EP0202974A1 - Colour matrix display, its production and device including the same - Google Patents

Abstract

The screen comprises electroluminescent zones (10, 12) distributed in a matrix and interposed between row electrodes (i) and crossed column electrodes (j), each row electrode (i) being formed of m first parallel conductive strips (3) of different widths and each column electrode (j) being formed of n second parallel conductive strips (4, 6) of different widths, m and n being positive integers of which at least one is 2. The electroluminescent zones (10, 12) are defined by the crossing of the first (3) and the second (4, 6) conductive strips. Application to the display in halftone by means of electrical addressing circuits operating in "all or nothing".

Description

The present invention relates to a matrix screen, its manufacturing process and a matrix display device with several shades of colors, controlled in all or nothing, comprising such a screen. It finds an application in optoelectronics and in particular in the analog display of complex images or in the display of alpha-numeric characters, these displays being either monochrome or polychrome.

Telematic and computer consoles, such as electronic directory terminals and microcomputers are becoming everyday objects of daily life. Most of these devices currently in use are equipped with cathode ray display tubes. However, other display devices such as for example flat matrix screens are increasingly supplanting cathode ray tubes, which are heavy, bulky and visually uncomfortable. However, some of these flat screens may offer halftone or multiple shade graphics and even color graphics.

More specifically, the invention relates to a flat matrix screen made of a material, having optical properties which can be modified electrically, sandwiched between a first family of p line electrodes formed by parallel conductive strips and a second family of q column electrodes formed from parallel conductive strips. The line electrodes and the column electrodes being crossed, an image point x _ij of the screen is defined by the region of overlap of a line electrode i and a column electrode j, where i and j are integers such as 1 5 i ≦ p and 1 5 j 5 q. Means make it possible to deliver on each electrode electrical signals making it possible to electrically modify the optical property of the material, in two different states.

Numerous flat matrix screens of this kind are known which use an electroluminescent material as sensitive material; this material is compatible with halftone or multiple shade display as well as color display. Such matrix screens are described in particular in an article by IEEE Transactions on Electron Devices, vol. ED-30, n ° 5 of May 1983, pages 460-463, entitled "Thin Film Electroluminescent Devices: Influence of Mn-Doping Method and Degradation Phenomena".

The invention applies particularly well to such matrix screens, but it applies more generally to all display screens comprising a material of which an optical property can be modified by means of an electrical excitation. This material can be a solid or liquid body, amorphous or crystalline. The optical property can be an opacity, a refractive index, a transparency, an absorption, a diffusion, a diffraction, a convergence, a rotary power, a birefringence, an intensity reflected in a determined solid angle, etc ...

The light-emitting matrix screens generally used operate all or nothing, that is to say that they only allow a display in two colors, for example black and white. Such a matrix screen is described in particular in document FR-A-2 489 023. Their advantage is to use relatively simple addressing or control integrated circuits.

To allow display with several shades of colors or half-tones, for example different from your shades of gray, various solely electronic methods have been envisaged. These different methods based on the application of different electrical signals according to the half-tone that it is desired to obtain, require the manufacture of relatively complex integrated control circuits whose cost price, relative to an electrode-column of the screen matrix, is six times the cost price of a control circuit operating in all or nothing. Given the number of row electrodes and column electrodes, the overall cost price of the control circuits is prohibitive.

The object of the present invention is precisely a matrix screen, in particular electro-luminescent allowing, for the eye, a display on a linear scale of half-tones or shades of the same color making it possible to remedy the various drawbacks given above. It makes it possible in particular to use integrated addressing or control circuits for the screen provided for all-or-nothing operation (economic advantages) as well as to operate the elements of the matrix with a single excitation voltage ( convenience of making the screen).

More specifically, the subject of the invention is a matrix screen comprising, in a known manner, a layer of material having electro-optical properties, interposed between p parallel electrode-lines and q parallel electrode-columns, the _ electrode-lines and the column electrodes being crossed, an image point _Xij of the screen being defined by the region of the electro-optical material covered by the line electrode i and the column electrode j, where i and j are integers such that 1 5 i ≦ p and 1 ≦ j ≦ q, and characterized in that each row electrode is formed of m first parallel conductive strips of different widths, and each column electrode is formed of n second parallel conductive strips of different widths, m and n being positive integers of which at least one is t 2, and in that the layer of - material is cut over its entire thickness into several zones distributed in a matrix, these zones being defined by the crossing of said first and second conductive strips.

In other words, at each intersection of a first conductive strip of the column electrodes and of a second conductive strip of the row electrodes, there is an area of electro-optical material, this area of material exactly coinciding with the covering surface of the first and second corresponding conductive strips.

The use of row electrodes and column electrodes each formed from parallel conductive strips has in particular been described in the document FR-A-2 489 023 cited above. However, this cutting of the electrodes was used to reduce the effects due to structural defects in the electroluminescent material and not to display several halftone displays.

According to a preferred embodiment, the p line electrodes have an identical structure. Similarly, the q column electrodes have an identical structure which may or may not be different from that of the row electrodes.

Advantageously, the layer of electro-optical material is formed from kz 2 materials in the solid state having different light-emitting properties, k being a positive integer. In particular when k = 2, these materials can both be zinc sulfide doped with Mn ²⁺ ions, the amount of dopant and / or the thickness of these materials being different.

Advantageously, the k? 2 materials are separated from each other by a dielectric material.

The particular subdivision of the layer of material having electro-optical properties as well as the use of materials having different electro-optical properties, in particular electroluminescent properties, make it possible to produce a matrix display with several shades of colors or half-tones while using integrated circuits for addressing or controlling said layer of conventional electro-optical material, operating in all or nothing.

The invention also relates to a matrix display device with several shades of colors comprising a matrix screen as described above, as well as means for applying, independently, to the conductive strips of each line electrode and of each column electrode of electrical signals used to control, in all or nothing, the electro-optical property of the layer of material.

The present invention also relates to a method of manufacturing a matrix screen as described above.

According to the invention, this method consists in producing zones of electro-optical material, distributed in matrices and separated from each other by a dielectric, between a first family of p parallel electrodes each formed of m first parallel conductive strips of different widths and a second family of q parallel electrodes each formed by n second parallel conductive strips of different widths, m and n being positive integers of which at least one is ≧ 2; the electrodes of the first family and the electrodes of the second family being crossed, the zones of electro-optical material are defined by the crossing zones of the first and of the second conductive strips, an image point X _ij of the screen being defined by the crossing of an electrode i of the first family and an electrode j of the second family, i and j being integers such that 1 ≤ i K p and 1 ≦ j ≦ q.

The method of manufacturing a matrix screen according to the invention consists of a succession of relatively simple implementation operations.

• a) -réalisation de l'une des deux familles d'électrodes sur un substrat,
• b) -dépôt d'une couche d'épaisseur donnée d'un premier matériau diélectrique,
• c) -réalisation dans la couche de premier matériau d'au moins une première ouverture à chaque croisement d'une électrode de la première famille et d'une électrode de la seconde famille, ces premières ouvertures étant définies par le croisement d'une première bande conductrice et d'une seconde bande conductrice,
• d) -remplissage partiel desdites premières ouvertures par un second matériau électro-optique,
• e) -recouvrement du second matériau par un troisième matériau diélectrique afin de combler totalement lesdites premières ouvertures, et
• f) -réalisation de la seconde famille d'électrodes.

According to a preferred embodiment of the method of the invention, the following successive steps are carried out:

• a) making one of the two families of electrodes on a substrate,
• b) depositing a layer of given thickness of a first dielectric material,
• c) -realization in the layer of first material of at least a first opening at each crossing of an electrode of the first family and an electrode of the second family, these first openings being defined by the crossing of a first conductive strip and a second conductive strip,
• d) - partial filling of said first openings with a second electro- material optical,
• e) covering of the second material with a third dielectric material in order to completely fill said first openings, and
• f) realization of the second family of electrodes.

Advantageously, m and n are at most equal to 2. In particular, m can be equal to 1 and n to 2, and conversely, m can be equal to 2 and n to 1; this makes it possible to obtain a number of halftones or shades equal to 4. Similarly, m and n can both be taken equal to 2, which makes it possible to obtain a display with eight shades or halftones. In addition, the values of m and n determine the maximum number of electroluminescent materials that can be used. This number is defined by the product m.n.

Of course, m and n can take much larger values, however, the economic interest risks decreasing as m and n increase since the number of electrical accesses to the different image points of the matrix increases in proportion.

• -réalisation dans la couche de premier matériau d'au moins une seconde ouverture à chaque croisement d'une électrode de la première famille et d'une électrode de la seconde famille, ces secondes ouvertures, définies par le croisement d'une première bande conductrice et d'une seconde bande conductrice, étant pratiquées en face des autres premières et secondes bandes conductrices,
• - remplissage partiel desdites secondes ouvertures par un quatrième matériau électro-optique, et
• -recouvrement du quatrième matériau électro-optique par un cinquième matériau diélectrique afin de combler totalement lesdites secondes ouvertures.

According to a preferred embodiment of the method of the invention, the first openings being made facing one of the first conductive strips of each electrode of the first family and one of the second conductive strips of each electrode of the second family, the following operations are carried out between steps e) and f):

• -realization in the layer of first material of at least a second opening at each crossing of an electrode of the first family and an electrode of the second family, these second openings, defined by the crossing of a first conductive strip and a second conductive strip, being formed opposite the other first and second conductive strips,
• partial filling of said second openings with a fourth electro-optical material, and
• covering of the fourth electro-optical material with a fifth dielectric material in order to completely fill said second openings.

The use of two materials having different electro-optical properties, and in particular different electroluminescent properties, greatly contributes to obtaining a display with several shades or half-tones of the same color.

Advantageously, the first and / or second openings are made in the layer of first material by depositing on it a resin mask, representing the image of these openings, that is to say serving to define their dimensions as well as their locations, then by etching said layer of first material. With such an etching process, the first and / or second openings are then filled with the corresponding electro-optical material by depositing on the body of the structure a layer of said material, this layer having a thickness less than that of the layer of first material, then a layer of a dielectric material is deposited on the electro-optical material. Finally, the resin mask is removed. This technology known as the Anglo-Saxon "LIFT-OFF" makes it possible to keep electro-optical material, covered with the corresponding dielectric material, only inside the first and / or second openings and thus obtain a structure that is practically plane.

Advantageously, there is interposed between the first family of electrodes and the layer of first dielectric material a layer of a sixth dielectric material making it possible to provide a kind of electrical protection of the layer of electro-optical material. Similarly, to increase the flatness of the structure if necessary, a layer of a seventh dielectric material is interposed between the second family of electrodes and the layers of the second and fifth dielectric materials.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows, given by way of explanation and without limitation.

For clarity, the description refers to a matrix screen whose electro-optical material is a solid material having electroluminescent properties. However, as indicated above, the invention is of much more general application.

• -la figure 1 représente schématiquement, en perspective éclatée, un dispositif d'affichage matriciel comportant un écran matriciel conformément à l'invention,
• -la figure 2 représente schématiquement, en vue de dessus, le croisement des électrodes-lignes et des électrodes-colonnes de l'écran de la figure 1,
• -les figures 3a à 3d représentent - schématiquement, en vue de dessus, les extrémités des électrodes de l'écran matriciel de la figure 1,
• -les figures 4 à 12 représentent - schématiquement, en coupe longitudinale, les différentes étapes du procédé de fabrication d'un écran matriciel selon l'invention.

The description refers to the appended figures, in which:

• FIG. 1 schematically represents, in exploded perspective, a matrix display device comprising a matrix screen according to the invention,
• FIG. 2 schematically represents, in top view, the intersection of the row electrodes and the column electrodes of the screen of FIG. 1,
• FIGS. 3a to 3d represent - schematically, in top view, the ends of the electrodes of the matrix screen of FIG. 1,
• FIGS. 4 to 12 represent - schematically, in longitudinal section, the different stages of the process for manufacturing a matrix screen according to the invention.

As shown in Figure 1, the matrix screen according to the invention comprises a transparent insulating substrate 2, made for example of glass. This substrate 2 constitutes the front face of the matrix screen. On the rear face of the screen, there is a first family of p parallel electrodes i, playing for example the role of line electrodes. These p line electrodes each consist of m parallel conducting strips 3, of different widths. In the case shown, m is equal to 1. These electrodes are made of a metallic material and in particular aluminum.

Furthermore, overcoming the substrate 2, there is a second family of q parallel electrodes j. These electrodes j play the role of column electrodes when the electrodes i play the role of row electrodes and vice versa. The electrodes j are each formed of n conductive strips parallel to each other, of different widths. In the case shown, each column electrode j is formed of two conductive strips respectively bearing the references 4 and 6. These electrodes j are transparent and can be made of In ₂ O ₃ , SnO ₂ , or of indium oxide and d tin, known by the abbreviation ITO

The conductive strips constituting the line electrodes i and those constituting the column electrodes j are perpendicular.

Between the line electrodes i and the column electrodes j is interposed a solid layer 8 having electroluminescent properties. The useful surface of this layer 8, as shown in FIG. 2, is broken down into a mosaic of image point x _ij corresponding to the areas of overlap of a line electrode i and a column electrode j. In order to obtain identical elementary image points x _ij , the line electrodes may be identical. The same is true for column electrodes. However, nothing prevents making different row electrodes and / or different column electrodes from each other.

As shown in FIGS. 1 and 2 and for m and n being respectively equal to 1 and 2, the layer 8 having the light-emitting properties and therefore the image points x _ij are formed from two types of zones 10 and 12 respectively distributed in matrix form. The light-emitting zones 10 are located opposite the conductive strips 4 of the column electrodes and the light-emitting zones 12 are located opposite the conductive strips 6 of said column electrodes (FIG. 2).

These two types of zones 10 and 12 in particular have the shape of a rectangular parallelepiped of thickness e. The two faces respectively 10a, 10b and 12a, 12b oriented parallel to the electrodes i and j of the matrix screen have an area equal to the corresponding crossing surface of the conductive strips constituting the row electrodes and the column electrodes. In particular, the faces 10a and 10b of each zone 10 of electroluminescent material exactly coincide with the zone of overlap of the conductive strip 4 of a column electrode j and of the single conductive strip 3 constituting a line electrode i (FIG. 2 ). Likewise, the faces 12a and 12b of each zone of electroluminescent material 12 exactly coincide with the zone of overlap of the conductive strip 6 of a column electrode j and of the single conductive strip 3 constituting a row electrode i.

According to the envisaged application, the electroluminescent materials constituting zones 10 and 12 respectively can be identical or different. Likewise, the thickness e of these materials can be identical or different. As the electroluminescent material, it is possible to use ZnS doped Mn, material emitting in yellow, ZnS doped TbF3, material emitting in green, or SrS doped CeF ₃ , material emitting in blue. Preferably, the material constituting the light-emitting zones 10 is zinc sulphide doped with manganese with a manganese concentration of 3 to 3.5 mol%, and that constituting the light-emitting zones 12 is zinc sulphide doped with manganese with a manganese concentration of 1.5 mol%, these two materials having the same thickness e.

As shown in FIG. 1, the two different zones 10 and 12 can be separated from each other by a dielectric material 14 which can be, for example, TiO ₂ , Ta ₂ O ₅ , Si, N., Al ₂ O ₃ , Si0 ₂ , Y ₂ O ₃ , etc ... Preferably, the dielectric 14 is Y ₂ O ₃ .

Advantageously, the electroluminescent layer 8 is covered with a layer 16 of a dielectric material cut according to the same configuration as that of the electroluminescent layer. Indeed, the electroluminescent zones 10 are each covered with a dielectric zone 18 and the electroluminescent zones 12 are each covered with a dielectric zone 20. These dielectric zones 18 and 20 can be produced using of the same dielectric material or using two different dielectric materials. These zones 18 and 20 can for example be made of Ta ₂ O ₅ , Y203, Al ₂ O ₃ , Si ₃ N ₄ , Zr0 ₂ , SiO ₂ , etc ... Preferably, these zones 18 and 20 are made of Ta ₂ 05.

As shown in FIG. 1, a uniform layer 21 of dielectric material can be interposed between the layer of electroluminescent material 8 and the column electrodes j. Likewise, a uniform layer 22 of a dielectric material can be inserted between the line electrodes i and the dielectric zones 18 and 20. These layers 21 and 22 can be made of a dielectric material identical or different from that constituting the dielectric zones 18 and 20. In particular, these two layers 21 and 22 can be made of Ta ₂ O ₅ , Ti0 ₂ , Y203, Al ₂ O ₃ , Zr02, Si ₃ N ₄ , SiO ₂ , etc ... Preferably, these two layers 21 and 22 are produced in Ta ₂ 05.

In Figures 3a to 3c, there is shown, in top view, the different possible shapes of the ends of the row electrodes and / or column electrodes of the matrix screen in the particular case where each of these electrodes is formed of two conductive strips respectively 24 and 26, of different widths. These row or column electrodes have a periodic structure; P which represents the pitch of this structure is worth for example 0.35 µm.

As shown in FIG. 3a, the ends 24a and 26a of the conductive strips 24 and 26 of the same electrode can retain the same shape as the body of the corresponding conductive strips and for example the shape of a strip of constant width. In this case, the ends 24a and 26a of the conductive strips 24 and 26 are therefore asymmetrical. For simultaneous control of the two conductive strips 24 and 26 of the same electrode, the asymmetrical shape of the ends of said strips requires the use of asymmetrical connectors to connect said electrodes by means of control of the matrix screen.

Conversely, as shown in FIGS. 3b to 3d, the ends 24a and 26a of the corresponding conductive strips 24 and 26 may have a shape different from that of the body of said strips.

In particular, these ends 24a and 26a can have the shape of a strip of variable width, thus making it possible to obtain symmetrical ends of resolution P / 2 or resolution P as shown respectively in FIGS. 3b and 3c. In FIG. 3b, in the plane of this figure, the ends 24a and 26a of the conductive strips have the shape of a trapezoid with two perpendicular sides and in FIG. 3c, in the plane of this figure, the shape of a trapezoid with three perpendicular sides.

The ends 24a and 26a of the conductive strips may also have the shape of a block of greater width than that of the corresponding conductive strip, as shown in FIG. 3d; the resolution of the extremities is P.

The electroluminescent matrix screen described above can allow a display of several shades of colors or half-tones using integrated circuits, to control the electroluminescent properties of the electroluminescent layer 8 and therefore of the electroluminescent zones 10 and 12, provided to function in all or nothing. A display can be obtained by applying, independently, to the m conductive strips of each row electrode and to the n conductive strips of each column electrode, suitable electrical signals.

Advantageously, the different light-emitting zones 10 and 12 of the matrix screen can be operated using the same excitation voltage.

Conventionally, the control of the screen can be obtained by applying for example on the line i a potential -V / 2 and simultaneously on the columns either a potential V / 2, for the image point x _ij displayed, or a potential -V / 2, for the image point x _ij not displayed, and by applying to the other lines a zero potential. The image points between line i and the columns are then subjected to a voltage V or zero and the other image points to a voltage V / 2 insufficient to allow them to be displayed. Advantageously, the potentials applied to the terminals of the image points x _ij are alternating signals with zero mean value.

In accordance with the invention, each elementary display point x _ij , defined by the crossing of a row electrode i and a column electrode j, is divided into mn zones of different surfaces, for example two in number, as shown in FIG. 2. In this figure, the hatched part of an elementary display point x _ij represents the active zone thereof, that is to say the zone having the light-emitting properties, and the non-hatched part represents the non-active area of said image point.

Furthermore, V represents the "vertical" width of the active area of the image point x _ij and H represents the "horizontal" width of said area. In the case where the active zone of the image point is formed by two different light-emitting zones 10 and 12, the α "vertical" width of the light-emitting zone 12 is called αV and (1-a) V the "vertical" width of the other electroluminescent zone 10.

In addition, the ratio of the luminescence of the electroluminescent zone 10 to the luminescence of the electroluminescent zone 12 is called y, the luminescence of these zones being determined by applying the same nominal voltage across said zones.

This luminescence ratio can be modified there in different ways for example by using the same electroluminescent materials, but having different thicknesses, by varying the doping of the phosphor (Mn ²⁺ for example) of these materials and by keeping a constant thickness, combining the two (different thickness and doping), or by subjecting these two materials to a different heat treatment during or after their deposition during the manufacture of the matrix screen. The influence of heat treatment on the luminescence of ZnS: Mn is described in particular in an article entitled "Electroluminescent flat screens with capacitive coupling: importance and study of the dielectric layer" published in Le Vide, Les Couches Thins, 222, de mai- June-July 1984, pages 205 to 212.

By taking L ₀ , the luminance obtained for a light point, for example white, a coefficient a equal to 1/3 and a luminescence ratio y equal to 1, it is possible to obtain, with the screen according to the invention, four shades or halftone for two light-emitting zones per image point: the first shade which is the darkest, for example black, has zero luminance, the second shade, slightly lighter, a luminance equal to 1/3 of L _o HV , the third shade, even lighter, a luminance equal to 2/3 of LHV and the fourth shade, corresponding to white, a luminance equal to L ₀ HV. In a concrete case, we can take H and V equal to 250 µm and L equal to 100 cd per m ² . The same result can be obtained by taking a equal to 0.5 and γ equal to 3.

By using line electrodes and column electrodes each formed from two conductive strips of different widths, it is possible to obtain eight levels of luminance which can be perceived by the eye in the form of very distinct half-tones or shades.

formules dans lesquelles n représente le nombre de niveaux de luminance donc de nuances désirées.As a first approximation, knowing that the sensation perceived by the eye is proportional to the logarithm of the light excitation received by it, we can choose a geometric law of progression with a progression ratio p. Thus, given the contrast C that the screen can provide, C being the ratio between the luminescence of the bright color such as white and that of the dark color such as black, the ratio p between two half-tones or shades is given by:

formulas in which n represents the number of levels of luminance therefore of desired shades.

Thus for contrasts C varying from 10 to 50, it is possible to obtain, with m and n equal to two, eight half-tones with 1.39 ≦ p ≦ 1.75.

Of course, the law given above can be, for economic or other reasons, brought to be replaced by other laws of progression of halftone. For example, it is possible to take a tiering of the different luminance levels representing respectively 100% of C, 90% of C, 80% of C, 70% of C, 60% of C, 50% of C, 40% of C, if C represents the maximum contrast between the bright color (white) and the dark color (black).

We will now describe with reference to FIGS. 4 to 12, a particularly original method for manufacturing the electroluminescent matrix screen described above.

The first steps of the method, as shown in FIG. 4, consist in producing one of the two families of row or column electroles on a substrate 30, in particular made of glass. This is achieved by depositing a transparent conductive layer 32 in particular in In ₂ O ₃ , SnO ₂ or ITO, for example by the chemical vapor deposition technique assisted by plasma or not, then by etching said layer 32 through a resin mask 34 representing the image of the electrodes to be produced, that is to say used for define the shape and location of these electrodes. This etching can be carried out dry anisotropically (reactive ion etching or by reverse sputtering) or alternatively wet, for example by simple chemical attack.

These electrodes are for example, as shown in Figure 5, in the form of two parallel conductive strips 32a, 32b of different widths, arranged alternately. In particular, these electrodes 32a and 32b may have a thickness ranging from 100 to 150 nm; the pitch of the structure may be 0.35 μm, the strips 32a having 150 μm in width, the strips 32b 100 μm in width and the inter-conductive zones 50 μm in width.

After elimination of the resin mask 34, for example by dissolution in acetone, in the case of a resin of the phenol formaldehyde type, the body of the structure is possibly covered, that is to say the entire structure except the ends. conductive strips 32a and 32b of the electrodes, by a layer 36 of a dielectric material. This layer 36 which plays the role of protective layer can be made of Ta ₂ O ₅ , Y ₂ O ₃ , Al ₂ O ₃ , ZrO ₂ , Si, N ₄ , SiO _z , TiO _z , etc ... Preferably, this dielectric layer 36 is made of Ta ₂ O ₅ with a thickness of 300 nm; it can be deposited by vacuum evaporation, by sputtering, or by any other technique for depositing thin layers.

The next step of the method consists in covering the dielectric layer 36 with a layer 38 in a dielectric material. This layer 38 must be inert to the agents dissolving the resins generally used as an etching mask in photolithography.

The role of the dielectric layer 38 is to protect the electroluminescent material or materials used, during the various stages of production of the matrix screen. For this reason, its thickness should be greater than that of the electroluminescent layer. Preferably, this layer 38 is made of a material different from that constituting the dielectric layer 36 in order to facilitate the stopping of the subsequent etchings of the layer 38. The latter can in particular be made of TiO ,, SiO ₂ , Al ₂ O ₃ , Si ₃ N ₄ , Ta ₂ O ₅ , Y ₂ O ₃ . In the case of a dielectric layer 36 made of Ta ₂ O ₅ , the dielectric layer 38 can be made of Y ₂ O ₃ . This dielectric layer 38 can for example be deposited by vacuum evaporation, sputtering, or any other technique of depositing thin layers, and have a thickness of 1200 nm.

The next step in the process, as shown in FIG. 6, consists in making a resin mask 40 making it possible to define the dimension and the location of the first openings 44 to be produced in the layer of dielectric material 38. This mask 40 is produced according to conventional photolithography methods, that is to say by depositing on layer 38 a layer of photosensitive resin, in particular positive, by insolating this resin through a suitable mask and then developing said resin. This positive resin is for example a resin of the phenol formaldehyde type.

The mask 40 is such that it represents the image of the first openings 42 to be produced in the dielectric layer 38; its shape therefore depends on the shape of the row electrodes and the column electrodes envisaged for the production of the matrix screen. This mask 40 comprises openings 44, an opening 44 at least being provided at each crossing of an electrode of the first family and of an electrode of the second family, that is to say at each crossing of a line electrode and a column electrode.

For row electrodes and column electrodes each consisting of two parallel conductive strips of different widths, such as 32a and 32b, the openings 44 of the mask 40 are located opposite a first conductive strip, for example 32a of each electrode of the first family and opposite a first conductive strip of each electrode of the second family; the width and the length of these openings are equal respectively to the widths of the conductive strips of the electrodes of the first and second families which cross.

In particular, this mask 40 is provided with openings 44 arranged, as shown in FIGS. 1 and 2, at the location of the light-emitting zones 10.

Through the mask 40, a first etching of the dielectric layer 38 is then carried out, over its entire thickness, so as to produce the openings 42. This etching can be carried out dry or wet using a isotropic etching (chemical attack) or anisotropic etching (reactive ion etching or _' reverse sputtering _' ). In the case of a layer 38 of Y ₂ O ₃ , the etching can be carried out by chemical attack in an aqueous medium with as attack agent a mixture of hydrochloric acid, orthophosphoric acid and acetic acid, the concentration of these acids being 0.1 N. Such a solution does not attack the Ta ₂ O ₅ preferably constituting the dielectric layer 36; stopping the etching of layer 38 is therefore easy to detect.

The next step in the process consists, as shown in FIG. 7, in covering the entire body of the structure (except at the ends of the electrodes) with a layer 46 of a first electroluminescent material. This layer 46 can for example be made of ZnS doped with manganese, of ZnS doped with TbF _" or of SrS doped with CeF3. Advantageously, this layer 46 is made of ZnS with a doping of manganese of 3 to 3.5 mol%; has a luminance of 55 cd / m ^2. This electroluminescent layer 46 having for example a thickness of 800 nm can be deposited by vacuum evaporation.

After deposition of the electroluminescent layer 46, a layer 48 of a dielectric material is deposited thereon. This layer 48, the role of which is to protect the electroluminescent layer 46, during the elimination of the resin mask 40, can be made with the same material as that used for the dielectric layer 36. For example, it can be made of Ta ₂ O ₅ , TiO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , Si ₃ N ₄ , Zr02, SiO ₂ , etc ... Preferably, this layer 48 is made of tantalum oxide and has a thickness of 300 nm . This layer 48 of Ta ₂ O ₅ can be obtained by vacuum evaporation or sputtering.

The resin layer 40, having served as a mask for the first etching of the dielectric layer 38, is then eliminated, using a suitable solvent, for example acetone for a phenol-formaldehyde resin. The elimination of the resin layer 40 also makes it possible to eliminate the regions of the electroluminescent layer 46 and the regions of the dielectric layer 48 surmounting the resin layer 40. The structure obtained is shown in FIG. 8.

The next step of the method consists in making, by the conventional methods of photolithography (deposition, exposure, development), a resin mask 50, as shown in FIG. 9. This mask 50 represents the image of the second openings 52 to make in the dielectric layer 38; its shape depends on the shape of the row electrodes and the column electrodes envisaged for producing the matrix screen. This resin mask 50 is provided with openings 54, at least one opening being located at each intersection of an electrode of the first family and an electrode of the second family.

These openings 54 are located opposite a second conductive strip for example 32b of each electrode of the first family and opposite a second conductive strip of each electrode of the second family, in the case where these electrodes are formed of two conductive strips. The dimensions of these openings are defined by the width of the conductive strips of the electrodes of the first and second families.

In particular, this mask 50 can be provided with openings 54 arranged, as shown in FIGS. 1 and 2, at the location of the light-emitting zones 12.

The next step of the process consists in eliminating the regions of the dielectric layer 38 not coated with resin, until the dielectric layer 36 is exposed. This etching can be carried out dry or wet using isotropic etching, for example by chemical attack, or anisotropic etching in particular by a reactive ion etching process or reverse sputtering. In the case of a layer 38 produced in Y ₂ O ₃ , the etching can be carried out by chemical attack using a 0.1N mixture of HCl, H ₃ PO ₄ and CH.COOH, an attacking agent not including the tazos constituting the dielectric layer _'36.

The next step in the process consists, as shown in FIG. 10, in covering the body of the structure (except at the ends of the electrodes) with a layer 56 of a second electroluminescent material. Preferably, the material constituting this layer 56 is different from that constituting the electroluminescent layer 46 in order to obtain different electroluminescent properties, even when the same voltage is applied to the terminals of these two materials on the finished matrix screen.

In particular, the luminescence ratio y between the two materials can be 2.4 for the same excitation voltage. This can be achieved by using as an electroluminescent material for the layer 56 of ZnS doped with manganese with a concentration of 1.5 mol% of manganese, this layer having, like the electroluminescent layer 46 in ZnS: Mn a thickness of 800 nm. The deposition of this layer 56 can be carried out as before by evaporation under vacuum.

After the deposition of the electroluminescent layer 56, a layer 58 of a dielectric material is deposited thereon. The purpose of this layer is to protect the electroluminescent layer 56 during the dissolution of the resin mask 50. This layer 58. Of material dielectric can be made of a material identical or different from that constituting the dielectric layer 48. It can in particular be made of Ta ₂ O ₅ , Y ₂ O ₃ , Al ₂ O ₃ , ZrO ,, Si ₃ N ₄ , TiO ,, Si0 ₂ , etc ... Preferably, this layer is made of Ta ₂ O ₅ like the dielectric layer 48. This layer of Ta ₂ O ₅ can have a thickness of 300 nm and can be deposited by evaporation under vacuum or sputtering .

As shown in FIG. 11, the resin mask 50 which was used for the second etching of the layer 38 is then eliminated. In the case of a mask 50 made of a resin of the phenol-formaldehyde type, this elimination can be carried out with acetone. The elimination of the resin layer 50 simultaneously entails the elimination of the regions of the layer 56 and 58 surmounting said mask.

The next step in the process optionally consists in covering the body of the structure obtained (except at the ends of the electrodes) with a layer 60 of a dielectric material as shown in FIG. 12. This layer 60, having the role of leveling the surface of the structure when the need arises, can for example be made of the same material as that constituting the layer of dielectric 36. For example this layer 60 can be made of Ta20s and have a thickness of 300 nm. This layer can be deposited by vacuum evaporation or by sputtering.

The following stages of the method consist in producing, by the conventional methods of photolithography, the second family of electrodes, playing the role of row electrodes when the electrodes of the first family play the role of column electrodes. These electrodes can be obtained by depositing a thin metallic layer on the body of the structure, for example by sputtering, then by etching said layer through an appropriate mask defining the dimensions and the location of the electrodes.

These electrodes can be made of aluminum, ... Preferably they are made of aluminum. These electrodes have for example a thickness of 100 to 150 nm and consist of conductive strips parallel to each other, the pitch of the structure being equal to 0.35 µm. The structure of these electrodes can be identical or different from that of the first family.

The final structure of the electroluminescent screen thus produced is for example that shown in FIG. 1.

The method of manufacturing a matrix screen according to the invention is simple to implement since the various stages which constitute it are well known to those skilled in the art.

The description given above has of course been given only for explanatory purposes; any modifications, in particular as regards the thickness and the nature of the various materials constituting the screen, can be envisaged without departing from the scope of the invention. Furthermore, the dielectric layers 36 and 60, directly in contact with the row electrodes and column electrodes can be eliminated when the technique of depositing layers 48 and 58 makes it possible to obtain faultless layers.

Claims (15)

1. Matrix screen comprising a layer of material (8) having electro-optical properties, interposed between p parallel electrode-lines (3) and q parallel column electrodes (4, 6), the line electrodes and the column electrodes being crossed, an image point x _{; j} of the screen being defined by the region of the electro-optical material covered by the row electrode i and the column electrode j, i and j being integers such as 1 5 i ≤ p and 1 ≦ j ≦ q, characterized in that each row electrode is formed of m first parallel conductive strips (3) of different widths, and each column electrode is formed of n second parallel conductive strips (4, 6) of different widths, m and n being positive integers at least one of which is ≧ 2, and in that the material layer (8) is cut over its entire thickness into several zones (10, 12) distributed in a matrix, these zones (10, 12) being defined by the crossing of said first (3) and second (4, 6) bands co nductrices. 2. Matrix screen according to claim 1, characterized in that the p row electrodes and / or the q column electrodes are identical. 3. Matrix screen according to claim 1 or 2, characterized in that the layer (8) of electro-optical material is a solid layer having electroluminescent properties. 4. matrix screen according to any one of claims 1 to 3, characterized in that the layer (8) of electro-optical material is formed k ≧ 2 solid materials (10, 12) having different electroluminescent properties, k being a positive integer. 5. A matrix display device with several shades of color comprising a matrix screen according to any one of claims 1 to 4, characterized in that it comprises means for applying, independently, to the bands. conductive (3, 4, 6) of each line electrode and each column electrode of the electrical signals used to control all or nothing the electro-optical property of the layer of electro-optical material (8). 6. A method of manufacturing a matrix screen, characterized in that zones (46, 56) of electro-optical material are produced, distributed in matrices and separated from each other by a dielectric (38), between a first family of p parallel electrodes each formed of m first parallel conductive strips (3) of different widths and a second family of q parallel electrodes each formed of n second parallel conductive strips (32a, 32b) of different widths, m and n being positive integers of which at least one is ≧ 2, the electrodes of the first family and the electrodes of the second family being crossed, the zones (46, 56) of electro-optical material being defined by the crossing zones of the first and second conductive strips, an image point x _ij of the screen being defined by the crossing of an electrode i of the first family and an electrode j of the second family, i and j being integers such that 1 5 i ≤ p and 1 ≤ j ≤ q. 7. The manufacturing method according to claim 6, characterized in that the electrodes of the first and / or second families of electrodes are identical. 8. Manufacturing method according to claim 6 or 7, characterized in that it comprises the following successive steps: a) making one of the two families of electrodes (32a, 32b) on a substrate (30), b) depositing a layer (38) of given thickness of a first dielectric material, c) -realization in the layer (38) of first material of at least one first opening - (42) at each crossing of an electrode of the first family and an electrode of the second family, these first openings (42 ) being defined by the crossing of a first conductive strip (32a) and a second conductive strip (3), d) partial filling of said first openings (42) with a second electro-optical material (46), e) covering the second material (46) with a third dielectric material (48) in order to completely fill said first openings - (42), and f) -realization of the second family of electrodes (3). 9. Manufacturing process according to any one of claims 6 to 8, characterized in that m and n are at most equal to 2. 10. The manufacturing method according to claim 9, characterized in that the first openings (42) being formed opposite one of the first conductive strips (32a) of each electrode of the first family and one of the second strips conductive (3) of each electrode of the second family, the following operations are carried out between steps e) and f): -realization in the layer (38) of first material of at least one second opening (52) at each crossing of an electrode of the first family and an electrode of the second family, these second openings (52), defined by the crossing of a first conductive strip (32b) and a second conductive strip - (3), being formed opposite the other first (32b) and second conductive strips, partial filling of said second openings (52) with a fourth electro-optical material (56), and covering of the fourth electro-optical material (56) with a fifth dielectric material (58) in order to completely fill said second openings (52). 11. The manufacturing method according to claim 8 or 10, characterized in that said openings (42, 52) are produced by depositing a resin mask (40, 50) on the layer of first material (38), defining the dimensions and location of the openings (42, 52), then by etching the layer of first material (38), said openings (42, 52) are filled with an electro-optical material (46, 56) by depositing on the structure obtained, a layer of said electro-optical material (46, 56), having a thickness less than that of the first material layer (38), a layer of dielectric material (48, 58) is deposited on the electro-optical material (46, 56) and the resin mask (40, 50) is eliminated. 12. Manufacturing method according to any one of claims 6 to 11, characterized in that one interposes between the first family of electrodes (32a, 32b) and the layer of first material (38) a layer (36) of a sixth dielectric material. 13. The manufacturing method according to any one of claims 6 to 12, characterized in that there is interposed between the second family of electrodes and the layers (48, 58) of fifth and second materials, a layer (60) of a seventh dielectric material. 14. The manufacturing method according to any one of claims 6 to 13, characterized in that the first and second families of electrodes are produced by depositing a layer - (32) of a conductive material, then defining the shape of these electrodes by means of a mask (34) and by etching, through this mask (34), the layer of conductive material. 15. The manufacturing method according to any one of claims 6 to 14, characterized in that said electro-optical material is an electroluminescent material.

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