EP1459345B1 - Plasma display device and control method therefor - Google Patents

Abstract

The plasma display has a chamber (17) retaining a gas, which is excited to emit visible light, in combination with a phosphorescent layer (18) that emits light when excited by ultraviolet light from the discharge. A uniformly distributed electric field (E) ignites the discharge, and a matrix of control elements (19) locally modulates the electric field to selectively illuminate screen points.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to the field of plasma screens or billboards. It relates in particular to the wall-mounted plasma television screens.

DESCRIPTION OF THE STATE OF ART

Plasma screens generally include an array of cells confined between two parallel glass plates. Each cell is controlled by at least one pair of electrodes in contact with the discharge gas. When sufficient voltage is applied between two electrodes, a discharge is generated in the gas contained in the cell. This discharge causes the emission of ultraviolet radiation by the gas. The walls of the cells are lined with luminophores that transform the invisible radiation (ultraviolet radiation) that it receives into visible radiation (color).

There are currently two types of screen structures shown in FIGS. 1 and 2. In these figures, cells 21, 22, 23 that are separated by partitions 31, 32, 33 are confined between two glass plates 11 and 12. extending perpendicular to the partitions. Phosphor layers 18 partially cover the inner walls of the cells 21, 22, 23.

FIG. 1 represents a plasma screen of the "matrix" type, that is to say having a Structure 1 Alternating Current with Matrix Maintenance (ACM). In this figure, the first glass plate 11 has on its inner surface an array of electrodes Xn, Xn + 1, Xn + 2 ... parallel. Each electrode Xn, Xn + 1, Xn + 2 ... corresponds to a display line of the screen. The electrodes are embedded in a thick layer 13 (about 20 μm thick) of dielectric material consisting for example of enamel, this layer 13 being covered with a layer 14 of dielectric material (less than 1 μm thick) ) consisting for example of oxide of magnesium (MgO) whose surface is in contact with the discharge gas. The second glass plate 12 also has on its inner surface an array of parallel electrodes Yn, Yn + 1 ... positioned perpendicularly to the row electrodes Xn, Xn + 1, Xn + 2 ... of the first glass plate 11 and constituting the column electrodes. Like the electrodes Xn, Xn + 1, Xn + 2 ... of lines, these electrodes are embedded in a thick layer 15 of dielectric material possibly covered with a thin layer 16 of magnesium oxide.

FIG. 2 represents a "coplanar" type plasma screen, that is to say having a Coplanar Maintenance Alternating Current (ACC) structure 2. In this structure, the two electrode arrays Xn, Xn + 1, Xn + 2 and Yn, Yn + 1 ... are arranged in parallel, intercalated, on the same glass plate 11. A network of electrodes Z addressing is embedded in the opposite glass plate 12.

In the two screen structures 1 and 2 shown in FIGS. 1 and 2, the two arrays of electrodes Xn, Xn + 1, Xn + 2 and Yn, Yn + 1 ... control the ignition (generally called "breakdown" By the person skilled in the art) of the plasma contained in each cell 21, 22, 23. In fact, the electrodes Xn, Xn + 1, Xn + 2 and Yn, Yn + 1 ... form with the dielectric layers 13 or In which they are embedded a capacitance capable of storing electrical charges on its surface and through which a voltage is applied to generate or maintain a luminous discharge (shown in dotted lines) in the plasma.

The operation of these discharges is similar to that of dielectric barrier discharges (DBD), simple high pressure glow discharges. When a discharge is caused between two electrodes X and Y, the layer 14 of magnesium oxide (MgO) in contact with the plasma undergoes a bombardment of ions present in the discharge and emits electrons e under the effect of this bombing raid. The magnesium oxide layer 14 plays a crucial role in obtaining a high secondary electron emission coefficient under ionic impact, this secondary electron emission e making it possible to maintain the discharge with tensions between electrodes X and Y all the lower as the secondary emission coefficient is high.

In response to the discharge, the plasma emits UV rays. The UV absorbing phosphors 18 re-emit C radiation in a visible frequency. The phosphors 18 are for example arranged in strips of cells of the plasma screen. Each strip of the screen emits in a basic color: red, green or blue. The phosphors 18 are thus distributed on the screen in a repeating pattern of three successive bands each having a different emission color.

Given the purely capacitive mode of operation of the elementary cells 21, 22, 23, the switching on and off of the cells is controlled by the superimposition of electrical pulses, namely: an alternating "maintenance" voltage (d a frequency of the order of 50 to 100 kHz), permanently applied between the X and Y electrodes of a cell and less than the breakdown voltage of the plasma, an "ignition" pulse to exceed the ignition voltage cells, and an "erase" pulse to cancel the electrical charge maintained by the AC voltage at the surface of the dielectric barriers. The plasma is thus excited by a succession of pulsed discharges created by the alternating maintenance voltage between the ignition pulse and the erase pulse. The pulse discharge current pulse lasts about 100 ns, during which time the electrons excite and ionize the gas. The voltage drop between the surfaces of the dielectric barriers due to the presence of the plasma causes the discharge to stop until the application of the new alternative maintenance pulse. Plasma and excited atoms then release the photons generated at each current pulse. In the case of a Neon-Xenon mixture, the UV photons emitted by the Xenon, (in particular since the resonant level Xe ( ³ P ₁ ) and the excimers) then excite the phosphors 18, arranged generally outside the active zones electrodes, which re-emit visible photons.

Typical operating values of plasma cells are, for Neon-Xenon mixtures at sub-atmospheric pressure of starting voltages between 250 V and 300 V, and maintenance voltages between 150 V and 200 V. The breakdown voltage depends on the product of the pressure by the inter-electrode distance, the minimum value of which is order of 5 to 10 torrxcm. The current density during the pulse discharge can reach 5 to 10 A / cm. The density of the plasma is of the order of 10 ¹¹ to 10 ¹⁴ cm ^-3 and the electronic temperature of some eV.

Other variants of the technology described above have been and are the subject of significant studies and development (maintenance of plasma by radio frequency voltage), but the principles of operation of flat screens, based on dielectric barrier discharges remain the same.

The documents WO 96/32827 and US 5877589 describe plasma screens in which electrodes are controllable to generate electric fields in cells containing a gas discharge.

A disadvantage of the previously described techniques is that the plasma operating window (difference between the extinction or erasing voltage and the breakdown voltage) is narrow, which leads to a relative complexity of the addressing of the cells and imposes a unsatisfactory compromise to a good light output.

Indeed, the existence of a discharge maintenance threshold (extinction voltage) lower than the breakdown voltage is imperative for the operation of cells that can go from the off state to the on state, and reciprocally, by firing and erasing pulses which modify the electrical charge of the cell. As all the cells of a plasma display are not identical, it is preferable that the difference between breakdown voltage and extinction voltage is not too low for the operating points of all the cells of the screen. fall within this margin.

In the case of a Neon-Xenon mixture, this margin increases with the proportion of Xenon in the Neon-Xenon mixture. This is because the starting voltage increases with the proportion of Xenon due to the low secondary emission coefficient of Xenon ions relative to Neon ions. However, the increase in maintenance and breakdown voltages causes an increase in the complexity and losses of the control circuits and the transport of the electrical power.

Therefore, to reduce the starting voltage, it is necessary to limit the proportion of Xenon in the gas, which correspondingly reduces the UV yield of the plasma. In this case, the margin between breakdown voltage and extinction voltage becomes very low, which imposes a more delicate adjustment of the control pulses.

Finally, the superposition of the three types of pulses (maintenance, ignition and erasure), to be fine-tuned, makes the addressing function relatively complex.

Another drawback of existing plasma screens is that the control of the cells requires high voltage pulses and high peak currents that can only be generated by means of electronic power circuits. These circuits represent a significant part of the cost of plasma screens.

In addition, the complexity of the addressing of the cells, based on the memory effects of the electrical charges facing the electrodes, also contribute to the high cost of the control electronics.

Another disadvantage of existing plasma screens is that they have a poor light output, inherent in the mode of operation of the discharge.

• la puissance dissipée dans les circuits de commande et d'adressage,
• le rendement en UV de la décharge, c'est-à-dire le rapport de l'énergie émise sous forme de photons UV par rapport à l'énergie injectée dans le plasma,
• l'efficacité de collection des UV par les luminophores,
• le rendement de conversion des photons UV en photons visibles par les luminophores,
• l'efficacité de collection des photons visibles.

Indeed, the efficiency of current plasma screens is of the order of 1 to a few Im / W (lumen per Watt), which means that only a few% of the electrical energy dissipated per cell is converted into visible light. The main factors that control the light output are, in logical order of the conversion chain:

• the power dissipated in the control and addressing circuits,
• the UV yield of the discharge, that is to say the ratio of the energy emitted in the form of UV photons relative to the energy injected into the plasma,
• the UV collection efficiency of the phosphors,
• the conversion efficiency of the UV photons into visible photons by the phosphors,
• the collection efficiency of visible photons.

As regards the power dissipated in the control and addressing circuits, this power can be reduced by reducing the starting and maintenance voltages, but to the detriment of the UV efficiency as we have seen previously.

The choice of the gas or gas mixture determines the yield of UV photons. In parallel, the presence of a layer of MgO as a secondary electron-emitting material requires the use of rare gases which do not modify its surface properties (the secondary emission coefficients being sensitive to changes in the surfaces). In the case of a Neon-Xenon mixture, Xenon is an effective UV emitter while Neon is an efficient secondary electron emitter by ionic bombardment of MgO. Therefore, low breakdown voltage can be achieved by using low Xenon mixtures (less than 10% percent). It can therefore be seen that, in an electric discharge type cell, a large part of the energy injected into the plasma is transferred not only to the excitation and ionisation of the Neon atoms (whose excitation energies and ionization rates are much higher than those of Xenon), but also in the ionic bombardment of MgO at the surface of dielectric barriers (and collisions with neutrals in collisional ionic sheaths). In other words, the energy injected into a cell is mainly dissipated in unproductive losses inherent to the operating mode of the dielectric barrier discharges.

The collection efficiency of the UV photons by the phosphors is also an important factor in the efficiency of the cell. Indeed, the photons that hit the surfaces not covered with luminophores, ie the surfaces covered with the MgO layer, are lost, which affects the overall efficiency of the cell.

The efficiency of converting the phosphors of the UV photons into visible photons does not depend on the structure of the cell or the characteristics of the plasma, but only on the intrinsic performances of the phosphors. Currently the conversion efficiency reaches values of the order of 20 to 25%.

Finally, the final luminous yield of the percentage of visible photons that can pass through the front face of the screen, some being lost on the rear face of the screen and others being absorbed at the crossing of the electrodes or dielectric layers present ( MgO, enamel).

Another disadvantage of existing plasma screens is the complexity of the cell structure which makes their manufacture complex. The manufacture of plasma screens is thus an important part of their final cost.

Finally, another disadvantage of existing plasma screens is the relatively short life of the cells.

The limitation of the life of the cells is due to the progressive spraying of the layer of magnesium oxide, the thickness of which is limited, under the effect of the pulses of ionic current. Once the magnesium oxide layer has been completely pulverized, the underlying thick dielectric layer, which does not exhibit such a high secondary emission coefficient, does not emit secondary electrons in sufficient quantity to enable the light to be ignited. discharge. The cell then remains permanently in the off state.

The limitation of cell life is also due to the degradation of phosphor performance over time. This degradation is generally attributed to the action of UV which would significantly affect the chemical composition of the surface of the phosphors, in particular by photo-desorption of volatile elements, for example oxygen in the case of oxides.

An object of the invention is to provide a plasma screen having improved technical performance: a better light output, a simplified cell structure, a longer life.

SUMMARY OF THE INVENTION

To this end, the invention proposes a plasma display device of the type comprising in a screen a chamber containing a discharge type gas capable of being excited to generate, alone or in combination with phosphor means intended to be themselves excited by radiation emitted by said gas, visible light, the device comprising means for generating on one side of said chamber a uniformly distributed electric field able to ignite a plasma in said gas, as well as on the one hand a matrix of controllable elements and on the other hand means that control said elements.

In one implementation of the invention, the matrix of controllable elements is arranged between the electric field and the gas and the control means control the elements so that they individually modulate the electric field and thus selectively generate light zones on the screen.

In another implementation of the invention, the matrix of controllable elements is arranged between the gas and the phosphors and the control means control said elements so that they individually modulate the radiation emitted by the plasma and intended to be received by the phosphors and thus selectively control the light appearing on the screen.

In another implementation of the invention, the matrix of controllable elements is disposed downstream of the gas or phosphor means and the control means control said elements so that they individually modulate the visible light generated and thus selectively control the light appearing on the screen.

In such a device, the functions of injection of the power and control of the light on the screen are dissociated: the power is supplied by the electric field generator means while the control of the light appearing on the screen is achieved by the controllable elements.

Because of this dissociation, the power required for the control of the controllable elements is reduced compared to the powers required in the control circuits of the plasma devices of the prior art.

Correlatively, the powers dissipated in the control are reduced.

Moreover, because of this dissociation, the power injection is performed more efficiently. Thus, the device of the invention is capable of operating independently of the differences between electrical breakdown field and electric extinction field. Therefore, a good light output of the screen can be obtained by choosing gases or gas mixtures to optimize photon production.

Finally, the device of the invention has a simplified structure, which reduces its manufacturing cost.

In a preferred embodiment of the invention, the electric field is generated by microwaves. The plasma is thus not excited by polarized electrodes as in the devices of the prior art, which makes it possible to eliminate the problem of sputtering the walls of the ion bombardment. The UV yield and the lifetime of the device are improved. In addition, this device does not require an MgO dielectric layer.

PRESENTATION OF THE DRAWINGS

• les figures 1 et 2 déjà commentées sont des schéma représentant en coupe transversale selon une ligne de cellules des structures d'écran à plasma de l'art antérieur, respectivement une structure d'écran à plasma de type matriciel et une structure d'écran à plasma de type coplanaire ;
• les figures 3 et 4 sont des diagrammes fonctionnels illustrant le fonctionnement de deux types de structures d'écran à plasma ;
• la figure 5 est un schéma représentatif en coupe transversale selon une ligne de cellules d'une structure d'écran à plasma conforme à un mode de réalisation du dispositif de l'invention ;
• la figure 6 est un schéma représentatif en coupe transversale selon une ligne de cellules d'une structure d'écran conforme à une variante de réalisation du dispositif de la figure 5 ;
• la figure 7 est un schéma représentatif en coupe transversale selon une ligne de cellules d'une structure d'écran à plasma conforme à un deuxième mode de réalisation du dispositif de l'invention ;
• la figure 8 est un schéma représentatif en coupe transversale selon une ligne de cellules d'une structure d'écran conforme à un troisième mode de réalisation du dispositif de l'invention ;
• la figure 9 est un schéma représentatif en vue de derrière d'un dispositif de commande des cellules pouvant être utilisé dans un dispositif de l'invention.

Other features and advantages will become apparent from the description which follows, which is purely illustrative and non-limiting and should be read with reference to the appended drawings among which:

• FIGS. 1 and 2 already commented are diagrams representing in cross-section along a line of cells of the plasma screen structures of the prior art, respectively a matrix type plasma screen structure and a screen structure to coplanar type plasma;
• Figures 3 and 4 are functional diagrams illustrating the operation of two types of plasma screen structures;
• Figure 5 is a representative cross-sectional diagram along a cell line of a plasma screen structure according to an embodiment of the device of the invention;
• Figure 6 is a representative cross-sectional diagram along a cell line of a screen structure according to an alternative embodiment of the device of Figure 5;
• Figure 7 is a representative cross sectional diagram along a cell line of a plasma screen structure according to a second embodiment of the device of the invention;
• Figure 8 is a representative cross sectional diagram along a cell line of a screen structure according to a third embodiment of the device of the invention;
• Figure 9 is a representative rear view diagram of a cell controller for use in a device of the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 3 is a functional diagram illustrating the operation of a plasma screen according to the invention of the type comprising luminophores.

According to this diagram, an electric field E is generated uniformly distributed near a chamber containing a gas. When this field is applied to the gas, it generates a plasma that emits ultraviolet radiation. This radiation is directed to a phosphor that absorbs ultraviolet radiation and re-emits radiation visible to the observer looking at the screen.

According to a first configuration, a matrix of controllable elements is positioned in (1), between the electric field and the gas. Control means control the elements so that they individually modulate the electric field transmitted to the gas and thus control the light generated on the screen. In this configuration, the intensity of the field E is greater than the ignition intensity of the plasma.

According to a second configuration, a matrix of controllable elements is positioned in (2), between the gas and the phosphors. Control means controls the elements to individually modulate the UV radiation emitted by the plasma and to be received by the phosphors and thus selectively control the light appearing on the screen. In this configuration, the electric field E is permanently applied to the gas and distributed so that a uniform plasma is generated continuously. The electric field E therefore has in steady state an intensity greater than the intensity of maintenance of the plasma. The intensity must be greater than the plasma firing intensity only when the screen is switched on.

According to a third configuration, a matrix of controllable elements is positioned at (3), downstream of the phosphor means (ie between the phosphor and the external observer). Control means controls the elements to individually modulate the visible light generated by the phosphors and thereby selectively control the light appearing on the screen. Just as when the controllable elements are positioned in (2), the electric field E has a steady state intensity greater than the holding intensity of the plasma and when the screen is switched on, an intensity greater than 1 ignition intensity of the plasma.

FIG. 4 is a functional diagram illustrating the operation of a plasma screen according to the invention of the type without phosphor.

According to this diagram, an electric field E is generated uniformly distributed near a chamber containing a gas. When this field is applied to the gas, it generates a plasma that emits radiation visible to the observer who is watching the screen.

This type of structure makes it possible in particular to produce "black and white" screens.

In the case where the screen comprises a plasma chamber divided into a cell, the cells may comprise gases of different compositions. Each cell thus generates radiation in a color (typically green, red or blue) depending on the composition of the gas it contains. This produces "color" screens.

According to a first configuration, a matrix of controllable elements is positioned in (4), between the electric field and the gas. This configuration is analogous to the configuration (1) of FIG. 3. Control means control the elements so that they individually modulate the electric field transmitted to the gas and thus control the light generated on the screen. In this configuration, the intensity of the field E is greater than the ignition intensity of the plasma.

According to a second configuration, a matrix of controllable elements is positioned at (5), downstream of the plasma (s). This configuration is analogous to the configuration (3) of FIG. 3. Control means control the elements so that they individually modulate the visible light generated by the plasma (s) and thus selectively control the light appearing on the screen. The electric field E has in steady state an intensity greater than the intensity of maintenance of the plasma and at the start of the screen, an intensity greater than the ignition intensity of the plasma.

FIG. 5 is a representative diagram of a plasma screen structure 3 according to an embodiment corresponding to the configuration (1) of FIG. 3.

The structure 3 comprises a chamber 17 divided into a matrix of cells 21, 22, 23 separated by partitions 31, 32, 33 and filled with a gas or gas mixture. The cells 21, 22, 23 are confined between a glass plate 11 defining the front face of the screen (that is to say the face facing the viewer's eye) and a cavity 41 defining the rear face of the screen and in which is generated an electric field E microwave uniformly distributed.

The cavity 41 may for example consist of a very low-loss dielectric material (such as, for example, silicon oxide SiO ₂ ) and a dielectric cooling liquid. The electric field E may be distributed uniformly, either by a two-dimensional network of microwave applicators, or by microwave resonators, such as ring resonators fed in parallel and in phase. The term "microwaves" here and throughout the present text means electromagnetic waves with a frequency greater than or equal to 200 MHz. The microwave frequencies used are for example the microwave frequencies ISM (Industrial Scientific and Medical) generally used for consumer applications (ie 433 MHz, 920 MHz, 2.45 GHz) or frequencies used for mobile telephony. Field E presents an amplitude capable of igniting the plasma at each of the cells, and in a very short time (for example of the order of one microsecond).

At least two control electrode arrays X and Y are positioned between the cavity 41 and the rear of the chamber 17 divided into cells 21, 22, 23. One of the arrays X comprises at least one series of electrodes Xn , Xn + 1, Xn + 2 ... positioned vertically, parallel to the columns of the screen. The other network Y comprises at least one series of electrodes Yn, Yn + 1, Yn + 2 ... positioned horizontally, parallel to the lines of the screen.

Controllable elements 19 are connected between each electrode of the network X and each electrode of the network Y. These controllable elements 19 are positioned at the rear of each cell, between the cell 21, 22 or 23 and the cavity 41 of uniform field E. An element 19 is thus controlled by a pair of electrodes Yn, Xn + 2. Depending on the command he has received, the element 19 modulates the electric field E transmitted from the cavity 41 to the cell 22.

As shown in FIG. 9, each of the elements 19 is controlled by at least one pair of given electrodes, this pair consisting of an electrode of the network X and an electrode of the network Y. Thus, the electrode arrays X and Y individually control the states of each element 19 of the matrix of elements.

Each element 19 may have at least two transmission states: a first state in which it transmits an ignition field to the cell 22, a second state in which it transmits a field smaller than the value for holding the plasma in the cell 22 .

Such elements 19 may for example be constituted by electro-mechanical micro-systems (MEMS).

The transmission elements 19 may also consist of structures of the semiconductor component type, such as, for example, quantum well structures.

When lighting a cell 22, the corresponding element 19 is controlled so as to modulate the field E to transmit to the cell 22 an electric field equal to the ignition field. This field generates a discharge in the gas contained in the cell 22 which produces UV radiation. Phosphors 18 present on the walls of cell 22 absorb UV radiation and re-emit C radiation in a visible frequency.

To keep the cell 22 on, it suffices to control the corresponding element 19 so as to modulate the field E to transmit to the cell 22 a field at least equal to the ignition maintenance field. This voltage maintains the discharge in the gas and consequently the production of visible radiation C.

Finally, to turn off the cell 22, it is sufficient to control the corresponding element 19 so as to modulate the field E to transmit to the cell 22 an electric field lower than the holding electric field. This electric field is not sufficient to maintain the discharge in the gas and the visible C radiation emission ceases.

It will be noted that the luminophores lined the walls of the cells on all available surfaces so as to collect the maximum of UV radiation and thus improve the luminous efficiency of the screen.

Figure 6 is a representative diagram of a plasma screen structure 4 according to an alternative embodiment of the invention. This variant corresponds to the configuration (4) of FIG.

The structure 4 is similar to the structure 3 of FIG. 5 except that the walls of the cells 21, 22, 23 are not covered with luminophores. In this variant, the gas contained in the chamber 17, under the effect of a discharge, directly generates a visible radiation C. This type of structure allows for "black and white" screens in the case where the cells are filled an identical gas or "color" in the case where the cells contain plasmas of different gas composition each emitting visible radiation in one of the three fundamental colors (red, green and blue).

Fig. 7 is a representative diagram of a plasma screen structure according to a second embodiment of the invention. This embodiment corresponds to the configuration (2) of FIG. embodiment, a matrix of controllable elements 19 is positioned between the gas and phosphors 18. The X and Y electrode arrays control the elements 19 to individually modulate the UV radiation emitted by the plasma and intended to be received by the luminophores 18 and thus selectively control the light appearing on the screen. In this embodiment, the field E is permanently applied to the gas so that uniform plasma is generated continuously.

Fig. 8 is a representative diagram of a plasma screen structure 6 according to a third embodiment of the invention. This embodiment corresponds to the configuration (3) of FIG. 3. The matrix of controllable elements 19 is positioned downstream of the visible light generating elements. The X and Y electrode arrays control the elements 19 so that they individually modulate the visible light generated (as the case may be by the plasma (s) or the phosphors) and thus selectively control the light appearing on the screen.

In the case of the screen structures of FIGS. 7 and 8 (corresponding to the configurations (2) and (3) of FIG. 3), the elements 19 may be constituted by electro-mechanical micro-systems (MEMS), micro opto-electro-mechanical systems (MOEMS), even Photonic Prohibited Band devices (photonic crystals or BIPs) whose transmission state can be controlled.

An advantage of the plasma screens described above is the simplicity of the technology used, both in terms of the structure of the cells and their addressing, since on the one hand the cells are free of electrodes, dielectric barrier and MgO secondary emission layer, on the other hand the low voltage circuits are sufficient for the addressing of the cells (the control of the transmission elements does not require power electronics).

Another advantage is the existence of a very wide operating window for the excitation of the plasma. The only condition is to apply an electric field greater than the electrical breakdown field for a gas or given gas mixture at a given pressure. The gas mixture can therefore be optimized to obtain the best UV efficiency of the discharge or the emission of radiation at well-defined wavelengths. For example, it is possible to obtain plasma priming with pure Xenon whose efficiency is known for the production of UV photons. The choice of gas and working pressure is considerably expanded compared to dielectric barrier discharge plasma screen technologies, which makes it possible to choose the point of operation of the cells of the screen.

Another advantage is also a better light output. Indeed, the energy dissipated in the plasma is entirely devoted to the excitation and the ionization of the only effective atoms (for example Xenon) for the production of UV photons.

Moreover, in the case of a microwave electric field, the absence of electrodes eliminates the problem of sputtering the walls due to ion bombardment. As a result, little energy is dissipated in this form. Since the walls are at floating potential, the energy of the ions on the walls does not exceed about ten electron volts (eV).

Another advantage is due to the absence of electrodes and the absence of MgO deposit opposite these electrodes. The corresponding place may therefore be occupied by luminophores, which makes it possible to improve the luminous efficiency of the cells.

Finally, another benefit is the increased cell life. Indeed, given the absence of MgO layer and energy ion bombardment, the life of the cells is not related to their operating time. With the technology used by the invention, the life of the cells is limited only by the lifetime of the phosphors.

It may be noted that in the implementations described corresponding to FIGS. 7 and 8, it is not necessary for the chamber 17 containing the discharge gas to be divided into cells, since the elements 19 directly control the ignition zones. and extinguishing the screen downstream of the plasma.

Claims (14)

1. Plasma display device of the type comprising, in a screen, a chamber (17) containing a discharge gas that can be excited in order to generate, alone or in combination with phosphor means (18) that are themselves intended to be excited by radiation emitted by said gas, visible light,
   characterized in that it includes means for generating, on one side of said chamber, a uniformly distributed electric field capable of igniting a plasma in said gas and, on the one hand, a matrix of drivable elements (19) which is placed between the electric field and the gas and, on the other hand, means (X, Y) that drive said elements (19) so that they individually modulate the electric field and thus selectively generate luminous areas on the screen.
2. Plasma display device of the type comprising, in a screen, a chamber (17) containing a discharge gas capable, under the effect of the electric field, of generating, in combination with phosphor means (18) intended to be excited by radiation emitted by said gas, visible light,
   characterized in that it includes means for generating, on one side of said chamber, a uniformly distributed electric field capable of igniting and then sustaining a plasma, and also, on the one hand, a matrix of drivable elements (19) which is placed between the gas and the phosphors (18) and, on the other hand, means (X, Y) that drive said elements (19) so that they individually modulate the radiation emitted by the plasma and intended to be received by the phosphors (18) and thus selectively control the light appearing on the screen.
3. Plasma display device of the type comprising, in a screen, a chamber (17) containing a discharge gas that can be excited in order to generate, alone or in combination with phosphor means (18) themselves intended to be excited by radiation emitted by said gas, visible light,
   characterized in that it includes means for generating, on one side of said chamber, a uniformly distributed electric field capable of igniting a plasma in said gas, and also, on the one hand, a matrix of drivable elements (19) that is placed between an external observer and the gas or the phosphor means (18) and, on the other hand, means (X, Y) which drive said elements (19) so that they individually modulate the visible light generated and thus selectively control the light appearing on the screen.
4. Plasma display device according to one of the preceding claims, characterized in that the drive means comprise at least two series of electrodes (X, Y) extending in the form of arrays so as to drive the drivable elements (19) in a matrix fashion.
5. Plasma display device according to one of the preceding claims, characterized in that the drivable elements (19) comprise microelectromechanical systems and/or microoptoelectromechanical systems and/or photonic bandgap devices, the transmission state of which may be controlled.
6. Plasma display device according to one of the preceding claims, characterized in that the electric field is generated by microwaves of 200 MHz frequency or higher.
7. Plasma display device according to one of the preceding claims, characterized in that the means for generating the electric field comprise a two-dimensional array of microwave applicators.
8. Plasma display device according to one of Claims 1 to 6, characterized in that the means for generating the electric field comprise microwave resonators supplied in parallel and in phase.
9. Plasma display device according to one of the preceding claims, characterized in that the chamber (17) containing the gas is divided into cells (21, 22, 23) coated with phosphors (18).
10. Plasma display device according to preceding Claim 9, characterized in that a cell (21; 22; 23) has a bottom coated over its entire surface with phosphors (18).
11. Plasma display device as claimed in one of Claims 1 to 8, characterized in that the chamber (17) is divided into cells (21, 22, 23) containing different gas mixtures capable of generating radiation of different wavelengths.
12. Method of driving a plasma display device of the type comprising, in a screen, a chamber (17) containing a discharge gas that can be excited so as to generate visible light, which method comprises the steps consisting:

    - in generating a uniformly distributed field (E) having a higher intensity than the intensity of the field needed to ignite a plasma in the gas; and

    - in modulating the field (E) thus generated, in order to transmit it to a portion of the plasma so as to selectively ignite or sustain or extinguish said portion.
13. Method of driving a plasma display device of the type comprising, in a screen, a chamber (17) containing a discharge gas that can be excited in order to generate visible light, which method comprises the steps consisting:

    - in generating a uniformly distributed field (E) having a higher intensity than the intensity of the field needed to ignite or sustain a plasma in the gas;

    - in applying the field (E) to the gas in order to generate visible or UV light radiation; and

    - in modulating the radiation emitted by a portion of the plasma so as to selectively control the light appearing.
14. Method of driving a plasma display device of the type comprising, in a screen, a chamber (17) containing a discharge gas that can be excited in order to generate ultraviolet radiation, which method comprises the steps consisting:

    - in generating a uniformly distributed field (E) having a higher intensity than the intensity of the field needed to ignite a plasma in the gas;

    - in applying the field (E) to the gas in order to generate ultraviolet radiation;

    - in collecting the ultraviolet radiation and re-emitting visible radiation; and

    - in modulating the visible light radiation.

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