Double Edge Structure for High Temperature Weak Links

Double Edge Structure for High Temperature Weak Links

      Disclosed is a means for fabricating
superconductor-normal-superconductor junctions having normal metal
bridges and high transition temperature electrodes.  Fine control of
two critical parameters, the separation of the superconducting
electrodes and the resistance of the two contacts between the metal
bridge and the superconducting electrodes, is provided by this
invention.

      Superconductor-normal metal-superconductor weak links with
noble metal bridges have proven to be the most reproducible high  T
sub c devices.  However, these devices have an extremely short bridge
length (typically around 20 nm), and the successful devices have been
made only by using an edge geometries, with this geometry, junction
length is controlled by step heights and edge angles.  Somewhat
reproducible devices have been made with this technique, but their
performance can only be understood if it is assumed that the a thin
and discontinuous superconducting film exists on the substrate edge
itself.  Such a process is unlikely to have manufacturing potential.

      The disclosed structure is illustrated in the Figure.  It is a
double edge structure that provides identical contacts to the ab
planes of c-axis oriented superconducting electrodes.  The structure
consists of a sandwich of superconductor S1, insulator I1,
superconductor S2, and insulator I2.  A sloped edge is formed by ion
milling with either the top in...