EP0894331B1

EP0894331B1 - Method of manufacturing a cathode ray tube

Info

Publication number: EP0894331B1
Application number: EP98900024A
Authority: EP
Inventors: André Van der Voort; Johannes Maria Azalina Antonius Compen
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 1997-01-17
Filing date: 1998-01-12
Publication date: 2003-09-03
Anticipated expiration: 2018-01-12
Also published as: TW392189B; DE69817711T2; CN1199228C; EP0894331A1; WO1998032152A1; JP2000507041A; DE69817711D1; CN1216152A

Abstract

A method of manufacturing a cathode ray tube having an antistatic, anti-reflective filter, in which method a first conductive layer (for example a layer on the basis of indium-tin oxide) is provided by means of sputtering. A second layer containing SiO2 is applied to the first conductive layer by means of a wet-chemical process, for example spinning and, subsequently, drying of a TEOS-compound. The method enables an antistatic, anti-reflective filter to be manufactured in a sample manner which can suitably be used on an industrial scale, which filter exhibits good antistatic and anti-reflective properties as well as a good shielding effect.

Description

The invention relates to a method of manufacturing a cathode ray tube provided with a multilayer antistatic filter on a display window.

Cathode ray tubes are used, inter alia, in television receivers and computer monitors.

A method of the type mentioned in the opening paragraph and a cathode ray tube of the type mentioned in the second paragraph are known from European Patent Application EP 649160. In said document a description is given of a method of applying a first conductive layer to a display window of a cathode ray tube by providing the display window with an aqueous suspension of conductive particles of antimony-doped tin oxide and, subsequently, drying said suspension, thereby forming a first conductive layer, whereafter a second layer is provided, which is composed of an alcoholic alkoxysilane compound, which is subsequently converted to silicon dioxide.

In operation, the display window is statically charged and incident light is reflected by the display window. The conductive layer provides for the removal of the static charge, and the conductive layer and the second layer together form or are part of an anti-reflective filter to reduce reflection of incident light.

Although the known method provides a filter having the desired antistatic effect, the conductance of the antistatic layer (approximately 1 MΩ/square) is insufficient to shield the viewer from electromagnetic fields emitted by the cathode ray tube. This would require resistance values ≤ approximately 1 kΩ/square. It is an object of the invention to provide a method of manufacturing a multilayer filter which demonstrates antistatic, shielding and reflection-suppressing properties, and which can be manufactured in a simple manner.

To achieve this, the method in accordance with the invention is characterized in that a first conductive layer having a surface resistance not greater than 1 K Ω / Square and a thickness of the ordes of 10-20 nm or less is sputtered onto the display window, said layer being provided, by means of a wet-chemical process, with a further layer comprising SiO₂, the first layer and the further layer being selected for together constituting a two-layer anti-reflection filter.

The surface resistance of the conductive layer provided by sputtering is so low that, unlike the known method, a surface resistance below 1 kΩ/square is achieved at layer thicknesses of the order of 10-20 nm or less. The layer may be, for example, a metallic layer or, preferably, a layer on the basis of indium-tin oxide (for example a layer containing ITO or ATO). Metallic layers absorb more visible light than indium-tin-oxide layers. If the contrast is to be improved, a metallic layer can be provided, for example a very thin layer of aluminium. If the light intensity of the image displayed is important, then, preferably, a transparent conductive layer on the basis of metal oxides, for example on the basis of indium-tin oxide, is applied. In the known method, such resistance values would require much larger layer thicknesses. A resistive layer of such thickness actually does not exhibit useful interference phenomena. On layers of such a large thickness, at least two further layers of materials having different refractive indices must be applied to bring about a reflection-influencing effect.

The further layer, which is predominantly composed of silicon dioxide, is in the method in accordance with the invention, not applied by sputtering but provided by means of a wet-chemical process, for example by means of spinning a TEOS solution as described in European Patent Application EP 649160 (PHN 14.663). The thickness of said further layer is preferably of the order of 80-150 nm, and forming one layer of such thickness by means of sputtering is very difficult. If sputtering were to be employed, the desired reflection-influencing effect could only be achieved by applying various layers to the first layer or by very long sputtering times.

From EP-A 200452 the use for display applications is known of a transparent plastic plate which carries a sputtered electroconductive layer having a thickness of 10-300 nm and a sputtered SiO₂ layer. The thickness of the SiO₂ layer may be any thickness, as long as the layer can appropriately prevent reflection to the transparent plastic plate. There is no disclosure of an anti-reflective effect mainly produced by interference phenomena in the assembly of the conductive layer and the SiO₂ layer such that the layers together constitute a double layer anti-reflection interference filter.

The combination of sputtering the conductive layer and providing a further layer containing silicon dioxide by means of a wet-chemical process, such as spinning, enables a multilayer antistatic filter to be manufactured which has a reflection-suppressing effect as well as a shielding effect, and which, nevertheless, can be applied in a relatively simple manner. Within the scope of the invention, "reflection-influencing" layers are to be understood to include layers which influence the glare (diffuse reflection) as well as layers which influence the specular reflection (the reflection coefficient R), either independently or in combination with the conductive layer.

In a first embodiment, the first, conductive, sputtered layer is provided, with an anti-reflective layer containing silicon dioxide. By means of this embodiment of the method a double layer ARES filter (Anti-Reflective Electromagnetic Shielding) filter is obtained. In such a filter the anti-reflective effect is mainly produced by interference phenomena in the assembly of the conductive layer and the anti-reflective layer. The anti-reflective layer is provided by means of a wet-chemical process, for example, by spinning,

In a further embodiment, the first, conductive, sputtered layer is provided with an anti-reflective layer containing silicon-dioxide which anti-reflective layer is coated with an anti-glare layer containing silicon dioxide. By means of this method, a three-layer IRES (Improved Anti-Reflective Electromagnetic Shielding) filter is obtained. Both the anti-reflective layer and the anti-glare layer are provided by means of a wet-chemical process.

In yet another embodiment, the first layer is provided with a second layer of a material other than silicon dioxide by means of sputtering, which second layer is provided with an anti-reflective layer containing silicon dioxide. By means of this method, a three-layer ARES (Anti-Reflective Electromagnetic Shielding) filter is obtained. The anti-reflective layer is provided by means of a wet-chemical process.

Preferably, the surface resistance of the first layer is below 500 Ω/square.

The shielding effect of such a layer is even greater.

Preferably, the further layer comprises an absorbing substance. By virtue thereof, the color of the filter can be influenced.

The anti-glare layer may be provided, for example, by spraying or atomizing an alcoholic solution of an alkoxysilane compound, followed by a treatment at an elevated temperature, thereby forming a layer of silicon dioxide. The resultant layer is scratch-resistant and has anti-glare properties owing to the surface texture formed by spraying. Said anti-glare effect is substantially independent of the wavelength of light. By spraying or atomizing the alkoxysilane solution, a matt surface texture is formed, which causes the resultant layer to exhibit an anti-glare effect. As a result, ambient light is reflected in a diffuse manner.

Further advantages of the additional layers of silicon dioxide include the reduced sensitivity to fingerprints and the greater hardness and scratch-resistance.

Advantageously the method according to the invention comprises an intermediate method step, between the sputtering process and the application of the further layer, in which intermediate method step the surface on which the further layer is to be provided is activated to increase the adhesion of the further layer.

This can e.g. be done by sputtering a preferably thin (1-15nm) layer of SiO₂, (or TiO₂,NbO₅, ZrO₂,Al₂O₃ etc) on the sputtered conductive layer, whereafter the surface of said layer is etched by an etching solution, ed, caustic solution.

The above-mentioned layer serves as a primer layer deposited on top of the sputtered conductive layer. Activation of said primer layer can alternatively be done by e.g. rubbing or etching in an Ar-gas.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

In the drawings:

Fig. 1 shows a display device,

Fig. 2 is a schematic, sectional view of a display window of a display device,

Figs. 3a through 3c illustrate an embodiment of the method in accordance with the invention,

Fig. 4 illustrates the embodiments of the method in accordance with the invention.

The Figures are diagrammatic and not drawn to scale; in the various embodiments, like reference numerals generally refer to like parts.

Fig. 1 is a schematic cut-away view of a cathode ray tube 1 having a glass envelope 2 comprising a display screen 3, a cone 4 and a neck 5. An electron gun 6 for generating an electron beam is accommodated in said neck. This electron beam is focused on a phosphor layer on the inner surface 7 of the display screen 3. In operation, the electron beam is deflected across the display screen 3 in two mutually perpendicular directions by means of a deflection-coil system (not shown). The display screen 3 is provided on the outside with an antistatic coating 8 in accordance with the invention.

Fig. 2 is a schematic, sectional view of a display screen in accordance with the invention. Display screen 3 is provided with an antistatic coating 8. Said antistatic coating 8 comprises a first layer 9 (AS), a second layer 10 and a third layer 11. The first layer 9 comprises tin oxide and is provided by sputtering. The second layer is made of silicon dioxide. The first layer and the second layer together form an antireflection filter (AR). The second layer may be provided with absorbing constituents, for example, polypyrrole-latex particles, by means of which the transmission properties of the second layer can be changed. The third layer 11 (AG) provides for an anti-glare effect and is made, for example, of silicon dioxide which is provided by spraying.

Figs. 3a through 3c illustrate a method in accordance with the invention.

A conductive layer 31, which is predominantly composed of indium-tin oxide (ITO), is sputtered onto the display screen 3. A second layer 32 of silicon dioxide is applied to said layer 31 by means of a wet-chemical process. To this end, for example, a TEOS-solution is spin coated onto layer 31. After provision of the TEOS-soluiion, a thermal treatment is carried out. This treatment results in the formation of a silicon-dioxide layer. Subsequently, a third layer, for example a silicon-dioxide anti-glare layer, is provided by spraying so as to achieve an anti-glare effect.

Fig. 4 illustrates a number of possible embodiments of the method in accordance with the invention.

In front of the first arrows, it is schematically indicated which layers are first provided on the substrate by means of sputtering, with S indicating the substrate, ES indicating a conductive layer, for example, a metallic layer or, preferably, a layer of a material which is substantially composed of indium-tin oxide (for example ITO or ATO) and AR indicating an anti-reflective layer of a material other than silicon dioxide, for example titanium oxide or niobium oxide. Subsequently, as indicated behind the first arrows, one or more layers containing silicon dioxide is/are provided on the sputtered layer(s) by means of a wet-chemical process, for example by spinning or spraying of a TEOS-solution. An anti-glare layer is indicated by AG, an anti-reflective layer is indicated by AR'. Finally, behind the last arrows there is a short indication of the layer formed, indicated by (IRES, ARES), and the number of layers constituting the filter is indicated in brackets. (3L meaning a three-layer filter, 2L meaning a two-layer filter etc). Fig. 4 shows the essence of the invention:

a substrate (S) is provided, by sputtering, with a number of layers including a conductive layer (ES) of a conductive material, for example a metal or a material on the basis of indium-tin oxide, whereafter
one or more layers (AG, AR') containing silicon dioxide, which influence the reflective properties of the filter, are provided by wet-chemical processes.

Apart from the above-mentioned advantages, the method in accordance with the invention has still other advantages which render the method very suitable for application on a large scale. Both sputtering and wet-chemical processes can be applied to cathode ray tubes which already are in the assembled state, and heating of the surface to be coated is hardly necessary, or perhaps not necessary at all. In preferred embodiments of the method in accordance with the invention, the filter is provided on a display window of an evacuated cathode ray tube. The method in accordance with the invention has a number of distinct advantages over methods requiring the display windows to be in the unassembled state, such as Chemical Vapor Deposition (CVD). If a filter is provided on an unassembled display window, said display window must subsequently be attached to the cone and evacuated. This process involves high temperatures (up to 450 °C). There is a risk that the filter provided is damaged by said high temperatures. Damage to the filter leads to reject and costs. In addition, if the sputtered layer is mainly composed of indium-tin oxide, the refractive index of a sputtered indium-tin oxide layer is relatively high (above 1.9), which has a positive effect in embodiments in which the conductive layer, in combination with a layer containing silicon dioxide (refractive index 1.46), should provide for an anti-reflective effect. The above-mentioned advantages (more suited for application on an industrial scale, applicable to an already assembled cathode ray tube, lower number of rejects) are independent of the exact value of the surface resistance of the conductive layer as well as of the composition of the conductive layer. Therefore, as regards these advantages, the surface resistance may he higher (for example 10³-10⁵ Ω/square) and/or the conductive layer may be composed predominantly of another material (for example tin oxide).

In the following, a detailed description of an embodiment in accordance with the invention (a so-called 3-layer IRES filter, see Fig. 4) will be given.

Example 1

A display screen 3 is disposed in a sputter arrangement. A layer of a conductive material, in this example indium-tin oxide (ITO) or antimony-doped indium-tin oxide (ATO) having a thickness of the order of 10-15 nm, is sputtered onto the display window. As the refractive index is approximately 2.1, the optical thickness of such a layer is approximately 20-30 nm.

A solution of an alkoxysilane compound in accordance with Table 1 is (being) manufactured.

The first layer (ES, see Fig. 4), which is obtained as described hereinabove, (a dried layer comprising conductive particles (for example ATO)), is provided, by means of spinning, with a layer of the TEOS-solution manufactured in accordance with Table 1. The temperature of the layer is maintained at 160 °C for approximately 90 minutes, thereby forming a properly adhering, smooth layer of silicon dioxide (AR', see Fig. 4). This additional layer of silicon dioxide has a thickness, for example, of 135 nm and a refractive index of 1.44. In combination with the antistatic layer (ES), this layer has an anti-reflective effect. The reflection of visible light is reduced to approximately 0.8% by this two-layer coating (ES-AR'). This is a substantial improvement in comparison with the known state of the art, as mentioned in European Patent Application EP 649160 (PHN 14.663). This can probably be attributed to the much greater difference in refractive index between the conductive layer ES and the anti-reflective layer AR'. In the method described hereinabove, said difference is 2.1 (refractive index of ITO) -1.46 = 0.64, whereas the method known from European Patent Application EP 640160 has a refractive index difference of 1.62 - 1.46 is 0.26. Consequently, in the embodiments in which the sputtered, conductive layer adjoins an anti-reflective layer, the high refractive index of the sputtered, conductive layer (preferably above 1.9) has the advantage that the reflection has been reduced relative to the known method. In addition, the surface resistance of a sputtered ITO layer having a thickness of 10-15 nm is approximately 500 Ω/square, which is much lower than the surface resistance of the known filter.

Subsequently, if necessary, a second, additional layer (AG) of silicon dioxide is provided by spraying a TEOS solution and subjecting said solution to a similar temperature treatment. This layer has a matt surface texture with anti-glare effect. By virtue thereof, the resultant coating is less sensitive to fingerprints. In addition, the reflection becomes less dependent on the wavelength because the incident light is scattered in a diffuse manner. The method described hereinabove can be applied to provide a (two-layer or multilayer) coating on an unassembled display screen, that is, a display screen which does not form part of a cathode ray tube (yet). Preferably, however, the method is used to provide a coating on a display screen which forms part of an already evacuated cathode ray tube. In this case, the risk of damage to the coating is reduced.

This can e.g. be done by sputtering a preferably thin (1-15nm) layer of SiO₂, (or TiO₂,NbO₅, ZrO₂,Al₂O₃ etc) on the sputtered conductive layer, whereafter the surface of said layer is etched by an etching solution, ed. caustic solution.

It is also possible to activate the surface of the ES or AR layer (see figure 4). Application of a separate primer layer is. however, preferred, since the activation may have detrimental effects on the properties of the ES or AR layer, in particular on the conductive properties of the ES layer.

In summary, the invention relates to a method of manufacturing a cathode ray tube comprising an antistatic filter, in which method a conductive layer (for example a material on the basis of tin oxide or tin-oxide compounds, such as indium-tin oxide) is applied by sputtering, and said conductive layer is provided with a further layer containing SiO₂ by means of a wet-chemical process, for example spinning and, subsequently, drying of a TEOS-compound. The method in accordance with the invention enables an antistatic filter to be manufactured in a simple manner which can suitably be used on an industrial scale, said filter exhibiting good antistatic and anti-reflective properties as well as a good shielding effect.

Within the scope of the invention, "cathode ray tube" is to be understood to mean, apart from conventional cathode ray tubes as shown in Fig. 1, devices in which electroluminescent phosphor is excited by means of controlled, charged particles (electrons and/or ions). Examples of such devices are so-called PDPs (Plasma Displays) in which phosphors are excited by means of plasma discharges, and flat display devices, as known from United States Patent US 5,313,136. The above-mentioned problems also occur in such devices.

Claims

A method of manufacturing a cathode ray tube provided with a multilayer antistatic filter on a display window, characterized in that a first, conductive, layer having a surface resistance not greater than 1 k Ω/square and a thickness of the order of 10-20 nm or less is sputtered onto the display window, said layer being provided by means of a wet-chemical process, with a further layer comprising SiO₂, the assembly of layers being selected for constituting a multilayer anti-reflection filter.
A method as claimed in claim 1, characterized in that the first, sputtered, conductive layer is provided with a second layer of a material other than silicon dioxide by means of sputtering, said second layer being coated, by means of a wet-chemical process, with said further layer comprising SiO₂, the assembly of layers being selected for constituting a multilayer anti-reflection filter.
A method as claimed in claim 1 or 2, characterized in that a first, conductive layer having a surface resistance ≤ 500 Ω/square is provided.
A method as claimed in claim 1 or 2, characterized in that the further layer contains an absorbing substance.
A method as claimed in claim 1 or 2, characterized in that the first, conductive, layer contains a conductive material on the basis ITO or ATO.
A method as claimed in claim 1 or 2, characterized in that the further layer is provided, by means of a wet-chemical process, with an anti-glare layer containing silicon dioxide.
A method as claimed in claim 1 or 2, characterized in that the method comprises an intermediate method step, between the sputtering and the provision of the further layer, in which intermediate method step, the surface on which the further layer is to be provided is activated.
A method as claimed in claim 7, characterized in that the intermediate step comprises the application by means of sputtering of an intermediate layer on the first layer and etching of the intermediate layer.