EP0423178A1 - Element de josephson a materiau supraconducteur en ceramique oxydee et son procede de fabrication - Google Patents

Element de josephson a materiau supraconducteur en ceramique oxydee et son procede de fabrication

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Publication number
EP0423178A1
EP0423178A1 EP89907704A EP89907704A EP0423178A1 EP 0423178 A1 EP0423178 A1 EP 0423178A1 EP 89907704 A EP89907704 A EP 89907704A EP 89907704 A EP89907704 A EP 89907704A EP 0423178 A1 EP0423178 A1 EP 0423178A1
Authority
EP
European Patent Office
Prior art keywords
layer
substrate
josephson element
electrode layers
weak coupling
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP89907704A
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German (de)
English (en)
Inventor
Gabriel Daalmans
Bernhard Roas
Hans Eckhardt Hoenig
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
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Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP0423178A1 publication Critical patent/EP0423178A1/fr
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/225—Oblique incidence of vaporised material on substrate
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/0021—Reactive sputtering or evaporation
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/04—Coating on selected surface areas, e.g. using masks
    • C23C14/042—Coating on selected surface areas, e.g. using masks using masks
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/04—Coating on selected surface areas, e.g. using masks
    • C23C14/042—Coating on selected surface areas, e.g. using masks using masks
    • C23C14/044—Coating on selected surface areas, e.g. using masks using masks using masks to redistribute rather than totally prevent coating, e.g. producing thickness gradient
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/24—Vacuum evaporation
    • C23C14/28—Vacuum evaporation by wave energy or particle radiation
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/01—Manufacture or treatment
    • H10N60/0268—Manufacture or treatment of devices comprising copper oxide
    • H10N60/0296—Processes for depositing or forming copper oxide superconductor layers
    • H10N60/0521—Processes for depositing or forming copper oxide superconductor layers by pulsed laser deposition, e.g. laser sputtering
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/01—Manufacture or treatment
    • H10N60/0912—Manufacture or treatment of Josephson-effect devices
    • H10N60/0941—Manufacture or treatment of Josephson-effect devices comprising high-Tc ceramic materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/10—Junction-based devices
    • H10N60/12—Josephson-effect devices
    • H10N60/124—Josephson-effect devices comprising high-Tc ceramic materials

Definitions

  • the invention relates to a Josephson element with a layered structure on a flat side of a substrate, which element
  • the invention further relates to a method for producing such a Josephson element.
  • a corresponding element with the features mentioned can be found in "Japanese Journal of Applied Physics", vol. 26, no. September 9, 1987, Part 2 - Letters, pages L1443 to L1444.
  • Superconducting metal oxide compounds with high transition temperatures T, in particular above 80 K, which can therefore be cooled with liquid nitrogen are generally known.
  • Corresponding metal oxide compounds are based, for example, on a material system of the Mel-Me2-Cu-0 type, the components Mel at least containing a rare earth metal such as Y and Me2 an alkaline earth metal such as Ba. Films or thin layers of these metal oxide compounds are often produced using special vapor deposition or sputtering processes.
  • a polycrystalline or amorphous precursor with the components of the selected material system is generally deposited on a suitable substrate, the oxygen content and thus the desired phase not yet being set exactly. This preliminary product is then converted into the material with the desired superconducting phase by means of heat and oxygen treatment.
  • a Josephson element using such an oxide-ceramic superconductor material is derived from the publication "ap.J.Appl.Phys.” forth.
  • This element contains a base electrode layer made of the same material on a sintered substrate of the Y-Ba-Cu-0 material system.
  • An Nb layer applied to the tunnel barrier layer serves as the counter electrode.
  • a so-called “weak link” configuration is thus formed in a known manner with the tunnel barrier layer, ie a region of weak coupling between the electrode layers (cf., for example, “Proc. IEEE”, Vol. 61, No. 1, Jan. 1973, pages 36 to 45). It turns out, however, that such a Josephson tunnel element at 77 K has to be ascertained for use in active electronic circuits Requirements for sufficient critical current density and low magnetic flux noise can not meet.
  • Films made of oxide-ceramic high-T superconductor material with high critical current densities are known per se. For this purpose, these films must have textured structures. This is because they show a strongly anisotropic behavior of the critical current density (current carrying capacity) as a function of the position of the crystal axes.
  • the production of corresponding YBa 2 Cu, 0 7 films on a single-crystalline SrTiO, substrate is described, for example, in "Physical Review Letters", Vol. 58, No. 25, June 22, 1987, pages 2684 to 2686. Accordingly, the three metallic components of the system (Y, Ba, Cu) are first evaporated from separate evaporation sources in an oxygen atmosphere onto the substrate heated to approximately 400'C.
  • Texture-coated layers with oriented crystals of the desired superconducting high-T phase are then obtained by means of a subsequent treatment with a supply of oxygen at a high temperature of about 900 ° C.
  • the films produced in this way show the aforementioned strong anisotropy of the critical current density.
  • Critical current densities of 10 to 10 A / cm 2 have to be measured perpendicular to the c-axes of the crystals at 77 K, while the critical current density is at least a power of 10 smaller parallel to the c-axis.
  • a target material of the corresponding material system is first evaporated by means of a laser and deposited on a single-crystal SrTiO ⁇ substrate.
  • the laser to be used can be a KrF excimer laser, the wavelength of which is in the UV spectral range and an energy density on the target material of approximately 2 J / cm 2 at Pulse frequency from 3 to 6 Hz possible.
  • the substrate should be heated to 450 ° C (see also "Appl.Phys.Lett.”, Vol. 51, No.
  • the layer obtained in this way is also incorrectly structured with regard to the desired superconducting high-T phase.
  • a subsequent heat treatment at about 900 C in a ⁇ Sauer ⁇ hydrogen atmosphere and followed by slow cooling to obtain single-crystalline then the desired or at least strongly textured film layers of the HS ⁇ estrebten high-Tc phase.
  • the object of the present invention is to design the Josephson element of the type mentioned at the outset such that it can be produced in a relatively simple manner.
  • a method is to be specified with which layers with critical current densities of at least 10 A / cm 2 can be formed reproducibly, without the high-temperature process mentioned being necessary.
  • a substrate which has a texture adapted to the crystal structure dimensions of the superconducting phase of the oxide-ceramic superconductor material, that the electrode layers are by means of a correspondingly textured distance some are made of insulating material, a step of predetermined step height having step edges and a connecting surface running therebetween being formed such that the electrode layers and the area of weak coupling are formed from the oxide ceramic superconductor material extending over the step with the same ordered crystal structure, whereby the area of weak coupling extends along the connecting surface between the step edges and has an extent perpendicular to the planes of less than 100 nm, and that the electrode layers have a critical current density in the direction of the planes which is at least 10 times greater than in the perpendicular direction to that through the Weak coupling area.
  • the anisotropy of the critical current density of the oxide-ceramic high-T superconductor material is thus used to form a Josephson element. Accordingly, a transition region is formed at the step between two layers of high critical current density in the layer planes, in which the critical current density perpendicular to the direction of expansion of these layers is substantially smaller.
  • the result of this is only a weak coupling between the two layers of high critical current density serving as the base electrode or counterelectrode, so that this transition region represents a "weak link" between these electrode layers.
  • the cross-sectional area of this area of weak coupling to be measured parallel to the planes of the electrode layers can of course only be so large that the desired “weak link” function is guaranteed.
  • Such a Josephson element can advantageously be the desired one
  • the Josephson according to the invention can be particularly advantageously Manufacture element by first applying a shadow mask with a hole structure adapted to the step to be formed and the element to be produced in a lithography process on the substrate and by depositing the layers of the element by oblique vapor deposition with uninterrupted vacuum conditions .
  • a target material made of an oxide ceramic of the superconductor material is advantageously vaporized by means of a pulsed laser, the wavelength of which lies in the ultraviolet spectral range, simultaneously with a heat treatment and oxygen treatment.
  • the advantages associated with these process steps are to be seen in particular in the fact that the desired superconducting phase can be crystallized virtually “in situ” and that subsequent formation of this phase by a special annealing step at high temperatures is therefore no longer necessary.
  • Higher substrate temperatures and activated oxygen on the substrate are necessary for the in-situ crystallization according to the invention.
  • a laser with a sufficiently high pulse energy can advantageously be used to activate the oxygen.
  • the molecular oxygen of the intended atmosphere is then activated by interaction with the UV laser radiation directly on the heated substrate with each pulse.
  • the amount of oxygen radicals generated in this way and the high substrate temperature are sufficient to epitaxially grow an approximately 1 nm thick layer with each pulse.
  • the high growth rates that can be achieved at conventional pulse frequencies ensure a short treatment time and low contamination of the layers.
  • FIG. 1 illustrates a method for producing a Josephson element.
  • FIG. 3 shows an apparatus for carrying out a manufacturing process. Parts that correspond in the figures are provided with the same reference symbols.
  • the Josephson element according to the invention is to be formed from a known superconducting high-T material on a predetermined substrate.
  • a material from the material system Mel-Me2-Cu-0 is selected as an exemplary embodiment.
  • Mel and Me2 can in particular be an element from the group of rare earth metals such as Y or an element from the group of alkaline earth metals such as Ba. In addition to Y and Ba, materials suitable for Mel and Me2 are generally known. If appropriate, Mel and Me2 are also alloys or compounds or other compositions of these metals with substitution materials; that is, at least one of the elements mentioned can be partially substituted by another element in a known manner.
  • the Cu or the 0 can also be exchanged, at least partially, for other elements.
  • the Josephson element according to the invention and the method for its production are not only limited to the material system mentioned; that is, other oxide ceramic, metallic components and oxygen-containing high-T superconductor materials are also suitable, which are not attributable to the system mentioned.
  • Corresponding materials are, for example, from "Superconductivity News", Vol. 1, No. 9, March 18, 1988, pages 1 to 5 and 13 to 16 are known.
  • the electrode layers of the Josephson tunnel element to be produced should have a high current carrying capacity in the order of magnitude of at least 10 A / cm z in the vicinity of the transition temperature T of the material enable. Also particularly advantageous are those materials whose transition temperature is significantly above the vaporization temperature of the liquid nitrogen of about 77 K.
  • the substrate to be selected materials are advantageously those having a structure with dimensions of their unit cells of the axes of the grown on them structures constitute at least about the one or more times the ent speaking dimensions of the sup r ra réelleden high-Tc material .
  • a single-crystalline or at least appropriately textured SrTiO- z - or (Ba, Sr) TiO ⁇ substrate is particularly advantageous.
  • other materials such as MgO, Al2O, Y-stabilized Zr0 2 or Ta 2 0 5 are also suitable.
  • the Josephson element according to the invention is not necessarily limited to such single-crystalline or textured substrates.
  • polycrystalline substrates such as, for example, polycrystalline SrTiO applied on a suitable support can also be provided.
  • the formation according to the invention of at least one Josephson element with a superconducting material of the known composition YBa 2 Cu 3 0 7 _ ⁇ with an orthorhombic structure on a single-crystal SrTiO, substrate is used as a basis.
  • a structure is provided which is shown schematically as a cross section in FIG. 1:
  • a special shadow mask technique which is referred to as a floating mask technique, is advantageously used to produce the at least one Josephson element.
  • a floating mask technique is generally known (cf. for example DE-PS 31 28 982 or the publication “SQUID '80 - Supercon- ducting quantum interference devices and their applications ", Berlin 1980, pages 399 to 415).
  • a suspension corresponding to the desired substrate structure and the intended Josephson element structure is applied to the substrate 2 with a texture indicated by lines 2a ⁇ mask 3.
  • This floating mask which consists, for example, of SiO, has a self-supporting film bridge 3a which hovers above the substrate at a height h of a few micrometers and has a span w of about 1 ⁇ m.
  • the height H of the steps or the base is to be selected as a function of the thickness of the high-T superconductor material to be applied and can thus be, for example, below 100 nm. It determines the distance between two parallel planes E1 and E2 in which the electrode layers of the Josephine element to be produced are to be arranged.
  • the base 7 can therefore be regarded as a spacing part between these planes, which also defines the spacing of the two electrode layers.
  • the correspondingly etched state of the substrate 3 is illustrated in the figure. From the step 9 in the figure, the step edges are designated by K1 and K2 and the lateral connecting surface extending between these edges by 12.
  • a layer 10 is then applied to the heated substrate 2 evaporated obliquely from the oxide ceramic high-T superconductor material.
  • a laser is advantageously used to generate a corresponding steam jet 11, which enables a sufficient energy density and pulse energy. It can be achieved that the high T material grows epitaxially or at least textured on the substrate surface 5.
  • the steam jet 11 strikes the substrate surface 5 at an evaporation angle ⁇ s of approximately 45 "relative to the normal on this surface, so that the layer 10 extends beyond the step 9.
  • the layer thickness d of the layer 10 must be smaller than the step height H.
  • the layer 10 has two layer parts 10a and 10b lying in the different parallel planes E1 and E2, these layer parts should represent the base electrode or the counter electrode of a Josephson element, between these layer parts 10a and 10b extends along the connecting surface 12 between the edges K1 and K2 of the stage 9, a layer region 13 which has the function of the weak coupling typical of a Josephson element.
  • the layer parts 10a and 10b serving as electrodes must ensure a high current density in the direction of the layer planes E1 or E2.
  • the layer parts are textured such that the c-axes of the crystal structure of their superconductor material, in the direction of which the critical current density is at least 10 times smaller than in the direction of the planes E1 or E2, are perpendicular to the substrate surface 5. These axes are indicated in the figure by individual arrowed lines 14.
  • the layer area 13 is also textured in accordance with the two layer parts 10a and 10b.
  • the thickness d of each layer part 10a, 10b is correlated with the distance (step height H) between the levels E1 and E2.
  • the layer part 10a serving as the base electrode must have a thickness d which is below the step height H.
  • the difference H - d which is the perpendicular to the levels to be measured height h 1 of the layer area 13 and thus corresponds to the effective step height, are below 100 nm.
  • This value is one of the prerequisites for ensuring that the weak coupling required between the layer parts 10a and 10b serving as electrodes is to be ensured.
  • the maximum cross-sectional area q of the area 13 to be measured perpendicular to its height h 1 must also be dimensioned such that the "weak link" function typical of a Josephson element is achieved. In general, q is therefore below 10 ⁇ m 2 .
  • Corresponding dimensions of the layer area 13 can easily be achieved in a deposition process of the layer 10 on the stepped substrate 2. Because of the layer-like anisotropy in the superconductor material, a region of weak coupling can be formed between the layer parts 10a and 10b which serve as superconducting electrodes and which represents a "weak link". In this area with the specified dimensions, a current must then deflect in the unfavorable c-direction in order to pass from one electrode to the other.
  • the Josephson element thus produced still has to be contacted with connecting conductors 16 and 17, the required high critical current densities also having to be ensured in the contact area.
  • the substrate 2 with its floating mask 3 and the deposited Josephson element 15 is rotated in such a way that an angle of incidence or vapor deposition (-o () of a steam jet 11 'of the superconducting material of approximately 45 ° is obtained
  • Deposition conditions as for layer 10 can thus epitaxially grow a second layer 18 made of the superconductor material without interrupting the vacuum conditions, although the thickness D of this layer must be chosen greater than the step height H. In this way it is achieved that Level 8 area corresponds to the formation of an area with only weak coupling chend area 13 is avoided.
  • step 9 of the Josephson element 15 is achieved by structuring the substrate 2 accordingly to form a base 7 as a spacer.
  • An exemplary embodiment of this is indicated as a detail in FIG. 2, for which a representation corresponding to FIG. 1 has been selected. Process steps for the production of a Josephson element 19 according to the description of FIG. 1 are not to be explained in detail.
  • a layer 21 serving as a base electrode is first applied to a flat substrate 20 by oblique vapor deposition.
  • a further layer 22 is then deposited on this layer 21 by vertical vapor deposition outside the area shaded by the suspension bridge 3a with a thickness which corresponds to the height h 1 according to FIG.
  • insulating material which, with the vapor deposition technique chosen for the superconducting layer, also obtains a texture which is adapted to the crystal structure of the oxide-ceramic superconductor material
  • a suitable material being, for example, SrTiO or a PrBaCu oxide
  • Suspension bridge 3a thus forms a step 9 corresponding to Figure 1 of the insulating layer 22 serving as a spacer, and then a layer 23 serving as counterelectrode and made of the oxide-ceramic superconductor material is vapor-deposited onto the structure obtained in this way the material also extends beyond step 9.
  • ei is oC ⁇ oC.
  • a layer area 13 with a predetermined maximum cross-sectional area q can then be formed at step 9 in accordance with FIG.
  • This layer region 13 between the part of the layer 23 lying in a plane E1 and the layer 21 lying in a plane E1 thus provides the "weak link" function typical of the Josephson element according to the invention due to its predetermined dimensions and its anisotropic crystal structure for sure.
  • the thicknesses d of the layers 21 and 23 are hardly critical. Only the thickness d of the layer 23 must be significantly larger than the effective step height h 1 .
  • FIG. 3 schematically illustrates a cross section through a corresponding separating device, generally designated 25.
  • This separating device contains a vacuum chamber 26 which is to be evacuated to a final pressure on a pump nozzle 27 by means of a corresponding pump, which e.g. is below 10 mbar.
  • a quartz window 29 the quartz window 29
  • Vacuum chamber 26 a laser beam 30 enters the chamber and strikes a target 31 made of the desired high-T superconductor material at an angle ⁇ of, for example, approximately 45 ".
  • the target is fastened to a holder 32 in the center of the chamber, which can be rotated with the aid of a motor via a linkage 33.
  • the vaporized material is emitted perpendicularly to the target surface as a steam jet 11 from the target 31. It strikes a substrate 2 which is located opposite the target Floating 1 mask, but is not shown in Figure 3. It is attached to a substrate carrier 35 which is arranged at an incline such that an evaporation angle of approximately 45 ° with respect to the axis of the steam jet 11 results.
  • This substrate carrier 35 can be heated to a temperature of at least 800 ° C. It is held by a linkage 36, which enables a variation in the distance a between the target 31 and the substrate 2. For example, a distance a can be set between 20 mm and 45 mm.
  • the linkage is also designed to be rotatable in such a way that an evaporation angle ( ⁇ ml) with respect to the steam jet 11 can be set within the vacuum chamber 26.
  • any oxygen partial pressure p (0 2 ) can be regulated in the chamber via a gas inlet 37.
  • a pulsed laser with a wavelength of its radiation which is in the UV spectral range is advantageously provided.
  • the wavelength range of interest here extends from approximately 110 nm to 400 nm.
  • the laser must be able to produce an energy density on the material of the target 31 which is above 3 J / cm 2 .
  • the pulse energy of the laser should be at least 1.5 J / pulse.
  • Its repetition frequency can be, for example, 5 Hz.
  • focusing optics of which only a quartz lens 38 is illustrated in FIG. 2
  • an energy density of a maximum of approximately 7.5 J / cm 2 can be generated by such a laser on the target 26.
  • energy densities of 4 to 5 J / cm 2 are sufficient.
  • this evaporation process must be carried out the substrate 2 are kept at a temperature between 600 ⁇ C and 800 ° C, an oxygen atmosphere between 0.02 mbar and 1 mbar being set in the chamber.
  • An oxygen partial pressure p (0 2 ) between 0.05 mbar and 0.5 mbar has proven to be particularly favorable.
  • the structure obtained in this way is subjected to an additional oxygen treatment in order to carry out a fine adjustment (loading) of oxygen in the crystal structure of the superconducting layers.
  • the oxygen can be supplied as a gas or ion current.
  • This treatment can advantageously be carried out at relatively low temperatures, in particular below 600 ° C. If necessary, even temperatures close to room temperature can be provided.
  • the layers of the Josepshon element according to the invention are produced by means of an evaporation step using a laser, with the heat treatment and the oxygen treatment being carried out simultaneously to form the desired superconducting metal oxide phase.
  • Such a method can be regarded as particularly advantageous. If necessary, however, other methods can also be used which enable the layers to be produced in situ without the need for excessive heat treatments which lead to an undesired interaction of the materials provided for the mask with the selected superconductor material .

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Abstract

Un élément de Josephson à structure stratifiée comprend une couche à électrode de base, une couche à contre-électrode, une zone intermédiaire de faible couplage et un substrat texturé (2). Les couches à électrodes (10a, 10b) sont écartées par une pièce d'écartement texturée correspondante (socle 7) qui forme un échelonnement (9). Les couches à électrodes (10a, 10b) et la zone (13) de faible couplage sont composées d'un matériau supraconducteur à haut Tc en céramique oxydée et ayant la même structure cristalline ordonnée qui s'étend sur l'échelonnement (9). La zone (13) de faible couplage est adjacente à l'échelonnement (9) et ses dimensions (h') dans le sens perpendiculaire (E1, E2) des couches à électrodes (10a, 10b) sont inférieures à 100 nm. On peut fabriquer de manière particulièrement avantageuse un élément de Josephson ayant les caractéristiques décrites par précipitation sur un substrat au moyen d'un laser pulsé ayant une longueur d'onde du domaine UV, accompagnée d'un traitement thermique et d'un traitement à l'oxygène.
EP89907704A 1988-07-06 1989-07-03 Element de josephson a materiau supraconducteur en ceramique oxydee et son procede de fabrication Withdrawn EP0423178A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3822904 1988-07-06
DE3822904A DE3822904A1 (de) 1988-07-06 1988-07-06 Josephson-element mit oxidkeramischem supraleitermaterial und verfahren zur herstellung des elements

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EP0423178A1 true EP0423178A1 (fr) 1991-04-24

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