Patent Publication Number: US-6338662-B1

Title: Fabrication of electron-emitting device having large control openings centered on focus openings

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a division of U.S. patent application 08/919,634, filed Aug. 28, 1997, now U.S. Pat. No. 6,201,343 B1, which is a division of U.S. patent application 08/866,150, filed May 30, 1997, now U.S. Pat. No. 6,002,199. 
    
    
     FIELD OF USE 
     This invention relates to electron-emitting devices. More particularly, this invention relates to the structure and fabrication, including testing, of an electron-emitting device suitable for use in a flat-panel display of the cathode-ray tube (“CRT”) type. 
     BACKGROUND 
     A flat-panel CRT display basically consists of an electron-emitting device and a light-emitting device that operate at low internal pressure. The electron-emitting device, commonly referred to as a cathode, contains electron-emissive elements that emit electrons over a wide area. The emitted electrons are directed towards light-emissive elements distributed over a corresponding area in the light-emitting device. Upon being struck by the electrons, the light-emissive elements emit light that produces an image on the viewing surface of the display. 
     Specifically, the electron-emissive elements are conventionally situated over generally parallel emitter electrodes that are opaque—i.e., impervious to light, typically ultraviolet (“UV”) and infrared (“IR”) light as well as visible light. In an electron-emitting device that operates according to field-emission principles, control electrodes typically cross over, and are electrically insulated from, the emitter electrodes. A set of electron-emissive elements are electrically coupled to each emitter electrode where it is crossed by one of the control electrodes. The electron-emissive elements are exposed through openings in the control electrodes. When a suitable voltage is applied between a control electrode and an emitter electrode, the control electrode extracts electrons from the associated electron-emissive elements. An anode in the light-emitting device attracts the electrons to the light-emissive elements. 
     The electron-emitting device in a flat-panel CRT display commonly contains a focusing structure that helps control the trajectories of the electrons so that they largely only strike the intended light-emissive elements. The focusing structure normally extends above the control electrodes. The lateral relationship of the focusing structure to the sets of electron-emissive elements is critical to achieving high display performance. In fabricating the electron-emitting device, the opaque nature of the emitter electrodes can present an impediment to achieving the requisite lateral spacing between the focusing structure and the sets of electron-emissive elements. Accordingly, it would be desirable to configure the emitter electrodes in such as way as to facilitate controlling the lateral positions of components, such as the focusing structure, in the electron-emitting device. 
     Short circuits sometime occur between the control electrodes, on one hand, and the emitter electrodes, on the other hand. The presence of a short circuit can have a very detrimental effect on the display&#39;s performance. For example, a short circuit at the crossing between a particular control electrode and a particular emitter electrode can prevent part or all of the set of electron-emissive elements associated with those two electrodes from operating properly. It would also be desirable to have a way for configuring the emitter electrodes to facilitate removal of short-circuit defects. 
     GENERAL DISCLOSURE OF THE INVENTION 
     In the present invention, an emitter electrode for an electron-emitting device is formed generally in the shape of a ladder. That is, a line of emitter openings extend through the emitter electrode. During fabrication of the electron-emitting device, the emitter openings can be utilized in a manner that permits features, such as a focusing system, to be self-aligned to other features, such as control electrodes, so as to achieve desired lateral spacings in the device. 
     For example, when at least part of the focusing system is created from actinic material, portions of the control electrodes typically overlie the emitter openings in the ladder-shaped emitter electrode. The actinic material is selectively exposed to backside actinic radiation that passes through the emitter openings. During the backside exposure, the portions of the control electrodes overlying the emitter openings serve as part of a radiation-blocking mask that results in edges of the focusing system being self-aligned to parts of the edges of the control electrodes. Similar self-alignment is achieved in creating other structures from actinic material using the control electrodes or other such features extending over the emitter openings as part of a mask for blocking backside actinic radiation that passes through the emitter openings. 
     The ladder shape of the present emitter electrode also enables defects such as short circuits to be removed from the electron-emitting device without significantly impairing device performance. In particular, the present emitter electrode typically contains a pair of rails connected by crosspieces. If a short circuit between the emitter electrode and an overlying control electrode occurs at one of the crosspieces, that crosspiece can be cut out of the emitter electrode. Likewise, if a short circuit occurs at one of the two rails at a location below a control electrode, that portion of the rail can be cut out of the emitter electrode. In either case, removal of the indicated portion of the emitter electrode does not significantly impair the ability of voltage to be impressed through the remainder of the emitter electrode. 
     Short-circuit removal can be performed through the back side (bottom) of the electron-emitting device utilizing a suitably focused energy beam such as a laser beam. Openings can be provided in the control electrodes to permit all short-circuit removals to be performed through the front side (top) of the electron emitter. The crosspieces of the ladder-shape emitter electrode can be specially shaped to facilitate short-circuit removal. For example, the ends of each crosspiece can neck down in width, thereby making it easier to cut through a crosspiece when necessary. 
     In short, the invention overcomes fabrication difficulties arising from the fact that the material of the emitter electrode is normally opaque and thus largely non-transmissive of actinic radiation. The openings in the present emitter electrode permit certain edges in the electron-emitting device to be self-aligned to other edges, thereby enabling certain critical spacings in the device to be well controlled. Device performance is improved. By facilitating short-circuit removal, the general ladder shape of the present emitter electrode leads to increased fabrication yield. The invention thus provides a significant advance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional side view of a portion of a electron-emitting device configured according to the invention so as to have emitter electrodes in the general shape of ladders. 
     FIG. 2 is a plan view of the portion of the electron-emitting device in FIG.  1 . 
     FIG. 3 is a plan view of the emitter electrode in the portion of the electron-emitting device in FIG.  1 . 
     FIG. 4 is a plan view of the base focusing structure, column electrodes, and two emitter electrodes in the electron-emitting device of FIG.  1 . 
     FIGS. 5 a - 5   d  are cross-sectional side views representing steps that employ the invention&#39;s teachings in manufacturing the base focusing structure of the electron-emitting device in FIGS. 1,  2 , and  4 . 
     FIG. 6 is a simplified cross-sectional side view of a short-circuited segment of the portion of the electron-emitting device in FIG.  1 . 
     FIG. 7 is a plan view of a short-circuited segment of the portion of the electron-emitting device in FIG.  6 . 
     FIG. 8 is a plan view of a short-circuited segment of another general configuration of a ladder-shaped emitter electrode in accordance with the invention. 
    
    
     The cross section of FIG. 1 is taken through plane  1 — 1  in each of FIGS. 2-4. The cross section of FIG. 6 is taken through plane  6 — 6  in FIG.  7 . 
     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 
     The present invention furnishes a matrix-addressed gated electron-emitting device having a layer of emitter electrodes which, in plan view, are shaped generally like ladders. With respect to the emitter electrodes, “plan view” means as viewed in a direction generally perpendicular to the emitter-electrode layer. The electron emitter of the invention typically operates according to field-emission principles in producing electrons that cause visible light to be emitted from corresponding light-emissive phosphor elements of a light-emitting device. The combination of the electron-emitting and light-emitting devices forms a cathode-ray tube of a flat-panel display such as a flat-panel television or a flat-panel video monitor for a personal computer, a lap-top computer, or a workstation. 
     In fabricating the present electron emitter, actinic material is typically created in a desired shape by a procedure that involves exposing part of the material to backside actinic radiation that passes through the openings between the crosspieces of the ladder-shaped emitter electrodes. A layer of material is “actinic” when the layer can be patterned by exposing the layer to radiation that causes the exposed material to change chemical structure and then developing the layer to remove either the exposed material or the unexposed material. The present invention normally employs negative-tone actinic material in which the material remaining after the development step is the exposed material, the chemical structure of the exposed material typically having changed by undergoing polymerization. Radiation, typically UV light, is referred to as “actinic” to indicate that the radiation causes the changes in chemical structure of the material exposed to the radiation. 
     In the following description, the term “electrically insulating” (or “dielectric”) generally applies to materials having a resistivity greater than 10 10  ohm-cm. The term “electrically non-insulating” thus refers to materials having a resistivity below 10 10  ohm-cm. Electrically non-insulating materials are divided into (a) electrically conductive materials for which the resistivity is less than 1 ohm-cm and (b) electrically resistive materials for which the resistivity is in the range of 1 ohm-cm to 10 10  ohm-cm. These categories are determined at an electric field of no more than 1 volt/μm. Similarly, the term “electrically non-conductive” refers to materials having a resistivity of at least 1 ohm-cm, and includes electrically resistive and electrically insulating materials. 
     Examples of electrically conductive materials (or electrical conductors) are metals, metal-semiconductor compounds (such as metal silicides), and metal-semiconductor eutectics. Electrically conductive materials also include semiconductors doped (n-type or p-type) to a moderate or high level. Electrically resistive materials include intrinsic and lightly doped (n-type or p-type) semiconductors. Further examples of electrically resistive materials are (a) metal-insulator composites, such as cermet (ceramic with embedded metal particles), (b) forms of carbon such as graphite, amorphous carbon, and modified (e.g., doped or laser-modified) diamond, (c) and certain silicon-carbon compounds such as silicon-carbon nitrogen. 
     Referring to the drawings, FIG. 1 illustrates a side cross section of part of a matrix-addressed gated electron-emitting device configured according to the invention. The device in FIG. 1 operates in field-emission mode and is often referred to here as a field emitter. FIG. 2 depicts a plan view of the part of the field emitter shown in FIG.  1 . To simplify pictorial illustration, dimensions in the vertical direction in FIG. 2 are illustrated at a compressed scale compared to dimensions in the horizontal direction. 
     The field emitter of FIGS. 1 and 2 is employed in a color flat-panel CRT display divided into rows and columns of color picture elements (“pixels”). The row direction—i.e., the direction along the rows of pixels—is the horizontal direction in FIGS. 1 and 2. The column direction, which extends perpendicular to the row direction and thus along the columns of pixels, extends perpendicular to the plane of FIG.  1 . The column direction extends vertically in FIG.  2 . Each color pixel contains three sub-pixels, one for red, another for green, and the third for blue. 
     The field emitter of FIGS. 1 and 2 is created from a thin transparent flat baseplate  10 . Typically, baseplate  10  consists of glass such as Schott D263 glass having a thickness of approximately 1 mm. 
     A group of opaque parallel laterally separated ladder-shaped emitter electrodes  12  are situated on baseplate  10 . Emitter electrodes  12  extend in the row direction and thus constitute row electrodes. Each emitter electrode  12  consists of a pair of parallel equal-width straight rails  14  and a group of parallel equal-width straight crosspieces  16 . The cross section of FIG. 1 is taken through a plane at which only crosspieces  16  are visible. FIG. 2 illustrates, in dashed line, rails  14  and crosspieces  16  of one emitter electrode  12 . 
     FIG. 3, oriented the same as FIG. 2, illustrates the plan-view shape of one emitter electrode  12  more clearly. As shown in FIG. 3, crosspieces  16  extend generally perpendicular to rails  14 . Each rail  14  has an outer longitudinal edge  14 A and an inner longitudinal edge  14 B. Each crosspiece  16  has a pair of ends that merge seamlessly into rails  14  along inner edges  14 B. Dashed lines  16 E in FIG. 3 indicate the locations of the ends of one crosspiece  16 . Emitter openings  18  are situated between crosspieces  16 . As FIG. 3 indicates, emitter openings  18  are generally rectangular and extend in a straight line. 
     The centerline-to-centerline spacing between the longitudinal centerlines (not shown) of emitter electrodes  12  is typically 270-300 μm. The overall width of each emitter electrode  12 —i.e., the distance between outer rail edges  14 A—is typically 210-230 μm. The width of each rail  14  is typically 30 μm. Accordingly, the dimension of each emitter opening  18  in the column direction is typically 150-170 μm. The width of each crosspiece  16  is typically 25-30 μm. The dimension of each emitter opening  18  in the row direction is typically 65-70 μm. 
     Rails  14  and crosspieces  16  of emitter electrodes  12  are typically of approximately the same thickness. Electrodes  12  typically consist of metal such as an alloy of nickel or aluminum. In this case, the thickness of electrodes  12  is typically 200 nm. Electrodes  12  can alternatively be formed with chromium, gold, silver, molybdenum or another corrosion-resistant metal of high electrical conductivity. 
     A blanket electrically resistive layer  20  is situated on emitter electrodes  12 . Resistive layer  20  extends down to baseplate  10  in emitter openings  18  and in the spaces between emitter electrodes  12 . While the configuration of blanket layer  20  may seem to electrically intercouple different emitter electrodes  12 , the resistance of such electrical intercoupling is so high that electrodes  12  are effectively electrically insulated from one another. Layer  20  provides a resistance of at least 10 6  ohms, typically 10 10  ohms, between each emitter electrode  12  and, as described below, each overlying electron-emissive element. 
     Resistive layer  20  transmits a substantial percentage of the incident backside actinic radiation utilized in fabricating the electron-emitting device of FIGS. 1 and 2. When the backside radiation is UV light, the percentage of UV light that passes directly through layer  20  (i.e., without significant scattering) is generally in the vicinity of 40-80%. For this purpose, layer  20  typically consists of cermet in which particles of a metal such as chromium are embedded in a transparent ceramic such as silicon oxide (silica). The thickness of layer  20  is typically 0.3-0.4 μm. 
     A transparent dielectric layer  22  overlies resistive layer  20 . Dielectric layer  22  typically consists of silicon oxide having a thickness of 0.1-0.2 μm. 
     A group of laterally separated sets of electron-emissive elements  24  are situated in openings  26  extending through dielectric layer  22 . Each set of electron-emissive elements  24  occupies an emission region that wholly overlies a designated region  16 D of a corresponding one of crosspieces  16  in each emitter electrode  12 . Each designated region  16 D is largely row-direction centered on, and of lesser row-direction dimension than, its crosspiece  16 . The same applies thus to the emission region for each set of electron-emissive elements  24 . Since crosspieces  16  are separated by emitter openings  18 , each designated region  16 D is located between a consecutive pair of openings  18 . 
     The particular electron-emissive elements  24  overlying each emitter electrode  12  are electrically coupled to that electrode  12  through resistive layer  20 . Electron-emissive elements  24  can be shaped in various ways. In the example of FIG. 1, elements  24  are generally conical in shape. When elements  24  are configured as cones, elements  24  typically consist of molybdenum. 
     A group of composite opaque laterally separated control electrodes  28  are situated on dielectric layer  22 . Control electrodes  28  extend generally in the column direction and thus constitute column electrodes. Each control electrode  28  controls one column of sub-pixels. Three consecutive control electrodes  28  thus control one column of pixels. 
     Control electrodes  28  cross over emitter electrodes  12  in a generally perpendicular manner. Each control electrode  28  overlies a corresponding one of crosspieces  16  in each emitter electrode  12 . Electrodes  28  are symmetrically wider in the regions generally overlying crosspieces  16  than in the regions overlying portions of rails  14  so as to reduce the capacitance associated with electrodes  28 . The centerline-to-centerline spacing between the longitudinal centerlines (not shown) of electrodes  28  is relatively constant along their lengths. As a whole, electrodes  28  thus extend generally parallel to one another. 
     Each control electrode  28  consists of a main control portion  30  and a group of adjoining gate portions  32  equal in number to the number of emitter electrodes  12 . Main control portions  30  extend fully across the field emitter in the column direction. Gate portions  32  are partially situated in large control openings  34  extending through main control portions  30  directly above designated regions  16 D of crosspieces  16 . Electron-emissive elements  24  are exposed through gate openings  36  in the segments of gate portions  32  situated in large control openings  34 . 
     Control openings  34  laterally bound (and therefore define) the emission regions for the laterally separated sets of electron-emissive elements  24 . Hence, each control opening  34  is sometimes referred to as a “sweet spot”. Designated regions  16 D are also defined by large control openings  34 . Since three consecutive control electrodes  28  control one pixel column, the three sets of electron-emissive elements  24  in three consecutive large control openings  34  in a row of openings  34  form a pixel in the field emitter. 
     Gate portions  32  partially overlie main control portions  30  in the example of FIG.  1 . Alternatively, main control portions  30  can partially overlie gate portions  32 . In either case, gate portions  32  are considerably thinner than main portions  30 . 
     The centerline-to-centerline spacing of control electrodes  28  between the longitudinal centerlines (again, not shown) is typically 90-100 μm. The width of each control electrode  28  typically varies from a maximum of 70-80 μm over designated regions  16 D to a minimum of 40-50 μm elsewhere. Main control portions  30  typically consist of chromium having a thickness of 0.2 μm. Gate portions  32  typically consist of chromium having a thickness of 0.04 μm. 
     A focusing system  37 , generally arranged in a waffle-like pattern as viewed perpendicularly to the upper (interior) surface of faceplate  10 , is situated on the parts of main control portions  30  and dielectric layer  22  not covered by control electrodes  28 . Referring to FIG. 1, focusing system  37  is formed with an electrically non-conductive base focusing structure  38  and a thin electrically non-insulating focus coating  39  situated over part of base focusing structure  38 . Inasmuch as focus coating  39  is thin and generally follows the lateral contour of base focusing structure  38 , only the plan view of base structure  38  of focusing system  37  is illustrated in FIG.  2 . 
     Non-conductive base focusing structure  38  normally consists of electrically insulating material but can be formed with electrically resistive material of sufficiently high resistivity as to not cause control electrodes  28  to be electrically coupled to one another. Focus coating  39  normally consists of electrically conductive material, typically a metal such as aluminum having a thickness of 100 nm. The sheet resistance of focus coating  39  is typically 1-10 ohms/sq. In certain applications, focus coating  39  can be formed with electrically resistive material. In any event, the resistivity of focus coating  39  is normally considerably less than that of base focusing structure  38 . 
     Base focusing structure  38  has a group of openings  40 , one for each different set of electron-emissive elements  24 . In particular, focus openings  40  expose gate portions  32 . Focus openings  40  are concentric with, and larger than, large control openings (sweet spots)  34 . 
     In FIG. 2, the greater dimensional compression in the column (vertical) direction than in the row (horizontal) direction causes focus openings  40  to appear longer in the row direction than in the column direction. Actually, the opposite case normally arises. The lateral dimension of openings  40  in the row direction is usually 50-150 μm, typically 80-90 μm. The lateral dimension of openings  40  in the column direction is usually 75-300 μm, typically 120-140 μm, and thus is normally significantly greater than the lateral dimension of openings  40  in the row direction. 
     Focus coating  39  lies on the top surface of base focusing structure  38  and extends partway, typically in the vicinity of up to 50-75% of the way, into focus openings  40 . Although non-conductive base focusing structure contacts control electrodes  28 , non-insulating focus coating  39  is everywhere spaced apart from control electrodes  28 . As viewed perpendicularly to the upper surface of baseplate  10 , each different set of electron-emissive elements  24  is laterally surrounded by base focusing structure  38  and therefore by focus coating  39 . 
     Focusing system  37 , primarily non-insulating focus coating  39 , focuses electrons emitted from each different set of electron-emissive elements  24  so that the emitted electrons impinge on phosphor material in the corresponding light-emissive element of the light-emitting device situated opposite the electron-emitting device. In other words, focusing system  37  focuses electrons emitted from electron-emissive elements  24  in each sub-pixel so as to strike phosphor material in the same sub-pixel. Efficient performance of the electron focusing function requires that focus coating  39  extend considerably above elements  24  and that certain lateral distances from each set of elements  24  to certain parts of focusing system  37 , specifically certain parts of coating  39 , be controlled well. 
     More particularly, pixels are typically largely square with the three sub-pixels of each pixel being arranged in a line extending in the row direction. Portions of the active pixel area between rows of pixels are typically allocated for receiving edges of spacer walls. The net result of this configuration is that large control openings  34  are typically considerably closer together in the row direction than in the column direction. Better focus control is thus necessary in the row direction than in the column direction. Accordingly, the critical distances that need to be controlled to achieve good electron focusing are the row-direction distances from lateral edges of focusing system  37  to the nearest edges  34 C of large control openings  34 . Since edges  34 C extend in the column direction, they are referred to here as column 5  direction edges. 
     The internal pressure in the final flat-panel display that contains the field emitter of FIGS. 1 and 2 is very low, generally in the vicinity of 10 −7 -10 −6  torr. With baseplate  10  being thin, focusing system  37  also serves as a surface contacted by spacers, typically spacer walls, that enable the display to resist external forces such as air pressure while maintaining a desired spacing between the electron-emitting and light-emitting parts of the display. 
     The preceding distance and spacer-contact considerations are addressed by configuring base focusing structure  38  as a tall main base portion  38 M and a group of opposing pairs of critically aligned further base portions  38 L. The two further base focusing portions  38 L in each of the opposing pairs of further base portions  38 L are situated on opposite sides of a corresponding one of large control openings  34  and thus on opposite sides of a corresponding one of the sets of electron-emissive elements  24 . As shown in FIG. 1, further base focusing portions  38 L are slightly shorter than main base focusing portion  38 M. Parts of focus coating  39  extend partway down the side surfaces of shorter focusing portions  38 L into focus openings  40 . 
     The portions of focus coating  39  overlying each pair of opposing shorter base focusing portions  38 L in focus openings  40  are situated at well-controlled row-direction distances from the corresponding set of electron-emissive elements  24 . Specifically, each pair of opposing shorter focusing portions  38 L have lateral edges  38 C vertically aligned to portions  28 C of the outer lateral longitudinal edges  30  of the particular control electrode  28  that controls the corresponding set of electron-emissive elements  24 . Similar to column-direction edges  34 C of large control openings  34 , focusing-structure edges  38 C extend in the column direction and are referred to here as column-direction edges. 
     The row-direction distances from each pair of control-electrode longitudinal edge portions  28 C, and therefore from the corresponding pair of focusing-structure column-direction edges  38 C, to the column-direction edges  34 C of large control opening  34  for the corresponding set of electron-emissive elements  24  are, as described below, determined by fixed photomask dimensions and are therefore well controlled. Since focus coating  39  extends partway down the sides of shorter focusing portions  38 L into focus openings  40 , the portions of focus coating  39  overlying each pair of opposing focusing portions  38 L are spaced apart the corresponding set of electron-emissive elements  24  by well-controlled row-direction distances. Important in achieving these well-controlled row-direction spacings is the fact that control-electrode edge portions  28 C, and thus focusing-structure column-direction edges  38 C, overlie emitter openings  18 . 
     The full plan-view configuration of base focusing structure  38  with respect to electrodes  28  and  12  can be seen in FIG. 4 oriented the same as FIG.  2 . FIG. 4 depicts two emitter electrodes  12 . Item  42  in FIG. 4 indicates the area between each pair of consecutive electrodes  12 . During display assembly, spacer walls are brought into contact with parts of focus coating  39  overlying main focusing portion  38 M generally along some or all of areas  42 . If desired, strips of main focusing portion  38 M above spacer-contact areas  42  can be replaced with focusing material that extends to approximately the same height as shorter focusing portions  38 L so as to provide grooves in base focusing portion  38 , as covered there with focus coating  39 , for receiving edges of the spacer walls. 
     Base focusing structure  38  is normally created from negative-tone electrically insulating actinic material which is selectively exposed to actinic radiation and developed. The actinic material is preferably photo-polymerizable polyimide, typically Olin OCG7020 polyimide. Main focusing portion  38 M typically extends 45-50 μm above dielectric layer  22 . Further focusing portions  38 L are normally 10-20% shorter than main portion  38 M. 
     During display operation, a suitable potential is applied to focusing system  37 , specifically to focus coating  39  to control the electron focusing. The focus control potential is of such a value, typically 25-50 volts relative to ground, so as to cause electrons emitted from each set of electron-emissive elements  24  to be focused on the corresponding (directly opposite) phosphor region in the light-emitting device. 
     The field emitter of FIGS. 1-4 is fabricated in the following manner. A blanket layer of the emitter-electrode material is deposited on baseplate  10  and patterned using a suitable photoresist mask to produce ladder-shaped emitter electrodes  12 . Resistive layer  20  is then deposited on top of the structure. Dielectric layer  22  is deposited on top of resistive layer  20 . 
     A blanket layer of the electrically conductive material for main control portions  30  is deposited on layer  22  and patterned using a suitable photoresist mask to form main control portions  30 , including large control openings  34 . The photoresist mask is created by exposing a blanket layer of positive-tone photoresist to UV light selectively through a photomask (reticle) bearing a light-blocking pattern that corresponds to the desired pattern of main control portions  30 . The row-direction distances from each pair of control-electrode longitudinal edge portions  28 C to column-direction edges  34 C of large control opening  34  for the corresponding set of electron-emissive elements  24  are established by fixed row-direction dimensions in this photomask. These photomask dimensions are largely the same for every control opening  34 . As a result, the resulting row-direction distances from each pair of control-electrode edge portions  28 C to column-direction edges  34 C of the corresponding control opening  34  are well controlled. 
     Also, the photomask dimensions that define the distances from each pair of control-electrode edge portions  28 C to the corresponding pair of control-opening column-direction edges  34 C are largely the same on both sides of each control opening  34 . Accordingly, each control-opening sweet spot  34  is row-direction centered in its control electrode  28 . 
     The dimension of control openings  34  in the row direction is determined by the magnitude of the row direction distance across which electrons emitted by a set of electron-emissive elements  24  can be focused by focusing system  37  to strike the intended light-emissive element in the light emitting device. For instance, an electron emitted from an electron-emissive element  24  at the row-direction center of a focus opening  40  can readily be focused to strike the intended light-emissive element. On the other hand, an electron emitted from an electron-emissive element situated along either focusing-structure column-direction edge  38 C of a focus opening  40  can generally not be regularly focused to strike the intended light emissive element. 
     Subject to each control opening  34  being row-direction centered in its control electrode  28 , the row-direction dimension of control openings  34  is generally in the range of 5-50% of the row-direction dimension of focus openings  40 . More particularly, the control-opening row-direction dimension is 15-25%, typically 20%, of the focus-opening row-direction dimension. 
     A blanket layer of the gate material is deposited on top of the structure and patterned using another photoresist mask to form gate portions  32 . If gate portions  32  are to underlie segments of main control portions  30  rather than overlie segments of main control portions  30 , the last two deposition/patterning operations are reversed. 
     At this point, various manufacturing techniques and sequences can be utilized to form dielectric openings  26 , electron-emissive elements  24 , and focusing system  37 . The common thread among all of these techniques and sequences is that base focusing structure  38  is normally created by a process involving (a) backside exposure of actinic material to actinic radiation using emitter electrodes  12  and control electrodes  28  as a radiation-blocking mask, (b) frontside exposure of the actinic material through a suitable photomask, and (c) removal of the unexposed actinic material in a development operation. 
     In one example, gate openings  36  and dielectric openings  26  are created respectively in gate portions  32  and dielectric layer  22  according to a charged-particle tracking procedure of the type described in U.S. Pat. No. 5,559,389 or 5,564,959. The contents of these two patents are incorporated by reference herein. Electron-emissive elements  24  are created as cones by depositing electrically conductive material through gate openings  36  and into dielectric openings  26  according to a deposition technique of the type described in either of these patents. As a result, eletron-emissive elements  24  in each set of elements  24  are situated at random locations relative to one another. 
     Base focusing structure  38  is now formed as illustrated in FIGS. 5 a - 5   d . A primary blanket layer  38 P of negative-tone electrically insulating actinic material is provided on top of the structure to a thickness sufficient to produce main base focusing portion  38 M. The electron-emitting structure is subjected to backside actinic radiation  46  that impinges perpendicularly on the lower (exterior) surface of faceplate  10  as shown in FIG. 5 b . Baseplate  10  is largely transmissive of backside radiation  46 . Accordingly, radiation passes through baseplate  10  traveling from its lower surface to its upper (interior) surface. 
     Electrodes  12  and  28  are largely non-transmissive of backside radiation  46 . Resistive layer  20  directly transmits a substantial percentage of radiation  46 , typically in the vicinity of 40-80% of radiation  46  as mentioned earlier. Dielectric layer  22  largely transmits radiation  46 . Hence, the portion  38 Q of primary actinic layer  38 P not shadowed by a radiation-blocking mask formed with electrodes  12  and  28  is exposed to radiation  46  and changes chemical structure. 
     Importantly, backside radiation  46  passes through openings  18  in emitter electrodes  12 . Segments of control electrodes  28 , specifically segments of main control portions  30 , extending up to portions  28 C of the longitudinal edges of electrodes  28  overlie emitter openings  18 . As a result, sections of primary layer  38 P vertically aligned with lateral control-electrode edges  28 C are exposed to radiation  46  to define column-direction lateral edges  38 C of base focusing structure  38 . 
     The partially finished electron-emitting structure is now subjected through a photomask  47  to frontside actinic radiation  48  that impinges perpendicularly on top of the electron-emitting structure. See FIG. 5 c . Photomask  47  has radiation-blocking areas  47 B at regions above focus openings  40 . Radiation-blocking areas  47 B are slightly larger than openings  40  in the row direction. Each of blocking areas  47 B corresponds to the region indicated by horizontal arrow  44  and vertical arrow  40  in FIG. 2 or  4 . Material of primary layer  46  not shadowed by blocking areas  47 B is exposed to frontside radiation  48  and changes chemical structure. 
     The order in which the backside and frontside exposures are performed is generally immaterial. Accordingly the backside exposure can be performed after the frontside exposure. When the actinic material is photo-polymerizable polyimide, such as Olin OCG7020 polyimide, the actinic radiation during both the backside and frontside exposures is typically UV light. Upon being exposed to the UV light, the polyimide changes chemical structure by undergoing polymerization. 
     A development operation is performed to remove the unexposed portions of primary layer  38 P, thereby producing base focusing structure  38  as shown in FIG. 5 d . Due to the presence of baseplate  10 , backside radiation  46  normally did not fully penetrate primary layer  38 P at the backside exposed areas. Since further base focusing portions  38 L were only exposed to backside radiation  46 , further focusing portions  38 L are normally shorter than main focusing portion  38 M. If backside radiation  46  fully penetrates primary actinic layer  46 P, the height differential between focusing portions  38 M and  38 L is reduced or, with sufficient backside exposure, eliminated. 
     Focus coating  39  is formed over base focusing structure  38 , typically by performing a suitably angled evaporation of the focus-coating material. The angled evaporation can be done in the manner described in Haven et al, co-filed U.S. patent application Ser. No. 08/886,554, filed May 30, 1997, now U.S. Pat. No. 6,013,974, the contents of which are incorporated by reference herein. 
     During fabrication of the field emitter of FIGS. 1 and 2, focusing system  37  is provided with one or more electrical conductors (not shown) which contact focus coating  39  and through which focusing system  37  is externally accessed for providing the focus control potential to focus coating  39 . The access conductor or conductors are typically configured and fabricated as described in Barton et al, U.S. patent application Ser. No. 08/866,151, filed May 30, 1997, now U.S. Pat. No. 5,920,151, the contents of which are incorporated by reference herein. This completes the formation of focusing system  37 , thereby yielding the field-emitter of FIGS. 1 and 2. 
     In subsequent operations, the field emitter is sealed to the light-emitting device through an outer  20  wall. The sealing operation typically entails mounting the outer wall and the spacer walls on the light-emitting device. This composite assembly is then brought into contact with the field emitter and hermetically sealed in such a manner that the internal display pressure is typically 10 −7 -10 −6  torr. The spacer walls contact focusing system  37  along part or all of areas  42  in FIG.  4 . 
     An alternative way of processing negative-tone primary actinic layer  38 P to produce a base focusing structure similar to base structure  38  involves first exposing primary layer  38 P to frontside actinic radiation  48  through a photomask having radiation-blocking stripes that extend in the row direction fully across the display&#39;s intended active area. Each row-direction radiation-blocking stripe overlies the intended locations for (a) a row of focus openings  40  and (b) the intervening generally rectangular primary actinic strips situated between the intended locations for focus openings  40  in that row. These rectangular primary actinic strips extend longitudinally in the column direction. Frontside radiation  48  fully penetrates layer  38 P at the exposed areas, causing the so-exposed actinic material below the row-direction radiation-blocking stripes to change chemical structure. 
     The exposure with backside radiation  46  is now performed so that radiation  46  partially penetrates primary layer  38 P at the exposed areas. The only unexposed primary actinic material subjected to radiation  46  (and thus not shadowed by the mask formed with electrodes  12  and  28 ) consists of the rectangular column-direction primary actinic strips situated between the intended locations for focus openings  40  in each focus opening row. Consequently, the exposed material of primary layer  38 P has column-direction edges vertically aligned to portions of control-electrode column-direction edges  28 C generally at the locations for column-direction focus edges  38 C in FIGS. 1 and 2. 
     Primary layer  38 P is now developed to remove the unexposed actinic material. The exposed remainder of layer  38 P forms the base focusing structure. Because backside radiation  46  only partially penetrated primary layer  38 P at the backside-exposed areas, the height of the full widths of the column-direction rectangular focusing strips between focus openings  40  is both largely uniform and less than the height of the remainder of the base focusing structure. Except for this and the fact focus openings  40  here are, in plan view, more rectangular than focus openings  40  in FIG. 2, the shape of the base focusing structure is generally the same as that shown for base structure  38  in FIGS. 1 and 2. 
     As with the backside exposure in the process of FIGS. 5 a - 5   d , the backside exposure in this alternative process can be performed under such conditions that backside radiation  46  fully penetrates primary actinic layer  38 P at the exposed areas. The height differential between (a) the column-direction rectangular focusing strips situated between focus openings  40  in each focus opening row and (b) the remainder of the base focusing structure is then reduced or eliminated. 
     The base focusing structure is provided with an electrically non-insulating focus coating analogous to focus coating  39  to form a composite focusing structure similar to focusing system  37 . The focus coating typically consists of electrical conductive material evaporatively deposited in the manner described above for focus coating  39 . The resultant field emitter appears generally as shown in FIGS. 1 and 2 subject to the above-mentioned focusing structure differences. 
     Instead of creating a base focusing structure from negative-tone actinic material, a base focusing structure similar to base structure  38  can be formed from non-actinic electrically non-conductive material using positive-tone actinic material, typically photoresist, combined with a lift-off step to achieve self-alignment to control-electrode edge portions  28 C. Specifically, the process described above for creating base structure  38  is modified by providing a primary blanket layer of positive-tone photoresist on top of the partially finished field emitter directly after removing the portion of the blanket layer of emitter cone material at the desired location for base structure  38 . 
     The exposures with backside actinic radiation  46  and frontside actinic radiation  48  are then performed. Emitter electrodes  12  and control electrodes  28  form a mask that prevents the directly overlying portions of the blanket photoresist layer from being exposed to backside radiation  46 . The exposed portion of the primary photoresist layer changes chemical structure. Radiation  46  and radiation  48  are both normally UV light. Either radiation exposure can be done first. 
     A development operation is conducted on the primary photoresist layer. Because the photoresist is positive-tone actinic material, the exposed material of the photoresist layer is removed during the development operation. In plan view, the remaining photoresist consists of portions having substantially the reverse configuration of base focusing structure  38  in FIGS. 1 and 2. Due to the backside exposure, sections of the remaining photoresist have lateral edges vertically aligned with control-electrode edge portions  28 C. 
     A blanket layer of non-actinic electrically non-conductive material, typically an electrical insulator such as spin-on glass, is formed on top of the structure. The remaining portions of the primary photoresist layer are removed so as to lift off the overlying portions of the blanket non-actinic non-conductive layer. The remainder of the non-actinic non-conductive layer forms a base focusing structure configured substantially the same as base focusing structure  38  except that the height difference between main portion  38 M and shorter portions  38 L is not present. In particular, the base focusing structure created from the non-actinic non-conductive material has pairs of opposing lateral column-direction edges vertically aligned with control-electrode edge portions.  28 C. Consequently, the row-direction spacings from each of these pairs of focusing-structure column-direction edges to column-direction edges  34 C of the corresponding control-opening sweet spot  34  are well controlled. 
     An electrically non-insulating focus coating, typically an electrical conductor analogous to focus coating  39 , is formed on the base focusing structure to create a composite focusing structure analogous to focusing system  37 . The non-conductive base focus structure has a considerably higher resistivity than the non-insulating focus coating. The resulting field emitter appears generally as shown in FIGS. 1 and 2 except that the composite focusing structure is of largely uniform height. 
     A variation of the foregoing process employs positive-tone actinic material in creating another focusing system similar to focusing system  37  except that largely the entire focusing system consists of electrically non-insulating material, typically electrically conductive material, spaced apart from control electrodes  28 . Since the focusing system is typically electrically conductive, there is no need to provide a separate electrically non-insulating focus coating corresponding to focus coating  39 . This variation begins with the structure existent after the portion of the blanket layer of emitter conductive material has been removed at the desired location for base focusing structure  38  so that portions of control electrodes  28  are uncovered. 
     A layer of electrically non-conductive material, typically an electrical insulator, transmissive of backside radiation  46  is provided on at least the uncovered sections of the lateral edges of control electrodes  28 . The non-conductive layer is normally a blanket layer that fully covers the previously uncovered portions of electrodes  28  and the portions of dielectric layer  22  between those portions of electrodes  28 . A primary blanket layer of positive-tone photoresist is provided on top of the non-conductive layer. The blanket photoresist layer lies on any material of electrodes  28  and/or dielectric layer  22  not covered by the non-conductive layer. 
     The exposures with radiation  46  and  48  are now performed. Electrodes  12  and  28  again form a mask that shields the overlying portions of the positive-tone photoresist from backside radiation  46 . Since the non-conductive layer is transmissive of radiation  46 , exposed photoresist of changed chemical structure is produced in largely the same pattern as in the foregoing process that employs positive-tone photoresist at this point. The primary photoresist layer is developed to remove the exposed photoresist material. Sections of the remaining photoresist thus have lateral edges vertically aligned to the outside sections of the surfaces of the non-conductive material covering the sections of the lateral edges of control electrodes  28 . 
     A blanket layer of electrically non-insulating material, typically an electrical conductor, is formed on top of the structure. The remaining portions of the primary photoresist layer are removed so as to lift off the overlying portions of the blanket non-insulating layer. The remainder of the blanket non-insulating layer forms an electrically non-insulating focusing structure of substantially the same configuration as base focusing structure  38  except that the height differential between portions  38 M and  38 L is again eliminated. The non-insulating focusing structure has pairs of opposing lateral column-direction edges vertically aligned to the outside surface sections of the non-conductive material covering the lateral edge sections of control electrodes  28 . Accordingly, the pairs of opposing lateral column-direction edges of the focusing structure are self-aligned to control-electrode edge portions  28 C. The row-direction spacings from each of these pairs of focusing-structure column-direction edges to column-direction edges  34 C of the corresponding sweet spot  34  are again well controlled. 
     If any of the remaining non-conductive material covers the top surface sections of control electrodes  28 , an etch is performed to remove this part of the non-conductive material. In the resulting field emitter, the non-insulating focusing structure forms an electron focusing system separated from control electrodes  28  by sections of non-conductive material and/or open spaces. To the extent that any of the non-conductive material separates the focusing system from electrodes  28 , the resistivity of the non-conductive material is sufficiently high that the focusing system is effectively electrically insulated from electrodes  28 . 
     Another variation of the foregoing process that employs positive-tone active actinic material in creating a focusing system consisting largely of electrically non-insulating material begins with the structure existing after the non-conductive layer is provided on at least the lateral edges of control electrodes  28 . A thin blanket seed metal layer is deposited on top of the structure. If any of the seed metal layer contacts control electrodes  28 , the seed metal is normally selectively etchable with respect to the control-electrode material. The seed layer is of such characteristics as to largely transmit backside actinic radiation  46 . 
     A primary blanket layer of positive-tone photoresist is provided on top of the seed metal layer. The exposures with radiation  46  and  48  are performed. Electrodes  12  and  28  form a mask that prevents the directly overlying photoresist from being exposed to backside radiation  46 . Since the seed layer transmits radiation  46 , the exposed photoresist of changed chemical structure has largely the same pattern as in the two foregoing process variations. 
     The exposed photoresist portions are removed in a development step. Accordingly, sections of the remaining photoresist again have lateral edges vertically aligned to the outside surface sections of the non-conductive material covering the lateral edge sections of control electrodes  28 . Also, a pattern of the seed metal layer is now exposed at the location of removed photoresist. 
     A focus structure metal is electrochemically deposited (electroplated) into the patterned opening in the remaining photoresist, using the exposed seed metal to initiate the electrochemical deposition. The deposition is terminated before the focus structure metal reaches the top of the photoresist. The remaining photoresist is removed after which the exposed seed metal is removed. The remainder of the focus structure metal forms an electrically non-insulating focusing structure, specifically an electrically conductive focusing structure, configured substantially the same as in the immediately previous process variation. Pairs of opposing lateral column-direction edges of the metal focusing structure are thus self-aligned to control-electrode edge portions  28 C. 
     Processing of the field emitter in this variation is then continued in the same manner as in the foregoing process variation. In the final field emitter, the electron focusing system formed with the metal focusing structure is separated from control  35  electrodes  28  by open spaces and/or sections of non-conductive material. The resistivity of any non-conductive material separating electrodes  28  from the focusing system is sufficiently high that the focusing system is effectively electrically insulated from electrodes  28 . 
     Short-circuit defects can occur between control electrodes  28 , on one hand, and emitter electrodes  12 , on the other hand, during fabrication of the present electron-emitting device. Moving to FIG. 6, it qualitatively illustrates an example of a short circuit between one control electrode  28  and one emitter electrode  12  in a segment of the portion of the field emitter shown in FIG.  1 . The cross section of FIG. 6 is taken in the column direction through one of crosspieces  16 . The illustrated short circuit is directly formed by electrically conductive material  50  that extends through dielectric layer  22  and resistive layer  20  to connect the illustrated control electrode  28  to the illustrated crosspiece  16  in emitter electrode  12 . Although conductive material  50  is shown as being distinct from column electrode  28 , conductive material  50  may consist of part of the conductive material employed to create electrodes  28 . 
     Occasionally, one of electron-emissive elements  24  in one of the sets of elements  24  becomes electrically connected to corresponding gate portion  32 . If resistive layer  20  were absent, such an electrical connection might be classified as a short circuit. However, due to the high resistance that layer  20  provides between crosspieces  16  and overlying electron-emissive elements  24 , the amount of current that can flow through column electrode  28  due to one of its electron-emissive elements  24  being connected to gate portion  32  is extremely small compared to the current that flows through a direct short circuit such as that represented by conductive material  50 . Accordingly, the electrical connection of gate portion  32  to one of its electron-emissive elements  24  is not classified here as a short circuit. 
     A short circuit of one control electrode  28  to one emitter electrode  12  can occur at any one of three basic places on that emitter electrode  12 : (a) at crosspiece  16  underlying column electrode  28 , (b) at the portion of one of rails  14  underlying electrode  28 , and (c) at a portion of the other rail  14  underlying electrode  28 . This is qualitatively shown in FIG. 7 which presents a partial plan view of a segment of the portion of the field emitter depicted in FIG.  6 . Short-circuit case (a), corresponding to conductive material So in FIG. 6, is represented by circled “X”  52  in FIG.  7 . Short-circuit cases (b) and (c) at locations on rails  14  are represented by circled “Xs”  54  and  56 . 
     Short circuits are typically detected during testing of the electron-emitting device subsequent to fabrication but before the device is sealed (through an outer wall) to the light-emitting device to form the flat-panel display. When done at this stage, a short-circuit defect can often be removed from the electron-emitting device. This is sometimes referred to as short-circuit repair. Removing or repairing short-circuit defects increases the yield of good flat-panel displays and thus is important to device fabrication and test. 
     Ideally, a short-circuit defect is removed in such a manner that no loss in performance is incurred. Nonetheless, display performance is often satisfactory when a few pixels or sub-pixels are partially or totally inoperative, provided that the remainder of the flat-panel display operates in the intended manner. Accordingly, removing a short-circuit defect in a way that causes a pixel or sub-pixel to be inoperative is often acceptable, again provided that the operation of the remainder of the display is largely unaffected and also provided that the number of removed short-circuit defects is not too high. 
     The ladder shape of each emitter electrode  12  facilitates removal of short-circuit defects from the present field emitter without causing its performance to be impaired except that the sub-pixel at the site of the short-circuit defect sometimes becomes inoperative. FIG. 7 is helpful in understanding how short-circuit defects are removed from the field emitter of the present invention. 
     Assume that a short-circuit defect at the site represented by circled “X”  52  has been detected. As indicated in FIG. 7, short-circuit defect  52  occurs on crosspiece  16 . Defect  52  is removed by making a pair of cuts  58  and  60  fully through the width of crosspiece  16  on opposite sides of defect  52 . The segment of crosspiece  16  between cuts  58  and  60  is thus disconnected from the remainder of emitter electrode  12 . 
     Any electron-emissive elements  24  overlying the disconnected segment of crosspiece  16  are normally disabled. As a result, part or all of the sub-pixel containing that crosspiece  16  becomes inoperative. However, the operation of the remainder of emitter electrode  12  is not significantly affected. With rails  14  being fully intact, voltage for controlling all of the sets of electron-emissive elements  24  overlying electrode  12  can be transmitted down the full length of electrode  12 . 
     Cuts  58  and  60  are typically made at predetermined locations near ends  16 E of crosspiece  16 . In this case, crosspiece  16  is fully disconnected from the remainder of emitter electrode  12 . The removal of short-circuit defect  52  then results in the loss of the entire sub-pixel containing disconnected crosspiece  16 . Again, rails  14  remain fully intact. Hence, the normal operation of the remainder of emitter electrode  12  is not significantly affected by the removal of short-circuit defect  52 . 
     For convenience, let the two rails  14  of emitter electrode  12  in FIG. 7 be respectively referred to as the higher and lower rails, where the higher rail is the top one of rails  14  in FIG. 7, and the lower rail is the bottom one of rails  14  in FIG.  7 . With these definitions in mind, assume that a short-circuit defect has been detected at a site represented by circled “X”  54 . Short-circuit defect  54  occurs on the portion of higher rail  14  underlying column electrode  28 . Defect  14  is removed by making three cuts  58 ,  62 , and  64  through parts of emitter electrode  12  surrounding defect  54 . Cut  58  is again made through crosspiece  16  near the higher one of ends  16 E. Cuts  62  and  64  are made through higher rail  14  on opposite sides of defect  54  just beyond the area where column electrode  28  overlies higher rail  14 . Cuts  62  and  64  can be made at locations predetermined for making cuts  62  and  64  should a short-circuit defect be detected at a site represented by circled “X”  54 . 
     The section of higher rail  14  underlying column electrode  28  is disconnected from the remainder of emitter electrode  12  due to cuts  58 ,  62 , and  64 . However, none of electron-emissive elements  24  underlies the disconnected section of rail  14 . Provided that a segment of lower rail  14  is not similarly removed in either of the directly adjoining sub-pixels on emitter electrode  12 , voltage for the sub-pixel containing the removed segment of higher rail  14  can be provided through the segment of lower rail  14  underlying column electrode  28 . Hence, the sub-pixel is still operative. Also, the normal operation of the remainder of emitter electrode  12  is not significantly affected by removing short-circuit defect  54  in this way. 
     Should a short-circuit defect be detected at a site represented by circled “X”  56 , a removal procedure symmetrical to that described for short-circuit defect  54  is performed. In particular, three cuts  60 ,  66 , and  68  are made through parts of emitter electrode  12  surrounding short-circuit defect  56 . Cut  60  is again made through crosspiece  16  near the lower one of ends  16 E. Cuts  66  and  68  are made through lower rail  14  on opposite sides of defect  56  just beyond the area where column electrode  28  overlies lower rail  14 . As with the locations for  62  and  64 , the locations for cuts  66  and  68  can be predetermined. 
     For reasons complementary to those given above with respect to short-circuit defect  54 , the sub-pixel that contains the disconnected section of lower rail  14  remains operative despite the removal of defect  56 , provided that a segment of higher rail  14  is not similarly removed from either of the directly adjoining sub-pixels on emitter electrode  12 . Also, removal of short-circuit defect  56  in this way does not significantly affect the operation of the remainder of emitter electrode  12 . 
     Removing any of short-circuit defects  52 - 56  in the preceding manner does not significantly affect the operation of column electrode  28 . Subject to the occasional loss of part or all of the sub-pixel, the performance of the display is not significantly degraded. Rails  14  provide redundant current/voltage paths for overcoming short-circuit defects. 
     Cuts  58 - 68  are made with a beam of focused energy, typically optical energy provided by a laser. Cuts  62 - 68  can be made through the top or bottom of the electron-emitting device. Since column electrode  28  overlies the location for cuts  58  and  60 , cuts  58  and  60  are made through the bottom of the device when the cutting is done with a focused energy beam. 
     FIG. 8 presents a plan view that illustrates how the present ladder-shaped emitter electrode can be varied to simplify short-circuit removal in a field-emission electron-emitting device fabricated according to the invention. The plan view of FIG. 8 is the same as that of FIG. 7 except that (a) emitter electrode  12  is replaced with emitter electrode  70  in the field emitter of FIG.  8  and (b) column electrode  28  is modified in the field emitter of FIG.  8 . Each emitter electrode  70  consists of a pair of rails  14  and a group of generally parallel crosspieces  72  situated between, and extending generally perpendicular to, rails  14 . Rails  14  in the field emitter of FIG. 8 are configured in the manner described above. Each crosspiece  72  has a pair of ends  72 E that merge seamlessly into rails  14 . 
     The difference between crosspiece  72  and crosspiece  16  is that crosspiece  72  necks down close to ends  72 E. As shown in FIG. 8, crosspiece  72  consists of a main portion  72 M and a pair of narrower portions  72 N through which main portions  72 M is connected to rails  14 . Emitter openings  18  in the field emitter of FIG. 7 are replaced with emitter openings  74  in the field emitter of FIG.  8 . Due to the necking down of crosspieces  72 , each emitter opening  74  is generally rectangular in shape with protrusions at the four corners. Emitter openings  74  are oriented longitudinally in emitter electrode  70 . 
     In variously removing short-circuit defects  52 - 56  from the electron-emitting device of FIG. 8, cuts  76  and  78  are respectively made through necked-down portions  72 N near ends  72 E of crosspiece  72 . Cuts  76  and  78  are shorter than cuts  58  and  60  in the field emitter of FIG.  7 . Aside from this difference, selectively making cuts  62 - 68 ,  74 , and  76  to variously remove short-circuit defects  52 - 56  in the field emitter on FIG. 8 is performed in the same way that cuts  58 - 68  are selectively made to remove defects  52 - 56  in the field emitter of FIG.  7 . 
     In the field emitter of FIG. 8, a pair of further openings  80  and  82  preferably extend through each column electrode  28  respectively above the predetermined locations for cuts  76  and  78 . Further openings  80  and  82  overlie largely all of necked-down portions  72 N of crosspiece  72  in the example of FIG.  8 . Using a focused energy beam, cuts  76  and  78  can be made through the top or bottom of the electron-emitting device. This provides additional flexibility. Also, when cuts  76  and  78  are made through the bottom of the field emitter, the presence of further openings  80  and  82  helps prevent damage that might otherwise occur to column electrode  28  due to the penetration of the focused energy beam through crosspiece  72  and into electrode  28 . 
     A flat-panel CRT display containing an electron-emitting device manufactured according to the invention operates in the following way. The anode in the light-emitting device is maintained at high positive potential relative to control electrodes  28  and emitter electrodes  12  or  70 . When a suitable potential is applied between (a) a selected one of control electrodes  28  and (b) a selected one of emitter electrodes  12  or  70 , the so-selected gate portion  32  extracts electrons from the selected set of electron-emissive elements  24  and controls the magnitude of the resulting electron current. Desired levels of electron emission typically occur when the applied gate-to-cathode parallel-plate electric field reaches 20 volts/μm or less at a current density of 0.1 mA/cm 2  as measured at the light-emissive elements when they are high-voltage phosphors. The extracted electrons pass through the anode layer and selectively strike the phosphor regions, causing them to emit light visible on the exterior surface of the light-emitting device. 
     Directional terms such as “top”, “bottom”, “upper”, and “lower” 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 the present electron-emitting device may be situated at orientations different from that implied by the directional items used here. The same applies to the way in which the fabrication steps are performed in the invention. Inasmuch as directional items 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 ladder shape of the emitter electrodes of the invention can differ more from a conventional ladder shape than that of emitter electrodes  70 . In general, each emitter electrode can be shaped like a bar with the line of emitter openings situated longitudinally relative to the bar. The emitter openings can have plan-view shapes other than rectangles, as with openings  18 , or near rectangles, as with openings  74 . The bar can have a curved centerline such that the line of emitter openings is similarly curved. 
     The frontside exposure can be deleted in fabricating the electron-emitting device of the invention, especially when base focusing structure  38  is not utilized to contact spacers such as spacer walls through conductive focus coating  39 . On the other hand, multiple frontside exposures can be performed on the actinic material utilized to make base structure  38 , each frontside exposure normally being performed through a different photomask. Likewise, multiple backside exposures can be performed on the actinic material employed to create structure  38 . In this case, each additional backside exposure is performed through a photomask, different photomasks normally being employed when there are two or more additional backside exposures. 
     Additional radiation-blocking features can be provided over dielectric layer  20  for use in combination with, or as substitutes for, control electrodes  28  in blocking part of the backside actinic radiation that passes through emitter openings  18  or  74  during the formation of base focusing structure  38 . Multiple layers of actinic material can be utilized in forming base structure  38 . 
     The backside exposure through the area not shadowed by control electrodes  28  and emitter electrodes  12  or  70  can be employed in forming a self-aligned structure other than a focusing structure. The above-mentioned variations involving eliminating the frontside exposure, employing multiple frontside exposures and/or multiple backside exposures, and utilizing multiple layers of actinic material are especially applicable to the formation of such other structures. Similarly, additional features can be provided above emitter electrodes  12  or  70  for use in combination with, or substitutes for, control electrodes  28  in blocking part of the backside actinic radiation that passes through emitter openings  18  or  74 . 
     Each opaque emitter electrode  12  or  70  can be part of a composite emitter electrode that includes one or more transparent electrically conductive portions situated above or below electrode  12  or  70 . The transparent emitter electrode material extends at least partially across, typically fully across, at least part of, typically all, of emitter openings  18  or  74 . The transparent emitter electrode material is largely transmissive of backside actinic radiation  46 . Indium-tin oxide is an example of an electrical conductor suitable for the transparent conductive material in such a composite emitter electrode. 
     Each emitter electrode  12  or  70  can have three or more rails  14 , provided that crosspieces  16  are present between at least two of rails  14 . When crosspieces  16  are located between each consecutive pair of all of three or more of rails  14 , emitter electrodes  12  or  70  essentially become grids. Backside radiation  46  then passes through the grid openings, exemplified by emitter openings  18  in the ladder shape described above for electrodes  12  or  70 . 
     Grid-shaped versions of opaque emitter electrodes  12  or  70  can be combined with electrically conductive transparent material, such as indium-tin oxide, to form composite emitter electrodes. This enables the composite electrodes to have greater electrical conductivity than that typically provided by indium-tin oxide. 
     One of rails  14  can be deleted from each emitter electrode  12  or  70 . Although doing so removes the rail redundancy that facilitates short-circuit repair, the so-modified emitter electrodes can still be employed in the manner described above to form self-aligned structures such as base focusing structure  38 . 
     The actinic radiation can consist of or include light other than UV light. One example is IR light. Similarly, the actinic radiation can consist of or include radiation other than light. Different types of actinic radiation can be employed in different radiation-exposure steps. During the frontside exposure step, the chemical structure of the exposed portions of primary actinic layer  38 P can be changed by selectively exposing layer  38 P to a directed energy beam, such as a laser, rather than exposing layer  38 P through photomask  47 . 
     The actinic material exposed to actinic radiation can change chemical structure by phenomena other than polymerization. This occurs especially when the actinic material is positive tone, the exposed actinic material being removed during the development step. With positive-tone actinic material, the exposed material is typically converted into an acid that can be removed with an aqueous base developer. With positive-tone actinic material, certain lateral edges of the unexposed actinic material remaining after the development step are vertically aligned to parts or all of the longitudinal edges of control electrodes  28  in a manner complementary to that described above. 
     As an example of variations in the type of actinic radiation and the way of changing chemical structure, primary actinic layer  38 P can be thermosetting polymeric material, typically a thermosetting plastic, while backside radiation  46  consists of IR light. Upon being subjected to the IR light, the exposed portions of primary layer  38 P harden. Inasmuch as the wavelength of IR light is so long that undesirable light scattering might occur if the frontside exposure were done through a photomask situated a short distance above the top of the field emitter, a laser can be scanned selectively over layer  38 P to perform the frontside exposure. 
     Each of the sets of electron-emissive elements  24  can consist of only one element  24  rather than multiple elements  24 . Multiple electron-emissive elements can be situated in one opening through dielectric layer  22 . Electron-emissive elements  24  can have shapes other than cones. One example is filaments, while another is randomly shaped particles such as diamond grit. 
     The principles of the invention can be applied to other types of matrix-addressed flat-panel displays. Candidate flat-panel displays for this purpose include matrix-addressed plasma displays and active-matrix liquid-crystal displays. 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.