JPH0227280A - Superconductor quantum interference element - Google Patents

Abstract

PURPOSE:To enhance measuring accuracy by distorting a magnetic field to be measured by mounting a superconductor ring containing two Josephson elements and the wiring formed from a non-magnetic normally conductive substance connected to said superconductor ring. CONSTITUTION:A part of the second insulating layer 12 covering a main coil 3 is contracted to expose a part of the coil 3 and wiring 19 is connected to the coil 3. The whole of elements is immersed, for example, in liquid helium along with a substrate 2 to be cooled and a part formed of a superconductive material is transferred to a superconductive state. The magnitude of a superconductor current made possible to flow to a superconductor ring consisting of the coil 3, an upper electrode 5, a connection layer 11 and a connection electrode 22 as is convensional without generating potential becomes a function of interlinking magnetic flux and changes in a cycle of a magnetic flux quantism phi0. Corresponding to this, an I-V characteristic also changes in the cycle of the quantum phi0. The magnetic flux density in the vicinity of the coil 3, for example, when a uniform magnetic field (a) to be measured is incident to a diagonally downward direction from an X-axis direction can be accurately measured without distorting the magnetic field even when the elements are placed in the magnetic field to be measured, because wirings 18, 19 are formed from a non- conductive material.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a superconducting quantum interference device used as a highly sensitive output meter.
mrnterrerence Device, abbreviated as 5
This is a book about C-8QUID, which is driven using DC bias current.

[Conventional technology]

Figure 8 is a plan view showing the conventional DC-8QUID, Figure 9
The figure is an enlarged plan view of the Josephson element forming portion +11 surrounded by the dotted line in FIG. 8, and FIG. 10 is A- in FIG.
It is a sectional view between B. In these FIGS. 8 to 10, a substrate (2) formed of 0, for example, 3i, 5i02, etc.
The surface is provided with the following: That is, (3)
is the main coil, (4) and (5) are the upper electrodes.

(51, +71 are the main coil +31 and the upper electrode +41.
These are Josephson elements formed between +51 and +51, respectively. Shunt resistors (8) connected to each other by wiring IQ3.

The central portions of (9) are both covered with a first insulating layer aO. The upper electrodes (4) and (5) are connected to the connection layer an
Connected to wiring 1 f13 by this wiring! The tip of α1 is a bonding pad fi9. Insulation between the main coil (3) and the connection layer C1υ is realized by the second insulating layer α2. On the other hand, a part of the main coil (31) extends as a wiring 141, and the tip thereof becomes a bonding pad αe.Here, a shunt resistance +81.
+91 is made of, for example, MO or Au, and the first insulating layer and the second insulating layer α2 are made of, for example, sio.
.

5j02, is made of an insulator such as Nb2O5. Furthermore, the main coil (3), the upper electrode 141.1
51. The connection layer (Ill, wiring ■ α3. Wiring 1 + 14. Bonding pad 9. αe is formed of a metal-based material such as PB gold alloy Nb, or a ceramic-based superconducting material such as Y-Ba-Cu-0, In particular, the main coil (31), the upper electrode (41° (5), the connection layer aυ, and the wiring 1+13 form a single superconducting ring.

As described above, the basic structure of DC-8QUID is a superconducting ring including two Josephson elements. Here is an example of the dimensions of each part: The size h of the board (2)
4wx4m, main coil (outer diameter of 31 is 300mx300
/Am, line width is 15 μm, and film thickness is 200 nm.

The size of Josephson elements (4) and (5) is 4JtmX
411rn.

Wiring■α3. The line width of the wiring 104 is 50 μm, and the film thickness is 20 μm.
0 nm, and the bonding pad α9. The size of αe is 300IJrn×300μm, and the film thickness is 300nm.
It is.

Next, the operation will be explained. The entire device, together with the substrate (2), is immersed in liquid helium to cool it and transform it into a superconducting state. Inside the superconductor, electrons form pairs called electron Cooper pairs. Due to the movement of this Cooper Bear, the Josephson elements (61, (71) each have a phase difference of θ1.
DC Josephson current depending on θ2 11. I2 can be examined respectively. Here θ,.

θ2 is the phase difference between the superconductors forming the main coil (31) and the upper electrode (41), the main coil +31 and the upper electrode (5
) is the phase difference of the superconductor forming the superconductor. From this, the superconducting current I that can be passed between the bonding pads becomes as shown in equation +11.

1 = 11 + 12 = IC(sinθ1 +3
10#2) Here, Ic is a Josephson element +61.
(These are the critical current values for each of 71.

On the other hand, from the quantization conditions of fluxoid in the superconducting ring, it is found that the magnetic flux φ interlinking with the superconducting ring (31 and 01.θ
2, a relationship such as the +21st equation holds true.

φ+(”')(#1-02)=n<Ilo (n:j
I number) -1212π However, I0 is an 8-bundle quantum, and its size is 2.07
It is X10 wb. From equation +11 and equation (2), θ
When 1-02 is deleted.

becomes. From this, the maximum value 1 m of the superconducting current that can be passed without generating a potential difference between the bonding pads a and αθ is expressed by equation (4), which is a function of the six interlinkage bundles φ.

From equation (4), 1m has a maximum value of 2fc when φ=nφ0.

The minimum value is 0 when φ=(n+1/2)I0.

It can be seen that the $ flux quantum φ0 changes with respect to φ. However, this means that the inductance of the superconducting ring is 0.
This is a case of 0, and since KFi actually has a finite inductance, the minimum value will not be 0.

Figure 11 (a) shows such current-voltage (1-v) characteristics of DC-8QUID, where r - v
The characteristic is φ=nφ0. When φ=(n+1/2)I0, each curve becomes like the curve 0 in FIG. A DC bias current Ib that is slightly larger than the critical current value ICI at the time of wiring! α3.
When the potential difference V between S is measured, it changes as shown in FIG.

Therefore, this DC-8QUIDf is placed in the magnetic field to be measured,
Changes in the field to be measured are captured as changes in the magnetic flux interlinking with the superconducting ring, converted to voltage, and output.

By the way, superconductors have a completely diamagnetic property called the Meissner effect, and it is a well-known fact that external flux cannot penetrate superconductors. For this reason, 9. For example, from the X-axis direction in FIG.
f! When the field A to be measured is incident, the magnetic flux density (S field strength) distribution near the main coil (3rd column) is distorted as shown in Fig. 1a, if shown along the cross section A-H in Fig. 8. Wiring (1)'j and wiring laJ used to increase the bias current "b" and to detect the voltage generated in the superconducting loop
This is because it has a completely diamagnetic property due to the Meissner effect. Problem 1] As mentioned above, in the conventional DC-8QUID, the wiring @TO3 and the wiring Iα4 made of superconductors are arranged near the main coil (31) that detects the magnetic field to be measured, which distorts the magnetic field to be measured. There was a problem in that highly accurate 8-field detection was not possible.Specifically, when a magnetic field is incident from the X-axis direction in Figure 8, the magnetic flux reflected by wiring ff13 interlinks with the superconducting ring. There was a problem in that the sensitivity increased.

This invention was made to solve the above-mentioned problems, and aims to obtain a DC-8QUID that can accurately measure a magnetic field to be measured without distorting it.

[Means for solving assignments]

In the superconducting quantum interference device according to the present invention, wiring connected to a superconducting ring for supplying a bias current and detecting an output voltage is formed of a non-magnetic normal conductive material.

[Effect]

In the superconducting quantum interference device according to the present invention, the wiring connected to the superconducting ring is formed of a non-magnetic normal conductive material.
There are no factors that distort the magnetic field to be measured, such as the Meissner effect.
The magnetic field to be measured can be measured with high precision.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a plan view showing DC-5QU10 which is an embodiment of the present invention, FIG. 2 is an enlarged view of the Josephnon element forming portion αn surrounded by the dotted line in FIG.
FIG. 3 is a sectional view taken along dotted line E-F in FIGS.

(2) to 0 are those explained in the conventional example above. a
S is, for example, Au or Cu.

Wiring formed from non-conductive normal conductive materials such as A/! .

is is a wiring I formed of a non-conductive normal conductive material. Here, a part of the second insulating layer side covering the main coil (3) is reduced compared to the conventional embodiment, and the main coil 13+
Part of? Cl5Fi in Figure 2 shows the case where it is connected to the wiring 1 (llif main coil (31).
This is a connection electrode, and is connected to the shunt resistors (8), (9) and the connection layer a9, similar to the wiring (2) α5 in the conventional embodiment. This connection electrode 123 has a shunt resistance of +81
．． In order to ensure the connection with +91, it is made of the same superconducting thin film as the main coil (3). Wiring 1 aS is connected to the above connection electrode (3). ■, 1211 are the bonding pads connected to the ends of the wiring tns and wiring [9], respectively. - For example, the wiring 1tll and the wiring 1 (the line width of 19 is 50 μm and the film thickness is 900 nm, and the bonding pads ■, The size of crt is 300μ
m×300 μm, and the film thickness is 300 nm.

Next, the operation of the DC-8QUID according to the present invention will be explained. The entire device, together with the substrate (2), is cooled by immersing it in liquid helium, etc., and the portion formed of the superconducting material is transformed into a superconducting state. As before, the main coil (
3), upper electrode (41, (51, connection layer all).

The quantization conditions for the superconducting ring fluxoid composed of connected 5ciz are satisfied, and the magnitude of the superconducting current that can flow through the superconducting ring without creating a potential difference is the interlinking 6 flux φ as shown in equation (4). It becomes a function of , and changes with the period of TB East quantum φ0. Correspondingly, the H-v characteristic also changes with the period φ0. FIG. 4 (Bonding pad 12 of DC-8QUID according to the invention of al.
The I-V% characteristics between 9 and 1 curve G1 curve H are each φ
=nφ0. This corresponds to the 1-v characteristic when φ=(n+1/2)φ0. Unlike the conventional case shown in FIG.
(Resistance exists in the range of IC or I<IC2.

This is because the wiring 1tll and the wiring (1) 9 are formed of a normal conductive material, and the resistance value thereof is at most 1Ω. 1b> By flowing a DC bias current 11) IC1, an output voltage having a period of φ0 for the interlinkage magnetic flux φ is obtained as in the conventional case. Next, as an example,
FIG. 3 shows the field flux density (magnetic field strength) distribution in the vicinity of the main coil (3) when the outside of the can to be measured is incident diagonally downward from the axial direction with respect to the plane of the paper. wiring! α9. Wiring 1a! Since I is made of a non-maternal normally conducting material, even if the element is placed in a magnetic field to be measured, the magnetic field can be accurately measured without distorting it. Here, the strength of the magnetic field to be measured is B,
Main coil (31, upper electrode (41° (51, connection layer a1
1. The area of the superconducting ring composed of the connecting electrodes is S
, the plane containing this superconducting ring.

In other words, the angle θ between the substrate (2) and the magnetic field to be measured is
When determined as shown in the figure, a relationship such as the formula (51) is established between φ and B, and the DC-8QUID operates as a vector sensor with respect to an external magnetic field.

φ=B・sinθ ・・・・・・・・・
(5) It would be convenient as an a-force meter if linearity between input and output could be maintained over a wide range of 6 inputs, which corresponds to many cycles of partial pressure of φ0, but it is necessary to maintain linearity between input and output. KD
When using the C-8QUID as a magnetometer, a drive circuit as shown in FIG. 6 is often used. This drive circuit is called the Flux-LockedLOOp circuit9.
For example, Review of ScientificIn
This is a well-known method whose detailed explanation is described in pages 952 to 957 of Strument Vol. 55.19114. In Figure 6, it is a direct current source, Q
aFi oscillator, ■ is a preamplifier, ■ is a phase detector, ■ is an integrator, ■ is a feedback resistor, and 019 is a modulation feedback coil magnetically coupled to the main coil (3). Next, the operation of the drive circuit shown in FIG. 6 will be described. A bias current is passed from a DC current source (2), and then a sinusoidal modulated magnetic flux of, for example, frequency f=IQOKHz is applied from an oscillator @ via a modulation feedback coil (2). Here, φ=nφ0 and DC-8QUID
If the operating point of is set to 1 or 1 in FIG. 4(b), the bonding pad ■.

The frequency of the output voltage generated between l2f1 is 2f.

Also, if the operating point is at the point, it is in phase with the modulation signal and the frequency is f.
voltage is output. Conversely, if the operating point is at the L point, a voltage with a frequency of f and a phase opposite to the modulation signal is output. The output voltage having such characteristics is amplified by a preamplifier (2) and then phase detected at a frequency f using a 0-phase detector (2). The output of the phase detector ■ is integrated by the integrator ■, and the feedback voltage iff flowing through the feedback resistor ■ is sent from the modulation feedback coil ■ to DC-8Q.
Negative feedback is given to UID. Due to this negative feedback, the operating point is always fixed at the working point or FiJ point, that is, the maximum or minimum position, and an output proportional to the amount of change in the magnetic field to be measured can be obtained as a potential difference generated across the feedback resistor. The above is the operating principle of this drive circuit. For example, if the modulation feedback coil (2) is formed integrally as a strip line on the second insulating layer (α) covering the main coil +31 as shown in FIG. The positional relationship with the main coil (3) is always kept constant against disturbances such as vibration, and the mutual inductance between the main coil (3) and the modulation feedback coil ■ is stabilized, improving the reliability of the measurement system. do.

As an example, this stripline structure.

Main coil (line width of 31 is 15 μm, film thickness is 200 nm,
The second insulating layer 13 has a thickness of 5QQnm, the modulation feedback coil 4 has a line width of 5 μm, and a thickness of 900 nm.

Note that 2 and C3n are bonding pads connected to the tip of the modulation feedback coil 2. - As an example, its size is 300 μm x 300 μm, and the film thickness is 300 nm.
It is m. Conventionally, the modulation feedback coil (2) was formed of the same superconducting material as the wire maintenance part (an) in order to facilitate the manufacturing process. For this reason, there was a problem in that the magnetic field to be measured interlinked with the main coil (3) was distorted due to the complete diamagnetism caused by the Meissner effect. , A/,
If it is made of a non-maternal normally conducting metal such as Au, the magnetic field to be measured can be measured with high accuracy.

Furthermore, for the purpose of facilitating the manufacturing process, bonding pads aS, αe, and ■, have conventionally been formed of any superconducting material. For this reason, a bonding pad with completely diamagnetic properties due to the Meissner effect, for example 4 (
1) Placed near the main coil (3) on the m x 4 fl board (2) and wired! It distorted the magnetic field to be measured in the same way as α3 and wiring iaa. If these bonding pads are made of a non-maternal normally conducting metal such as Cu, Al/Au, etc., the influence of the Meissner effect is eliminated, and the magnetic field to be measured can be measured with high accuracy without being distorted.

〔Effect of the invention〕

As explained above, the DC-8QUID according to this invention
Since the wiring a connected to the superconducting ring of the DC-8QUID is formed of a non-maternal normal conductive material such as AJ+Cu or Au, the magnetic field to be measured can be measured accurately without being distorted. In addition.

Modulating feedback coil magnetically coupled to a superconducting ring.

If the wiring and the bonding pad for distributing power to the tip of the modulation feedback coil are similarly made of a non-maternal normal conductive material, there is an effect that measurement can be carried out with even higher accuracy.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a DC-8QUID which is an embodiment of the present invention, FIG. 2 is an enlarged plan view of the Josephson element forming portion aη in FIG. -1 to E-1 and the measured output field strong variation distribution diagram to E-1.
The figures show an example of the incident angle of the magnetic field to be measured in the above embodiment, Fig. 6 is a configuration diagram of the Flux-Locked LQOT (Flux-Locked LQOT) drive circuit, and Fig. 7 is a plan view of the DC-8QUID according to the further invention of the present invention. Figure 8 shows the conventional DC-5
A plan view of the QUID, FIG. 9 is an enlarged plan view of the Josephson element forming portion +11 in FIG. 8, and FIG. 10 is a sectional view between A and B in FIG. The intensity distribution diagram, FIG. 11, is an illustrative diagram of the current-voltage characteristics and output voltage characteristics of the conventional DC-8QUID. In the figure, (3) is the main coil, and 141 and 151 are the upper electrodes. 161, +71 is a Josephson element, α9 is a connection layer,
■ is the connection electrode, α・ is the wiring! , α9 is the wiring seal, ■, 2
+1 is bonding pad, ■ is modulation feedback coil, 3
m, (Ill is a bonding pad. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] (1) A superconducting ring including two Josephson elements,
A superconducting quantum interference device comprising: a wiring formed of a non-magnetic normal conductive material connected to the superconducting ring. (2) A superconducting quantum interference element according to claim (1), comprising: a modulation feedback coil formed from a non-magnetic normal conductive material magnetically coupled to a superconducting ring. . (3) A bonding pad formed of a non-magnetic normal conductive material connected to a wiring connected to a superconducting ring or a tip of a modulation feedback coil is provided. The superconducting quantum interference device described in (2).