ( 302 ), soft baking ( 303 ), conducting mask alignment ( 304 ), exposing ( 305 ), developing ( 306 ), etching ( 307 ), striping ( 308 ), lapping ( 309 ), and dicing ( 310 ). 
         [0028]    After formation of the grid, the reflective material layer can be coated on the grid by solution method, wet chemical method, vapor deposition or sputtering. The solution method includes spray coating, dipping, or electroplating; the wet chemical method includes mixing a glucose solution and silver nitrate solution; the vapor deposition includes physical vapor deposition, chemical vapor deposition and other vapor deposition processes. The reflective material can also be deposited on the grid by sputtering of silver, aluminum, platinum and/or other metals. 
         [0029]      FIG. 4  is a photo showing a light out-coupling device according to an embodiment of the presently claimed invention. The light out-coupling device comprises an array of grid  41  with high reflective surface  42 . 
         [0030]      FIG. 5  is a schematic diagram depicting a light out-coupling device according to another embodiment of the presently claimed invention. The light out-coupling device  51  comprises a grid  52 , having a plurality of channels  53  and coated with a reflective material layer  54 , as well as light converting phosphor particles embedded within a polymer to form a polymer composite  57 , which is filled into the channels  53  of the grid  52 . A plurality of light beams  55 , came from an array of pointed-light source and comprising a substantially amount of scattered light, are converted by the light converting phosphor particles into light beams with longer wavelength. After passing through the polymer composite  57  and the channels  53 , the light beams  55  are converted into aligned light beams with longer wavelength  56 . Since there is the reflective material layer  54  deposited on the sidewalls of the channels  53 , the light beams with longer wavelength are substantially reflected by the reflective material layer  54 , that avoids the light beams with longer wavelength being absorbed by the grids, ultimately reducing the loss of output light intensity. 
         [0031]    Preferably, the polymer includes epoxy or silicon polymer. The polymer composite comprises 10-50 wt % of phosphor content. 
         [0032]      FIG. 6  is a photo showing a light out-coupling device according to another embodiment of the presently claimed invention. The light out-coupling device comprises an array of grid  61 , and a polymer composite  62  incorporated with light converting phosphors. The polymer composite  62  is filled into the channels of the grid  61 . 
         [0033]      FIG. 7  is a schematic diagram depicting a LED display with a light out-coupling device according to an embodiment of the presently claimed invention. The LED display  71  comprises a silicon active matrix control  72 , LED arrays  73 , and a sapphire substrate  74 . The light out-coupling device  75  of the present invention, placed on top of the sapphire substrate  74 , further comprises a high refractive index fluid layer  76 . The high refractive index fluid layer  76  is located between the sapphire substrate  74  and a grid  77 , and filled into the gap between the sapphire substrate  74  and the grid  77 . The channels of the grid  77  are filled with a polymer composite  78  incorporated light converting phosphor particles. The LED arrays  73  emit light beams, in which some of them are scattered by the sapphire substrate  74 . The light beams are further converted by the light converting phosphor particles to provide light beams with longer wavelength. After passing through the grid  77 , the light beams emitted from the LED arrays are converted and aligned into aligned light beams with longer wavelength  79 . The high refractive index fluid layer  76 , being inert and stable, is able to further minimize the scattering effect from the sapphire substrate  74  due to stepwise decrease of refractive index from the sapphire substrate to air. 
         [0034]    Preferably, the high refractive index fluid layer comprises, but not limited to silicone oil. The high refractive index fluid layer has a refractive index higher than 1.5. 
         [0035]      FIG. 8A  is a photo showing a LED display filled with red phosphors but without grid installation. The red phosphors are blended with a polymer, which is deposited on top of the LED array of the LED display.  FIG. 8B  is a photo showing a LED display with a light out-coupling device filled with red phosphors according to an embodiment of the presently claimed invention. As shown in both  FIG. 8A  and  FIG. 8B , the image on the screen of  FIG. 8B  shows much sharper and better quality than that of  FIG. 8A , illustrating that the light out-coupling device of the present invention is able to solve the light scattering problem came from the sapphire substrate and the phosphor particles. 
         [0036]      FIG. 9  is a photo showing a LED display with a light out-coupling device filled with green phosphors according to an embodiment of the presently claimed invention. As shown in the  FIG. 9 , a sharp and clear image is provided. 
         [0037]    According to an embodiment of the present invention, red, green and yellow phosphor particles are filled within their corresponding channels respectively to generate white light. 
         [0038]    While embodiments of the present invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.