Classifications

• • 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
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
  • C23C16/45502—Flow conditions in reaction chamber
  • C23C16/45504—Laminar flow
• • 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
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
  • C23C16/40—Oxides
  • C23C16/408—Oxides of copper or solid solutions thereof
• • 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
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/448—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for generating reactive gas streams, e.g. by evaporation or sublimation of precursor materials
  • C23C16/4486—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for generating reactive gas streams, e.g. by evaporation or sublimation of precursor materials by producing an aerosol and subsequent evaporation of the droplets or particles
• • 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
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/56—After-treatment
• • 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
  • H10N60/0324—Processes for depositing or forming copper oxide superconductor layers from a solution

Definitions

• the present invention relates to a process for preparing thick layers of YBa 2 Cu 3 ⁇ 7 - y , as well as the thick layers obtained.
• YBa 2 Cu 3 0 7 - y (hereinafter referred to as YBCO) is an interesting compound for its properties of superconductor.
• the main quantities which characterize the superconductive state are the critical temperature (T c ), the critical current density (J c ) and the critical magnetic field (H c ).
• the process known as "ultrasonic pyrolysis spray" hereinafter referred to as the USP process is a known deposition technique for the synthesis of YBCO layers.
• the USP process consists of spraying a solution containing the precursors of the chemical elements to be deposited to form an aerosol, transporting the aerosol using a carrier gas at a temperature close to ambient temperature from its source to to a reaction zone where it comes into contact with the surface of a heated substrate on which it undergoes pyrolysis.
• the precursor solution can be sprayed using different techniques.
• the ultrasonic technique is preferred because it allows the droplet size to be controlled and relatively small droplets ( ⁇ 3 ⁇ m) to be produced, with a very homogeneous and narrow size distribution.
• the USP process known as "ex situ" is implemented with a substrate temperature below 500 ° C. It is therefore essential to subject the layer obtained to a subsequent heat treatment.
• the aerosol is sent to a substrate heated to a temperature between 800 ° C and 900 ° C, by 30 cycles of 30 sec each, because of the drop in temperature of the substrate.
• the three precursor nitrates were prepared by dissolving the corresponding oxides in nitric acid.
• Other precursor solutions were prepared with a respective overall concentration of 3,75.10 -3 M, 1.5x10 -3 M and 0,75.10 -3 M.
• the best properties were obtained for the concentration 1.5.10 ⁇ 3 M to give a good crystalline structure, a microstructure having a certain porosity, but nevertheless a good connectivity of the grains, and a T c of 85 K. a J c> April 10 A.c ⁇ f 2-77 K is mentioned in the abstract .
• JL MacManus-Driscoll, et al (“In-plane aligned YBCO thick films grown in situ by high temperature ultrasonic spray pyrolysis", Supercond. Sci. Technol. 14, (2001) 96-102) describe the deposition of YBCO on various substrates , especially LAO, Ag single crystal, MgO, Ag in textured polycrystalline sheet.
• the overall concentration of nitrates in the precursor solution was 1.10 "2 M, 7.5.10 ⁇ 3M, 3.75.10 ⁇ 3M, 1.5.10 ⁇ 3M and 0.75.10 ⁇ 3M.
• the authors of this article recommend using more dilute solutions to improve the T c and J c of the thick layers obtained, by increasing the duration of the treatment. Indeed, the objective is to form films having a thickness of a few microns. However, the size of the drops used in the USP technique is around ten ⁇ m.
• the inventors have found that, contrary to what was suggested by the prior art, it was possible to obtain layers having a thickness of a few microns having a roughness of less than ⁇ m and whose value of J c is substantially improved, using higher precursor concentrations than those recommended in the prior art when implementing a USP process. This is why the present invention relates to a process for the preparation of thick layers of YBa 2 Cu 3 ⁇ _ y (y ⁇ 0.08), as well as the layers obtained.
• the method according to the present invention consists in spraying an aqueous solution of precursors of the chemical elements to be deposited to form an aerosol, in transporting the aerosol using a carrier gas from its source to a reaction zone, where it comes into contact with the surface of a heated substrate on which it undergoes pyrolysis, followed by annealing, and it is characterized in that: a) the solution of precursors is a solution of yttrium nitrate, nitrate of barium and copper nitrate in which the total concentration of nitrates is substantially equal to the concentration at saturation, and the relative concentrations of the various precursors in the solution are such that 0.11 ⁇ FY ⁇ 0.28, 0.46 ⁇ FBa ⁇ 0.58, 0.2 ⁇ FCu ⁇ 0.37, FY, FBa and FCu being the respective atomic fractions of the cations, b) the precursor solution is sprayed for a period of 1 min to 5 min; c) the carrier gas is an inert gas whose
• FY denotes the atomic fraction N (Y) / [N (Y) + N (Ba) + N (Cu)]
• FBa represents the atomic fraction N (Ba) / [N (Y) + N (Ba) + N ( Cu)]
• FCu represents the atomic fraction N (Cu) / [N (Y) + N (Ba) + N (Cu)]
• N (Y) represents the number of moles of Y per unit volume or mass of Y
• N (Cu) represents the number of moles of Cu per unit volume or mass of Cu
• N (Ba) represents the number of moles of Ba per unit volume or mass of Ba.
• the preferred precursors are copper nitrate Cu (N0 3 ) 2 .nH 2 0 (n> 2.5), yttrium nitrate Y (N0 3 ) 3 .mH 2 0 (m> 4) and nitrate of barium Ba (N0 3 ) 2 .
• the substrate on which the layer of YBa 2 Cu 3 0 7 - there is deposited may be chosen especially from MgO, LAO (LaA10 3)
• STO SrTi0 3
• YSZ yttrium oxide
• the inert carrier gas used for transporting the aerosol can be chosen from argon and nitrogen.
• the implementation of the process of the invention makes it possible to obtain micrometric layers of YBa 2 Cu 3 0 7 - y , y ⁇ 0.08 (that is to say layers having a thickness of 1 ⁇ m to 10 ⁇ m) for which the value of J c at 77 K and in the residual magnetic field of the earth is greater than 10 6 A. cm -2 .
• the layers of YBCO which are obtained by the process of the invention are particularly suitable for the applications of superconductive materials relating to the transport of electric current and the uses in strong magnetic field.
• the materials used must be in the form of a layer having a thickness between 1 and several microns, have a high critical current density at least equal to 10 6 A / cm 2 , a temperature of use greater than 77 K , and great robustness.
• the materials obtained by the process of the invention meet these criteria and the low production cost makes them particularly attractive.
• the method can be implemented continuously, unlike other deposition methods using physical channels (laser ablation, magnetron, sputtering, MBE, etc.).
• the deposition of a layer of YBCO on a monocrystalline substrate (STO, MgO ...) is particularly advantageous for applications in the field of electronics. Metal substrates will be preferred for the preparation of cables.
• An apparatus comprising a cold-walled reactor with a vertical configuration, comprising a spraying zone, a transport zone and a pyrolysis zone.
• the spray area is the generating part of the aerosol. It consists of an enclosure containing a piezoelectric transducer placed in a transmitting medium and connected to an aerosol generator operating at a frequency close to 800 kHz and with a maximum ultrasonic power of 150 watts.
• the enclosure is surmounted by a container provided with a membrane intended to receive the solution to be sprayed.
• the membrane is a flexible membrane, which does not degrade on contact with the precursor solution and which transmits ultrasound with a minimum of damping. Teflon® membranes are particularly suitable for this use.
• Said container comprises an inlet for the carrier gas connected to a flow meter, and an outlet for the sprayed liquid.
• the aerosol transport area links the spray area to the deposition area. It can be constituted by a glass nozzle connected to the other parts by suitable seals, for example in Teflon ®.
• the deposition zone consists of an enclosure in which a support is placed for the substrate on which the deposition of YBCO will be carried out.
• the support is a metal plate provided with a heating means comprising a regulation device, making it possible to maintain the temperature sufficiently constant for the duration of the operation, between 800 ° C and 900 ° C.
• the operator adjusts the output voltage of the aerosol generator to vary the intensity of the nascent geyser on the surface of the liquid in the spray container. It is thus possible to modify the quantity of aerosol sprayed while keeping the flow rate of carrier gas constant.
• the aerosol is set in motion using the carrier gas introduced into the spray container, through the nozzle of the transport zone from the surface of the liquid to the pyrolysis zone.
• Oxygenation in situ Gas oxygen, 3 1 / min
• Each layer obtained was characterized by an inductive magnetic measurement in a magnetic field of less than 10 Oe.
• This magnetic measurement well known and conventional in the field, consists in measuring the alternative susceptibility of the sample as a function of the temperature.
• the phase part ⁇ ' is used to determine the critical temperature Te.
• Annealing is necessary to induce the crystallinity adequate for the appearance of the superconducting phase and for the organization of the grains necessary for the passage of the current.
• the critical temperature is measured at 89 K, and the corresponding critical current density does not exceed 10 5 A / cm 2 at 77 K.
• the T c has increased very slightly (2%) while the critical current density has been multiplied by 10 and now exceeds 10 6 A / cm 2 .
• the texture is characterized by grains in the form of platelets which can be placed flat on the surface of the substrate, designated by c ⁇ to recall that their crystallographic axes c are perpendicular to the substrate and grains placed on the wafer, designated by ai. It is known that the best properties are observed when all the grains are present.
• the texture analysis makes it possible to determine the volume fraction (aj_ / c ⁇ ) of the grains ai. It was carried out by the method described in the thesis of D. Chateigner (D. Chateigner, doctoral thesis of the University of Grenoble, 1994).
• the grains Ci have orientations in the plane of the substrate which are not arbitrary, as shown by the studies of ⁇ scan. The disorientation of one with respect to the other is deduced from the line width in this measurement mode.
• the grains cj_ also have disorientations compared to the normal to the substrate which one can appreciate by studying the profile of the lines (001) in tilting mode ⁇ (rocking curve). The measurement of the width of this profile gives the disorientation of the grains ci relative to the normal to the surface.
• the disorientation of the crystallites cj_ along the axis c is less than 0.5 ° and the grains are disoriented by less than 3 ° in the plane of the substrate.
• These remarkable quantities remain stable for one and two hours of treatment. It is these quantities which give the layer the high value of the critical current rarely observed for such layer thicknesses. Beyond 2 hours of annealing, the density of the critical current J c , then the T c decreases due to pollution by the substrate which occur all the more as the annealing temperature is higher and its duration longer. It is clear that the high value of J c , of the order of 10 6 A / cm 2, is only obtained for an annealing of 1 to 2 hours.
• the current profile induced in the layer (5 mm x 5 mm sample) was analyzed by mapping the induced field detected by a Hall microprobe displaced on the sample at a temperature of 77 K.
• the induced field is then translated into critical current term (according to Bean's law known to those skilled in the art) and the mapping represented by level lines every 0.5 A / cm 2 .
• the fact that these lines are continuous proves that the grains are very well connected.
• At the edge of the sample there are areas of lower current where the field penetrates.
• the core of the sample has a very high critical current zone exceeding 3 MA / cm 2 while in the weak zones, it remains greater than 1.1 MA / cm 2 .

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