Abstract: A stabilized carbon cluster conducting material comprising (i) a core comprising a conducting or superconducting carbon cluster and (ii) a sheath covering the core; a device comprising a substrate having thereon a film of a conducting or superconducting carbon cluster covered with a protective film capable of substantially preventing permeation of oxygen and water in the atmosphere; and processes for producing the stabilized carbon cluster conducting material and the device.

Abstract: This invention relates to a process of forming multilayered thallium-containing superconducting composites, wherein a first thallium-containing superconducting layer, an intermediate thallium-containing oxide layer and a second thallium-containing superconducting layer are successively deposited on a substrate by a vapor phase process by controlling the heating temperature, pressure of oxidizing gas and thallium vapor pressure during post-deposition annealing of the superconducting films.

Abstract: A thin film of oxide superconductor consisting of more than two portions (1, 11, 12) each possessing a predetermined crystal orientation and deposited on a common surface of a substrate (2). At least one selected portion (10) of thin film of oxide superconductor is deposited on a thin under-layer (4, 100) which facilitates crystal growth of selected portions and which is deposited previously on the substrate. The selected portions (10) may consist of a-axis oriented thin film portions while non-selected portions (11, 12) may consists of c-axis oriented thin film portions. The thin under-layer can be a buffer layer (4) or a very thin film (100) of oxide superconductor.

Abstract: A lanthanum aluminate (LaAlO.sub.3) substrate on which thin films of layered perovskite copper oxide superconductors are formed. Lanthanum aluminate, with a pseudo-cubic perovskite crystal structure, has a crystal structure and lattice constant that closely match the crystal structures and lattice constants of the layered perovskite superconductors. Therefore, it promotes epitaxial film growth of the superconductors, with the crystals being oriented in the proper direction for good superconductive electrical properties, such as a high critical current density. In addition, LaAlO.sub.3 has good high frequency properties, such as a low loss tangent and low dielectric constant at superconductive temperatures. Finally, lanthanum aluminate does not significantly interact with the superconductors. Lanthanum aluminate can also be used to form thin insulating films between the superconductor layers, which allows for the fabrication of a wide variety of superconductor circuit elements.

Abstract: For manufacturing a superconducting device, a first oxide superconductor thin film having a very thin thickness is formed on a principal surface of a substrate, and a stacked structure of a gate insulator and a gate electrode is formed on a portion of the first oxide superconductor thin film. A second oxide superconductor thin film is grown on an exposed surface of the first oxide superconductor thin film, using the gate electrode as a mask, so that first and second superconducting regions having a relatively thick thickness are formed at opposite sides of the gate electrode, electrically isolated from the gate electrode. A source electrode and a drain electrode is formed on the first and second oxide superconducting regions. The superconducting device thus formed can functions as a super-FET.

Abstract: A superconducting film including 0.1-5% by weight of magnesium oxide wherein the superconducting film has a thickness in a range from 300 to 1000 .mu.m. A superconducting device for magnetic shielding comprises: a substrate; and a superconducting layer supported by the substrate, the superconducting layer including grains of a Bi-type superconducting oxide so that the superconducting layer has a critical temperature higher than -196.degree. C., the superconducting layer having a thickness in a range from 300 to 1,000 .mu.m, the superconducting layer including 0.1-5% by weight of magnesium oxide, where the superconducting device has a laminated structure including the substrate and the superconducting layer. A process for producing a superconducting film comprises the steps of: firing a mixture of calcined powders of a superconducting oxide and 0.1-5% by weight of magnesium oxide powders at a temperature at which the superconducting oxide is partially melted.

Abstract: An oxide-based superconductor ccmprising Tl, Pb, Sr, Ca and Cu or Tl, Pb, Ba, Sr, Ca and Cu, prepared by subjecting a low melting point composition comprising the superconductor-constituting elements and a solid composition comprising the superconductor-constituting elements, prepared in advance, to reaction under melting conditions for the low melting point composition, has distinguished current pass characteristics in a high magnetic field due to improvement of electric contact among grains through reduction of non-superconductor phase, increase in crystal grain sizes (reduction of crystal boundaries), orientation of crystal and cleaning of crystal boundaries.

Abstract: An oxide superconductor thin film is formed on a substrate by emitting molecular beams of constituent elements of the oxide superconductor to the substrate under high vacuum, wherein at first a molecular beam of one of the constituent elements of the oxide superconductor, of which an oxide thin film can be deposited so as to have a smooth surface, is emitted so as to form the oxide thin film of one or two unit cells. And then, all the molecular beams of constituent elements of the oxide superconductor are emitted to the oxide thin film so as to form the oxide superconductor thin film.

Abstract: A superconductor element includes a first layer of an oxide superconductor, a second layer of an insulator, semiconductor, or metal, and an interlayer interposed between the first and second layers and formed of AgO.sub.x (where in 0<.times.< 1/2) .

Abstract: There is disclosed a method for annealing oxide thin film superconductors having layered structures including at least Cu--O layers in which each oxide thin film superconductor is heated partially by a heating means and the heating portion is moved at a predetermined speed.

Abstract: A lanthanum aluminate (LaAlO.sub.3) substrate on which thin films of layered perovskite copper oxide superconductors are formed. Lanthanum aluminate, with a pseudo-cubic perovskite crystal structure, has a crystal structure and lattice constant that closely match the crystal structures and lattice constants of the layered perovskite superconductors. Therefore, it promotes epitaxial film growth of the superconductors, with the crystals being oriented in the proper direction for good superconductive electrical properties, such as a high critical current density. In addition, LaAlO.sub.3 has good high frequency properties, such as a low loss tangent and low dielectric constant at superconductive temperatures. Finally, lanthanum aluminate does not significantly interact with the superconductors. Lanthanum aluminate can also used to form thin insulating films between the superconductor layers, which allows for the fabrication of a wide variety of superconductor circuit elements.

Abstract: A lanthanum aluminate ( LaAlO.sub.3) substrate on which thin films of layered perovskite copper oxide superconductors are formed. Lanthanum aluminate, with a pseudo-cubic perovskite crystal structure, has a crystal structure and lattice constant that closely match the crystal structures and lattice constants of the layered perovskite superconductors. Therefore, it promotes epitaxial film growth of the superconductors, with the crystals being oriented in the proper direction for good superconductive electrical properties, such as a high critical current density. In addition, LaAlO.sub.3 has good high frequency properties, such as a low loss tangent and low dielectric constant at superconductive temperatures. Finally, lanthanum aluminate does not significantly interact with the superconductors. Lanthanum aluminate can also used to form thin insulating films between the superconductor layers, which allows for the fabrication of a wide variety of superconductor circuit elements.

Abstract: In accordance this invention, there is provided a process for making a bulk superconductive material. In the first step of this process, a diffusion couple is formed from superconductor oxide and impurity oxide. Thereafter, the diffusion couple is heated to a temperature in excess of 800 degrees Centigrade, cooled at a controlled rate, and annealed.

Abstract: A superconducting device or a super-FET has a pair of superconducting electrode regions (20b,20c) consisting of a thin film (20)oxide superconductor being deposited on a substrate (5) and a weak link region (20a), the superconducting electrode regions (20b, 20c) being positioned at opposite sides of the weak link region (20a) these superconducting electrode regions (20b, 20c) and the weak link region (20a) being formed on a common plane surface of the substrate (5). The weak link region (20a) is produced by local diffusion of constituent element(s) of the substrate (5) into the thin film (20) of the oxide superconductor in such a manner that a substantial wall thickness of the thin film (20) of the oxide superconductor is reduced at the weak link region (20a) so as to leave a weak link or superconducting channel (10) in the thin film (20) of oxide superconductor over a non-superconducting region (50) which is produced by the diffusion.

Abstract: The present invention comprises a high quality, epitaxial thallium-based HTS thin film on MgO and other substrates and methods of providing the same. The present invention is achieved using a nucleation layer which provides a template for subsequent growth. Specifically, YBCO and/or YBCO analog films (films having growth characteristics and physical structures analogous to YBCO) are used as nucleation layer(s) on MgO and other substrates to enable the growth of epitaxial thallium-based HTS films.

Abstract: A superconducting device comprising a substrate having a principal surface, a non-superconducting oxide layer having a similar crystal structure to that of the oxide superconductor, a first and a second superconducting regions formed of c-axis oriented oxide superconductor thin films on the non-superconducting oxide layer separated from each other and gently inclining to each other, a third superconducting region formed of an extremely thin c-axis oriented oxide superconductor thin film between the first and the second superconducting regions, which is continuous to the first and the second superconducting regions.

Abstract: Superconductors using oxide superconducting materials having pinning centers inside crystal grains are enhanced in transmissible critical current density and allowed to have a high critical current density even in the magnetic field. A superconductor is produced comprising superconducting materials having a high irreversible magnetic field where the c axes of their crystals are oriented in one direction. This can be practically realized by heat-treating a superconducting material having the composition (Tl.sub.1-X1-X2 Pb.sub.X1 Bi.sub.X2)(Sr.sub.1-X3 Ba.sub.X3).sub.2 Ca.sub.2 Cu.sub.3 O.sub.9+X4 together with Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8 having a tendency of growing in the form of plate crystal. Various apparatuses capable of working under cooling with liquid nitrogen let alone with liquid helium and having a high superconducting critical current density even in a high magnetic field can be produced.

Abstract: A process for preparing an oxide thin film which has a crystalline, clean and smooth surface on a substrate. The process is conducted by using an apparatus comprising a vacuum chamber in which an oxidizing gas of O.sub.2 including O.sub.3 can be supplied near the substrate so that pressure around the substrate can be increased while maintaining high vacuum near an evaporation source and Knudsen cell evaporation sources arranged in the vacuum chamber wherein the substrate is heated, molecular beam of constituent atoms of the oxide excluding oxygen are supplied from the K cell evaporation sources and an oxidizing gas is locally supplied to the vicinity of the substrate.

Abstract: A method for activating superconducting material comprises generating a species of oxygen ions, heating the material and introducing the oxygen ions to said material by the application of a low-gradient drift field between the source of oxygen ions and a substrate including the superconducting material.

Abstract: A method is disclosed for forming polycrystalline thallium system superconductors having high current carrying capacity and high magnetic field behavior. A precursor deposit is formed comprised of silver, in an amount of about 1 to 20 mole percent of total metals in the precursor deposit, and the balance oxides of calcium, barium, and copper in ratios for forming the superconductor. The precursor deposit is annealed in an oxidizing atmosphere, and in the presence of a source of thallous oxide. The source of thallous oxide is heated to a first temperature selected to incorporate thallium into the deposit in an amount of about 6 to 22 mole percent of metals in the superconductor, and the precursor deposit is heated to a second temperature to form the superconductor.

Abstract: A method for producing microcomposite powders for use in superconducting and non-superconducting applications.

Abstract: A superconductor device is provided including a base, a base electrode formed on the base which is made of a Bi-system oxide superconductive material containing an alkaline earth metal, a barrier layer formed on the base electrode which is made of Bi--Sr--Cu--O, a counter electrode formed on the barrier layer which is made of a Bi-system oxide superconductive material containing an alkaline earth metal, a contact electrode formed so as contact with the counter electrode, and a separation layer for separating said contact electrode from said base electrode.

Abstract: Methods and reactors are described for the production of high temperature superconductor films on a variety of substrates, particularly those films which include volatile components during their manufacture. The reactors are particularly useful for producing films containing thallium. The reactors provide for relatively low volume cavities in which the substrate is disposed, and control of the thallium oxide overpressure during the processing. In a preferred embodiment, one or more holes or apertures are made in the reactor to permit thallium and thallium oxide to controllably leak from the reactor. For manufacture of double sided superconducting films, a reactor is used having top and bottom plates each with one or more holes in them. Uniform high temperature superconducting films are obtained while inhibiting reaction between the substrate and superconducting film during the processing.

Abstract: An anisotropic superconductor junction device consisting of a lower superconducting layer and an upper superconducting layer separated by a barrier layer, in which the upper and lower superconducting layers and the barrier layer each have a (103) crystal orientation in which the c axis is arranged in the same direction at an angle of 45 degrees relative to the plane of the junction.

Abstract: A stacked Josephson junction device includes a pair of copper oxide superconductor layers and a non-superconductor layer formed between the pair of oxide superconductor layers. The copper oxide superconductor layers are composed of a compound copper oxide having the composition expressed by the general formula:LnBa.sub.2 Cu.sub.3 O.sub.v(where Ln is Y or rare earth element and 6<v.ltoreq.7).The non-superconductor layer is composed of a chemical compound having the composition expressed by the general formula:Bi.sub.2 Y.sub.x Sr.sub.y Cu.sub.z O.sub.w(where x, y, z and w indicate ratio of components0.ltoreq.x.ltoreq.2,1.ltoreq.y.ltoreq.3,1.ltoreq.z.ltoreq.3,6.ltoreq.w.ltoreq.13.

Abstract: Disclosed is a method of manufacturing a thin film of an oxide superconductor represented by formula Sr.sub.1-x Nd.sub.x CuO.sub.2 on a substrate. The oxide superconductor has a tetragonal crystal structure, the lattice constant in a-axis falling within a range of between 0.385 nm and 0.410 nm, and the lattice constant in c-axis being an integer number of times as much as a level falling within a range of between 0.310 nm and 0.350 nm. The method includes the steps of forming by epitaxial growth a film of a crystal having lattice constants close to those of the crystal of said oxide superconductor on a substrate, and forming a thin film of the oxide superconductor of a tetragonal crystal structure represented by general formula (I) by a thin film-forming technique.

Abstract: A method of manufacturing a superconducting device involves forming a thin film on the surface of a substrate, forming a superconducting gate electrode on a portion of the thin film, etching the portions of the thin film using the gate electrode as a mask thereby providing a superconducting channel under the gate, forming a step portion on the superconducting channel and under the gate, converting the oxide portion of the step portion into a gate insulation portion by heating the substrate in a vacuum, forming a second oxide superconducting film on the exposed surface of the channel so that superconducting source and drain electrodes are formed on each side of the gate such that the drain and source have a thickness greater than that of the channel and are electrically isolated from the gate electrode.

Abstract: A thin film of oxide superconductor consisting of more than two portions (10, 11, 12) each possessing a predetermined crystal orientation and deposited on a common surface of a substrate (2). At least one selected portion (10) of the thin film of oxide superconductor is deposited on a thin under-layer (4, 100) which facilitates crystal growth of the selected portion and which is deposited previously on the substrate. The selected portions (10) may consist of a-axis oriented thin film portions while non-selected portions (11, 12) may consists of c-axis oriented thin film portions. The thin under-layer can be a buffer layer (4) or a very thin film (100) of oxide superconductor.

Abstract: In one aspect, the present invention is a precursor powder to an oxide superconductor, namely a coated particle comprising a metal oxide particle core (including a mixed metal oxide, e.g., BSCCO-2212 or YBCO-123) on which is deposited a secondary metal oxide coating (e.g., M.sub.n CuO.sub.x or CuO). The metal oxide particle and secondary metal oxide coating together comprise metallic elements having a stoichiometry appropriate for the formation of a desired oxide superconductor. The metal oxide reacts with the secondary metal oxide under suitable conditions (e.g., heating) to form the desired oxide superconductor (e.g., BSCCO-2223 or YBCO-124). In another aspect, the invention is a method for preparing such a coated particle, comprising: preparing a precursor solution comprising a metal .mu.

Abstract: An outer surface of a superconducting thin film of compound oxide such as YBa.sub.2 Cu.sub.3 O.sub.7-.delta. deposited on a substrate such as MgO and SrTiO.sub.3 is protected with a protective layer which is composed of amorphous inorganic material such as inorganic glass, amorphous oxide.

Abstract: A method of manufacturing a single crystal of a superconductive oxide by a travelling solvent floating zone method (TSFZ Method). In this manufacturing method, a sintered feed rod of an oxide belonging to a tetragonal system, exhibiting anisotropic properties and superconductive properties and having a stoichiometric composition of the superconductive oxide is melted into a layer of a solvent mainly consisting of a oxidized copper and arranged in an infrared heating furnace under an oxygen pressure thereby growing a large single crystal of the superconductive oxide which is 5 mm or over in diameter and 40 mm or over in length.The superconductive oxide is one selected from the group consisting of La.sub.2-x A.sub.x CuO.sub.4 (A:Sr,Ba), Nd.sub.2-x Ce.sub.x CuO.sub.4, YBa.sub.2 Cu.sub.3 O.sub.7-x, BiSrCaCu.sub.2 O.sub.x, Tl.sub.2 Ba.sub.2 Ca.sub.2 Cu.sub.3 O.sub.

Abstract: A superconducting transistor having a source region and a drain region are formed by a YBCO film on a barrier layer, which is composed of a PBCO film formed on an STO substrate. A gate electrode is disposed on the thinner wall at the back of the STO substrate. In a superconducting transistor so constructed the electric field created by the gate voltage works effectively at an interface with the barrier layer, more carriers can be drawn out relative to the applied gate voltage, and it becomes possible for a large superconduction current to flow.

Abstract: A method for depositing a thin film of a material on an oxide thin film having a perovskite type crystal structure formed on a substrate comprising steps of depositing a seed layer of a single crystal of the material having an extremely thin thickness at a relatively high substrate temperature on the oxide thin film having a perovskite type crystal structure and depositing a thin film of the material on the seed layer at a lower substrate temperature.

Abstract: A thin-film superconductor includes a substrate, a ferroelectric film, and a superconducting oxide film. The ferroelectric film extends on the substrate. The ferroelectric film is made of a crystal contains Bi and O. The superconducting oxide film extends on the ferroelectric film, and containing Bi, Cu, and an alkaline-earth metal element. The superconducting oxide film may contain at least two different alkaline-earth metal elements.

Abstract: A process for depositing a biaxially aligned intermediate layer over a non-single crystal substrate is disclosed which permits the subsequent deposition thereon of a biaxially oriented superconducting film. The process comprises depositing on a substrate by laser ablation a material capable of being biaxially oriented and also capable of inhibiting the migration of substrate materials through the intermediate layer into such a superconducting film, while simultaneously bombarding the substrate with an ion beam. In a preferred embodiment, the deposition is carried out in the same chamber used to subsequently deposit a superconducting film over the intermediate layer. In a further aspect of the invention, the deposition of the superconducting layer over the biaxially oriented intermediate layer is also carried out by laser ablation with optional additional bombardment of the coated substrate with an ion beam during the deposition of the superconducting film.

Abstract: A superconducting thin film formed on a substrate, comprising an a-axis orientated oxide superconductor layer, a c-axis orientated oxide superconductor layer and an oxide semiconductor layer inserted between the a-axis orientated oxide superconductor layer and the c-axis orientated oxide superconductor layer, in contact with them in which superconducting current can flow between the a-axis orientated oxide superconductor layer and the c-axis orientated oxide superconductor layer through the oxide semiconductor layer by a long-range proximity effect.

Abstract: c-axis oriented YBa.sub.2 Cu.sub.3 O.sub.7 layers are grown with intervening SrTiO.sub.3 layers bridged over steps at which there is a transformation to a-axis crystal-oriented growth. The multilayer superconductor has YBa.sub.2 Cu.sub.3 O.sub.7 layers which are not thicker than 500 nm while the intervening layers of SrTiO.sub.3 have thicknesses of 20 to 30 nm.

Abstract: A superconducting thin film formed on a substrate, comprising at least one oxide superconductor layer formed on the principal surface of said substrate and at least one oxide layer formed of an oxide which compensates for crystalline incompleteness at the surface of said oxide superconductor layer, and which is arranged on or under the superconducting layer.

Abstract: A superconducting thin film of compound oxide material deposited on a substrate, comprising a plurality of a-axis or b-axis oriented unit layers (2) and a plurality of c-axis oriented unit layers (1), each unit layer (1, 2) being made of the compound oxide material and being laminated alternately one over another on the substrate (3).

Abstract: A high frequency superconducting device structure is disclosed which comprises an alkaline earth fluoride substrate with a magnesium oxide lower buffer layer on the alkaline earth substrate and an upper buffer layer epitaxial template layer on the magnesium oxide layer for providing a template for epitaxial growth of a high temperature superconducting film on the upper buffer layer, providing reduced dielectric and conducting losses at high frequencies. The disclosed structure may be incorporated into a multi-chip module (MCM) for providing very high speed interconnections.

Abstract: A LnBaCuO-series superconducting thin film is provided over a surface of a substrate of Y.sub.2 O.sub.3 single crystal to form a composite superconductor. Ln stands for Y or a lanthanoid element. The composite superconductor has an improved interfacial diffusion.

Abstract: c-axis oriented microwave quality HTSC films are deposited onto single crystals of gadolinium gallium garnet (GGG) using pulsed laser deposition (PLD) with conditions of 85 mTorr of oxygen partial pressure, a block temperature of 730.degree. C., a substrate surface temperature of 790.degree. C. and a laser fluence of 1 to 2 Joules/cm.sub.2 at the target, a laser repetition rate of 10 Hz and a target to substrate distance of 7 cm and in which the a and b lattice parameters of the GGG exhibit a mismatch of less than 2.5 percent with the a and b lattice parameters of the HTSC.

Abstract: A structure having a silicon substrate with an epitaxially grown magnesium oxide layer on a surface onto which is epitaxially grown, either directly or on an intermediary layer, a layer of high temperature superconducting material.

Abstract: A superconducting device has a superconducting channel formed of an oxide superconductor on the principal surface of a substrate. A source electrode and a drain electrode likewise formed of oxide superconductor, are electrically connected by the channel to provide for superconducting current flow. A superconducting gate electrode is isolated by a side insulating region which completely covers each of opposite side surfaces of the gate electrode. The relative thicknesses of both the source and drain electrodes are much greater than that of the channel thickness. The superconducting channel and the gate insulator are both formed by one oxide thin film, and in a preferred embodiment, the gate electrode likewise is provided by the same film which forms the gate insulator and channel.

Abstract: A thin film of oxide superconductor deposited on a single crystal substrate of silicon wafer. A buffer layer of (100) or (110) oriented Ln.sub.2 O.sub.3, in which Ln stands for Y or lanthanide elements is interposed between the thin film of oxide superconductor and the silicon wafer. A surface of silicon wafer is preferably cleaned satisfactorily by heat-treatment in vacuum before the buffer layer is deposited. An under-layer of metal oxide; ZrO.sub.2, YSZ or metal Y, Er is preferably interposed between the Ln.sub.2 O.sub.3 buffer layer and the silicon wafer.

Abstract: A method for producing a thin oxide superconducting film possessing high crystallinity and excellent quality and a novel single crystal as a substrate allowing easy formation of an epitaxial film of high quality usable for the method are provided. The method for the production of the thin oxide superconducting film is characterized by using as a substrate a single crystal of SrLaGaO.sub.4 which is a high-melting oxide and effecting epitaxial growth of a thin oxide superconducting film on the substrate. The single crystal used as a substrate is an oxide single crystal possessing a crystal structure of the K.sub.2 NiF.sub.4 type and having a composition of Sr.sub.1-X La.sub.1-Y Ga.sub.1-Z O.sub.4-W (wherein X, Y, Z, and W fall in the following respective ranges; -0.1<X<0.1, -0.1<Y<0.1, -0.1<Z<0.1, and -0.4<W<0.4).

Abstract: A method and article of manufacture of a lead oxide based glass coating on a high temperature superconductor. The method includes preparing a dispersion of glass powders in a solution, applying the dispersion to the superconductor, drying the dispersion before applying another coating and heating the glass powder dispersion at temperatures below oxygen diffusion onset and above the glass melting point to form a continuous glass coating on the superconductor to establish compressive stresses which enhance the fracture strength of the superconductor.

Abstract: A superconducting device comprises a substrate having a principal surface and a non-superconducting oxide layer having a similar crystal structure to that of the oxide superconductor, which has a projection at its center portion. A superconducting source region and a superconducting drain region formed of an .alpha.-axis oriented oxide superconductor thin film are positioned at the both sides of the projection of the non-superconducting oxide layer separated from each other and an extremely thin superconducting channel formed of a c-axis oriented oxide superconductor thin film is positioned on the projection of the non-superconducting oxide layer. The superconducting channel electrically connects the superconducting source region to the superconducting drain region, so that superconducting current can flow through the superconducting channel between the superconducting source region and the superconducting drain region.

Abstract: A superconducting device comprises a substrate, a non-superconducting layer formed in a principal surface of said substrate, an extremely thin superconducting channel formed of an oxide superconductor thin film on the non-superconducting layer. A superconducting source region and a superconducting drain region of a relatively thick thickness are formed of the oxide superconductor at the both sides of the superconducting channel separated from each other but electrically connected through the superconducting channel, so that a superconducting current can flow through the superconducting channel between the superconducting source region and the superconducting drain region.

Abstract: This field-effect transistor comprises a conductive substrate (2) serving as the gate electrode, an insulating barrier layer (3), and a superconducting channel layer (1) on top of the barrier layer (3). The superconductor layer (1) carries a pair of mutually spaced electrodes (4, 5) forming source and drain, respectively. The substrate is provided with an appropriate gate contact (6).The substrate (2) consists of a material belonging to the same crystallographic family as the barrier layer (3). In a preferred embodiment, the substrate (2) is niobium-doped strontium titanate, the barrier layer (3) is undoped strontium titanate, and the superconductor (1) is a thin film of a material having a lattice constant at least approximately similar to the one of the materials of the substrate (2) and barrier (3) layers. A preferred material of this type is YBa.sub.2 Cu.sub.3 O.sub.7-.delta., where 0.ltoreq..delta..ltoreq.0.5.