NDLI: Moat-guarded Josephson SQUIDs

Content Provider	IEEE Xplore Digital Library
Author	Bermon, S. Gheewala, T.
Copyright Year	1965
Abstract	We report experimental investigations of a simple structure, called a moat, which significantly reduces the probability of flux-trapping in Josephson SQUIDs. Proper operation of Josephson logic and memory circuits requires that the SQUIDs be free of stray magnetic flux that may become trapped in the superconducting groundplane upon cooling through the critical temperature. The problem is particularly severe for so-called holey SQUIDs which rely on holes in the groundplane to obtain suitably large device inductances. Moats are rectangular channels in the groundplane surrounding the SQUID's which provide preferred sites for trapping flux, thus preventing such flux from coupling to the SQUID. We have measured the effectiveness of moats by monitoring the flux trapped in the moats and comparing it to the flux trapped in the associated SQUID as a function of applied field. The number of flux quanta in the moat is determined by measuring the shift of the threshold curve of a two-junction SQUID coupled to the moat. The data indicates that at fields on the order of a mG, moats reduce the sensitivity of holey SQUIDs to trapped flux by at least several orders of magnitude. As the chips are cooled through Tc, transient magnetic fields are produced in the metallic sample holder parts surrounding the chip by thermal-gradient-induced EMF's. The effects of such magnetic fields on the flux trapping behaviour of the SQUIDs are also reported.
Sponsorship	IEEE Magnetics Society
Starting Page	1160
Ending Page	1164
Page Count	5
File Size	724882
File Format	PDF
ISSN	00189464
Volume Number	19
Issue Number	3
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	1983-05-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	SQUIDs Magnetic field measurement Josephson junctions Magnetic circuits Magnetic flux Superconducting logic circuits Cooling Temperature Monitoring Semiconductor device measurement
Content Type	Text
Resource Type	Article
Subject	Electronic, Optical and Magnetic Materials Electrical and Electronic Engineering

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