Browse Prior Art Database

Flexible Superconducting Quantum Interference Device

IP.com Disclosure Number: IPCOM000109983D
Original Publication Date: 1992-Oct-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 4 page(s) / 129K

Publishing Venue

IBM

Related People

Ketchen, MB: AUTHOR

Abstract

A technique is described whereby a superconducting micro-mechanical structure produces a low noise flexible SQUID, thereby providing a key element in micro-mechanical technology.

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This is the abbreviated version, containing approximately 52% of the total text.

Flexible Superconducting Quantum Interference Device

       A technique is described whereby a superconducting
micro-mechanical structure produces a low noise flexible SQUID,
thereby providing a key element in micro-mechanical technology.

      The use of the flexible superconducting quantum interferencce
device (SQUID) for certain applications, such as the measurement of
acceleration, can offer a new measure of sensitivity in the field of
integrated micro-mechanical sensors.  In other applications, such as
the measurement of force, pressure, flow, gas adsorption and
absorption, etc., in low and ultra-low temperature environments, the
flexible SQUID provides a new dimension in instrumentation.

      Prior art has directed considerable attention towards building
micro-mechanical resonant structures using silicon technology (1).
Various techniques have been used on single crystal, or
poly-crystalline Si, to fabricate a variety of beam, bridge and plate
configurations.  Pick-off electronics, typically relying on
capacitive transducers to detect position, are integrated into the
same substrate with micro-mechanical structures.  Either the absolute
deflection or the resonant frequency change of the structure becomes
a measure of the quantity of interest, such as acceleration,
pressure, or a mass change related to the adsorption or absorption of
a gas by the micro-mechanical structure.

      The concept described herein provides a superconducting micro-
mechanical structure where a cantilever beam arrangement is part of
the inductive loop of an ultra-low-noise DC SQUID.  The SQUID is
configured in such a way that the flux resolution of the SQUID is
transformed into a resolution in position of the cantilever beam.

      Figs. 1a and 1b show a simplified top and side view of the
flexible SQUID illustrating how much of the SQUID loop is configured
as a cantilever structure.  Fig. 2 shows the electrical configuration
of the SQUID.  IG is the gate current bias, IC is the control current
that is used to set the flux bias point of the SQUID and IB is
a DC current that is directly coupled to the SQUID loop.  The total
inductance of the SQUID loop is L, and the inductance of that portion
of the loop through which IB flows is MB.  The flux applied to the
SQUID by IB is MBIB, where MB is a reasonable fraction of L.  If the
loop bends slightly, such that its outboard portion over the hole in
the insulation moves by an amount Wt, then there is a change in the
applied flux da given by:

                            (Image Omitted)

where g1 and g2 are the superconducting penetration depths of the
ground plane and SQUID loop, respectively, and t is the distance from
the underside of the SQUID loop to the top surface of the
groundp...