Abstract:
A flat panel display system utilizing a light pipe having vapor deposited highly reflective material on a light pipe. The flat panel display may be used in a portable electronic device. One embodiment discloses deposition of a highly reflective material (e.g., SiO2 or TiO2) around the non-viewing areas of a light pipe that provides light to the display screen. Front lighting embodiments and back lighting embodiments are described. One embodiment further discloses deposition of reflective material on the surface of microstructures of the light pipe to enhance light reflection and to prevent light escape. Another embodiment of the present invention discloses the coating or vapor deposition of phosphor material on the light pipe. This embodiment utilizes a blue light or IR light with the phosphor layer, to create a long lasting white light which is appealing for many portable electronic device displays.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of display screens. More specifically, an embodiment of the present invention relates to the field of flat panel displays for portable electronic devices, such as personal digital assistants (PDAs), cell phones, pagers, digital watches etc. 
     2. Background of the Invention 
     Flat panel displays are commonly used in portable computer devices to display images and characters. The viewing area of some display panels is generally illuminated with at least one light source. The light source may be positioned behind or in front of the display matrix layer. The light from the light source may be distributed uniformly across the display panel. The efficiency of light distribution, uniformity of the distribution, intensity of the illumination and color of the light illuminating the display panel has always been a subject of development and improvement. 
     The efficiency of light distribution may be function of several factors including maximizing the use of the light source available and improving the light source used. Maximization of any resource can substantially be achieved by prevention of waste. In providing light to a display screen, light pipes are used to transfer the light from a light source across the display screen. Maximized use of the light source can be achieved using a light pipe that increases the amount of reflected light that illuminates the display matrix. 
     Flat panel display thickness is always a concern regarding portable electronic devices. Each layer of a flat panel display screen adds cost and thickness to the display subassembly. The display component of many portable electronic devices typically contributes a significant percentage of the overall thickness of the device. Therefore, it would be desirable to reduce the thickness of a flat panel display subassembly to thereby reduce the overall thickness of the portable electronic device. 
     Another factor of concern for maximizing illumination efficiency of a display screen is the color of the light used for illumination. For instance, a white color light is an appealing color for the users of portable devices under many environments. Commonly, white light may be achieved by using blue LEDs which illuminate an epoxy secured phosphor layer. These conventional displays have a very limited lifetime, maybe a few thousand hours due to heat related phosphor degradation. Consumers may not tolerate such a short lifetime for portable devices. 
     Thus a need exists for a portable computer system having a uniformly bright display screen which is efficiently illuminated. Furthermore, a need exists for a portable computer with a display screen properly illuminated to prevent undue stress on the user&#39;s eyes. Additionally, a need exists for such a flat panel display screen having a white color source with extended operating life. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide a portable electronic device, e.g., a computer system, pager, cell phone, etc., with a thin, uniformly bright display screen, which is efficiently illuminated. Furthermore, one embodiment of the present invention provides a portable computer with a display screen properly illuminated to prevent undue stress on the user&#39;s eyes. Additionally, another embodiment of the present invention provides a white color light source with an improved operating life over conventional systems. 
     An efficient technique for illuminating a display screen in a portable computer is disclosed. One embodiment discloses vapor deposition of a highly reflective material around the non-viewing areas of a light pipe for providing light to a display matrix area of the display screen. The brightness enhancement film may be made of silicon oxide (SiO2) or titanium oxide (TiO2), or combination of metal oxides for instance. The vapor deposited reflector may be used in front lighting and backlighting embodiments. Another embodiment further discloses deposition of reflective material on the surface of microstructures (of the light pipe) to enhance light reflection and to prevent light escape. Another embodiment of the present invention discloses a display technique using vapor deposition or coating of a phosphor layer on a light pipe for producing long lasting white light. 
     With respect to the back lighting embodiments, the reflective material may be vapor deposited on the back surface, and some of the sides of the light pipe. With respect to the front lighting embodiments, reflective material may be vapor deposited on the sides of the light pipe. 
     More specifically, an embodiment of the present invention discloses a flat panel display assembly comprising a flat panel display layer for generating an image using discrete elements; and a planar light pipe disposed to receive light from a light source and for back-illuminating the flat panel display layer from a rear position, the planar light pipe comprising a reflective material deposited on its bottom surface, the reflective material deposited on the planar light pipe using a chemical vapor deposition process. An embodiment include the above and wherein the light pipe has thereon a vapor-deposition or coating deposited phosphor layer. 
     A second embodiment discloses a flat panel display assembly comprising a flat panel display layer for generating an image using discrete elements; a planar light pipe disposed to receive light from a light source and for illuminating the flat panel display layer from a front position, the planar light pipe comprising a reflective material deposited on the edges of the light pipe thereon using a chemical vapor deposition process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a planar light pipe and a planar light bar used for illuminating display screen of a handheld computer. 
     FIGS. 2A and 2B depict masked areas of the top and the bottom surfaces of a planar light pipe, used in front light illumination, before any vapor deposition or coating operation. 
     FIGS. 3A and 3B depict masked areas of the top and the bottom surfaces of a planar light pipe, used in back light illumination, before any vapor deposition or coating operation. 
     FIGS. 4 depicts masked areas of the top and the bottom surfaces of a planar light bar before any vapor deposition or coating operation. 
     FIG. 5A depicts a cross section of a planar light pipe and a display screen in a front light illumination assembly in accordance with an embodiment of the present invention. 
     FIG. 5B depicts a cross section of a planar light pipe and a display screen in a back light illumination assembly in accordance with an embodiment of the present invention. 
     FIG. 6A illustrates the top view of a vaporized planar light pipe molded with a plastic frame in a front light illumination assembly in accordance with an embodiment of the present invention. 
     FIG. 6B illustrates the top view of a vaporized planar light pipe molded with a plastic frame, a planar light bar and brightness enhancement film (BEF) in a front light illumination assembly. 
     FIG. 6C illustrates the top view of a vaporized planar light pipe molded with plastic frame in a back light illumination. 
     FIG. 6D illustrates the bottom view of a vaporized planar light pipe molded with plastic frame, planar light bar and BEF in a back light illumination. 
     FIG. 7 illustrates vaporized molecules filling the air gaps between microstructures and a highly reflective material disposed along a bottom surface of a light pipe in accordance with an embodiment of the present invention. 
     FIG. 8 is an embodiment of this invention where a long lasting white light illumination is supplied to the display screen of a portable computer. 
     FIG. 9A illustrates top view of a planar light pipe and a planar light bar molded and masked for front lighting prior to vapor deposition or coating. 
     FIG. 9B illustrates bottom view of a planar light pipe and a planar light bar molded and masked for front lighting prior to vapor deposition or coating. 
     FIG. 10A illustrates top view of a planar light pipe and a planar light bar molded and masked for back lighting prior to vapor deposition or coating. 
     FIG. 10B illustrates bottom view of a planar light pipe and a planar light bar molded and masked for back lighting prior to vapor deposition or coating. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, vapor deposition or coating of reflective material and phosphorescent material in a lighting system, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention. 
     FIG. 1 illustrates a planar light pipe  110  and a planar light bar  120  used for illuminating a display screen of an electronic device, e.g., a handheld computer. Planar light bar  120  receives light from a light source disposed along at least one edge  122 ,  125  of the planar light bar  120  or the edge opposite to edge  122  (not shown). Planar light pipe  110  receives light from planar light bar  120  and distributes the light substantially uniformly across viewing area  140 . As described in more detail herein, the light pipe, in accordance with embodiments of the present invention, has deposited therein, using chemical vapor deposition techniques, a highly reflective material, along selected surfaces thereof. 
     In one embodiment, the highly reflective material may be silicon di-oxide (SiO2) or titanium di-oxide (TiO2) or combination of metal oxides. 
     FIGS. 2A and 2B depict masked areas of the top and the bottom surfaces of planar light pipe  110  in accordance with a front light illumination embodiment. The masking regions relate to those areas that will not receive any vapor deposited reflective material. It is appreciated that the light pipe may be of glass or plastic material. 
     FIG. 2A depicts a portion of top view of planar light pipe  110  masked in a front light illumination system. Viewing area  210  of the top surface (and a similar region of the bottom surface shown in FIG. 2B) are both masked off and are not exposed to a subsequent chemical vapor deposition of the reflective material. Planar light pipe  110  is vaporized substantially (with the reflective material) in all areas except the masked areas. In effect, with respect to the front lighting system, only the edges  130  of the light pipe (and some small area along the periphery of the top and bottom surfaces) receive the vapor-deposited reflective material. It is appreciated that at least one edge remains masked in order to receive light from the light bar (not shown). 
     FIG. 2B depicts masking of the bottom surface of planar light pipe  110  in a front light illumination system. In a front light system, the light pipe is situated between the display matrix layer and eyes and therefore viewing area  210  remains transparent and free of any viewing obstacles thereby enabling a user to view the displayed characters and images of the display surface. The viewing area  220  is substantially the same size as the top surface viewing area  210  of FIG.  2 A. Vaporization of planar light pipe  110  coats all surfaces of planar light pipe  110  except viewing areas  210  and  220 . It is appreciated that at least one edge remains masked in order to receive light from the light bar (not shown). 
     FIGS. 3A and 3B depict masked areas of the top and the bottom surfaces of planar light pipe  110  in a back light illumination embodiment. With respect to a rear or back illumination embodiment, the light pipe sits behind the display matrix layer and therefore the rear surface may be completely coated with the reflective material. 
     FIG. 3A depicts a masked portion of top surface  320  of planar light pipe  110 . Viewing area portion  310  of the top surface of planar light pipe  110  is the masked portion of top surface  320  of planar light pipe  110 . In a back light illuminating system (except for one edge which remains masked in order to receive light from the light bar) only viewing area  310  is otherwise masked and not exposed to the subsequent vaporization of highly reflective material. All other surfaces and edges are unmasked and are coated with a highly reflective material during the vapor deposition process. 
     In one embodiment, region  310  can include vapor deposited or coated yellowish phosphor for generating white light when exposed by blue LED light. In another embodiment, the phosphor may have red, green and blue components of or generating white light when exposed to an IR LED. 
     FIG. 3B depicts the lack of masking of the bottom surface of planar light pipe  110  in a back light illumination system. Planar light pipe  110 &#39;s bottom surface  340 , edges  350 ,  360  and the edge opposite to edge  330  (not shown) are unmasked and subject to vapor deposition. 
     In one embodiment, a plurality of microstructures (not shown) are properly located on the bottom surface  340  of planar light pipe  110 . The microstructures cause light traveling along planar light pipe  110  to be reflected towards viewing area  310  to increase brightness and uniformity. By applying the reflective material to the back surface having microstructures, by vapor deposition, the material can be filled into the microstructure itself for maximum efficiency. This eliminates the need of any back reflecting film. 
     FIG. 4 illustrates that the vapor deposition processes can also be applied to the light bar  120 . FIGS. 4A and 4B are used to illustrate masked areas of the top and the bottom surfaces of planar light bar  120  before any vaporization operation. 
     FIG. 4 is top view of planar light bar  120 . Planar light bar  120  receives light from at least one light source, which may be located along at least one edge of edges  420 ,  410 . At least one other edge illuminates the light pipe  110 . Assuming the light source is positioned at edge  410  and edge  420  optically couples with the light pipe, then all other edges and surfaces are coated with the reflective material. These surfaces are left unmasked and exposed to be deposited with highly reflective material during a vapor deposition process. The only masked edges of planar light bar  120  are edges  410  and  420 , in this example. 
     FIG. 5A depicts a cross section  500   a  of a flat panel display screen including a planar light pipe  110  and a display matrix layer  510  in a front light illumination assembly. In one example, layer  510  can be a liquid crystal display (LCD) layer. Highly reflective material  520  deposited along the edges of light pipe  110 , as described in FIGS. 2A and 2B, causes reflection of that portion of light hitting the edges to be reflected back into planar light pipe  110  to illuminate layer  510 . Furthermore, highly reflective material  520  deposited along the edges of planar light pipe  110  also prevents light from escaping from the planar light pipe  110 . A user can view displayed images and characters on display screen  510  through transparent viewing area  210 . 
     FIG. 5B depicts cross section  500   b  of a flat panel display screen including a planar light pipe  110  and flat panel display matrix layer  530  in a back light illumination assembly. Highly reflective material  520  deposited along the edges (and bottom) of light pipe  110 , as described in FIGS. 3A and 3B, prevents light from escaping and increases brightness. Light reflected by microstructures (not shown) upwardly along general direction  560  (i) illuminates display screen  530 . In one embodiment, the top surface  310  may contain a vapor deposited or coated phosphor layer. 
     FIG. 6A illustrates the top view  600   a  of a vapor-deposited planar light pipe  110  molded with a plastic frame  620  in a front light illumination embodiment. Viewing portion  210  (upper and lower surfaces) of planar light pipe  110  is a transparent and a user can observe images and characters displayed on the opposite side of viewing area  210 . Planar light pipe  110  portion receives light from a light source through front edge  630 . 
     FIG. 6B depicts a vapor-deposited planar light pipe  110  with a planar light bar  120  molded with a plastic frame in a front light illumination embodiment. It is appreciated that viewing portion  210  of planar light pipe  110  is prepared in accordance with FIGS. 2A and 2B and planar light bar  120  is vapor-deposited in accordance with FIG.  4 . View  600   b  illustrates vapor-deposited planar light pipe  110 , vapor-deposited planar light bar  120 , and plastic frame  620  molded to form a single component. 
     It is appreciated that planar light pipe  110 , planar light bar  120 , Brightness Enhancement Film  690  and plastic frame  620  may be molded together forming a single component prior to the vapor deposition process. 
     FIG. 6C illustrates the top view  600   c  of a vapor-deposited planer light pipe  110  molded with a plastic frame  620  in a back light illumination embodiment. Planar light pipe  110  portion receives light through edge  630 . A plurality of microstructures (not shown) are properly located on the bottom surface of planar light pipe  120 . Light traveling along planar light pipe  110  are redirected upwardly upon contact with the plurality of microstructures. Viewing area  670  is clear from vapor deposition, and light traveling along planar light pipe portion can travel outwardly in the general direction of  671 ( j ). Planar light pipe  110  is coated with highly reflective material in accordance with process  300 . In one embodiment, region  670  may be coated or vapor-deposited with a phosphor layer. 
     FIG. 6D illustrates a view  600   d  of a vapor-deposited planar light pipe  110  and planar light bar  120  with molded with plastic frame  620  in a back light illumination embodiment. Planar light pipe  110 &#39;s bottom surface  330  and planar light bar  120 &#39;s bottom surface  450  are substantially coated with a highly reflective material during a vapor deposition process. 
     It is appreciated that planar light pipe  110 , planer light bar  120 , and BEF  690  may be molded with plastic frame  620  forming a single component prior to the vapor deposition process. It is appreciated that vapor-deposited reflective material may be applied to the light pipe before any frame material, or other mechanical structures, are molded thereon. Alternatively, the vapor-deposited reflective material may be applied to the light pipe after any frame material, or other mechanical structures, are molded thereon. 
     FIG. 7 illustrates a cross section  700  of a vapor-deposited planar light pipe  110  in a back light illumination system. Microstructures  710 ( i ) are properly placed along the bottom surface  720  of planar light pipe  110 . Light traveling in a general direction  750 ( i ) hits microstructure  710 ( j ) and gets redirected upwardly towards viewing area  310 , thus illuminating a display screen of a handheld computer. Reflective material in  770  deposited against the bottom surface of planar light pipe  110  fills the space  780  of the microstructures. Material area  780  is highly exaggerated for the purpose of representation and is occupied with highly reflective material  770  deposited during vapor deposition. 
     Highly reflective material  770  coats the very small cavities  760 ( i ) in the backs of microstructures  710 ( j ). Coating the backside of cavities  710 ( j ) enhances the reflection of incident light  750  and prevents light from escaping upon light contact with microstructures  710 ( j ). 
     FIG. 8 illustrates an embodiment of this invention where light source  810  is a Light Emitting Diode (LED) emitting blue color light. Blue light from light source  810  is piped inside planar light pipe  110  via planar light bar  120 . In one embodiment of the present invention planar light pipe  110 &#39;s viewing area  830  is coated with phosphorous molecules. In another embodiment of this invention viewing area  830  is printed with phosphorous molecules. The remainder of the light pipe  110  and the light bar  120  may be coated with vapor-deposited highly reflective material as described above with respect to the backlighting embodiments. 
     Blue light from light source  810  travels along planar light pipe  110 . The blue light is redirected upwardly when hitting microstructures  710 ( i ) of FIG.  7 . Redirected blue light shining on yellow phosphorous material causes the phosphor to release white light thereby causing the viewing area to be lit with white light. In addition, redirected IR light shining on an RGB phosphorous material causes the phosphor to release white light. Also, by applying a phosphor material to the front surface where all the light is being directed, higher brightness and better uniformity can be achieved. In some cases, it is appreciated that blue LEDs are cheaper, more reliable and have longer lifetimes than white LEDs. 
     Embodiments of the present invention disclose a means for generating white light with substantially longer life. A conventional source for generating white light is a blue light emitting LED encapsulated in epoxy or epoxy mixed with yellow phosphorous material. Heat generated by an LED combined with the ambient temperature causes the epoxy to become cloudy and material break down of phosphorous, which results in a relatively short lifetime. The present invention generates white light where the light source has substantially the same life time as a typical LED, over approximately 50,000 hours. 
     FIG. 9A illustrates top view  900   a  of planar light pipe  110  co-molded with planar light bar  120  and masked prior to vapor deposition in a front light illumination system. 
     FIG. 9B illustrates bottom view  900   b  of planar light pipe  110  co-molded with planar light bar  120 . Viewing area  220  is masked in a front light illumination system prior to vapor deposition. 
     FIG. 10A illustrates top view  1000   a  of planar light pipe  110  co-molded with planar light bar  120 . Top surface  330  is masked for back light illumination prior to vapor deposition. Edges  430 ,  410 ,  360  and planar light bar top surface  440  are unmasked. 
     FIG. 10B illustrates bottom view  1000   b  of planar light pipe  110  co-molded with planar light bar  120 . Bottom surface  340  of planar light pipe  110  and bottom surface  450  of light bar  120  are unmasked. Edges  350 ,  410  and  430  are also unmasked for back light illumination prior to vapor deposition. 
     In summary the present invention provides an improved illumination for display screen in a portable electronic devices, e.g., portable computers. In accordance with the present invention a portable computer system is equipped with an enhanced front light or back light illumination system. Furthermore, the present invention discloses a white light source for the display screen of a portable computer with improved brightness and life span in order of magnitudes. 
     The foregoing description of specific embodiment of the present invention has been presented for purpose of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.