Abstract:
A transparent emissive display is created using a transparent anode and a transparent cathode so that images can be viewed from both sides of the field emission display panel. When the phosphor material emits the image, it can pass through the field emission material, if such a material is effectively made transparent by the manner in which it is deposited. The cathode conducting layer and the cathode substrate are thus also made transparent. Alternatively, multiple displays can be stacked together.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This Application claims priority to U.S. Provisional Patent Application Ser. No. 60/371,356, filed Apr. 10, 2002. 
    
    
     TECHNICAL FIELD 
     The present invention relates in general to displays, and in particular to field emission displays. 
     BACKGROUND INFORMATION 
     Transparent emissive displays are of special interest due to a variety of possible applications such as electronic windows, layer displays, stacked display panels, 3-D displays. Feasibility of making such a display has not been obvious since current display technologies use non-transparent materials such as silicon, thin film metal coatings, opaque dielectric layers, etc. Liquid crystal displays can be transparent, but they are not emissive and cannot target the applications mentioned above. An emissive display is a display in which the formation of an image involves mechanisms of light emission and which does not require an external light source. A non-emissive display is a display in which the formation of an image involves mechanisms of light reflection or absorption, and which requires an external light source. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates an embodiment of the present invention; 
     FIG. 2 illustrates another embodiment of the present invention; 
     FIG. 3 a  illustrates another embodiment of the present invention; 
     FIG. 3 b  illustrates another alternative embodiment of the present invention; and 
     FIG. 4 illustrates a system configured in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth such as specific field emitters, etc. to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known circuits have been shown in block diagram form in order not to obscure the present invention in unnecessary detail. For the most part, details concerning timing consideration and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art. 
     Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
     Referring to FIG. 1, one way of making a transparent emissive display is to design a field emission display such that it has a transparent anode  303 , or screen, and transparent cathode  403 , or electron emitting panel, both enclosed in a vacuum package  100 , or constituting the parts of such a vacuum package, where a vacuum gap  200  exists between those anode  303  and cathode  403  panels. The display  100  is viewable from the side of the anode  303  or the cathode  403 . A background screen  500  may be placed behind such a transparent display  100  to change viewability or transparency of, the display  100 , which can be a black background, or another display, or still image, or any other background. 
     The transparent anode  303  can be made of a glass, plastic, or other transparent substrate  300 , covered with a transparent layer of phosphor  302 . This can be an inorganic or organic thin film phosphor, or phosphor consisting of particles, like most of the phosphors used in cathode ray tubes and vacuum fluorescent displays, but having low density or treated such a way that it is transparent for visible light. The transparent conducting layer  301 , such as indium tin oxide (ITO), is deposited between the phosphor  302  and the glass plate  300 . The phosphor  302  and the conducting layer  301  can be patterned to provide addressability of different parts of the anode  303  to enable formation of an image. Such anode address lines  303  are shown in FIG.  2 . 
     The transparent cathode  403  may comprise transparent plate  400  similar to the plate  300 , and the transparent conducting layer  401  that covers the plate  400 . A transparent field emission material  402  in the form of field emitting particles such as single-wall or multi-wall carbon nanotubes or similar emitters with size aspect ratios higher than 10, are attached to the layer  401 , so that these particles are so rarely spaced and/or so small that they are effectively transparent to visible light. The emitter layer  402  and the conducting layer  401  can be patterned to provide addressability of different parts of the cathode  403  to enable formation of an image. Such cathode address lines  403  are shown in FIG.  2 . 
     Applying a voltage (not shown) between the cathode  403  and the anode  303  will cause electrons to emit from the cathode  403 , fly through the vacuum gap  200 , and excite the phosphor  302 . The vacuum in the vacuum gap  200  may be in the range of 10 −3  to 10 −10  torr, preferably in the range of 10 −6  to 10 −9  torr. The anode  303  and cathode  403  panels can be separated by spacers  102  to ensure the uniformity of the gap  200 . 
     Referring to FIGS. 3 a  and  3   b , the display panels may be stacked together to form a multi-layered (sandwiched) display. Such a display may consist of alternating plates, each of which may have similar types of electrodes on both plate sides—anode or cathode (see FIG. 3 b ), or different electrodes (FIG. 3 a ). Inside the vacuum package, the inner glass plates  600 ,  601  may be thin enough since there is no requirement to withstand the atmospheric pressure. This enables making a higher resolution display of this type. Spacers  102  can be used inside the transparent field emission display to make the gap  201  uniform over the display area. 
     A representative hardware environment for practicing the present invention is depicted in FIG. 4, which illustrates an exemplary hardware configuration of data processing system  413  in accordance with the subject invention having central processing unit (CPU)  410 , such as a conventional microprocessor, and a number of other units interconnected via system bus  412 . Data processing system  413  includes random access memory (RAM)  414 , read only memory (ROM)  416 , and input/output (I/O) adapter  418  for connecting peripheral devices such as disk units  420  and tape drives  440  to bus  412 , user interface adapter  422  for connecting keyboard  424 , mouse  426 , and/or other user interface devices such as a touch screen device (not shown) to bus  412 , communication adapter  434  for connecting data processing system  413  to a data processing network, and display adapter  436  for connecting bus  412  to display device  438 . CPU  410  may include other circuitry not shown herein, which will include circuitry commonly found within a microprocessor, e.g., execution unit, bus interface unit, arithmetic logic unit, etc. Display device  438  may comprise any one of the displays described herein. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.