JPH06140679A - Dc-squid - Google Patents

Abstract

PURPOSE:To miniaturize a transformer, and shorten the distance to a SQUID ring, and achieve the equalization of transformer property by forming the transformer by a film, and providing it on the same substrate as a SQUID ring. CONSTITUTION:A SQUID ring 3 and a transformer are provided on a common quartz substrate 60. The SQUID ring 3 is made of a lower electrode 31, an insulating layer 34, an upper electrode 33, and a bridge 34 astride both surfaces of the upper electrode 33 and the lower electrode 31. Moreover, the transformer is fully made of a film, and has a four-layer structure. That is, it has an insulating layer 41, an Nb film 42, an insulating film 43, and an Nb film 44 in order starting with its innermost layer. Furthermore, the transformer can be made by patterning a film, using photolithography technology.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-SQUID used, for example, in biomagnetism measurement and ultra-fine magnetometer.

[0002]

2. Description of the Related Art In DC-SQUID, generally,
As shown in the modulation type circuit configuration example in FIG. 5, a measurement circuit called a magnetic flux lock circuit is used. In this circuit, the magnetic flux picked up by the pickup coil 1 and transmitted to the SQUID ring 3 via the input coil 2 is SQUID.
It is converted into a voltage by the D ring 3. This voltage signal is input to the amplifier 5 via the transformer 4, and then introduced to the integrator 7 via the phase detector 6. The output of the integrator 7 is SQUI via the feedback resistor 8 and the modulation coil 9.
It is fed back to the D ring 3.

Further, an alternating current from the oscillator 10 is supplied to the modulation coil 9, and the alternating current is supplied to the phase detector 6, and the phase detector 6 causes the SQUID ring 3 after amplification by the amplifier 5. The output voltage of is detected by phase.

By performing such AM modulation to demodulation, the influence of noise of the amplifier 6 is removed. Transformer 4
Has the function of matching the low output impedance of the SQUID ring 3 with the high input impedance of the amplifier 6 and amplifying the signal.

In the above DC-SQUID,
As shown in FIG. 6, the SQUID ring 3 is conventionally formed by patterning an Nb thin film together with the input coil 2 on a substrate 50 such as quartz using a photolithography technique.

On the other hand, conventionally, the transformer 4 is generally formed by winding a Nb-Ti wire or a Cu wire around a cylindrical body such as Bakelite as illustrated in FIG.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
According to C-SQUID, the transformer 4 becomes large, which is a factor that hinders downsizing of the device.
The distance between the UID ring 3 and the transformer 4 is long, and DC
-It is also a cause of noise on the output of the SQUID. Further, since the transformer 4 is wound by hand, it is difficult to make the characteristics uniform, and further, it takes a lot of time to connect the SQUID ring 3 and the transformer 4.

The present invention aims to solve such problems all at once.

[0009]

To achieve the above object, in the DC-SQUID of the present invention, the transformer 4 is formed of a thin film and is formed on the same substrate as the SQUID ring 3. Characterized.

[0010]

The transformer can be formed by patterning a thin film using the photolithography technique. Therefore, this thin film transformer is
Smaller size and SQ when formed on the same substrate as the ID ring
The distance between the UID ring and the transformer can be shortened, the characteristics can be made uniform, and the connection with the SQUID ring can be easily achieved at once.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a SQUID which is a main part of an embodiment of the present invention.
FIG. 6 is a cross-sectional view showing a structure near a ring 3 and a transformer 4. In this embodiment, the overall circuit configuration is the same as that shown in FIG.

The SQUID ring 3 and the transformer 4 are formed on a common quartz substrate 60. In this example, the SQUID ring 3 includes an insulating layer 32 on the lower electrode 31.
The upper electrode 33 is formed via the bridge 34 so as to extend over the surfaces of both the upper electrode 33 and the lower electrode 31.
It is a so-called quasi-plane type DC-SQUID ring having a structure formed therein, and its structure is well known, and a more detailed description thereof will be omitted here.

The transformer 4 is entirely formed of a thin film and has a four-layer structure. That is, the outer peripheral surface of the insulating layer 41 made of SiO ₂ or the like provided in the innermost layer is entirely covered with the Nb thin film 42, and these form the superconducting bobbin 40. The outer peripheral surface of the Nb thin film 42 is further entirely covered with an insulating layer 43, and primary and secondary windings formed by patterning the Nb thin film 44 are formed around the insulating film 43. The winding structure of the Nb thin film 44 has a structure as shown in a perspective view in which only the winding is extracted in FIG. 2, and has a spiral structure equivalent to that of the conventional transformer shown in FIG. Both ends of the secondary and secondary windings are thin-film wiring 45 formed on the surface of the substrate 60,
Via S46, they are connected to the SQUID ring 3 and the amplifier 6, respectively.

According to the structure of the embodiment of the present invention,
The transformer 4 is formed of a thin film, and the SQUID
Since it is formed on the same substrate as the ring 3, the transformer 4 is downsized and the distance from the SQUID ring 3 is greatly shortened. Further, since the transformer 4 is formed by using a photolithography technique as described later, its characteristics are made uniform, and a wiring for connection with the SQUID ring 3 is simultaneously formed in these manufacturing steps. It becomes possible.

Further, a point to be noted in the above-mentioned embodiments is that a winding using the Nb thin film 44 which is also a superconductor is provided around the superconducting bobbin 40 using the Nb thin film 42. The inductance is large, the mutual inductance between the primary side and the secondary side is large, the coupling coefficient can be increased to 0.9 or more, and the voltage amplification factor can be increased. .

Next, the manufacturing method of the embodiment of the present invention having the above structure will be described. 3A to 3C are explanatory views showing the steps in order with schematic cross-sectional views of the element. First,
As shown in (A), a Nb thin film is formed on the surface of the quartz substrate 60 and patterned by photolithography to form the lower electrode 31 of the SQUID ring 3 and the lower portion 44a of the winding of the transformer 4. . At this time, although not shown, the winding of the transformer 4 and the SQUID
The wiring for connection with the ring 3 and the like are formed at the same time.

Next, by forming an insulating film from above and patterning it, as shown in FIG.
The insulating layer 32 of the D ring 3 and the lower portion 43a of the insulating layer 43 between the bobbin 40 and the winding of the transformer 4 are formed.

After that, an Nb thin film is formed from above and patterned to obtain SQU as shown in (C).
The upper electrode 33 of the ID ring 3 and the bobbin 4 of the transformer 4
A lower portion 42a of the Nb thin film 42 that covers the outer periphery of 0 is formed.

Next, an insulating film is further formed from above and patterned to form the innermost insulating layer 41 of the transformer 4 as shown in (D). Then on it
By forming and patterning Nb thin film, (E)
As shown, the bridge 34 of the SQUID ring 3 and the lateral and upper portions 42b of the Nb thin film 42 that covers the outer circumference of the bobbin 40 of the transformer 4 are formed.

Next, an insulating film is further formed thereon and patterned, and as shown in (F), a lateral portion and an upper portion 43 of the insulating layer 43 between the bobbin of the transformer 4 and the winding wire.
b is formed.

Finally, an Nb thin film is formed and patterned from above, and the side portion and the upper portion 44b of the winding of the transformer 4 are formed as shown in FIG.
The SQUID ring 3 and the transformer 4 having the structure shown in FIG.

In the above embodiments, the winding of the transformer 4 is provided around the superconducting bobbin 40 in a spiral shape. Of course, the winding may be formed directly around the insulating layer 41.

The winding of the transformer 4 is Nb as described above.
Not limited to the superconductor thin film including, but may be a normal conductor thin film such as Au. Further, as the structure of the transformer 4, in addition to the structure of the above-described embodiment, as shown in a conceptual perspective view in FIG.
A planar structure having the primary wiring 402 and the secondary wiring 402 may be used.

[0024]

As described above, according to the present invention,
The transformer interposed between the SQUID ring of DC-SQUID and the amplifier is formed of a thin film, and
Since it is formed on the same substrate as the QUID ring, the size of the transformer is reduced, the distance between the transformer and the SQUID ring is shortened, the characteristics of the transformer are made uniform, and the SQUI
Connection wiring work between the ID ring and the transformer can be simplified.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure in the vicinity of a SQUID ring 3 and a transformer 4 according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a winding portion of the transformer 4 in an extracted manner.

3 is an explanatory view of a manufacturing process for obtaining the structure of FIG.

FIG. 4 is a perspective view conceptually showing the structure of a transformer according to another embodiment of the present invention.

FIG. 5 is an overall circuit configuration diagram of a DC-SQUID to which the present invention is applied.

FIG. 6 is an SQUI used in a conventional DC-SQUID.
External view showing the structure of the D ring

FIG. 7 is an external view showing the structure of a transformer used in the conventional DC-SQUID.

[Explanation of symbols]

 3 SQUID ring 31 Lower electrode 32 Insulating layer 33 Upper electrode 34 Bridge 4 Transformer 40 Superconducting bobbin 41 Insulating layer 42 Nb thin film 43 Insulating layer 44 Nb thin film (primary and secondary winding)

Claims (1)

[Claims] 1. A DC-SQUI that guides the output of a SQUID ring made of a superconductor thin film having two Josephson junctions in a superconducting loop to a measuring circuit via a transformer.
In ID, the transformer is formed of a thin film,
A DC-SQUID formed on the same substrate as the SQUID ring.