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Temperature-Selectable Superconductive Wiring

IP.com Disclosure Number: IPCOM000111727D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 144K

Publishing Venue

IBM

Related People

Dinger, TR: AUTHOR [+3]

Abstract

Disclosed is a wiring scheme which permits the switching of circuit elements through the manipulation of operating temperature and the transition temperature of high temperature superconducting wiring elements. The utility of this invention results due to several peculiarities of high temperature superconductors: 1) in their normal state, above the superconducting transition temperature, (T sub c), they possess relatively high electrical resistivities [1], and 2) their transition temperatures vary quite widely depending on, among other things, their chemistry [2]. This last attribute provides a means by which the programmable wiring switch's turn-on temperature (T sub c) can be manipulated during the fabrication stage.

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Temperature-Selectable Superconductive Wiring

      Disclosed is a wiring scheme which permits the switching of
circuit elements through the manipulation of operating temperature
and the transition temperature of high temperature superconducting
wiring elements.  The utility of this invention results due to
several peculiarities of high temperature superconductors: 1) in
their normal state, above the superconducting transition temperature,
(T sub c), they possess relatively high electrical resistivities [1],
and 2) their transition temperatures vary quite widely depending on,
among other things, their chemistry [2].  This last attribute
provides a means by which the programmable wiring switch's turn-on
temperature (T sub c) can be manipulated during the fabrication
stage.  Advantage can be taken of these behaviors in the design of
thin-film superconducting circuitry in which the wires themselves are
used as switches which turn on (low resistance) below T sub c and off
(high resistance) in the normal state above T sub c.

      It has been recognized that conduction paths can be defined in
high temperature superconducting thin films by deposition of a
previously patterned layer of Si sub 3 N sub 4 which reacts
chemically with the high T sub c film at high temperatures (annealing
temperatures) to effectively "poison" the film, thus eliminating
superconductivity.  The method of suppressing T sub c, which is
described here, draws on this approach but utilizes only enough Si
sub 3 N sub 4 to lower T sub c, not eliminate it entirely.
Alternatively, a variety of "poisoning" elements may be utilized to
achieve this end, namely, Al, Fe, Ni, Co, Zn, etc.  These results
have been documented in the technical literature in a large number of
citations which will not be reproduced here.  By varying the amount
of Si which enters the high temperature superconducting oxide, a
hierarchy of transition temperatures can be established.  This
effectively allows different circuits within a given network of
superconductive wiring to turn on at a predescribed temperature which
is determined by the level of Si doping in the wiring.  Similar
schemes can be envisioned which utilize conventional superconductors
in a manner consistent with that described above.  Such schemes would
not permit operation to high temperatures, would not provide the ease
of T sub c variation by doping, and, generally would not provide the
large change in resistivity upon transition to the normal state that
the high temperature superconductors do and which is required to
provide the switching action.

      Fig. 1 shows an example of thin film processing steps required
to produce a superconducting cuprate wire with T sub c equals T sub
cl.  For the cuprate superconductors, T sub cl can be as high as 125
K for 'Tl' sub 2 Ba sub 2 Ca sub 2 Cu sub 3 O sub 10 with no doping.
The initial blanket film of cuprate superconductor is deposited onto
an appropriate substrate (Fig. 1b)...