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
  • 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
  • H01J29/48—Electron guns
  • H01J29/481—Electron guns using field-emission, photo-emission, or secondary-emission electron source
• • 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
• • 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 invention relates to a cathode structure, especially for a flat display screen with refocusing grid.
• a field emission excited cathodoluminescence display device comprises a cathode or electron-emitting structure and a facing anode coated with a luminescent layer.
• the anode and the cathode are separated by a space where the vacuum has been made.
• the cathode is either a source based on micro-peaks or a source based on a low threshold field emissive layer.
• the emissive layer may be a layer of carbon nanotubes or other structures based on carbon or based on other materials or multilayers (AlN, BN).
• the structure of the cathode may be diode or triode type.
• Document FR-A-2,593,953 (corresponding to US Pat. No. 4,857,161) discloses a method of manufacturing a cathodoluminescence display device excited by field emission.
• the structure of the cathode is of the triode type.
• the electron-emitting material is deposited on a conductive layer apparent at the bottom of holes made in an insulating layer which supports an electron extraction grid.
• Document FR-A-2,836,279 discloses a cathode structure of triode type for emissive screen.
• the cathode structure includes, in superposition on a carrier, a cathode electrode electrically connected to an electron emitting material, an electrical insulator layer, and a gate cathode.
• An opening in the gate electrode and an opening in the electrical insulator layer expose the electron emitting material which is located in the central portion of the gate electrode opening.
• the apertures are slit-shaped and the electron-emitting material, exposed by the slits, consists of elements aligned along the longitudinal axis of the slits.
• the electron-emitting material may consist of nanotubes, for example carbon nanotubes.
• FIG. 1 is a sectional and diagrammatic view of a triode-type cathode structure as disclosed in FR-A-2,836,279.
• the cathode structure is formed on a support 1. It comprises, in superposition on the support 1, a cathode 2 supporting a resistive layer 3, an insulating layer 4 and a metal layer 5 forming an electron extraction grid.
• a slot 6 exposes the resistive layer 3.
• growth pads 7 rest on the resistive layer 3.
• a single growth pad is visible in the figure.
• the growth pads 7 are made of electrically conductive material covered with a catalyst. They allow the growth of nanotubes 8, for example carbon.
• an image element or pixel comprises a few tens or hundreds of pads arranged in parallel slots.
• the nanotubes must be electrically isolated from the electron extraction grid, which leads to arranging the grid back of the nanotube pads as shown in FIG.
• a flat field emission screen comprises grid conductors, generally organized in lines, and cathode conductors, generally organized in columns.
• the pixels or pixels are formed at the intersection of the lines (grid conductors) and columns (cathode conductors), each pixel having a few tens or hundreds of electron emitting elements.
• a pixel may be constituted by the intersection of a line, shown at the pixel in Figure 2, and a column, shown at the pixel in Figure 3.
• the gate conductor (line) and the cathode conductor (column) have been shown in different figures. We understand that grid and cathode conductors are superimposed so that the slots 11 (see FIG. 2) and 21 (see FIG.
• a gate conductor such as the gate conductor 10 consists of two parallel strips 12 and 13 regularly connected by zones 14, each zone defining a pixel.
• Each zone 14 comprises a number of slots 11 corresponding to the slot 6 of FIG. 1.
• two successive zones 14 are separated by a free space 15. Between two grid conductors 10 successive, there is also a free space 16.
• a cathode conductor such as the cathode conductor 20 consists of two parallel strips 22 and 23 regularly connected by zones 24, each zone defining a pixel.
• Each zone 24 comprises a number of slots 21 corresponding to the slot 6 of FIG.
• the electrical operation of the screen is ensured by sequential time scanning of the lines (grid conductors).
• lines grid conductors
• the electronic emission of the emitting elements (for example the carbon nanotubes) of each pixel of a line is controlled by the potential difference between the line addressed and the column associated with the pixel in question.
• This potential difference of the order of 80 to 100 volts creates an electric field at the end of the nanotubes, and allows the extraction of electrons.
• the emitted electrons are then accelerated to an anode covered with phosphors, brought to a high voltage and located a few millimeters from the cathode structure. Under the impact of these energetic electrons the luminophores emit a light radiation of red, green or blue color allowing the realization of monochrome screens or colors.
• This type of FED screen is limited by the size of the optical spot obtained on this anode.
• this spot size is conditioned by the anode voltage, the cathode-anode distance as well as by the initial kinetic energy and the initial angular divergence of the electron beam. from the cathode.
• FIG. 4 illustrates this configuration. It shows a cathode structure formed on a support 31.
• the structure comprises, superimposed on the support 31, a cathode conductor 32 supporting a resistive layer 33, a first insulating layer 34, a metal layer 35 forming an extraction grid.
• a slot 36 exposes the resistive layer 33 which supports growth pads 37 (only one stud is visible) which allowed the growth of the nanotubes 38.
• US 2006/001359 discloses a triode-type cathode structure comprising, superimposed on a support, a cathode electrode, an electrical insulator layer and a gate electrode, the electrical insulator layer and the gate having emission openings revealing at least one electron-emitting element electrically connected to the cathode electrode, the structure further comprising a refocusing electrode arranged to refocus the electrons extracted by the gate electrode.
• the refocusing electrode is disposed on said electric insulation layer and is connected to electrical connection means for applying to it a refocusing voltage.
• the refocusing electrode is polarized at the upper gate metal, which necessarily requires an additional electrode at this level to drive the focusing electrode since this electrode must be biased to a potential lower than that of the gate electrode. .
• An object of the present invention is to provide a flat screen display cathode structure having an electron refocusing grid but which does not require, as in the prior art, a second insulating layer supporting a third level of metallization.
• the present invention finds a particularly advantageous application in the case of a cathode structure for matrix display flat screen display. Nevertheless, the invention can also be applied to less complex cathode structures, for example to cathode structures having at least one electron emitting element.
• the subject of the invention is therefore a cathode structure of the triode type comprising, in superposition on a support, a cathode electrode, an electrical insulator layer and a gate electrode, the electrical insulator layer and the gate electrode having emission apertures revealing at least one electrically connected electron emitting element at the cathode electrode, the structure further comprising a refocusing electrode arranged to refocus the electrons extracted by the gate electrode, the refocusing electrode being disposed on said electrical insulating layer and being connected to electrical connection for applying to it a refocusing voltage, characterized in that the refocusing electrode is connected to the electrical connection means through electrically conductive nanotubes, for example carbon nanotubes.
• the electrical connection means may comprise the cathode electrode.
• the electron emitting element can be electrically connected to the cathode electrode by means of a resistive layer.
• the electrical connection means may comprise a resistive material which may be that of the resistive layer.
• the nanotubes of the connection means are housed in at least one opening of the electrical insulating layer.
• the electron emitting element may consist of nanotubes.
• the nanotubes of the electron emitting element are carbon nanotubes.
• the emission apertures in the electrical insulator layer and in the gate electrode comprise at least one slot-shaped aperture in the electrical insulator layer associated with a slot-shaped aperture corresponding in the gate electrode.
• the slot-shaped aperture in the electrical insulator layer and the corresponding slot-shaped aperture in the gate electrode reveal at least one row of electron emitting elements aligned in the direction of the electrodes. slots.
• the invention also relates to a matrix-controlled field emission device consisting of a plurality of cathode structures as defined above, arranged in the form of a matrix arrangement defining lines and columns, the gate electrodes of the same line being grouped into a gate conductor, the cathode electrodes of the same column being grouped into a cathode conductor, the intersection of a cathode conductor and a gate conductor defining an image element or pixel.
• the gate conductor and the refocusing electrode can be nested inside a pixel. They can form two interdigital combs.
• each zone of the refocusing electrode has at least one opening communicating with said at least one opening of the electrical insulation layer housing the nanotube of the connection means and allowing the nanotubes connection means to provide an electrical connection with the refocusing electrode.
• each zone of the refocusing electrode has at least one circular opening communicating with said at least one opening, also circular, of the electrical insulation layer housing the nanotubes of the connection means. These openings may reveal a plurality of electrically conductive nanotubes occupying the entire space of the openings.
• FIG. 1, already described is a sectional view of a triode type cathode structure, according to the prior art
• FIGS. 2 and 3, already described respectively represent a grid conductor and a limited column conductor to a single pixel of a flat display screen according to the prior art
• FIG. 4, already described is a sectional view of a triode-type cathode structure with a refocusing gate, according to the prior art
• FIG. 5 is a sectional view of a cathode structure of the triode type, with a refocusing grid, according to the invention
• FIG. 6 is a partial view from above of a field emission device according to the present invention
• FIG. 7 is a partial view from above of another field emission device according to the present invention
• FIG. 8 is an enlarged view showing another embodiment
• FIGS. 9A to 9G illustrate a first method of producing a cathode structure according to the invention
• FIGS. 10A to 1OG illustrate a second embodiment of FIG. A cathode structure according to the invention
• Figures HA to HH illustrate a third method of producing a cathode structure according to the invention.
• FIG. 5 is a sectional view of a triode-type cathode structure with a refocusing gate according to the invention. It shows a cathode structure formed on a support 41.
• the structure comprises, superimposed on the support 41, a cathode conductor 42 supporting a layer resistive 43, a single insulating layer 44 and a metal layer 45 forming an electron extraction grid.
• Slots 46 expose the resistive layer 43 which supports growth pads 47 which have allowed the growth of the nanotubes 48. Note that the growth pads 47 are centered in the slots 46 and that there is a certain distance between the pads of growth and the edge of the insulating layer supporting the extraction grid 45. This avoids a short circuit between the nanotubes 48 and the extraction grid 45.
• Figure 5 also shows the presence, on part of the insulating layer 44 of another metal layer, the metal layer 50 constituting the refocusing grid advantageously made with the same level of metal as the metal layer 45 forming extraction grid.
• An electrical connection between the refocusing gate 50 and the resistive layer 43 is provided by the presence of a growth pad 57 formed at the bottom of an opening 56 made in the insulating layer 44 and by electrically conductive nanotubes 58, advantageously carbon nanotubes which cause a short circuit between the growth pad 57 and the refocusing gate 50.
• the growth pad 57 advantageously occupies the entire bottom of the opening 56 to promote short circuits between the nanotubes 58 and the refocusing grid 50.
• the cathode structure shown in Figure 5 is a partial view.
• the refocusing grid (or self-focusing grid), for to be effective, must surround, depending on the applications, an electron emitting element or a group of electron emitting elements, for example each group of electron emitting elements constituting a pixel for a flat screen display.
• an electron emitting element or a group of electron emitting elements for example each group of electron emitting elements constituting a pixel for a flat screen display.
• These free spaces can receive the refocusing grid according to the invention.
• These refocusing grid pads may be substantially identical in shape to the electron emission zones defined by the slots shown in FIGS. 2 and 3.
• FIG. 6 is a partial view from above of a field emission device intended for the constitution of a matrix-controlled flat display screen.
• This figure shows gate conductors 10, similar to the gate conductor of FIG. 2, supported by an insulating layer 63 and whose slots 11 reveal the electron emitting elements 68 aligned in the direction of the slots.
• the slots 11 are, in Figure 6, oriented in the direction of the lines of the screen, but it is possible alternatively to orient them in the direction of the columns of the screen.
• the free spaces 15 and 16 form four pads surrounding the pixel 14. Each of these pads comprises a portion of the refocusing electrode for this pixel. Each of these parts also participates in the refocusing electrode of the neighboring pixel.
• FIG. 10 shows gate conductors 10, similar to the gate conductor of FIG. 2, supported by an insulating layer 63 and whose slots 11 reveal the electron emitting elements 68 aligned in the direction of the slots.
• the slots 11 are, in Figure 6, oriented in the direction of the lines of the screen,
• FIG. 6 thus shows four portions 71, 72, 73 and 74 provided with slits whose principal axes are, in this embodiment, in the same direction as the axes of the slits 75 made in the grid conductors 10.
• parts 71, 72, 73 and 74 to maximize the short circuits between the nanotubes and the refocusing gate, for example small circular openings at the rate of one opening per growth pad.
• the slits 75 reveal the electron emitting elements consisting of carbon nanotubes which electrically connect the pads of the refocusing electrode to the cathode conductor via or not the resistive layer depending on whether the resistive layer has been previously or not. engraved.
• This refocusing grid will thus be brought to the potential of the cathode which will produce the desired effect of refocusing the electron beam from the central emitting zone.
• These grid pads will therefore become “self-refocusing” without adding a new level of metal and without adding a new contact at the lower cathode metal to bias this refocusing gate.
• This option remains possible, however, at the lower cathode metal. It will be possible to define at the level of the lower cathode metal a first subset of cathode conductors columns as shown in Figure 3 and a second subset of electrically insulated column conductors of the first subset.
• This second subset of column conductors parallel to the first subassembly will have all its columns short-circuited on the same polarization output contact of the refocusing grids.
• the interest of this somewhat more complex structure, in the design only, is to be able to control the focusing effect by applying on this new contact a potential different from that of the cathodic columns intended for the video. In this case, it will be preferable to etch the resistive ballast layer to avoid any consumption in this layer due to the potential difference of the video column conductors and those of control of the refocusing potential.
• the resistive ballast layer 43 may be etched locally at the refocusing grids to promote the short circuit on the metal level of the cathode.
• the growth pads of the connecting nanotubes of the refocusing gate are deposited directly on the cathode and the nanotubes directly interconnect the refocusing gate and the cathode.
• FIG. 7 is a top view, at the pixel level, of an extraction grid 80 having a series of fingers 81 interdigitated with a series of fingers 91 of an electron refocusing electrode 90.
• the openings made in the grids were not shown to locate the nanotubes.
• each finger 81 of the extraction grid 80 has, in its central zone, one or more openings (advantageously in the form of a slot extending over the entire length of the finger).
• each finger 91 of the refocusing electrode 90 comprises one or more openings, advantageously circular.
• the focus will be improved along a vertical axis y taking into account the nesting of the "fingers" of extraction and focusing.
• the reference 92 represents the openings comprising means of connection electrical (eg carbon nanotubes) bypassing the refocusing electrode and occupying the entire opening to maximize short circuits.
• connection electrical eg carbon nanotubes
• FIGS 9A to 9G illustrate a first method of making a cathode structure according to the present invention. For the sake of simplicity, only one transmitter element will be represented.
• FIG. 9A shows a substrate 101, for example made of glass, on which a metal layer has been deposited and etched to form a cathode conductor 102, this metal layer being able to be made of molybdenum or of a tungsten-titanium alloy and which can typically have 0 , 1 to a few microns thick.
• a resistive layer 103 also known as a ballast, is deposited, for example an amorphous silicon layer. thickness between 0.5 microns and 2 microns.
• an insulating layer 104 is deposited, for example a silica layer having a thickness of between 1 and 3 ⁇ m.
• a conductive layer 105 is deposited, for example a layer of molybdenum or copper 0.1 to a few microns thick. It is possible alternatively to etch the resistive layer 103 locally at the level of the future growth zone of the nanotubes intended for the connection of the refocusing gate.
• the conductive layer 105 is then etched to define an extraction gate conductor 105 'and a refocusing electrode 105' '(see Fig. 9B).
• a resin layer 106 is deposited on the resulting stack (see FIG. 9C).
• An opening 107 is caused in the resin layer 106 at the size of the growth pad provided for the refocusing electrode until the refocusing electrode 105 "is revealed.
• the growth pad may have a diameter of a few microns if it is circular or a few ⁇ m side if it is rectangular or square.
• the etching of the opening 107 is continued to extend this opening through the refocusing electrode 105 '' and through the insulating layer 104 until it reaches the resistive layer 103.
• a reactive dry etching can be used for this purpose. (see Figure 9D).
• a catalyst layer 108 growth pad of 1 nm to 20 nm thick is deposited.
• the catalyst may be iron, nickel or iron / silicon / palladium / nickel alloys.
• a metal sub-layer of TiN, TaN, Al or Ti of 50 nm thick can be provided under the catalyst.
• Resin layer 106 is removed and a new resin layer 109 is deposited (see FIG. 9E) to allow an aperture 110 to be etched at the future location of the electron emitter element to reveal the grid conductor. extraction 105 '.
• the opening 110 has a size of a few microns over a few microns.
• the resin layer 109 then protects the growth pad 108.
• the extraction gate conductor 105 'and the insulating layer are then etched by reactive wet etching while controlling the shrinkage with respect to the opening 110.
• the catalyst or growth pad 111 is then deposited, which may be of the same type. as the growth pad 108 (see Figure 9F).
• FIG. 9G shows the nanotubes 112 which do not reach the extraction grid conductor 105 'and the nanotubes 113, some of which are in electrical contact with the refocusing electrode 105''.
• FIGS 10A to 10G illustrate a second method of making a cathode structure according to the present invention. For the sake of simplification, only one issuer element will be represented. This second method applies to the case where the extraction grid is covered with a protective resistive layer.
• FIG. 10A shows a substrate 201, for example made of glass, on which a metal layer has been deposited and etched to form a cathode conductor 202, this metal layer possibly being made of molybdenum or of a tungsten-titanium alloy and capable of having 0, 1 to a few microns thick.
• a resistive layer 203 also called a ballast layer, is then deposited, for example an amorphous silicon layer having a thickness of between 0.5 ⁇ m and 2 ⁇ m.
• an insulating layer 204 is deposited, for example a silica layer having a thickness of between 1 and 3 ⁇ m.
• a conductive layer 205 is deposited, for example a layer of molybdenum or copper 0.1 to a few microns thick.
• the conductive layer 205 is then etched to define an extraction gate conductor 205 'and a refocusing electrode 205' '(see Fig. 10B). Etching was conducted to also obtain apertures 230 and 217 respectively in the extraction grid conductor 205 'and in the refocusing electrode 205' '.
• a protective resistive layer 220 is then deposited on the structure obtained previously
• This resistive layer 220 may be a highly resistive amorphous silicon layer or an amorphous carbon layer called DLC (for "Diamond Like Carbon"). If the resistive layer 220 is amorphous silicon, its resistivity is at least ten times greater than the resistivity of the ballast layer
• a layer of resin 206 is then deposited on the previously obtained structure and the growth pad patterns are insulated by means of a mask (see FIG. 10D). Openings in the resin 206 of a few ⁇ m to a few ⁇ m are obtained: the opening 210 centered on the opening 230 of the extraction grid conductor 205 'and the opening 207 centered on the opening 217 of the electrode refocusing.
• the openings 210 and 207 may be of different sizes in the emission and focusing areas.
• the resistive layer 220 and the insulating layer are then etched by reactive dry etching.
• catalyst layers (growth pads) 208 are deposited for the opening 207 and 211 for the opening 210.
• the catalyst can be that of the first embodiment method (see Figure 10F).
• FIG. 1OG shows the nanotubes 212 which can not short-circuit the extraction gate conductor 205 'because of the protective resistive layer 220. This figure also shows the nanotubes 213, some of which are in electrical contact with the electrode. refocusing 205 ''.
• FIGS HA to HH illustrate a third method of making a cathode structure according to the present invention.
• This third embodiment is a variant of the second embodiment which makes it possible to independently adjust the surgraving of the insulating layer between the emitter elements and the electrical connection means connecting the ballast layer to the refocusing electrode.
• FIG. HA shows a substrate 301 on which a metal layer has been deposited and etched to form a cathode conductor 302.
• a resistive layer 303 (ballast layer) is then deposited, then an insulating layer 304 and finally a conductive layer 305.
• These different elements may be identical to those of the second embodiment.
• the conductive layer 305 is then etched to define an extraction gate conductor 305 'and a refocusing electrode 305 '' (see Figure HB). The etching was conducted to also obtain openings 330 in the extraction grid conductor 305 'but not in the refocusing electrode 305''.
• the protective resistive layer 320 is then deposited on the structure obtained previously
• This resistive layer may be of the same nature as that of the second embodiment method.
• a resin layer 306 is then deposited on the previously obtained structure and the growth pad patterns are insulated by means of a mask covering the location of the future emission growth pads and the electrical connection means. Openings in the resin 306 of a few ⁇ m by a few ⁇ m are obtained: the opening 310 centered on the opening 330 of the extraction grid conductor 305 'and the opening 307 above the refocusing electrode 305' '(see figure HD).
• the openings 310 and 307, and therefore the growth pads may be of different sizes in the emission and focusing zones.
• the resistive layer 320 is then etched by reactive dry etching. From the opening 310, the etching continues in the insulating layer 304 until the resistive layer 303 is revealed.
• the insulating layer 304 is checked by resin 306 by wet etching the insulating layer 304.
• the refocusing electrode 305 "serves as a stop layer for etching in the aperture 307 (see FIG. Then, by reactive etching and in the extension of the opening 307, the refocusing electrode 305 "and the insulating layer 304 are etched to reveal the ballast layer 303 (see FIG. HF).
• the catalyst can be that of the first and second methods of realization (see Figure HG).
• Figure HH shows the nanotubes 312 which can not short-circuit the extraction gate conductor 305 'because of the protective resistive layer 320. This figure also shows the nanotubes 313, some of which are in electrical contact with the electrode. refocusing 305 ''.

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• 2006
  • 2006-12-19 FR FR0655622A patent/FR2910175B1/fr not_active Expired - Fee Related
• 2007
  • 2007-12-19 WO PCT/EP2007/064195 patent/WO2008074825A1/fr active Application Filing
  • 2007-12-19 EP EP07857818A patent/EP2104944A1/de not_active Withdrawn
  • 2007-12-19 US US12/518,661 patent/US20100013365A1/en not_active Abandoned
  • 2007-12-19 JP JP2009542047A patent/JP2010514119A/ja not_active Withdrawn

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