International Business Machines Corporation

Carl A Mueller

Johannes Georg Bednorz

Jochen D Mannhart

Darrell G Schlom

Volker Graf

Pierre L Gueret

Hans P Wolf

Erich Maechler

Johannes G Bednorz

Jean Pierre Locquet

Andrei Catana

Preveen Chaudhari

A new class of superconducting compositions, and methods for making and using them are described. These compositions exhibit superconductivity at temperatures in excess of 26&#xb0; K. and are comprised of transition metal oxides having at least one additional element therein which may create a multivalent state of the transition metal oxide. The composition can be a ceramic-like material having a layer-like crystalline structure, where the structure is distorted having either an oxygen excess or deficiency. An example is RE-AE-TM-O, where RE is a rare earth or rare earth-like element, AE is an alkaline earth element, TM is a transition metal element (such as Cu) and O is oxygen.

Superconductive compounds having high transition temperature, and methods for their use and preparation

A new class of superconducting compositions, and methods for making and using them are described. These compositions exhibit superconductivity at temperatures in excess of 26&#xb0; K. and are comprised of transition metal oxides having at least one additional element therein which may create a multi-valent state of the transition metal oxide. The composition can be a ceramic-like material having a layer-like crystalline structure, where the structure is distorted having either an oxygen excess or deficiency. An example is RE-AE-TM-O, where RE is a rare earth or rare earth-like element, AE is an alkaline earth element, TM is a transition metal element (such as Cu) and O is oxygen.

Described is a process for manufacturing thin films by periodically depositing (DEP) a number of block layers consisting of different base materials on a substrate (multilayer deposition), wherein the thickness of the layers (LT) is restricted to one to 20 monolayers and deposition as well as crystallization of the thin film is completed at approximately constant temperature without performing a separate annealing step. The method can be used to produce thin films of high-T.sub.c -superconductors. It allows a better control of the crystal growth of ternary or higher compounds with comparatively large unit cells.

Process for manufacturing thin films by multi-layer deposition

This method for manufacturing lattice-matched substrates for high-T.sub.c superconductors employs at least two materials chosen from the group of known suitable substrate materials, of which one has a lattice constant smaller than the lattice constant(s) of the perovskite subcell of the selected superconductor material, while the other one has a lattice constant greater than the lattice constant of the perovskite subcell of the selected superconductor. These materials are then powdered and mixed intimately for providing a single-crystal either from the molten mixture of the chosen materials or by thin film deposition, said single-crystal containing appropriate molar percentages of the chosen materials so that resulting lattice constant is essentially the same as that of the selected superconductor material.

Method for manufacturing lattice-matched substrates for high-T.sub.c

Proposed is a method for operating a field-effect device comprised of a superconducting current channel having source and drain electrodes connected thereto, said superconducting current channel being separated from a gate electrode by an insulating layer, where the resistance of said current channel is controlled by varying the critical current of the superconducting material through the application of an electrical field across the superconducting current channel, which in turn changes the density of the mobile charge carriers in the superconducting material. Taught is also an inverted MISFET device for performing that method, the device being characterized in that on an electrically conductive substrate an insulating layer is provided which in turn carries a layer consisting of a superconducting material, and that a gate electrode is attached to said substrate, and source and drain electrodes are electrically connected to said superconductor layer. Advantageously, between the substrate and the superconducting layer, a metallic passivation layer may be provided.

Superconductive-channel electric field-effect drive

A method for making layered structures of artificial high T.sub.c superconductor compounds by which on top of a seed crystal having a lattice structure matching the lattice structure of the superconductor compound to be made, oxide layers of all constituent components are epitaxially grown in a predetermined sequence so as to create a sandwich structure not found in natural crystals. The epitaxial deposition of the constituent components is performed in a reaction chamber having evaporation facilities, inlets for metal-organic gases, and inlets for background gases including oxygen.

Method of making artificial layered high T.sub.c superconductors

A field-effect structure formed on a substrate and comprising a channel with source and drain as well as a gate that is separated from the channel by an insulating layer. The channel is made of a high T.sub.c metal-oxide superconductor, e.g., YBaCuO, having a carrier density of about 10.sup.21 /cm.sup.3 and a correlation length of about 0.2 nm. The channel thickness is preferrable in the order of 1 nm. The superconductor is preferably a single crystalline and oriented such that the superconducting behavior is strongest in the plane parallel to the substrate. With a signal of a few volts applied to the gate, the entire channel cross-section is depleted of charge carriers whereby the channel resistance can be switched between a 'zero resistance' (undepleted, superconducting) state and 'very high resistance' (depleted state).

Field-effect device with a superconducting channel

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.

Superconducting field-effect transistors with inverted MISFET structure

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 .cent..delta..ltoreq.0.5. While the preferred embodiment of the present invention has been herein described, numerous modifications, changes and improvements will occur to those skilled in the art without departing from the spirit and scope of the present invention.

Method for making a superconducting field-effect transistor with

An inverted MISFET structure with a high transition temperature superconducting channel comprises a gate substrate, an interfacial layer with one or more elements of the VIII or IB subgroup of the periodic table of elements, an insulating layer and a high transition temperature superconducting channel. An electric field, generated by a voltage applied to its gate alters the conductivity of the channel.

Enhanced superconducting field-effect transistor

The transistor comprises two electrodes, source (12) and drain (13), with a semiconductor tunnel channel (11) arranged therebetween. A gate (14) for applying control signals is coupled to the channel. The semiconductor, at low temperatures, behaves like an insulator with a low barrier (some meV) through which charge carriers can tunnel under the influence of an applied drain voltage. The tunnel current can be controlled by a gate voltage V.sub.G which modifies the barrier height between source and drain thereby changing the tunnel probability.

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Hedingen, Switzerland

Carl A Mueller