Voltage Contrast Method for Isolating Defects in High-TC Superconducting Lines
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Jenkins, KA: AUTHOR [+2]
Disclosed is a method for finding defects in high critical temperature ("high-Tc") superconductors, using a scanning electron microscope (SEM) modified for low temperature operation, and the application of voltage contrast.
Voltage Contrast Method for Isolating Defects in High-TC
a method for finding defects in high
critical temperature ("high-Tc") superconductors, using a scanning
electron microscope (SEM) modified for low temperature operation, and
the application of voltage contrast.
fabricating "high temperature", or high-Tc,
superconductors suggests the possibility of using these materials for
wiring and interconnecting low temperature electronic circuits.
This, in turn, requires the patterning of films of the materials into
narrow lines with widths on the order of microns. For circuit
applications, it is necessary that these lines be free of defects
which prevent their becoming superconducting below their critical
temperature. This requires electrical testing. However, testing of
the terminals of a long or complex wiring pattern will not, in
general, identify poor quality or defective lines. To find and
diagnose localized faults, the voltage at internal nodes must be
measured. Because the circuits are at temperatures near to that of
liquid nitrogen (77oK), such measurements cannot be done with simple
proposes to use voltage contrast and a low
temperature electron microscope for such measurements. The mechanism
of voltage contrast in the scanning electron microscope makes it
possible to visualize voltage differences on conducting lines of a
circuit. Using a scanning electron microscope (SEM) which is
modified to cool a specimen circuit to liquid nitrogen temperature,
voltage contrast can be used to visualize the voltage on lines of
high-Tc materials above and below the critical temperature. The
application of voltage contrast in a specialized SEM results in a
unique diagnostic tool for use with patterned high-Tc materials.
Faults on a
wiring test site can be located with this
instrument by examining the secondary electron images of the specimen
while currents are flowing through it. In the normal, resistive
(room temperature), state, currents lead to voltage drops through the
wiring which can be seen in the SEM as voltage contrast. Below the
critical temperature, all resistance should vanish...