JPH0773133B2 - SQUID - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to SQUIDs having a remarkably high magnetic field resolution.

[0002]

2. Description of the Related Art SQUID is a high-sensitivity magnetic sensor using a Josephson junction, which utilizes quantum interference effect to reduce magnetic flux quantum φ ₀ (1.5 × 10 ⁻¹⁵ Wb) to 1 / 100,000.
The magnetic flux of is converted into a voltage and measured. Therefore, such a SQUID is useful for measuring weak magnetism, and is applied to biomagnetic measurement, physical constant measurement, nondestructive inspection, and the like. Among them, the application to biomagnetic field measurement is a big driving force in the applied research of superconductivity. For example, the QRS wave of the heart and the EEG of the electroencephalogram if a special magnetic shield is applied.
It is known that D can be easily detected.

There is one Josephson junction in this SQUID
There are two rfSQUIDs and two dcSQUIDs,
The area of the washer portion was as small as about 0.1 mm ² . This is SQUI using Nb or NbN
This is because, in D, it was considered that when the washer area was increased, the magnetic flux noise was increased.

[0004]

However, in the conventional SQUID as described above, since the magnetic field resolution of the SQUID itself is not excellent, it has to be used in combination with the magnetic flux transformer. In addition, this magnetic flux transformer has a complicated structure, requires an extremely advanced technique especially for production using a high temperature superconductor, and has a low yield.

[0005]

The present invention has been proposed in view of the above, and has a washer portion formed of an oxide superconductor thin film, a hole portion formed substantially in the center of the washer portion, and a high temperature SQUID including at least one Josephson junction formed of a superconductor thin film and a slit provided from the Josephson junction toward the outer circumference
And the area of the washer part is 25 to 1000 mm.
It is related to SQUID characterized by being ² .

The washer portion in the SQUID of the present invention is not particularly limited in its shape, but it is desirable that it is a square, a rectangle close to a square, or a circle. The area is 25 to 100 as described above.
It is 0mm ² and enhances the effect of magnetic flux concentration, and the conventional SQUI
The magnetic flux resolution can be dramatically improved 10 to 100 times or more as compared with D. And the area is 2
If it is smaller than 5 mm ² , the above-mentioned magnetic flux concentration effect is low and sufficient magnetic field resolution cannot be obtained. Also, the area is 10
If it is larger than 00 mm ² , the position resolution will be reduced. Therefore, for example, it is desirable that the area of the washer portion for maintaining the above effect stably regardless of its shape is in the range of 25 to 1000 mm ² ,
Furthermore, it is even more desirable to set it to 100 to 400 mm ² .

On the other hand, the hole portion in the SQUID of the present invention is not particularly limited in its shape, but it is desirable that the hole portion be a square, a rectangle close to a square, or a circle like the washer portion. The area is preferably ⁴ to 2000 μm ² , and the area is 2
If it is larger than 000 μm ² , the inductance of the SQUID itself increases and the SQUID output voltage decreases, so that the magnetic field resolution decreases. If the area is smaller than 4 μm ² , the amount of trapped magnetic flux is small and the magnetic field resolution is reduced. Therefore, for example, the area of the hole portion for maintaining the above effect stably without depending on its shape is 10
It is desirable in the range of 0~2000μm ^2, more and even more preferably to 100-400 ^2.

The SQUI of the present invention having such a configuration
D is not particularly limited to its manufacturing method, and after forming the oxide superconductor thin film on the substrate by using a known method, the washer portion, the hole portion, or the slit portion having the above-mentioned structure is processed. Just mold it. For example, as the substrate, SrTiO ₃ , MgO, LaAlO ₃ , NeGaO
_It is sufficient to use a material composed of ₃ etc., and as a method for producing an oxide superconductor thin film, laser vapor deposition method, sputtering method, vacuum vapor deposition method, MBE, etc. are applied to apply Y (yttrium) system or Bi. It is sufficient to form a (bismuth) -based or Tl (thallium) -based oxide superconductor thin film, and further processing the washer portion, hole portion, and slit portion.
For molding, ion milling, chemical etching, or the like may be applied. The Josephson junction is
It is possible to use a weak-coupling type utilizing a step difference in the substrate, a bicrystal type, a tunnel type, or the like.

The SQUID of the present invention is the conventional SQUID.
Since the magnetic flux resolution can be dramatically improved by 10 to 100 times or more compared with the QUID, the conventional SQUID
It is not necessary to use a magnetic transformer in combination as in the above.
And, it can be applied to a smaller magnetic field measurement.

Further, a magnetic flux composed of a washer portion formed of an oxide superconductor, a hole portion opened substantially in the center of the washer portion, and a slit portion extending from the hole portion toward the outer periphery. When the shielding layer is laminated, leakage of magnetic flux from the slit portion of the SQUID can be prevented, and the magnetic flux resolution can be further improved. That is, in this case, the washer portion of the magnetic flux shielding layer is made to face the washer portion of the SQUID having the above-mentioned configuration, and the slit portion of the magnetic flux shielding layer and the SQUID are further arranged.
The slits are stacked so that they do not overlap.

The washer portion and the hole portion of the magnetic flux shielding layer may be processed and molded in the same size as the washer portion and the hole portion of the SQUID. The slit portion provided in the magnetic flux shielding layer is configured to prevent a shielding current from flowing and preventing the magnetic flux from entering the hole portion. In order to manufacture such a magnetic flux shielding layer, a thin film washer portion may be formed on a supporting substrate according to the above-mentioned SQUID manufacturing method, or the whole sintered body is integrally molded. It may be manufactured as a (magnetic flux shielding plate).

When the Josephson junction of the SQUID is covered with this magnetic flux shielding layer, the influence of the magnetic flux on the junction is reduced, so that the Franhoffer diffraction behavior in the magnetic-voltage characteristics of the SQUID is reduced. be able to. Further, the above effect can be expected by making the size of the hole portion of the magnetic flux shielding layer equal to or smaller than the hole portion of the SQUID.
If only the effect of preventing the leakage of magnetic flux from the slit portion of the ID is expected, it may be larger than the hole portion of the SQUID.

Although such a magnetic flux shielding layer may be formed on a substrate (or a thin film layer provided on another substrate) different from the SQUID as described above, an insulating layer is formed on the surface of the SQUID. After that, an oxide superconducting thin film (magnetic flux shielding layer) may be formed thereon. Since the SQUID thus configured has improved adhesion to the slit portion, it is possible to further improve the above-described magnetic flux leakage prevention effect.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments of the drawings.

Example 1 In order to manufacture the SQUID ₁ 1 shown in FIG. 1, first, Sr having a height difference of 2000 Å was formed.
YB was formed on the TiO ₃ (100) substrate 2 by the laser deposition method.
A CO oxide superconductor thin film (film thickness 2000Å) was formed. The film forming conditions are a laser wavelength of 248 nm, a laser power of 300 mJ / Pulse, a substrate temperature of 670 ° C., a film forming rate of 500 Å / min, and an oxygen partial pressure of 400 mTorr.
Next, the washer part 3 (10 mm
× 10 mm), the hole portion 4 (25 μm × 25 μm), and the slit portions 5 and 5 (width 10 μm) are processed and molded to form the Josephson joint portions 6 and 6 between the hole portion 4 and the slit portions 5 and 5. did.

SQUID 1 of Example 1 thus obtained
_When a measurement system (not shown) was connected to ₁ and the magnetic field resolution was measured in liquid nitrogen, it was 0.5 pTesla / Hz ^1/2
It was at 10 Hz. The conventional SQUID with a washer size of 250 μm × 250 μm has 10 pTes.
It was la / Hz ^{1/2 at} 10 Hz. Therefore, the SQUID ₁ 1 of Example ₁ has a magnetic field resolution improved by about 20 times as compared with the conventional SQUID.

Example 2 First, a magnetic flux shielding layer (plate) 1'shown in FIG. 2 was produced according to the method shown in Example 1 above. In the figure, 2'is a support substrate, 3'is a washer part (10 mm x 10 mm), 4'is a hole part (25 μm).
× 25 μm) and 5 ′ are slit portions (width 5 μm). Next, as shown in FIG. 3, the washer portion 3 ′ of the magnetic flux shielding layer 1 ′ is replaced with the washer portion 3 of the SQUID1 _1.
And the slit portion 5'of the magnetic flux shielding layer 1 '
And the slit portion 5 of SQUID1 ₁ are laminated and integrated so as not to overlap.

SQUID 1 of Example 2 thus obtained
_When a measurement system (not shown) was connected to ₂ and the magnetic field resolution was measured in liquid nitrogen, it was found to be 0.2 pTesla / Hz ^1/2
It was at 10 Hz. Thus, the SQUI of the second embodiment
The magnetic field resolution of D1 ₂ was further improved as compared with SQUID ₁ 1 of Example 1 because the slit portions 5 and 5 of SQUID _{1 2} were
It was considered that the magnetic flux leaking from the magnetic field was blocked by the magnetic flux shielding layer 1 '.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-mentioned embodiments, and can be carried out in any manner as long as the configuration described in the claims is not changed. You can

[0020]

As described above, the SQUID of the present invention
Has high magnetic flux concentration effect and high position resolution,
The magnetic flux resolution can be dramatically improved 10 to 100 times or more as compared with UID. Therefore, the conventional SQ
It is not necessary to use a magnetic transformer having a complicated structure such as UID in combination, and can be applied to a smaller magnetic field measurement.

Further, the area of the hole portion is 4 to 2000 μm.
^The SQUID of ² can suppress the increase in the inductance of the SQUID itself and increase the SQUID output voltage to improve the magnetic field resolution.

Further, the area of the hole portion is 100 to 200.
The SQUID of 0 μm ² achieves the above effect more stably without depending on the shape or the like.

Further, a magnetic flux composed of a washer portion formed of an oxide superconductor, a hole portion opened substantially in the center of the washer portion, and a slit portion extending from the hole portion toward the outer periphery. The SQUID has a structure in which the washer portion of the shielding layer is opposed to the washer portion of the SQUID and the slit portion of the magnetic flux shielding layer and the slit portion of the SQUID are laminated so as not to overlap each other. It is hindered by the magnetic flux shielding layer and further improves the magnetic field resolution.

[Brief description of drawings]

FIG. 1 is a plan view showing the configuration of an SQUID according to a first embodiment.

FIG. 2 is a plan view showing a configuration of a magnetic flux shielding layer to be laminated on the SQUID of Example 2.

FIG. 3 is a perspective view showing a stacked state of SQUIDs according to a second embodiment.

[Explanation of symbols]

1 ₁ , 1 ₂ SQUID 2 substrate 3 washer part 4 hole part 5 slit part 6 Josephson junction part 1'flux shielding layer 2'support substrate 3'washer part 4'hole part 5'slit part

Claims (4)

[Claims] 1. A washer portion formed of an oxide superconductor thin film, a hole portion formed substantially in the center of the washer portion, and at least one Josephson junction formed of a high temperature superconductor thin film. , A SQUID including a slit portion provided from the Josephson junction portion toward the outer periphery
And the area of the washer part is 25 to 1000 mm.
SQUID characterized by being ² . 2. The SQUID according to claim 1, wherein the area of the hole portion is 4 to 2000 μm ² . 3. The area of the hole portion is 100 to 2000 μm.
^3. The SQ according to claim 1, wherein the SQ is 2.
UID. 4. A magnetic flux comprising a washer portion formed of an oxide superconductor, a hole portion opened substantially in the center of the washer portion, and a slit portion extending from the hole portion toward the outer periphery. The washer part of the shielding layer,
The SQUID according to any one of claims 1 to 3, wherein the slit portion of the magnetic flux shielding layer and the slit portion of the SQUID are laminated so as not to overlap each other while facing the washer portion of the SQUID.