EP1073088A1 - Fabrication of an anode of a flat viewing screen,anode obtained by said method and flat screen using such anode - Google Patents

Abstract

The technique includes formation of all conducting bands in a single layer, with resistances formed in serpentine fashion to provide electrical connections. A series of conducting bands (34R, 34B, 34V) are formed, each carrying the luminophore elements for the three colours. The conducting bands of each of the three sets are connected by interconnecting rails (32R, 32B, 32V), with resistance elements (36R, 36B, 36V) linking each band to its respective rail. The conducting bands and their resistances are formed from the same conductive layer. The bands may be formed in groups, in which case one resistance is provided for the connection of each group. The resistances may be formed by a serpentine conducting track on the substrate, and both the substrate and the resistances are formed of a transparent material. The conducting layer may be an oxide of indium, doped with tin.

Description

TECHNICAL AREA

The present invention relates to a method manufacturing an anode of a flat screen display as well as an anode obtained by this process and a flat screen using this anode.

The invention relates in particular to manufacture of an anode of a flat screen microtip display ("microtips").

The invention applies in particular to the manufacture of anodes for flat display screens in colors.

PRIOR STATE OF THE ART

Figure 1 is a schematic view and partial of a known flat screen structure with microtips with which one can implement the invention.

Such a microtip screen includes essentially a microtip cathode 2 and a cathodoluminescent anode 4 which is placed opposite this cathode.

The cathodoluminescent anode 4 comprises a transparent substrate 6, generally made of glass, which lets in the light produced by cathodoluminescence and through which we observe the screen.

The operating principle and the detail of the constitution of such a screen are described in particular in the following document to which we report to :

FR 2623013 A corresponding to EP 0316214 A and to US 4,940,916 A (Borel et al.).

About microtip flat screens we may also consult the following documents:

US 4,857,161 A (Borel et al.), US 4,908,539 A (Meyer), US 5,194,780 A (Meyer) and US 5,534,744 A (Leroux et al.).

Returning to Figure 1, the cathode 2 includes a set of parallel conductors 8 forming the columns of this cathode. Only one of these conductors is shown in Figure 1. These conductors 8 are formed on a substrate electrically insulating 10 generally made of glass.

This set of conductors 8 is covered an electrically insulating layer 12 on which the grid 14 of the cathode is formed. This grid is a set of parallel lines 16. A single line is shown in Figure 1. Lines 16 are orthogonal to columns 8.

Holes 18 are formed through the insulating layer 12 and the grid 14 to the columns 8. The microtips 20 are formed in these holes 18.

The screen schematically represented on the Figure 1 uses the electric field created between the conductors 8 and grid 14 so that the electrons are extracted from microtips 20 and reach the phosphor elements of the anode.

In the case of a color screen the anode 4 is provided with strips of phosphor elements 22R, 22B and 22V which alternate with each other and correspond respectively to the three colors red, blue and green.

These bands of phosphor elements are respectively deposited on electrically tapes conductors 24R, 24B and 24V which are formed on the substrate 6, parallel to columns 8, from an electrically conductive and transparent layer for example indium oxide doped with tin.

In the case of the screen in Figure 1 there has three bands referenced 24R, 24B and 24V for each column 8 and the strip sets 24R, 22B and 24V are alternately polarized with respect to the cathode 2 so that the electrons extracted from the microtips 20 of a pixel, i.e. of an intersection of a line 16 and a column 8 of the cathode, either alternately directed towards the phosphor elements of each color that are next to this pixel.

In the case of Figure 1, only one strip 22R of red phosphor elements is excited by electrons 26 emitted by one of the pixels corresponding to this strip 22R.

Figure 2 is a schematic view and partial view of another known flat screen structure with microtips with which one can implement the invention.

It is specified that in the case of FIGS. 1 and 2 the same references correspond to the same elements.

In the screen of figure 2 all conductive strips 24R, 24B and 24V from anode 4 are respectively associated with columns 8R, 8B and 8V of cathode 2 of the screen. 24R conductive strips, 24B and 24V of the anode are then polarized simultaneously and the columns 8R, 8B and 8V which are located opposite these bands 24R, 24B and 24V. In other words, we excite the red pixels, blue and green which are selected.

In the case of Figure 2, only one pixel red is excited by electrons.

For questions of screen brightness in Figure 1 or Figure 2, we are looking for a maximum voltage between anode 4 and cathode 2 of this screen. Electric arcs can occur between the grid 14 and the phosphor elements which , are polarized to attract the electrons emitted by the microtips 20.

Electric arcs can also produce, in the case of figure 1, between two bands neighboring phosphor elements due to the potential difference between these two bands.

Conventionally, to resolve this problem, the conductive strips of the anode are connected to one or more interconnection conductors through electrical resistors.

This is schematically illustrated on the Figure 3 where we see part of an anode of a screen microtip dish and, in this part, two groups each comprising three conductive strips 24R, 24B and 24V.

In each group, bands 24R, 24B and 24V are respectively connected to three conductors 28R, 28B and 28V interconnection via electrical resistors 30R, 30B and 30V.

On this subject we will refer to the document next :

FR 2725072 A corresponding to US 5,592,056 A (Peyre et al.).

Different techniques are known for form these electrical resistances.

We use for example the technique of thin layers by depositing a resistive material and then engraving this material or the layering technique thick by forming these resistances by screen printing resistive ink or resistive paste.

All of these techniques translate into a number of additional steps during the manufacture of screens, which complicates this manufacturing and increases the cost of these screens.

STATEMENT OF THE INVENTION

The object of the present invention is to remedy this drawback.

It relates to an anode for flat screen display, simpler than known anodes, mentioned above.

It also relates to a method of manufacture of such an anode, simpler than known methods, mentioned above.

To do this, the present invention proposes to form resistors and bands conductive on which the elements are formed phosphors during the same stage of a process manufacture of the anode of a flat screen visualization.

Specifically, the present invention has relates to a method for manufacturing an anode of a flat display screen, in particular a screen microtip, process in which one forms, on a electrically insulating substrate, at least one set of electrically conductive strips carrying bands of phosphor elements and respectively minus one interconnected electrical conductor to the conductive strips through electrical resistance, this process being characterized by what, to form the conductive strips and the resistors, an electrically formed layer is formed conductive on the substrate and these bands are formed conductive and these resistors from this conductive layer.

We can form a resistance by strip conductive.

Alternatively, the bands can be distributed conductive in groups and form resistance by group of conductive strips.

According to a first mode of implementation particular of the process which is the subject of the invention, a single interconnection conductor and we connect all resistances to this conductor interconnection.

According to a second embodiment particular, we form a plurality of conductors interconnection and we connect alternately resistances to these interconnection conductors.

In order to form an anode for a screen in colors we can form three sets of bands alternate conductors carrying respectively strips of phosphor elements of different colors.

Resistors can have a form corrugated to reduce the size of the substrate the anode.

In the case where we want to form an anode for a screen intended to be observed through this anode, an anode substrate and a layer are used conductive which are transparent so as to leave pass the light produced by the elements phosphors.

This conductive layer is for example in indium oxide doped with tin or ITO.

The formation of conductive strips and resistors can include photolithography and an etching of the conductive layer.

The present invention also relates to a anode of a flat display screen comprising, on an electrically insulating substrate, at least one set of electrically conductive strips carrying bands of phosphor elements and respectively minus one interconnected electrical conductor to the conductive strips through electrical resistance, this anode being characterized in that the resistors are formed on the substrate, from the same electrically conductive material as the conductive strips.

The electrically conductive material is for example indium oxide doped with tin.

The invention also relates to a screen display plate including anode cathodoluminescent object of the invention, placed in gaze of a cathode capable of emitting electrons by field effect.

BRIEF DESCRIPTION OF THE DRAWINGS

les figures 1 et 2 sont des vues en perspective schématiques et partielles d'écrans plats de visualisation à micropointes connus et ont déjà été décrites,

la figure 3 est une vue schématique de résistances électriques utilisables de façon connue dans les écrans des figures 1 et 2 et a déjà été décrite, et

les figures 4 et 5 illustrent schématiquement deux modes de réalisation particuliers de l'invention qui sont utilisables respectivement dans l'écran de la figure 1 et dans l'écran de la figure 2.

The present invention will be better understood on reading the description of exemplary embodiments given below, by way of purely indicative and in no way limiting, with reference to the appended drawings in which:

FIGS. 1 and 2 are schematic and partial perspective views of known microtip display flat screens and have already been described,

FIG. 3 is a schematic view of electrical resistors usable in a known manner in the screens of FIGS. 1 and 2 and has already been described, and

FIGS. 4 and 5 schematically illustrate two particular embodiments of the invention which can be used respectively in the screen in FIG. 1 and in the screen in FIG. 2.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

As we saw above, the screens of Figures 1 and 2 use, for their anode, strips transparent conductors. These conductive strips are for example made of indium oxide doped with tin.

By acting on the doping in tin and by adapting the deposition parameters of indium oxide doped with tin or ITO as well as the heat treatments after this deposition, it is known to obtain an ITO in a range of resistivities going from about 10 ^-4 Ω.cm up to a few thousandths of an ohm. centimeter.

By choosing a resistivity and a suitable geometry, it is possible to form space-saving resistors, in a range of values ranging from a few hundred kilo-ohms to a few megohms.

Starting from a transparent substrate, by glass example, on which a layer has been formed indium oxide doped with tin having the desired characteristics, we then form the strips conductive and the access resistors to these strips in a single step including a photolithography and a engraving, techniques well known to those skilled in the art.

Figure 4 is an exemplary embodiment an anode A1 according to the invention, for a screen like the one shown on the figure 1.

It is formed beforehand, on a substrate in glass 31, two parallel interconnection conductors and adjacent 32R and 32B on one side of an area of the substrate which is reserved for conductive strips and to the resistances that we want to form in accordance with the invention.

This area constitutes the useful surface of the screen.

On the other side of this area, we form a other 32V interconnection conductor parallel to 32R and 32B conductors.

These interconnection conductors 32R, 32B and 32V are for example made of indium oxide doped with tin, which allows them to be made at the same time that the conductive strips and the resistors, or another conductive material, for example from aluminum.

We then form three sets of bands parallel to indium oxide doped with tin on the substrate 31, in the zone provided for this purpose. These bands are perpendicular to the conductors interconnection and have the references 34R for the first set, 34B for the second set and 34V for the third set.

They are intended to receive respectively strips of phosphor elements 35R, 35B and 35V (red for the 34R bands, blue for the bands 34B and green for bands 34V).

Each conductive strip is connected to one of the interconnection conductors and includes, in its end closest to this conductor, a resistance which is therefore in ITO.

The bands 34R, 34B and 34V are respectively connected to conductors 32R, 32B and 32V and the corresponding resistors are respectively referenced 36R, 36B and 36V.

We see that the resistors 36R and 36V are respectively in contact with the conductors 32R and 32V interconnection while the ends respective resistors 36B form pads 38.

Each pad 38 is subsequently connected to interconnection conductor 32B by a technique of classic interconnection, for example the technique called "bonding".

In a screen using the anode of the Figure 4, the sets of bands 34R, 34B and 34V are alternately polarized and their voltage alternately applied is less than 1 kV. She is for example 500 V.

There is then a risk of formation of a electric arc between a polarized strip and a strip neighbor as well as between a polarized strip and the grid of the screen cathode.

If the resistors have a value such that the current in the conductive strips 34R, 34B and 34V either limited to a few milliamps an electric arc will not be able to start. For example with tension anode of 500 V and resistances of 500 kΩ maximum current is limited to 1 mA, which prevents the formation of electric arcs.

The current per pixel being of the order of 20 µA an indium oxide doped with tin is used, the resistance per square is 500 Ω. Each of resistors 36R, 36B and 36V of 500 kΩ then form by example a 20 µm wide and 20 mm long strip.

This strip can be straight but has preferably a wavy shape, as seen on the Figure 4, to less clutter the substrate 6 of the anode.

We get a display screen according to the invention by replacing, in the screen of Figure 1, the anode 4 by the anode A1 according to the invention of FIG. 4, the bands 34R, 34B and 34V being parallel to the columns 8 of the cathode 2.

Figure 5 is another example of manufacture of an anode A2 in accordance with the invention, for a screen like the one shown on Figure 2.

In the case of the anode of FIG. 5, we forms a single interconnection conductor beforehand 32 (instead of the three interconnection conductors of Figure 4) and all bands 34R, 34B and 34V are then formed, with their respective resistances 36R, 36B and 36V and are in contact with the conductor interconnection 32 through these resistances.

In a screen using the anode of the figure 5 all conductive strips 34R, 34B and 34V are polarized simultaneously and the voltage that their is applied may be several kilovolts and is worth for example 3 kV.

An electric arc is then likely to occur between the conductive strips 34R, 34B and 34V of the anode and the grid of the cathode of the screen.

If we tolerate a voltage drop of 2%, that is to say for example around 60 volts, within resistances when these are crossed by the current of a pixel, i.e. approximately 20 µA, these resistors must have a value of 3 MΩ. The current in each band is then limited to 1 mA, this which prevents the formation of electric arcs.

Such resistances can for example each be formed of a straight strip or preferably wavy, in ITO of square resistance 1000 Ω, 20 µm wide and 60 mm long.

We get another display screen according to the invention by replacing, in the screen of FIG. 2, the anode 4 by the anode A2 in accordance with the invention of FIG. 5, the bands 34R, 34B and 34V being parallel to columns 8R, 8B and 8V of the cathode 2.

Various variants and modifications may be made to the invention as described and will appear to those skilled in the art.

In particular, we have only described the case where only one resistance is used per conductive strip anode but it is possible to form groups comprising multiple bands and using one resistance adapted by group.

Likewise, reference was made in the description above to a color screen but the invention also applies to a monochrome screen if this screen has an anode provided with bands phosphor elements.

In addition, examples of manufacture of anodes in which the substrate is transparent to observe the screen through this substrate. However, in other examples, we can form conductive strips and resistors associated as well as the phosphor elements on a opaque substrate in the case where we form a screen that you can observe through its cathode.

The invention does not only apply to microtip screens. It also applies to the manufacture of all emission screens field including carbon emission screens or microcrack screens.

Claims (13)

Method of manufacturing an anode of flat display screen, in particular a screen microtip, process in which one forms, on a electrically insulating substrate (31), at least one set of electrically conductive strips (34R, 34B, 34V) respectively carrying bands of elements phosphors and at least one electrical conductor interconnection (32, 32R-32B-32V) connected to the bands conductive via resistors electric (36R, 36B, 36V), this process being characterized in that, to form the strips conductive and resistors, we form a layer electrically conductive on the substrate and one forms these conductive strips and these resistances to from this conductive layer. Method according to claim 1, in which we form a resistor (36R, 36B, 36V) by conductive strip (34R, 34B, 34V). Method according to claim 1, in which the conductive strips are divided into groups and we form resistance by group of conductive strips. Method according to any one of claims 1 to 3, in which one is formed interconnection conductor (32) and we connect all resistors (36R, 36B, 36V) to this conductor interconnection. Method according to any one of claims 1 to 3, in which a plurality of interconnection conductors (32R, 32B, 32C) and the resistors are connected alternately (36R, 36B, 36C) to these interconnection conductors. Method according to any one of claims 1 to 5, in which three are formed sets of alternating conductive strips (34R, 34B, 34V) respectively carrying strips of elements phosphors of different colors. Method according to any one of claims 1 to 6, wherein the resistors (36R, 36B, 36V) have a wavy shape. Method according to any one of claims 1 to 7, wherein the substrate (31) and the conductive layer are transparent so that let in the light produced by the elements phosphors. Method according to any one of claims 1 to 8, wherein the conductive layer is made of indium oxide doped with tin. Method according to any one of claims 1 to 9, wherein the formation of conductive strips (34R, 34B, 34V) and resistors (36R, 36B, 36V) includes a photolithography and a etching of the conductive layer. Anode of a flat display screen comprising, on an electrically insulating substrate (31), at least one set of bands electrically conductors (34R, 34B, 34V) respectively carrying bands of phosphor elements (35R, 35B, 35V) and at minus an electrical interconnection conductor (32, 32R-32B-32V) connected to the conductive strips by through electrical resistors (36R, 36B, 36V), this anode being characterized in that the resistors are formed on the substrate, from the same electrically conductive material as the strips conductive. Anode according to claim 11, in which the electrically conductive material is indium oxide doped with tin. Flat display screen including: a cathode capable of emitting electrons by field effect, and a cathodoluminescent anode placed opposite the cathode and according to any one of claims 11 and 12.

Images