Abstract:
A resistive spacer coating for a carbon nanotube (CNT)/field emission device (FED) display is described. The resistive spacer coating reduces electrostatic charging of the spacer during operation of the display while maintaining the field potential between the cathode and the phosphor screen. The resistive coating includes one or more resistive materials which are combined with binders that are then applied to the spacer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an emission displays and, more particularly to coatings for spacers therein. 
         [0003]    2. Description of the Background Art 
         [0004]    Carbon nanotube (CNT)/field emission device (FED) displays typically include a cathode with CNT emitters thereon, a metal gate, insulating spacers and a phosphor screen. The insulating spacers are interposed between the cathode and the phosphor screen. The phosphor screen is located on an inner surface of a faceplate of the display. The metal gate functions to direct electron beams generated from the CNT emitters toward appropriate color-emitting phosphors on the screen of the display. 
         [0005]    The screen may be a luminescent screen. Luminescent screens typically comprise an array of three different color-emitting phosphors (e.g., green, blue and red) formed thereon. Each of the color-emitting phosphors is separated from another by a matrix line. The matrix lines are typically formed of a light-absorbing black, inert material. 
         [0006]    The insulating spacers are used in CNT/FED displays to keep the distance between the cathode and the phosphor screen constant under vacuum. However, the spacers can develop surface electrostatic charges during operation of the display, adversely affecting picture quality. Poor picture quality is a particular concern for CNT/FED displays. 
         [0007]    Thus, a need exists for a CNT/FED display with spacers having reduced surface electrostatic charging during operation. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention relates to a resistive spacer coating for a carbon nanotube (CNT)/field emission device (FED) display. The resistive spacer coating reduces electrostatic charging of the spacer during operation of the display while maintaining the field potential between the cathode and the phosphor screen. The resistive coating includes one or more resistive materials which are combined with binders that are then applied to the spacer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will now be described in greater detail, with relation to the accompanying drawings, in which: 
           [0010]      FIG. 1  is a schematic view of a CNT/FED display, showing a luminescent screen and cathode separated by an insulating spacer. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    As shown in  FIG. 1 , a carbon nanotube (CNT)/field emission device (FED) display  1  includes a cathode  10  with CNT emitters  12  thereon, a metal gate  14 , insulating spacers  16  and a phosphor screen  18 . The insulating spacers  16  (only one spacer is shown in  FIG. 1 ) are interposed between the cathode  10  and the phosphor screen  18 . The phosphor screen  18  is located on an inner surface of a faceplate  20  of the display. The metal gate  14  functions to direct electron beams  22  generated from the CNT emitters  12  toward appropriate color-emitting phosphors  24  on the screen  18  of the display  1 . 
         [0012]    The screen  18  may be a luminescent screen. Luminescent screens typically comprise an array of three different color-emitting phosphors  24  (e.g., green, blue and red) formed thereon. Each of the color-emitting phosphors  24  is separated from another by a matrix  26 . The matrix  26  is typically formed of a light-absorbing black, inert material. 
         [0013]    The three-color phosphors  24  may include a ZnS:Cu, Al (green) phosphor, a ZnS:Ag, Cl (blue) phosphor and a Y 2 O 2 S:Eu +3  (red) phosphor. This RGB phosphor system is suitable for a carbon nanotube (CNT)/field emission device (FED) display operated between about 4-10 kV. 
         [0014]    The insulating spacers  16  are used in CNT/FED displays to keep the distance between the cathode  10  and the phosphor screen  18  constant under vacuum. The insulating spacers  16  may be made for example, of glass. The insulating spacers  16  have a resistive coating  30  thereon. The resistive coating  30  should have adhesive properties for the insulating spacers  16 . The resistive coating  30  may be applied over portions of each surface of the insulating spacers  16 . 
         [0015]    The resistive coating  30  functions to reduce electrostatic charging while maintaining the field potential between the cathode  10  and the screen  18 . Such coatings that exhibit a surface resistivity in the range of about 10 10  ohms/square to about 10 15  ohms/square are sufficient for reducing electrostatic charging of the spacer surfaces. 
         [0016]    The resistive coating  30  may comprise a metal oxide mixed with at least one silicate glass. A dispersant may optionally be added to the resistive coating. The amount of the metal oxide in the resistive coating is used to control the resistivity thereof. 
         [0017]    Suitable metal oxides may include, for example, chromium oxide, among others. Suitable silicate glasses may include, for example, potassium silicate, sodium silicate, lead-zinc-borosilicate glass, and devitrifying glass, among others. 
         [0018]    An exemplary resistive coating may comprise a mixture of 37 weight % chromium oxide powder, 2 weight % dispersant, 11 weight % sodium silicate and 20 weight % potassium silicate in about 30 weight % deionized water. The resistive coating mixture is milled in a ball mill to achieve a homogeneous mixture suitable for application onto the insulating spacers  16 . 
         [0019]    According to one embodiment of the invention, the resistive coating mixture is applied to the insulating spacers  16 , e.g., by spraying. The resistive coating  30  preferably has a thickness of about 0.05 mm to about 0.09 mm (2-3.5 mils). 
         [0020]    The insulating spacers  16 , having the resistive coating  30  thereon, is dried at room temperature. After drying, the resistive coating  30  on the insulating spacers  16  is hardened (cured) by heating the spacers  16  in an oven. The spacers  16  are heated over a period of about 30 minutes to a temperature of about 300° C., and held at 300° C., for about 20 minutes. Then, over a period of 20 minutes, the temperature of the oven is increased to about 460° C., and held at that temperature for two hours to melt and crystallize the coating and form a resistive layer on the insulating spacers  16 . The resistive coating  30 , after firing, will typically not remelt. 
         [0021]    Although an exemplary luminescent screen for a carbon nanotube (CNT)/field emission display (FED) which incorporates the teachings of the present invention has been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.