APPARATUS AND METHOD FOR THE DEPOSITION OF METAL OR
METAL OXIDE COATINGS ON AN ELONGATED SUBSTRATE
Field of the invention. The invention relates to an apparatus and to a method for the deposition of a metal or metal oxide coating on elongated flexible substrates. The apparatus is in particular suitable to deposit superconducting metal oxide coatings.
The invention further relates to an elongated substrate coated with a metal or metal oxide coating.
Background of the invention.
Since superconducting materials such as YBa2Cu3O7.x (YBCO) can be successfully produced by a number of techniques, new problems such as how to increase the production capacity and the cost effectiveness are coming up.
Both production capacity and cost effectiveness are directly related to the average volume deposition rate.
Since the volume deposition rate is determined by the thickness deposition rate and the area on which the material can simultaneously be deposited, at present one is trying to optimize the existing methods in order to increase either the thickness deposition rate or the area on which material can simultaneously be deposited.
In order to obtain a high quality YBCO coating over a larger area a homogeneous temperature distribution over the substrate is required. This can be achieved by using a fast rotating turntable with heating elements above, below and around it, as described in WO 98/20521. However, the coated surface is limited to a surface of about 400 cm2 and the method can not be applied to coat long lengths of a substrate.
A possible solution to coat tapes is by helicoidally winding a tape around a cylindrical holder and growing a superconducting film on the substrate while rotating the holder as described in US 5,731 ,271.
However, even when a long cylindrical holder with a large diameter is used, the surface of the tape to be coated is always limited.
Summary of the invention. It is an object of the present invention to provide an apparatus and a method of depositing a metal or metal oxide coating on elongated substrates.
It is another object of the present invention to provide an apparatus and a method for the deposition of a superconducting coating and more particularly for the deposition of a thick superconducting coating with an excellent crystallinity.
It is still a further object to provide a method to deposit a metal or metal oxide coating having a high production capacity and a high cost effectiveness.
According to a first aspect of the present invention an apparatus for the deposition of a metal or a metal oxide coating is provided. The apparatus comprises a winding system for an elongated substrate comprising at least an unwind and a rewind roll and means to deposit the metal or metal oxide coating.
The winding system is surrounded by a housing. This housing is interrupted by at least one deposition window. The means to deposit the metal or metal oxide coating are located in front of this deposition window. The housing is provided with a heating system. The winding system holding the elongated substrate is mounted in such a way that it can be rotated inside the housing.
The winding system comprises at least an unwind and a rewind roll. The unwind and rewind roll are located inside the housing. Possibly, the winding system further comprises one or more support roll(s).
Preferably, at least a part of the inner side of the housing is provided with a heating system, in such a way that the elongated substrate is surrounded by this heating system.
The heating system may comprise any heating element known in the art such as metal wires, strips or coils. Preferred metals are for example Ni- Cr alloys such as Inconel® or Hastelloy®. A preferred heating element comprises a Thermocoax heating element. Also infrared heating elements, such as infrared lamps can be used.
As described above, the housing and thus also the heating system is interrupted by at least one deposition window. Preferably, the size of the deposition windows is as small as possible, since the bigger the deposition windows are, the higher the temperature fluctuations can be.
It can be desired that the housing is thermally isolated. The housing can for example be provided with thermally insulating shields, such as metal shields or it can be provided with thermally insulating material, such as ceramic material. Alternatively, the housing can be provided with a combination of thermally insulating shields and thermally insulating material.
The housing preferably comprises a side wall, a back wall and a front wall. The side wall may have a round cross-section, or it may have a polygonal cross-section.
The side wall and the heating system are interrupted at a number of deposition zones.
Possibly, also the front and the back wall are provided with a heating system.
In a preferred embodiment the side wall is a cylindrical wall provided with heaters, forming a cylindrical heating system.
The coating can be deposited by a number of different techniques such as sputtering for example magnetron sputtering, ion beam sputtering and ion assisted sputtering, evaporation or co-evaporation, laser ablation, chemical vapour deposition or plasma enhanced chemical vapor deposition.
The elongated substrate is preferably a flexible substrate. With flexible is meant that the substrate can be wound and rewound without problems.
The elongated substrate can for example be a tape or foil, such as a plastic, ceramic or metallic tape or foil. Preferred substrates are for example made of aluminium oxide, zirconium oxide, steel, nickel or nickel alloys, titanium, polyester or polyimide, for example known as Kapton®or Upilex®.
In principle, the apparatus can be used for the deposition of any metal or metal oxide coating on an elongated substrate.
The apparatus is in particular suitable for the deposition of superconducting coatings such as YBCO coatings.
For the purpose of this application YBCO has to be understood to comprise not only YBa2Cu3O7.x but also YBCO coatings whereby Y is replaced partially or totally by a rare earth element or YBCO coatings doped with for example Ca. Also other deviations from the conventional
1 ,2,3 compositions known in the art are supposed to be included.
Other examples of coatings that can be deposited by the apparatus according to the present invention are TiO2, BaTiO3, SrTiO3, CeO2, yttrium stabilized zirconia (YSZ) and MgO coatings.
The apparatus can also be used to deposit silicon or germanium coatings or mixtures thereof, for example to deposit crystalline silicon or germanium coatings.
Since small temperature variations during deposition may have a serious influence on the crystal structure and quality of the deposited material, the requirements of the homogeneity and stability of the temperature during deposition are extremely high. As the elongated substrate is surrounded by the heating system, a homogeneous temperature of the substrate during deposition can be obtained.
Furthermore, the apparatus according to the present invention is designed so that the winding system holding the elongated substrate can be rotated inside the housing. By rotating the winding system inside the housing possible changes in temperature are minimized or even avoided.
The rotating speed is for example dependent upon the number and width of the deposition windows, the required temperature and the heating power of the heating system.
Preferably, the rotating speed is higher than 1 rotation/min and is for example between 10 and 1000 rotations/min.
The winding speed is dependent upon the number of deposition windows, the width of the deposition windows, the deposition rate and the required thickness of the coating.
Preferably, the winding speed is higher than 0.1 cm/min, for example between 0.1 and 100 cm/min. More preferably the winding speed is higher than 10 cm/min.
The winding speed of the substrate can be adjusted independently from the rotation speed without influencing the temperature stability and homogeneity of the substrate.
The winding speed is preferably low to obtain a sufficiently thick coating, whereas the rotating speed is preferably high to minimize temperature fluctuations.
The temperature of the substrate is dependent upon the material to be deposited and dependent upon the deposition technique, but is preferably between 200 and 1000 °C, more preferably the temperature is between 400 and 800 °C.
The temperature is important since it has a direct influence on the crystal structure and quality of the deposited material.
The apparatus according to the invention does not impose any restrictions to the ultimate thickness of the coating. It allows to deposit thick coatings and/or to deposit multilayered structures. The apparatus may comprise different deposition zones. The same material can be deposited at the different deposition zones or alternatively, different materials are deposited at the different deposition zones, allowing to deposit a multi-layered coating. If in a winding or rewinding run the deposition of one of the materials has to be avoided a shutter can be used in the corresponding deposition zone.
The apparatus can be constructed in such a way that the elongated substrate can be wound and rewound without changing the substrate. This allows to grow thicker coatings in several subsequent runs.
Also buffer layers like yttrium stabilized zirconia (YSZ), MgO or CeO2 can be applied by the apparatus according to the present invention. These buffer layers can be deposited by a number of different techniques such
as s guttering for example magnetron sputtering, ion beam sputtering and ion assisted sputtering, evaporation or co-evaporation, laser ablation, chemical vapour deposition or plasma enhanced chemical vapor deposition.
The apparatus may further comprise one or more oxygen supplies. Possibly, the oxygen supply is limited to an oxygen pocket.
According to a second aspect of the present invention a method for the deposition of a metal or metal oxide coating is provided. The method is performed by using an apparatus comprising a winding system and a housing as described above. The method comprises the steps of : providing a winding system holding an elongated substrate; - winding the elongated substrate from an unwind roll to a rewind roll; heating the substrate by means of a heating system surrounding the elongated substrate; depositing a metal or metal oxide coating on the elongated substrate; rotating the winding system holding said elongated substrate inside the housing to obtain a homogeneous temperature of the substrate during deposition.
The steps of winding the substrate, heating the substrate, depositing the metal or metal oxide coating on the elongated substrate and rotating the winding system are all performed simultaneously. This allows to keep the temperature of the substrate stable during the deposition of the coating.
The coating may be deposited in one run or in a number of subsequent runs. The substrate can thereby be wound and rewound in a to and fro movement without changing the substrate.
According to a further aspect of the present invention, an article comprising at least one coating layer of a metal or metal alloy is provided.
The article is obtainable by the above described method. The article comprises an elongated substrate; at least one metal or metal oxide coating layer deposited on said elongated substrate.
A preferred metal oxide layer comprises a YBCO coating; a preferred metal layer comprises silicon.
The metal or metal oxide layer has for example a thickness of 0.1 or 0.2 μm. Also metal or metal oxide coating with a rather high thickness, such as a thickness higher than 0.5 μm or 1 μm, can be obtained.
Possibly, the article further comprises one or more intermediate layers. Such an intermediate layer is for example functioning as an adhesion layer or as a buffer layer.
The buffer layer can for example be a yttrium stabilized zirconia layer, a CeO2 layer or a Y2O3 layer.
Brief description of the drawing. The invention will now be described into more detail with reference to the accompanying drawing wherein
FIGURE 1 is a schematic drawing of a winding and heating system according to the invention.
Description of the preferred embodiments of the invention.
FIGURE 1 is a schematic view of an apparatus 10 comprising a winding system and a housing according to the present invention.
The elongated flexible substrate 1 1 is transferred from an unwind roll 12 to a rewind roll 13 (or vice versa) and passes over a number of support rolls 14.
The winding system holding the elongated flexible substrate is surrounded by a housing 15. The housing comprises a cylindrical wall, a back wall and a front wall. The cylindrical wall has typically a diameter of 150 cm.
The cylindrical wall, surrounding the winding path of the elongated substrate, is provided at its inner side with heater elements forming a heating array 16. Preferably, the cylindrical wall is also provided with insulatings shields (not shown).
In a preferred embodiment also the front wall and the back wall are provided with heater elements and possibly also with thermally insulating shields.
In the cylindrical wall and in the heating array 16 several windows 17 are foreseen for the deposition of the coating.
Preferably, one or all the deposition windows are provided with a shutter.
If necessary, several heater elements 18 can be foreseen along the winding path of the substrate to provide a local additional heating of the substrate.
Furthermore, roll masks 19 can be provided above the support rolls.
They can avoid the accumulation of material on the rolls.
The winding system holding the flexible substrate is rotating around the axis 20 inside the surrounding housing, and thus inside the surrounding heating system.