The cryotron is a switch that operates using superconductivity. [1] The cryotron works on the principle that magnetic fields destroy superconductivity. This simple device consists of two superconducting wires (e.g. tantalum and niobium) with different critical temperature (Tc). The cryotron was invented by Dudley Allen Buck of the Massachusetts Institute of Technology Lincoln Laboratory.
As described by Buck, [2] a straight wire of tantalum (having lower Tc) is wrapped around with a wire of niobium in a single layer coil. Both wires are electrically isolated from each other. When this device is immersed in a liquid helium bath both wires become superconducting and hence offer no resistance to the passage of electric current. Tantalum in superconducting state can carry large amount of current as compared to its normal state. Now when current is made to pass through the niobium coil (wrapped around tantalum) it produces a magnetic field, which in turn reduces (kills) the superconductivity of the tantalum wire and hence reduces the amount of the current that can flow through the tantalum wire. Hence one can control the amount of the current that can flow in the straight wire with the help of small current in the coiled wire. We can think of the tantalum straight wire as a "gate" and the coiled niobium as a "control".
The article by Buck [2] includes descriptions of several logic circuits implemented using cryotrons, including: one stage of a binary adder, carry network, binary accumulator stage, and two stages of a cryotron stepping register.
A planar cryotron using thin films of lead and tin was developed in 1957 by John Bremer at General Electric's General Engineering Lab in Schenectady, New York. This was one of the first integrated circuits, although using superconductors rather than semiconductors. In the next few years, a demonstration computer was made and arrays with 2000 devices operated. A short history of this work is in the November 2007 newsletter of the IEEE History Center. [3]
Juri Matisoo [4] developed a version of the cryotron incorporating a Josephson junction switched by the magnetic field from a control wire. He also explained the shortcomings of traditional cryotrons in which the superconductive material must transition between superconducting and normal states to switch the device, and thus switch relatively slowly. Matisoo's cryotron switched between a conducting state in which 'pair tunneling' of electrons through the gate took place and a 'resistive' state where only single electrons were able to tunnel. The circuit was (like the traditional cryotron) capable of some amplification (i.e gain greater than unity) had a switching rate of less than 800 picoseconds. Although the requirement for cryogenic cooling limited its practicality, it wasn't until the late 2010s that commercial transistors came close to matching this performance.[ citation needed ]
There have been periods of renewed interest in various types of cryotron. IBM experimented with using them for limited applications in supercomputers during the 1980s,[ citation needed ] and (as of 2020) there has been some investigation of their potential applications both to I/O and logic in prototype quantum computers.[ citation needed ]
The Cryotron brought Buck a number of interviews with various news agencies at the time, international scientific renown, and while the work didn't survive Buck's death, many of the techniques for the research of the device would be used at Intel and other chip manufacturers and in the research of other more modern and interactive computers, especially at MIT.
Niobium is a chemical element; it has symbol Nb and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has similar ductility to iron. Niobium oxidizes in Earth's atmosphere very slowly, hence its application in jewelry as a hypoallergenic alternative to nickel. Niobium is often found in the minerals pyrochlore and columbite. Its name comes from Greek mythology: Niobe, daughter of Tantalus, the namesake of tantalum. The name reflects the great similarity between the two elements in their physical and chemical properties, which makes them difficult to distinguish.
Superconductivity is a set of physical properties observed in superconductors: materials where electrical resistance vanishes and magnetic fields are expelled from the material. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered, even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source.
Superconducting magnetic energy storage (SMES) systems store energy in the magnetic field created by the flow of direct current in a superconducting coil that has been cryogenically cooled to a temperature below its superconducting critical temperature. This use of superconducting coils to store magnetic energy was invented by M. Ferrier in 1970.
A SQUID is a very sensitive magnetometer used to measure extremely weak magnetic fields, based on superconducting loops containing Josephson junctions.
Technological applications of superconductivity include:
Spintronics, also known as spin electronics, is the study of the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices. The field of spintronics concerns spin-charge coupling in metallic systems; the analogous effects in insulators fall into the field of multiferroics.
This is an index of articles relating to electronics and electricity or natural electricity and things that run on electricity and things that use or conduct electricity.
Magnesium diboride is the inorganic compound with the formula MgB2. It is a dark gray, water-insoluble solid. The compound has attracted attention because it becomes superconducting at 39 K (−234 °C). In terms of its composition, MgB2 differs strikingly from most low-temperature superconductors, which feature mainly transition metals. Its superconducting mechanism is primarily described by BCS theory.
A superconducting magnet is an electromagnet made from coils of superconducting wire. They must be cooled to cryogenic temperatures during operation. In its superconducting state the wire has no electrical resistance and therefore can conduct much larger electric currents than ordinary wire, creating intense magnetic fields. Superconducting magnets can produce stronger magnetic fields than all but the strongest non-superconducting electromagnets, and large superconducting magnets can be cheaper to operate because no energy is dissipated as heat in the windings. They are used in MRI instruments in hospitals, and in scientific equipment such as NMR spectrometers, mass spectrometers, fusion reactors and particle accelerators. They are also used for levitation, guidance and propulsion in a magnetic levitation (maglev) railway system being constructed in Japan.
An electronic component is any basic discrete electronic device or physical entity part of an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components and elements. A datasheet for an electronic component is a technical document that provides detailed information about the component's specifications, characteristics, and performance. Discrete circuits are made of individual electronic components that only perform one function each as packaged, which are known as discrete components, although strictly the term discrete component refers to such a component with semiconductor material such as individual transistors.
Superconductivity is the phenomenon of certain materials exhibiting zero electrical resistance and the expulsion of magnetic fields below a characteristic temperature. The history of superconductivity began with Dutch physicist Heike Kamerlingh Onnes's discovery of superconductivity in mercury in 1911. Since then, many other superconducting materials have been discovered and the theory of superconductivity has been developed. These subjects remain active areas of study in the field of condensed matter physics.
Niobium–tin is an intermetallic compound of niobium (Nb) and tin (Sn), used industrially as a type-II superconductor. This intermetallic compound has a simple structure: A3B. It is more expensive than niobium–titanium (NbTi), but remains superconducting up to a magnetic flux density of 30 teslas [T] (300,000 G), compared to a limit of roughly 15 T for NbTi.
Niobium–titanium (Nb-Ti) is an alloy of niobium and titanium, used industrially as a type II superconductor wire for superconducting magnets, normally as Nb-Ti fibres in an aluminium or copper matrix.
Andreev reflection, named after the Russian physicist Alexander F. Andreev, is a type of particle scattering which occurs at interfaces between a superconductor (S) and a normal state material (N). It is a charge-transfer process by which normal current in N is converted to supercurrent in S. Each Andreev reflection transfers a charge 2e across the interface, avoiding the forbidden single-particle transmission within the superconducting energy gap.
Quantum dot cellular automata are a proposed improvement on conventional computer design (CMOS), which have been devised in analogy to conventional models of cellular automata introduced by John von Neumann.
In condensed matter physics, scanning SQUID microscopy is a technique where a superconducting quantum interference device (SQUID) is used to image surface magnetic field strength with micrometre-scale resolution. A tiny SQUID is mounted onto a tip which is then rastered near the surface of the sample to be measured. As the SQUID is the most sensitive detector of magnetic fields available and can be constructed at submicrometre widths via lithography, the scanning SQUID microscope allows magnetic fields to be measured with unparalleled resolution and sensitivity. The first scanning SQUID microscope was built in 1992 by Black et al. Since then the technique has been used to confirm unconventional superconductivity in several high-temperature superconductors including YBCO and BSCCO compounds.
Flux pumping is a method for magnetising superconductors to fields in excess of 15 teslas. The method can be applied to any type II superconductor and exploits a fundamental property of superconductors, namely their ability to support and maintain currents on the length scale of the superconductor. Conventional magnetic materials are magnetised on a molecular scale which means that superconductors can maintain a flux density orders of magnitude bigger than conventional materials. Flux pumping is especially significant when one bears in mind that all other methods of magnetising superconductors require application of a magnetic flux density at least as high as the final required field. This is not true of flux pumping.
The superconducting tunnel junction (STJ) – also known as a superconductor–insulator–superconductor tunnel junction (SIS) – is an electronic device consisting of two superconductors separated by a very thin layer of insulating material. Current passes through the junction via the process of quantum tunneling. The STJ is a type of Josephson junction, though not all the properties of the STJ are described by the Josephson effect.
(Dr.) Dudley Allen Buck (1927–1959) was an electrical engineer and inventor of components for high-speed computing devices in the 1950s. He is best known for invention of the cryotron, a superconductive computer component that is operated in liquid helium at a temperature near absolute zero. Other inventions were ferroelectric memory, content-addressable memory, non-destructive sensing of magnetic fields, and writing printed circuits with a beam of electrons.
Superconducting logic refers to a class of logic circuits or logic gates that use the unique properties of superconductors, including zero-resistance wires, ultrafast Josephson junction switches, and quantization of magnetic flux (fluxoid). As of 2023, superconducting computing is a form of cryogenic computing, as superconductive electronic circuits require cooling to cryogenic temperatures for operation, typically below 10 kelvin. Often superconducting computing is applied to quantum computing, with an important application known as superconducting quantum computing.
