Browse Prior Art Database

Shielded Thin Film Squid System

IP.com Disclosure Number: IPCOM000049459D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 63K

Publishing Venue

IBM

Related People

Ketchen, MB: AUTHOR [+3]

Abstract

A thin film SQUID (Superconducting Quantum Interference Device) system capable of operating in both high and low magnetic fields by means of on-chip shielding is disclosed. Nb thin films are used in the following description as the typical superconductor, although other metals can be used. Nb has a high shielding capability and rugged Josephson devices can be fabricated from it.

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Shielded Thin Film Squid System

A thin film SQUID (Superconducting Quantum Interference Device) system capable of operating in both high and low magnetic fields by means of on-chip shielding is disclosed. Nb thin films are used in the following description as the typical superconductor, although other metals can be used. Nb has a high shielding capability and rugged Josephson devices can be fabricated from it.

In Fig. 1, a cross sectional view of the basic vertical structure 1 is shown. The SQUID system 2 itself contains Josephson junctions, shunt resistors, a coupling coil which couples signals from an outside experiment into the SQUID and possibly modulation and other biasing circuitry. A single overlaying Nb film 3 for shielding purposes is shown in Fig. 1. However, multilayering of the shielding film 3 may also be used, as shown in Fig. 2. Leads to the SQUID and its coupling coil (modulation circuit also) must be brought through the structures of Figs. 1 and 2. Insulator via holes may be used through the Nb films, or leads can be brought directly through or along insulators I and/or II. An example is shown in Fig. 3 wherein leads 4 are sandwiched between insulators I and II.

A thermal switch is also provided in the coupling circuit for cases in which a large magnetic field is applied. If SQUID system 1 (configured, for example, as a magnetometer with a pick-up loop outside of the shielded region connected to the SQUID's coupling coil) is initially cooled in a low magnetic field, a large circulating current will result in the input circuit when a high magnetic field is applied. This current could lead to nonlinearity and hysteresis in the SQUID response as a result of induced flux trapping phenomena. If a portion of the input circuit is maintained normal with a thermal switch as the field is applied, no persisten...