Method for minimizing zero current shift in a flat panel display

Abstract
In a flat-panel display structure having a spacer with laterally segmented face electrodes, one embodiment of the present invention defines the length of the laterally segmented face electrode sections to minimize zero current shift variation in electron trajectories. Advantageously, the present embodiment of the invention prevents image quality degradation. In one embodiment, values for variation in the uniformity of and dicing tolerance are combined to calculate a design optimum for the length of laterally segmented face electrodes. Zero current shift variation from fluctuations in wall resistance falls off with the length of laterally segmented face electrodes. Zero current shift due to first order angular alignment during dicing varies linearly with the dashed electrode length. In one embodiment of the present invention, an optimal value is calculated by combining these effects to minimize zero current shift. Advantageously, in one embodiment, the electrode segments are individually testable.
Description




FIELD OF USE




This invention relates to flat-panel displays and, in particular, to the configuration of a spacer system utilized in a flat-panel display, especially one of the field emission type.




BACKGROUND ART




A flat-panel field emission display is a thin, flat display which presents an image on the display's viewing surface in response to electrons striking light-emissive material. The electrons can be generated by mechanisms such as field emission and thermionic emission. A flat-panel field emission display typically contains a faceplate (or frontplate) structure and a backplate (or baseplate) structure connected together through an annular outer wall. The resulting enclosure is held at a high vacuum. To prevent external forces such as air pressure from collapsing the display, one or more spacers are typically located between the plate structures inside the outer wall.





FIGS. 1 and 2

, taken perpendicular to each other, schematically illustrate part of a conventional flat-panel field emission display such as that disclosed in Schmid et al, U.S. Pat. No. 5,675,212. The components of this conventional display include backplate structure


20


, faceplate structure


22


, and a group of spacers


24


situated between plate structures


20


and


22


for resisting external forces exerted on the display. Backplate structure


20


contains regions


26


that selectively emit electrons. Faceplate structure


22


contains elements


28


that emit light upon being struck by electrons emitted from electron-emissive regions


26


. Each light-emissive element


28


is situated opposite a corresponding one of electron-emissive regions


26


.




Each of spacers


24


, one of which is fully labeled in

FIGS. 1 and 2

, consists of main spacer wall


30


, end electrodes


32


and


34


, a pair of face electrodes


36


, and another pair of face electrodes


38


. End electrodes


32


and


34


are situated on opposite ends of spacer wall


30


so as to contact plate structures


20


and


22


. Face electrodes


36


form a continuous U-shaped electrode with end electrode


32


. Face electrodes


38


form a continuous U-shaped electrode with end electrode


34


.




It is desirable that spacers in a flat-panel field emission display not produce electrical effects which cause electrons to strike the display's faceplate structure at locations significantly different from where the electrons would strike the faceplate structure in the absence of the spacers. The net amount that the spacers cause electrons to be deflected sideways should be close to zero. Achieving this goal is especially challenging when, as occurs In the conventional display of

FIGS. 1 and 2

, the spacing between consecutive wall-shaped spacers is more than two electron-emissive regions. If spacers


24


cause net electron deflections, the net deflections of electrons emitted from regions


26


located different distances away from the nearest spacer


24


are typically different. This can lead to image degradation such as undesired features appearing on the display's viewing surface.




Face electrodes


36


and


38


are utilized to control the electric potential field along spacers


24


in order to reduce their net effect on the trajectories of electrons moving from regions


26


to elements


28


. However, as discussed in Schmid et al, spacers


24


are typically made by a process in which large sheets of wall material having double-width strips of electrodes


36


and


38


formed on the sheets are mechanically cut along the centerlines of electrodes


36


and


38


. Due to mechanical limitations in performing the cutting operation, the width of each face electrode


36


or


38


can vary along its length.




In turn, the variation in face-electrode width causes the electrical effect that spacers


24


have on the electron trajectories to vary along the spacer length. The net electron deflection resulting from spacers


24


thus varies along their length. Even if the net electron deflection is largely zero at one location along the spacer's length, the net electron deflection at other locations along the spacer's length can cause substantial image degradation. It is desirable to avoid image degradation that arises from width variations of face electrodes that contact end electrodes. However, attempts at correction of the distortion due to interference with intended electron trajectories meet with effects caused by construction imperfections.




Imperfections in the construction of the wall results include variations in wall resistance uniformity and dicing alignment tolerance. This causes a zero current shift variation, 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 display generated by the beam.




The conventional approach to attempting to prevent zero current shift has been to apply wall coatings and install and connect separate electrodes. However, these conventional approaches are complex and expensive. Further, they have the effect of rendering testing for defects nearly impossible. Quality testing is an often crucial requirement in fabrication of flat panel displays. Interfering with defects testing is problematic.




What is needed is a method for minimizing zero current shift variation in a flat panel field emission display. What is also needed is a method of fabricating a flat panel field emission display which minimizes zero current shift distortion in electron beams and resultant image degradation. Further, what is needed is a method of fabricating flat panel field emission display which minimizes zero current shift distortion in electron beams and resultant image degradation, and which facilitates testing and failure analysis. Further still, what is needed is a method which achieves these advantages without undue complexity and expense.




DISCLOSURE OF THE INVENTION




In accordance with one embodiment of the invention, a segmented face electrode overlies a face of a main portion of a spacer situated between a pair of plate structures of a flat-panel display. The segmented face electrode is spaced apart from both plate structures, one of which provides the display's image, and also from any spacer end electrodes contacting the plate structures. The face electrode is segmented laterally. That is, the face electrode is divided into a plurality of electrode segments spaced apart from one another as viewed generally perpendicular to either plate structure.




The flat-panel display is normally a flat-panel field emission display in which the image-producing plate structure emits light in response to electrons emitted from the other plate structure. As electrons travel from the electron-emitting plate structure to the light-emitting plate structure, the laterally separated segments of the face electrode typically cause the electrons to be deflected in such a manner as to compensate for other electron deflection caused by the spacer. By suitably choosing the location and size of the electrode segments, the net electron deflection caused by the spacer can be quite small.




The segments of the face electrode normally reach electric potentials largely determined by resistive characteristics of the spacer. Although the potential along the spacer generally increases in going from the electron-emitting plate structure to the light-emitting plate structure, the potential is largely constant along each electrode segment. The effect of this constant potential produces the compensatory electron deflection.




Division of the face electrode into multiple laterally separated segments facilitates achieving appropriate compensatory electron deflection along the entire active-region length of the spacer, the spacer's length being measured laterally, generally parallel to the plate structures. In particular, the value of electric potential that each electrode segment needs to attain in order to cause the requisite amount of compensatory electron deflection varies with distance from the plate structures in approximately the same way that the resistive characteristics of the spacer cause the segment potential to vary with distance from the plate structures. Once the desired segment potential is established for one distance from the plate structures, the distance from each segment to the plate structures can vary somewhat without significantly affecting the amount of compensatory electron deflection.




In contrast, consider what would happen if (a) a non-segmented face electrode were substituted for the present segmented face electrode and (b) the non-segmented face electrode were placed in approximately the same position over the main spacer portion as the segmented face electrode. The entire non-segmented face electrode would be at substantially a single electric potential. If the non-segmented face electrode were tilted relative to the plate structure for some reason, e.g., due to fabrication misalignment, one vertical slice through the non-segmented face electrode might be at largely the correct potential. However, a vertical slice anywhere else through the non-segmented face electrode would normally be at a wrong potential, leading to a wrong amount of compensatory electron deflection. Segmentation of the face electrode in the present flat-panel display provides tolerance in positioning the electrode segments to achieve the desired compensatory electron deflection across substantially all the active-region length of the spacer, thereby overcoming the lack of positioning tolerance that would occur with a non-segmented face electrode.




The amount of compensatory electron deflection caused by each segment of the present face electrode depends on the segment's width. Accordingly, the widths of the electrode segments normally need to be controlled well.




In applying the invention's teachings to the fabrication of a flat-panel display, particularly one of the field emission type, a masking step is typically utilized in defining the widths of the segments of the face electrode. In general, better dimensional control can be achieved with a masking operation, especially photolithographic masking as is normally utilized to implement the masking step, than with a mechanical cutting operation as employed conventionally by Schmid et al to define the widths of the face electrodes in U.S. Pat. No. 5,675,212. The net electron deflection arising from the presence of a spacer can thus more uniformly be made closer to zero in the invention than in Schmid et al.




One embodiment of the present invention provides a method for minimizing zero current shift and its variation in a flat panel field emission display. The present invention also provides a method of fabricating a flat panel field emission display which minimizes zero current shift distortion in electron beams and resultant image degradation. Further, the present invention provides a method of fabricating flat panel field emission display which minimizes zero current shift distortion in electron beams and resultant image degradation, and which facilitates testing and quality control. Further still, the present invention provides a method which achieves these advantages, which is simple and inexpensive.




In one embodiment, the length of the segment electrodes is defined to be effective to minimize zero current shift variation. A component of zero current shift variation resulting from wall resistance variations is determined. Another component of zero current shift variation resulting from fabrication misalignment is also determined. Both components of zero current shift variation are combined in a specific manner, which is operated upon to define a length at which zero current shift variation is minimal.




In one embodiment, flat panel field emission displays are fabricated utilizing segment electrodes of the lengths determined to minimize zero current shift variation. In one embodiment, the segment electrodes are sufficiently long to allow individual electrical testing thereof. Importantly, fabrication of flat panel field emission displays with segment electrodes of the defined length for minimizing zero current shift adds neither undue complexity nor expense.




In one embodiment, individual electrical testing of segment electrodes is applied to promote quality assurance during fabrication. Conventionally, individual electrical testing of segment electrodes was precluded due to their small size and unmanageably large number. Importantly, in one embodiment, individual electrical testing of segment electrodes is applied to enable quality control.











BRIEF DESCRIPTION OF THE DRAWINGS




Conventional Art

FIGS. 1 and 2

are schematic cross-sectional side views of part of a conventional flat-panel field emission display. The cross section of

FIG. 1

is taken through plane


1





1


in FIG.


2


. The cross section of

FIG. 2

is taken through plane


2





2


in FIG.


1


.





FIGS. 3 and 4

are cross-sectional side views of part of a flat-panel field emission display configured according to the invention. The cross section of

FIG. 3

is taken through plane


3





3


in FIG.


4


. The cross section of

FIG. 4

is taken through plane


4





4


in FIG.


3


.





FIG. 5

is a graph of electric potential as a function of vertical distance at various locations in the flat-panel display of

FIGS. 3 and 4

.





FIGS. 6



a


-


6




d


are cross-sectional side views representing steps in a process for manufacturing a spacer suitable for the flat-panel display of

FIGS. 3 and 4

.





FIGS. 7 and 8

are cross-sectional side views of part of another flat-panel field emission display configured according to the invention. The cross section of

FIG. 7

is taken through plane


7





7


in FIG.


8


. The cross section of

FIG. 8

is taken through plane


8





8


in FIG.


7


.





FIGS. 9



a


and


9




b


are cross-sectional side views of a section of segmented electrodes configured with optimal segment lengths, in accordance with one embodiment of the present invention.





FIG. 10

is a flow chart of the steps in a process for minimizing zero current shift, in accordance with one embodiment of the present invention.





FIG. 11

is a flow chart of the steps in a process for fabricating a flat panel field emission display, which exhibits minimal zero current shift, in accordance with one embodiment of the present invention.




Like reference symbols are employed in the drawings and in the description of the preferred embodiments to represent the same, or very similar, item or items.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




Subject to the comments given in the following paragraph about certain types of thin coatings, the term “electrically resistive” generally applies here to an object, such as a plate or a main portion of a spacer, having a sheet resistance of 10


10


-10


13


ohms/sq. An object having a sheet resistance greater than 10


13


ohms/sq. is generally characterized here as being “electrically insulating” (or “dielectric”). An object having a sheet resistance less than 10


10


ohms/sq. is generally characterized here as being “electrically conductive”.




A thin coating, whether a blanket coating or a patterned coating, formed over an electrically resistive main portion of a spacer is characterized here as “electrically resistive”, “electrically insulating”, or “electrically conductive” depending on the relationship between the sheet resistance of the coating and the sheet resistance of the main spacer portion. The coating is “electrically resistive” when its sheet resistance is from 10% to 10 times the sheet resistance of the underlying main spacer portion. The coating is “electrically insulating” when its sheet resistance is greater than 10 times the sheet resistance of the main spacer portion. The coating is “electrically conductive” when its sheet resistance is less than 10% of the sheet resistance of the main spacer portion.




The term “electrically non-insulating” applies to an object, including a thin coating, that is electrically resistive or electrically conductive. For example, an object having a sheet resistance of no more than 10


13


ohms/sq. is generally characterized here as “electrically non-insulating”. The term “electrically non-conductive” similarly applies to an object that is electrically resistive or electrically insulating. An object having a sheet resistance of at least 10


10


ohms'sq. is generally characterized here as “electrically non-conductive”. These electrical categories are determined at an electric field of no more than 10 volts/μm.




A spacer situated between a backplate structure and a faceplate structure of a flat panel field emission display as described below typically consists of (a) a main spacer portion, (b) a pair of end electrodes that respectively contact the backplate and faceplate structures, and (c) one or more face electrodes. The end electrodes extend along opposite ends (or end surfaces) of the main spacer portion. If these two opposite ends of the main spacer portion are also edges as arises when the main spacer portion is shaped like a wall, the end electrodes can also be termed edge electrodes. Each face electrode extends along a face (or face surface) of the main spacer portion and is normally spaced apart from both end electrodes.




The spacer has two electrical ends, referred to here generally as the backplate-side and faceplate-side electrical ends, in the immediate vicinities of where the end electrodes respectively contact the backplate and faceplate structures. The positions of the spacer's two electrical ends relative to the physical ends of the spacer at the two end electrodes are determined as follows for the case in which each face electrode is spaced apart from both end electrodes. Firstly, when an end electrode extends along substantially an entire end of the main spacer portion, the corresponding electrical end of the spacer occurs at that end electrode and thus is coincident with the corresponding physical end of the spacer. Secondly, should an end electrode extend along only part of an end of the main spacer portion, the corresponding electrical end of the spacer is moved beyond the physical end of the spacer by a resistively determined amount. Specifically, the spacer (including both the end and face electrodes) has a resistance approximately equal to that of a vertically wider (or taller) spacer having an end electrode that extends along the entire spacer end in question. The difference in physical width (or height) between the two spacers, i.e., the one having the abbreviated end electrode and the longer one having the full end electrode, is the distance by which the indicated electrical end of the spacer with the abbreviated end electrode is moved beyond the physical end of that spacer.




In some embodiments of a flat-panel display configured according to the invention, a face electrode may contact an end electrode. When this occurs, the corresponding electrical end of the spacer is moved up the spacer toward the other end electrode by a resistively determined amount. Should a face electrode contact an end electrode that extends along only part of the end of the main spacer portion, the corresponding electrical end of the spacer is either moved up the spacer toward the other end electrode, or beyond the spacer, by a resistively determined amount depending on various factors. The distance by which the electrical and physical ends of the spacer differ in these two cases is determined according to the technique described in the previous paragraph.





FIGS. 3 and 4

, taken perpendicular to each other, schematically illustrate an active region part of a flat-panel field emission display having a spacer system configured according to the invention. The flat-panel field emission display of

FIGS. 3 and 4

can serve as flat-panel television or a flat-panel video monitor suitable for a personal computer, a lap-top computer or a work station. In discussing the electrical capabilities of this flat-panel display, electric potentials are generally surface potentials, including work functions, rather than voltage supply potentials.




The flat-panel display of

FIGS. 3 and 4

includes a backplate structure


40


, a faceplate structure


42


, and a spacer system situated between plate structures


40


and


42


. The spacer system consists of a group of laterally separated spacers


44


. In the example of

FIGS. 3 and 4

, each spacer


44


is roughly shaped like a wall.




The display of

FIGS. 3 and 4

also includes an annular outer wall (not shown) situated between plate structures


40


and


42


to form a sealed enclosure in which spacers


44


are situated. The sealed enclosure is held at low pressure, typically 10


−7


Torr or less. The spacer system formed with spacers


44


resists external forces, such as air pressure, exerted on the display and maintains a relatively uniform spacing between plate structures


40


and


42


.




Backplate structure


40


contains an array of rows and columns of laterally separated regions


46


that selectively emit electrons in response to suitable control signals. Each electron-emissive region


46


typically consists of multiple electron-emissive elements. Regions


46


overlie a flat electrically insulating backplate (not separately shown). Further information on typical implementations of electron-emissive regions


46


is presented in Spindt et al, U.S. patent application Ser. No. 09/008,129, filed Jan. 16, 1998, now U.S. Pat. No. 6,049,165, the contents of which are incorporated by reference herein.




Backplate structure


40


also includes a primary structure


48


which is raised relative to electron-emissive regions


46


. That is, primary structure


48


extends further away from the exterior surface of backplate structure


40


than regions


46


. Structure


48


is typically configured laterally in a waffle-like pattern. Regions


46


are exposed through openings


50


in structure


48


.




Primary structure


48


is typically a system that focuses electrons emitted from electron-emissive regions


46


. For this purpose, electron-focusing system


48


consists of an electrically non-conductive base focusing structure


52


and an electrically conductive focus coating


48


that lies on top of base focusing structure


52


and extends onto its sidewalls. In the example of

FIGS. 3 and 4

, focus coating


48


extends only partway down the sidewalls of focusing structure


52


and is therefore spaced apart from electron-emissive regions


46


. Alternatively, focus coating


54


can extend fully down the sidewalls of structure


52


provided that coating


54


is spaced apart from regions


46


. In either case, focus coating


54


receives a low electron-focusing potential V


L


, normally constant, during display operation.




Faceplate structure


42


contains an array of rows and columns of laterally separated light-emissive elements


56


respectively corresponding to electron-emissive regions


46


. Light-emissive elements


56


, typically phosphor, overlie a transparent electrically insulating faceplate (not separately shown). Upon being struck by electrons selectively emitted from electron-emissive regions


46


, light-emissive regions


56


emit light to produce an image on the exterior surface of faceplate structure


42


.




The flat-panel display of

FIGS. 3 and 4

may be a black-and-white or color display. In the black-and-white case, each light-emissive region


56


and corresponding electron-emissive region


46


form a picture element (pixel). For a color display each light-emissive element


56


and corresponding electron-emissive region


46


form a sub-pixel. A color pixel consists of three adjoining sub-pixels, one for red, another for green, and the third for blue. The display has an active region defined by the lateral extent of the pixels.




Faceplate structure


42


further includes an electrical conductive anode layer


58


. In the example of

FIGS. 3 and 4

, anode layer


58


is a light reflector that lies on top of light-emissive elements


56


and extends into the generally waffle-shaped region that laterally separate elements


56


. This waffle-shaped region of faceplate structure


42


normally includes a “black” matrix that underlies anode layer


58


. During display operation, anode layer


58


reflects back some of the rear-directed light to increase the image intensity. Alternatively, light-reflective anode layer


58


can be replaced with a transparent electrically conductive layer that underlies light-emissive elements


56


. In either case, the anode layer receives a high anode potential V


H


, normally constant, during display operation. Anode potential V


H


is typically 4-10 kilovolts and is typically approximately this amount above focus potential V


L


.




Wall-shaped spacers


44


extend laterally in the row direction, i.e., along the rows of electron-emissive regions


46


or light-emissive elements


56


. The row direction extends into the plane of FIG.


3


and horizontally in FIG.


4


. The length of each spacer


44


is measured in the row direction. The width (or height) of each spacer


44


is measured vertically in

FIGS. 3 and 4

, i.e., from backplate structure


40


to faceplate structure


42


, or vice versa. As indicated in

FIG. 3

, spacers


44


are laterally separated by more than two rows of regions


46


(or elements


56


). In a typical implementation, thirty rows of regions


46


separate consecutive spacers


44


.




Each spacer


44


consists of an electrically resistive main spacer portion


60


, an electrically conductive backplate-side end electrode


62


, an electrically conductive faceplate-side end electrode


64


, and a laterally segmented electrically conductive face electrode


66


. Main spacer portion


60


is typically shaped as a wall that extends at least across the active region of the display. The width (or height), measured vertically, of main spacer wall


60


is 0.3-2.0 mm, typically 1.25 mm; it may be, in one embodiment, as wide (high) as 5.0 mm. The thickness of main wall


60


is 40-100 μm, typically 50-60 μm. Main wall


60


consists of electrically resistive material and possibly electrically insulating material so distributed within wall


60


that the overall nature of wall


60


is electrically resistive from its top end to its bottom end.




Each main wall


60


can be internally configured in various ways. Main wall


60


can be formed as one layer or as a group of laminated layers. In a typical embodiment, wall


60


consists primarily of a wall-shaped substrate formed with electrically resistive material whose sheet resistance is relatively uniform at a given temperature such as standard temperature (0° C.). Alternatively, wall


60


can be formed as an electrically insulating wall-shaped substrate covered on both substrate faces with an electrically resistive coating of relatively uniform sheet resistance at a given temperature. The thickness of the resistive coating is typically in the vicinity of 0.1 μm. In either case, resistive material of wall


60


extends continuously along the entire width of wall


60


.




Also, the resistive material of main wall


60


is typically covered on both faces with a thin electrically nonconductive coating that inhibits secondary emission of electrons. The secondary-emission-inhibiting coating typically consists of electrically resistive material. Specific examples of the constituency of main wall


16


are presented in Schmid et al, U.S. Pat. No. 5,675,212, also cited above, Spindt et al, U.S. Pat. No. 5,614,781, Spindt et al, U.S. Pat. No. 5,532,548, and Spindt et al, U.S. patent application Ser. No. 08/883,409, filed Jun. 26, 1997, now U.S. Pat. No. 5,872,424.




End electrodes


62


and


64


of each spacer


44


are situated on opposite ends of main spacer wall


60


and typically extend along the entirety of those two wall ends. Backplate-side end electrode


62


contacts backplate structure


40


along the top of focusing system


48


, specifically the top surface of focus coating


54


. Faceplate-side end electrode


64


contacts faceplate structure


42


along anode layer


58


in the waffle-like recession between light-emissive elements


56


. The thickness of end electrodes


62


and


64


is 50 nm-1 μm, typically 100 nm. End electrodes


62


and


64


typically consist of metal such as aluminum, chromium, nickel, or a nickel-vanadium alloy.




Main spacer wall


60


of each spacer


44


has two opposing faces. Face electrode


66


lies on one of these faces spaced apart from end electrodes


62


and


64


. Consequently, face electrode


66


is physically and electrically spaced apart from both of plate structures


40


and


42


. Face electrode


66


extends laterally along the length of main wall


60


. Face electrode


66


is at least approximately a quarter of the way from backplate structure


40


to backplate structure


42


. That is, without having electrode


66


electrically touch faceplate structure


42


, the minimum distance from backplate structure


40


to electrode


66


is approximately one fourth of the distance between plate structures


40


and


42


. Normally, electrode


66


is somewhat closer to structure


42


than structure


40


. The thickness of electrode


66


is 50 nm-1 μm, typically 100 nm. Electrode


66


typically consists of metal such as aluminum, chromium, nickel, or a nickel-vanadium alloy.




Focusing system


48


provides highly advantageous locations for spacers


44


to contact backplate structure


40


. However, for the reasons discussed below, electrons emitted from electron-emissive regions


46


, especially regions


46


directly adjacent to spacers


44


, are deflected away from the nearest spacers


44


due to the way in which spacers


44


are arranged relative to plate structures


40


and


42


, particularly backplate structure


40


. The presence of face electrodes


66


causes the electrons to be deflected back towards the nearest spacers


44


to compensate for the deflection away from the nearest spacers


44


. The net electron deflection is close to zero.




To accurately provide the compensatory electron deflection, face electrode


66


of each spacer


44


is divided into N electrode segments


66




1


,


66




2


, . . .


66




N


.

FIG. 4

depicts seven electrode segments


66




1


-


66




7


, N thereby being at least 7. Electrode segments


66




1


-


66




N


are spaced laterally apart from one another. That is, as viewed in the lateral direction perpendicular to main spacer wall


60


or as viewed in the vertical direction from backplate structure


40


to faceplate structure


42


(or vice versa), electrode segments


66




1


-


66




N


are laterally separated. Segments


66




1


-


66




N


are arranged generally in a line extending in the row direction parallel to the exterior surface of backplate structure


40


. Electrode segments


66




1


-


66




N


extend across substantially all the active-region length of wall


60


.




Electrode segments


66




1


-


66




N


of each spacer


44


are all typically of substantially the same size and shape. In the example of

FIG. 3

, segments


66




1


-


66




N


are shown as equal-size rectangles. For the rectangular case, each segment


66




i


has a width w


Fi


, measured vertically, of 50-500 μm, typically 70 μm, where i is an integer varying from 1 to N. Each segment


66




i


in the rectangular case has a length, measured laterally in the row direction, of 100 μm-2 mm, typically 300 μm. The lateral separation between consecutive ones of segments


66




1


-


66




N


is 5-50 μm, typically 25 μm. Segments


66




1


-


66




N


can have various other shapes such as ellipses (including circles), diamonds, trapezoids, and so on. Both the size and shape of segments


66




1


-


66




N


can vary from segment


66




i


to segment


66




i


of each spacer


44


.




Electrode segments


66




1


-


66




N


“float” electrically. In other words, none of segments


66




1


-


66




N


is directly connected to an external voltage source. Each segment


66




i


reaches an electric potential V


Fi


determined by resistive characteristics of spacer


44


, particularly main spacer wall


60


. Although segments


66




1


-


66




N


in

FIG. 4

are arranged generally in a line extending parallel to the exterior surface of backplate structure


40


, the line may not be exactly straight. The line of segments


66




1


-


66




N


may also be slanted slightly relative to the exterior backplate surface. As a consequence, potential V


Fi


achieved by one segment


66




i


may differ from potential V


Fi


achieved by another segment


66




i


.




Electric potential V


Fi


of each electrode segment


66




i


of each spacer


44


normally penetrates largely through its main spacer wall


60


to the mirror-image location on the face of main wall


60


opposite the face having face electrode


66


. Specifically, segment potential V


Fi


penetrates largely through wall


60


when it consists entirely of electrically resistive material. Due to the electric potential penetration through wall


60


, it is usually unnecessary to provide a segmented face electrode on the opposite wall face at a location corresponding to electrode


66


. Nonetheless, such an additional segmented face electrode can be provided on the opposite wall face. Also, when any intervening electrically insulating material is thick enough to significantly inhibit the electric potential penetration through wall


60


, an additional segmented face electrode generally matching electrode


66


is normally placed on the wall face opposite that having electrode


66


.




An understanding of the corrective electron-deflection function performed by segmented face electrode


66


involves the following electrical considerations. Referring to

FIG. 3

, the electron-emissive elements in regions


46


emit electrons generally from an emission-site plane


70


extending generally parallel to the exterior surface of backplate structure


40


. Emission-site plane


70


is slightly below the upper surface of electron-emissive regions


46


.




Backplate structure


40


has an electrical end located in a backplate-structure electrical-end plane


72


extending parallel to emission-site plane


70


at a distance d


L


away from emission-site-plane


70


. The electrical end of backplate structure


40


is the approximate planar location at which the interior surface of structure


40


appears to terminate electrically as viewed from a long distance away. Local differences in the topography of the interior surface of structure


40


are electrically averaged out in determining its electrical end. As discussed below, the position of backplate-structure electrical-end plane


72


moves up and down slightly during display operation depending on the potentials applied to electron-emissive regions


46


.




The top of focus coating


54


is at a distance d


S


above emission-site plane


70


. Distance d


S


is normally 20-70 μm, typically 40-50 μm. Distance d


L


to backplate-structure electrical-end plane


72


is normally less than distance d


S


. Distance d


L


is positive in the example of

FIG. 3

in which electrical-end plane


72


overlies emission-site plane


70


. In some embodiments, distance d


L


can be negative so that electrical-end plane


72


lies below emission-site plane


70


.




Spacers


44


have backplate-side electrical end located in a backplate-side spacer electrical end plane


74


extending parallel to emission-site plane


70


. Since backplate-side end electrodes


62


fully cover the backplate-side edges of main spacer walls


60


, the backplate-side electrical ends of spacers


44


are coincident with their backplate-side physical ends at end electrodes


62


. Hence, backplate-side spacer electrical-end plane


74


is located largely at distance d


S


above emission-site plane


70


. Because distance d


L


is less than distance d


S


, the backplate-side electrical end of each spacer


44


is situated above electrical-end plane


72


in which the electrical end of backplate structure


40


is located. This separation between backplate-structure electrical-end plane


72


and the backplate-side electrical end of each spacer


44


affects the potential field along spacers


44


near backplate structure


40


in such a way that electrons emitted from nearby electron-emissive regions


46


are initially deflected away from the nearest spacers


44


.




In a similar manner, faceplate structure


42


has an electrical end located in a faceplate-structure electrical-end plane


76


extending parallel to emission-site plane


70


at a distance d


H


above plane


70


. The electrical end of faceplate structure


42


is the approximate planar location at which the interior surface of structure


42


along anode layer


58


appears to terminate electrically as viewed from a long distance away.




Spacers


44


have faceplate-side electrical ends located in a faceplate-side spacer electrical-end plane


78


extending parallel to emission-site plane


70


at a distance d


T


above plane


70


. With faceplate-side end electrodes


64


fully covering the faceplate-side edges of main spacer walls


60


, the faceplate-side electrical ends of spacers


44


are coincident with their faceplate-side physical ends at end electrodes


64


. Since spacers


44


extend into the waffle-like recession between light-emissive elements


56


, the faceplate-side electrical end of each spacer


44


is spaced apart from faceplate-structure electrical-end plane


76


.




More particularly, relative to backplate structure


40


, the faceplate-side electrical ends of spacers


44


are situated above faceplate-structure electrical-end plane


76


. The effect of this geometry is to cause electrons emitted from regions


46


to be deflected away from nearest spacers


44


. Face electrodes


66


cause the potential field along spacers


44


to be perturbed in such a way as to compensate for electron deflection away from nearest spacers


44


caused by the faceplate-side electrical ends of spacers


44


being above faceplate-structure electrical-end plane


76


as well as electron deflection away from nearest spacers


44


caused by the backplate-side electrical ends of spacers


44


being located above backplate-structure electrical-end plane


72


.




Alternatively, relative to backplate structure


40


, the faceplate-side electrical ends of spacers


44


could be situated below faceplate-structure electrical-end plane


76


. Such a configuration would cause electrons emitted from regions


46


to be deflected toward nearest spacers


44


, thereby reducing the amount of compensatory electron deflection that face electrodes


66


need to cause.





FIG. 5

is a graph that qualitatively illustrates the electric potential field at various locations in the flat-panel display of FIG.


3


. This graph is helpful in understanding how spacers


44


, including segmented face electrodes


66


, affect the movement of electrons from backplate structure


40


to faceplate structure


42


. The graph of

FIG. 5

is also helpful in understanding how distances d


L


and d


H


are determined and, consequently, how the electrical ends of plate structures


40


and


42


are determined.




More particularly,

FIG. 5

illustrates how electric potential varies with distance along vertical lines


80


,


82


, and


84


in FIG.


3


. In

FIG. 5

, vertical distance is zero at emission-site plane


70


. Curves


80


*,


82


*, and


84


* in

FIG. 5

respectively represent the electric potentials along lines


80


,


82


, and


84


. As discussed below, potential curves


80


* and


84


* converge in the space between plate structures


40


and


42


. This convergence is represented by common potential curve


86


in FIG.


5


.




Referring to

FIG. 3

, vertical line


80


originates along emission-site plane


70


at an electron-emissive region


46


separated by at least one row of regions


46


from the nearest spacer


44


. Line


80


terminates at a portion of anode layer


58


overlying the corresponding light-emissive element


56


. Accordingly, line


80


extends from a vertical distance of zero to a vertical distance of d


H


.




Vertical line


82


extends along one face of main spacer portion


60


of left-hand spacer


44


in

FIG. 3

from a top portion of focus coating


54


to a portion of anode layer


58


situated in the recession between light-emissive elements


56


. In the example of

FIG. 3

, line


82


passes through face-electrode segment


66




3


of left-hand spacer


44


. Alternatively, line


82


could extend along the opposite face of main spacer portion


60


of left-hand spacer


44


. In that case, corresponding potential curve


82


* would appear basically the same as shown in

FIG. 5

except that the flat area corresponding, as indicated below, to face-electrode segment


66




3


would be rounded downward to the left and upward to the right.




Vertical line


84


originates at a top portion of focus coating


54


separated by at least one row of electron-emissive regions


46


from the nearest spacer


44


, and terminates at a portion of anode layer


58


situated in the recession between light-emissive elements


56


. Lateral-wise, lines


82


and


84


originate at points spaced largely equal lateral distances away from the edges of the underlying portions of focus coating


54


. Each of lines


82


and


84


extends from a vertical distance of d


S


to a vertical distance of d


T


.




The electrical end of backplate structure


40


at electrical-end plane


72


is defined with reference to an equipotential surface at V


L


, the low focus potential applied to focus coating


54


. For exemplary purposes in determining the location of the electrical end of backplate structure


40


, the potential along plane


70


where regions


46


emit electrons is taken to be V


L


in FIG.


5


. The equipotential surface at potential V


L


in the example of

FIG. 5

thus extends through focus coating


54


and through the portions of plane


70


at electron-emissive regions


46


.




With the foregoing in mind, electric potential


80


* along vertical line


80


increases from low focus value V


L


at a vertical distance of zero to high anode value V


H


at a vertical distance between d


H


and d


T


. Electric potential


84


* along vertical line


84


increases from low value V


L


at distance d


S


to high value V


H


at distance d


T


. Reference symbols


88


and


90


in

FIG. 5

respectively indicate the end points of potential curve


84


* at vertical distances d


S


and d


T


. As the distance away from plate structures


40


and


42


increases, potentials


80


* and


84


* converge to potential


86


that varies linearly with increasing vertical distance, i.e., curve


86


is a straight line.




Dashed straight line


86


L in

FIG. 5

is an extrapolation of straight line


86


to low value V


L


on the horizontal axis. Straight line


86


L reaches V


L


at distance d


L


thereby defining the electrical end of backplate structure


40


. In essence, distance d


L


is the average distance electrically-to the backplate-side equipotential surface, primarily focus coating


54


here, at low potential V


L


. During display operation, the portions of the V


L


equipotential surface at the locations of electron-emissive regions


46


move upward and downward depending on the potentials applied to each region


46


. This movement of the V


L


equipotential surface causes the electrical end of backplate structure


40


to move slightly upward and downward during display operation, typically less than 1 μm. One primary reason for the movement of the electrical end of backplate structure


40


being so small here is that the ratio of distance d


L


to the column-direction spacing between consecutive regions


46


is (comparatively) large in the display of

FIGS. 3 and 4

.




Similarly, dashed straight line


86


H in

FIG. 5

is an extrapolation of straight line


86


upward to high value V


H


. Straight line


86


H reaches V


H


at distance d


H


, thereby defining the electrical end of faceplate structure


42


. Distance d


H


is the average distance electrically to the faceplate-side equipotential surface (anode layer


58


) at high potential V


H


. The electrical end of faceplate structure


42


is substantially stationary during display operation.




Each face-electrode segment


66




i


is located at an average vertical distance do above emission-site plane


70


. In other words, distance d


Fi


is the vertical distance to half the width w


Fi


of segment


66




1


.

FIG. 3

illustrates distance d


F3


and width w


F3


for segment


66




3


. Let d


FBi


and d


FTi


respectively represent the vertical distances from plane


70


to the bottom and top of segment


66




i


. Bottom distance d


FBi


then equals d


Fi


-w


Fi


/2. Top distance d


FTi


equals d


Fi


+w


Fi


/2.




As mentioned above, vertical line


82


passes through face-electrode segment


66




3


of left-hand spacer


44


. However, line


82


could as well be a vertical line passing through any other face-electrode segment


66




i


of that spacer


44


. For the sake of generality, potential


82


* on line


82


is hereafter treated here as being the potential on a vertical line passing through any electrode segment


66




i


of left-hand spacer


44


.




Potential curve


82


* originates from the same starting condition at point


88


as potential curve


84


*, i.e., from low value V


L


at distance d


S


. Except near backplate structure


40


and face-electrode segment


66




i


, potential


82


* increases from this starting condition in a generally linear manner as a function of vertical distance to face-electrode potential V


Fi


at distance d


FBi


. The approximately linear variation of potential


82


* with vertical distance from d


S


to d


FBi


occurs because the sheet resistance of main spacer portion


60


is approximately constant along the width (or height) d


T


-d


S


of spacer portion


60


at a given temperature. In going from low value V


L


to face-electrode potential V


Fi


, curve


82


* crosses the common portion


86


of curves


80


* and


84


* at a point


92


.




Potential


82


* stays substantially constant at V


Fi


across electrode segment width w


Fi


from distance d


FBi


to distance d


FTi


. In so doing, curve


82


* again crosses common portion


86


of curves


80


* and


84


*, this time at a point


94


. As indicated in

FIG. 5

, point


94


occurs at distance d


Fi


approximately halfway across segment width w


Fi


.




Except near face-electrode segment


66




i


and faceplate structure


42


, potential


82


* increases in a generally linear manner from face-electrode potential V


Fi


at distance d


FTi


to high value V


H


at distance d


T


, thereby terminating at the same ending condition at point


90


as potential


84


*. The approximately linear variation of potential


82


* with vertical distance from d


FTi


to d


T


occurs because the sheet resistance of main spacer portion


60


is approximately constant along its width at a given temperature. Except near electrode segment


66




i


and plate structures


40


and


42


, the slope of curve


82


* across the d


FTi


-d


T


region closely approximates the slope of curve


82


* across the d


S


-d


FBi


region.




When the electrical ends of a spacer, such as any of spacers


44


, in a flat-panel field emission display are not respectively coincident with the electrical ends of the display's backplate and faceplate structures, the electric potential field along at least part of the surface of the spacer invariably differs from the electric potential field that would exist at the same location in free space between the backplate and faceplate structures, i.e., in the absence of the spacer. The trajectories of electrons moving from the backplate structure to the faceplate structure in the proximity of the spacer are affected differently by the so-modified potential field along the spacer then by the potential field that would exist at the same location in free space between the two plate structures. Consequently, the spacer affects the electron trajectories.




Spacers


44


, including segmented face electrodes


66


, affect the trajectories of electrons emitted from electron-emissive regions close to spacers


44


by compensating for undesired electron deflection that arises because the electrical ends of spacer


44


are spaced apart from the electrical ends of plate structures


40


and


42


. In particular, the backplate-side electrical ends of spacers


44


are situated in electrical-end plane


74


at distance d


S


and thus are located above the electrical end of backplate structure


40


at distance d


L


. The non-matching of the backplate-side electrical ends of spacers


44


to the electrical ends of backplate structure


40


generally causes the potential field along spacers


44


near structure


40


to be more negative (lower) in value than what would occur if the backplate-side electrical ends of spacer


44


were located in backplate-structure electrical end plane


72


and thereby matched to the electrical end of structure


40


. As a result, electrons emitted from electron-emissive regions


46


close to spacers


44


are initially deflected away from the nearest spacers


44


. Face electrodes


66


compensate for these initial undesired electron deflections by causing the electrons to be deflected back towards the nearest spacers


44


.




Similarly, relative to backplate structure


40


, the faceplate-side electrical ends of spacers


44


are situated in electrical-end plane


78


at distance d


T


and thus are located above faceplate-structure electrical-end plane


76


at distance d


H


. The non-matching of the faceplate-side electrical ends of spacers


44


to the electrical end of faceplate structure


42


causes the potential field along spacers


44


near structure


42


to be more negative in value than what would occur if the faceplate-side electrical ends of spacers


44


were located in plane


76


and thus matched to the electrical end of structure


42


. This causes electrons emitted from regions


46


to be deflected away from nearest spacers


44


. Face electrodes


66


also compensate for this undesired electron deflection by causing electron deflection back towards the nearest spacers


44


.




Face electrode


66


of each spacer


44


provides the deflection compensation in the following manner. As mentioned above, potential curves


82


* and


84


* originate from the same condition at point


88


and terminate at the same condition at point


90


. This occurs because vertical lines


82


and


84


originate at corresponding locations relative to the top of focus coating


54


. In effect, curve


84


* represents the potential that would exist along line


82


in free space between plate structures


40


and


42


, i.e., in the absence of spacers


44


.




With anode potential V


H


exceeding the potential along emission-site plane


70


, electrons emitted by electron-emissive regions


46


accelerate in traveling from backplate structure


40


to faceplate structure


42


. Hence, the emitted electrons move faster near faceplate structure


42


than near backplate structure


40


. Slower moving electrons are attracted or repelled more in response to the potential field near spacers


44


than faster moving electrons.




If face electrodes


66


were absent from spacers


44


, the resulting potential along vertical line


82


next to so-modified left-hand spacer


44


in

FIG. 3

would vary from point


88


to point


90


in

FIG. 5

in an approximately linear manner with increasing vertical distance as represented by straight dashed line


96


in FIG.


5


. In the illustrated example, electric potential


96


is always more negative in value than electric potential


84


* (except at end points


88


and


90


). In the absence of face electrodes


66


, the potential at the surface of so-modified left-hand spacer


44


would cause electrons emitted from nearby electron-emissive regions


46


, especially the two regions


46


nearest left-hand spacer


44


, to be deflected away from it. This would occur even if the faceplate side of the display were modified so that curve


96


crosses curve


84


* at a vertical distance corresponding to a point in the vicinity of one quarter of the way (or more) up the height of left-hand spacer


44


.




With face electrodes


66


present, curve


82


* crosses curve


84


* at points


92


and


94


. Between points


88


and


92


, potential


82


* is more negative in value than potential


84


*. Consequently, electrons emitted from nearby electron emissive regions


46


, especially the two regions


46


nearest to left-hand spacer


44


, are deflected away from that spacer


44


due to the potential field experienced in traveling from the vertical distance at point


88


to the vertical distance at point


92


. Although potential


82


* is more negative in value than potential


84


*, potential


82


* is relatively close to potential


84


*. The electron deflection away from left-hand spacer


44


due to the potential field in the lower region demarcated by points


88


and


92


is thus relatively small.




Between points


92


and


94


, potential


82


* is more positive (higher) in value than potential


84


*, here represented by common potential


86


. The electrons emitted from nearby electron-emissive regions


46


thereby undergo corrective electron deflections towards left-hand spacer


44


due to the potential field experienced in traveling from the vertical distance at point


92


to the vertical distance at point


94


. As

FIG. 5

illustrates, the area between curves


82


* and


84


* in the intermediate region demarcated by points


88


and


92


is considerably greater than the area between curves


84


* and


82


in the lower region demarcated by points


88


and


92


. Even though electrons travel faster in the intermediate region than in the lower region, the electron deflection towards left-hand spacer


44


due to the potential field in the intermediate region is significantly greater than the electron deflection away from that spacer


44


due to the potential field in the lower region. The magnitude of the area between curves


82


* and


84


* in the intermediate region, and thus the magnitude of the corrective electron deflection towards left-hand spacer


44


, is determined by width w


Fi


of each face-electrode segment


66




i


of that spacer


44


.




Between points


94


and


90


, potential


82


* is again more negative in value than potential


84


*. Consequently, electrons emitted from nearby electron-emissive region


46


are deflected away from left-hand spacer


44


due to the potential field experienced in traveling from the vertical distance at point


94


to the vertical distance at point


90


. The electrons reach their greatest velocity in the upper region demarcated by points


94


and


90


, and thus are less affected by unit changes in potential


82


* in the upper region than by unit changes in potential


82


* in the intermediate region demarcated by points


92


and


94


. With the mean value of face-electrodes segment width w


Fi


exceeding some specified minimum value and with each face-electrode-segment


66




i


being located at least approximately one fourth of the distance from backplate structure


40


to faceplate structure


42


, the net result is that face electrode


66


causes electrons emitted from nearby electron-emissive regions


46


to be deflected towards left-hand spacer


44


.




By appropriately choosing suitable mean values for segment widths w


Fi


and average segment distances d


Fi


, the electron deflections toward spacers


44


correct for the undesired electron deflections away from spacers


44


due to the backplate-side electrical ends of spacers


44


being above the electrical end of backplate structure


40


and due to the faceplate-side electrical ends of spacers


44


being above the electrical end of faceplate structure


42


. Curved dotted line


98


in

FIG. 3

illustrates the trajectory of a typical electron emitted from one of the electron-emissive regions nearest to left-hand spacer


44


. As electron trajectory


98


indicates, the initial and final electron deflections away from left-hand spacer


44


are corrected by an intermediate deflection towards that spacer


44


so that the net electron deflection is close to zero.




The magnitude of the compensatory electron deflection caused by each face-electrode segment


66




i


depends on segment width w


Fi


and segment potential V


Fi


. The magnitude of the particular V


Fi


value that each electrode segment


66




i


needs to be at in order to achieve the right amount of corrective electron deflection generally increases with increasing segment distance d


Fi


.




As mentioned above, the resistive characteristics of spacers


44


determine face-electrode segment potentials V


Fi


. In particular, the magnitude of segment potential V


Fi


for each spacer


44


increases with increasing segment distance d


Fi


, and vice versa. Importantly, the rate at which the resistive characteristics of each spacer


44


cause its V


Fi


magnitude to increase with increasing vertical distance is approximately the same as the rate at which the V


Fi


magnitude needs to increase with vertical distance to achieve the right amount of compensatory electron deflection. When the V


Fi


magnitude needed to achieve a desired compensatory electron deflection is determined for one selected value of distance d


Fi


, the amount of compensatory electron deflection caused by electrode segment


66




i


varies relatively slowly as distance d


Fi


is varied upward and downward from the selected d


Fi


value.




The value of segment potential V


Fi


needed to achieve a specific compensatory electron deflection can vary along the length, measured laterally, of electrode segment


66




i


if it is tilted. Although such tilting can lead to a compensation error along the length of a tilted segment


66




i


, the compensation error can be made quite small by making electrode segments


66




i


suitably short.




Importantly, the relative insensitivity of the deflection compensation to segment distance d


Fi


means that different ones of electrode segments


66




1


-


66




N


can be at different d


Fi


values without significantly affecting the magnitude of the deflection compensation along the length of face electrode


66


. While segments


66




1


-


66




N


are typically arranged in a straight line, each face electrode


66


can be tilted or curved in various ways.




The flat-panel display of

FIGS. 3 and 4

is manufactured in the following manner. Plate structures


40


and


42


and the outer wall (not shown) which laterally encloses spacers


44


and connects plate structures


40


and


42


together are separately manufactured. Spacers


44


are also separately manufactured. Components


40


,


42


, and


44


and the outer wall are assembled in such a way that the pressure inside the sealed display is quite low, normally no more than 10


−7


Torr. In assembling the display, spacers


44


are inserted between plate structures


40


and


42


such that the backplate-side and faceplate-side ends of each spacer


44


respectively contact focus coating


54


and anode layer


58


at the desired locations.




Spacers


44


are normally fabricated by a process in which a masking operation is employed to define the shape of segmented face electrodes


66


. The masking operation enables segment width w


Fi


to be highly uniform from segment


66




i


to segment


66




i


. The fabrication of spacers


44


typically entail depositing a blanket layer of the material intended to form electrodes


66


and then selectively removing undesired portions of the blanket layer using a mask to define where the undesired material is to be removed. The mask can cover the electrode material that forms electrodes


66


or can be used to define the shape of a patterned lift-off layer which is provided below the blanket electrode-material layer and which is removed to lift off undesired electrode material. Alternatively, electrode


66


can be selectively deposited using a mask, typically referred to as a shadow mask, to prevent the electrode material from accumulating elsewhere.





FIGS. 6



a


-


6




d


(collectively “FIG.


6


”) illustrate how spacers


44


are fabricated using a blanket-deposition/selective-removal technique in which a mask covers the desired electrode material. The starting point for the process of

FIG. 6

is a generally flat sheet


100


of spacer material. See

FIG. 6



a


. Except for not being cut into main spacer portions


60


, sheet


100


contains the material(s) of main spacer portion


60


arranged the same thickness-wise as in main portions


60


.




A blanket layer


102


of the material that forms face electrodes


66


is deposited on sheet


100


as shown in

FIG. 6



b


. Blanket electrode layer


102


is of approximately the same thickness as electrodes


66


. A photoresist mask


104


configured laterally in the shape of at least one electrode


66


, typically multiple electrodes


66


, is formed on top of electrode layer


102


.

FIG. 6



b


illustrates the typical situation in which photoresist mask


104


is in the shape of multiple electrodes


66


. The exposed portions of electrode layer


102


are removed with a suitable etchant. Photoresist mask


104


is removed.

FIG. 6



c


shows the resultant structure in which the remaining portions of electrode layer


102


form multiple face electrodes


66


, two of which are depicted.




Sheet


100


is now cut into main spacer portions


60


by a process in which end electrodes


62


and


64


are formed over the backplate-side and faceplate-side ends of each spacer portion


60


. See

FIG. 6



d


. The fabrication of spacers


44


is complete. Spacers


44


are subsequently inserted between plate structures


40


and


42


during the display assembly process.




In using a lift-off procedure to create face electrode


66


, the starting point is the structure of

FIG. 6



a


. A blanket lift-off layer is deposited on top of sheet


100


. The lift-off layer is patterned in the reverse shape of electrodes


66


by forming a suitable photoresist mask on the lift-off layer, removing the uncovered lift-off material with a suitable etchant, and then removing the mask. A blanket layer of the face-electrode material is deposited on the remaining patterned lift-off layer and on the uncovered material of sheet


100


. The lift-off layer is then removed with a suitable etchant, thereby removing the overlying electrode material. The remainder of the electrode material forms face electrodes


66


.




When the shapes of segmented face electrodes


66


are defined by a shadow mask, the starting point for the fabrication process is again the structure of

FIG. 6



a


. The shadow mask is positioned above sheet


100


and has openings at the intended locations for electrode


66


. The face-electrode material is deposited over the shadow mask and into the openings to produce the structure of

FIG. 6



c


. Cutting of sheet


100


and formation of end electrodes


62


and


64


is conducted to produce spacers


44


as shown in FIG.


6


D.





FIGS. 7 and 8

, taken perpendicular to each other, illustrate a variation of the flat-panel field emission display of

FIGS. 3 and 4

configured according to the invention. Except for the configuration of face electrodes formed on main spacer portions


60


of spacers


44


, the flat-panel display of

FIGS. 7 and 8

is configured the same as that of

FIGS. 3 and 4

. Aside from masking modifications needed to account for the different face-electrode configuration, the display of

FIGS. 7 and 8

is also fabricated in the same way as that of

FIGS. 3 and 4

.




In the flat-panel display of

FIGS. 7 and 8

, multiple laterally segmented electrically conductive face electrodes that extend laterally across the display's active region are situated on one face of main spacer


60


of each spacer portion


44


.

FIGS. 7 and 8

illustrate an example in which each spacer


60


contains three segmented electrically conductive face electrodes


110


,


112


, and


114


. Each of face electrodes


110


,


112


, and


114


is located at least approximately a quarter of the way from backplate structure


40


to faceplate structure


42


, face electrodes


110


and


114


being respectively closest to and furthest from faceplate structure


42


. Electrodes


110


,


112


, and


114


are normally somewhat closer to faceplate structure


42


than to backplate structure


40


. Electrodes


110


,


112


, and


114


consist of the same material as electrodes


66


. The thickness of each of electrodes


110


,


112


, and


114


is typically the same as that of electrodes


66


. Each face electrode


110


is divided into N laterally separated segments


110




1


,


110




2


, . . .


110




N


. Each face electrode


112


is likewise divided into N laterally separated segments


112




1


,


112




2


, . . .


112




N


. Each electrode


114


is also divided into N laterally separated segments


114




1


,


114




2


, . . .


114




N


.

FIG. 8

depicts seven segments for each of electrodes


110


-


112


, and


114


, N thereby again being at least 7. The lateral separation between electrode segments


101




1


-


110




N


, between electrode segments


112




1


-


112




N


, and between electrode segments


114




1


-


114




N


is typically the same as the lateral separation between electrode segments


66




1


-


66




N


.




Segments


110




1


-


110




N


are all typically of the same size and shape. The same applies to segments


112




1


-


112




N


and segments


114




1


-


114




N


. However, the size and shape of the segments in segment groups


110




1


-


110




N


,


112




1


-


112




N


, and


114




1


-


114




N


can differ from the size and shape of the electrodes in either or both of the other two of segment groups


110




1


-


110




N


,


112




1


-


112




N


, and


114




1


-


114




N


. Although segments


110




1


-


110




N


,


112




1


-


112




N


, and


114




1


-


114




N


are shown as rectangles in

FIG. 8

, they can have any of the other shapes mentioned above for electrode segments


66




1


-


66




N


.




Each electrode segment


110




i


is typically situated fully above electrode segment


112




i


. In turn, each electrode segment


112




i


is typically situated fully above electrode segment


114




i


, For the rectangular case, the composite width of segments


110




i


,


112




i


, and


114




i


is typically slightly greater than width w


Fi


.




As in the display of

FIGS. 3 and 4

, the non-matching of the electrical ends of spacers


44


to the electrical ends of plate structures


40


and


42


, especially the non-matching of the backplate-side electrical ends of spacers


44


to the electrical end of backplate structure


40


, in the display of

FIGS. 7 and 8

leads to undesired electron deflection away from the nearest spacers


44


. Each set of electrode segments


110




i


,


112




i


, and


114




i


typically functions in the same way as electrode segment


66




i


to cause electrons emitted from nearby electron-emissive regions


46


, especially the nearest regions


46


, to be deflected towards the closest spacers


44


. This compensates for the undesired electron deflection away from the nearest spacers


44


.




The width of each electrode segment


110




i


,


112




i


, or


114




i


invariably differs somewhat from the target (desired) width for that segment


110




i


,


112




i


, or


114




i


. The face-electrode configuration of

FIGS. 7 and 8

is particularly useful when there are uncorrelated, i.e., essentially random, errors in the widths of electrode segments


110




i


,


112




i


, and


114




i


. By having multiple segments


110




i


,


112




i


, and


114




i


, the uncorrelated errors tend to average out so that the actual composite width of each group of three segments


110




i


,


112




i


, and


114




i


is relatively close to the composite target width for that group of three segments


110




i


,


112




i


, and


114




i


.




The errors in the widths of features created by a photolithographic masking in procedure such as either of the blanket-depositions/selective-removal processes described above for manufacturing face electrodes


66


tend to be correlated. That is, when the actual width of one of the features is greater than, or less than, the target width for that feature, the actual width of each other of the features is typically greater than, or less than, the corresponding target width for that other feature by approximately the same amount.




In a variation of the flat-panel field emission display of

FIGS. 7 and 8

, only two of segmented face electrodes


110


,


112


, and


114


are present. For example, consider the case in which only segmented electrodes


110


and


114


are present. As in the display of

FIGS. 7 and 8

, upper segmented electrode


110


in this variation is at least approximately one quarter of the way from backplate structure


40


to faceplate structure


42


and is normally closer to faceplate structure


42


than backplate structure


40


. On the other hand, lower segmented electrode


114


in the variation is less than approximately one quarter of the way from faceplate structure


40


to backplate structure


42


. Due to this positioning of lower electrode


114


, it causes electrons to be deflected away from nearest spacers


44


. Upper electrode


110


thus has an additional duty. Besides producing electron deflection towards nearest spacers


44


to compensate for the non-matching of the electrical ends of each spacer


44


to the electrical ends of plate structures


40


and


42


, upper electrode


110


provides compensation for the electron deflection away from nearest spacers


44


due to the positioning of lower electrode


114


.




The magnitude of the electron deflection away from nearest spacers


44


due to the positioning of lower face electrode


114


is relatively small compared to the electron deflection towards nearest spacers


44


caused by upper face electrode


110


. This difference in deflection magnitude is achieved by suitable adjustment of the target widths of electrodes


110


and


114


. Importantly, when there are correlated errors in the widths of electrodes


110


and


114


, the error in the width of each upper electrode segment


110




i


approximately equals the error in the width of lower electrode segment


114




i


.




These errors approximately cancel so that the difference between the actual width of upper segment


110




1


and the actual width of lower segment


114




i


is quite close to the difference between the target width of upper segment


110




i


and the target width of lower segment


114




i


. In other words, the actual, difference in face-electrode segment width is quite close to the target difference in the face-electrode segment width even though errors occur in the widths of both segment


110




i


and segment


114




i


. By appropriately choosing the locations and target widths of electrodes


110


and


114


in this variation, excellent compensation for electron deflection is obtained.




The present flat-panel display typically operates in the following manner. With focus coating


54


and anode layer


58


respectively at potentials V


L


and V


H


, a suitable potential difference is applied to a selected one of electron-emissive regions


46


to cause that region


46


to emit electrons. As anode layer


58


attracts the emitted electrons towards faceplate structure


42


, focus coating


54


focuses the electrons towards the corresponding one of light-emissive regions


56


. The face electrodes, such as segmented electrodes


66


, control the electron trajectories in the manner described above. When the electrons reach faceplate structure


42


, they pass through anode layer


58


and strike corresponding light-emissive region


56


, causing it to emit light visible on the exterior surface of structure


42


. Other light-emissive elements


56


are selectively activated in the same way.




Directional terms such at “upper” and “top” have been employed in describing the present invention to establish a frame of reference by which the reader can more easily understand how the various parts of the invention fit together. In actual practice, the components of a flat-panel field emission display may be situated at orientations different from that implied by the directional terms used here. Inasmuch as directional terms are used for convenience to facilitate the description, the invention encompasses implementations in which the orientations differ from those strictly covered by the directional terms employed here.




While the invention has been described with reference to particular embodiments, this description is solely for the purpose of illustration and is not to be construed as limiting the scope of the invention claimed below. For instance, the main portions of the spacers can be formed as posts or as combinations of walls. The cross section of a spacer post, as viewed along the length of the post, can be shaped in various ways such as a circle, an oval, or a rectangle. As viewed along the length of a main spacer portion consisting of a combination of walls, the spacer portion can be shaped as a “T”, an “H”, or a cross. In these variations, each laterally segmented face electrode formed on a main spacer portion may extend fully or partially around, e.g., halfway or more around but not all the way around, the main spacer portion depending on factors such as the extent to which the segment potentials penetrate laterally through the main spacer portion.




Segmented face electrodes


66


can form parts of spacers configured similar to spacers


44


for causing electrons emitted from nearby electron-emissive regions in a flat-panel field emission display to be deflected toward the spacers in situations where undesired electron deflections away from the spacers are caused by mechanisms other than the backplate-side and faceplate-side electrical ends of the spacers being respectively located above the electrical ends of the backplate and faceplate structures. With each face electrode


66


still typically being closer to the faceplate structure than the backplate structure, the compensatory electron deflections toward the nearest spacers are produced according to the principles described above for face electrodes


66


. In this regard, two or more laterally segmented face electrodes, such as face electrodes


110


,


112


, and


114


, may be substituted for each face electrode


66


.




On the other hand, as in the above-mentioned variation to the display of

FIGS. 7 and 8

, laterally segmented face electrodes generally akin to face electrodes


66


can be employed to cause electrons emitted by electron-emissive regions in a spacer-containing flat-panel field emission display to be deflected away from the nearest spacers when other mechanisms cause undesired electron deflections toward the spacers. The undesired deflections away from the nearest spacers can arise for various reasons such as the backplate-side electrical ends of the spacers being located below the electrical end of the backplate structure. In this case, the segmented face electrodes are typically located less than approximately one fourth of the distance from the backplate structure to faceplate structure. The compensatory electron deflections toward the nearest spacers are produced according to the reverse of the principles applied to face electrodes


66


. Each such segmented electrode can be replaced with two or more laterally segmented face electrodes.




Other mechanisms for controlling the potential field along spacers


44


may be used in conjunction with segmented face electrodes


66


. Electron deflections that occur due to thermal energy (heat) flowing through spacers


44


can be reduced to a very low level by applying the design principles described in Spindt, U.S. patent application Ser. No. 09/032,308, filed Feb. 27, 1998, now U.S. Pat. No. 5,990,614 Externally generated potentials may, in some instances, be applied to certain or all of electrode segments


66




1


-


66




N


. In other instances, face electrodes that contact end electrodes


62


or/and end electrodes


64


may be provided on main spacer portions


60


.




Conversely, end electrodes


62


or/and end electrodes


64


may sometimes be deleted. In such cases, each face electrode


66


is still spaced apart from the physical ends of its main spacer portion


60


, and thus from plate structures


40


and


42


. The same applies to face electrodes


110


,


112


, and


114


.




Field emission includes the phenomenon generally termed surface emission. Backplate structure


40


in the present flat-panel field emission display can be replaced with an electron-emitting backplate structure that operates according to thermionic emission or photoemission. While control electrodes are typically used to selectively extract electrons from the electron-emissive elements, the backplate structure can be provided with electrodes that selectively collect electrons from electron-emissive elements which continuously emit electrons during display operation. Various modifications and applications may thus be made by those skilled in the art without departing from the true scope and spirit of the invention as defined in the appended claims.




With reference to

FIG. 9A

, a segmented electrode is described with segments lengths defined according to one embodiment of the present invention. Zero current deviations in the wall surface potential due to slightly nonuniform resistivity of the wall are significant enough to cause deflection of an electron beam adjacent to the wall.




For an exemplary Edison beta tube in the present embodiment, the length defined for an electrode segment, to minimize zero current, in accordance with the present embodiment, is on the order of 1 cm. Advantageously, this larger size also allows individual electrode sections to be probed and tested.

FIG. 9A

depicts an exemplary array of eight segmented electrodes


66




i


through


66




8


along a wall


60


of a length of 10 cm. In the present embodiment, end segments


66




i


and


66




8


each have optimal lengths of 1.3736 cm; intermediate (e.g., non-end) segments


66




2


through


66




7


each have an optimal length of 1.3400 cm.




As depicted in

FIG. 9B

, in the present embodiment, the distance


6




g


between any electrode segment


66




n


and the adjacent electrode segment


66


n−1, defined to minimize zero current shift, is 40 μm. Every corner of each segment


66




i


through


66




8


is curved to a radius of 24 μm. Advantageously, curving the segment edges prevents a concentration of electric field lines around the segment ends which could contribute to distortion.




With reference to

FIG. 10

, the length of the segment lengths effective to minimize zero current shift are defined by a process


1000


, in accordance with one embodiment of the present invention.




Along an electrode segment, the wall is forced to the same potential. This averages out resistance variations in the wall material. Zero current shifting variations from wall resistance fluctuations fall off with electrode segment length as




 Δ


ZCS=ασ




p


(


L+L




0


)


−½






where ΔZCS is the change in zero current shift from wall resistance fluctuation, α is a first beam deflection sesitivity factor, (e.g., the height of the electrode segment relative to the total wall height), σ


p


is the nonuniformity of the wall resistance, L is the wall length and L


0


is the dimension over which the resistance would naturally average by the current flow, on the order of half the height of the wall. In step


1010


, the change in zero current shift due to fluctuation in wall resistance is determined.




Breaking the electrode up into short segments reduces the sensitivity dicing alignment because each segment floats to a potential appropriate to its height up the wall. Zero current shift due to a first order angular misalignment during dicing varies linearly with the length of the electrode segment by






Δ


ZCS=βδL








where ΔZCS is the change in zero current shift variation, β is a second beam deflection sensitivity factor (e.g., the pixel pitch), δ is a measure of dicing tolerance, and L is the wall length. In step


1020


, the change in zero current shift due to first order dicing misalignment is determined.




The change in zero current shift due to fluctuation in wall resistance is combined with the change in zero current shift due to first order dicing misalignment; step


1030


.




The root summed square is then taken, in step


1040


, to obtain




 α


2


σ


p




2


(


L+L




0


)


−1





2


δ


2




L




2


.




Differentiating the root summed square of the total zero current shift variation with respect to L, step


1050


, defines the electrode segment length L


opt


for minimal zero current shift as








L




opt


=(α


2


σ


p




2


/(2β


2


δ


2


))


⅓.








Electrode segments are fabricated accordingly; step


1060


.




With reference to

FIG. 11

, the steps in an exemplary process


1100


for fabricating a flat panel field emission display with segmented face electrode segments of lengths defined to minimize zero current shift, in accordance with one embodiment of the present invention, are described. Beginning at step


1110


, a lift-off layer is formed over a sheet of spacer material.




The lift-off layer is masked; step


1102


. Masking, a photolithographic technique well known in the art, templates the surface whereon the face electrodes are to be deposited. The template designates the contour to which the electrodes will conform. This contour includes the electrodes' length, which is defined to minimize zero current shift.




In step


1103


, etching, performed by photolithographic techniques well known in the art, removes material of the lift-off layer not covered by the mask. The mask is then removed.




An electrode layer is then deposited over remaining material of the lift-off layer, exposed by etching and mask removal; step


1104


. Electrode material is deposited by metal deposition techniques well known in the art. Such techniques may include, but are not limited to, chemical vapor deposition, electroplating, and electroless plating.




Remaining lift-off layer material is then removed by techniques well known in the art; step


1105


. This exposes the electrode segments on the face of the spacers. The length of the electrode segments is defined to minimize zero current shift.




It is appreciated that process


1100


exemplifies one embodiment of the present invention for fabricating a flat panel display with spacers having face electrodes of lengths that minimize zero current shift. However, other fabrication techniques may be applied to accomplish the equivalent effect of exemplary process


1100


. Although specific steps are disclosed in flowchart


1100


, such steps are exemplary. That is, the present invention is well suited to performing various other steps or variations of the steps recited in FIG.


11


.




Various modifications and applications may thus be made by those skilled in the art without departing from the true scope and spirit of the invention as defined in the appended claims.



Claims
  • 1. A method of forming laterally segmented face electrodes for a flat panel display spacer comprising:a) defining a length for said electrodes, wherein said length is effective for minimizing zero current shift, wherein said defining a length for said electrodes comprises: a1) determining a value for change in zero current shift from fluctuation in resistance of said spacer; a2) determining a value for change in zero current shift from misalignment; a3) combining said value determined in said a1) and said value determined in said a2) into a total zero current shift value; a4) taking a root summed square of said total zero current shift value: and a5) differentiating said root summed square of said total zero current value with respect to length to determine the length for minimum zero current shift variation; and b) fabricating said face electrodes of said length.
  • 2. The method as recited in claim 1, wherein said b) further comprises:b1) forming a liftoff layer over a sheet of material constituting said spacer; b2) masking said lift-off layer; b3) removing a portion of said lift-off layer not masked; b4) removing the mask; b5) depositing an electrode layer over remaining material of the lift-off layer and over uncovered material of the sheet of spacer material; and b6) removing the remaining material of the lift-off layer to remove overlying material of the electrode layer.
  • 3. The method as recited in claim 2, wherein said b2) further comprises templating to form said electrode segments at said length defined.
  • 4. The method as recited in claim 3, wherein said b6) further comprises exposing said electrodes of said length defined.
  • 5. A method for achieving low zero current shift for flat panel displays having spacers with laterally segmented face electrodes of a plurality of segments, comprising:a) determining a first component of said zero current shift resulting from a nonuniformity in resistivity of said spacers; b) determining a second component of said zero current shift resulting from misalignment; c) combining said first component and said second component into a total zero current shift value; d) differentiating a derivative of said value with respect to length of said electrodes; e) defining a length for said electrodes by setting said derivative to zero and solving for length; and f) fabricating each segment of said electrodes accordingly.
  • 6. The method as recited in claim 5, wherein said first component comprises a first product, said first product formed by multiplying first multiplicands.
  • 7. The method as recited in claim 6, wherein said first multiplicands comprise:a) a first beam sensitivity factor; b) a value for said nonuniformity of resistivity; and c) a square root of the reciprocal of the sum of the length of said spacer and a dimension over which the resistance would naturally average by current flow.
  • 8. The method as recited in claim 5, wherein said second component comprises a second product, said second product formed by multiplying second multiplicands.
  • 9. The method as recited in claim 8, wherein said second multiplicands comprise:a) a second beam deflection sensitivity factor; b) a measure of tolerance of dicing performed in fabricating said spacer; and c) the length of said spacer.
  • 10. A method for achieving low zero current shift for flat panel displays having spacers with laterally segmented face electrodes comprising:a) determining a first component of said zero current shift resulting from fluctuations in the resistivity of said spacers; b) determining a second component of said zero current shift resulting from misalignment; c) combining said first component and said second component into a total zero current shift value; d) taking a root summed square of said value; e) differentiating a derivative of said value with respect to length of said electrodes; f) defining a length for said electrodes, wherein said length comprises a length at which said derivative is zero; and g) fabricating said electrodes according to said length.
  • 11. A method for forming a spacer to comprise a main spacer portion and a face electrode which overlies a face of the main spacer portion and is segmented into a plurality of electrode segments wherein said electrodes are (a) spaced apart from opposite first and second ends of the spacer, (b) spaced apart from one another as viewed generally and (c) of a length effective to minimize zero current shift, comprising:depositing an electrode layer over a sheet of spacer material; and selectively removing part of the electrode layer to largely form the electrode segments from the remainder of the electrode material; and inserting the spacer between a first plate structure and a second plate structure of a flat-panel display such that the first and second ends of the spacer respectively contact the first and second plate structures, wherein an image is provided on the second plate structure during display operation.
  • 12. The method as recited in claim 11 wherein said second plate structure emits light to produce the image in response to electrons emitted from the first plate structure.
  • 13. The method as recited in claim 11 further comprising cutting the sheet of spacer material to form the main spacer portion.
  • 14. The method as recited in claim 11 wherein said removing comprises using a mask to control where the part of the electrode layer is selectively removed, the remaining electrode segment of a length effective to minimize zero current shift.
  • 15. The method as in claim 14 wherein said removing comprises:masking over said electrode layer to template an electrode of a length effective to minimize zero current shift; and removing material of said electrode layer not covered by the said mask to form an electrode of a length effective to minimize zero current shift.
  • 16. The method as in claim 14 wherein said removing and depositing comprise:forming a lift-off layer over said sheets of spacer material; masking over the lift-off layer with a mask; removing material of the lift-off layer not covered by the said mask; removing said mask; depositing said electrode layer over remaining material of the lift-off layer and over uncovered material of the sheet of spacer material; and removing the remaining material of the said lift-off layer to remove overlying material of said electrode layer to leave an electrode of a length effective to minimize zero current shift.
RELATED US APPLICATION

This patent application is a continuation-in-part of co-pending U.S. patent application Ser. No. 09/566,697, filed on May 8, 2000 now U.S. Pat. No. 6,405,346, and entitled “FABRICATION OF FLAT-PANEL DISPLAY HAVING SPACER WITH LATERALLY SEGMENTED FACE ELECTRODES”, by Christopher Spindt and John Field, and assigned to the assignee of the present invention, which is incorporated herein by reference and which is a divisional application of U.S. patent application Ser. No. 09/053,247, filed on Mar. 31, 1998, now U.S. Pat. No. 6,107,731, issued on Aug. 22, 2000 and entitled “Structure and Fabrication of Flat-Panel Display Having Spacer With Laterally Segmented Face Electrode,” by Christopher Spindt and John Field, and assigned to the assignee of the present invention, which is incorporated herein by reference.

US Referenced Citations (9)
Number Name Date Kind
6107731 Spindt et al. Aug 2000 A
6403209 Barton et al. Jun 2002 B1
6406346 Spindt et al. Jun 2002 B1
6512335 Dunphy et al. Jan 2003 B1
6541900 Ando Apr 2003 B1
6541905 Fushimi et al. Apr 2003 B1
6566794 Miyazaki May 2003 B1
6583549 Takenaka et al. Jun 2003 B2
6583553 Sasaguri Jun 2003 B2
Continuation in Parts (1)
Number Date Country
Parent 09/566697 May 2000 US
Child 09/895531 US