Patent Grant
7090554
This invention relates to flat-panel displays of the cathode-ray tube (“CRT”) type, including the fabrication of flat-panel CRT displays.
A flat-panel CRT display basically consists of an electron-emitting component and a light-emitting component. The electron-emitting component, commonly referred to as a cathode, contains electron-emissive regions that emit electrons over a relatively wide area. The emitted electrons are suitably directed towards light-emissive elements distributed over a corresponding area in the light-emitting component. Upon being struck by the electrons, the light-emissive elements emit light that produces an image on the display's viewing surface.
The electron-emitting and light-emitting components are connected together to form a sealed enclosure normally maintained at a pressure much less than 1 atm. The exterior-to-interior pressure differential across the display is typically in the vicinity of 1 atm. In a flat-panel CRT display of significant viewing area, e.g., at least 10 cm2, the electron-emitting and light-emitting components are normally incapable of resisting the exterior-to-interior pressure differential on their own. Accordingly, a spacer (or support) system is conventionally provided inside the sealed enclosure to prevent air pressure and other external forces from collapsing the display.
The spacer system typically consists of a group of laterally separated spacers positioned so as to not be directly visible on the viewing surface. The presence of the spacer system can adversely affect the flow of electrons through the display. For example, electrons coming from various sources occasionally strike the spacer system, causing it to become electrically charged. The electric potential field in the vicinity of the spacer system changes. The trajectories of electrons emitted by the electron-emitting device are thereby affected, often leading to degradation in the image produced on the viewing surface.
More particularly, electrons that strike a body, such as a spacer system in a flat-panel display, are conventionally referred to as primary electrons. When the body is struck by primary electrons of high energy, e.g., greater than 100 eV, the body normally emits secondary electrons of relatively low energy. More than one secondary electron is, on the average, typically emitted by the body in response to each high-energy primary electron striking the body. Although electrons are often supplied to the body from one or more other sources, the fact that the number of outgoing (secondary) electrons exceeds the number of incoming (primary) electrons commonly results in a net positive charge building up on the body.
It is desirable to reduce the amount of positive charge buildup on a spacer system in a flat-panel CRT display. Jin et al, U.S. Pat. No. 5,598,056, describes one technique for doing so. In Jin et al, each spacer in the display's spacer system is a pillar consisting of multiple layers that extend laterally relative to the electron-emitting and light-emitting components. The layers in each spacer pillar alternate between an electrically insulating layer and an electrically conductive layer. The insulating layers are recessed with respect to the conductive layers so as to form grooves. When secondary electrons are emitted by the spacers in Jin et al, the grooves trap some of the secondary electrons and prevent them from escaping the spacers. Because fewer secondary electrons escape the spacers than what would occur if the grooves were absent, the amount of positive charge buildup on the spacers is reduced.
The technique employed in Jin et al to reduce positive charge buildup is creative. However, the spacers in Jin et al are relatively complex and pose significant concerns in dimensional tolerance and, therefore, in reliability. Manufacturing the spacers in Jin et al could be problemsome. It is desirable to have a relatively simple technique, including a simple spacer design, for reducing charge buildup on a spacer system of a flat-panel CRT display.
The present invention furnishes a flat-panel display in which a spacer situated between a pair of plate structures has a rough face. An image is supplied by one of the plate structures in response to electrons provided from the other plate structure. Somewhat similar to what occurs in Jin et al, the roughness in the face of the present spacer prevents some secondary electrons emitted by the spacer from escaping the spacer. Accordingly, positive charge buildup on the spacer is normally reduced. The image is thereby improved.
In particular, secondary electrons emitted by the present spacer as a result of being struck by primary electrons are, on the average, normally of significantly lower energy than the primary electrons. Due to the roughness in the spacer's face, the lower-energy secondary electrons are more prone to impact the spacer and be captured by it than what would occur if the spacer's face were smooth. The lower-energy secondary electrons captured by the spacer cause relatively little further secondary electron emission from the spacer.
Roughness in the face of a body being struck by primary electrons may sometimes itself cause the body to emit an increased number of secondary electrons, especially when the energy of the primary electrons is quite high. This increase in the secondary electron emission is offset by the number of secondary electrons captured by the body due to its facial roughness. In the present flat-panel display, the primary electron energy, while high, is normally sufficiently low that the roughness in the spacer's face leads to a reduction in the overall number of secondary electrons that escape the spacer.
To the extent that the spacer used in the present flat-panel display has multiple levels of spacer material, the levels typically extend vertically relative to the electron-emitting and light-emitting components rather than laterally as in Jin et al. A spacer with vertically extending spacer-material levels is generally simpler in design, and can be fabricated to high tolerances more easily, than a spacer having laterally extending spacer-material levels. When the present spacer has multiple vertically extending levels of spacer material, reliability concerns associated with the spacer design are considerably less severe than those that arise with the spacer design of Jin et al. When the spacer used in the present display has only a single level of spacer material, the display essentially avoids the reliability concerns that arise in Jin et al. The net result is a substantial improvement over Jin et al.
A flat-panel display that employs the teachings of the invention is generally configured in the following way. The display contains a first plate structure, a second plate structure situated opposite the first plate structure, and a spacer situated between the plate structures. The first plate structure emits electrons. The second plate structure emits light to produce an image upon receiving electrons emitted by the first plate structure. The spacer has a rough face that extends at least partway from either plate structure to the other plate structure.
Primary electrons which strike the spacer include electrons that follow trajectories directly from the first plate structure to the spacer as well as electrons that reflect off the second plate structure after having traveled from the first plate structure to the second plate structure. The reflected electrons are generally referred to as “backscattered” electrons. While the flat-panel display can normally be controlled so that only a small fraction of the electrons emitted by the first plate structure directly strike the spacer, the backscattered electrons travel in a broad distribution of directions as they leave the second plate structure. As a result, electron backscattering off the second plate structure is difficult to control direction-wise.
By inhibiting secondary electrons emitted by the present spacer from escaping the spacer, the roughness in the spacer's face also reduces spacer charging that would otherwise result from backscattered primary electrons striking the spacer. In certain embodiments of the present display, the spacer facial roughness is provided with a directional roughness characteristic that enhances the ability of the spacer's rough face to prevent secondary electrons, especially those caused by backscattered primary electrons, from escaping the spacer.
In one aspect of the invention, the present spacer is implemented as a spacer wall. The roughness in the face of the spacer wall is adjustable according to the average strength EAV of the electric field directed from the second plate structure to the first plate structure during operation of the display. The roughness in the wall's face can take various forms such as depressions or/and protuberances. The depressions can, for example, be implemented as pores, trenches, or/and notches. The depressions can be rounded three-dimensionally, typically to have portions of roughly constant radius of curvature. When the wall's face is defined by grains, the depressions can be formed by valleys between adjoining grains. The protuberances can take the form of ridges, particles, pillars, or/and spires.
Regardless of the actual form of the roughness in the face of the spacer wall, the facial roughness can be approximated by identical cylindrical pores of pore diameter dP. The representation of the wall's facial roughness using identical pores ideally has the same total electron yield coefficient that occurs with the actual roughness in the wall's face. In this representation, the wall's facial roughness corresponds to a wall porosity of at least 10% along the wall's face and a pore height hp of at least 15% of pore height parameter hMD Parameter hMD is given by the following relationship as a function of average electric field strength EAV and pore diameter dP:
hMD=√{square root over (2dP2DMD/eEAV)}
where e is the electron charge, and 2DMD is the median energy of secondary electrons as they depart from (leave) the spacer wall. By using this relationship, the characteristics of the identical pores that approximate the actual roughness in the wall's face can be suitably adjusted, as electric field strength EAV changes, to reduce the number of secondary electrons that escape the spacer wall.
Magnetic material may be present in the spacer wall along its face. The magnetic material causes the trajectories of secondary electrons emitted by the wall to be altered in a way that further inhibits them from escaping the wall.
In another aspect of the invention, the spacer contains a main spacer body having a rough face. The main body of the spacer is typically shaped like a wall but can have other shapes. The roughness in the main body's face is achieved with pores that extend into the main body along its face. The pores have an average diameter of 1–1,000 nm and provide a porosity of at least 10% along the main body's face.
The main body of the spacer in this aspect of the invention can be internally configured in various ways. As one example, the main body can be implemented simply as a porous electrically non-conductive substrate. The term “electrically non-conductive” here generally means electrically insulating or electrically resistive. A coating may overlie the substrate in a generally conformal manner. With the pores acting to inhibit secondary electrons from escaping the main body, the that itself emits a relatively low level of secondary electrons.
As another example, the main body of the spacer can be implemented with a substrate and a porous layer that overlies the substrate. The porous layer normally has an average electrical resistivity of 108–1014 ohm-cm, preferably 109–1013 ohm-cm, at 25° C. The porous layer is preferably of at least ten times greater resistance per unit length than the substrate. By implementing the main body in this way, the substrate largely determines the non-emissive electrical characteristics of the main body, while the pores largely determine the secondary electron escape characteristics of the main body. Separating these two types of spacer characteristics in this way makes it easier to design the spacer. A generally conformal coating, which typically emits a relatively low level of secondary electrons, may overlie the porous layer.
Various techniques are suitable for manufacturing the present flat-panel display, especially the spacer, in accordance with the invention. For instance, the spacer can be fabricated by a procedure that entails furnishing a composite in which support material and further material are interspersed with each other. At least of part of the further material is removed from the composite to convert it into a porous body. Depending on whether the porous body is larger than, or of approximately the same size as, the main body of the spacer, part or all of the porous body is utilized as at least part of the spacer.
The support material of the composite may be ceramic, while the further material is organic material consisting of carbon and non-carbon material. The porous body is created by removing at least part of the non-carbon material from the composite. Alternatively, the composite can be a gel or open network of solid material, while the further material is liquid. The porous body is then created by removing at least part of the liquid without causing the support material to completely fill the space previously occupied by the removed liquid.
The composite can be created according to a process in which a liquidous body is formed from a composition of the support material, the further material, and liquid. In the liquidous body, the further material may be in the form of discrete particles, typically roughly spherical in shape. The liquid is removed to transform the liquidous body into a solid composite. Alternatively, a layer of discrete particles can be formed, after which the support material is introduced into spaces between the particles. A layer of support material may also be provided below the particle layer. In either case, at least a portion of the particles are later removed from the solid composite to form the porous body.
In another technique for fabricating the present flat-panel display, an initial face of a primary body is roughened to form a rough face. The primary body may, or may not, be porous (or otherwise facially roughened) prior to the roughening step. The roughening step typically entails etching the primary body. The etching step can be performed in such a way as to impose the above-mentioned directional roughness characteristic on the primary body's face, especially when the initial face of the primary body is defined by grains.
Alternatively, protuberances can be provided over a primary body to furnish the body with a rough face. Regardless of which of the preceding techniques is employed, part or all of the primary body forms at least part of the spacer.
When carbon is employed in the conformal coating that emits secondary electrons at a relatively low level, the carbon can be provided by chemical vapor deposition. The carbon can also be provided by thermally decomposing carbon-containing material over an underlying body that forms at least part of the spacer. This can be done subsequent to forming the underlying body or during an anneal operation used in creating the underlying body.
In short, the rough-faced spacer utilized in the present flat-panel display typically reduces the number of secondary electrons that escape the spacer, thereby reducing positive charge buildup on the spacer. The present spacer is of relatively simple configuration and can be manufactured according to readily controllable manufacturing techniques. The invention thus provides a large advance over the prior art.
a–3l are cross-sectional side views of facial portions of twelve general variations of the spacer wall in the display portion of
a–4g are plan views of the facial wall portions in
a and 8b are cross-sectional views that form a secondary electron emission model of a typical pore for the respective situations of secondary electron capture and secondary electron escape.
a–11d are cross-sectional side views of four general embodiments of the main wall of the wall-shaped spacer in
a and 12b are cross-sectional views that form secondary electron emission models of a typical pore for the respective situations of magnetic material being absent and present along the pore.
a–13d are cross-sectional side views representing a first set of steps in manufacturing a main wall, such as that of
a–14e are cross-sectional side views representing a second set of steps in manufacturing a main wall, such as that of
a–15f are cross-sectional side views representing a third set of steps in manufacturing a main wall, again such as that of
a–16c are cross-sectional side views representing a fourth set of steps in manufacturing a main wall, such as that of
a–17d are cross-sectional side views representing a fifth set of steps in manufacturing a main wall, such as that of
a–18e are cross-sectional side views representing a sixth set of steps in manufacturing a main wall, such as that of
a and 19b are cross-sectional side views representing a pair of steps that can be performed on the structure of
a–20c are cross-sectional side views representing a seventh set of steps in manufacturing a main wall, such as that of
The symbol “e1−” in the drawings represents a primary electron. The symbol “e2−” in the drawings represents a secondary electron.
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.
General Display Configuration An internal spacer system for a flat-panel CRT display configured and fabricated according to the invention is formed with spacers that have rough faces for reducing spacer charging during display operation. Primary electron emission in the present flat-panel CRT display typically occurs according to field-emission principles. A field-emission flat-panel CRT display (often referred to as a field-emission display) having a spacer system configured according to the invention can serve as a flat-panel television or a flat-panel video monitor for a personal computer, a lap-top computer, or a workstation.
In the following description, the term “electrically insulating” (or “dielectric”) generally applies to materials having an electrical resistivity greater than 1012 ohm-cm at 25° C. The term “electrically non-insulating” thus refers to materials having an electrical resistivity of up to 1012 ohm-cm at 25° C. Electrically non-insulating materials are divided into (a) electrically conductive materials for which the electrical resistivity is less than 1 ohm-cm at 25° C. and (b) electrically resistive materials for which the electrical resistivity is in the range of 1 ohm-cm to 1012 ohm-cm at 25° C. Similarly, the term “electrically non-conductive” refers to materials having an electrical resistivity of at least 1 ohm-cm at 25° C., and includes electrically resistive and electrically insulating materials. These categories are determined at an electric field of no more than 10 volts/μm.
In the FED of
Backplate structure 20 contains an array of rows and columns of laterally separated electron-emissive regions 30 that face enclosure 26. Electron-emissive regions 30 overlie an electrically insulating backplate (not separately shown) of plate structure 20. Each electron-emissive region 30 normally consists of a large number of electron-emissive elements shaped in various ways such as cones, filaments, or randomly shaped particles. Plate structure 20 also includes a system (also not separately shown) for focusing electrons emitted by regions 30.
Faceplate structure 22 contains an array of rows and columns of laterally separated light-emissive elements 32 formed with light-emissive material such as phosphor. Light-emissive elements 32 overlie a transparent electrically insulating faceplate (not separately shown) of plate structure 22. Each electron-emissive element 32 is situated directly opposite a corresponding one of electron-emissive regions 30. The light emitted by elements 32 forms an image on the display's viewing surface at the exterior surface of faceplate structure 22.
The FED of
A border region 34 of dark, typically black, material laterally surrounds each of light-emissive elements 32 above the faceplate. Border region 34, referred to here as a black matrix, is typically raised relative to light-emissive elements 32. In view of this and to assist in pictorially distinguishing elements 32 from black matrix 34,
In addition to components 32 and 34, faceplate structure 22 contains an anode (not separately shown) situated over or under components 32 and 34. During display operation, the anode is furnished with a potential that attracts electrons to light-emissive elements 32.
During FED operation, electron-emissive regions 30 are controlled to emit primary electrons that selectively move toward faceplate structure 22. The electrons so emitted by each region 30 preferably strike corresponding target light-emissive element 32, causing it to emit light. Item 38 in
Some of the primary electrons emitted by each region 30 invariably strike parts of the display other than corresponding target light-emissive element 32. To the extent that the emitted primary electrons are off-target, the control provided by the electron-focusing system and any other electron trajectory-control components of the FED display is normally of such a nature that the large majority of the off-target primary electrons strike black matrix 34. However, off-target primary electrons occasionally follow trajectories directly from an electron-emissive element 30 to nearest spacer wall 24 as represented by electron trajectory 40 in
Also, some of the primary electrons that travel from an electron-emissive region 30 to faceplate structure 22 are scattered backward off plate structure 22 rather than directly causing light emission. The reverse electron-travel direction is from faceplate structure 22 to backplate structure 20 generally parallel to spacer walls 24. While the FED is normally controlled so that the vast majority of primary electrons emitted by each region 30 impact directly on or close to its target light-emissive element 32, electrons scattered backward off faceplate structure 22 move initially in a broad distribution of directions. A substantial fraction of the backscattered electrons strike spacer walls 24. Item 42 in
Main wall 46 has a pair of opposing rough faces 54 and 56. The roughness in main wall faces 54 and 56 is typically present along largely all of each face 54 or 56. Also, the facial roughness is shown qualitatively in
Some of the primary electrons that strike a spacer wall 24 occasionally hit electrodes 48, 50, and 52, primarily electrode 48. However, as represented in
Spacer wall electrodes 48, 50, and 52 preferably consist of electrically conductive material, typically metal such as aluminum, chromium, nickel, or gold, including a metallic alloy such as a nickel-vanadium alloy, or a combination of two or more of these metals. In any event, electrodes 48, 50, and 52 are of considerably lower average electrical resistivity than main wall 46. Electrode 48 is a face electrode situated on wall face 54. Another such face electrode (not shown) may be situated on wall face 56 opposite face electrode 48. Electrodes 50 and 52 are end (or edge) electrodes situated on opposite ends (or edges) of main wall 46 so as to respectively contact plate structures 20 and 22.
Wall electrodes 48, 50, and 52 cooperate with the electron-focusing system in controlling the movement of electrons from backplate structure 20 through sealed enclosure 26 to faceplate structure 22. Further examples of how spacer wall electrodes, such as electrodes 48, 50, and 52, function to control the forward electron movement are presented in Spindt et al, U.S. patent application Ser. No. 09/008,129, filed 16 Jan. 1998, now U.S. Pat. No. 6,049,165, and Spindt et al, U.S. patent application Ser. No. 09/053,247, filed 31 Mar. 1998, now U.S. Pat. No. 6,107,731. The contents of application Ser. Nos. 09/008,129 and 09/053,247 are incorporated by reference herein. Alternative implementations for electrodes 48, 50, and 52 are also presented in applications Ser. Nos. 09/008,129 and 09/053,247.
Types of Spacer Facial Roughness
a–3l present twelve cross-sectional examples of how the roughness in spacer wall faces 54 and 56 is achieved. Each of
The spacer facial roughness can be achieved in two basic ways: (a) depressions in main wall 46 along faces 54 and 56 and (b) protuberances, i.e., raised portions, of wall 46 along faces 54 and 56. In most of
One general type of depressions can be characterized as pores. See
In
b presents an example in which generally straight pores 62 are present along wall face 54. In contrast to
In
The term “porosity” is employed here in characterizing rough faces 54 and 56 of main wall 46. Porosity results from openings that are shaped like pores as well as other types of openings. The volume porosity of a porous body is the percentage of the body's volume occupied by the pores or/and other openings in the porous body. The porosity of wall 46 along face 54 or 56, variously referred to here as the main wall facial porosity or as the main wall porosity along face 54 or 56, is therefore the percentage of area occupied by the pores or other openings along an imaginary plane running generally through face 54 or 56 along the tops of the openings. If the pores or other openings along face 54 or 56 are of such a nature that this definition of main wall facial porosity is inappropriate or difficult to apply, the main wall porosity along face 54 or 56 is equivalently the percentage of area occupied by the openings along an imaginary smooth reference surface located a short reference distance below an imaginary plane running generally through face 54 or 56 along the tops of the openings. When the spacer facial roughness is formed by depressions, the reference distance is typically one half the average depression depth.
Main wall 46 normally has a porosity of at least 10% along each of wall faces 54 and 56. The minimum main wall facial porosity of 10% applies to pores 60, 62, and 64 and to other implementations of pores along face 54 or 56. The main wall porosity along face 54 or 56 is preferably at least 20%, more preferably at least 40%. The main wall facial porosity is typically 60% or more, often up to 80% or more. In some embodiments, especially when main wall 46 contains irregular pores such as pores 64 in
The pores, whether implemented with any of pores 60, 62, and 64 or/and implemented in other ways, normally have an average pore diameter in the range of 1–1,000 nm. The average pore diameter subranges of 1–20 nm and 5–1,000 nm are of particular interest. When main wall 46 is provided with pores 60 in
d and 4b depict an embodiment in which the depressions in main wall 46 are implemented with three-dimensionally rounded recessions 66 along wall face 54. The large majority of rounded recessions 66 have portions of roughly constant radius of curvature. In particular, each such recession 66 is generally shaped roughly like at least one open sphere with part of its volume cut off. The average diameter of recessions 66 is normally 10–1,000 nm, preferably 50–500 nm, typically 150 nm. Recessions 66 may be viewed as pores of generally low height-to-width aspect ratio. In light of this, main wall 46 in
Rounded recessions 66 are formed with only a monolayer of open spheres in the example of
In
f depicts a variation of main wall 46 in
The directional roughness characteristic along face 54 in
As discussed further below, the electric field in sealed enclosure 26 is directed from faceplate structure 22 to backplate structure 20. Since electrons are negatively charged particles, the electric field in enclosure 26 causes electrons in enclosure 26 to be accelerated towards faceplate structure 22. This applies to both primary electrons and secondary electrons in enclosure 26. Because the electric field attracts electrons towards faceplate structure 22, the directional roughness characteristic causes secondary electrons emitted by main wall 46 to be more prone to strike steepened outer-grain upper-half surfaces 72F and be captured by wall 46 than what would occur in the absence of the directional roughness characteristic. Consequently, a reduced number of secondary electrons normally escape wall 46.
High-energy primary electrons backscattered off faceplate structure 22 slow down due to the electric field in enclosure 26. The reduced speed and correspondingly modified trajectories of these backscattered electrons cause them, on the average, to penetrate deeper into depressions, such as valleys 70, along rough face 54 then high-energy primary electrons that follow trajectories directly from backplate structure 20 to main wall 46. In turn, the deeper penetration of backscattered primary electrons into valleys 70 normally leads to an increase in the fraction of resulting secondary electrons captured by wall 46. Since the ability to capture secondary electrons is enhanced by the directional roughness characteristic provided to face 54 in
Another way of providing wall face 54 with a directional roughness characteristic that reduces the number of secondary electrons which escape main wall 46 is illustrated in
Notches 74 are typically straight and extend approximately parallel to one another, as illustrated in the example of
In the example of
Each notch 74 is defined by a pair of notch surfaces 76B and 76F along face 54. For notch surfaces 76B and 76F of each notch 74, surface 76B is closest to backplate structure 20, while surface 76F is closest to faceplate structure 22. Although notch surfaces 76B and 76F are illustrated as generally being flat in the profile of
The directional roughness characteristic in
Each notch surface 76F is at an angle α to an imaginary plane 78 extending generally parallel to wall face 54. Plane 78 is indicated in dashed line in
The directional roughness characteristic for wall face 54 in
In
Similar to notches 74, trenches 80 are typically straight and extend approximately parallel to one another. Likewise, trenches 80 also typically extend approximately parallel to plate structure 20 or 22. However, trenches 80 can be angled relative to structure 20 or 22. The angle between each trench 80 and structure 20 or 22 is normally no more than 15°. In addition, trenches 80 can be angled relative to each other or/and curved in various ways. Trenches 80 can also variously intersect one another. For example, trenches 80 can be configured in an array of rows and columns.
Trenches 80 are depicted as being largely identical in the example of
Trenches 80 typically have an average width of 1–50 μm. The average depth to which trenches 80 extend into main wall 46 is typically 0.5–10 μm. For the example shown in
i and 4e illustrate the first of four examples in which the spacer facial roughness is achieved with protuberances along wall face 54. In
Ridges 82 can be created (a) according to a procedure that entails removing material from a precursor to main wall 46 at the locations between the desired locations for ridges 82 or (b) according to procedure that entails depositing electrically non-conductive material on a generally flat portion of wall 46 at the desired locations for ridges 82. Aside from the fact that creating ridges 82 according to the second-mentioned procedure may result in ridges 82 consisting of material totally different from the material underlying ridges 82, ridges 82 are essentially the complement of trenches 80 in
In particular, ridges 82 can be straight and extend approximately parallel to each other and to plate structure 20 or 22. Alternatively, ridges 82 can variously extend at angles relative to one another or/and can be variously curved. Ridges 82 can also variously intersect one another, e.g., to form an array of rows and columns. Ridges 82 can be largely identical to, or variously different from, one another.
As the average width of ridges 82 increases relative to the average spacing between consecutive ones of ridges 82 in the example of
In
Alternatively, protuberances 84 may have largely the same shape. Protuberances 84 are typically located at substantially random locations relative to one another. In a typical implementation, protuberances 84 consist of particles, including coated particles.
Protuberances 84 are typically created according to a procedure that entails providing suitable particles on a generally flat portion 86 of main wall 46, or on a generally flat portion of a precursor to wall 46. While protuberances 84 may consist of largely the same material as that underlying protuberances 84 along flat portion 86, protuberances 84 typically consist primarily of material of different chemical composition than the directly underlying material.
The space between protuberances 84 is considered to be an opening for determining the main wall facial porosity. With this in mind, the main wall porosity along face 54 in
k and 4g depict an embodiment in which the protuberances in main wall 46 are formed with pillars 88 situated on a smooth, generally flat portion 90 of wall 46. Pillars 88 are normally situated at largely random locations relative to one another and extend approximately perpendicular to the upper surface of flat wall portion 90. Each pillar 88 is normally roughly cylindrical in shape along most of its height. That is, as viewed vertically (perpendicular to the upper surface of wall portion 90), each pillar 88 is normally of approximately constant cross section along most of its height. The heights of pillars 88 are normally relatively uniform from one pillar 88 to another.
The cross section of each pillar 88 is typically roughly circular as viewed vertically but can be shaped differently. The diameters of pillars 88 can be roughly the same from one pillar 88 to another pillar 88, or can vary somewhat from one pillar 88 to another. The variation in the diameters of pillars 88 is typically comparable to the variation in their heights.
Similar to what was said about protuberances 84 in
In
The aspect ratio of height to average diameter of spires 92 is typically in the vicinity of 2–10. The heights of spires 92 vary somewhat from one spire 92 to another. The same applies to the locations of the bottoms of spires 92.
The space that separates spires 92 above their bottoms is considered to be an opening for determining the main wall facial porosity. Using the second approach mentioned above for determining the main wall facial porosity with the reference distance being approximately one half the average height of spires 92, the main wall porosity along face 54 in
The fraction of secondary electrons captured by main wall 46 may sometimes be increased when two or more of the types of wall roughness shown in
Effect of Facial Roughness on Electron Escape
An understanding of how the roughness in wall faces 54 and 56 reduces the fraction, and normally the number, of secondary electrons that escape main spacer wall 46 is facilitated with the assistance of 1SMD varies with the energy
D of the escaping electrons just as they depart from the surface. The number of electrons that escape a unit area of a smooth surface, or a projected unit area of a rough surface, at any value of electron departure energy
D is the electron yield Ne. The vast majority of the electrons that escape such a surface are secondary electrons. Consequently, electron departure energy
D is largely the departure energy of the escaping secondary electrons.
Referring to
Items 100 in
An electric field Ē of average strength EAV is directed generally from faceplate structure 22 to backplate structure 20. Electric field Ē is the principal force that acts on secondary electrons emitted by main wall 46. To a first approximation, trajectories 100 and 102 followed by the secondary electrons are roughly parabolic, at least in the immediate vicinity of wall 46. Since electrons are negatively charged, trajectories 100 and 102 bend towards faceplate structure 22 as electric field E causes the secondary electrons to be accelerated towards faceplate structure 22.
The initial directions of secondary electrons that follow trajectories such as trajectories 100 and 102 are largely random. Some of the secondary electrons rapidly strike other recessed points along wall face 54. Other secondary electrons strike recessed points along wall 54 after their trajectories 100 or/and 102 bend significantly towards faceplate structure 22. Yet other secondary electrons escape spacer wall 24 and follow trajectories 100 and 102 towards faceplate structure 22.
A large majority of the electrons that return to main wall 46 impact wall 46 close to where they were emitted from wall 46 and therefore are of relatively low energy at impact. Consequently, these secondary electrons are largely captured by wall 46. Because their energy is relatively low at impact, they also do not cause significant further secondary electron emission from wall 46.
Whether a secondary electron is captured by, or escapes from, main wall 46 depends on a number of factors, including (a) the secondary electron's emission departure direction, (b) departure energy 2D and thus the departure speed of the secondary electron, (c) where the primary electron strikes wall face 54 and therefore where the secondary electron is emitted from face 54, (d) the characteristics of the roughness in face 54, and (e) the magnitude of EAV, the average strength electric field Ē between plate structures 20 and 22.
The recessed areas in face 54 tend to trap secondary electrons by providing them with surfaces to hit and thereby be captured. Since a secondary electron is emitted from largely the point at which a primary electron strikes face 54, the average probability of capturing a secondary electron emitted from a recessed area along face 54 normally increases as the emission-causing primary electron penetrates deeper into the recessed area. The so-emitted secondary electron has increased distance to travel and, on the average, greater likelihood of traveling in an initial direction which results in the electron striking a point in the recessed area than a secondary electron emitted from a shallower point in the recessed area. In contrast, secondary electrons emitted from high points on face 54 have few places to contact face 54 and have low probabilities of being captured by face 54.
If a completely smooth face were substituted for rough face 54, there would be no recessed areas for secondary electrons to strike. A very high fraction of the secondary electrons emitted by the body having the smooth face would escape the body. Hence, the roughness in faces 54 and 56 causes the fraction of emitted secondary electrons that escape main wall 46 to be less than the fraction of emitted secondary electrons that escape the smooth reference surface.
On the other hand, roughness in a surface appears to cause the number of secondary electrons to increase, at least for certain types of surface roughness. The increase in the number of secondary electrons emitted from such a rough surface varies with the energies of the primary electrons as they strike the rough surface and typically increases with increasing primary electron striking energy 1SMD greater than approximately 1,000 eV. Whether the roughness in the surface leads to an increase or decrease in the total number of secondary electrons that actually escape the rough surface thus depends on the magnitudes of the incident energies of the primary electrons. In the FED that contains spacer wall 24, the primary electrons strike wall face 54 or 56 with energies which, although high compared to median secondary-electron departure energy
2DMD, are sufficiently low that the roughness in face 54 or 56 causes a reduction in the total number of secondary electrons that escape main wall 46 and, accordingly, that escape spacer wall 24.
Electric field Ē causes backscattered primary electrons moving away from faceplate structure 22 to slow down. More specifically, the backscattered electrons lose velocity in the reverse electron-travel direction. To a first approximation, the backscattered electrons maintain the components of their velocity parallel to plate structure 22 or 20. As a result, the backscattered electrons are more likely to penetrate deeper into the recessed areas along wall face 54 than electrons traveling directly from backplate structure 20 to main wall 46. Due to the deeper penetration of the backscattered primary electrons into the recessed areas along face 54, the resulting secondary electrons emitted by wall 46 are more prone to be captured by wall 46 than the secondary electrons caused by primary electrons traveling directly from backplate structure 20 to wall 46. The roughness in wall faces 54 and 56 thereby especially reduces positive spacer charging due to electron backscattering off faceplate structure 22.
Two curves 106 and 108 are shown in 1SMD impact the smooth reference surface. This yield, referred to here as the “natural” electron yield, is normally determined for primary electrons that impinge perpendicularly on the reference surface. Curve 108 represents the yield Ne of electrons that escape rough face 54 along a projected unit area of face 54, i.e., along a unit area of an imaginary plane running through the top of face 54, while high-energy primary electrons of median striking energy
1SMD impact face 54. The electron yield represented by curve 108 is referred to here as the “roughness-modified” electron yield.
The secondary electrons emitted by rough face 54 or the reference surface upon being struck by primary electrons of median striking energy 1SMD have a median energy
2DMD as they are emitted from, and therefore start to depart from, face 54 or the reference surface. Energy
2DMD is referred to here as the median secondary-electron departure energy.
Each of curves 106 and 108 has two peaked portions as a function of electron departure energy D: a low-energy left-hand peak and a high-energy right-hand peak. In some cases, the left-hand peaks of curves 106 and 108 occur at, or essentially at, the vertical axis where electron departure energy
D is zero. The left-hand peak of each of curves 106 and 108 tails off relatively slowly with increasing electron departure energy
D. The end of the tail of each of the left-hand peaks occurs approximately at a dividing electron energy
DD between median secondary-electron departure energy
2DMD and primary-electron striking energy
1SMD The right-hand peaks of curves 106 and 108 are much closer to each other than the left-hand peaks are to each other.
The low-energy left-hand peak of curve 106 largely represents the yield of secondary electrons that are emitted by, and escape from, the smooth reference surface as a function of electron departure energy D. Integration of the left-hand peak of curve 106 from zero to dividing energy
DD largely gives the total natural secondary electron yield, i.e., the total number of electrons that escape a unit area of the reference surface. The ratio of the total natural secondary-electron yield to the total number of primary electrons that strike a unit area of the reference surface is the natural secondary electron yield coefficient δ.
The low-energy left-hand peak of curve 108 largely represents the yield of secondary electrons that actually escape main wall 46 along rough face 54. Since some of the secondary electrons emitted from face 54 are subsequently captured by face 54 due to the spacer facial roughness, the left-hand peak of curve 108 is largely the difference, per projected unit area of face 54, between the number of secondary emitted by face 54 and the number of secondary electrons captured by face 54 as a function of electron departure energy D. The left-hand peak of curve 108 is lower than the left-hand peak of curve 106 because primary electrons strike both (a) face 54 in the present FED and (b) the smooth reference surface with median primary-electron striking energy
1SMD which, while generally high, is sufficiently low that the total number of secondary electrons which escape face 54 is less than the total number of secondary electrons which escape the reference surface.
Integration of the left-hand peak of curve 108 from zero to dividing energy DD largely gives the total roughness-modified secondary electron yield. The ratio of the total roughness-modified secondary electron yield to the total number of primary electrons that pass through a projected unit area of face 54 is the roughness-modified secondary electron yield coefficient δ*. Since (a) face 54 captures some of the emitted secondary electrons and (b) primary-electron striking energy
1SMD is sufficiently low in the present FED, roughness-modified secondary electron yield coefficient δ* of face 54 is less than natural secondary electron yield coefficient δ of the (type of) material that forms face 54.
Some of the high-energy primary electrons that strike rough face 54 or the smooth reference surface are reflected, or scattered, rather than causing secondary electron emission. The high-energy right-hand peaks of curves 106 and 108 largely represent primary electrons that scatter off face 54 or the reference surface and escape face 54 or the reference surface. Some of the primary electrons scattered off face 54 strike face 54 elsewhere, largely due to the spacer facial roughness, and cause secondary electron emission there. The effect of primary electrons that scatter off face 54 but do not escape face 54 is included within the roughness-modified secondary electron yield. Because secondary electrons emitted from face 54 are of lower departure energy D than primary electrons scattered off face 54, the fraction of secondary electrons captured by face 54 is normally considerably greater than the fraction of scattered primary electrons captured by face 54.
Electrons are emitted from rough face 54 or the smooth reference surface due to phenomena other than high-energy primary electrons striking face 54 or the reference surface. In
Integration of curve 106 from dividing energy DD to the right-hand edge of the right-hand peak gives the total natural non-secondary electron yield, i.e., the total number of scattered primary electrons and other non-secondary electrons that escape a unit area of the reference surface. The ratio of the total natural non-secondary electron yield to the total number of primary electrons that strike a unit area of reference surface is the natural non-secondary electron yield coefficient η. Similarly, integration of curve 108 from dividing energy
DD to the right-hand end of the right-hand peak gives the total roughness-modified non-secondary electron yield. The ratio of the total roughness-modified non-secondary electron yield to the total number of electrons that pass through a projected unit area of face 54 is the roughness-modified non-secondary electron yield coefficient η*.
Curves 106 and 108 are quite close to each other across the integration range above dividing energy DD, curve 108 typically being no greater than curve 106 across this range. Hence, roughness-modified non-secondary electron yield coefficient η* is close to natural non-secondary electron yield coefficient η and, in any event, is no more than coefficient η.
The sum of natural secondary electron yield coefficient δ and natural non-secondary electron yield coefficient η is the total natural electron yield coefficient σ for the reference surface. Likewise, the sum of roughness-modified secondary electron yield coefficient δ* and roughness-modified non-secondary electron yield coefficient η* is the total roughness-modified electron yield coefficient σ* for rough face 54. As mentioned above, coefficient δ* is less than coefficient δ at the magnitude of median primary-electron striking energy 1SMD typically present in the FED of the invention. Since coefficient η* is no more than coefficient η, total roughness-modified electron yield coefficient σ* of face 54 is less than natural electron yield coefficient σ of the material that forms face 54 at the
1SMD magnitude which typically occurs in the present FED.
Natural coefficients σ, δ, and η, although determined for a smooth surface at specific primary electron impingement conditions (i.e., normal to the smooth surface), are generally considered to be properties of the material that forms the smooth surface. In the present situation, coefficients σ, δ, and η are properties of the material that forms wall face 54 without regard to the roughness in face 54.
Spacer Facial Roughness Model
To help assess how the various types of spacer facial roughness impact FED performance, the roughness in wall face 54 of
Pores 110 are arranged in a regular pattern along wall face 54. In the forward (or reverse) electron-travel direction, consecutive ones of pores 110 are laterally separated from each other by a constant spacing dS. Although not evident from
The porosity P along wall face 54 is generally given as:
P=nPAPAV (1)
where nP is the pore density along face 54, and APAV is the average cross-sectional area of a pore as viewed perpendicular to an imaginary plane (not shown) extending through the pores located along face 54. Pore density nP is the number of pores per unit projected area along face 54.
For the model of
Inasmuch as each pore 110 in
Upon combining Eqs. 1–3, porosity P along face 54 in the model of
Using Eq. 4, the spacing-to-diameter ratio dS/dP is adjusted to achieve a desired value of main wall facial porosity P. Consistent with what is described above, wall facial porosity P can be as small as 10%, the value arising from Eq. 4 when ratio dS/dP is approximately 1.8. The maximum value of wall facial porosity P attainable with the model of
Modeling parameters hP, dP, and dS are appropriately adjusted to represent any particular type of roughness in wall face 54. The adjustment of parameters hP, dP, and dS is governed by the constraint that the modeled representation of the roughness by identical pores 110 have the same value of total roughness-modified electron yield coefficient σ* that actually arises with the roughness being modeled. This broad constraint, which is normally applied at a representative value of average electric field strength EAV, is largely achieved when the facial roughness represented by pores 110 has the same value of roughness-modified secondary electron emission yield coefficient δ* that arises with the actual facial roughness.
Preferably, the adjustment of modeling parameters hP, dP, and dS is governed by the tighter constraint that the identical cylindrical pore representation of the roughness in wall face 54 have the same total electron yield as a function of electron departure energy D as occurs with the actual roughness in face 54. The tighter constraint is likewise normally applied at a representative value of field strength EAV. Similar to the broad modeling constraint, the tighter constraint is largely achieved when the identical cylindrical pore roughness representation has the same secondary electron emission yield as a function of electron departure energy
D as the actual facial roughness.
The foregoing constraints are ideal ones. While these constraints can be achieved nearly exactly for some types of roughness in wall face 54, the ideal constraints can be approximately achieved in various ways. For instance, appropriate computer modeling can be developed for the actual spacer facial roughness and then utilized to adjust modeling parameters hP, dP, and dS. Alternatively, the electron yield characteristics for the actual roughness in face 54 can be experimentally measured and then employed in adjusting parameters hP, dP, and dS.
If there is any constraint on the main wall facial porosity available with the roughness being modeled, Eq. 4 places further constraint on the adjustment of parameters dP and dS. If not, Eq. 4 simply gives the resulting value of modeled main wall facial porosity P. Note that the value of modeled porosity P may differ from the actual porosity along wall face 54 for the roughness being modeled.
An example is helpful in understanding how the model of
In the model of
A suitable modeling example for assessing the effect of parameters such as secondary-electron departure energy 2D, average electric field strength EAV, and pore characteristics hP and dP on the capture or escape of secondary electrons is the situation in which secondary electrons are emitted from the center of the bottom of a pore 110 and initially move directly out of that pore 110.
Items 112 and 114 in
Parameter hC in
At the instants that secondary electrons are emitted from the center of the bottom of pore 110 in 2D of each secondary electron is:
where me is the electron's mass, and Vy is the initial velocity of the secondary electron in the y direction. Solving Eq. 5 for velocity Vy results in:
No forces act on the secondary electron in the y direction. Velocity Vy is thus constant in the model. Accordingly, critical distance hC is given as:
where tC is the critical time that the secondary electron takes to travel distance hC in the y direction.
In the x direction, a force Fx produced by average electric field EAVîx acts on each secondary electron in the x direction according to:
Fx=meax=−eEAV (8)
where ax is the acceleration of the electron in the x direction, and e is the electron charge. Integrating Eq. 8 results in the following expression for the velocity Vx of the secondary electron in the x direction as a function of time t:
In turn, integrating Eq. 9 leads to the following expression for the distance dx that the secondary electron travels in the x direction:
At critical time tC, distance dx equals −dP/2. Consequently:
Combining Eqs. 7 and 11 to eliminate critical time tC yields:
Critical distance hC thus increases with increasing pore depth dP or secondary-electron departure energy 2D, but decreases with increasing electric field strength EAV. As mentioned above, a secondary electron is captured when critical distance hC is less than hP, and escapes when critical distance hC is greater than hP.
Secondary-electron departure energy 2D can vary somewhat as indicated earlier by the left-hand peaked portions in
2DMD for secondary-electron departure energy
2D range from 5 eV to 15 eV.
2D are taken respectively to be 1 and 30 eV. Lines 118 and 120 respectively represent Eq. 12 for the
2D values of 1 and 30 eV. A fixed value of 6 volts/μm is employed in
When pore height hP and pore diameter dP are of such values as to be in the region above line 120, all the secondary electrons emitted in the y direction from the centers of the bottoms of pores 110 with departure energy 2D less than 30 eV are captured. All the secondary electrons emitted in the y direction from the centers of the pore bottoms with departure energy
2D greater than 1 eV escape when parameters hP and dP are of such values to be in the region below line 118. Between lines 118 and 120, some of so-emitted secondary electrons with departure energy
2D between 1 and 30 eV are captured and others escape. Starting from a point in the region below line 118 where all such secondary electrons escape, pore height hP must be increased and/or pore diameter dP must be decreased to reach the region above line 120 where all such secondary electrons are captured.
It is helpful to access the capture/escape situation in terms of pore aspect ratio hP/dP. For this purpose, critical distance hC in Eq. 12 is divided by pore diameter dP to produce:
The capture/escape situation established by Eq. 13 is graphically illustrated in 2D values of 1 and 30 eV. In this case, starting from a point in the region below line 124 where all the secondary electrons emitted in the y direction from the centers of the bottoms of pores 110 with departure energy
2D less than 30 eV escape, pore aspect ratio hP/dP and/or pore diameter dP must be increased to reach the region above line 126 where all the secondary electrons emitted in the y direction from the centers of the pore bottoms with departure energy
2D greater than 1 eV are captured.
It is not necessary that all secondary electrons emitted in the y direction from the centers of the bottoms of pores 110 be captured. An adequate reduction in positive charge buildup on spacer wall 24 can be achieved when only part of these secondary electrons are captured. Also, the capture/escape criteria for secondary electrons emitted in other directions and from other locations in pores 110 are different from those modeled in
More particularly, pore height parameter hMD is the value of critical distance hC when secondary-electron departure energy 2D equals median secondary-electron departure energy
2DMD. That is:
Provided that main wall facial porosity P is at least 10%, an adequate reduction in the number of secondary electrons that escape main wall 46 is achieved in the model of 2IMD is normally in the range of 5–15 eV.
For given values of pore density nP and median primary-electron striking energy 1SMD increasing the main wall facial porosity generally leads to a reduction in the number of secondary electrons that escape rough face 54. Consistent with the porosity levels described above for the examples of
Electrical Characteristics, Constituency, and Internal Configuration of Main Spacer Body
Main wall-shaped spacer body 46 normally has a sheet resistance of 108–1016 ohms/sq. The sheet resistance of main wall 46 is preferably 1010–1014 ohms/sq., typically 1011–1012 ohms/sq. Wall 46 normally has a breakdown voltage of at least 1 volt/μm. The wall breakdown voltage is preferably greater than 4 volts/μm, typically greater than 6 volts/μm.
Main wall 46 may consist of various materials along rough faces 54 and 56. Subject to achieving the preceding electrical characteristics and dependent on the internal configuration of main wall 46, candidates for the materials that form faces 54 and 56 include (a) carbon (b) compositions of carbon and one or more of silicon, nitrogen, and hydrogen, especially compositions of carbon and silicon, (c) compositions of boron and one or more of carbon, silicon, nitrogen, and hydrogen, especially compositions of boron and nitrogen, (d) compositions of silicon and nitrogen, (e) oxides of one or more cation elements in Groups 2a, 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides, (f) hydroxides of one or more cation elements in Groups 2a, 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides, (g) nitrides of one or more cation elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides, and (h) carbides of one or more non-carbon cation elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides.
Multiple ones of the preceding candidate materials may be present along rough face 54 or 56. More particularly, the phrase “or more” as used in describing cation elements contained in candidate materials for a body means that two or more of the identified cation elements, e.g., the elements in Groups 2a, 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table for the oxide or hydroxide case, may be present in the identified body, e.g., the material that forms face 54 or 56 here.
The candidate materials may be in mixed form, such as a solid solution, a multi-phase mixture, a multi-phase mixture of solid solutions, and so on, with respect to the cation elements. For example, in the case of a solid solution of binary mixed oxide and/or binary mixed hydroxide, the body contains LuMvOw and/or LxMy(OH)z where L and M are different ones of the identified cation elements, e.g., the elements in Groups 2a, 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, u, v, w, x, y, and z are numbers, O is oxygen, and H is hydrogen. For a multi-phase mixture of binary mixed oxide and/or binary mixed hydroxide, the body contains LuOw1.MvOw2 and/or Lx(OH)z1.My(OH)x2, where w1, w2, z1, and z2 are numbers. Similarly, for a multi-phase mixture of solid solutions of binary mixed oxide and/or binary mixed hydroxide, the body contains Lu1Mv1Ow1.Lu2Mv2Ow2 and/or Lx1My1(OH)z1.Lx2My2(OH)x2, where u1, v1, u2, v2, x1, y1, x2, and y2 are numbers.
Particularly attractive oxides and hydroxides are those of beryllium, carbon, magnesium, aluminum, silicon, titanium, vanadium, chromium, manganese, iron, yttrium, niobium, molybdenum, lanthanum, cerium, praseodymium, neodymium, europium, and tungsten, including mixed oxide and/or hydroxide of two or more of these elements. Rather than being in the form of carbon dioxide, an oxide of carbon is typically in the form of carbon terminated with oxygen. Similarly, a hydroxide of carbon is typically in the form of carbon terminated with a hydroxyl group (OH−). Non-carbon oxides are ceramic. Non-carbon hydroxide is often present in the ceramic with non-carbon oxide. Except for beryllium, carbon, magnesium, aluminum, and silicon, all of the particularly attractive oxides and hydroxides are oxides and hydroxides of transition metals. Particularly attractive nitrides are those of boron, aluminum, silicon, and titanium. Particularly attractive carbides are those of boron and silicon.
Main wall 46 may be internally configured in various ways.
In
The composition of primary substrate 130 is typically relatively uniform throughout its bulk, i.e., away from rough faces 54 and 56. The composition of the bulk of substrate 130 can, however, vary somewhat from place to place. The composition of the material that forms faces 54 and 56 may be largely the same as, or somewhat different from, the material that forms the bulk of substrate 130. The thickness of substrate 130 is normally 10–100 μm, typically 50 μm.
Primary substrate 130 has the general electrical characteristics prescribed above for main wall 46. That is, the sheet resistance of substrate 130 is normally 108–1016 ohms/sq., preferably 1010–1014 ohms/sq., typically 1011–1012 ohms/sq. The breakdown voltage of substrate 130 is normally at least 1 volt/μm, preferably more than 4 volts/μm, typically more than 6 volts/μm.
Primary substrate 130 typically consists of ceramic, including glass-like ceramic. Primary candidates for the material of substrate 130 are oxides and hydroxides of one or more non-carbon elements in Groups 2a, 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides. Other candidates for the substrate material include nitrides of one or more non-carbon elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, again including the lanthanides. Further substrate material candidates are carbides of one or more non-carbon elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, again including the lanthanides. Multiple ones of these materials may be present in substrate 130. Particularly attractive oxide and hydroxide candidates for primary substrate 130 are those of beryllium, magnesium, aluminum, silicon, titanium, vanadium, chromium, manganese, iron, yttrium, niobium, molybdenum, lanthanum, cerium, praseodymium, neodymium, europium, and tungsten, including mixed oxide and/or hydroxide of two or more of these elements. In a typical implementation, substrate 130 consists largely of oxide of one or more of aluminum, titanium, and chromium. Other particularly attractive substrate candidates are aluminum nitride and silicon carbide.
b illustrates an embodiment in which main wall 46 is a primary wall-shaped electrically non-conductive spacer body consisting of a wall-shaped electrically non-conductive core substrate 132, which provides mechanical strength, and a pair of rough-faced electrically non-conductive layers 134 and 136 respectively situated on the opposite faces of wall-shaped core substrate 132. Rough-faced layers 134 and 136, which are largely identical, may connect to each other around the ends and/or side edges of substrate 132. The outside faces of rough layers 134 and 136 respectively form rough faces 54 and 56. Substrate 132 may have, but need not have, significant facial roughness. Any facial roughness of substrate 132 is normally much less than the roughness of faces 54 and 56. The thickness of substrate 132 is normally 10–100 μm, typically 50 μm.
The roughness in faces 54 and 56 of layers 134 and 136 can be achieved in various ways, including all the ways shown in
Core substrate 132 normally has approximately the same general electrical characteristics as primary substrate 130. Accordingly, the sheet resistance of core substrate 130 is normally approximately 108–1016 ohms/sq., preferably approximately 1010–1014 ohms/sq., typically approximately 1011–1012 ohms/sq. The breakdown voltage of substrate 132 is normally at least approximately 1 volt/μm, preferably more than approximately 4 volts/μm, typically more than approximately 6 volts/μm.
Each of rough layers 134 and 136 is of much greater sheet resistance than core substrate 132. Specifically, the sheet resistance of layer 134 or 136 is normally at least ten times, preferably at least one hundred times, the sheet resistance of substrate 132. This corresponds to each of layers 134 and 136 normally being at least ten times, preferably being at least one hundred times, greater resistance per unit length than substrate 132, the length dimension for resistance being taken from end electrode 52 to end electrode 50 (or vice versa). Equivalently stated, for the situation in which layers 134 and 136 each extend fully along the length of substrate 132, the resistance of each of layers 134 and 136 is normally at least ten times, preferably at least one hundred times, the resistance of substrate 132. With layers 134 and 136 being much more electrically resistant than substrate 132, layers 134 and 136 determine the electron-emission characteristics of main wall 46 while substrate 132 determines other electrical characteristics of wall 46. This separation of electronic functions facilitates spacer design.
Each of rough layers 134 and 136 normally has an average electrical resistivity of 108–1014 ohm-cm at 25° C. The average electrical resistivity of layer 134 or 136 is preferably 109–1013 ohm-cm, more preferably 109–1012 ohm-cm, at 25° C. As mentioned above, electrically resistive materials have an electrical resistivity of 1–1012 ohm-cm at 25° C., while electrically insulating materials have an electrical resistivity of greater than 1012 ohm-cm at 25° C. Consequently, layers 134 and 136 may be electrically resistive or electrically insulating. Substrate 132 is typically electrically resistive, but may be electrically insulating.
Each of rough layers 134 and 136 is normally no more than 20 μm thick. The minimum thickness of layer 134 or 136 is normally 20 nm. The average thickness of each of layers 134 and 136 is normally 20–1,000 nm, preferably 20–500 nm. These thickness specifications, along with the preceding specifications on sheet resistance, resistance, resistance per unit length, and electrical resistivity, apply especially to the situation in which layers 134 and 136 are porous layers.
Subject to meeting the preceding electrical characteristics, core substrate 132 typically consists of ceramic, including glass-like ceramic. The candidates for the ceramic in substrate 132 include all the materials described above for primary substrate 130. The particularly attractive candidates for substrate 130 are also particularly attractive for substrate 132.
Rough layers 134 and 136 likewise typically consist of ceramic, including glass-like ceramic. Candidate materials for layers 134 and 136 are (a) carbon, (b) compositions of carbon and one or more of silicon, nitrogen, and hydrogen, especially compositions of carbon and silicon, (c) compositions of boron and one or more of carbon, silicon, nitrogen, and hydrogen, especially compositions of boron and nitrogen, (d) compositions of silicon and nitrogen, (e) oxides of one or more elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides, (f) hydroxides of one or more elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides, (g) nitrides of one or more elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides, and (h) carbides of one or more non-carbon elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides.
Particularly attractive oxide and hydroxide candidates for rough layers 134 and 136 are those of carbon, aluminum, silicon, titanium, vanadium, chromium, manganese, iron, yttrium, niobium, molybdenum, lanthanum, cerium, praseodymium, neodymium, europium, and tungsten, including mixed oxide and/or hydroxide of two or more of these elements. In an example described further below in connection with
c and 11d illustrate two embodiments in which a pair of generally conformal electrically non-insulating coatings 138 and 140 are respectively situated on opposite faces of a primary rough-faced wall-shaped electrically non-conductive body. The term “conformal” here means that coatings 138 and 140 approximately conform to the surface topology of the underlying primary wall and thus approximately replicate its facial roughness. The outside faces of conformal coatings 138 and 140 respectively form rough faces 54 and 56 of main wall 46. Coatings 138 and 140 consist of material whose total natural electron yield coefficient σ is less than coefficient σ of the underlying material of the primary wall. Total natural electron yield coefficient σ of coatings 138 and 140 is normally no more than 2.5, preferably no more than 2.0, more preferably no more than 1.6.
Two effects operate together in the embodiments of
The primary wall in
The thickness of each of conformal coatings 138 and 140 is normally 1–100 nm, typically 5–50 nm. In the embodiment of
Subject to the specifications given above for total natural electron yield coefficient σ, conformal coatings 138 and 140 may be formed with various materials including (a) carbon, (b) compositions of carbon and one or more of silicon, nitrogen, and hydrogen, (c) compositions of boron and one or more of carbon, silicon, and nitrogen, (d) oxide of one or more of titanium, chromium, manganese, iron, yttrium, niobium, molybdenum, cerium, praseodymium, neodymium, europium, and tungsten, (e) hydroxide of one or more of titanium, chromium, manganese, iron, yttrium, niobium, molybdenum, cerium, praseodymium, neodymium, europium, and tungsten, and (f) nitrides of one or more of aluminum and titanium. Two or more of these materials, including oxide and/or hydroxide in mixed form, may be present in coatings 138 and 140.
Carbon, cerium oxide, chromium oxide, manganese oxide, and neodymium oxide are especially attractive for conformal coatings 138 and 140. In one implementation, coatings 138 and 140 consist of carbon in the form of one or more of graphite, amorphous carbon, and diamond-like carbon. The material, either rough-faced substrate 130 or rough layers 134 and 136, that directly underlies coatings 138 and 140 in this implementation consists of oxide of one or more of aluminum, silicon, titanium, chromium, and iron.
Main wall 46 may consist of magnetic material along rough faces 54 and 56. The magnetic material causes the number of secondary electrons that escape each spacer 24 to be further reduced.
In
For comparison purposes, dashed line 144 in 2D, and in the same departure direction, as the secondary electron that follows trajectory 114 in
As the secondary electron leaves the magnetic pore surface in
The magnetic material typically consists of ceramic, including glass-like ceramic. Candidates for the magnetic ceramic typically include (a) oxides of one or more elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides, and (b) hydroxides of one or more elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a, of Periods 2–6 of the Periodic Table, including the lanthanides. The magnetic material can be used to implement any of substrate 130, rough layers 134 and 136, and conformal coatings 138 and 140 in
Fabrication of Flat-Panel Display, Including Spacer
The present FED is manufactured in the following manner. Backplate structure 20, faceplate structure 22, spacer walls 24, and the peripheral outer wall (not shown) are fabricated separately. Components 20, 22, and 24 and the outer wall are then assembled to form the FED in such a way that the pressure in sealed enclosure 26 is at a desired high vacuum level, typically 10−7 torr or less. During FED assembly, each spacer wall 24 is suitably positioned between plate structures 20 and 22 such that each of rough faces 54 and 56 extends approximately perpendicular to both of plate structures 20 and 22.
Spacer 24 can be fabricated in a variety of ways. In one general spacer fabrication process, the starting point is a flat structural substrate that serves as a precursor to core substrate 132 in
Using a suitable cutting device such as a saw, the resulting combination of the precursor substrate, the patterned face-electrode layer, and the protective layer is cut into multiple segments. Each segment of the precursor substrate in the combination constitutes one of core substrates 132. Although the cuts may extend partway into the support structure, the support structure remains intact. At this point, one or more face electrodes formed from the patterned face-electrode layer are situated on the upper face of each substrate 132.
A shadow mask is placed above core substrates 132 and the overlying material, including above the segments of the protective layer, at the intended locations for the side edges of substrates 132, i.e., the substrate edges that extend in the forward (or reverse) electron-travel direction and thus perpendicular to the ends of substrates 132. With the segments of the protective layer overlying substrates 132, electrically non-insulating end-electrode material is deposited on the ends of substrates 132 to form end electrodes 50 and 52 on opposite ends of each substrate 132. The shadow mask prevents the end-electrode material from being deposited on the side edges of substrates 132. The segments of the protective layer are removed. Substrates 132, along with the various electrodes, are removed from the support structure by dissolving the remainder of the adhesive.
Rough-faced layers 134 and 136 are subsequently formed on opposite faces of each core substrate 132 to produce main wall 46 of
Various modifications can be made to the preceding spacer fabrication process. As one alternative, a pair of rough-faced layers that serve as precursors to rough layers 134 and 136 can be respectively provided on the opposite faces of the precursor substrate before the bonding operation at the beginning of the fabrication process. The resulting combination is then bonded along the rough face of one of layers 134 and 136 to the support structure. Subject to this change, further processing is performed as described above. In each final spacer wall 24, the patterned face-electrode material overlies one of rough layers 134 and 136. If conformal coatings 138 and 140 are present, one of them overlies the patterned face-electrode material.
As another alternative, both the formation of the rough-faced precursors to rough layers 134 and 136 and the formation of a pair of conformal coatings that serve as precursors to conformal coatings 138 and 140 can be performed before the bonding operation. The resulting structure at this point appears, in part, as shown in
In the first-mentioned alternative, a rough-faced generally wall-shaped substrate that serves as a precursor to rough-faced substrate 130 can replace the combination of the precursor to core substrate 132 and the precursors to rough layers 134 and 136. Main wall 46 in resulting spacer wall 24 therefore appears as shown in
The patterned face-electrode layer is typically formed by depositing a blanket layer of the desired face-electrode material and selectively removing undesired parts of the face-electrode material using a suitable mask to prevent the face-electrode material from being removed at the intended locations for the face electrodes. Alternatively, the patterned face-electrode layer can be selectively deposited using, for example, a shadow mask to prevent the face-electrode material from accumulating at undesired locations. When the patterned face-electrode material overlies one of conformal coatings 138 and 140 and/or one of rough layers 134 and 136, use of this alternative avoids possible contamination of rough faces 54 and 56 with material used in forming the face electrodes.
Other modifications can be made to the foregoing spacer fabrication process. For example, the support structure can be eliminated. End electrodes 50 and 52 can be formed in different ways than described above. Instead of cutting the precursor substrate into core substrates 132 and then using a shadow mask to prevent the end-electrode material from being deposited on the side edges of substrates 132, the precursor substrate and overlying material can be cut into strips that each contain a row (or column) of substrates 132 arranged side edge to side edge. After the end-electrode material is deposited, the strips are then cut into segments that each contain one substrate 132. In some cases, the formation of end electrodes 50 and 52 and/or the formation of face electrodes such as face electrodes 48 can be eliminated. The spacer fabrication process is then simplified accordingly.
All of the steps involved in the formation of the patterned face-electrode material, end electrodes 50 and 52, rough layers 134 and 136, and conformal coatings 138 and 140, to the extent that these components are present, can be performed directly on each substrate 130 or 132 rather than on a larger precursor to each substrate 130 or 132. In the general spacer fabrication process first mentioned above and in the variations, the end result is that spacers 24, each containing at least a segment of the material that variously forms substrate 130 or 132, layers 134 and 136, when present, and coatings 138 and 140, when present, are positioned between plate structures 20 and 22.
Fabrication of Main Wall of Spacer
a–13d (collectively “FIG. 13”),
a–18e (collectively “FIG. 18”) illustrate a process sequence for manufacturing a sixth variation of main wall 46 according to the invention.
The starting point for the process sequence of
Various techniques can be utilized to form thin-film composites 150 and 152 on core substrate 132. If the further material is liquid, part of a liquidous composition of the support material and the further material can be deposited on both faces of core substrate 132. Spinning may be utilized to ensure that composites 150 and 152 are of relatively uniform thickness. Alternatively, core substrate 132 can be dipped in the liquidous composition.
If the further material is solid, a liquidous composition of the support material, the further material, and a suitable liquid is prepared. Layers of the liquidous composition are respectively formed on both faces of core substrate 132. Either a deposition step, typically including a spinning step, or a dipping step of the type described in the previous paragraph can be utilized to form the liquidous layers. A drying operation is performed to remove at least part of the liquid, thereby creating thin-film composites 150 and 152.
At least part of the further material in thin-film composites 150 and 152 is removed to convert them into solid porous layers that respectively implement rough-faced layers 134 and 136.
If conformal coatings 138 and 140 are to be provided over rough layers 134 and 136, the combination of core substrate 132 and layers 134 and 136 in
Depending on various factors, pores 154 and either pores 64 or pores 160 in
Various procedures may be utilized to go from the stage of
The carbon-containing material may be liquid or solid. If the carbon-containing material is liquid, pyrolysis in an oxidizing environment is normally employed to remove the carbon-containing material. The pyrolysis typically entails subjecting the structure consisting of core substrate 132 and composites 150 and 152 to a temperature of 200–900° C., typically 400–600° C., in air or oxygen. The structure of
The carbon-containing material may be, or may include, a polymeric precursor. If so, polymerization of the polymeric precursor may occur in going from the point at which the precursor is initially provided over core substrate 132 to the stage of
In another process for going from the stage of
The gels or liquid-filled open solid networks are created from a ceramic polymeric precursor or from ceramic particles. Thin-film solid composites 150 and 152 in this procedure can be generally formed according to the porous-ceramic preparation techniques described in Saggio-Woyansky et al, “Processing of Porous Ceramics,” Technology, November 1992, pages 1674–1682, or the sol-gel techniques described in Hench et al, “The Sol-Gel Process,” Chem. Rev., Vol. 90, No. 1, pages 33–72, and Brinker et al, “Sol-Gel Thin Film Formation,” J. Cer. Soc. Japan, Cent. Mem. Iss., Vol. 99, No. 10, 1991, pages 862–877. The contents of Saggio-Woyansky et al, Hench et al, and Brinker et al are incorporated by reference herein.
When composites 150 and 152 are polymeric gels, the support material in the gels typically consists of polymerized alkoxide. The ceramic cations in the gels are typically silicon and/or one or more other non-carbon elements in Groups 3b, 4b, 5b, 6b, 7b, 8, 1b, 2b, 3a, and 4a of Periods 2–6 of the Periodic Table, including the lanthanides. At least part of the liquid in each gel is typically a byproduct of the gel processing.
Rough layers 134 and 136 are created as porous layers by removing at least part of the liquid in the gels or liquid-filled open solid networks without causing the support material to fully collapse and complete fill the space previously occupied by the removed liquid. Heat is normally applied to the porous layers to reduce their porosity to a desired level. Further polymerization or other cross-linking may occur in the course of removing the liquid, especially during the heat treatment. In
A third procedure for going from the stage of
In a general fourth procedure for going from the stage of
Turning to the process sequence of
A liquidous composition, or slurry, is prepared from a liquid, particles of a support material, and further particles of different chemical composition than the support material. The chemical nature of the support material is normally chosen such that, in final spacer wall 24, total natural electron yield coefficient σ of the support material is relatively low, normally no more than 2.0, preferably no more than 1.6. For this purpose, the support material is typically an oxide of metal such as chromium or/and neodymium. The further particles typically consist of organic material such as latex or/and polystyrene.
The further particles are normally rounded. Preferably, the further particles are roughly spherical so they have roughly constant radius of curvature. The further particles have an average diameter in the range of 50–500 nm. The average diameter of the further particles is typically relatively uniform from particle to particle but can vary significantly from one particle to another.
Portions of the liquidous composition are provided on the two faces of core substrate 132 to respectively form thin liquidous bodies, or films, 170 and 172. See
Liquidous films 170 and 172 can be formed by depositing parts of the liquidous composition on the opposite faces of core substrate 132. A spinning step can be performed to ensure that the thickness of each of films 170 and 172 is relatively uniform. Alternatively, core substrate 132 can be dipped in the liquidous composition to form films 170 and 172.
The liquid in thin films 170 and 172 is removed to produce the structure shown in
In the illustrated example, no more than a monolayer of rounded particles 174 is present in each of thin-film composites 178 and 180. The formation of liquidous films 170 and 172 and the removal of the liquid in films 170 and 172 is done in such a manner that particles 174 protrude out of support material 182 in composites 178 and 180.
If liquidous films 170 and 172 each consist of more than a monolayer of rounded particles 174, more than a monolayer of particles 174 is present in each of thin-film composites 178 and 180. In that case, parts of those particles 174 most distant from core substrate 132 protrude out of support material 182. Other particles 174 are fully covered by material 182.
When no more than a monolayer of rounded particles 174 is present in each of thin-film composites 178 and 180, all (or largely all) of rounded particles 174 are removed from composites 178 and 180 to produce the structure shown in
The removal of part or (largely) all of particles 174 from thin-film composites 178 and 180 acts to roughen their exterior faces, thereby converting composites 178 and 180 respectively into rough layers 134 and 136. An etching operation is typically employed to perform the particle removal. The etching operation can be done with a plasma, according to a reactive-ion etch technique, chemically, electrochemically, or using two or more of these etching techniques. Depending on the characteristics of particles 174 relative to support material 182, particles 174 may also be removed by bombarding them with an ion beam. When particles 174 consist of organic material, pyrolysis may be performed in an oxidizing environment to remove particles 174. The pyrolysis temperature is 200–900° C., typically 400° C.–600° C. Should the thickness of each of composites 178 and 180 be in the vicinity of 1 μm or less, the pyrolysis temperature can readily be lowered to as little as 250° C.
If conformal coatings 138 and 140 are not to be provided over rough layers 134 and 136 in the process sequence of
If conformal coatings 138 and 140 are to be provided over rough layers 134 and 136, the combination of core substrate 132 and layers 134 and 136 in
Instead of providing portions of the above-mentioned liquidous composition on the two faces of core substrate 132, portions of a liquidous composition of the support-material particles, the generally rounded particles, and the liquid can be provided on a generally flat surface of an auxiliary body to a thickness greater than that needed for primary substrate 130 in
The rounded particles are then removed along the two faces of the flat-solid composite to form primary substrate 130 or a larger wall-shaped precursor substrates from which multiple substrates 130 can be made. For convenience, both substrate 130 and the larger precursor substrate are referred to as the “primary substrate” and are identified by reference symbol “130”. If conformal coatings 138 and 140 are not to be provided on the two faces of primary substrate 130, the resulting structure implements main wall 46 of
The process sequence of
The further particles, such as rounded particles 174, can be replaced with further material that is dispersed throughout the support material on a microscopic, e.g., atomic or molecular, scale. For example, a wall-shaped electrically non-conductive primary body that serves as a precursor to primary substrate 130, or to the combination of core substrate 130 and rough layers 134 and 136, may contain silicon and carbon, at least along the two opposite faces of the primary body. An operation is performed to roughen both faces of the primary body by preferentially removing silicon from the faces. The resultant rough faces of the primary body consist primarily of carbon. This variation of the process sequence of
In the preceding variation, material other than silicon may be present with carbon along the primary body's initial face. This other material is preferentially removed during the above-mentioned removal step so as to roughen both of the primary body's faces in such a way that they consist primarily of carbon. The removal of the silicon and/or other material can be performed in various ways such as etching. The etching can be done chemically, electrochemically, with a plasma, by reactive-ion etching, or by ion bombardment.
Only part of material of rounded particles 174 may be removed. The remainder of the particle material then coats the insides of pores 190 and 184. For example, when particles 174 consist of organic material, pyrolysis can be performed on particles 174 to largely remove their non-carbon material. The carbon that was in particles 174 then coats the insides of pores 190 and 184. The pyrolysis is done in a non-oxidizing (or non-reactive) environment at a temperature sufficient to cause the organic material to decompose into carbon material and non-carbon material. Most of the pyrolized non-carbon material normally becomes volatile during the pyrolysis and separates from the structure. The pyrolysis temperature is normally 200–900° C., typically 400–600° C.
With the foregoing in mind, a lower layer 200 of support material is formed on the upper face of core substrate 132 as shown in
Lower support layer 200 serves two basic purposes. Firstly, support layer 200 acts as an adhesive (or adhesion) layer. That is, layer 200 adheres well to core substrate 132 and to additional material deposited on layer 200. Secondly, layer 200 is of lower total natural electron yield coefficient σ than core substrate 132 and, in final spacer wall 24, is sufficiently thick to block the less desirable a characteristics of core substrate 132. In final wall 24, coefficient σ of the support material in layer 200 is normally no more than 2.0, preferably no more than 1.6. The foregoing purposes are typically achieved by creating layer 200 as an oxide of metal such as chromium or neodymium.
A layer 202 of further particles 204 is deposited on lower support layer 200 to a thickness of one or more particle diameters. That is, the thickness of particle layer 202 is a monolayer or more of further particles 204. See
An upper layer 206 of support material is formed in the space between rounded particles 204 as shown in
The chemical nature of the support material in upper layer 206 is chosen such that, in final spacer wall 24, total natural electron yield coefficient σ of the support material in layer 206 is relatively low, normally no more than 2.0, preferably no more than 1.6. The support material in layer 206 is thus normally of lower coefficient σ than core substrate 132. Upper layer 206 typically consists of the same support material as lower layer 200. Hence, layer 206 is typically formed as an oxide of metal such as chromium or neodymium.
Rounded particles 204 in the topmost level and any underlying particles 204 that substantially touch topmost particles 204 or are substantially coupled to topmost particles 204 through one or more intervening particles 204 are removed. Also, particles 204 exposed to the external environment through various openings in support layer 206 are simultaneously removed. See
Depending on how the particle-removal operation is performed, some particles 204, or combinations of particles 204, that are fully surrounded by layer 134 may not be fully removed. The unremoved material of these particles 204, two examples of which are illustrated in
The particle-removal operation can be performed in various ways. When rounded particles 204 consist of organic material, the particle-removal operation is typically done by pyrolysis in an oxidizing environment. The pyrolysis temperature is 200–900° C., typically 400–600° C. when the oxidizing environment is air or oxygen. By using ozone or nitrous oxide as the oxidizing environment, the pyrolysis temperature can be reduced. If the composite thickness of support layers 200 and 206 is in the vicinity of 1 μm or less, the pyrolyis temperature can be readily be as low 250° C. When support layers 200 and 206 consist primarily of chromium oxide, the pyrolysis causes the chromium oxide to densify. Alternatively, particles 204 can be removed by any of the etching techniques utilized to remove rounded particles 174 in the process sequence of
When rough layer 134 consists primarily of chromium oxide in the process sequence of
If desired, conformal coating 138 can be formed-over rough layer 134 in the process sequence of
The process sequence of
The starting point for the process sequence of
Primary substrate 130 or rough layer 134 has a rough face 210 defined by grains 68. Adjoining ones of grains 68 form valleys 70 along rough face 210. As described above, each valley 70 has a pair of outer-grain upper-half surfaces 72B and 72F that are continuous with each other. For each valley 70, outer-grain upper-half surface 72B is closest to backplate structure 20, while outer-grain upper-half surface 72F is closest to faceplate structure 22. At the stage of
Referring to
Part of the material along the rough face of primary substrate 130 or rough layer 134 is removed during the etching step. Because ions 212 impinge on the rough face at average angle β relative to the forward electron-travel direction, more material is removed from the half of each valley 70 closest to faceplate structure 22 than from the half of each valley 70 closest to backplate structure 20. Consequently, the average steepness of outer-grain upper-half surfaces 72F is now greater than the average steepness of outer-grain upper-half surfaces 72B. Using the terminology employed above in connection with
Ions 212 are normally particles that physically erode the rough face of primary substrate 130 or rough layer 134 but do not otherwise significantly interact with grains 68. For example, no significant chemical activity normally occurs between ions 212 and grains 68. Ions 212 are typically inert gas ions such as argon ions. Instead of ions 212, the etch operation can be performed with other particles, such as ionized atom clusters or/and abrasive powders, that directly erode the rough surface of primary substrate 130 or rough layer 134 in the preceding manner without otherwise significantly interacting with grains 68. Alternatively, ions 212 or these other particles may chemically react with grains 68 in addition to physically eroding grains 68 in the directional manner described above. The chemical reaction serves to enhance the erosion caused by the ion bombardment.
If conformal coating 138 is not to be provided over primary substrate 130 or rough layer 134, the etch with ions 212 transforms initial rough face 210 into further roughened face 54. The structure in
Moving to the process sequence of
Metal layers 220 and 222 are then anodically oxidized to convert them into porous layers that respectively implement rough layers 134 and 136. See
If conformal coatings 138 and 140 are not to be provided on rough layers 134 and 136, main wall 46 appears as shown in
If conformal coatings 138 and 140 are to be provided over rough layers 134 and 136, the combination of core substrate 132 and layers 134 and 136 in
The techniques employed in
The trenches can be formed directly in primary substrate 130 or in rough layers 134 and 136 that overlie core substrate 132. The so-trenched structure forms main wall 46 or can be cut up to form multiple main walls 46. Conformal coatings 138 and 140 can also be added to the trenched structure that implements each wall 46.
Alternatively, starting with a wall-shaped primary body having a pair of opposing generally smooth faces, protuberances can be formed on both smooth faces to convert them into rough faces. The protuberances can be in a regular pattern as exemplified by ridges 82 in
Similar to the trenches, the ridges can be formed directly on primary substrate 130 or on rough layers 134 and 136. The so-ridged structure forms main wall 46 or can be cut up to form multiple walls 46. Conformal coatings 138 and 140 can also be added to the ridged structure that implements each wall 46.
The process sequence of
A precursor layer 240 of pedestal material is deposited on the upper face of core substrate 132 as depicted in
Particles 242 are provided at largely random locations on the upper face of precursor pedestal layer 240. See
Using particles 242 as etch masks, the pedestal material not covered by particles 242 is removed with a suitable etchant.
Particles 242 may, or may not, be removed. If particles 242 remain in place and if conformal coating 138 is not to be provided over rough layer 134 in the process sequence of
Turning to the process variation of
The starting point for the process sequence of
If conformal coatings 138 and 140 are not to be provided over rough layers 134 and 136 in the process sequence of
If conformal coatings 138 and 140 are to be provided over rough layers 134 and 136 in the process sequence of
When conformal coatings 138 and 140 consist of carbon, one technique for creating coatings 138 and 140 of carbon is to chemically vapor deposit carbon on primary substrate 130 or on a larger wall-shaped primary body from which multiple substrates 130 can be made. Similarly, carbon can be chemically vapor deposited on rough walls 134 and 136 or on a larger wall-shaped primary body from which multiple main walls 46 containing components 132, 134, and 136 can be made.
Another technique for creating conformal coatings 138 and 140 of carbon is to thermally decompose carbon-containing material over primary substrate 130 or on a larger wall-shaped primary body from which multiple substrates 130 can be made. Likewise, coatings 138 and 140 can be formed as carbon by thermally decomposing carbon-containing material over the exterior faces of rough layers 134 and 136 or over the exterior faces of a larger wall-shaped primary body from which multiple main walls 46 containing components 132, 134, and 136 can be made. The carbon containing material is typically a hydrocarbon such as ethyne (acetylene). When primary substrate 130 or rough layers 134 and 136 consist of porous silicon oxide, typically of the aerogel-type, the thermal decomposition of ethyne to form carbon is typically done at 500–800° C.
An anneal operation is conducted in the course of forming primary substrate 130 as porous silicon oxide of the aerogel-type or in forming a porous aerogel-type silicon-oxide wall-shaped primary body from which multiple substrates 130 can be made. An anneal operation is likewise conducted in forming porous silicon oxide of the aerogel type on core substrate 132 to create rough layers 134 and 136 or in forming a pair of thin porous aerogel-type silicon-oxide layers on a wall-shaped substrate to create a structure from which multiple main walls 46 containing components 132, 134, and 136 can be made. Thermal decomposition of carbon-containing material to form conformal coatings 138 and 140 as carbon can be done during these anneal operations. Again, the carbon-containing material is typically a hydrocarbon such as ethyne.
Additional Variations
Directional terms such as “lateral”, “above”, and “below” 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 CRT 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 spacers in the spacer system 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 a circle, an oval, or a rectangle. As viewed along the length of a spacer consisting of a combination of walls, the spacer can be shaped as a “T”, an “H”, or a cross.
The sheet resistance R□ of a spacer of arbitrary shape is approximately:
where R is the spacer's resistance between plate structures 20 and 22, PDAV is the average dimension of the perimeter of the spacer as viewed in the forward (or reverse) electron-travel direction, and L is the length of the spacer in the forward (or reverse) electron-travel direction. Ignoring the thickness of a wall-shaped spacer (including a spacer shaped like a curved wall), perimeter PDAV of a wall-shaped spacer is twice its average width WAV as viewed in the forward electron-travel direction. For a wall-shaped spacer, Eq. 15 simplifies to:
By using Eqs. 15 and 16, the sheet resistance information specified above for main wall 46 in wall-shaped spacer 24 can be correlated to that appropriate to a spacer shaped as a post, as a combination of walls, or in another configuration besides a single wall.
Field emission includes the phenomenon generally termed surface conduction emission. Backplate structure 20 that operates in field-emission mode can be replaced with an electron emitter that operates according to thermionic emission or photoemission. Rather than using control electrodes to selectively extract electrons from the electron-emissive elements, the electron emitter 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.
This is a division of U.S. patent application Ser. No. 09/210,085, filed 11 Dec. 1998, now U.S. Pat. No. 6,617,772 B1.
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