Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
1998-11-18
2001-07-03
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S495000
Reexamination Certificate
active
06255773
ABSTRACT:
BACKGROUND OF THE INVENTION
As is known in the art, field emission displays (FEDs) are a type of cathode ray tube which include a cathode comprising a dielectric substrate on which an array of field emission elements are formed and a cathodoluminescent anode comprising a dielectric substrate on which an array of phosphor elements are formed. In assembly, the anode and cathode structures are bonded together so that the field emission elements face the phosphor elements and the enclosed structure is evacuated. In a color FED, each pixel includes phosphor elements of different colors. Typically, each set of a red, a green, and a blue phosphor element forms a pixel. Control electrodes control the flow of electrons between the field emission elements and respective pixels.
The voltage between the FED anode and cathode determines the brightness of the display. In particular, the higher the operating voltage, the brighter the display. Operating voltages between 4KV and 10KV are desirable.
The size and spacing of the phosphor elements, as well as the physical separation between the anode and cathode, affect the display resolution. In particular, the closer the anode and cathode, the higher the resolution. However, as such spacing gets smaller, the likelihood of arcing, particularly at high operating voltage levels, increases. Suitable anode to cathode separation for operating voltages of 4-10KV is on the order of 3-4 millimeters.
Spacers are sometimes positioned between the anode and the cathode in order to accurately and reliably maintain the small separation between these structures. In one such arrangement, the spacers are attached to the cathode substrate and, when the anode and cathode structures are bonded together and the tube is evacuated, the spacers come into contact with the anode.
One technique for forming a cathodoluminescent anode includes depositing a phosphor and photoresist slurry onto a dielectric substrate and then patterning the layer, such as with the use of photolithography, in order to provide the phosphor pixel elements. These steps may be repeated multiple times using different slurries in order to provide the different colors comprising the pixels. A layer of lacquer is applied over the phosphor elements in order to provide a relatively smooth surface for the subsequent application of a conductive layer, such as aluminum applied by evaporation. The structure is then baked at a temperature between 400° C. and 450° C. to remove any organics, including the lacquer and any photoresist, which causes the aluminum layer to be held onto the substrate and phosphor elements by electrostatic forces.
The force of the spacers against the aluminum layer can cause loose particles of aluminum to be generated. Loose particles can cause the anode and cathode to become electrically shorted together, thereby resulting in dead areas on the display. Such particles can also cause stray emissions resulting in illumination of areas of the display that should not be illuminated. Further, the loose particles can cause arcing which, in turn can cause more loose particles to be generated.
SUMMARY OF THE INVENTION
According to the invention, a cathodoluminescent anode for use in an FED includes a substrate on which an array of phosphor elements is provided to form pixels. At least a pair of the phosphor elements is spaced by a gap into which a spacer will extend in assembly. A conductive layer is disposed over the phosphor elements, with a portion disposed in the gap, in contact with the substrate. In assembly, the anode is bonded to a cathode having a spacer, such that the spacer extends into the gap to contact the conductive layer.
With this arrangement, the conductive layer is securely, electrostatically and mechanically bonded to the substrate in the gap. Thus, when the conductive layer is contacted by the spacer in assembly, loose conductive particles do not tend to be generated. This is in contrast to conventional cathodoluminescent anodes for FEDs in which the conductive layer is held onto the anode by electrostatic forces and contact by the spacer tends to generate loose conductive particles.
In accordance with a further embodiment of the invention, a conductive layer disposed over the phosphor elements has an aperture in the gap between adjacent phosphor elements, so as to expose a portion of the substrate in the gap. In assembly, the anode is bonded to a cathode having a spacer, such that the spacer extends into the gap to contact the substrate. Since the spacer does not contact the conductive layer, loose conductive particles are not generated.
Also described are techniques for fabricating a cathodoluminescent anode. In accordance with one such technique, a plurality of phosphor elements are provided in a pattern on a substrate, with a gap between a pair of the phosphor elements. A lacquer is applied over the phosphor elements and a portion of the lacquer in the gap is removed, such as with the use of photolithography. A conductive layer is deposited over the structure so that a first portion of the conductive layer is disposed in the gap in contact with the substrate and a second portion of the conductive layer is disposed over the lacquer. The structure is then baked to remove of the lacquer.
According to an alternative technique, a lacquer is applied over the phosphor elements and a conductive layer is deposited over the lacquer. Thereafter, a portion of the conductive layer disposed in a gap between adjacent phosphor elements is removed, such as by reactive ion etching.
REFERENCES:
patent: 5103144 (1992-04-01), Dunham
patent: 5262698 (1993-11-01), Dunham
patent: 5543691 (1996-08-01), Palevsky et al.
patent: 5734224 (1998-03-01), Tagawa et al.
patent: 5777432 (1998-07-01), Xie
patent: 5814934 (1998-09-01), Tsai
Kozlowski Robert
Powers William C.
Daly, Crowley & Mofford LLP
Patel Ashok
Raytheon Company
Williams Joseph
LandOfFree
Field emission display having a cathodoluminescent anode does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Field emission display having a cathodoluminescent anode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Field emission display having a cathodoluminescent anode will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2562529