EP0155895B2 - Method for making flat display screens and flat screens made according to this method - Google Patents

Abstract

A device and method for formation of images with flat video screens by a line- and column-addressed point matrix. Field point matrix uses field emission micro tips as fluorescent screen portions being connected in columns. An electric field is applied between each tip and the fluorescent screen portion corresponding thereto, such that the respective tip emits electrons and a light spot is formed on the video screen, the intensity of which depends upon the applied voltage for attracting electrons. Emission from other tips is blocked by applying a negative voltage to the other columns. Thus, by successive switchings, successive luminous spots are formed on the video screen as desired.

Description

We know that, in the field of flat display screens, different techniques have been proposed. The ideal system should be able to generate both small and large screens, be compatible for black and white as well as color, have low power consumption, and be simple to manufacture.

The conventional television tube with scanning of the electron beam cannot be reduced in thickness for physical reasons: distortion of the image if the beam arrives too grazing on the screen, and lack of precision to reach the masks on the screen in the case of color. Furthermore, the dimensions of the screen cannot be thoughtlessly increased for reasons of vacuum and therefore of resistance of the materials to pressure.

We are therefore moving more towards the formation of images, not by a scanned beam, but by a matrix of points addressed row-column.

In this area, liquid crystals are attractive because they have a very low power consumption, but they do require an external source of light to be visible. In addition, it is very difficult to make grayscale gradations, and to produce color images.

Other techniques have been proposed for the production of flat screens. One of them uses a plasma micro-discharge in a gas as a source of electrons, these electrons then being attracted to a fluorescent screen. Row-column addressing enables the desired point on the screen to be lit. Unfortunately, using a plasma source as an electron source is tricky because the plasma works all or nothing, that is, it is either on or off. As a result, gray levels cannot be obtained.

In addition, intermediate solutions between the traditional cathode ray tube and the flat screen have been proposed, such as, for example, the subject of French patent no. 2,348,561 comprising systems for producing electrons by field emission from matrices. emitters with low electron emission thresholds, the charge of which is provided by a system with two electron guns depositing an electrical charge modulated by the video signal. Such a system is complex and it involves a high manufacturing cost for its implementation.

The present invention relates to a method for producing flat display screens, according to claim 1.

The invention also relates to flat display screens obtained by implementing the above method.

• - La figure 1 est un schéma de principe de base de l'invention.
• - La figure 2 est un schéma explicatif d'une première forme de réalisation d'un écran de visualisation plat mettant en oeuvre le principe de base de la figure 1, à montage de type diode.
• - La figure 3 est une variante plus évoluée du principe de base de l'invention, à montage du type triodes.
• - La figure 4 est un schéma explicatif d'une variante de réalisation d'un écran de visualisation plat mettant en oeuvre le principe de la figure 3.
• - La figure 5 est un schéma d'une variante plus évoluée du principe de base de l'invention, à montage du type tétrode.
• - Et la figure 6 est un schéma explicatif d'une variante de réalisation d'un écran de visualisation plat mettant en oeuvre le principe de la figure 5.

Other characteristics, advantages and particularities of the present invention will emerge from the description which is given below with reference to the drawings, very schematic, appended, representing different possible embodiments of the said invention. In these drawings:

• - Figure 1 is a basic block diagram of the invention.
• - Figure 2 is an explanatory diagram of a first embodiment of a flat display screen implementing the basic principle of Figure 1, with diode type mounting.
• - Figure 3 is a more advanced variant of the basic principle of the invention, mounting the triode type.
• FIG. 4 is an explanatory diagram of an alternative embodiment of a flat display screen implementing the principle of FIG. 3.
• - Figure 5 is a diagram of a more advanced variant of the basic principle of the invention, mounting of the tetrode type.
• - And Figure 6 is an explanatory diagram of an alternative embodiment of a flat display screen implementing the principle of Figure 5.

The basic principle of the invention, shown diagrammatically in FIG. 1, essentially consists in using as field source microtips as the electron source. A field emission tip, such as 1, having a radius of curvature of a few hundred Angstroms, emits electrons e simply by applying an electric field between the tip 1 and a fluorescent screen 2 thanks to the potential E.

A simple solution for manufacturing a flat display screen according to the invention consists, as shown diagrammatically in FIG. 2, of connecting: on the one hand, the tips in lines, for example the tips 1 _A1 , 1 ₈₁ , 1 _C1 ... along line L _A1 ; points 1 _A2 , ₁₈₂ , 1 _{C2 ...} along line L _A2 ; points 1 _A3 , 1 _B3 , 1 _C3 ... along line L _A3 etc ...; on the other hand, the screens in columns 2A, 2 _B , 2 _c ... This arrangement makes it possible by matrixing and row-column addressing, successive light points to be emitted on the screen.

The tips can be produced by deposition or etching techniques using the conventional methods of microelectronics, that is to say masking and then wet etching in acid baths or dry etching by plasma or particle beam.

The different columns of the screen are made of transparent material, for example glass, covered with a metallic film and a fluorescent material.

When, for example, the line L _A2 and the column 2 _B are addressed with the suitable potentials, there is emission of electrons by the tip 1 _B2 and formation of a luminous point P ₁ on the screen, the intensity depends on the voltage V = -E applied to the line L _A2 , the radius of curvature of the tip l _B2 and the distance screen tip, it being understood that the last two factors are constant for all the tips.

We immediately see that to prevent the tips of line L _A2 , other than those located on column 2 ₈ , namely the tips 1 _A2 , 1 _C2 , from emitting electrons, we must apply a negative potential V = -E to the other screen columns 2A, 2 _c ..., the potential being zero, V = O, on the column considered 2 ₈ .

Likewise, to prevent the points located on column 2 ₈ , other than those of line L _A2 , namely points 1 ₈₁ , 1 _B3 ..., from emitting electrons, it is necessary to apply a zero potential V = O to the other lines L _A1 , L _A3 ..., the potential applied on line L _A2 being negative V = -E.

In this way, only the diode constituted by the tip 1ε2 in line L _A2 and the screen in column 2 _B is in the on state, all the other diodes being blocked.

The radius of curvature of the point considered and the point-screen distance constituting constant values fixed by construction, it is apparent that the light intensity of point P ₁ is a function of the voltage E applied.

It is thus possible to perform the formation of images on the screen by a matrix of points addressed row-column.

In order to eliminate the problem of manufacturing a large number of microtips having very close radii of curvature, and also to overcome the possible failure of one of these points, it is advantageous to constitute each light point by a set of several microtips. Each micro-point having a width at the base close to 1 µm, it is possible to place up to a hundred of these points per elementary light point, which, statistically, will ensure uniformity of intensity bright across the entire screen.

To achieve color, it suffices, without wanting to go into unnecessary technical details, to triple the rows or columns, and to put fluorescent materials of different colors, for example red, green, blue, arranged in triads on the screen next to each elementary light point.

The type of screen configuration according to the invention that has just been described is of the diode type, and constitutes the simplest solution from the conceptual point of view, but problems appear at the level of the control voltages. Indeed, for the electron extraction voltage E to be low enough to allow rapid switching, the point-screen distance must be of the order of a few microns, which obviously creates technical manufacturing problems.

A solution, both more advanced and simpler, of the invention facilitating the problems of rapid switching and making it possible to considerably reduce the technical problems which have just been mentioned above, is shown diagrammatically in FIG. 3.

This solution essentially consists in using a triode type assembly with a control grid 3 which makes it possible to modulate the electric intensity. We immediately see that by varying the voltage E ₂ , we change the intensity of electrons emitted, and by varying the voltage E ₁ , we change the energy of the electrons e reaching the light screen 2.

• 1 pointe 1 -grille 3, la troisième composante, en l'occurence l'écran 2, étant à un potentiel fixe;
• 2 pointe 1 -écran 2, la troisième composante, en l'occurence la grille 3, étant à un potentiel fixe;
• 3 grille 3-écran 2, la trosième composante, en l'occurence la pointe 1, étant à un potentiel fixe.

In the case of triode mounting, the matrixing is similar to that of diode mounting, however it is important to note that unlike the latter, there is here the possibility of three combinations, namely:

• 1 tip 1 -grid 3, the third component, in this case the screen 2, being at a fixed potential;
• 2 point 1 - screen 2, the third component, in this case the grid 3, being at a fixed potential;
• 3 grid 3-screen 2, the third component, in this case the tip 1, being at a fixed potential.

As can be seen in the diagram in Figure 4 (which is similar to that in Figure 2, but in which only the tips 1 _A1 , 1 ₈₁ , 1 _C1 ... and the corresponding grids 3 _A1 , 3 _B1 , 3 _c , ... have been shown for clarity of the drawing), one can also use in the case of a triode type mounting a three-component solution by doing a row-column addressing for the tips and the screens, but without modulating the values of the applied voltages E ₁ and E ₃ , by connecting all the grids 3 _A1 , 3 _B1 , 3 _C1 ... together and by modulating the common voltage E ₂ to vary the light intensity.

In the same way, it is possible to carry out a row-column addressing between grid and screen with fixed voltages E ₂ and E ₁ and connect all the tips together in order to vary the light intensity by modulating the common voltage E ₃ .

One can also carry out a row-column addressing between tip and grid with fixed voltages B ₃ and E ₂ and connect all the screens together in order to vary the light intensity by modulating the common screen voltage E ₁ .

We see that this technique has three components to separate the addressing and intensity modulation functions.

It is quite obvious that for this triode type assembly, color can be produced as in the case of the diode type assembly by tripling the rows and the columns and by putting fluorescent materials of different colors on the screen.

For manufacturing reasons, both of the screen and the points, it seems advisable to connect all the points together and all the screens together, because otherwise difficulties appear as for the manufacture of points on insulating support which separates the columns or tip lines.

The invention makes it possible to solve the above problem simply and effectively by adopting the tetrode type arrangement shown diagrammatically in FIGS. 5 and 6.

This arrangement comprises, as in the previous cases, for each unit light point, a field emission tip 1, a fluorescent screen 2, a first extraction grid 3, a second extraction grid 4.

As can be seen in the diagram in Figure 6 which is similar to that in Figure 4, all the tips 1 _A1 , 181, Here ... are connected together as well as the screens 2A, 2 _B , 2 _c .. .

It follows that thanks to this tetrode assembly, the row-column addressing is done by playing on the voltages E ₂ and E ₃ while the modulation of the light intensity is obtained by the variation of the voltage E ₁ .

It is quite obvious that for this tetrode assembly, it is possible, as in the previous cases, to produce color by tripling the rows and the columns and by putting fluorescent materials of different colors on the screen.

It will be noted in particular that the matrixing and the row-column addressing constituting two of the phases of the process of the invention are operations well known to those skilled in the art and their modes of implementation, in detail, can be chosen from those most generally used.

Claims (10)

1. A method of using flat display screens of the type in which image formation is obtained on a fluorescent screen by a line- and column-addressed point matrix comprising the following steps consisting of :

- using field emission microtips as electron sources;

- connecting, on the one hand, the tips in lines and, on the other hand, the fluorescent screens in columns;

- applying an electric field, successively, between each of the tips and the corresponding screen by applying to the line comprising the tip in question a negative voltage (-E) and to the column comprising the corresponding screen a zero potential, in such a way that the tip in question emits electrons and forms a luminous spot on the screen, the intensity of which depends on the voltage applied for extracting electrons, the said method being characterized in that it consists of:

- simultaneously blocking all the othertips by applying a negative voltage to the other columns not involved in the emission of electrons and applying a zero potential to the other columns not involved in the emission of electrons;

- and then successively switching to form successive luminous spots on the screen corresponding to those of the matrix.

2. A method according to claim 1, characterized in that between each tip and the corresponding screen there is an electron excitation grid enabling modulation of both the intensity of the electrons emitted and the energy of the electrons reaching the screen.

3. A method according to claim 2, characterized in that one of three possible combinations is chosen for the matrixing : tip-grid, tip-screen or grid-screen, the third component in each case then being set at a fixed voltage.

4. A method according to claim 2, characterized in that the addressing and light intensity modulation functions are separated, and forthis purpose one of three possible combinations is chosen : tip-grid, tip-screen or grid-screen, the third component then being connected to a source of variable voltage, to cause the light intensity to vary.

5. A method according to one of claims 2 or 4, characterized in that for separating the addressing and light intensity modulation functions, line and column addressing is effected forthe tips and the screens, but without modulation of the values of the applied voltages, and all the grids are connected together and the applied voltage is modulated for varying the light intensity.

6. A method according to one of claims 2 or 4, characterized in that for separating the addressing and light intensity modulation functions, line and column addressing is effected for the grids and the screens, but wit hout modulation of t he values of the applied voltages, and all the tips are connected together and the applied voltage is modulated for varying the light intensity.

7. A method according to one of claims 2 or4, characterized in that for separating the addressing and light intensity modulation functions, line and column addressing is effected forthe tips and the grids, but without modulation of the values of the applied voltages, and all the screens are connected together and the applied voltage is modulated for varying the light intensity.

8. A method according to one of claims 2 or 4, characterized in that a first electron excitation grid and then a second excitation grid for the said electrons are incorporated between each tip and the corresponding screen, all the tips are connected together and all screens are connected together, as a result of which the line and column addressing is effected by modifying the voltages appled to the first and second excitation grids respectively, whilst the variation in light intensity is obtained by modulation of the voltage applied between tip and screen.

9. A method according to any one of claims 1 to 8, characterized in that each luminous spot is produced on the screen by a plurality of mictotips which may be up to about a hundred per elementary luminous spot.

10. A method according to any one of claims 1 to 9, characterized in that to produce colours, in addition the number of lines or columns is tripled and materials having different fluorescence colours are arranged in triads on the screen opposite each elementary luminous spot.

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