In a luminescent display such as a Field Emission Display (FED), as shown in FIG. 1, electrons 18 from a plurality of emitters 16 in a cathode 7 strike phosphor elements 33 on an anode plate 4 and cause photon emission 46. As shown in FIG. 1, a current practice in FED technology is to apply a transparent conductor 1 (e.g., indium tin oxide) to the glass substrate 2 of the anode plate 4. Phosphor elements 33 are applied over the transparent conductor 1. Potential 15 is applied to the anode 4 during display operation. To emit electrons 18 from particular array emitter apertures 25, a gate potential Vq is applied to specific gates 26 which may be supported on some dielectric material 28. The dielectric material 28 and electron emitters 16 can be supported on a cathode assembly 31 which can be supported on a cathode back plate 29, which in turn is supported on back plate support structure 30.
The brightness of the image that results can be greatly enhanced by applying a thin, reflective metal film 21 on the cathode side of the phosphor. Essentially, the reflective metal film 21 can double the light 46 observed by the viewer. The reason is the reflective metal film 21 reflects the portion of emitted light that propagates away from the viewer toward the viewer. (When the phosphor is excited, light is emitted in all directions. Also, the intensity of the light initially emitted from the phosphor toward and away from the viewer is about equal).
In FEDs, the reflective metal film 21 must be smooth and continuous in regions over the phosphor to efficiently direct light 46 toward the viewer. If the film is rough or discontinuous (i.e., having voids) or both, some emitted light initially propagating away from the viewer may not be reflected toward the viewer. FIG. 2 shows a profile of an individual phosphor element 33 in a finished assembly. The individual phosphor particles 39 are also shown. The aluminum layer 21 is shown having voids 38 which tend to reduce the light output, because light will escape through the voids. Some of the voids are created when the anode plate is baked-out to remove organic materials and some voids can be created due to the topography of the deposited phosphor elements 33. FIG. 3 shows an example of the phosphor element after the reflective metal film 21 is applied (which is typically by chemical vapor deposition of aluminum) and prior to bake out. Pockets 41 within the phosphor elements can comprise binder and/or organic materials used in the deposition process. (The organic material can include those used to print the phosphor elements using a photoresist process or other known printing processes.) Organic materials need to be baked out to have an operational FED. FIG. 3 also shows a lacquer film layer 42 which is applied before the reflective metal film 21. (The lacquer film layer 42 is typical applied by spin coating). The film layer 42 is used to provide a smooth continuous substrate onto which the aluminum is applied. Without the lacquer film layer 42 to provide a smooth substrate, the reflective metal film 21 is typical very poor in quality and may not assist in increasing light output to an extent otherwise possible.
To provide FEDs which efficiently propagate light toward the viewer, reflective metal films 21 of high quality are necessary and screen structure characteristics promoting the propagation of emitted light toward the viewer are needed.