Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
2002-09-04
2004-09-14
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S496000, C313S292000, C313S257000
Reexamination Certificate
active
06791255
ABSTRACT:
TECHNICAL FIELD
The present claimed invention relates to the field of electronic displays. More specifically, the present claimed invention relates to a spacer (e.g., support) structure for an electronic display, including flat panel displays.
BACKGROUND ART
In some displays including flat panel displays, a backplate is commonly separated from a faceplate using a spacer (e.g., support) structure. In high voltage applications, for example, the backplate and the faceplate are separated by spacer structures having a height of approximately 1-3 millimeters. For purposes of the present application, high voltage refers to an anode to cathode potential greater than 1 kilovolt. Illustratively, in flat panel displays, the backplate deploys an array of cathodes (e.g., electron emitters) and the faceplate deploys an array of pixels and serves as an accelerating anode for electrons emitted by the cathode array, which travel through high vacuum between the anode and the cathode. The space between the cathode array and the anodes is sealed by fusing frit, a mixture of powdered glass and various other agents that joins the backplate and the faceplate. The space is then evacuated.
Upon evacuation, atmospheric pressure exerts a force tending to collapse the faceplate into the backplate. The spacer structures are deployed to withstand this force and thus support the faceplate. In one embodiment, the spacer structure is comprised of several strips or individual wall structures each having a width of about 50 microns. The strips are arranged in parallel horizontal rows with each strip extending across the width of the flat panel display. The spacing of the rows of strips depends upon the strength and size of the backplate and the faceplate and the strips, their surface areas, and the concomitant force of atmospheric pressure. Because of this, it is desirable that the strips be extremely strong. The spacer structure must meet a number of intense physical requirements.
In a typical flat panel display, the spacer structure must comply with a long list of characteristics and properties. More specifically, the spacer structure must be strong enough to withstand the atmospheric forces which compress the backplate and faceplate towards each other. Additionally, each of the rows of strips in the spacer structure must be essentially equal in height, so that the rows of strips accurately fit between respective rows of pixels. Furthermore, each of the rows of strips in the spacer structure must be very flat to insure that the spacer structure provides uniform support across the interior surfaces of the backplate and the faceplate.
Spacer structures must also have good stability. More specifically, the spacer structure should not degrade severely when subjected to electron bombardment, high operating temperatures, temperature variations, and/or subjection to a vacuum. As yet another requirement, a spacer structure should not significantly contribute to contamination of the vacuum environment of the flat panel display. Spacer structures therefore should not significantly out-gas in vacuo at any point within its operational temperature and voltage ranges. Further, spacer structures should not be susceptible to contamination that may evolve within the evacuated space such that any of their required properties degrade.
Another requirement for a spacer structure for a display is that it cannot interfere with the trajectories of the electron beams emitted by the display's cathode, for example a Spindt emitter array cathode, toward their target pixels on the faceplate, which functions electrically as an anode. Interfering with the electrons' trajectories can cause image distortion, degradation, or failure. For these reasons, a spacer structure must not retain any significant electrostatic charge which could deflect the electrons' trajectories by attraction or repulsion. Thus, the coefficient of emission of secondary electrons, e.g., the secondary electron coefficient of emission, must suffice such that, ideally, for every electron absorbed by the spacer structure, a numerically corresponding electron is emitted.
Special coatings may be applied to spacer structures to ensure a satisfactory secondary electron coefficient of emission. The energy of electrons impinging on different parts of the wall varies. Electrons impinging on the spacer structure near the cathode have an energy which is typically much less than the energy of electrons which strike the spacer structure near the anode. Thus, such coatings may be tailored such that the secondary electron coefficient of emission varies from one part of the spacer structure to another, e.g., the position of a part relative to the cathode and the anode. As a result of the variation in energy of impinging electrons, the secondary electron emission coefficient function of the wall will also vary significantly from the portion of the spacer structure near the cathode to the portion of the spacer structure near the anode.
Spacer structures should have a consistent and well-managed thermal coefficient of resistivity, such that its Ohmic resistance does not vary significantly with temperature, over the operating ranges of the display. In so far as the resistivity of the spacer structure does change with temperature, it is important that it varies uniformly and as little as possible. Further, spacer structures for displays should meet sheet resistance specifications. Further still, variations in wall resistance uniformity, especially in the resistance uniformity across the height of the wall, can cause a zero current shift, e.g., a variation in the electron beam along the wall due to improper electrical potential on the wall surface. Zero current shift variation causes image degradation due to visible distortion of a displayed image generated by the beam.
Excellent thermal conductivity is another important characteristic of a well-designed spacer structure. This ensures that the heat generated in the structures by the electron bombardment is transferred uniformly across the entire spacer structure. It also ensures that the temperature variation in a spacer structure is minimized significantly. Such variation could otherwise result in mechanical stresses and strains and/or structural changes, which can cause cracking, deformation, and failure. Such variation can also result in resistance changes.
Display cathodes and anodes can be somewhat intricate structures. For example, the cathode structure of a flat panel display can be an array of microscopic Spindt emitters and associated gates and other structures interconnected by a matrix of rows and columns of conductors. A corresponding anode can be an array of sub-pixels and a matrix of opaque material, such as what is sometimes called black chrome, placed proximately to the sub-pixels themselves to separate the regions between the sub-pixels. Since the support structures for such display are designed to resist the force of atmospheric pressure tending to collapse the faceplate towards the backplate, the ends of the support structures are in physical contact with the inner surfaces of both the faceplate and backplate. The support structures must therefore touch or be in close proximity to both the cathode and the anode. The support structures may or may not be buttressed in these areas, to prevent lateral movement. Buttressed or not, the support structures of such a flat panel display are mounted in focus waffles on their cathode-abutting end and in small indentations, such as in the black chrome on their anode-abutting end.
However, during the thermal cycling associated with the operation of the display, the support structures heat up during temperature rises with concomitant physical expansion and cool off during temperature drops with concomitant physical contraction. The degree to which the dimensions of the support structures change with thermal cycling is a function of its coefficient of thermal expansion (CTE), measured in units of meters per meter-degree Celsius. With reference illustratively to Prior Art
F
Derouin Timothy A.
Gopalakrishnan Sudhakar
Candescent Intellectual Property Services Inc.
Patel Vip
Perry Anthony
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