DE102008040087B4 - Electrically conductive high-temperature superconductor layer structure and method for its production - Google Patents

Abstract

Electrically conductive high-temperature superconductor layer structure consisting of an electrically conductive, metallic substrate, at least one electrically conductive seed layer located on it with an amorphous and / or nanocrystalline structure made of Ta1-xNix, Ta1-xCox, Ta1-xFex, Nb1-xNix, Nb1- xCox or Nb1-xFex, where x is in the range from 0.1 to 0.9, on which there is at least one highly textured, electrically conductive layer applied by means of the IBAD process, on which in turn at least one highly textured, electrically conductive barrier layer and on top of it at least one high temperature -Supconductor layer are present.

Description

The invention relates to the field of materials science and relates to an electrically conductive high-temperature superconductor layer structure, as it can be used for example as a high current-carrying conductor and a method for its preparation.

For the fabrication of high-current superconducting conductors based on the high-temperature superconductors REBa ₂ Cu ₃ O _7-x (= REBCO), where RE can be both Y and a rare earth element, layers with a biaxial texture over long lengths are required. This can be realized by an epitaxial growth of the REBCO on textured documents. In general, the conductor consists of a metallic carrier tape on which additionally one or more barrier layers and then the superconductor are applied. These are the so-called REBCO band conductors.

The desired biaxial texture can be known either directly in the metallic carrier tape by strong deformation and subsequent heat treatment can be realized (so-called RABiTS - rolling assisted biaxially textured substrates, Goyal et al., Appl. Phys. Lett. 69 (1996) 1795) or alternatively in one of the barrier layers induced by a special deposition method.

One possibility for producing highly textured barrier layers on any desired substrates is ion beam-assisted deposition (IBA (Iijima et al., Appl. Phys. Lett. 60 (1992) 769). US 6,190,752 B1 ; US 2006/0142164 A1 ). In this method, an ion beam with a defined energy is directed at a defined angle to the substrate surface during the layer growth on this. As materials for this IBAD process, it is known that various oxides such as Y-stabilized ZrO ₂ (YSZ; iijima et al., Appl. Phys. Lett. 60 (1992) 769), MgO (Wang et al., Appl. Phys. Lett. 71 (1997) 2955) or Gd ₂ Zr ₂ O ₇ (Iijima et al., Physica C 378 (2002) 960).

However, additional barrier layers are needed to achieve epitaxial REBCO layers with high current carrying capacity.

Furthermore, in the case of application, a high-current cable based on REBCO must be protected against destruction of the superconductor by overload (eg caused by current peaks, local heating, etc.). In this case, the current must be dissipated via an electrical bridge to prevent destruction of the REBCO due to excessive heating during the sudden transition from the superconducting to the normal conducting state. In order to realize such an electrical bridge, thick metallic layers (eg Ag, Cu, etc.) are currently applied to the superconductor, which are able to carry the corresponding current in the event of overloading.

An alternative approach to this is the use of the metallic carrier tape for this purpose. In this case, however, electrically conductive barrier layers are necessary to realize an electrical contact between the carrier tape and the superconducting layer. The standard buffer layers used, such as Y ₂ O ₃ , YSZ, CeO ₂ , MgO, La ₂ Zr ₂ O ₇ , etc. are not suitable for this purpose.

Electrically conductive barrier layer architectures have in the past been realized for REBCO band conductors on the basis of the RABiTS approach ( US 2003/0211948 A1 . US 2005/0239658 A1 ). Among others, noble metals (Ir, Pt) and conductive oxides (La _0.7 Sr _0.3 MnO ₃ , SrRuO ₃ , LaNiO ₃ , etc.) were used (Aytug et al., Appl. Phys. Lett., 76 (2000) 760; Aytug et al., Appl. Phys. Lett. 85 (2004) 2887).

Using the IBAD method, it has hitherto been attempted to obtain an electrically conductive barrier layer architecture by the texturing of indium tin oxide (ITO) (Thiele et al., J. Mater. Res. 18 (2003) 442).

As an alternative material for texturing using the IBAD process, the electrically conductive TiN is known (Hahn et al., Appl. Phys. Lett. 85 (2004) 2744).

Among others, Ta _1-x Nix, Ta _1-x Fe _x or Ta _1-x Co _{x are known} as temperature-stable, amorphous and electrically conductive barrier layers in microelectronics (Fang et al., J. Electr. Mater. 36 (2007) 614; Fang et al., J. Electr. Mater. 35 (2006) 15).

From the WO 01/26165 A2 Furthermore, a method for producing an oxide buffer layer for superconducting layers is known. In this case, the surface of a metallic substrate is cleaned, heated and subsequently applied an epitaxial layer. Embodiments of this method indicate that an intermediate layer, a textured buffer layer applied by means of IBAD processes, a metallic layer and a high-temperature superconductor layer can be applied to the metallic substrate.

The disadvantage of the prior art is that it has not yet been possible to produce a conductive layer structure on a metallic carrier tape by means of the IBAD method.

The object of the present invention is to specify an electrically conductive high-temperature superconductor layer structure in which, in the case of overload, the current can be dissipated via the layer structure and the metallic substrate and a simple and easily reproducible method for its production.

The object is achieved by the invention specified in the claims. Advantageous embodiments are the subject of the dependent claims.

The electrically conductive high-temperature superconductor layer structure according to the invention consists of an electrically conductive, metallic substrate, at least one electrically conductive seed layer having an amorphous and / or nanocrystalline structure made of Ta _1-x Ni _x , Ta _1-x Co _x , Ta _{1 -x} Fe _x, Nb _1-x Ni _x, Nb _1-x Co _x or Nb _1-x Fe _x, where x is in the range of 0.1 to 0.9, on the at least one deposited by the IBAD method highly-textured, electrically conductive layer is present, on which in turn at least one hochtexturierte, electrically conductive barrier layer and in turn at least one high-temperature superconductor layer are present.

Advantageously, the electrically conductive, metallic substrate consists of Ni, Ni-based alloys, stainless steel, Cu or copper alloys.

Further advantageously, the highly textured, electrically conductive layer applied by means of the IBAD method consists of nitrides having a NaCl structure.

It is also advantageous if the layer consists of TiN, NbN, ZrN, HfN, CrN, VN or mixtures thereof.

It is also advantageous if the highly textured, electrically conductive barrier layer consists of Au, Ag, Pt, Ir, Rh, Mo, Nb, Pd or alloys thereof.

It is also advantageous if the high-temperature superconductor layer consists of YBa ₂ Cu ₃ O _7-x .

It is also advantageous if the high temperature superconductor layer consists of REBa ₂ Cu ₃ O _7-x , where RE is of Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb or mixtures thereof.

It is also advantageous if an electrically conductive oxide covering layer is present under the high-temperature superconductor layer, and it is even more advantageous if the electrically conductive oxide covering layer comprises Nb- and / or La- and / or Au-doped SrTiO ₃ , SrRuO ₃ , LaNiO ₃ , (La, Sr) MnO ₃ or mixtures thereof.

In the method according to the invention for producing an electrically conductive high-temperature superconductor layer structure, at least one seed layer of an electrically conductive material with an amorphous and / or nanocrystalline structure of Ta _1-x Ni _x , Ta _1-x is deposited on an electrically conductive, metallic substrate Co _x , Ta _1-x Fe _x , Nb _1-x Ni _x , Nb _1-x Co _x or Nb _1-x Fe _x where x is in the range of 0.1 to 0.9 are deposited and thereon by the IBAD method at least one highly textured electrically conductive layer is applied to which subsequently at least one highly textured, electrically conductive barrier layer and subsequently at least one high-temperature superconductor layer is applied.

Advantageously, a seed layer made of an electrically conductive material having an amorphous and / or nanocrystalline structure by means of sputtering, evaporation, electrodeposition or laser ablation is applied to an electrically conductive, metallic substrate.

Also advantageously, the highly textured electrically conductive layer is deposited by ion bombardment using the IBAD method at an angle of 35 ° to 55 ° to the substrate normal and an ion energy of greater than 400 eV.

Furthermore advantageously, the highly textured, electrically conductive barrier layer is applied by the IBAD process or by sputtering, evaporation, chemical solution deposition, metal-organic chemical vapor deposition or laser ablation.

And also advantageously, the highly textured high temperature superconductor layer is deposited by evaporation, chemical solution deposition, organometallic chemical vapor deposition or laser ablation.

With the method according to the invention, it becomes possible for the first time to realize a continuous electrically conductive high-temperature superconductor layer construction on the basis of the IBAD method, in which the highly textured structure of the layers is also continuously penetrated by the highly textured, electrically conductive layer which is produced by means of the IBAD method. Method has been applied (IBAD layer) is realized to at least the superconducting layer. The entire inventive, electrically conductive high-temperature superconductor layer structure is shown schematically in FIG 1 shown. The task of the individual layers is explained in more detail below.

So far, it has not been possible to apply a highly textured conductive layer to an electrically conductive, metallic substrate ( 1 ) by means of the IBAD method without using non-electrically conductive intermediate layers. In order to realize the desired highly textured structure or the biaxial texture during the IBAD process in materials having a NaCl structure, according to the invention an amorphous and / or nanocrystalline seed layer (US Pat. 2 ), which is stable in structure up to temperatures of 500 ° C. The amorphous and / or nanocrystalline seed layer ( 2 ) can be applied with a variety of deposition methods, such as sputtering, evaporation, electrode position or laser ablation, on the electrically conductive, metallic substrate. In order to ensure electrical contact between the electrically conductive, metallic substrate ( 1 ) and the highly textured, electrically conductive IBAD layer ( 3 ), the amorphous and / or nanocrystalline seed layer must also be electrically conductive.

According to the invention, it has been possible to specify and apply an electrically conductive seed layer having an amorphous and / or nanocrystalline structure on a substrate, on which the highly textured, conductive layer can then be grown by means of the IBAD method.

In this case, advantageously, the thickness of the highly textured conductive layer produced by the IBAD process can be further increased by the epitaxial growth. To a high-temperature superconductor layer ( 6 ) on the highly textured conductive IBAD layer is the presence of at least one highly textured, electrically conductive barrier layer ( 4 ) necessary.

Such barrier layers may for example consist of Au, Ag, Ir, Pt, Rh, Mo, Nb or Pd or their alloys. Since the high-temperature superconductor layer ( 6 ) is produced at temperatures above 650 ° C under a high oxygen pressure, proves to be a conductive, oxidic cover layer ( 5 ) on the high-temperature superconductor layer as helpful to prevent oxidation of the underlying metallic layers.

Finally, the high-temperature superconductor layer ( 6 ) are applied to the completely electrically conductive layer structure by a deposition method such as evaporation, chemical solution deposition, organometallic chemical vapor deposition or laser ablation.

The invention will be explained in more detail using an exemplary embodiment.

Showing:

1 FIG. 2: a schematic sketch of the high-temperature superconductor layer structure, FIG.

2 Figure 4: The RHEED images during the growth of an electrically conductive barrier layer architecture on electropolished Hastelloy: (a) amorphous Ta _0.75 Ni _0.25 seed layer; (b) highly textured IBAD-TiN; (c) epitaxial TiN; (d) Au; (e) Ir

3 : biaxially textured YBCO layer on IBAD-TiN with electrically conductive barrier layers

example 1

On an electro-polished substrate made of 57% Ni, 16% Mo, 15.5% Cr, 5.5% Fe, 4% W, 2.5% Co, 1% Mn (Hastelloy ^® C-276) is deposited by sputtering at room temperature an amorphous, electrically conductive Ta _0.75 Ni _0.25 layer applied as an electrically conductive seed layer with a thickness of 50 nm. Subsequently, the substrate with the seed layer is heated to 350 ° C. in a high-vacuum chamber, the amorphous structure of the Ta _0.75 Ni _0.25 seed layer being retained. In the next step, at this temperature, the biaxially textured TiN (IBAD) layer is laser-deposited from a Ti target in a nitrogen atmosphere with ion bombardment (IBAD) with argon and nitrogen ions at 800 eV energy at an angle of 45 ° to the substrate normal. At a layer thickness between 5 to 10 nm, the ion bombardment is turned off and the further growth of the TiN layer by means of continuous reactive laser deposition at a temperature of 700 ° C to a thickness of 40 nm. Subsequently, as a barrier layers, a 10 nm thick gold layer and a 20 nm thick iridium layer is epitaxially deposited on the TiN layer by pulsed laser deposition at a temperature of 600 ° C. Throughout the deposition, surface growth was observed with high energy electron diffraction (RHEED). Thus, both the amorphous structure of the seed layer and the highly textured growth of all other layers could be detected ( 2 ). Furthermore, a 120 nm thick Nb-doped SrTiO ₃ cover layer with pulsed laser deposition is deposited at a temperature of 550 ° C. In the final step, a 300 nm thick high-temperature superconductor layer YBa ₂ Cu ₃ O _7-x (= YBaCuO) is produced by means of pulsed laser deposition at a temperature of 810 ° C. and an oxygen pressure of 300 Pa. The YBCO layer had an in-plane half-width of 7.2 ° ( 3 ) and showed a superconducting transition temperature of 88 K. For all layers a good electrical conductivity was determined.

Example 2

On a electropolished non-magnetic stainless steel with an amorphous seed layer of Ta _0.5 Co _0.5 , a biaxially textured, electrically conductive TiN layer is produced by the IBAD process. For this purpose, a reactive deposition by pulsed laser deposition of a Ti target in a nitrogen atmosphere with simultaneous ion bombardment (argon and nitrogen ions with an energy of 800 eV) at an angle of 45 ° to the substrate normal at a temperature of 400 ° C is used. At a layer thickness between 5 to 10 nm, the ion beam is turned off and the further growth of the TiN layer by means of continuous reactive laser deposition at a temperature of 700 ° C to a thickness of 40 nm. Subsequently, as a barrier layers, a 10 nm thick gold layer and a 20 nm thick iridium layer is epitaxially deposited on the TiN layer by pulsed laser deposition.

Furthermore, a 200 nm thick SrRuO ₃ cover layer with pulsed laser deposition is deposited at a temperature of 550 ° C. In the final step, a 300 nm thick high-temperature superconductor layer (GdBa ₂ Cu ₃ O _7-x ) is produced by means of pulsed laser deposition at a temperature of 800 ° C. and an oxygen pressure of 300 Pa. All layers have a good electrical conductivity after deposition.

LIST OF REFERENCE NUMBERS

1

electrically conductive substrate

2

electrically conductive germ layer

3

highly textured electrically conductive IBAD layer

4

highly textured electrically conductive barrier layer

5

oxide cover layer

6

High temperature superconductor layer

Claims (14)

Electrically conductive high-temperature superconductor layer structure consisting of an electrically conductive, metallic substrate, at least one electrically conductive seed layer thereon having an amorphous and / or nanocrystalline structure of Ta _1-x Ni _x , Ta _1-x Co _x , Ta _1-x Fe _x , Nb _1-x Ni _x , Nb _1-x Co _x or Nb _1-x Fe _x , where x is in the range of 0.1 to 0.9, on which at least one highly textured, electrically conductive layer applied by the IBAD method is present is, on which in turn at least one hochtexturierte, electrically conductive barrier layer and in turn at least one high-temperature superconductor layer are present. An electrically conductive high-temperature superconductor layer structure according to claim 1, wherein the electrically conductive metallic substrate consists of Ni, Ni-base alloys, stainless steel, Cu or copper alloys. An electrically conductive high-temperature superconductor layer structure according to claim 1, wherein the highly textured, electrically conductive layer of nitrides having a NaCl structure applied by the IBAD method. The electrically conductive high-temperature superconductor layer structure according to claim 3, wherein the layer consists of TiN, NbN, ZrN, HfN, CrN, VN or mixtures thereof. An electrically conductive high-temperature superconductor layer structure according to claim 1, wherein the highly textured, electrically conductive barrier layer consists of Au, Ag, Pt, Ir, Rh, Mo, Nb, Pd or alloys thereof. An electrically conductive high-temperature superconductor layer structure according to claim 1, wherein the high-temperature superconductor layer consists of YBa ₂ Cu ₃ O _7-x . An electrically conductive high-temperature superconductor layer structure according to claim 1, wherein the high-temperature superconductor layer consists of REBa ₂ Cu ₃ O _7-x , where RE is Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb or mixtures thereof. An electrically conductive high-temperature superconductor layer structure according to claim 1, wherein below the high-temperature superconductor layer, an electrically conductive oxide cover layer is present. An electrically conductive high-temperature superconductor layer structure according to claim 8, wherein the electrically conductive oxide cover layer of Nb- and / or La and / or Au-doped SrTiO ₃ , SrRuO ₃ , LaNiO ₃ , (La, Sr) MnO ₃ or mixtures of which consists. A method for producing an electrically conductive high-temperature superconductor layer structure, wherein on an electrically conductive, metallic substrate at least one seed layer of an electrically conductive material having an amorphous and / or nanocrystalline structure of Ta _1-x Ni _x , Ta _1-x Co _x , Ta _1-x Fe _x , Nb _1-x Ni _x , Nb _1-x Co _x or Nb _1-x Fe _x , where x is in the range of 0.1 to 0.9, and then deposited thereon by the IBAD method at least a highly textured electrically conductive layer is applied to which subsequently at least one highly textured, electrically conductive barrier layer and subsequently at least one high-temperature superconductor layer is applied. The method of claim 10, wherein a seed layer of an electrically conductive material having an amorphous and / or nanocrystalline structure by means of sputtering, evaporation, electrode position or laser ablation is applied to an electrically conductive, metallic substrate. The method of claim 10, wherein the highly textured electrically conductive layer is deposited by ion bombardment using the IBAD method at an angle of 35 ° to 55 ° to the substrate normal and an ion energy of greater than 400 eV. The method of claim 10, wherein the highly textured, electrically conductive barrier layer by the IBAD process or by sputtering, evaporation, chemical solution deposition, metal-organic chemical vapor deposition or laser ablation is applied. The method of claim 10, wherein the highly textured high temperature superconductor layer is deposited by evaporation, chemical solution deposition, metalorganic chemical vapor deposition or laser ablation.

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