Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
  • H01J29/467—Control electrodes for flat display tubes, e.g. of the type covered by group H01J31/123
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
  • H01J3/02—Electron guns
  • H01J3/021—Electron guns using a field emission, photo emission, or secondary emission electron source
  • H01J3/022—Electron guns using a field emission, photo emission, or secondary emission electron source with microengineered cathode, e.g. Spindt-type
• • 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 device for producing a modulated electric field at an electrode. It applies in particular to flat screens with field emission.
• Such a device comprises a cathode disposed opposite an anode.
• the cathode is a planar structure emitting electrons and the anode is another planar structure covered with a luminescent layer. These structures are separated by a space in which a vacuum has been created.
• the cathode can be a microtip source or a source equipped with an emissive material with a low threshold field (the threshold field being the electric field necessary for extracting electrons from a material), for example nanostructures or carbon.
• Sources equipped with an emissive material are used in display devices generally in two forms: a diode type structure or a triode type structure.
• FIG. 1 represents, seen in cross section, a flat screen with field emission operating according to a diode type structure.
• the cathode 1 consists of a plate of insulating material 3 supporting metal tracks 4 parallel to each other and covered with layers of an emissive material 5.
• the anode 2 is an insulating and transparent plate 6, for example made of glass, supporting conductive tracks 7 parallel to each other and perpendicular to tracks 4 of the cathode. Tracks 7 are produced by etching a layer of transparent conductive material such as mixed tin and indium oxide (ITO). The tracks 7 are covered with layers of phosphor 8.
• ITO mixed tin and indium oxide
• the cathode and anode plates are placed one opposite the other, the tracks being opposite to form a matrix structure.
• the crossing of the networks of tracks forms picture elements or pixels.
• An emissive material with a low threshold field such as carbon requires, for the emission of electrons to occur, a minimum electric field of a few V / ⁇ m between an anode track and a facing cathode track. If the spacing between these tracks is 1 mm, it is therefore necessary to apply a potential difference of a few kV, typically from 5000 to 10 000 V. This causes two main problems.
• the first problem is the voltage withstand: there is a risk of breakdown between anode and cathode and especially between two adjacent tracks.
• the second problem results from the need to switch a voltage of several kv when scanning the screen.
• This problem can be solved by reducing the space between anode and cathode, which makes it possible to reduce the potential difference between them by the same amount while maintaining the same electric field.
• the drawback of this solution is that this reduction in potential leads to a reduction in the efficiency of the phosphors and a reduction in the brightness of the screen.
• FIG. 2 shows, in cross-sectional view, a flat screen with field emission implementing such a structure.
• the cathode 11 consists of a glass plate 13 supporting metal tracks 14 parallel to each other and covered with layers 15 of an emissive material, for example carbon.
• the tracks 14 are placed at the bottom of trenches etched in a layer of insulating material 10, this layer 10 being covered with a metal layer 19 serving as an extraction grid.
• the anode 12 can be formed of a transparent plate 16 supporting for example a transparent and conductive layer 17 covered with a layer of luminescent material 18.
• An emission of electrons by the emissive material can be obtained by applying, between grid extraction 19 and track 14, a potential difference such that the resulting electric field at the level of the emissive material is greater than the threshold field of this material, typically a few V / ⁇ m.
• the distance separating the extraction grid from the tracks being much smaller than the distance separating the anode from the cathode, the difference in potential to be applied is correspondingly reduced.
• the electric field lines going from tracks 14 to the extraction grid 19 a large part of the emitted electrons will be trapped by the grid.
• the triode-type structure therefore has the drawback resulting from the fact that very few of the emitted electrons reach the phosphor layer.
• Such a display device with a triode type structure therefore makes it possible to avoid the risks of electrical breakdown and the problems of switching high voltages.
• these improvements are obtained at the expense of the density of emitted electrons that reach the phosphor layer.
• this type of structure requires the deposition of the emissive material only at the bottom of the trenches, which presents significant difficulties.
• the present invention solves the problems set out above.
• the solution consists in applying an electric modulation field near an electrode in the vicinity of which one wants to obtain an electric field of determined value.
• the electric modulation field will have the effect of decreasing or increasing the value of the electric field in the vicinity of the electrode in question.
• a first object of the invention relates to a device making it possible to produce an electric field between a first electrode and a second electrode, comprising:
• control means for applying a potential difference between the means forming the modulation electrode and the first electrode so as to obtain, by the contribution of said potential differences, another predetermined value of electric field in said vicinity of the first electrode.
• the means for applying a potential difference between the first and the second electrode and the control means provide potential differences such that the value of the electric field in said vicinity of the first electrode is greater than the value which would be due to the only potential difference between the first and the second electrode.
• the means for applying a potential difference between the first and " the second electrode and the control means provide potential differences such that the value of the electric field in said vicinity of the first electrode is less than the value which would be due to the only potential difference between the first and the second electrode.
• the first and second electrodes and the means forming the modulation electrode are arranged in parallel planes.
• the modulation electrode means may comprise two electrodes framing the first electrode.
• the modulation electrode means can consist of a single electrode.
• a second object of the invention relates to a method for producing an electric field between a first electrode and a second electrode, comprising:
• the application of the potential difference between the first and the second electrode is such that, if this potential difference were applied alone, the electric field in said vicinity of the first electrode would be greater than said other predetermined value.
• the application of the potential difference between the first and the second electrode is such that, if this potential difference were applied alone, the electric field in said vicinity of the first electrode would be less than said other predetermined value.
• a third object of the invention relates to a field emission display screen comprising an anode plate and a cathode plate arranged facing each other, the anode plate comprising on its face internal to the screen at least one electrode supporting phosphor means, the cathode plate comprising on its internal face to the screen at least one electrode emitting electrons at least partially opposite the anode electrode, this cathode electrode becoming emitting electrons when the electric field in its vicinity exceeds a threshold value, the screen also comprising means for applying a potential difference between said anode electrode and said cathode electrode, characterized in that the screen also comprises modulation electrode means close to the cathode electrode, either in the same plane as it, or so that one electrode "cathode is interposed e between the anode electrode and - said modulation electrode means, the screen also comprising control means for applying a potential difference between the cathode electrode and the modulation electrode means, the means for applying potential differences are such that they make it possible to obtain in said vicinity of the cathode
• the means for applying a potential difference between said anode electrode and said cathode electrode are such that, in the absence of a potential difference applied between the cathode electrode and the electrode means modulation, said predetermined electric field value is less than said threshold value.
• the means for applying a potential difference between said anode electrode and said cathode electrode are such that, in the absence of a potential difference applied between the cathode electrode and the electrode means modulation, said predetermined electric field value is greater than said threshold value.
• the modulation electrode means may comprise two electrodes framing the cathode electrode.
• the modulation electrode means may consist of a single electrode.
• the cathode electrode and the means forming the modulation electrode are separated by a layer of insulating material.
• the cathode electrode comprises a conductive element on which is deposited a layer of emissive material.
• This layer of emissive material can be separated from the conductive element by a resistive layer.
• the emissive material layer may cover only part of the resistive layer.
• the emissive material can be a material deposited on the resistive layer by means of a catalyst material deposited on the resistive layer and on which the emissive material is preferentially deposited.
• the display screen is advantageously of the matrix type, the crossing of lines and columns defining pixels.
• the anode plate comprises a common electrode supporting phosphor means
• the cathode plate comprises a plate supporting lines' of conductors constituting the means forming modulation electrode, covered with a layer of dielectric material, the layer of dielectric material supporting columns of conductors, the rows and columns forming a matrix arrangement connected to addressing means and defining pixels, the columns of conductors supporting an emissive material.
• Each pixel can correspond to the crossing of a row and several column conductors.
• the lines of conductors have windows facing the columns of conductors, the emissive material supported by the columns of conductors being present only in the areas of the columns of conductors corresponding to the windows.
• a fourth object of the invention relates to a method of using a field emission display screen comprising at least one anode electrode and at least one facing cathode electrode, the cathode electrode comprising an emissive material emitting electrons when the electric field in the vicinity of the cathode electrode exceeds a threshold value, characterized in that it comprises, for obtain an emission of electrons from the emissive material:
• a fifth object of the invention relates to a method of using a field emission display screen comprising at least one anode electrode and at least one facing cathode electrode, the cathode electrode comprising an emissive material emitting electrons when the electric field in the vicinity of the cathode electrode exceeds a threshold value, characterized in that it comprises, to avoid emission of electrons from the emissive material:
• FIG. 3A and 3B are sectional views illustrating the operation of a device according to one invention.
• FIGS. 5 to 9 show alternative embodiments of a flat screen element with field emission according to the invention
• FIG. 10 is a perspective view of a cathode plate for a flat screen with field emission according to the invention.
• FIGS. 11 to 13 are diagrams of the voltages to be applied to address a pixel of display screens according to the invention.
• FIGS 3A and 3B are sectional views illustrating the operation of a device according to the invention.
• the device comprises a plate 21 designated in this example as a cathode plate.
• the cathode plate 21 comprises a support plate 23 supporting an electrode 25 framed by two parts 28 and 29 of the same electrode.
• the device also includes a plate 22 designated in this example as an anode plate.
• the anode plate 22 comprises a support plate 26 supporting an electrode 27.
• the anode and cathode plates are arranged facing one another and in parallel planes, their corresponding electrodes facing each other. They are separated by the distance d.
• FIG. 3A represents the case in which a + V potential is applied to the electrode 27 and to the electrode 25 as well as to the parts 28 and 29 a zero potential.
• a uniform electric field of V / d value is established inside the device.
• Equipotential lines are shown in broken lines in FIG. 3A. The line shown closest to the electrode 25 corresponds to the potential V x , intermediate between the potential of the cathode electrode 25 and that of the anode electrode 27.
• FIG. 3B represents the case where a + V potential is applied to the electrode 27, a zero potential on the electrode 25 and a potential Vi on the parts 28 and 29. There is then a displacement and a deformation of the equipotentials which cause a tightening of the equipotentials above the cathode electrode 25, therefore an increase in the electric field at the level thereof. The same effect is obtained if a difference is fixed 'in potential between the electrode 27 and regions 28 and 29 and that one gate electrode 25 to a more negative potential than that of portions 28 and 29 relative to electrode 27.
• the parts 28 and 29 can be brought to potential - Vi.
• FIG. 4 is a partial view, in cross section of a flat screen with field emission to which the control mode according to the invention applies.
• This screen comprises a cathode plate 31 and an anode plate 32 placed opposite one another in parallel planes. They carry electrodes on their internal face. Spacers not shown ensure a constant spacing between the cathode and anode plates and a vacuum is created inside the screen.
• the cathode plate 31 comprises a support plate 33 made of insulating material, for example glass, on which a network of metal strips 38, 39 is successively deposited to form the modulation electrodes, an insulating layer 34 (for example silica) then a network of cathode electrodes 35 placed in the intervals of the underlying network.
• a single cathode electrode has been shown. It is either made of a material with a low threshold field, or covered with a layer of material with low output work, for example carbon or nanostructures.
• the cathode electrode 35 supports a layer '30 of such a material.
• the strips 38 and 39 corresponding to an electrode 35 are electrically connected together to form a modulation electrode.
• the anode plate 32 comprises a support plate 36 of insulating and transparent material, typically glass, successively covered with a layer 37 of transparent and conductive material, for example ITO, and with a layer 20 of a luminescent material.
• the screen can be used in the first following operating mode.
• a potential difference is applied between the anode electrode 37 and the cathode electrode 35 such that the resulting electric field at the level of the emitting electrode is less than the threshold field of extraction of the electrons from the emissive material 30. There is therefore no emission of electrons under the effect of this single field.
• the modulation electrode 38, 39 is brought to a potential intermediate between that of the anode and that of the emitting electrode, there is a displacement and a deformation of the equipotentials resulting in an increase in the electric field at the level of the emitting electrode.
• the potential of the modulation electrode can be chosen such that the electric field at the emitting electrode becomes greater than the threshold field of the emissive material. There will then be emission of electrons. These electrons are emitted perpendicular to the emission electrode. They are then accelerated by the anode field and strike the luminescent layer 20 covering the anode electrode 37.
• V s of potential which, applied to the modulation electrode, allows to have an electric field at the level 'of the equal emitter electrode in emission threshold field of the material, V ⁇ being greater than V:
• V s V + ⁇ V ⁇
• V s V + ⁇ V ⁇
• the anode plates 32 and cathode 31 may be spaced 1 mm apart, the metal strips 38 and 39 may be 20 ⁇ m wide and be spaced 10 ⁇ m apart.
• the insulating layer 34 can be a layer of silica 1 ⁇ m thick.
• the cathode electrode 35 can have a width of 5 ⁇ m and be centered in the spacing separating the metal strips 38 and 39.
• a potential of + 3000 V is applied to the anode relative to the cathode, which gives an electric field of 3 V / ⁇ m at the emitting electrode, this field being less than the threshold field.
• the cathode electrode 35 being maintained at 0 V, if the modulating electrode 38, 39 is brought to + 30 V, the electric field on the surface of the emissive electrode changes to 7 V / ⁇ m, which is higher than the threshold field. It therefore appears that the voltages to be switched remain low, typically a few tens of volts, which poses no problem.
• the screen can also be used according to the following second operating mode.
• a potential difference is applied between the electrode 37 and the cathode electrode 35 and this results in an electric field at the level of the emitting electrode. If this electric field is greater than the threshold field for extracting electrons from the emissive material 30, there is emission of electrons under the effect of this single field. If the modulation electrode 38, 39 is brought to a lower potential than one electrode of the cathode 35, there occurs a displacement and deformation of the equipotential lines resulting in a decrease of the electric field at the emitter electrode.
• the potential of the modulation electrode can be chosen such that the electric field at the level of the emission electrode becomes lower than the threshold field of the emissive material and thus makes it possible to stop the emission of electrons.
• V s of potential which, applied to the modulation electrode, makes it possible to have an electric field at the level of the emitting electrode equal to the threshold field emission of the material, Vs being less than V:
• V s V - ⁇ V S
• V ⁇ V - ⁇ V S
• the cathode plate and in particular the distribution of the electrodes, can have different variants.
• Figures 5 to 9 show some of the possible variants. For the sake of clarity, we have shown in these figures as a single cathode electrode.
• FIG. 5 represents a cathode plate 41 comprising a plate 43 of insulating material (for example glass) supporting a network of modulating electrodes each formed by two conductive strips 48 and 49 connected together.
• the plate 43 also supports an insulating layer 44, for example made of silica.
• cathode electrodes 45 have been deposited in correspondence with the modulating electrodes 48, 49. Each cathode electrode is deposited above the interval separating the corresponding conductive strips 48 and 49 and symmetrically with respect to these.
• On these cathode electrodes 45 are successively deposited a resistive layer 46 and a layer of emissive material 47.
• the resistive layer 46 has the function of standardizing the emission on the surface of the emissive electrode which is formed by the superposition of the elements 45, 46 and 47. Thus, very strong point emissions, which can lead to breakdowns, are prevented from occurring.
• This arrangement makes it possible to minimize the superposition of the cathode electrode and of the modulating electrode and therefore to minimize the parasitic capacitance which exists between them, which is important when the surface of the screen is large. Some devices do not require this precaution against parasitic capacity.
• the shape of the modulation electrode can range from that shown in Figure 5 to that shown in Figure 6 where it consists of only one strip. It can obviously take all intermediate forms.
• FIG. 6 represents a cathode plate comprising, as for FIG. 5, a plate support 53, an insulating layer 54, a cathode electrode 55, a resistive layer 56 and a layer of emissive material 57.
• the modulating electrode 50 consists of a single conductive strip, the emitter electrode being centered on the modulator electrode.
• FIG. 7 illustrates an intermediate form.
• the cathode plate 61 comprises a support plate 63, two conductive strips 68 and 69 forming the modulating electrode, the insulating layer 64 supporting the emitting electrode constituted by the electrode cathode 65, the resistive layer 66 and the emissive material layer 67.
• the emitting electrode has the same width as the gap separating the two conductive strips 68 and 69.
• the cathode plate 71 comprises a support plate 73, two conductive strips 78 and 79 forming the modulating electrode, the insulating layer 74 supporting the electrode.
• emitter consisting of one cathode electrode 75, the resistive layer 76 and the layer " of emissive material 77.
• the layer of emissive material 77 covers only the central part of the resistive layer 76. This arrangement makes it possible to 'Obtain a more focused electron beam by eliminating the electrons which could be subjected to the edge effects of the cathode electrode 75. This arrangement can be combined with the other variants described above.
• the cathode plate 91 comprises a support plate 93, two conductive strips 98 and 99 forming the modulating electrode, the insulating layer 94 supporting the emitting electrode comprising the cathode electrode 95 and the resistive layer 96.
• the emitting electrode also comprises pads 92 made of catalyst material , for example nickel, iron, cobalt or an alloy of these metals, these pads being deposited on the resistive layer 96.
• the pads 92 support the emissive material 97, for example carbon which is deposited preferentially on the catalyst material for constitute emissive sites.
• FIG. 10 is an exploded and perspective view of a cathode plate for a flat screen with field emission of the matrix type implementing the invention.
• the cathode plate 81 comprises a plate 83, for example made of glass, supporting a network of conductive strips Y forming lines, for example Yi, Y j , Y k . In these strips, openings or windows 80, for example of rectangular shape, have been arranged.
• This network of lines is covered with a layer of dielectric material 84 on which conductive strips 85 are deposited which are mutually parallel and perpendicular to the Y strips.
• the conductive strips 85 are grouped in threes to form columns X 1; X- ,, X ⁇ .
• the conductive strips 85 are each covered with a layer of resistive material 86 and of emissive material.
• the emissive material 87 has only been deposited on the useful zones, that is to say say on the zones of the columns located above the windows 80 formed in the lines. This gives two networks, one of lines and the other of columns, orthogonal to each other. A pixel is formed by the crossing of a row and a column.
• FIG. 11 is an example of the diagrams of the voltages to be applied to address a pixel of a display screen comprising a cathode plate of the type represented in FIG. 10 and in the case where the voltage applied between the anode and the cathode creates an electric field lower than the emission threshold field.
• This example minimizes the number of voltage values required.
• the anode is brought to a potential V A , the column X D to the potential V 0 and the line Y 3 to a potential Vi ⁇ V 1 being intermediate between V 0 and V A ).
• the other columns X are brought to the potential VI while the other rows Y are brought to the potential V 0 .
• the potential V 1 is chosen so that the increase in the electric field at the level of the emitting electrode is such that this electric field becomes greater than the threshold field.
• FIG. 12 is a diagram of the voltages to be applied to address a pixel of a display screen comprising a cathode plate of the type represented in FIG. 10 and in the case where the voltage applied between the anode and the cathode creates a field electric higher than the emission threshold field.
• the anode To address a pixel X-,, Y-, the anode, not shown, is brought to a potential V A and the column X-. at potential V 0 . " If we call d the distance between the anode and the cathode, the electric field resulting from this potential difference (V A -V 0 ) / d is greater than the emission threshold field of the material.
• the potential Vi of the line Y- must be greater than the voltage V s .
• the potential V 2 of the lines Y and Y k is less than V ⁇ on the Y- * line, the two pixels X 17 Y 3 and X k, Y, must be turned off. for this, the potential V 3 of columns X x and X k must be greater than Vi + ⁇ v s , ⁇ V ⁇ being equal to V 0 -V s .
• Pixels X ll Y 1 / X ll Y k / X L , Y 1 and X k , Y have a column voltage equal to V 3 and a line voltage equal to V 2 .
• the difference between the column voltages X x -X k and the lines Yi-Y k being greater than ⁇ V ⁇ and the line voltages being less than the column voltages, the corresponding pixels do not emit.
• Figure 13 is also a voltage diagram applicable to the previous case.
• Vi V 2 and V 3
• V ⁇ V 0 and ⁇ V> ⁇ V ⁇
• V 0 V 0 and ⁇ V> ⁇ V ⁇
• Y 3 it is necessary to apply a voltage V 0 on the column X- and the line Y-.
• the other columns being brought to a voltage V 0 + ⁇ v and the other lines at a voltage V 0 - ⁇ v.

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• Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
• Electrodes For Cathode-Ray Tubes (AREA)

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• 2000
  • 2000-02-15 FR FR0001832A patent/FR2798508B1/fr not_active Expired - Fee Related
  • 2000-09-08 WO PCT/FR2000/002487 patent/WO2001018838A1/fr active IP Right Grant
  • 2000-09-08 JP JP2001522564A patent/JP5159011B2/ja not_active Expired - Fee Related
  • 2000-09-08 US US10/049,777 patent/US6815902B1/en not_active Expired - Fee Related
  • 2000-09-08 DE DE60026044T patent/DE60026044T2/de not_active Expired - Lifetime
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