Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J31/00—Cathode ray tubes; Electron beam tubes
  • H01J31/08—Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
  • H01J31/10—Image or pattern display tubes, i.e. having electrical input and optical output; Flying-spot tubes for scanning purposes
  • H01J31/12—Image or pattern display tubes, i.e. having electrical input and optical output; Flying-spot tubes for scanning purposes with luminescent screen
  • H01J31/123—Flat display tubes
  • H01J31/125—Flat display tubes provided with control means permitting the electron beam to reach selected parts of the screen, e.g. digital selection
  • H01J31/127—Flat display tubes provided with control means permitting the electron beam to reach selected parts of the screen, e.g. digital selection using large area or array sources, i.e. essentially a source for each pixel group

Definitions

• the present invention relates to a display screen without moire effect. It finds an application in the production of any display devices, in particular microtips, also called field effect ("Field Emission Display” in English or FED for short).
• field effect Field Emission Display
• moiré effect is meant a moiré effect sufficiently attenuated so as not to be visible to an observer.
• a field effect display screen is described in particular in document FR 2 623 013.
• the essentials of this device are shown in the appended figures 1 and 2.
• the device shown in these figures comprises, on a substrate 2, for example made of glass, a thin layer of silica 4 and, on this layer, a plurality of electrodes 5 in the form of parallel conductive strips playing the role of cathode conductors and constituting addressing columns. These cathode conductors are covered by a continuous resistive layer 7 (except on the ends to allow the connection of the cathode conductors with polarization means 20).
• An electrically insulating layer 8, made of silica, covers the resistive layer 7.
• Electrodes 10 are formed above the insulating layer 8 in the form of parallel conductive strips. These electrodes 10 are perpendicular to the electrodes 5 and act as a grid constituting the addressing lines.
• the device also includes a plurality of elementary electron emitters (microtips), a single copy of which (for the sake of simplification) is schematically represented in FIG. 2: in each of the crossing zones (corresponding to an image or pixel point) of the cathodic conductors 5 and grids 10, the resistive layer 7 corresponding to this zone supports microtips 12, for example made of molybdenum and the grid 10 corresponding to said zone has an opening 14 facing each of the microtips.
• Each of these latter wife substantially the shape of a cone, the base of which generally rests on the layer 7 and the apex of which is situated at the level of the corresponding opening 14.
• the insulating layer 8 is also provided with openings 15 allowing the passage of the microtips 12.
• This first sub-assembly defined by the crossing zone of the cathode conductors and of the grid conductors 10 can be qualified as an "intermediate sub-assembly", possibly associated with other elements, for example an additional grid inside the screen or a filter on the face of the screen observed.
• each intermediate subset corresponds to a pixel.
• a substrate 30 covered with a conductive layer 32 serving as an anode.
• This layer is covered with a layer or strips of luminescent materials 34.
• the emissive part opposite the pixel (or intermediate subset) will be called an "anode sub-assembly".
• the size of the anode sub-assembly corresponds to that of the intermediate sub-assembly.
• the pixel is opposite three bands of luminescent materials of which only one emits at a time, the anode subset corresponds to the part of the excited band.
• the light emitted by the luminescent materials under the impact of the electrons emitted by the microtips is received by the observer 0.
• the observation is carried out on the anode side, therefore through the sub-assembly anode, on the side opposite to the excitation of luminescent materials.
• This operating mode is all the more advantageous since the entire quantity of light emitted can be returned to the intermediate sub-assembly by the use of a reflective layer placed behind the luminescent materials (this layer can be the anode itself or an additional layer, for example of aluminum).
• this layer can be the anode itself or an additional layer, for example of aluminum.
• the intermediate subset since the intermediate subset is partially transparent, it plays the role of neutral filter and thus reduces the effects linked to diffuse reflection, in the case in particular where the luminescent materials are phosphors in powder form.
• the intermediate subset defined by the crossing of a row and an addressing column can take various forms.
• the cathode conductors have a lattice structure and the gate conductors an openwork structure. This embodiment is illustrated in FIGS. 3A and 3B, which are views from above and in section respectively.
• the cathode conductors bear the reference 5a and the gate conductors the reference 10g.
• the grids have openings 11 facing the crossing zones of the conductive tracks 5a and are centered on these zones as seen in FIG. 3A.
• the grids also have holes 14a respectively opposite the microtips 12.
• each grid 10g has substantially the structure of a trellis identical to the trellis of the corresponding cathode conductor, but the trellis of this grid is offset, with respect to the trellis of the cathode conductor, by half a step parallel to the lines and d half a step parallel to the addressing columns.
• this grid has, in top view, a square surface 10a which is pierced by the holes 14a and to which four tracks 10b forming part of the lattice of this grid lead.
• the intermediate subset, through which the observation takes place, if it is generally semi-transparent, is, in reality, made up of very diverse zones if it is examined on a small scale.
• Each pixel defined by the overlap of a row and an addressing column therefore comprises a central zone (which one could call the "pupil" of the pixel) and four lateral half-parts. The four side parts separate each area from its four neighbors. Each pixel therefore has an optical transmission which is not uniform.
• FIGS. 5A and 5B show the shape of such a pixel where the central part 40 with its repetitive subsets corresponding to the mesh of the grid conductor and the cathode conductor, and the lateral parts 42a, 42b, 42c, can be discerned, 42d.
• This complex periodic structure of the intermediate subset, superimposed on the also periodic structure of the anode subset (in terms of emission as previously defined) can lead to display faults due to moiré effects. These faults are illustrated in FIGS. 5A and 5B, on the one hand, and in FIG. 6, on the other hand.
• FIGS. 5A and 5B correspond to the case where the intermediate sub-assembly and the anode sub-assembly are not rigorously aligned. This appears when there are several strips of luminescent materials (tri-color screen switched or not). It is assumed that the columns of luminescent materials placed on the anode are not strictly parallel to the addressing columns of the intermediate sub-assembly.
• FIGS. 5A and 5B are sections along a plane perpendicular to the columns, at two different places on the screen (for example at the top and at the bottom).
• the intermediate sub-assembly has the general reference 50 and is represented schematically with regions 52 corresponding to the central part of the pixels, relatively transparent zones, and half-regions 54 corresponding to the lateral, less transparent half-zones. ; the anode sub-assembly is represented in the form of the emitting luminescent strip 62.
• FIGS. 5A and 5B represent, by way of example, the case of a trichromatic screen switched or not.
• FIG. 6 shows, moreover, as well in the case of a monochrome screen as of a trichrome screen switched or not, that the light flux emitted by an anode subset 62 is not strictly the same in the direction of an observer 70 placed facing the sub-assembly 62 and in the direction of an observer 72 placed on the side, whatever the direction of movement.
• the intermediate subset necessarily presents patterns with more or less complex shapes (meshes, lattices and ...) so that variations within a single pixel cannot be avoided local transparency.
• the invention considers that what counts above all, for the observer, is the overall transparency of the intermediate subset for a given anode subset.
• the anode subsets are always of dimensions smaller (or at most equal) than the dimensions of a pixel.
• the anode subsets are smaller than the pixels. They are only the same size as for monochrome screens, or for non-switched three-color screens.
• the invention recommends giving the various sub-assemblies of the intermediate sub-assembly shapes and optical properties such as average transparency, taken at the scale of an anode sub-assembly, ie substantially constant over the entire surface of the intermediate sub-assembly.
• the intensity of the light transmitted by the intermediate sub-assembly, coming from an anode sub-assembly must remain substantially constant whatever the relative position of the anode sub-assembly with respect to the sub - intermediate assembly.
• substantially constant is meant that the quantity considered (transparency, intensity transmitted) varies by less than 10% when the intermediate subset is scanned. Preferably, this amount varies by less than 5%.
• the invention recommends a homogeneity -of- transmission of the intermediate subset on a particular scale, which is that of the anode subset.
• the present invention therefore relates to a display screen comprising:
• anode sub-assemblies each comprising a luminescent part, at least one anode sub-assembly being placed opposite an intermediate sub-assembly and which can be observed by transparency through the intermediate subsets; this screen being characterized by the fact that the intermediate sub-assemblies have, over the entire surface corresponding to the geometry of an anode sub-assembly, a substantially constant average transparency whatever the position of this surface.
• the average transparency of each intermediate subset is constant to better than ten percent.
• the elementary subsets of the pixels are repeated in a first step along a first direction and in a second step along a second direction, the second step being less than the first and being equal to a fraction of the size of the anode subsets along this second direction.
• said fraction is between 1/8 and 1/20 and, for example, close to 1/10.
• the elementary subsets of the pixels repeat in a first step along a first direction and in a second step along a second direction, these first and second directions being inclined relative to the lines and addressing columns.
• the first and second directions are inclined at 45 ° relative to the rows and the addressing columns.
• the first and / or the second pitch are equal to a fraction of the dimensions of the anode subsets. This fraction can be between 1/5 and 1/8.
• the patterns of the intermediate subset are determined, in an advantageous mode, by iterative modeling, until an average transmission of the intermediate subset is substantially constant, whatever the position of the subset. anode (on the scale of the latter).
• a spreadsheet comprising a first series of inputs for the introduction of the transmission characteristics of the patterns of an intermediate sub-assembly. This produces a first mesh of the intermediate subset.
• This spreadsheet includes a second series of inputs for the introduction of the positioning characteristics of the anode sub-assembly relative to the intermediate sub-assembly. A second mesh of the anode subset is thus produced.
• the two meshes are then superimposed for different relative positions of the anode subset with respect to the intermediate subset, and we look, for each position, at the transmission obtained.
• This step corresponds to a mathematical convolution of the anode subset by any part of the intermediate subset. If the transmission is not sufficiently constant, then the patterns of the intermediate subset are modified and the process is repeated.
• three anode sub-assemblies are opposite an intermediate sub-assembly.
• Figure 2 already described, shows schematically and in section, an emissive tip and a luminescent screen
• Figure 7 illustrates a top view of a first embodiment of the invention with elongated subsets along the lines;
• FIG. 9 illustrates, in top view, a second embodiment with sub-assemblies inclined at 45 ° to the addressing lines and columns;
• Figure 10 shows in more detail a sub-assembly inclined at 45 °.
• Figures 7 and 8 illustrate a first embodiment in which the short period required for the patterns of the intermediate sub-assembly is obtained in one direction, for example that of the columns. These patterns therefore have a double periodicity, with an elongated shape along the lines.
• FIG. 7 shows, in top view, an addressing element 90 with elongated sub-assemblies 92.
• This sub-assembly is detailed in FIG. 8.
• the microtips 94 are connected to a cathode conductor 96 in the form of a lattice.
• the grid controlling the emission has the form of a conductive strip 98 connected to conductors 100.
• Each pattern of the intermediate sub-assembly therefore has the appearance of an elongated rectangle delimited by the cathode conductors 96 and crossed in its center by the grid 98.
• the length of this rectangle can be equal to one third of the width of a pixel and the width to one tenth. This short period in the direction of the columns ensures the uniformity of the required transparency.
• FIG. 7 illustrates a second embodiment in which the periodicity is the same in two orthogonal directions, the latter being oriented at 45 ° from the addressing lines and columns.
• FIG. 9 shows a pixel in top view and FIG. 10 a pattern 120 with its microtips 122, its cathode conductors 124 and its grid conductors 126.
• the double periodicity can correspond to a pitch of the order of 1/5 to 1/8 of the dimensions of the luminescent anode sub-assembly.

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• Devices For Indicating Variable Information By Combining Individual Elements (AREA)
• Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
• Electroluminescent Light Sources (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1997
  • 1997-03-14 FR FR9703103A patent/FR2760894A1/fr not_active Withdrawn
• 1998
  • 1998-03-12 WO PCT/FR1998/000507 patent/WO1998042005A1/fr not_active Application Discontinuation
  • 1998-03-12 US US09/380,603 patent/US6262529B1/en not_active Expired - Fee Related
  • 1998-03-12 EP EP98914907A patent/EP0966751A1/de not_active Withdrawn
  • 1998-03-12 JP JP54019298A patent/JP2001516494A/ja active Pending

Non-Patent Citations (1)

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