Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
  • H01J9/02—Manufacture of electrodes or electrode systems
  • H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes
  • H01J9/025—Manufacture of electrodes or electrode systems of cold cathodes of field emission cathodes

Definitions

• the present invention relates to a method for manufacturing a microtip electron source ("microtips").
• microtip sources One of the most important applications of these cold sources of electrons, also called “microtip sources”, is the manufacture of flat television tubes.
• Figure 1 is a schematic and partial sectional view of such a flat screen and Figure 2 is a schematic and partial perspective view of this flat screen.
• the flat screen of FIGS. 1 and 2 comprises a source of microtip electrons 2 and a glass substrate 4 which is separated from the source 2 by a thin space in which a vacuum has been created.
• the substrate 4 carries, facing the source
• this layer 6 for example made of indium and tin oxide, this layer 6 itself carrying cathodoluminescent elements 8, also called “phosphors".
• the microtip source 2 comprises, on an electrically insulating substrate 10, for example made of glass, a set of parallel cathode conductors 12 which constitute the columns of the screen.
• cathode conductors are covered by a layer 14 of an electrically insulating material such as silica.
• a set of other parallel electrical conductors 15 is placed above the insulating layer
• holes 18, 19 are formed through the insulating layer 14 and these grids 15 and microtips 20 made of an electron-emitting material are formed in these holes and rest on cathode conductors 12.
• the phosphors 8 are formed on the transparent conductive layer 6, facing these intersections, as seen in FIG. 2.
• the electrons are extracted by applying appropriate electrical voltages between the grids and the microtips, then these electrons are accelerated by appropriate electrical voltages applied between the grids and the conductive layer 6 constituting the anode of the screen.
• Each phosphor 8 excited by electrons are extracted by applying appropriate electrical voltages between the grids and the microtips, then these electrons are accelerated by appropriate electrical voltages applied between the grids and the conductive layer 6 constituting the anode of the screen.
• Each pixel is in fact "excited" by several hundred microdots whose dimensions are of the order of 1 ⁇ m, generally 1.5 ⁇ m, and which are spaced apart from each other by a distance of the order of a few micrometers, typically 5 ⁇ m.
• a flat screen thus typically uses around 10,000 microtips per square millimeter over areas of several square decimetres.
• the flat screens currently manufactured have surfaces of the order of 5 dm : and we plan to manufacture flat screens whose surfaces would go up to approximately 1 m 2 .
• FIG. 3 which schematically illustrates this process, shows a structure comprising the insulating substrate 10 on which the cathode conductors 12 are formed, and the insulating layer 14 which is formed on these cathode conductors and which carries a grid layer 16 electrically conductive.
• the grids themselves are obtained from this grid layer 16, after having formed the microtips as will be seen.
• the microtips 20 are obtained by evaporation of an electron-emitting material 26.
• a layer 28 of this material then forms on the surface of the grid layer 16a.
• the holes 19 formed in these layers 16 and 16a decrease progressively as the thickness of the layer 28 increases.
• the diameter of the deposits of material 26 in the holes 18 of the insulating layer 14 varies like the diameter of the holes of the layer 16a and of the grid layer 16, which leads to the point shape of the deposits in the holes 18, that is to say at the microtips 20.
• the layer is then eliminated: layer 28 by selective dissolution of the nickel layer 16a, which makes these microtips appear.
• the main advantage of this known method is that it does not require precise alignment of microlithography masks since it is the holes in the grid layer which themselves define the microtips.
• FIG. 4 shows a silicon substrate 30. We begin by oxidizing this substrate superficially then discs 32 are formed from the silica layer which results from this oxidation.
• Reactive ion etching of the silicon substrate 30 then allows the formation of silicon pedestals 34, the disks 32 serving as masks.
• a layer of silica 36 is then formed on the substrate 30 by evaporation of silica 38.
• a layer 40 of silica is then formed on each disc 32.
• the pedestals 34 are then thermally oxidized, which leads to the formation of microtips 42 from these pedestals.
• a grid layer 44 is then formed by evaporation of an electrically conductive material on the silica layer 36.
• a layer 46 of this material also forms on the layer 40 of silica associated with each disc 32.
• the silica which covers the microtips 42 is then eliminated, as well as the discs 32 and the corresponding layers 40 and 46.
• the angle of incidence ⁇ of an evaporation beam F varies as a function of the position of the holes 19 of the grid layer 16, which leads to the phenomenon illustrated in the Figure 5, that is to say to microtips whose axes Y are all the less perpendicular to the surface of the substrate 10 that the angle of incidence ⁇ is large.
• FIGS. 6A and 6B This other method is schematically illustrated by FIGS. 6A and 6B.
• FIG. 6A shows an insulating substrate 10 on which there is successively a conductive layer 12, an insulating layer 14 and a conductive layer 16.
• Coaxial holes 19 are then made through the layers 16 and 14.
• the surface of the conductive layer 16 is oxidized so as to cover this conductive layer 16 with an insulating layer 50.
• Each hole 18 is then filled, by electrolysis using an electrolytic bath 54, a metal block 56 and a suitable voltage source 58, with a metal deposit which must take the form 60 indicated in FIG. 6A.
• FIG. 6B it can be seen that, after this electrolytic deposition, the layer 50 is removed by etching and then, by electrolysis, by taking the layer 12 as the anode and the layer 16 as the cathode and with suitable electrolysis conditions, there is dissolution of the deposit 60 (substantially symmetrical about the axis Z of the hole 18), dissolution such that at the end there remains only a microtip 62.
• references 64 and 66 respectively represent an electrolytic bath and a voltage source suitable for dissolving the deposit 60.
• the reference 68 represents a piece of the deposit 60 which detaches from the microtip 62 and falls into the bath 64.
• the electrolytic deposit 60 must have the indicated form.
• the part of the deposit 60 which is located above the layer 50 must not significantly cover this layer 50 because, if the overlap is significant, the subsequent removal of the layer 50 becomes very difficult and the subsequent electrochemical attack on deposit 60 is made practically impossible.
• the object of the present invention is to remedy these drawbacks.
• a structure is made up comprising an electrically insulating substrate, at least one cathode conductor on this substrate, a first electrically insulating layer which covers each cathode conductor, an electrically conductive grid layer which covers this first electrically insulating layer and a second electrically insulating layer which covers the grid layer,
• microtip is formed in each hole which is made of an electron-emitting metallic material and which rests on the cathode conductor corresponding to this hole, this process being characterized in that the formation of the microtips comprises the following steps:
• a treatment is made of the deposit of the metallic material, this treatment being able to minimize or prevent a chemical attack on this deposit of the material metallic from the top of it,
• the deposition of the metallic material emitting electrons is an electrolytic deposition.
• the deposition of the metallic material emitting electrons is a chemical deposition also called “electroless deposition”.
• the treatment of the deposit of the metallic material can comprise the formation of another deposit, on this deposit of the metallic material, of a material capable of withstanding said chemical attack.
• this treatment may comprise the formation of another deposit, on the deposit of the metallic material, of this same metallic material, this other deposit partially covering the second insulating layer.
• this other deposit can have substantially the shape of a mushroom cap, the height of this cap being at least equal to the diameter of the holes formed in the second insulating layer.
• the second insulating layer can be given an additional thickness such that the total thickness of this second insulating layer is of the order of twice the diameter of the holes formed in the second insulating layer or greater than twice this diameter , the treatment then comprising the formation of a deposit of the metallic material up to upper level of each hole formed in the second insulating layer.
• the metallic material can be chosen from the group comprising iron, iron-nickel, nickel, chromium, copper, gold, silver and cadmium.
• FIG. 1 is a schematic and partial sectional view of a flat screen
• FIG. 2 already described, is a schematic and partial perspective view of this flat screen
• FIG. 3 already described, schematically illustrates a known method of manufacturing the microtips of an electron source with microtips
• FIG. 4 already described, schematically illustrates another known method for manufacturing the microtips of an electron source with microtips
• FIGS. 7 and 8 schematically illustrate two stages of a particular mode of implementation of the method which is the subject of the invention
• FIGS. 9, 10 and 11 schematically illustrate three possible treatments of a metallic material emitting electrons, from which it is desired to form microtips,
• FIGS. 12, 13 and 14 schematically illustrate steps which respectively follow the treatments illustrated by FIGS. 9, 10 and 11,
• FIGS. 15A to 15D schematically illustrate steps which follow the step illustrated in FIG. 12, • FIGS. 16A to 16D schematically illustrate steps which follow the step illustrated in FIG. 13, and
• FIGS. 17A to 17D schematically illustrate steps which follow the step illustrated in FIG. 14.
• FIGS. 7 and 8 schematically illustrate two successive stages of a particular mode of implementation of the method which is the subject of the invention.
• FIG. 7 a structure 70 which comprises: the electrically insulating substrate 10 on which the cathode conductors 12 are formed,
• the structure could comprise only a single cathode conductor.
• substantially circular holes 18, 19 and 72 respectively formed through the insulating layer 14, through the grid layer 16 and through the insulating layer 71.
• the methods for obtaining such a structure are known in the art. state of the art.
• the holes formed in the layers 14 and 16 are for example obtained by photolithography using a photosensitive resin mask ("photoresist").
• the substrate 10 is made of glass
• the cathode conductors are made of niobium or consist of a niobium-nickel bilayer
• the layer 14 is made of silica
• the gate layer 16 is made of niobium.
• the insulating layer 71 can be made of silica or advantageously consist of the photosensitive resin layer (“photoresist”) which served as a mask for making the holes in the layers 14 and 16.
• the structure 70 is placed in an appropriate electrolytic bath 74 (containing ions of the metallic material to be deposited) and a block 76 of this metallic material is also placed in this electrolytic bath.
• An appropriate electrical voltage is then applied, thanks to a voltage source 78, between the cathode conductors 12 and this block 76.
• the cathode conductors 12 serve as the cathode and the block 76 serves as the anode.
• the deposited metallic material 80 can, as already mentioned, be iron, nickel or iron-nickel for example, and constitutes the electron-emitting material.
• iron-nickel is chosen as the metallic material, it can be deposited from a bath whose composition is as follows:
• deposition conditions voltage: 1 to 2 V current density: 0.5 to 2 mA / c ⁇ r ambient temperature pH: 2 to 3.
• the deposit of metallic material 80 has substantially the shape of a cylinder of revolution, the holes 18, 19 and 72 having substantially the same diameter.
• One of them consists in forming by electrolysis another metallic deposit 81 on the top from the deposit of metallic material 80 above (FIG. 9), this other metallic deposit 81 having to resist the chemical attack of the electron-emitting material.
• deposit 81 can be gold if the emitting material is Fe-Ni.
• Another solution consists in continuing the deposition of emitting material 80 (FIG. 10) in such a way that it has, above the insulating layer.
• the total thickness of the layer 71 in the case of FIG. 11, being of the order of twice the diameter of the holes 72 or greater than twice this diameter, then raise the deposit of the emitting material 80 to the top of the holes 72.
• the next step is to etch the insulating layer 71 to eliminate it.
• FIGS. 9 to 11 we will then obtain the three structures schematically represented in FIGS. 12, 13 and 14 which correspond respectively to FIGS. 9, 10 and 11.
• the structure obtained comprises balusters of metallic material 80 which each exit from a hole and the top of which is protected by a deposit 81.
• the structure obtained comprises mushrooms made of metallic material 80 each emerging from a hole.
• the structure obtained comprises columns made of metallic material 80 which each exit from a hole and whose height h above the layer 16 is approximately twice the diameter of the hole 19 or more than double this diameter.
• a chemical attack is then made on the material 80 emitting electrons.
• the diameter of the baluster will gradually decrease at the same time as we will dig in these holes 18 and 19 and the baluster will successively take the forms indicated in the figures
• a microtip 82 is generally formed and the etching is stopped when the top of this microtip is at the level of the grid layer 16 as shown in FIG. 15D.
• microtips in accordance with the process which is the subject of the invention are carried out by a chemical attack on metal bars emitting electrons embedded in holes.
• this requires, to avoid the disturbance that the etching of the upper part of each bar could bring, either to modify the upper face of this bar by a treatment preventing attack of this part (this treatment consisting for example of making a metallic deposit suitable or a surface treatment such as oxidation or nitriding for example) or to give this bar a configuration making it possible to push back the upper face of this one at a distance such that, during the chemical attack, the attack of this upper face does not disturb the formation of the microtip corresponding to this bar.
• this treatment consisting for example of making a metallic deposit suitable or a surface treatment such as oxidation or nitriding for example
• the advantage of the process which is the subject of the present invention is that it allows the manufacture of self-aligned microtips on the holes in the grid layer 16, by means of a non-directive technique, in an isotropic liquid medium.
• This process which is the subject of the invention is therefore independent of the surface of the structure where it is desired to form the microtips. It should be noted that, after having formed the microtips, the formation of the microtip electron source is then terminated by producing, in a known manner, from the grid layer 16, parallel grids (not shown) making an angle with the conductors cathodic (but if there was only one cathodic conductor, we would keep the grid layer as it is).

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• Cold Cathode And The Manufacture (AREA)

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• 1997
  • 1997-11-03 FR FR9713794A patent/FR2770683B1/fr not_active Expired - Fee Related
• 1998
  • 1998-11-02 EP EP98952833A patent/EP1029338A1/de not_active Withdrawn
  • 1998-11-02 JP JP2000519451A patent/JP2001522126A/ja not_active Withdrawn
  • 1998-11-02 WO PCT/FR1998/002337 patent/WO1999023680A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

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