Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
1998-07-31
2001-03-13
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
Reexamination Certificate
active
06200181
ABSTRACT:
TECHNICAL FIELD
The present claimed invention relates to the field of flat panel displays. More specifically, the present claimed invention relates to a flat panel display having walls that have superior heat conductivity and thermal coefficient of resistivity.
BACKGROUND ART
A Cathode Ray Tube (CRT) display generally provides the best brightness, highest contrast, best color quality and largest viewing angle of prior art computer displays. CRT displays typically use a layer of phosphor which is deposited on a thin glass faceplate. These CRTs generate a picture by using one to three electron beams which generate high energy electrons that are scanned across the phosphor in a raster pattern. The phosphor converts the electron energy into visible light so as to form the desired picture. However, prior art CRT displays are large and bulky due to the large vacuum envelopes that enclose the cathode and extend from the cathode to the faceplate of the display. Therefore, typically, other types of display technologies such as active matrix liquid crystal display, plasma display and electroluminescent display technologies have been used in the past to form thin displays.
Recently, a thin flat panel display has been developed which uses a backplate including a matrix structure of rows and columns of electrodes to generate a visible display. Typically, the backplate is formed by depositing a cathode structure (electron emitting) on a glass plate. The cathode structure includes emitters that generate electrons. The backplate typically has an active area surface within which the cathode structure is deposited. Typically, the active area surface does not cover the entire surface of the glass plate, a thin strip is left around the edges of the glass plate. The thin strip is referred to as a border or a border region. Conductive traces extend through the border to allow for electrical connectivity to the active area surface. These traces are typically covered by a dielectric film as they extend across the border so as to prevent shorting.
Prior art thin flat panel displays include a thin glass faceplate (anode) that is separated from the backplate by about 1 millimeter. Walls or “spacers” are currently used in prior art thin flat panel display assembly to separate the faceplate and the backplate. The faceplate includes an active area surface within which the layer of phosphor is deposited. The faceplate also includes a border region. The border is a thin strip that extends from the active area surface to the edges of the glass plate. The faceplate is attached to the backplate using a glass sealing structure. This sealing structure is typically formed by melting a glass frit in a high temperature heating step. This forms an enclosure that is pumped out so as to produce a vacuum between the active area surface of the backplate and the active area surface of the faceplate. Individual regions of the cathode are selectively activated to generate electrons which strike the phosphor so as to generate a visible display within the active area surface of the faceplate. These FED flat panel displays have all of the advantages of conventional CRTs but are much thinner.
The faceplate of a thin flat panel display requires a conductive anode electrode to carry the current used to illuminate the display. Conventional walls are resistive in order to bleed off charge which may otherwise result in deleterious electron deflection. The walls should not interfere with the travel path of electrons as the electrons pass from the backplate to the faceplate. Typically, prior art walls are made of ceramic. However, though ceramic material can be made to have the required resistivity, ceramic material also has relatively low thermal conductivity and high coefficient of thermal resistivity.
In order to generate a bright image on a region of a thin flat panel display, a high level of electron emission is required. As a bright image is generated on a region of a thin flat panel display, electrons lose energy as they penetrate the faceplate at the brightly illuminated region, thereby heating up the faceplate. This results in regions of the faceplate that are heated.
Because of the relatively low thermal conductivity of prior art walls and the glass faceplate and the vacuum environment, the local faceplate heating generated at bright regions of the visible display is not dissipated readily. The walls are one of the heat dissipative components, but because prior art walls are poor thermal conductors, they tend to heat up locally. A temperature gradient is then generated across the wall. Since the thermal coefficient of resistivity of prior art walls is high, the local heating of the walls decreases(or increases) the resistivity of the walls locally. This local decrease(or increase) in resistivity results in a voltage gradient along the wall from anode to cathode that is non-linear compared to that of free space next to the wall.
The local nonlinear voltage gradient along the walls causes the deflection of electron beams either towards or away from the wall. This produces regions within the visible display that are not illuminated. More particularly, the deflection and attraction of the wall surfaces causes visible non-illuminated regions in the form of non-illuminated lines that extend across the visible display. Also, the non-linear voltage gradient along the wall can result in arcing between the cathode and the wall.
Thus, a need exists for a flat panel display that does not produce non-illuminated regions of the visible display as a result of local heating effects. More particularly, a need exists for a flat panel display that does not produce visible non-illuminated regions of the visible display as a result of heating of walls. More particularly, a need exists for walls that can conduct heat away from the faceplate and that do not produce voltage variations as a result of local heating. The present invention meets the above needs.
DISCLOSURE OF THE INVENTION
The present invention provides a thin flat panel display that includes walls that have a high thermal conductivity and a low thermal coefficient of resistivity. This produces a flat panel display that does not produce non-illuminated regions of the visible display as regions of the visible display are brightly illuminated.
In one embodiment of the present invention a backplate is formed by forming a cathode on an active area surface of a glass plate. The faceplate is formed by depositing luminescent material within an active area surface formed on a glass plate. Walls are attached to the faceplate using supporting structures which mechanically hold each wall to the faceplate. A glass sealing material is placed within the border of the faceplate. The backplate is then placed over the faceplate such that the walls and the glass frit are disposed between the faceplate and the backplate. The assembly is then sealed by thermal processing and evacuation steps so as to form a complete flat panel display.
The walls of the present invention have a high thermal conductivity and a low thermal coefficient of resistivity. In one embodiment, a ceramic material that includes dispersed metal is used to obtain the desired properties.
In one embodiment, spacer walls are fabricated using materials that include ceramic and a metal oxide. First, metal oxide particles are mixed with a ceramic powder and binders so as to form a slurry. The slurry is then tape cast into thin sheets. A heating step is then performed on the thin sheets so as to burn-out the binder and sinter the sheets. This reduces the metallic oxide into metallic particles uniformly dispersed in a ceramic matrix. The resulting thin sheets are then diced so as to form spacers.
In one embodiment, a layer of metal is selectively applied to the spacers so as to form conductive strips that allow for bleed-off of electrical charge. Additionally, in one embodiment, the walls are coated with a material that reduces secondary electron emission.
The spacer walls of the present invention have a higher thermal conductivity than prior
Fahlen Theodore S.
Hopple George B.
Klatt John P.
Narayanan Kollengode S.
Candescent Technologies Corporation
Ramsey Kenneth J.
Wagner , Murabito & Hao LLP
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