WO2002050579A2

WO2002050579A2 - Method for the production of an auxiliary shield for a plasma display and corresponding auxiliary shield produced by said method

Info

Publication number: WO2002050579A2
Application number: PCT/EP2001/015062
Authority: WO
Inventors: Franz Schedlbauer
Original assignee: Flabeg Gmbh & Co. Kg
Priority date: 2000-12-20
Filing date: 2001-12-19
Publication date: 2002-06-27
Also published as: AU2002229672A1; WO2002050579A3

Abstract

The invention relates to a method for the production of an auxiliary shield (1), for a plasma display, in particular for plasma TVs, whereby a layered system (4) is applied to a transparent base body (2), in particular a blue glass, white glass or float glass sheet. The aim of the invention is the production of high-grade coatings, in particular with good transmission properties with comparatively low cost. According to the invention, said aim is achieved, whereby in a first treatment step, a number of dielectric layers (6, 8, 10, 12) and metallic layers (14, 16, 18), forming the layer system (4), are sputtered onto the base body (2), in a gas atmosphere maintained essentially constant and in a second treatment step, the base body provided with the layer system is subjected to a heat treatment.

Description

description

Process for producing a cover plate for plasma screens and cover plate produced by the process

The invention relates to a method for producing a cover plate for plasma screens, in particular TV screens. It also relates to an attachment disc manufactured using the method.

When producing a filter disk for EMC and / or interference field suppression in the wavelength range between 700 nm and 1600 nm, i. H. In the infrared range, silver layers that are embedded between reactively sputtered metal oxide layers are protected against oxidation by barrier layers or so-called blockers. Without these blockers, the silver layers would be irreversibly damaged. Since at least three silver layers are required for physical reasons, a corresponding coating system is usually equipped with six additional cathodes for the blocker layers. In addition, the coating system must previously have had six to twelve gas separation devices or separate chambers in order to ensure a separation between the reactive and the metallic process or manufacturing steps.

A particular problem is to get uniform layer thicknesses of the very thin blocker layers. When the metal oxide layers are applied, sub-stoichiometric layers are formed which, after the bonding process in the autoclave, can or can lead to a change in the optical properties. In order to achieve homogeneous metal oxide layers that are uniform over the coating width, a lengthy adjustment process and a complicated process control have so far been required.

Layer systems that reflect light in the infrared range are known for use as a cover plate for plasma screens. Such layer systems can consist of a sequence of reactive sputtered dielectric layers and z. B. there are three silver layers lying between the dielectric layers. The dielectric Layers can in particular be constructed on the basis of indium tin oxide (ITO), since this material is well suited for use in combination with silver layers due to its optical properties, in particular its transparency. The silver layers can be protected from degradation by partially applied before and after the respective silver layer.

So-called Fabry-Perot interference filters are also known which do without these blocker layers and consist of, for example, four ITO and three silver layers with the structure ITO-Ag-ITO-Ag-ITO-Ag-ITO. Such front screens and methods for their production are known, for example, from JP 2000-141 539, EP 1 008 871 or US 6,316,110. However, the known methods for producing these cover plates are comparatively complex, especially since the silver layers are usually applied by sputtering in an inert gas atmosphere and the ITO layers are applied by reactive sputtering, so that gas separation is required when the individual layers are applied.

The invention is therefore based on the object of a method for producing a cover plate for a plasma screen, in particular for plasma TV sets, in which a layer system on a transparent base body, in particular a blue glass, white glass or float glass plate is applied to indicate that the production of high-quality coatings, which are particularly favorable with regard to their transmission properties, is possible with comparatively little effort. Furthermore, an attachment lens that is particularly suitable for use with a plasma screen is to be specified.

With regard to the method, this object is achieved according to the invention in that in a first treatment step a number of dielectric layers and metallic layers forming the layer system are sputtered onto the base body under a substantially constant gas atmosphere, in a second treatment step the base body provided with the layer system of a heat treatment is subjected. Essentially, dabeio means in particular that the gas composition of the sputtering atmosphere is the same, but the gas pressure between the individual steps can be varied by a factor of five (5). The invention is based on the consideration that a significant simplification in the manufacture of the front lens can be achieved by consistently avoiding the gas separation usually provided between the application of successive layers. This can be achieved by applying the individual layers that define the layer system in their entirety under an essentially constant gas atmosphere. However, due to the systematic difference between the metallic silver layers on the one hand and the dielectric, oxidic ITO layers on the other hand, it must be accepted that one of these two categories must be separated under non-ideal conditions. As has surprisingly been found, it is nevertheless possible to produce high-quality coatings by depositing the individual layers essentially under sputtering conditions which are favorable for the application of metallic layers. The lack of oxygen which arises during the production of the ITO layers under these conditions and which actually leads to insufficient transmission properties can be compensated for by a suitable aftertreatment. This aftertreatment is designed in such a way that there is no further impairment of the metallic silver layers.

It is known from EP 0 599 071 to subject a glass substrate coated with a single silver layer and an ITO cover layer assigned to it to a subsequent heat treatment after the coating. However, due to its transmission properties, the coated glass produced in this way is completely unsuitable for use as a cover plate for a plasma screen, especially since the surface resistance of the glass coated in this way is approximately 3.2 Ω and thus significantly more than that for use as a cover plate for a plasma screen is still a permissible limit of 1.5 Ω. This simply coated glass also differs fundamentally from the multi-layer system now provided in terms of the complexity and dynamics of the interdiffusion processes that occur.

Advantageous embodiments of the invention are the subject of the dependent claims. All individual layers of the filter layer are advantageously in a pure noble gas or. Inert gas atmosphere applied using ceramic targets for the transparent dielectric layers and metallic targets (pure metals and alloys) for the metal layers. The dielectric layers are preferably sputtered suboxidically or sub-stoichiometrically, which means that there is no need for blocker layers.

Subsequent temperature treatment (T> 200 ° C) oxidizes the suboxidic dielectric layers and crystallizes the metal layers, whereby the sheet resistance is almost halved and the transmission increases by approx. 10% without damaging the silver layers. This represents a drastic improvement to previously known Fabry-Perot interference filters.

Due to the high transmission of the filter disk, it is now possible to make the transmission area of the cover disk adjustable without impairing the low reflection of less than 2%. The durability of the coating of the filter disc before the bond could also be increased. By subsequent to the application of the filter layers and subsequent to the sputtering subsequent heat treatment at z. B. 300 ° C to 350 ° C over a period of about 30 min. the transparent dielectric layers are oxidized and the metal layers crystallized, the surface resistance falling from approx. 2 Ω to approx. 1.2 Ω and the transmission increasing by approx. 10% from approx. 50% after coating on the HKZ3 to approx. 60% , The listed values apply to the transmission for blue glass from PPG (thickness: 3.2 nm). For float and white glasses, the final values for the transmission should be set at 70% to 75%.

In this subsequent tempering process, which is preferably carried out in air, it has surprisingly been found that in addition to the oxidation of the transparent dielectric layers, there was no damage to the silver layers and that the surface resistance could be reduced by a factor of almost two. This low surface resistance of the layer system is an important factor, in particular for use as a cover plate for plasma TV sets, to describe the EMC shielding of the cover plate against interference radiation and infrared radiation. With regard to the front lens, the above-mentioned object is achieved in that the layer system of a front lens manufactured according to the method has a surface resistance of less than 5 Ω, and in that the front lens has a transmittance of greater than 53% at a wavelength less than or equal to 600 nm and at a wavelength above 600 nm has a transmittance of less than 53%.

With a layer system produced according to the described method, the front lens preferably has a transmission of 72% at a wavelength λ of 450 nm compared to a target value greater than 53%. At a wavelength λ of 600 nm, a transmission of 55% is expediently achieved compared to a target value greater than 53%. At 650 nm, a transmission of about 34% is preferably achieved, while at a wavelength of 800 nm, the electromagnetic radiation emitted by a plasma screen and to be filtered via the composite pane or to be derived via the layer system 5 already reduces the transmission to 3% (target value > 8%) and at 850 nm to 2% (target value <4%).

A lens which is particularly favorable with regard to its optical and electrical properties advantageously has an infrared-reflecting layer system in the manner of a Fabry-Perot interference filter with the structure: ITO 45 nm, Ag 11 nm, ITO 90 nm, Ag 11 nm, ITO 90 nm, Ag 6 nm, ITO 48 nm.

An embodiment of the invention is explained in more detail with reference to a drawing. It shows: 5

Fig. 1 in a cut-out for a plasma screen, and

2 shows a transmission / wavelength diagram of the cover plate according to FIG.

1. 0

1 is designed as a so-called Fabry-Perot interference filter and for a comparatively high transmission in the optical range, that is to say at wavelengths of more than 600 nm, and for a comparatively low transmission in the infrared range, i.e. at wavelengths of less than 600 nm. For this purpose, the front lens 1 comprises a base body 2, which is provided with a layer system 4 applied thereon. The base body 2 is the actual pane, which is made of glass, in the exemplary embodiment of white glass or float glass.

The layer system 4 applied to the base body 2 consists of an alternating sequence of transparent dielectric layers 6, 8, 10, 12 and silver (AG) layers 14, 16, 18. The dielectric layers 6, 8, 10, 12, from four of which are provided in the exemplary embodiment are each based on indium tin oxide (ITO) and each embed one of the three provided silver layers 14, 16, 18 in pairs.

The lowest ITO layer 6 in the exemplary embodiment according to FIG. 1, which u. a. also fulfills the function of an adhesion promoter for the layer system 4 to the base body 2, has a layer thickness of approximately 45 nm. By contrast, the lowermost silver layer 14 applied to the layer 6, like the next silver layer 16, has an average layer thickness of approximately 11 nm. The second ITO layer 8, like the subsequent ITO layer 10, has an average layer thickness of approximately 90 nm. The top silver layer 18 in the exemplary embodiment is set to an average layer thickness of approximately 6 nm, and the ITO layer 12 provided as the top finishing layer has an average layer thickness of approximately 48 nm.

In the manufacture of the front lens 1, on the one hand, a particularly high transmission in the optical range, that is to say at wavelengths of more than 600 nm, of more than 53% is set. On the other hand, it is ensured with comparatively simple means that the layer system 4 has a sufficiently low surface resistance of, for example, approximately 1.5 Ω or less, so that electromagnetic interference radiation in the infrared range can be reliably derived.

In order to be able to reliably meet these criteria with comparatively simple means, the base body 2 is first provided with the layer system 4 in a first treatment step in the manufacture of the cover plate 1. In this first treatment step, ITO layer 6 is applied in a first coating step. introduced. The ITO layer 6 is sputtered on using ceramic targets in a pure noble gas or inert gas atmosphere. The application of the layer takes place at an operating pressure of 3.0 to 10 ^"5 Pa in an Ar atmosphere at a sputtering rate of about 17.5 nm / min. In a second coating step 8 is followed by the silver layer, while maintaining the sputtering atmosphere , ie without gas separation, but the working pressure can be changed slightly and set to a value of about 1.7-10 ^"5 Pa. The sputter rate is 7.8 nm / min. set.

Then in alternating order and also while maintaining the set conditions, i.e. H. without gas separation, the further ITO layers 8, 10 and 12 and the further silver layers 16 and 18 sputtered on. The aforementioned first treatment step, that is to say the complete application of the layer system 4, is thus carried out under essentially constant atmospheric conditions. As an intermediate result, a blank is obtained for the front lens 1 after the first treatment step, but because of the selected sputtering conditions and the non-stoichiometric ceramic targets used, it does not yet have the desired transmission and conduction properties.

This blank for the front lens 1 is then subjected to a heat treatment or a tempering step in a second treatment step. In this temperature treatment, the blank for the front lens 1 is in an air atmosphere over a treatment period of about 30 minutes. exposed to an elevated temperature of about 270 ° C to 350 ° C by heating. This heat treatment compensates for the lack of oxygen in the sub-stoichiometric ITO layers 6, 8, 10, 12 applied during the production of the blank, so that the desired composition is now established.

By means of the aforementioned choice of treatment parameters, this oxidation of the transparent dielectric layers 6, 8, 10, 12 can be carried out without any appreciable damage to the silver layers 14, 16, 18. Rather, the silver layers 14, 16, 18 crystallize out appropriately, so that the surface resistance layer system 4 was reduced by a factor of two as a result of the heat treatment.

The wavelength λ of electromagnetic radiation between 380 nm and 780 nm is plotted on the abscissa of the diagram in FIG. 2, while the transmission is plotted in percent on the ordinate. The course of the measurement curve clearly shows a transmission above 70% at a wavelength of 450 nm. The transmission, which drops significantly from about 550 nm of about 65%, is already below 20% at 700 nm and below 5% above 750 nm.

The conductivity or the sheet resistance of the layer system (cover plate) applied to a pane could be measured at approximately 1.2 Ω and is therefore advantageously less than 1.5 Ω. This enables reliable derivation of electromagnetic interference radiation, in particular in the infrared range. At the same time, an advantageously adjustable transmission of more than 60% in the visible range is achieved, while at the same time reliable EMC shielding with simultaneous color neutrality of the front lens or the layer system is achieved.

LIST OF REFERENCE NUMBERS

front cover lens

body

Layer system, 8, 10, 12 dielectric layers, 16, 18 silver layers

Claims

Expectations

1. A method for producing a cover plate (1) for a plasma screen, especially for plasma TV sets, in which a transparent base body

(2), in particular a blue glass, white glass or float glass pane, a layer system (4) is applied, a number of dielectric layers (6, 8, 10, 12) forming the layer system (4) being applied in a first treatment step and metallic layers (14, 16, 18) are sputtered onto the base body (2) under a substantially constant gas atmosphere, and in a second treatment step the base body (2) provided with the layer system (4) is subjected to a heat treatment ,

2. The method of claim 1, wherein the first treatment step in inert gas atmosphere 5 sphere is carried out at a working pressure of about 10 ^"5 to 10 ^{" 4} Pa.

3. The method according to claim 1 or 2, in which in the first treatment step for applying the dielectric layers (6, 8, 10, 12) an oxidic ceramic target is used. 0

4. The method according to any one of claims 1 to 3, in which in the second treatment step the heat treatment is carried out at a tempering temperature of more than 200 ° C, preferably from about 300 ° C to 350 ° C.

5 5. The method according to any one of claims 1 to 4, in which the heat treatment is carried out in an air atmosphere in the second treatment step.

6. The method according to any one of claims 1 to 5, wherein in the second treatment step, the heat treatment for a treatment period of about 30 minutes. 0 is made.

7. attachment disc (1), produced by a method according to any one of claims 1 to 6, the layer system (4) having a sheet resistance less than 5 Ω, and which has a transmittance of greater than 53% for at least one wavelength in the wavelength range less than 600 nm and a transmittance of less than 53% for at least one wavelength in the wavelength range above 600 nm.

8. front lens (1) according to claim 7, the transmittance above a wavelength of 650 nm less than 35% and / or at a wavelength of about 800 nm less than 8% and / or at a wavelength of about 850 nm less than 4%.

9. front lens (1) according to claim 7 or 8, wherein the surface resistance of the layer system (4) is less than 2 Ω, preferably less than 1.5 Ω, in particular less than 1.3 Ω.

10. front lens (1) according to any one of claims 7 to 9, the layer system (4) comprises three silver layers (14, 16, 18) and four indium tin oxide layers (6, 8, 10, 12).

11. front lens (1) according to claim 10, the layer system (4) a layer structure of the sequence: indium tin oxide layer (6) an average layer thickness of 45 nm, silver layer (14) an average layer thickness of 11 nm, indium tin oxide

Layer (8) an average layer thickness of 90 nm, silver layer (16) an average layer thickness of 11 nm, indium tin oxide layer (10) an average layer thickness of 90 nm, silver layer (18) an average layer thickness of 6 nm and Indium tin oxide layer (12) has an average layer thickness of 48 nm.