WO1991011031A1

WO1991011031A1 - Processes for making thin films and circuit elements of high temperature superconductors

Info

Publication number: WO1991011031A1
Application number: PCT/US1990/007416
Authority: WO
Inventors: Graciela Beatriz Blanchet-Fincher; Curtis Robinson Fincher
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1990-01-16
Filing date: 1990-12-27
Publication date: 1991-07-25
Also published as: AU7222991A

Abstract

Processes are provided for making patterned or non-patterned film elements comprised of an oxide superconductor having the formula MBa2Cu3Ow wherein M is selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; w is from about 6.5 to about 7.0, preferably from about 6.8 to about 7.0. The process comprises forming on a suitable substrate a patterned or non-patterned film comprised of a mixture of nitrates or oxides of M, Ba and Cu, by spraying an aerosol formed from a solution of nitrates of M, Ba and Cu, heating the nitrate or oxide film in an oxygen-containing atmosphere and cooling appropriately.

Description

PROCESSES FOR MAKING THIN FILMS AND CIRCUIT ELEMENTS OF HIGH TEMPERATURE SUPERCONDUCTORS Field of the Invention

This invention relates to processes for making high temperature superconductor oxide thin films and patterning them for use as circuit elements. Background of the Invention Bednorz and Muller, Z. Phys . B64, 189 (1986), disclose a superconducting phase in the La-Ba-Cu-O system with a superconducting transition temperature of about 35 K. The existence of this phase was subsequently confirmed by a number of investigators. The superconducting phase has been identified as the composition Laι__x(Ba,Sr,Ca)_xCuθ₄-y with the tetragonal K2 iF₄~type structure and with x typically about 0.15 and y indicating oxygen vacancies. u et al., Phys. Rev. Lett. 58, 908 (1987), disclose a superconducting phase in the Y-3a-Cu-0 system with a superconducting transition temperature of about 90 X. The compounds disclosed were prepared with nominal compositions (Yι-_xBa_x)₂Cuθ₄-_y and x - 0.4 by a solid-state reaction of appropriate amounts of Y2O3, BaC0₃ and CuO in a manner similar to that described in Chu et al., Phys. Rev. Lett. 58, 405 (1987). The reaction comprises heating the oxides in a reduced oxygen atmosphere of 2xl0"⁵ bars (2 Pa) at 900°C for 6 hours. The reacted mixture is pulverized and the heating step is repeated. The thoroughly reacted mixture is then pressed into 3/16 inch (0.5 cm) diameter cylinders for final sintering at 925°C for 24 hours in the same reduced oxygen atmosphere. Cava et al., Phys. Rev. Lett. 58, 1676 (1987), identified the superconducting phase as orthorhombic, distorted. oxygen-deficient perovskite Ba2C 3θc>-δ where δ is about 2.1; they provide the powder X-ray diffraction pattern and lattice parameters .

Hundreds of other papers have since disclosed various properties of these materials.

SUMMARY OF THE INVENTION This invention provides a process for making a patterned or non-patterned film element comprised of an oxide superconductor having the formula Ba2Cu3θ_w wherein M is selected from the group consisting of Y, Nd, Sm,

Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; w is from about 6.5 to about 7.0, preferably from about 6.8 to about 7.0, said process comprising

(a) forming on a suitable substrate a patterned or non-patterned nitrate film comprised of- a mixture of nitrates of M, Ba and Cu by spraying onto said substrate an aerosol formed from a solution of nitrates of M, Ba and Cu, or a patterned or non- patterned oxide film comprised of a mixture of oxides of M, 3a and Cu, by spraying onto said substrate an aerosol formed from a solution of nitrates of M, Ba and Cu, and converting said nitrates to the corresponding oxides,

(b) heating the patterned or non-patterned nitrate or oxide film in an oxygen-containing atmosphere, to a temperature of about 900°C to about 1000°C and maintaining said temperature for about 1 minute to about 8 hours, and

(c) reducing the temperature to ambient temperature over a period of about 2 to about 12 hours in a flowing oxygen-containing atmosphere, preferably pure oxygen, to obtain the superconductor element on the substrate.

This invention also provides a process for making a patterned film element wherein the patterned nitrate film is formed by a process consisting essentially of (a) forming an aerosol from a solution of nitrates of M, Ba and Cu with an atomic ratio of M:Ba:Cu of x:y:z where 0.1 ≤ x < 0.2, 0.3 < y < 0.35 and 0.5 ≤ z < 0.55 and x + y + z =1, preferably, x = 0.13, y = 0.33, and z = 0.53, in a solvent, preferably water, and spraying this aerosol onto a substrate heated to a temperature above the boiling point of the solvent, preferably 20 or more Centigrade degrees above the boiling point of the solvent, but below the decomposition temperature of the nitrates, preferably more than 100 Centigrade degrees below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate film of thickness of about 1 to about 10 μ , (b) applying a photohardenable polymer film of thickness of about 0.5 μm to about 50 μ to the nitrate film,

(c) exposing the photohardenable polymer to radiation effective to harden the polymer to produce an exposed image portion and an unexposed portion of said polymer, the exposed image portion defining the desired pattern of oxide superconductor,

(d) contacting the polymer with a solvent to remove selectively the unexposed portion of the polymer, said unexposed portion defining regions where oxide superconductor is not wanted, thereby exposing the nitrate film in those regions,

(e) contacting the exposed nitrate film with a solvent to remove the exposed nitrate film, and (f) contacting the exposed image portion of said polymer with a solvent to remove the polymer in said exposed image portion, thereby providing the desired pattern of oxide superconductor nitrate film on the substrate. This invention also provides a process for making a patterned superconducting film element wherein a patterned nitrate film is formed by a process consisting essentially of (a) applying a photohardenable polymer film of thickness of about 0.1 μm to about 25 μm to a substrate,

(b) exposing the photohardenable polymer to radiation effective to harden the polymer to produce an exposed portion and an unexposed image portion of said polymer, the unexposed portion of said polymer defining the desired pattern of oxide superconductor, c) contacting the polymer with a solvent to remove selectively from the substrate the unexposed image portion of said polymer, (d) forming an aerosol^' from a solution of nitrates of M, Ba and Cu with an atomic ratio of M:Ba:Cu of x:y:z where 0.1 < x < 0.2, 0.3 ≤ y ≤ 0.35 and 0.5 < z < 0.55 and x + y + z =1, preferably, x = 0.13, y = 0.33, and z = 0.53, in a solvent, preferably water, and spraying this aerosol onto the substrate containing the exposed portion of the polymer produced in step (c), said substrate heated to a temperature above the boiling point of the solvent, preferably 20 or more Centigrade degrees above the boiling point of the solvent, but below the decomposition temperature of the nitrates, preferably more than 100 Centigrade degrees below the decomposition temperature of the nitrates, thereby producing a homogeneous, fine-grained nitrate film of thickness of about 0.5 to about 5 μm, (e) stripping from the substrate the exposed portion of said polymer and the nitrate film deposited thereon by contacting the exposed portion with a solvent for the polymer, thereby providing the patterned nitrate film on the substrate. This invention also provides a process for making a superconducting non-patterned film element, i.e., a film of essentially uniform thickness, wherein the non- patterned oxide film is formed by a multiple deposition process consisting essentially of

(a) forming a solution of nitrates of M, Ba and Cu with an atomic ratio of M:Ba:Cu of x:y:z where 0.1 < x ≤ 0.2, 0.3 < y < 0.35 and 0.5 < z ≤ 0.55 and x + y + z =1, preferably, x = 0.13, y = 0.33, and z = 0.53, in a solvent, preferably water, and spraying an aerosol of the solution onto a substrate heated to a temperature above the boiling point of the solvent, preferably 20 or more Centigrade degrees above the boiling point of the solvent, but below the decomposition temperature of the nitrates, preferably more than 100 Centigrade degrees below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate layer of thickness of about 1 to about 10 μ ,

(b) heating the nitrate layer to a temperature of from about 500°C to about 750°C in an oxygen or inert gas atmosphere and maintaining said temperature for about 5 to about 45 minutes to produce a first homogeneous, fine-grained oxide layer of M, Ba and Cu oxides of thickness of about 0.1 to about 0.5 μm, (c) spraying an aerosol of the solution used in step (a) onto the first oxide layer on the substrate heated to a temperature above the boiling point of the solvent, preferably 20 or more Centigrade degrees above the boiling point of the solvent, but below the decomposition temperature of the nitrates, preferably more than 100 Centigrade degrees below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate layer of thickness of about 1 to about 10 μm on the oxide layer, (d) heating the nitrate layer to a temperature of from about 500°C to about 750°C in an oxygen or inert gas atmosphere and maintaining said temperature for about 5 to about 45 minutes to produce a second homogeneous, fine-grained oxide layer of M, Ba and Cu oxides, and

(e) repeating steps (c) and (d) 1-7 times to produce a homogeneous, fine-grained film of M, Ba and Cu oxides . The above thicknesses of nitrate film depositions and the number of such depositions were chosen to provide a practical process with conventional equipment. It is believed that if even thinner layers of nitrate films were deposited in steps (a) and (c) , superconducting films with better properties would result. For example, layers of a few Angstroms (a few tenths of a nm) could be deposited. Depositions of such thicknesses will require 1000 repetitions of steps (c) and (d) to produce final films of appropriate thickness. Automatic equipment designed to carry out these steps in a reasonable time is needed to make such processes practical.

This invention also provides a process for making a non-patterned superconducting film element, i.e., a film of essentially uniform thickness, wherein a non- patterned oxide film is formed by a process comprising forming a solution of nitrates of M, Ba and Cu with an atomic ratio of M:Ba:Cu of x:y:z, where 0.15<x<0.2, 0.55<y<0.65 and 0.20<z<0.30 and x+y+z - 1, preferably, x=0.18, y=0.60 and z=0.22, in a solvent, preferably water, and spraying an aerosol of the solution onto a substrate heated to a temperature above the decomposition temperature of the nitrates thereby forming a homogeneous, fine-grained oxide film of thickness of about 0.1 to about 4 μm. This invention also provides a process for making a patterned film element by a process consisting essentially of

(a) forming a non-patterned film element, i.e., a superconducting oxide film of essentially uniform thickness, by either of the two processes described immediately above,

(b) applying a photohardenable polymer film of thickness of about 0.5 μm to about 50 μm to the non- patterned film element,

(d) contacting the polymer with a solvent to remove selectively from the substrate the unexposed portion of the polymer, said unexposed portion corresponding to those regions where oxide superconductor is not wanted, thereby exposing the oxide film in said unexposed portion,

(e) contacting the exposed oxide film with a solvent to remove the exposed oxide film, and

(f) contacting the polymer in the unexposed portion with a solvent to remove the polymer and thereby provide the patterned film on the substrate.

Preferred are the processes using an oxide film and especially preferred are processes using an oxide film prepared by multiple deposition. This invention also provides a similar process for making a patterned or non-patterned film element comprised of superconductors of Bi-Sr-Ca-Cu oxide. For example, this invention provides a process for making a non-patterned film element comprised of an oxide superconductor having the formula Bi2Sr2CaCu2θ8, said process comprising

(a) forming a solution of nitrates of bismuth, strontium, calcium and copper with an atomic ratio of Bi:Sr:Ca:Cu of w:x:y:z where 0.15 ≤ w < 0.25, 0.15 < x < 0.25, 0.15 < y < 0.35 and 0.20 < z < 0.40, preferably w = 0.18, x = 0.18, y = 0.27 and z = 0.36, in a solvent, preferably water, and spraying an aerosol of the solution onto a substrate heated to a temperature above the boiling point of the solvent, preferably 20 or more Centigrade degrees above the boiling point of the solvent, but below the decomposition temperature of the nitrates, preferably more than a 100 Centigrade degrees below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate layer of thickness about 1 to about 10 μm,

(b) heating the nitrate layer to a temperature of from about 500"C to about 750^*C in an oxygen or inert gas atmosphere and maintaining said temperature for about 5 to about 45 minutes to produce a first homogeneous, fine-grained oxide layer of Bi, Sr, Ca and Cu oxides of thickness about 0.1 to about 0.5 μm,

(c) spraying an aerosol of the solution used in step (a) onto the first oxide layer on the substrate heated to a temperature above the boiling point of the solvent, preferably 20 or more Centigrade degrees above the boiling point of the solvent, but below the decomposition temperature of the nitrates, preferably more than a 100 Centigrade degrees below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate layer of thickness about 1 to about 10 μm on the oxide layer,

(d) heating the nitrate layer to a temperature of from about 500^*C to about 750"C in an oxygen or inert gas atmosphere and maintaining said temperature for about 5 to about 45 minutes to produce a second homogeneous, fine-grained oxide layer of Bi, Sr, Ca and Cu oxides of thickness about 0.1 to about 0.5 μm,

(e) repeating steps (c) and (d) 1-7 times to produce a homogeneous, fine-grained oxide layer of Bi,

Sr, Ca and Cu oxides,

(f) heating the oxide film in an inert gas, preferably argon, atmosphere, to a temperature of about 850^*C to about 900^*C and maintaining said temperature for about 1 minute to about 8 hours, and

(g) cooling to ambient temperature to obtain the superconductor element on the substrate.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 is a plot of the X-ray diffraction results, intensity versus 2θ, obtained for- a non-patterned

YBa2Cu3θ_x film.

Fig. 2 is a plot of resistance versus temperature for a non-patterned YBa2Cu3θ_w film.

Fig. 3 is a plot of resistance versus temperature along a 20 mil (0.50 mm) wide YBa2Cu3θ_w line.

Fig. 4 is a plot of resistance versus temperature for a non-patterned Y3a2Cu3θ_w film.

Fig. 5 is a plot of critical current density as function of temperature for a non-patterned YBa2Cu3θ_w film.

Fig. 6 is a plot of the X-ray diffraction results, intensity versus 2θ, obtained for a non-patterned

YBa2Cu3θ_w film.

Fig. 7 is a plot of the X-ray diffraction results, intensity versus 2θ, obtained for non-patterned YBa2Cu3θ_w films made by depositing 1, 6 and 8 layers of nitrates.

Fig. 8 is a plot of critical current density and T_c for a non-patterned 3a2Cu3θ_w film as a function of the number of layers, i.e., depositions, of nitrates used in making the film. Fig. 9 is a plot of resistance versus temperature for a non-patterned YBa₂Cu₃θ_w film made by using two layers of nitrates.

Fig. 10 is a plot of resistance versus temperature for a non-patterned Ba₂Cu₃θ_w film.

Fig. 11 is a plot of the X-ray diffraction results, intensity versus 2θ, obtained for a non-patterned

Bi2Sr2CaCu2θ8 film.

Fig. 12 is a plot of resistance versus temperature obtained for a non-patterned Bi2Sr2CaCu2θ8 film. DETAILED DESCRIPTION OF THE INVENTION This invention provides a process for making a patterned or non-patterned film circuit element comprised of an oxide superconductor having the formula B ₂Cu₃θ_w for use as a circuit connection, as the element of a circuit device such as a Josephson junction or as a thin superconducting film.

The process of this invention comprises forming a patterned or non-patterned film, comprised of a mixture of nitrates of M, Ba, and Cu or a mixture of oxides of M, 3a, and Cu, on a suitable substrate by spraying an aerosol formed from a solution of nitrates of M, Ba and Cu, and then heating and cooling this film appropriately to obtain the superconductor. If a patterned element is to be produced, the film of nitrates or oxides has the pattern desired for the superconductor.

The nitrate solution used in making the patterned nitrate film contains nitrates of M, Ba and Cu in a solvent, preferably water. The nitrate solution can be prepared by starting with the appropriate nitrate salts. Alternatively, an aqueous nitrate solution can be prepared by reacting oxides or hydroxides of M, Ba, and Cu with sufficient concentrated nitric acid to convert the metals present to metal nitrates. Excess nitric acid can be used to speed the process. ,The aerosol can be formed from a solution of nitrates using a compressed gas such as N₂ or O2 as the carrier and sprayed onto a suitable substrate to produce a uniform fine-grained film of the nitrates or of the oxides. With a standard aerosol nozzle, typical parameters for the deposition are 10 liters per minute of the carrier gas mixed with 1 ml per minute of the nitrate solution. Typically concentration of the nitrate solution is from about 0.5 wt% to about 10 wt%. For convenience, all of the experiments described in the Examples were carried out by distributing the aerosol over an area of approximately 100 cm². With this area and the deposition conditions used, a nitrate film approximately 10 to 50 μm was expected. In practice, the film was found to be thinner by a factor of about 1-5, i.e., the film thickness was about 1/5 to about 1 times the thickness expected. The film thickness is reduced further during heating, and the thickness of the film of the final superconductor oxide element is thinner than the nitrate film by a factor of 6-7. These reductions in thickness must be allowed for and a correspondingly thicker film deposited in order to obtain the proper thickness for the element. Generally, as the ratio of the gas to liquid is raised by decreasing the liquid flow rate or by increasing the gas velocity at the nozzle, a finer aerosol is formed and a superior element results. The aerosol can also be formed using ultrasonic nebulization. This method allows even tighter control of the droplet size distribution and hence more control over the deposition. A suitable substrate is one which is compatible with the formation of the oxide superconductor. Preferred substrates are MgO, SrTiθ₃, YSZ (yttria- stabilized zirconia) LaAlθ₃ and LaGaθ₃- To form a nitrate film on the substrate or on a substrate containing a patterned polymer film, the substrate is heated during the spraying to a temperature above the boiling point of the solvent, preferably more than 20 Centigrade degrees above the boiling point, but below the decomposition temperature of the nitrates, preferably more than 100 Centigrade degrees below the decomposition temperature. In the case of an aqueous solution, the_.typical temperature used is from about 120°C to about 180°C. When deposition is onto a substrate containing a patterned polymer film, lower temperatures, i.e., nearer to 120°C, are preferred in order to minimize any degradation of the polymer. When deposition is onto a substrate containing no polymer film, higher temperatures can be used. To directly form an oxide film on the substrate, the substrate is heated during the spraying to a temperature above the decomposition temperature of the nitrates. The decomposition of the nitrates and the nature of the films are affected by the carrier gas. Decomposition of 3a(Nθ₃)₂ occurs at about 600°C in O₂ and N2. The use of O₂ as a carrier gas results in an appreciable amount of oxygen being incorporated into the oxide film. The incorporation of the oxygen lowers the preferred subsequent heating temperatures thereby lessening the degree of interaction with the substrate during the heating. However, the higher decomposition temperature results in more interaction during the deposition step.

When a patterned nitrate or oxide is desired a photohardenable polymer is used. In one embodiment, a photohardenable polymer film is deposited onto the nitrate or oxide film. The thickness of the photohardenable polymer film is from about 1 μm to about 20 μm. The photohardenable polymer is then exposed imagewise to radiation effective to harden the polymer. If the photohardenable polymer used is a negative resist type, the exposed (hardened) polymer is the desired pattern of oxide superconductor. The polymer is then contacted with a solvent to selectively remove those portions of the polymer film that have not been exposed to the radiation and thereby expose the nitrate or oxide film in those regions where oxide superconductor is not wanted. The exposed nitrate or oxide film is then removed with a solvent. In contrast, if the photohardenable polymer used is a positive resist type, the unexposed polymer is the desired pattern of oxide superconductor. The polymer is then contacted with a solvent to selectively remove those portions of the polymer film that have been exposed to the radiation and thereby expose the nitrate or oxide film in those regions where oxide superconductor is not wanted. The exposed nitrate or oxide film is then removed with a solvent.

High quality, high resolution (5 μm wide lines) have been obtained by using a positive resist obtained from American Hoescht Corporation, AZ5214-E, a propylene glycol monomethyl ether acetate cresol novolak resin. Another positive resist used is KTI 820 (KTI chemicals incorporated) . Both these resists are developed in basic solutions. In general, two baths of either sodium or potassium hydroxide (1 part in 80 parts of H₂O) were used. The resist is developed 2 minutes in the first bath, 1 minute in the second bath and rinsed in water.

In a second embodiment of the invention, a photohardenable polymer film is deposited directly onto a suitable substrate, chosen as described above. The thickness of the photohardenable polymer film is from about 0.5 μm to about 10 μm. The photohardenable polymer is then exposed imagewise to radiation effective to harden the polymer with the exposed image being the negative of the desired pattern of oxide superconductor. The polymer is then contacted with a solvent to selectively remove those portions of the polymer that have not been exposed to radiation to thereby expose the substrate in those regions where oxide superconductor is wanted.

An aerosol is formed from the solution of nitrates as described above and sprayed onto the substrate containing the hardened polymer. During spraying, the substrate is heated to a temperature above the boiling point of the solvent, preferably more than 20 Centigrade degrees above the boiling point, but below the decomposition temperature of the nitrates, preferably more than 100 Centigrade degrees below the decomposition temperature. The remaining polymer and that portion of the nitrate film on this polymer are then removed using a stripping solvent which causes the polymer to-swell and delaminate from the substrate. The swelling and delamination cause the nitrate film to fracture along the boundaries of the polymer. As the polymer floats and/or dissolves away from the substrate the nitrate film above it is also removed. The result is the patterned nitrate film on the substrate.

Besides the monomer itself, the "photohardenable polymer" can be comprised of a binder, a photoinitiator, a chain transfer agent and additional components in addition to the monomer, and these are understood to be possible components when the term photohardenable polymer is used. Examples of the kinds of materials that can be used follow. The photohardenable film is comprised of a binder such as: pol (styrene/methyl methacrylate) , poly methyl methacrylate, poly(phenyl methacrylate), poly(t-butyl- met acrylate) , poly(isobornylmethacrylate) , polystyrene, poly(vinyl chloride), poly(vinylidene chloride), poly(isopropylmethacrylate) , polyvinyl acetatal. poly(vinylformal) , poly(ethylmethacrylate) , poly- (isobutyl ethacrylate) methyl methacrylate copolymers, poly-(n-butyl methacrylate), poly(n-butyl/isobutyl methacrylate) , polycyclohexyl methacrylate) , poly t-butyl acrylate), poly(vinyl acetate), polyurethane, and poly(tetramethylene terephthalate) among others.

Preferred monomers which have at least two terminally ethylenically unsaturated groups are di-, tri-, and tetra-acrylates and methacrylates such as ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, glycerol diacrylate, glycerol triacrylate, glycerol propoxylated triacrylate, ethylene glycol dimethacrylate, 1,2- propanediol dimethacrylate, 1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate, 1,4- benzenediol dimethacrylate, pentaerythritcl triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, 1,3-propanediol diacrylate, 1,5- pentanediol dimethacrylate, trimethylopropane triacrylate, ethoxylated trimethyloropane triacrylate, the bisacrylates and bismethacrylates of polyethylene glycols of molecular weight 100-500, tris-(2- hydroxyethyl)isocyanurate triacrylate, etc. Especially preferred monomers are glyceryl propoxylated triacrylate, trimethylol propane triacrylate and tris- (2-ydroxyethyl)isocyanaurate triacrylate. Isocyanurate triacrylate and trimethylolppane triacrylate show good temperature stability. Initiators and/or Initiator Systems A large number of free-radical generating compounds can be utilized in the photopolymerizable compositions. Preferred initiator systems are 2, 4,5-triphenyl- imidazolyl dimers with hydrogen donors, also known as the 2,2 ', 4, 4 ',5, 5'-hexaaryl-biimidazoles (HABI's), and mixtures thereof, which dissociate on exposure to actinic radiation to form the corresponding triarylimidazolyl free radicals. HABI's and use of HABI-initiated photopolymerizable systems for applications other than for electrostatic uses have been previously disclosed in a number of patents. These include Chambers, U.S. Patent 3,479,185, Chang et al., U.S. Patent 3,549,367, Bau and Henry, U.S. Patent 3,652,275, Cescon, U.S. Patent 3,784,557, Dueber, U.S. Patent 4,162,162, Dessauer, U.S. Patent 4,252,887, Chambers et al., U.S. Patent 4,264,708, Wada et al.,

U.S. 4,410,621, and Tanaka et al., U.S. 4,459,349, the disclosures of which are incorporated herein by reference. Useful 2,4,5-triarylimidazolyl dimers are disclosed in Baum and Henry, U.S. Patent 3,652,275^' column 5, line 44 to column 7, line 16, the disclosure of which is incorporated herein by reference. Any 2-o_- substituted HABI disclosed in the prior patents can be used in this invention.

The HABI's can be represented by the general formula

where the R's represent aryl, e.g., phenyl, naphthyl, radicals. The 2-£-substituted HABI's are those in which the aryl radicals at the 2- and 2'-positions are ortho- substituted or with polycyclic condensed aryl radicals. The other positions on the aryl radicals can be unsubstituted or carry any substituent which does not interfere with the dissociation of the HABI UDOΠ exposure or adversely affect the electrical or other characteristics of the photopolymer system.

Preferred HABI's are 2-a-chlorosubstituted hexaphenylbiimidazoles in which the other positions on the phenyl radicals are unsubstituted or substituted with chloro, methyl or methoxy. The most preferred initiators include 2-(.a-chlorophenyl)-4,5-bis (m- methoxyphenyl) imidazole dimer, 1, 1'-biimidazole, 2,2'- bis(£-chlorophenyl)-4,4',5,5'-tetraphenyl-, and 1H- imidazole, 2,5-bis (o.-chlorophenyl)-4-[3,4-dimethoxy- phenyl]-, dimer, each of which is typically used with hydrogen donor or chain transfer agent described below.

Photoinitiators that are also useful in the photohardenable composition in place of the HABI type photoinitiators include: the substituted or unsubstituted polynuclear quinones, aromatic ketones, and benzoin ethers. Examples of such other photoinitiators are quinones such as 9,10-anthraquinone, 1-chloroanthraquinone, 2-ethylanthraquinone, 2-tert- butylanthraquinone, octamethylanthraquinone, 1,4- naphthoquinone, 9-10-ρhenanthrenequinone, 1,2- benzanthraquinone, 2,3-benzanthraquinone, 2-methyl-l,4- naphthoquinone, 2,3-dichloronaphthoquinone, 1,4- dimethylanthraquinone, 2,3-dimethylanthraquinone, 2- phenylanthraquinone, 2,3-diphenylanthraquinone, sodium salt of anthraquinone alpha-sulfonic acid, 3-chloro-2- methylanthraquinone, retenequinone, 7,8,9,10- tetrahydronaphthacenequinone, 1,2,3,4- tetrahydrobenz(a)anthracene-7-12-dione; aromatic ketones, for example, benzophenone, Michler's ketone (4, '-bis (dimethylamino)benzophenone) , 4,4'- bis (diethylamino)benzophenone, 4-acryloxy-4'- diethylaminobenzophenone, 4-methoxy- '- dimethylaminobenzophenone, xantones, thioxanthones; and benzoin ethers, for example, benzoin methyl and ethyl ethers. Still other photoinitiators which are also useful, are described in U.S. Patent 2,760,863 and include vicinal ketaldonyl alcohols, such as benzoin, pivaloin, acyloin ethers, alpha-hydrocarbon-substituted aromatic acyloins, including alpha-methylbenzoin, alpha- allylbenzoin and alpha-phenylbenzoi . Additional systems include alpha-diketones with amines as disclosed in Chang, U.S. Patent 3,756,827, and benzophenone with p-dimethylaminobenzaldehyde or with esters of p- dimethylaminobenzoic acid as disclosed in Barzynski et al., U.S. Patent 4,113,593.

Redox systems, especially those involving dyes, e.g., Rose Bengal 2-dibutylaminoethanol, are also useful in the practice of this invention. Photoreducible dyes and reducing agents such as those disclosed in U.S. Patents 2,850,445; 2,875,047; 3,097,096; 3,074,974; 3.097,097; 3,145,104; and 3,579,339; as well as dyes of the phenanzine, oxazine and quinone classes can be used to initiate polymerization, the disclosures of which are incorporated herein by reference. A useful discussion of dye sensitized photopolymerization can be found in "Dye Sensitized Photopolymerization" by D. F. Eaton in Adv. in Photochemistry, Vol. 13, D. H. Volman, G. S. Hammond, and K. Gollinick, eds., Wiley-Interscience, New York, 1986, pp. 427-487.

Chain Transf r ftgents

Any chain transfer agent, or hydrogen donor, identified in the prior patents for use with HABI- initiated photopolymerizable systems can be used. For example, Baum and Henry, U.S. Patent 3,652,275 discloses N-phenylglycine, 1,l-dimethyl-3,5-diketocyclohexane, and organic thiols such as 2-mercaptobenzothiazole, 2- mercaptobenzoxazole, 2-mercaptobenzimidazole, pentaerythritol tetrakis (mercaptoacetate) , 4- acεtamidothiophenol, mercaptosuccinic acid, dodecanethiol, and beta- ercaptoethanol, the disclosure of which is incoporated by reference. Also useful are various tertiary amines known in the art, e.g., 2- mercaptoethane sulfonic acid, l-phenyl-4H-tetrazole-5- thiol, 6-mercaptopurine monohydrate, bis-(5-mercapto- 1,3,4-thiodiazol-2-yl, 2-mercapto-5-nitro-benzimidazole, and 2-mercapto-4-sulfo-6-chlorobenzoxazole. Other hydrogen donor compounds useful as chain transfer agents in photopolymer compositions include various other types of compounds, e.g., (a) ethers, (b) esters, (c) alcohols, (d) compounds containing allylic or benzylic hydrogen, e.g., cumene, (e) acetals, (f) aldehydes, and (g) amides, as disclosed in column 12, lines 18 to 58, of MacLachlan, U.S. Patent 3,390,996, the disclosure of which is incorporated herein by reference. The preferred chain transfer agents are 2- mercaptobenzoxazole (2-MBO) and 2-mercaptobenzthiazole (2-MBT) . Additional Components The photohardenable compositions may also contain other ingredients which are conventional components used in photopolymerizable systems. Such components include thermal stabilizers or thermal polymerization inhibitors, antihalation agents, optical brightening agents, release agents, colorants, surfactants, and plasticizers.

Normally a thermal polymerization inhibitor will be present in small quantities, to increase stability in the storage of the photopolymerizable composition. Useful thermal polymerization inhibitors or thermal stabilizers include: hydroquinone, phenidone, 2-methoxyphenol, alkyl and aryl-substituted hydroquinones and quinones, tert-buty catechol, pyrogallol, copper resinate, naphthylamines, beta- naphthol, cuprous chloride, 2,6-di-tert-butyl o-cresol. phenothiazine, pyridine, nitrobenzene, dinitrobenzene, E-toluquinone and chloranil. The dinitroso dimers described in Pazos, U.S. Patent 4,168,982 are also useful, the disclosure of which is incorporated herein. The preferred stabilizer is TAOBN, i.e., 1,4,4- trimethyl-2,3-diazobicyclo-(3.2.2)-non-2-ene-N,N- dioxide. Proportions

In general, the components of the photohardenable polymer should be used in the following approximate proportions: binder 40-70%, preferably 50-65%; monomer - 20-40%, preferably 20-35%, initiator 1-20%, preferably 1-5%, and chain transfer agent or hydrogen donor 0-10%, preferably 0.1-4%. These are weight percentages based on total weight of the photopolymerizable system.

It was found that formulations with high levels of initiators and inhibitors were the most suitable for a "lift-off" process, i.e., the removal of a portion of the polymer film such that the cross section of a line of resist left on the substrate has a width at the resist surface larger than its width at the substrate interface. That is, there is overhanging and the resist exhibits a mushroom shaped cross section. The overhang was achieved by using high levels of initiators and inhibitors. The solubility of the exposed material across the thickness of the resist was modulated by confining the penetration depth of the light to the resist surface layer with the high levels of initiator and the additional inhibitor. The polymerization profile of the resist cross section therefore varied across the resist thickness with a higher degree of polymerization (and therefore less solubility in a solvent such as trichloroethane) at the resist surface than at the interface with the substrate. As a result, the cross section of the developed resist was either in the shape of a trapeziod with the side of the trapezoid at the resist surface or in the shape of a mushroom. By using "lift-off" resists, patterns of nitrates lines with 1-2 mil resolution were achieved. The formulation of the preferred lift-off resist is: wt % Trimethylolpropane triacrylate (TMPTA) 15 Ethoxylated trimethylolpropane triacrylate (TMPEOTA) 15

Polymethyl methacrylate (PMMA) 58.65 Brilliant Green 0.05

2-mercaptobenzoxazole (2-MBO) 1- 2,2', ,4'-tetrakis(o-chloropheny)-

5,5'-bis (m,p-dimethoxyphenyl) Bii idazole (TCTM-HABI) 10

Phenidone 0.1

1-(2 '-nitro-4',5'-dimethoxy)phenyl- 1-(4-tbutylphenoxy)ethane

(TLA-454) 0.2

The formulations were coated with 22.2% solids. The solvent comprised 66.6% of methylene chloride and 11.1% of methanol. The solution was spin coated at 2000 RPM for 30 seconds on a MgO substrate. The resist was exposed using a Nu-Arc source for 15 seconds to a pattern, e. g., a 2 mil (0.05 mm) lines/2 mil (0.05 mm) spacing pattern. Afterwards, the pattern was developed in tri-chloroethane (TCE) . It was found that 45 seconds in a first bath of TCE followed by 15 seconds in a second TCE bath were sufficient to dissolve the unexposed regions and provide resist free channels for the nitrate deposition. The developed resist is then post baked for 45 seconds at 110°C on a hot plate. The nitrate is sprayed on the pattern resist as described above.

The lower limit for lateral dimensions of patterned elements roughly corresponds to the thickness of the first layer of material on the substrate, either the film comprised of a mixture of nitrates or oxides or the film of photohardenable polymer. When the polymer is applied directly to the substrate, layers where 7-12 microns thick have been used, and patterned features as small as 10 μm were produced. In order to produce higher quality material, as judged by the superconducting properties, it may be necessary to use a thicker layer of nitrates or oxides in which case the polymer must also be thicker, thereby resulting in a loss of resolution. When patterning the nitrate or oxide film by the mask and etch method, the resolution is determined by the thickness of the nitrate or oxide layer. In general, to produce a film of about 1-2 μ , a nitrate film of about 5-15 μm is used. As a result the patterns produced have had somewhat larger features than those of the other method.

The concentrations of solids in the solutions described in the Examples are given in weight %.

EXAMPLES OF THE INVENTION EXAMPLE 1

An aqueous solution of the nitrates of yttrium, barium and copper in 1.00% , 1.11% and 0.98% respectively was prepared with an atomic ratio of Y:5a:Cu of 0.13:0.33:0.53. An aerosol was formed from this solution using an air brush and was deposited on a substrate consisting essentially of a polished MgO single crystal cleaved to provide a (100) surface. The substrate was held at a temperatue of 130°C during the deposition of the nitrate film. The solution was delivered in three 20 ml aliquots. Following each of the three depositions, the film and substrate were subjected to a temperature of 700°C in an argon atmosphere for 5 minutes, thereby pyrolizing the nitrates to their respective oxides. After completion of these three depositions and heatings, the film was placed in a furnace at 960°C with pure oxygen flowing at 4 L/min through the volume of the furnace. The film was held at this temperature for 2 hours and then allowed to cool at 70°C/min in flowing oxygen to ambient temperature, about 20°C.

Upon removal from the furnace the film was characterized by X-ray analysis. The data shown in Figure 1 indicates highly textured 1-2-3 material with c-axis ordering as indicated by the presence of the (0,0,1) peaks. The results obtained from measurements of the resistance as a function of temperature are displayed in Figure 2 and show that the film is superconducting with zero resistance at about 82 K.

EXAMPLE 2 The photohardenable polymer used in this example had the following formulation: t %

Trimethylolpropane triacrylate (TMPTA) 15 Ethoxylated trimethylolpropane triacrylate (TMPEOTA) 15

Polymethyl methacrylate (PMMA) 58.65 Brilliant Green 0.05

2-mercaptobenzoxazole (2-MBO) 1 2,2' ,4,4 '-tetrakis (o-chloropheny) -

5,5 '-bis (m,p-dimethoxyphenyl)

Biimidazole (TCTM-HABI) 10

Phenidone 0.1 1-(2 '-nitro-4 *,5 '-dimethoxy)phenyl- 1-( -tbutylphenoxy)ethane (TLA-454) 0.^'2

The formulations were coated with 22.2% solids. The solvent comprised 66.6% of methylene chloride and 11.1% of methanol.

A 10 μ layer of this photohardenable polymer was spincoated onto a MgO single crystal substrate at 2000 RPM for 30 seconds. The resist was exposed using a Nu-Arc source TF-40APRNS (Nu-Arc, Chicago, 111.), a tungsten hologen lamp with the appropriate ultraviolet emission spectrum, for 15 seconds to a 30 mil (0.75. mm) lines - 30 mil (0.75 mm) spacing pattern. Afterwards, the pattern was developed in tri-chloroethane (TCE) . It was found that 45 seconds in a first bath of TCE followed by 15 seconds in a second TCE bath were sufficient to dissolve the unexposed regions and provide resist free channels for the nitrate deposition. The developed resist was then baked for 45 seconds at 110°C on a hot plate.

An 2% aqueous solution of the nitrates of yttrium, barium and copper was prepared with an atomic ratio of Y:Ba:Cu of 0.17:0.33:0.50. An aerosol was formed from this solution using an air brush and was deposited onto the patterned polymer film and the exposed substrate. The substrate was heated to 120°C during the deposition. A single aliquot of 30 ml of the solution was used. After deposition of the nitrate film the piece was placed into a rinse of methylene chloride. This is a very good solvent for the polymer, but is inert with respect to the nitrate film. This solvent causes a rapid swelling of the patterned polymer film and results in the removal of the patterned polymer film from the substrate. The swelling fractures the nitrate film along the boundary of the patterned polymer film. Therefore, as the patterned polymer film lifts off the surface of the substrate, the polymer takes with it the portion of the nitrate film that had been deposited onto the polymer and leaves a patterned nitrate film of lines 30 mil (0.75 mm) wide separated by 30 mil (0.75 mm) spaces. This patterned film was then heated at 950°C for 30 minutes in flowing oxygen. The film was then allowed to cool to ambient temperature over a period of approximately 4 hours.

The results obtained from measurements of the resistance as a function of temperature for a 30 mil (0.75 mm) line .of the superconductor show that the film is superconducting with an onset of superconductivity at about 60 K.

EXAMPLE 3 A 2% aqueous solution of the nitrates of yttrium, barium and copper was prepared with an atomic ratio of Y:Ba:Cu of 0.17:0.33:0.50. An aerosol was formed from this solution using an air brush and was deposited on a substrate consisting essentially of a MgO single crystal cleaved to provide a (100) surface. The substrate was held at a temperature of 130°C during the deposition of the nitrate film. The solution was delivered in one 50 ml aliquot. A 25 μ layer of Riston®, a photopolymer dry film resist, was laminated onto the nitrate film by pressure at a temperature of about 100°C. This photohardenable layer was then imagewise exposed to actinide radiation using a 20 mil (0.50mm) line - 20 mil (0.50mm) spacing pattern. The unexposed areas were selectively removed by rinsing the sample in trichloroethane, exposing the nitrate film underneath. These exposed areas of the nitrate film were removed by rinsing the sample in tri-chloroethane for 45-60 seconds. Finally, the remaining hardened polymer was removed by rinsing the sample in methylene chloride, leaving a patterned nitrate film of 20 mil (0.50mm) lines and 20 mil (0.50mm) spacings. This film was then heated in flowing oxygen to 950°C for 30 minutes. The sample was allowed to cool over a period of approximately 4 hours to ambient temperature. Results of the measurement of the resistance along a line as a function of temperature are shown in Figure 3 and show an onset of superconductivity at about 77 K. EXAMPLE 4

A 2% aqueous solution of the nitrates of yttrium, barium and copper was prepared with an atomic ratio of Y:Ba:Cu of 0.18:0.60:0.22. The solution contained 7.0% nitrates by weight. An aerosol was formed from this solution using an air brush and was deposited on a substrate consisting essentially of a MgO single crystal cleaved to provide a (100) surface. The substrate was held at a temperature of 800°C during the deposition degrees Centigrade. The solution was delivered in one 40 ml aliquot over a period of one hour. The sample was then placed in a furnace in flowing oxygen at 980°C for 1 hour. The sample was then allowed to cool over a period of approximately 4 hours to ambient temperature. The results obtained from measurements of the resistance as a function of temperature and the critical current density as a function of temperature below the superconducting transition temperature are displayed in Figures 4 and 5, respectively, and show that the film is superconducting with an onset of superconductivity at about 76 K.

The X-ray diffraction pattern for this film is shown in Figure 6. These data show that the material produced is a pure MBa₂θu₃θ_w phase material and very highly textured, i.e., ordered, with a c-axis ordering. EXAMPLE 5 A 2% aqueous solution of the nitrates of yttrium, barium and copper was prepared with an atomic ratio of Y:Ba:Cu of 0.13:0.33:0.53. An aerosol was formed from this solution using an air brush and was deposited on a substrate consisting essentially of a MgO single crystal cleaved to provide a (100) surface. The substrate was held at a temperature of 130°C during the deposition of the nitrate film. The solution was delivered in 15 ml aliquots. Samples were prepared using 1, 2, 4, 6 and 8 aliquots of solution. Following each of the nitrate film depositions, the film and substrate were subjected to a temperature of 720°C in an argon atmosphere for 20 minutes, thereby pyrolizing the nitrates to their respective oxides. After completion of the' respective number of depositions and heatings, the film was placed in a furnace at 980°C with pure oxygen flowing through the volume of the furnace. The film was held at this temperature for 1 hour and then allowed to slowly cool in flowing oxygen to ambient temperature, about 20°C, over a period of approximately 4 hours.

Upon removal from the furnace the films were characterized by X-ray analysis and transport. The X-ray data shown in Figure 7 for films made with 1, 6 and 8 depositions indicate that the products are highly oriented (c-axis normal to the plane of the film) Ba₂Cu₃θ_w films of good phase purity.

Measurements were made of the resistance as a function of temperature and the critical current density as a function of temperature below the superconducting transition temperature. The results obtained for the T_c and the critical current at 4.2 K as a function of the number of layers deposited in forming the films are show in Figure 8. The data demonstrate that there is an exceptional enhancement of the critical current for the 2-3 layer film.

EXAMPLE 6 A 5.3% aqueous solution of the nitrates of yttrium, barium and copper was prepared with an atomic ratio of Y:Ba:Cu of 0.18:0.60:0.22. An aerosol was formed of this solution using an air brush and was deposited on a substrate consisting essentially of a polished MgO single crystal cleaved to provide a (100) surface. The substrate was held at a temperature of 600^βC during the deposition of the oxide film. The solution was delivered in one 200 ml aliquot at a rate of 1.66 ml/min. The temperature gradient across the heater plate was lower than 10°C. After completion of the deposition, the film was placed in a large furnace and heated at 1000°C for 2 minutes in an argon atmosphere. It was then heated at 960°C for 60 minutes in an oxygen atmosphere with an oxygen flow rate of 4 liters/min. and then was allowed to slowly cool down at a rate of 10°C/min to ambient temperature.

The results obtained from the measurements of the resistivity versus temperature are shown in Figure 9. The transition temperature is about 76 K. The critical current at 4.2 K is 3900 A/cm². The surface uniformity and smoothness of samples sprayed at high temperature is excellent, similar to those materials deposited by laser ablation and sputtered films.

EXAMPLE 7

A 5.5% aqueous solution of yttrium, barium and copper nitrates was prepared with the stochiometric ratio of Y:Ba:Cu of 0.18:0.60:0.22. The solution was doped with sodium nitrate (Na = 1/10 of metal weight) . An aerosol was formed from this solution using an air brush and was deposited on a ceramic substrate consisting of MgO single crystal cleaved to provide a (100) surface. The substrate was held at 600°C during the deposition of the oxide film. The sample was prepared using 1 aliquot of 200 ml of solution. Following the deposition, the film was placed in a tube furnace at 960°C for 1 hour in a pure oxygen atmosphere with an oxygen flow rate of 4 liters/min. and allowed to cool to ambient temperature at a rate of 10°C/min.

The results obtained from measurements of resistivity are showed in Figure 10. The transition temperature is about 78 K and the critical current at 4.2 K is 7000 A/cm².

EXAMPLE 8 This example describes the preparation of a patterned ring resonator using a positive resist. Individual water solutions of yttrium, barium and copper nitrates, were prepared with nominal concentrations of 2%. The exact concentration of the solutions was verified by using inductive coupled plasma measurements. A 2% nitrate solution with an atomic ratio of Y:Ba:Cu of 0.17:0.33:0.50 was prepared by mixing appropriate amounts of the individual nitrate solutions.

This solution was sprayed on a polished MgO substrate. The substrate temperature was maintained at 130°C during spraying. The sample, consisting of four thin layers of nitrates with intermediate annealing cycles, was deposited in the following fashion. A layer of 15 ml of nitrate solution was sprayed and afterwards pyrolized at 720°C in Ar for 20 minutes. The sample was allowed to cool down to room temperature for a second 15 ml layer to be sprayed on top on the existing layer. After deposition of the second layer is completed it is pyrolized similarly to the first layer. The deposition/annealing cycles are repeated until four layers are built onto the MgO surface. A layer of AZ5214E positive resist is spin coated at 4000 RPM and baked 30 minutes at 70°C. Then, a second layer of resist is spin coated on top of the first layer and baked again at 70°C for 30 minutes. The resist is exposed through a mask with a positive image of ring resonator for 5 minutes using a Nu-Arc source TF-40APRNS (Nu-Arc, Chicago, 111.), a tungsten hologen lamp with the appropriate ultraviolet emission spectrum. The polymer is then contacted with two sequential baths of NaOH water solution (1:80) to selectively remove those portions of the polymer that have been imaged to thereby expose the oxide film in those regions where oxide film is not wanted. The film is left in the- first developer bath for 40 seconds and 10 seconds in a second bath; the latter bath assures complete remo^'val of the exposed resist. The exposed oxide film is then etched away using a H₃PO₄/water solution (1:15) for 5 minutes. The remaining resist, i.e., those portions of the polymer that were not imaged, is contacted with AZ polymeric stripper (KOH/water solution) for 30 seconds to remove the polymer and thereby provide the patterned nitrate or oxide film on the substrate. Finally, the patterned oxide is sonicated in H₂O, stripped with NaOH and sonicated again to assure that no acid was retained. The ring resonator was then placed in a furnace and heated at 980°C for 30 minutes in an oxygen flow of 1.5 liters/minute. The sample was cooled to room temperature at a rate of 10°C/min. Resisitivity measurements showed a critical temperature of 76.7 K and a critical current at 4.2 K of 40,000 A/cm².

EXAMPLE 9

A 2% aqueous solution of the nitrates of bismuth, strontium, calcium and copper was prepared with an atomic ratio of Bi:Sr:Ca:Cu of 0.18:0.18:0.27:0.36. An aerosol was formed of this solution and was deposted using an air brush on a substrate consisting essentially of polished MgO single crystal cleaved to provide a (100) surface. The substrate was held at a temperature of 130^*C during the deposition of the nitrate film. The solution was delivered in three 20 ml aliquots.

Following each of the three depositions, the film and the substrate were subjected to a temperature of 650^*C in an argon atmosphere for 5 minutes, thereby pyrolyzing the nitrates to their respective oxides. After completion of these three depositions and heatings, the film was placed in a furnace at 880^*C in an argon atmosphere and quenched to 870^*C. The atmosphere was changed to oxygen and the film was held at 870^*C for 2 hours in the oxygen atmosphere and then allowed to cool . at 70^*C/min in flowing oxygen to ambient temperature, about 20^*C.

Upon removal from the furnace the film was characterized by X-ray analysis. The data shown in Figure 11 indicates highly textured 2-2-1-2 material with c-axis ordering as indicated by the presence of the (0,0,1) peaks. The results obtained from measurements of the resistance as a function of temperature are displayed in Figure 12 and show that the film is superconducting with zero resistance at about 80 K.

Claims

CJ__i____L The Invention Being Claimed Is:

1. A process for making a patterned film element comprised of an oxide superconductor having the formula

MBa2Cu3θ_w wherein M is selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; w is from about 6.5 to about 7.0, preferably from about 6.8 to about 7.0, said process comprising (a) forming on a substrate a patterned nitrate film comprised of a mixture of nitrates of M, Ba and Cu, by spraying an aerosol formed from a solution of nitrates of M, Ba and Cu;

(b) heating said patterned nitrate film in an oxygen-containing atmosphere, to^"a temperature of about

900°C to about 1000°C and maintaining said temperature for about 1 minute to about 8 hours; and

(c) reducing the temperature to ambient temperature over a period of about 2 to about 12 hours in a flowing oxygen-containing atmosphere, to obtain the superconductor element on the substrate.

2. The process of Claim 1 wherein said patterned nitrate film is formed by (i) forming said aerosol from a solution of nitrates of M, Ba and Cu with an atomic ratio of M:Ba:Cu of x:y:z wherein 0.1 < x < 0.2, 0.3 < y < 0.35 and 0.5 < z ≤ 0.55 and x + y + z -1 , in a solvent and spraying the aerosol onto the substrate heated to a temperature above the boiling point of the solvent but below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate film of thickness of about 1 to about 10 μm; (ii) applying a photohardenable polymer film of thickness of about 0.5 μm to about 50 μm to the nitrate film;

(iii) exposing the photohardenable polymer to radiation effective to harden the polymer to produce an exposed image portion and an unexposed portion of the polymer, the exposed portion defining the desired pattern of oxide superconductor;

(iv) contacting the polymer with a solvent to remove selectively the unexposed portion of the polymer, said unexposed portion defining regions where oxide superconductor is not wanted, thereby exposing the nitrate film in those regions;

(v) contacting the exposed nitrate film with a solvent to remove the exposed nitrate film; and

(vi) contacting the exposed image portion of the polymer with a solvent to remove the polymer in said exposed image portion, thereby providing the desired pattern of oxide superconductor on the substrate.

3. The process of Claim 2 wherein, in step (i) , said solvent is water.

4. The process of Claim 3 wherein, in step (i) , said substrate is heated to a temperature that is 20 or more Centigrade degrees above the boiling point of the solvent and more than 100 Centigrade degrees below the decompostion temperature of the nitrates.

5. The process of Claim 2 wherein said substrate is MgO.

6. The process of Claim 1 wherein said patterned nitrate film is formed by (i) applying a photohardenable polymer film of thickness of about 0.1 μm to about 25 μm o a substrate;

(ii) exposing the photohardenable polymer to radiation effective to harden the polymer to produce an exposed portion and an unexposed image portion of said polymer, the unexposed portion of said polymer defining the desired pattern of oxide superconductor;

(iii) contacting the polymer with a solvent to remove selectively the unexposed image portion of said polymer;

(iv) forming said aerosol from a solution of nitrates of M, Ba and Cu with an atomic ratio of M:Ba:Cu of x:y:z wherein 0.1 < x < 0.2, 0.3 < y ≤ 0.35 and ^'0.5 ≤ z ≤ 0.55 and x + y + z =1, in a solvent and spraying this aerosol onto the substrate containing the exposed portion of the polymer produced in step (iii) , said substrate heated to a temperature above the boiling point of the solvent but below the decompostion temperature of the nitrates, thereby producing a homogeneous, fine-grained nitrate film of thickness of about 0.5 to about 5 μm; and

(v) stripping from the substrate exposed portion of said polymer and the nitrate film deposited thereon by contacting the exposed portion with a solvent for the polymer, thereby providing the patterned nitrate film on the substrate.

7. The process of Claim 6 wherein, in step (iv) , said solvent is water.

8. The process of Claim 7 wherein, in step (iv) , said substrate is heated to a temperature that is 20 or more Centigrade degrees above the boiling point of the solvent and more than 100 Centigrade degrees below the decompostion temperature of the nitrates .

9. The process of Claim 6 wherein said substrate is MgO.

10. A process for making a non-patterned film element of essentially uniform film thickness, said element comprised of an oxide superconductor having the formula Ba2Cu3θ_w wherein M is selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; w is from about 6.5 to about 7.0, said process comprising

(a) forming a nitrate film on a substrate by forming an aerosol from a solution of nitrates of M, Ba and Cu with an atomic ratio of M:Ba:Cu of x:y:z wherein 0.1 < x < 0.2, 0.3 ≤ y < 0.35 and 0.5 < z ≤ 0.55 and x + y + z =1, in a solvent and spraying the aerosol onto said substrate heated to a temperature above the boiling point, of the solvent but below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate film of thickness of about 1 to about 10 μm;

(b) heating the patterned nitrate film in an oxygen-containing atmosphere, to a temperature of about 900°C to about 1000°C and maintaining said temperature for about 1 minute to about 8 hours; and

(c) reducing the temperature to ambient temperature over a period of about 2 to about 12 hours in a flowing oxygen-containing atmosphere to obtain the superconductor element on the substrate.

11. The process of Claim 10 wherein, in step (a), said solvent is water.

12. The process of Claim 11 wherein, in step (a), said substrate is heated to a temperature that is 20 or more Centigrade degrees above the boiling point of the solvent and more than 100 Centigrade degrees below the decompostion temperature of the nitrates.

13. The process of Claim 10 wherein said substrate is MgO.

14. A process for making a non-patterned film element of essentially uniform film thickness, said element comprised of an oxide superconductor having the formula MBa2Cu3θ_w wherein M is selected from the group consisting of Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu; w is from about 6.5 to about 7.0, said process comprising

(a) forming on a substrate an oxide film comprised of a mixture of oxides of M, Ba and Cu, by spraying an aerosol formed from a solution of nitrates of M, Ba and Cu;

(b) heating said oxide film in an oxygen- containing atmosphere, to a temperature of about 900°C to about 1000°C and maintaining said temperature for about 1 minute to about 8 hours; and (c) reducing the temperature to ambient temperature over a period of about 2 to about 12 hours in a flowing oxygen-containing atmosphere to obtain the superconductor element on the substrate.

15. The process of Claim 14 wherein said oxide film is formed by

(i) forming said aerosol from a solution of nitrates of M, Ba and Cu with an atomic ratio of M:Ba:Cu of x:y:z wherein 0.1 < x < 0.2, 0.3 < y < 0.35 and 0.5 ≤ z < 0.55 and x + y + z =1, in a solvent and spraying the aerosol onto a substrate heated to a temperature above the boiling point of the solvent but below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate layer of thickness of about 1 to about 10 μm;

(ii) heating the nitrate layer formed in step (i) to a temperature of from about 500°C to about 750°C in an oxygen or inert gas atmosphere and maintaining said temperature for about 5 to about 45 minutes to produce a homogeneous, fine-grained layer of M, Ba and Cu oxides of thickness of about 0.1 to about 0.5 μm;

(iii) spraying the aerosol used in step (i) onto the oxide layer on the substrate heated to a temperature above the boiling point of the solvent but below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate layer of thickness of about 1 to about 10 μm on the oxide layer;

(iv) heating the nitrate layer formed in step (iii) to a temperature of from about 500°C to about 750°C in an oxygen or inert gas atmosphere and maintaining said temperature for about 5 to about 45 minutes to produce a homogeneous, fine-grained layer of M, Ba and Cu oxides; and (v) repeating steps (iii) and (iv) one to seven times to produce a homogeneous, fine-grained film of M, Ba and Cu oxides.

16. The process of Claim 15 wherein said inert gas atmosphere used in steps (ii) and (iv) is argon.

17. The process of Claim 16 wherein, in step (i) , said solvent is water.

18. The process of Claim 17 wherein, in steps (i) and (iii) , said substrate is heated to a temperature that is 20 or more Centigrade degrees above the boiling point of the solvent and more than 100 Centigrade degrees below the decompostion temperature of the nitrates.

19. The process of Claim 15 wherein said substrate is MgO.

20. The process of Claim 14 wherein said oxide film is formed by making said aerosol from a solution of nitrates of M, Ba and Cu with an atomic ratio of M:Ba:Cu of x:y:z, where 0.15<x<0.2, 0.55<y<0.65 and 0.20<z<0.30 and x+y+z = 1, in a solvent and spraying the aerosol onto a substrate heated to a temperature above the decomposition temperature of the nitrates thereby forming a homogeneous, fine-grained oxide film of thickness of about 0.1 to about 4 μ .

21. The process of Claim 20 wherein said solvent is water.

22. The process of Claim 20 wherein said spray drying is carried out using oxygen as a carrier gas.

23. The process of Claim 4 wherein x = 0.13, y - 0.33, and z = 0.53.

24. The process of Claim 8 wherein x = 0.13, y = 0.33, and z = 0.53.

25. The process of Claim 12 wherein x = 0.13, y = 0.33, and z = 0.53.

26. The process of Claim 18 wherein x = 0.13, y = 0.33, and z - 0.53.

27. The process of Claim 21 wherein x = 0.18, y = 0.60, and z = 0.22.

28. This invention provides a process for making a non-patterned film element comprised of an oxide superconductor having the formula Bi2Sr2CaCu2θ8, said process comprising

(a) forming a solution of nitrates of bismuth, strontium, calcium and copper with an atomic ratio of Bi:Sr:Ca:Cu of w:x:y:z where 0.15 ≤ w < 0.25,

0.15 < x < 0.25, 0.15 < y ≤ 0.35 and 0.20 < z < 0.40, in a solvent and spraying an aerosol of the solution onto a substrate heated to a temperature above the boi-ling point of the solvent but below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate layer of thickness about 1 to about 10 μm;

(b) heating the nitrate layer to a temperature of from about 500"C to about 750^*C in an oxygen or inert gas atmosphere and maintaining said temperature for about 5 to about 45 minutes to produce a first homogeneous, fine-grained oxide layer of Bi, Sr, Ca and Cu oxides of thickness about 0.1 to about 0.5 μm;

(c) spraying an aerosol of the solution used in step (a) onto the first oxide layer on the substrate heated to a temperature above the boiling point of the solvent but below the decomposition temperature of the nitrates, thereby forming a homogeneous, fine-grained nitrate layer of thickness about 1 to about 10 μm on the oxide layer;

(d) heating the nitrate layer to a temperature of from about 500^*C to about 750"C in an oxygen or inert (d) heating the nitrate layer to a temperature of from about 500^*C to about 750^*C in an oxygen or inert gas atmosphere and maintaining said temperature for about 5 to about 45 minutes to produce a second homogeneous, fine-grained oxide layer of Bi, Sr, Ca and Cu oxides of thickness about 0.1 to about 0.5 μm;

(e) repeating steps (c) and (d) 1-7 times to produce a homogeneous, fine-grained oxide layer of Bi, Sr, Ca and Cu oxides; (f) heating the oxide film in an inert gas, preferably argon, atmosphere, to a temperature of about 850^*C to about 900^*C and maintaining said temperature for about 1 minute to about 8 hours; and

(g) cooling to ambient temperature to obtain the superconductor element on the substrate-.