EP0012920B1 - Luminescent screen for picture display tubes and method of its manufacture - Google Patents

Abstract

A luminescent screen for flat image display devices, having improved light efficiency comprises a glass screen (1) provided on its inner surface with a pattern of recesses (2) corresponding to a desired luminescent dot pattern with luminescent dot surfaces (5) positioned not only along the bottom of such recesses but also along the upwardly extending recess walls and a contrasting border layer (3) is positioned on the land areas between each recess. In producing such screens, the contrasting border layer is utilized as an etch mask for the recesses and as an application mask for the luminescent material.

Description

The invention relates to a fluorescent screen for display tubes according to the preamble of patent claim 1.

In picture display tubes, in particular in picture display devices with a flat screen, such as are known, for example, according to the principle of gas discharge display as a plasma panel or plasma display and are described in DE-OS 24 12 869, there is a single or multi-colored finely screened luminescent screen with a high Luminous efficacy required. A plasma serves as the actual cathode, from which an electron beam is drawn via a control perforated plate with matrix control for each illuminated spot to be excited. Compared to the classic.

Cathode-ray picture tubes, where a single electron beam has to reach all the luminous points and can experience very high accelerations with the dimensions of the picture tube required as a result, the electron beams in gas discharge display devices are low-energy due to the gas filling and the flat design. It is therefore extremely important to get a high luminous efficacy when converting the electron energy into light energy or also when controlling the light points with UV light, for example.

For this purpose, it is already known in the classic cathode ray tube and described, for example, in US Pat. No. 3,858,083, to coat the phosphor dots on the inside with a reflective metal layer. Most of the light emitted by the excited phosphor is reflected by this metal layer and added to the light emitted to the front. However, the exciting electrons are also weakened on this metal layer, which does not play a major role in the case of the high-energy cathode-ray electrons, but makes it difficult to use such metal mirrors in the case of the low-energy electrons of the flat gas discharge display devices. Such a metal layer would also be desirable for the phosphor layer at the luminous points as a protective layer against mechanical loads, in particular when building a flat screen, where spacers are necessary between the fluorescent screen and the control perforated plate. For the reasons mentioned above, however, it would have to be so thin that it could no longer perform these protective functions.

From the above-mentioned US Pat. No. 3,858,083, it is also known to separate the luminous dots from one another by means of opaque borders in order to increase the contrast. In connection with flat image display devices, this is also described as a "black border" in the earlier patent application P 28 06 436. “Contrast border” is to be understood here to mean such an opaque border of the individual illuminated dot areas. It consists of granular glass solder or organometallic compounds that are subjected to an annealing process. Again, from the point of view of necessary spacers, such contrast border layers are unfavorable as supports for the spacers. Grainy documents cannot withstand the mechanical loads sufficiently.

The US-PS 27 05 765 describes a fluorescent screen with the features of the preamble of claim 1. There are described electrical control lines, which can consist of a silver layer, which is applied to previously made webs between luminous dots.

The webs serve as a contrast border. A separate contrast border layer is not suggested by this US patent. The graphite layer described there only serves to carry current in the case of galvanic metallization. In particular, the silver specified as the preferred metal is also highly reflective through the usually very thin graphite layer, the contrast border is thereby deteriorated rather than improved.

The present invention has for its object to construct a fluorescent screen so that the luminous dots have a sufficiently high luminous efficacy even without a metal mirror and that there is the possibility of supporting spacers on the fluorescent screen without endangering the contrast border or fluorescent layers.

To solve this problem, the features of the characterizing part of claim 1 are proposed for a fluorescent screen according to the preamble of patent claim 1.

With the aid of the fluorescent screen according to the invention, the active fluorescent area can be increased considerably. The electron beam hits more phosphor particles. The amount of light emitted towards the front becomes significantly larger per luminous point than if only one fluorescent surface corresponding to the luminous point and only lying in the luminous point plane is used. Not only primary electrons are used. Also secondary electrons, i.e. For example, electrons reflected at the plane of the red dot can hit fluorescent particles on the walls of the depressions and contribute to better light output.

The illuminated dots are largely separated from one another. If the depressions are large enough, electrons scattered from a light spot can hardly reach an adjacent light spot. This decoupling of the luminous dots significantly improves the contrast and color purity compared to purely flat screen arrangements.

Opposite a glass solder layer as Kon Trastumrandung is a particularly vaporized contrast border layer as a carrier layer for spacers much more stable. It is harder and adheres better.

• 1) die Schirmglasplatte wird auf ihrer Innenseite mit einer dunkel, insbesondere schwarz, gefärbten Kontrastumrandungsschicht aus einer Mischung von Metall mit Dielektrikum versehnen;
• 2) in die Kontrastumrandungsschicht werden entsprechend dem Leuchtpunktraster Fenster geätzt;
• 3) die so gerasterte Kontrastumrandungsschicht dient als Maske für das Ätzen der Vertiefungen in der Schirmglasplatte;
• 4) die Kontrastumrandungsschicht dient als Maske für das Einbringen der Leuchtstoffschicht in die Vertiefungen, insbesondere durch Aufsprühen.

In addition, such a contrast border layer offers the possibility of being used in several functions when building the screen. For this purpose, according to the invention, the following are used in a method for screen manufacture. Steps suggested:

• 1) the inside of the screen glass plate is covered with a dark, in particular black, contrasting border layer made of a mixture of metal and dielectric;
• 2) windows are etched into the contrast border layer in accordance with the red dot grid;
• 3) the contrast border layer thus rasterized serves as a mask for the etching of the depressions in the screen glass plate;
• 4) the contrast border layer serves as a mask for introducing the phosphor layer into the depressions, in particular by spraying.

This multiple function of the contrast border layer makes the manufacture considerably cheaper.

Another function of the contrast border layer can be added if it is electrically conductive and serves as a carrier for the fluorescent screen potential. Then there is no need to provide a separate anode layer.

For this extended function of the contrast border layer, it is proposed as a further development of the production method according to the invention that the composition of metal and dielectric changes in the course of the layer thickness, with first pure dielectric being applied, then more and more metal being added with a decreasing dielectric component and finally a pure metallic final layer is applied.

Another possibility consists in that the composition of metal and dielectric changes in the course of the layer thickness, that layers of dielectric and layers of metal are applied alternately with preferably varying layer thicknesses and the last layer is metallic.

The metallic components ensure electrical conductivity. Due to the fine distribution of these metallic components, the density of which increases with increasing thickness as viewed by the luminescent screen, the contrasting border layer absorbs light from the viewer side very strongly without reflecting metal. The last, purely metallic, part of the layer additionally makes the layer opaque and increases the absorption, so that even very thin layers appear dark or black.

For the subsequent function of the contrast border layer as a mask for the etching of the screen glass during the production process, it is advantageous if the metal component consists of nickel, copper, platinum or gold.

According to a further development, it is provided that the contrast border layers and the depressions under the phosphor layer are covered with a continuous electrically conductive potential layer, which then serves as an anode layer. This does not affect the resilience above the contrast border layer for the applied spacer.

The invention will be explained in more detail with reference to an embodiment shown in the drawing.

1 designates a screen glass plate, which is, for example, the front window of a gas discharge display in the form of a flat screen. The screen glass plate 1 is shown cut from the side. At the bottom is the viewer side, at the top the inside of the gas discharge display device. The spacers then placed on top, the perforated control disk supported on it and the entire rear part of the gas discharge display device, as seen by the viewer, are omitted.

On the inside of the screen glass plate 1 there are depressions 2 with an approximately rectangular cross section. The bottoms of these depressions are the illuminated dot areas of the fluorescent screen and are accordingly attached in the same grid. A contrast border layer 3 is located on the remaining webs. The bottoms and walls of the depressions 2 and the contrast border layer 3 are covered by a potential layer 4. In the recesses 2 on the floor and pulled up on the walls, there is a phosphor layer 5 above the potential layer 4. The electrons accelerated in the direction of the fluorescent screen are indicated by arrows.

• Auf die Schirmglasplatte 1, in der sich die Vertiefungen 2 noch nicht befinden, wird ein Gemisch aus einem Dielektrikum, wie Ceroxid (Ce02) oder Aluminiumoxid (AI₂0₃) oder Siliciumoxid (SiO) und aus einem Metall, wie Nickel (Ni), aufgedampft. Dabei wird der Nickelanteil während der Aufdampfung von 0 auf 100% vergrößert. Die Aufdampfraten können durch einen über zwei mit den entsprechenden Verdampfungsmaterialien gefüllten Tiegeln oszillierenden Elektronenstrahl mit gesteuerter Verweilzeit oder durch zwei gesteuerte Elektronenstrahlen oder auch durch temperatur- und druckgesteuerte Verdampfung des Dielektrikums in Verbindung mit einer aufdampfratengesteurten Elektronenstrahlkanone für das Metall eingestellt werden. Auf diese Weise entsteht dann eine vom Betrachter her schwarz erscheinende und auf der Innenseite des Gasentladungsanzeigegeräts spiegelnde Kontrastumrandungsschicht 3 mit einer Dicke von beispielsweise 300 nm.
• Anschließend wird Fotolack aufgebracht, der dann im Leuchtpunktraster entfernt wird, d.h. an den Stellen, an denen die Vertiefungen 2 entstehen sollen. Durch die dabei entstehenden Fotolackfenster wird zunächst die oberste Nickelschicht mit einem geeigneten Ätzmittel, beispielsweise mit einer Mischung aus Salpetersäure und Salzsäure oder Kupfersulfat, entfernt.

The fluorescent screen shown is manufactured for example as follows:

• A mixture of a dielectric, such as cerium oxide (Ce02) or aluminum oxide (Al ₂ O ₃ ) or silicon oxide (SiO), and a metal, such as nickel (Ni), is placed on the screen glass plate 1, in which the depressions 2 are not yet located. , evaporated. The nickel content is increased from 0 to 100% during the vapor deposition. The evaporation rates can be set by means of an electron beam oscillating over two crucibles filled with the corresponding evaporation materials with a controlled dwell time or by means of two controlled electron beams or also by temperature and pressure-controlled evaporation of the dielectric in connection with an electron beam gun controlled by evaporation rate. In this way, the viewer gets black appearing and reflecting on the inside of the gas discharge display device contrast border layer 3 with a thickness of 300 nm, for example.
• Subsequently, photoresist is applied, which is then removed in the red dot grid, ie at the locations where the depressions 2 are to be created. The uppermost nickel layer is first removed with a suitable etching agent, for example with a mixture of nitric acid and hydrochloric acid or copper sulfate, through the resulting photoresist window.

Then the recesses 2 are etched first through the remaining contrast border layer 2 in the windows and then into the screen glass plate 1, for example with hydrofluoric acid or with a mixture of hydrofluoric acid and sulfuric acid. After this etching process, the photoresist is removed and the screen glass plate 1, which is now provided with the depressions 2, is cleaned with the aid of an aqueous ultrasound bath.

In the next step, the potential layer 4 made of indium oxide (In ₂ 0 ₃ ) is sputtered on. This is followed, for example, by spraying the floors and walls of the depressions 2 with the phosphor layer 5, so that this covers the bottom of the depressions and is pulled up on the walls thereof.

Claims (7)

1. A luminescent screen for picture display tubes comprising a glass screen plate and phosphor dots which are positioned thereon and the areas of which are separated from one another by a contrast border, where the phosphor material is accommodated in recesses in the glass screen plate and rises up at the walls thereof, characterised by the following features:

a) a contrast border layer (3) is located on the inner side of the glass screen plate (1) as a boundary of the recesses (2);

b) the contrast border layer (3) comprises a metal layer which is resistant to etching agents for the glass of the glass screen plate (1);

c) the contrast border layer (3) is provided between its metal layer and the glass screen plate with a layer in which metal particles are distributed in a di-electric layer;

d) the concentration of the metal particles in the contrast border layer decreases towards the glass screen plate.

2. A luminescent screen as claimed in Claim 1, chracterised in that nickel particles are distributed in a dielectric layer made of substances of the group Ce0₂, AI_ZO₃, SiO.

3. A luminescent screen as claimed in Claim 1, characterised in that the contrast border layer (3) serves as a carrier for the luminescent screen potential.

4. A luminescent screen as claimed in Claim 1, characterised in that the contrast border layer (3) and the recesses (2) below the phosphor material layer (5), are covered with a continuous, electrically conductive, potential layer (4).

5. A process for the production of a luminescent screen as claimed in Claim 1 having the features:

a) on its inner side, the glass screen plate is provided with a dark contrast border layer;

b) windows are etched into the contrast border layer in accordance with the phosphor dot raster;

c) recesses are etched into the glass screen plate into which the phosphor material layer is inserted;

characterised by the features:

d) there is applied to the glass screen plate, a contrast border layer (3) made of a mixture of a metal and a dielectric in which the proportion of the metal component increases with increasing thickness of the layer, pure metal finally being applied in order to form a covering layer;

e) the contrast border layer (3) which has been provided with windows, serves as a mask for the etching of recesses (2) into the glass screen plate (1);

f) after the etching of the recesses, the phosphor material layer (5) is inserted into the recesses in such a way that it covers the floors of the recesses and rises up at the walls thereof.

6. A process for the production of a luminescent screen as claimed in Claim 5, characterised in that the composition of the mixture of metal and dielectric changes continuously in the course of the layer thickness, pure dielectric being first applied.

7. A process for the production of a luminescent screen as claimed in Claim 5, characterised in that the composition of the mixture of metal and di-electric changes in the course of the layer thickness, layers made of dielectric and layers made of metal being alternately applied, preferably with varying layer thicknesses, and the last layer applied being a metal layer.

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