Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1998-02-20
2001-09-04
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C505S846000
Reexamination Certificate
active
06285186
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a superconducting quantum interference device for detecting a very small magnetic field, current, voltage, electromagnetic wave and the like and, more particularly, to a superconducting quantum interference device having a high sensitivity and a low noise.
FIG. 7
shows a basic structure of a DC-SQUID which is one type of known superconducting quantum interference device formed using the prior art. A superconductive ring is formed by a washer coil
2
and a pair of Josephson junctions
1
connected to both ends thereof. A bias line
7
for supplying a bias current is connected between the pair of Josephson junctions
1
and to a central portion of the washer coil
2
and is routed to bonding pads
11
a
. The washer coil
2
includes a slit cover
3
for reducing stray inductance at a slit portion. In this structure, the bias line
7
is routed such that it surrounds the periphery of the DC-SQUID.
The DC-SQUID is a device used for converting a magnetic flux into a voltage whose output varies relative to the magnetic flux crossing a superconductive ring internally at a cycle of one flux quantum ((&PHgr;
0
: 2.07×10
−15
Wb). The higher the modulated voltage, the more sensitive the device.
In the structure shown in
FIG. 7
, a magnetic flux is produced by the bias current flowing through the bias line
7
. The magnetic flux couples to the DC-SQUID itself and also has an influence on the neighborhood thereof. The bias line
7
has significant influence because it forms a large ring.
FIG. 8
shows a configuration diagram of a superconducting quantum interference device wherein two DC-SQUIDs are integrated on a single substrate using the prior art. Bonding pads
11
a
are arranged in a row on one side of a substrate
12
to facilitate connection to a driving circuit. Each of the two sets of bonding pads
11
a
are provided close to each other. A bias current is applied to each of the DC-SQUIDs from a bias line
7
. In this case, a magnetic flux produced by the bias line
7
of one of the DC-SQUID couples to the other DC-SQUID. The SQUID
1
for detecting an external magnetic flux also detects the magnetic flux produced at the SQUID
2
by the bias current.
FIG. 9
is a view of a SQUID array configured using the prior art. A SQUID array is used for increasing a voltage modulated by DC-SQUIDs and impedance output by the same. A SQUID array is formed by connecting N DC-SQUIDs in series into a row to provide a modulated voltage which is N times that available with one DC-SQUID. In a SQUID array, offset components of magnetic fluxes crossing of the DC-SQUIDs must be nullified or equalized. When offset magnetic fluxes in the superconductive rings are not equal, the periods of magnetic flux-voltage characteristics of the DC-SQUIDs do not match, which makes it impossible to increase the modulated voltage efficiently.
In
FIG. 9
, the bonding pads hla are provided close to each other taking connection to a driving circuit into consideration. Since the SQUID
1
and SQUID
2
are surrounded by the bias lines
7
in different ways, the bias lines couple different amounts of magnetic flux. Therefore, the offset magnetic fluxes of all of the DC-SQUIDs are different, which disallows matching of magnetic flux-voltage characteristics and hence makes it difficult to increase the modulated voltage efficiently.
In a superconducting quantum interference device according to the prior art, a bias line for supplying a bias current to a DC-SQUID, a SQUID array or the like has been routed so as to surround the periphery thereof taking connection to a driving circuit into consideration. As a result, a bias line forms a large loop which couples an unnecessary magnetic flux into a superconductive ring of a DC-SQUID. There has been another problem in that when a plurality of DC-SQUIDs are integrated on the same substrate, interference occurs between magnetic fluxes produced by the bias currents of each other.
Further, in the case of a SQUID array wherein a plurality of DC-SQUIDs are connected in series, the amount of magnetic flux coupled by the bias lines varies between the DC-SQUIDs. As a result, it has been difficult to increase the modulated voltage efficiently because it has been impossible to match the period of the magnetic flux-voltage characteristics of each of them.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a bias wiring layer to cancel a magnetic flux produced by a bias current flowing through a DC-SQUID in order to suppress the generation of a magnetic flux due to a bias current flowing through a bias line.
It is a further object of the present invention to allow flexible arrangement of SQUIDs by the suppression of a magnetic flux produced by a bias current when a plurality of DC-SQUIDs are provided on the same substrate or when a SQUID array is formed.
REFERENCES:
patent: 5252921 (1993-10-01), Nakane et al.
patent: 5625290 (1997-04-01), You
patent: 5854492 (1998-12-01), Chinone et al.
patent: 0566499 (1993-10-01), None
patent: 64-021379 (1989-01-01), None
patent: 64-027671 (1989-02-01), None
patent: 8-334555 (1996-12-01), None
Adams & Wilks
Patidar Jay
Seiko Instruments Inc.
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