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Superconducting Flux-Flow Bipolar Diode

IP.com Disclosure Number: IPCOM000112816D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 241K

Publishing Venue

IBM

Related People

Brady, MJ: AUTHOR [+6]

Abstract

A number of three-terminal devices based on Josephson junctions and exploiting the solitary motion of the Josephson vortices have been proposed [1]. These devices suffer from very low output impedances and therefore have only a limited case. It is possible, although difficult, to use many such devices in series to boost the impedances and the voltages to eventually drive other electronic stages, but it is difficult. Clearly, it is desirable to be able to control the impedance via material parameters, while maintaining the speed and gain of the device. The motion of Abrikosov vortices in thin superconducting films can form a basis for such devices. The underlying idea is the electrical duality [2] between the transport of magnetic vortices and the transport of electrons and holes in a semiconductor.

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Superconducting Flux-Flow Bipolar Diode

      A number of three-terminal devices based on Josephson junctions
and exploiting the solitary motion of the Josephson vortices have
been proposed [1].  These devices suffer from very low output
impedances and therefore have only a limited case.  It is possible,
although difficult, to use many such devices in series to boost the
impedances and the voltages to eventually drive other electronic
stages, but it is difficult.  Clearly, it is desirable to be able to
control the impedance via material parameters, while maintaining the
speed and gain of the device.  The motion of Abrikosov vortices in
thin superconducting films can form a basis for such devices.  The
underlying idea is the electrical duality [2]  between the transport
of magnetic vortices and the transport of electrons and holes in a
semiconductor.

      Ideally, a superconductor of type I is a perfect diamagnet and
thus a flux insulator.  A thin superconducting film (or a type II
superconductor) admits magnetic field in a form of quantized
vortices, where a quantum of flux is <Phi sub O> = 2 mul <10 sup -7>
Gauss <cm sup 2>.  When a transport current J is applied, a vortex
feels a Lorentz force <F sub L> = J mul <Phi sub O>, with the sign
reversed for vortices and anti-vortices.  When a vortex is able to
move (is not pinned), it generates an electric field in the direction
of the current, E = B mul v, and thus dissipation or resistance.  In
the simplest model this resistance R = <R sub n> <H over <H sub c2>>,
where R sub n is the normal state resistance and <H sub c2> = <<Phi
sub 0> over <2 pi <xi sup 2>> is the upper critical field with the
superonducting coherence length &xi.  defining the core of the
vortex.  Or, the flux-flow resistivity can be written as <rho sub ff>
= n<Phi sub 0><mu sub v>, where the effective vortex mobility <mu sub
v> = <rho sub n>/<H sub c2> and n = B/Phi sub 0 is the vortex
density.

So the analogy with the semiconductor is as follows:  the vortices
and anti-vortices are equivalent to the electrons and holes, and the
conductivity &sigma.= ne&mu.  in a semiconductor becomes flux-flow
resistivity <rho sub ff> = n<mu><Phi sub 0> in a superconductor.

      Proposed is a superconducting device operating in a flux-flow
regime which is an electrical dual of a bipolar semiconducting p-n
junction rectifier.  The device consists of a narrow (~10-100
micron) strip of a thin (~ 300A) superconducting film with
very low pinning and a flux flow regime, which extends over a wide
temperature range.  The film can be an amorphous Mo&sub3.Si or
Mo&sub3.Ge for operation in liquid He (4.2 K) or it can be a thin
film of high temperature superconductor, such as YBaCuO, BiCaSrCuO or
TlCaBaCuO, suitably deposited to minimize pinning of vortices.  The
doping of the strip with vortices and anti-vortices is accomplished
with a control line (Fig. 1) symmetrically placed along the strip and
separated from it by a...