JPH08139376A - Input coil for superconducting quantum interference device - Google Patents

Abstract

PURPOSE: To provide an input coil for a superconducting quantum interference device which has a multilayer structure with which the decline of a critical current caused by the existence of a local large slant angle grain boundary in a closed circuit composed of a superconducting thin films can be suppressed. CONSTITUTION: The turn part 22 of a superconducting thin film coil is buried under the surface of a substrate 11. An interlayer insulating film 24 is buried in a trench 14 which is formed under the surface of the coil 22 at the position where a superconducting thin film cross-connection wiring part 25 connected to the inner side coil end 25a crosses the coil 22. The superconducting thin film wiring part and the superconducting thin film cross-connection wiring part 25 are formed on the substrate surface of a region which is practically flat and which includes the surface of the interlayer insulating film 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input coil for a superconducting quantum interference device, and more specifically,
Superconducting quantum interference device (SQ) for high-sensitivity magnetic field measurement used for biomagnetic measurement, nondestructive inspection, mineral resource exploration, etc.
UID) is formed as a thin film laminated structure on a substrate so as to be electromagnetically coupled to a superconducting ring including a Josephson junction to form a magnetic field detecting pickup coil and a closed circuit magnetic flux transformer. The present invention relates to the structure of a superconducting thin film coil to be connected.

[0002]

2. Description of the Related Art A SQUID is an element for converting a magnetic signal into an electric signal by interposing a Josephson junction in a part of a superconducting ring wiring, and a magnetic flux transformer is practically used for pickup of the magnetic signal. The magnetic flux transformer uses the principle of magnetic flux conservation that the total sum of magnetic flux in a closed loop composed of superconductors is invariable. A superconducting closed circuit composed of two superconducting coils, a pickup coil and an input coil. Equipped with a SQUID input coil
Is arranged close to the main ring of the SQUID and the closed circuit is magnetically coupled to the SQUID with a predetermined mutual inductance. In this case, the size of the SQUID itself is limited due to the sensitivity, and its diameter is usually several tens of μm to at most 100 μm.

It is necessary that the pickup coil and the input coil, each of which is a superconducting coil, have the same inductance, but since the pickup coil is the part that actually detects magnetism, it usually has a relatively large area of the order of about cm ^2. On the other hand, the input coil must have a relatively small area of the same degree as the SQUID main ring described above in relation to the magnetic flux transmission efficiency, and therefore the input coil is inevitably required to obtain a required inductance in a small area. There is no choice but to take the form of a spiral coil with multiple turns.

Specific examples of the input coil in the conventional magnetic flux transformer are shown in A and B of FIG. 3 and A to C of FIG. Figure 3A
Is an input coil (B. Oh et al .; Applied Physics Letters, Vo) using a 7-turn high-temperature superconductor prototyped by IBM.
. l 59 (1), p.123-125 ; 1991) is an enlarged plan view showing a
FIG. 3B is a schematic sectional view taken along the line BB of FIG. In addition, FIG. 4A shows an input coil (FC Wellstood et al .; Appl;
ied Physics Letters, Vol. 56 (23), p.2336-2338; 1990)
4B and C are schematic cross-sectional views taken along arrows BB and CC in FIG. 4A, respectively.

The conventional input coil shown in FIG. 3 uses YBa ₂ Cu ₃ O _X (YBCO) as a high temperature superconductor. In FIG. 3, a spiral superconducting thin film coil 32 formed on a substrate 31 is used. Inner coil end 32a is connected to one superconducting thin film wiring 33a through a superconducting thin film cross connecting wiring 35, and outer coil end 32b is connected to the other superconducting thin film wiring 33b integrally formed therewith. The thin film wirings 33a and 33b are connected to both ends of a one-turn superconducting pickup coil (not shown), and these two coils form a closed-circuit magnetic flux transformer.

Similarly in the case of FIG. 4, the inner coil end 42 of the spiral superconducting thin film coil 42 formed on the substrate 41 is also formed.
a is connected to one superconducting thin film wiring 43a through a superconducting thin film cross connection wiring 45, and also has an outer coil end 42b.
Is connected to the other superconducting thin film wiring 43b formed integrally with the superconducting thin film wiring 43b.
Is connected to both ends of a one-turn superconducting pickup coil (not shown), and these two coils form a closed-circuit magnetic flux transformer.

As is apparent from FIGS. 3 and 4, one of the pair of superconducting thin film wirings 33a, 33b or 43a, 43b, that is, the inner coil of the coil 32 or 42, as long as the coil 32 or 42 has a spiral shape. End 32a or 4
Superconducting thin film wiring 33a or 43a connected to 2a
Is always connected to the inner coil end by the superconducting thin film cross connection wiring 35 or 45 that crosses the turn pattern of the coil in the radial direction. Therefore, in order to electrically insulate the coil turn portion, which is a superconducting thin film, and the superconducting thin film cross connection wiring, it is necessary to interpose the insulating film 34 or 44 between these layers. In the input coils shown in FIGS. 3 and 4, SrTiO ₃ thin films are used as the insulating film, although they have different shapes.

A specific laminated structure will be described with reference to FIG.
In the input coil shown in (1), the superconducting thin film formed as the first layer on the substrate 31 allows the coil 32 and the outer coil end 32b to be integrated into one superconducting thin film wiring 33b and the other independent superconducting thin film wiring 33a. The insulating film 34 is formed as a second layer to be laminated on the first layer.
Superconducting thin film cross connection wiring for connecting between the inner coil end 32a of the coil 32 and the superconducting thin film wiring 33a by a superconducting thin film formed as a third layer on the second layer. 35 is formed.

In the input coil shown in FIG. 4, contrary to the above, the superconducting thin film formed as the first layer on the substrate 41 causes the inner coil end 42a of the coil 42 and the superconducting thin film wiring 43a to be separated from each other. The superconducting thin film cross connection wiring 45 for connection is first formed, and then the insulating film 44 is formed on the substrate 41 in a limited region so as to cover the first layer from above. Therefore, the insulating film 44 becomes the second layer on the superconducting thin film cross connection wiring 45 of the first layer, and becomes the first layer on the other substrate surface in the limited region. Further, by the superconducting thin film formed on the entire surface of the substrate including the limited region covered with the insulating film 44, one superconducting thin film wiring 43a connected to the superconducting thin film cross connecting wiring 45 and the inner coil end 42a are connected to the superconducting thin film. The spiral coil 42 connected to the thin film cross connection wiring 45 and the other superconducting thin film wiring 43b integrated with the outer coil end 42b of the coil 42 are formed, and therefore, at the portion intersecting with the superconducting thin film cross connection wiring 45. Coil 4
The turn part of 2 is the third layer.

[0010]

In such a laminated structure of superconducting thin films, any one of the superconducting thin films has different height levels such as the first layer, the second layer and the third layer. Since the extended portion is included, the following inconvenience occurs.

That is, paying attention to the laminated structure of the partial cross section,
For example, in the input coil shown in FIG. 3, as shown in FIG. 3B, the third layer superconducting thin film cross-connecting wiring 35 has a plurality of irregularities appearing on the surface of the second layer insulating film 34 in accordance with coil turns. Following the above, it is formed in a corrugated shape having a plurality of steps.

In addition, in the input coil shown in FIG.
Insulating film 44 that crosses coil 42 in the radial direction as shown in FIG.
Since the turn portion of the coil 42 gets over the surface step between the substrate 41 and the insulating film 44 appearing at the boundary edge portion of the coil 42 every half turn, the coil 42 has a step portion as much as twice the number of turns, and As shown in FIG. 4C, the turn portion of the coil 42 overcomes the step difference of the convex portion appearing on the surface of the insulating film 44 at the portion of the superconducting thin film cross connection wiring 45, so that the coil 42 as a whole has the same number of turns. Will have a convex step.

By the way, when the input coil as described above is formed by a film forming technique such as sputtering using a high temperature superconductor known as an oxide superconductor having a perovskite structure, the thin film of the formed high temperature superconductor is as described above. If such a step is included, as shown schematically in FIG. 5, in the step portion 54 of the superconducting thin film 52, the crystal growth direction of the superconducting thin film is different from other portions, and as a result,
There is a problem that grain boundaries with a large inclination angle are generated. It is well known that the presence of such a grain boundary having a large inclination angle in the closed circuit of the superconducting thin film reduces the critical current Ic flowing in the closed circuit in the superconducting state, and thus in SQUID. In the input transformer that constitutes the magnetic flux transformer, if a local high-angle grain boundary portion is present in the superconducting thin film for forming a closed circuit, it may cause a decrease in SQUID detection sensitivity.

By the way, the input coil shown in FIG. 3 uses YBa ₂ Cu ₃ O _X (YBCO) as a high temperature superconductor and has an interlayer insulating film.
Although SrTiO ₃ is used and the critical temperature Tc is 84K,
The critical current is as low as 0.18 mA at 77K, and the input coil shown in Fig. 4 also uses YBCO as the high temperature superconductor and SrTiO ₃ for the interlayer insulating film, and the critical temperature Tc is 82K. 1.4 mA at 77K
And it is said that it is still insufficient.

Therefore, an object of the present invention is to provide a local high-angle grain boundary part in a superconducting thin film even when it is formed by a film-forming technique such as sputtering using a high-temperature superconductor known as an oxide superconductor having a perovskite structure. Input for a superconducting quantum interference device with a layered structure that can prevent the formation of grains as much as possible, and thus can suppress the reduction of the critical current due to the presence of a local high-angle grain boundary in the closed circuit of the superconducting thin film. Is to provide a coil.

[0016]

An input coil for a superconducting quantum interference device according to a first aspect of the present invention is a substrate to be magnetically coupled to a superconducting ring including a Josephson junction for forming a superconducting quantum interference device. An input coil that is formed as a thin film laminated structure on the top and is connected so as to form a magnetic field detection pickup coil and a magnetic flux transformer of a superconducting closed circuit. This input coil is a spiral superconducting thin film coil with a plurality of turns. , A superconducting thin film wiring part for connecting the outer coil end of the superconducting thin film coil and one end of the pickup coil, and an inner coil of the superconducting thin film coil for connecting the inner coil end of the superconducting thin film coil and the other end of the pickup coil The superconducting thin film cross connection wiring part that crosses the turn part of the superconducting thin film coil from the end in the radial direction, and And an interlayer insulating film for insulating between the thin film cross connection wiring portion and the turn portions of the superconducting thin film coil.

In the input coil according to the present invention, in order to solve the above-mentioned problems, the turn portion of the superconducting thin film coil is buried in the first groove formed below the surface of the substrate, and the interlayer insulating film is It is embedded in a second groove formed below the surface of the turn portion of the superconducting thin-film coil at a portion where the superconducting cross-connect wiring portion and the turn portion of the superconducting thin-film coil overlap, and the surface of the turn portion of the superconducting thin-film coil and the interlayer On the substantially flat substrate surface in the region including the surface of the insulating film,
A superconducting thin film wiring portion and a superconducting thin film cross connecting wiring portion are formed.

Further, in the input coil for a superconducting quantum interference device according to a second aspect of the present invention, in addition to the features of the first aspect of the invention, a connecting portion between the inner coil end of the superconducting thin film coil and the superconducting thin film cross connecting wiring portion and the superconducting The surfaces of both the outer coil end of the thin-film coil and the connection between the superconducting thin-film wiring part and the surface of the interlayer insulating film are on the same level as the surface of the substrate along with the surface of the interlayer insulating film. A superconducting thin film wiring portion and a superconducting thin film cross connecting wiring portion are formed from one flat superconducting thin film layer.

Further, the input coil for a superconducting quantum interference device according to the invention of claim 3 is a thin film laminated structure on a substrate so as to be magnetically coupled to a superconducting ring including a Josephson junction for constructing the superconducting quantum interference device. Is an input coil connected to form a pickup coil for magnetic field detection and a magnetic flux transformer of a superconducting closed circuit, and the input coil is composed of a spiral superconducting thin film coil having a plurality of turns and a superconducting thin film coil. A first superconducting thin film wiring portion for connecting the outer coil end and one end of the pickup coil, and a second superconducting thin film wiring portion for connecting the inner coil end of the superconducting thin film coil and the other end of the pickup coil. A second superconducting thin-film wiring part that radially crosses the turn part of the superconducting thin-film coil from the inner coil end of the superconducting thin-film coil A superconducting thin cross connection wiring portion reaching, and an interlayer insulating film for insulating between the superconducting thin cross connection wiring portion and the turn portions of the superconducting thin film coil.

In the input coil according to the present invention, in order to solve the above-mentioned problems, the superconducting thin film cross connecting wiring portion is formed in the first groove formed below the surface of the substrate at the portion crossing the turn portion of the superconducting thin film coil. And the interlayer insulating film is under the surface of the superconducting thin film cross connecting wiring part at a portion except for each connecting part of the superconducting thin film cross connecting wiring part to the inner coil end of the superconducting thin film coil and the second superconducting thin film wiring part. A superconducting thin film coil and a first superconducting thin film wiring, which are buried in the second groove formed on the substrate, and are formed on the substantially flat substrate surface in the region including the surfaces of the connection portions and the surface of the interlayer insulating film. And a second superconducting thin film wiring portion are formed.

Further, in the input coil for a superconducting quantum interference device according to the invention of claim 4, in addition to the invention of claim 3, the superconducting thin film cross connection to the inner coil end of the superconducting thin film coil and the second superconducting thin film wiring part is provided. The surface of each connection part of the wiring part is on the same level as the surface of the substrate together with the surface of the interlayer insulating film, and from the single flat superconducting thin film layer formed on this plane to the superconducting thin film coil and the first superconducting thin film coil. A superconducting thin film wiring part and a second superconducting thin film wiring part.

[0022]

The input coil for a superconducting quantum interference device according to the present invention having the above-described thin film laminated structure can be formed by a film forming technique such as sputtering using a high temperature superconductor known as an oxide superconductor having a perovskite structure. Moreover, in that case, it is possible to eliminate the step of forming a film on the surface having irregularities or steps when forming the high temperature superconducting thin film.

That is, the thin film laminated structure according to the invention of claim 1 can be formed by, for example, the following film forming process. First, a first groove for burying the superconducting thin film coil portion is provided on the surface of the substrate by a photolithography method. The opening shape of the first groove is defined by a mask opening of lithography according to a predetermined contour shape of the superconducting thin film coil portion, and the depth of the first groove is predetermined. Is determined by etching so as to correspond to the sum of the thickness and the thickness of the interlayer insulating film, and thus the first groove having a flat bottom surface is formed.

After forming the first groove, a high-temperature superconducting thin film is formed on the entire surface of the substrate including the inside of the first groove as a first layer. The thickness of this film formation is equivalent to the depth of the first groove, whereby the inside of the first groove is filled with the high temperature superconducting thin film. The high temperature superconducting thin film on the other substrate surface is etched away to the same level as the substrate surface, leaving the high temperature superconducting thin film in the first groove. As a result, the grain boundaries of the high-temperature superconducting thin film left in the first groove are parallel to the groove bottom because they are formed on the flat bottom surface of the first groove, and the inclination angle is uniform. It is almost zero.

Then, a second groove for forming an interlayer insulating film is provided on the surface of the high temperature superconducting thin film left in the first groove by photolithography. The second groove is formed by removing, by etching, a portion corresponding to an area of the turn portion of the superconducting thin-film coil and the superconducting thin-film cross-connecting wiring portion which are widened with some margin in the circumferential direction of the turn. The etching depth is equal to the design depth of the interlayer insulating film.
The high temperature superconducting thin film thus left forms the turn portion of the superconducting thin film coil.

An insulating film is formed on the entire surface of the substrate including the inside of the thus formed second groove as a second layer. The film thickness of this insulating film is equal to the depth of the second groove, and the inside of the second groove is thereby filled with the insulating film. The other insulating films on the substrate surface are removed by etching to the same level as the substrate surface, leaving the insulating film in the second groove. The insulating film thus left constitutes the interlayer insulating film.

By the above process, the surface of the interlayer insulating film, the connecting portion between the inner coil end of the superconducting thin film coil and the superconducting thin film cross connecting wiring portion, and the connecting portion between the outer coil end of the superconducting thin film coil and the superconducting thin film wiring portion. The surface of both connection parts of will appear flush with the surface of the substrate,
Therefore, a high-temperature superconducting thin film is formed as a third layer on the entire surface of this flat surface. The film thickness at this time is the design thickness required for the superconducting thin film wiring part and the superconducting thin film cross connecting wiring part, and since the film forming surface is flat, the grain boundaries of the high temperature superconducting thin film should be flat. They are parallel, and their tilt angles are almost zero.

Finally, the high-temperature superconducting thin film of the third layer is patterned by a lithographic method to form the superconducting thin film cross connecting wiring portion and the superconducting thin film wiring portion at predetermined positions and shapes.

The thin film laminated structure according to the invention of claim 3 can be formed by, for example, the following film forming process. First, a first groove for embedding the superconducting thin film cross connecting wiring portion is provided on the surface of the substrate by a photolithography method. The opening shape of the first groove is defined by a mask opening of lithography according to a predetermined contour shape of the superconducting thin film cross connecting wiring portion, and the depth of the first groove is determined by the predetermined superconducting thin film. The first groove having a flat bottom surface is formed by etching so as to correspond to the sum of the thickness of the cross connection wiring portion and the thickness of the interlayer insulating film.

After the first groove is formed, a high temperature superconducting thin film is formed on the entire surface of the substrate including the inside of the first groove as a first layer. The thickness of this film formation is equivalent to the depth of the first groove, whereby the inside of the first groove is filled with the high temperature superconducting thin film. The high temperature superconducting thin film on the other substrate surface is etched away to the same level as the substrate surface, leaving the high temperature superconducting thin film in the first groove. As a result, the grain boundaries of the high-temperature superconducting thin film left in the first groove are parallel to the groove bottom because they are formed on the flat bottom surface of the first groove, and the inclination angle is uniform. It is almost zero.

Then, a second groove for forming an interlayer insulating film is provided on the surface of the high temperature superconducting thin film left in the first groove by photolithography. The second groove is formed by removing a portion of the superconducting thin film cross connecting wiring portion other than each connection portion with respect to the inner coil end of the superconducting thin film coil and the second superconducting thin film wiring portion by etching, and the etching depth thereof. The thickness is equal to the design depth of the interlayer insulating film. The high temperature superconducting thin film left by this constitutes the superconducting thin film cross connecting wiring portion.

An insulating film is formed on the entire surface of the substrate, including the inside of the thus formed second groove, as the second layer. The film thickness of this insulating film is equal to the depth of the second groove, and the inside of the second groove is thereby filled with the insulating film. The other insulating films on the substrate surface are removed by etching to the same level as the substrate surface, leaving the insulating film in the second groove. The insulating film thus left constitutes the interlayer insulating film.

By the above process, the surface of the interlayer insulating film and the surface of each connecting portion of the superconducting thin film cross connecting wiring portion to the inner coil end of the superconducting thin film coil and the second superconducting thin film wiring portion are formed on the substrate surface. Therefore, a high temperature superconducting thin film is formed as a third layer on the entire surface of the flat surface. The film-forming thickness at this time is a design thickness required for the superconducting thin-film coil and the first and second superconducting thin-film wiring portions, and since the film-forming surface is flat, the grain boundaries of the high-temperature superconducting thin film are flat. Parallel to the membrane plane,
Its tilt angle is almost zero.

Finally, the high-temperature superconducting thin film of the third layer is patterned by a lithographic method to form the superconducting thin-film coil and the first and second superconducting thin-film wiring portions at predetermined positions and shapes.

As described above, each of the input coils according to the invention of claim 1 or 3 has a thin film laminated structure capable of forming a superconducting thin film on a substantially flat surface. Therefore, even when a film is formed by a high-temperature superconductor such as an oxide superconductor using a general film forming technique such as sputtering, a local high-angle grain boundary is formed in the superconducting thin film. Never.

Therefore, a sufficiently large critical current can be passed through the closed circuit of the magnetic flux transformer constituted by the input coil according to the present invention, and the sensitivity of the SQUID can be remarkably increased as compared with the conventional case.

According to the invention of claim 1 or 3, the film-forming surface on which the high-temperature superconducting thin film is to be formed in the film formation of the above-mentioned third layer does not have to be exactly a flat surface. It may be practically acceptable to include a relatively small-scale unevenness or a level difference that only causes an allowable grain boundary tilt angle with respect to the reduction of the critical current flowing in the closed circuit.

However, according to the invention of claim 2 or 4,
The film-forming surface on which the high-temperature superconducting thin film should be formed in the above-mentioned third layer film formation can be made exactly flush with the flat surface. A portion where the grain boundary tilt angle locally changes is hardly included, and the reduction of the critical current in the input coil does not substantially occur.

As a high temperature superconductor that can be used for forming a superconducting thin film in the thin film laminated structure of the present invention, for example, YBa ₂
Cu ₃ O _X (YBCO), Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _X , Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _X (BSCC
O), Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _X (TBCCO), and other various oxide superconducting materials, and examples of the material of the substrate and the interlayer insulating film include MgO and SrTiO ₃ , A material having a perovskite structure such as LaAlO ₃ and having a lattice constant similar to that of the oxide superconducting material and capable of epitaxial growth with each other can be mentioned.

[0040]

【Example】

= First Example = A thin film laminated structure of an input coil for a superconducting quantum interference device according to a first example of the present invention is shown in FIGS. 1 and 2 in the order of a film forming process. That is, FIGS. 1A to H are schematic plan views showing the steps A to H of the film forming process described below in order, and FIGS. 2A to H similarly correspond to FIG.
It is a schematic cross section shown in the order of.

(Step A) Substrate 1 made of MgO (100) single crystal
A photoresist is applied to the surface of 1 by a spin coater and the surface of the substrate 11 is entirely covered with a photoresist layer having a thickness of 0.5 μm. Then, a mask pattern corresponding to a plan shape of a turn portion of a superconducting thin-film coil which is previously planned. The resist was exposed using the photomask of No. 1 and the resist was developed using an alkali developing solution. As a result, an opening having the same shape as the planar shape of the turn portion of the superconducting thin film coil was formed in the resist layer. Next, ion beam etching with argon is performed on the substrate surface of the portion exposed from this opening to form a groove 1 having a flat bottom surface with the same opening shape as that of the turn portion of the superconducting thin film coil and having a depth of 0.4 μm
2 is formed at a predetermined position on the substrate 11 (see FIGS. 1A and 2).
A).

(Step B) The substrate 11 having the groove 12 formed in the step A is set in a high frequency magnetron sputtering apparatus,
A YBCO thin film 13 is formed on the entire surface to form a first layer of 0.4 μm.
Grown to a thickness of. The film forming conditions at this time are the substrate 11
Is heated to 700 ° C., a 1: 1 mixed gas of argon and oxygen is introduced as a sputtering gas, and the total gas pressure is 150 mTo.
rr, a YBCO sintered body was used as the target, and the film formation time was 4 hours. This allows the groove 12 to reach the opening edge.
It is filled with YBCO thin film.
A 4 μm thick YBCO thin film was laminated (FIGS. 1B and 2).
B).

(Step C) YB of the substrate 11 obtained in Step B
A photoresist is coated on the CO thin film 13 by a spin coater, and the surface of the YBCO thin film 13 is entirely covered with a photoresist layer having a thickness of 0.5 μm. Then, a photomask having a mask pattern complementary to that used in the step A is formed. Was used to expose the resist, and the resist was developed using an alkaline developer. As a result, the groove 12 under the YBCO thin film 13 is formed.
The resist layer was removed, leaving a portion corresponding to. Next, the 0.4 μm-thick YBCO thin film exposed at this removed portion was removed by ion beam etching with argon. The etching time at this time was about 40 minutes. afterwards,
When the residual resist was removed using a stripping solution, the groove 12
The YBCO thin film 13 filling the inside becomes the turn part 22 of the superconducting thin film coil, the connecting part 25a between the inner coil end of the superconducting thin film coil and the superconducting thin film cross connecting wiring part, and the outer coil end of the superconducting thin film coil and the superconducting thin film wiring. The connection portion 23a with the portion is at the same level as the surface of the substrate 11 around it, and a flush surface is formed (FIG. 1).
C and FIG. 2C).

(Step D) A photoresist is applied by a spin coater to the surface of the substrate 11 in which the groove 12 is filled with the turn portions 22 of the superconducting thin film coil in step C, and the surface of the substrate 11 is 0.5 μm thick. After the entire surface was covered with a layer, the resist was exposed using a photomask having a mask pattern corresponding to the predetermined planar shape of the interlayer insulating film, and the resist was developed using an alkali developing solution.
As a result, an opening having the same shape as the planar shape of the interlayer insulating film was formed in the resist layer on the turn portion 22 of the superconducting thin film coil in the groove 12. Then, the surface of the turn portion 22 of the superconducting thin film coil in the portion exposed from this opening was subjected to ion beam etching with argon for about 20 minutes. After that, the residual resist was removed using a stripping solution. As a result, at a predetermined position on the surface of the turn portion 22 of the superconducting thin film coil in the groove 12, a depth of 0.2 μm having the same opening shape as that of the interlayer insulating film was formed. Another groove 14 was formed (FIGS. 1D and 2D).

(Step E) In Step D, the groove 14 for the interlayer insulating film is formed.
The substrate 11 on which was formed was set in a high frequency magnetron sputtering apparatus, and an insulating film 15 made of MgO was grown to a thickness of 0.2 μm on the entire surface as a second layer film formation. The film forming conditions at this time are that the substrate 11 is heated to 500 ° C., argon gas is introduced as a sputtering gas, and the total gas pressure is 1 m.
Torr. A MgO sintered body was used as the target, and the film formation time was 2 hours. As a result, the groove 14 on the surface of the turn portion 22 of the superconducting thin-film coil is filled with the MgO insulating film just up to the opening edge, and the substrate surface around the groove 14 is 0.2 μm.
An m-thick MgO insulating film was laminated (FIGS. 1E and 2E).

(Step F) A photoresist is applied on the insulating film 15 of the substrate 11 obtained in the step E by a spin coater to cover the entire surface of the insulating film 15 with a photoresist layer having a thickness of 0.5 μm. The resist was exposed using a photomask having a mask pattern complementary to that used in step D, and the resist was developed using an alkali developing solution. As a result, the resist layer was removed, leaving a portion corresponding to the groove 14 under the insulating film 15. Next, the insulating film 15 having a thickness of 0.2 μm exposed at the removed portion was removed by ion beam etching with argon. The etching time at this time was about 60 minutes. After that, when the residual resist was removed using a stripping solution, the interlayer insulating film 24 was formed by the insulating film 15 filling the inside of the groove 14, and the surface of the interlayer insulating film 24, the substrate 11 around the interlayer insulating film 24, and the superconductor. A connecting portion 23a between the outer coil end of the thin film coil and the superconducting thin film wiring portion, and a connecting portion 25 between the inner coil end of the superconducting thin film coil and the superconducting thin film cross connecting wiring portion.
The surface of a was at the same position level, and a flat surface was formed (FIGS. 1F and 2F).

(Step G) The substrate 11 having a flat surface obtained in the step F is set in a high frequency magnetron sputtering apparatus, and a YBCO thin film 16 having a thickness of 0.4 μm is formed on the entire flat surface as a third layer. Grow in thickness. The film forming conditions at this time were the same as those in the step B. As a result, the YBCO thin film 16 having a thickness of 0.4 μm is laminated on the entire surface of the substrate 11, and the turn portion 22 of the superconducting thin film coil is located under the YBCO thin film 16 via the interlayer insulating film 24. The outer coil end and the inner coil end of the coil are respectively connected to the connecting portion 2
It became a state of being bonded to the YBCO thin film 16 at 3a and 25a (FIGS. 1G and 2G).

(Step H) A photoresist is applied by a spin coater to the surface of the substrate 11 on which the YBCO thin film 16 is laminated in step G, and the YBCO thin film 16 on the surface of the substrate 11 is entirely covered with a photoresist layer having a thickness of 0.5 μm. After coating, the resist was exposed using a photomask having a mask pattern corresponding to the plane shapes of the superconducting thin film wiring portion and the superconducting thin film cross connection wiring portion, which were previously planned, and the resist was developed using an alkali developing solution. . As a result, the surface of the YBCO thin film 16 was exposed, leaving a resist pattern having the same shape as the planar shape of the superconducting thin film wiring portion and the superconducting thin film cross connection wiring portion.

Next, the exposed portion of the YBCO thin film 16 was subjected to ion beam etching with argon for about 40 minutes, and then the residual resist was removed using a stripping solution. The superconducting thin film wiring portion 23 and the superconducting thin film were then removed. The cross-connect wiring part 25 having a thickness of 0.4 μm was formed at a predetermined position of the substrate 11, and the input part 20 for the superconducting quantum interference device was obtained together with the turn part 22 of the superconducting thin-film coil previously embedded in the substrate 11. (Fig. 1H and Fig. 2
H).

Gold electrodes were formed in the superconducting thin film wiring portion 23 and the superconducting thin film cross connecting wiring portion 25 of the input coil 20 of the first embodiment prepared as described above, and their critical temperatures Tc and When the critical current Ic was measured, the critical temperature Tc was 85K and the critical current Ic was 77.
It was 55 mA in K.

= Second Embodiment = An input coil for a superconducting quantum interference device was prepared in the same process as in the first embodiment by using a substrate made of SrTiO ₃ (100) single crystal instead of MgO (100) single crystal. , A gold electrode is similarly formed, and its critical temperature Tc and critical current I are measured by the DC four-terminal method.
When c was measured, the critical temperature Tc was 86K and the critical current Ic was 62 mA at 77K.

= Third Example = An input coil for a superconducting quantum interference device was prepared in the same manner as in the second example except that the interlayer insulating film was changed from MgO to SrTiO ₃ . In this case, the conditions for forming SrTiO ₃ as the interlayer insulating film are as follows: the substrate is set in a high-frequency magnetron sputtering device and heated to 300 ° C., argon gas is introduced into the chamber of the device as a sputtering gas, and the total gas pressure is set to It was set to 2 mTorr. A SrTiO ₃ sintered body was used as the target, and the film formation time was 1 hour.

Gold electrodes are similarly formed in the first and second superconducting thin film wiring portions of the input coil of the third embodiment thus produced, and their critical temperature Tc is obtained by the DC four-terminal method.
When the critical current Ic is measured, the critical temperature Tc is 8
6K, and the critical current Ic was 68mA at 77K.

= Fourth Embodiment = An input coil for a superconducting quantum interference device was prepared in the same manner as in the first embodiment except that the material of each superconducting thin film was changed from YBCO to Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _X. . In this case, the film forming conditions of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _X as each superconducting thin film are as follows: the substrate is set in a high frequency magnetron sputtering device and heated to 800 ° C. The mixed gas of No. 3 was introduced, and the total gas pressure was 100 mTorr. Further, a Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _X sintered body was used as a target, and the film formation time was 5
It was time.

Gold electrodes are similarly formed in the first and second superconducting thin film wiring portions of the input coil of the fourth embodiment thus produced, and their critical temperature Tc is obtained by the DC four-terminal method.
When the critical current Ic is measured, the critical temperature Tc is 8
It was 2K and the critical current Ic was 41mA at 77K.

= Fifth Embodiment = FIG. 6 and FIG. 7 show a thin film laminated structure of an input coil for a superconducting quantum interference device according to a fifth embodiment of the present invention in the order of the film forming process. That is, FIGS. 6A to 6H are schematic plan views showing the steps A to H of the film forming process described below in order, and FIGS. 7A to 7H also correspond to FIG.
It is a schematic cross section shown in order of H.

(Step A) Substrate 6 made of MgO (100) single crystal
1 is coated with a photoresist by a spin coater, and the surface of the substrate 61 is entirely covered with a photoresist layer having a thickness of 0.5 μm. Then, a photomask having a mask pattern corresponding to a plan shape of a cross-connect wiring portion is prepared in advance. The resist was exposed using a mask, and the resist was developed using an alkaline developer. As a result, an opening having the same shape as the plan shape of the cross connection wiring portion was formed in the resist layer.
Next, ion beam etching with argon is performed on the substrate surface of the portion exposed from this opening to form a 0.4 μm deep groove 62 having a flat bottom surface with the same opening shape as the plane shape of the cross connection wiring portion. Was formed at a predetermined position (FIGS. 6A and 7A).

(Step B) The substrate 61 having the groove 62 formed in the step A is set in a high frequency magnetron sputtering apparatus,
A YBCO thin film 63 is formed on the entire surface to form a first layer of 0.4 μm.
Grown to a thickness of. The film forming conditions at this time are as follows:
Is heated to 700 ° C., a 1: 1 mixed gas of argon and oxygen is introduced as a sputtering gas, and the total gas pressure is 150 mTo.
rr, a YBCO sintered body was used as the target, and the film formation time was 4 hours. This allows the groove 62 to reach the opening edge YBCO
Filled with a thin film, 0.4μ on the substrate surface around the groove 62
An m-thick YBCO thin film was laminated (FIGS. 6B and 7B).

(Step C) YB of the substrate 61 obtained in Step B
A photoresist is applied onto the CO thin film 63 by a spin coater, the surface of the YBCO thin film 63 is entirely covered with a photoresist layer having a thickness of 0.5 μm, and then a photomask having a mask pattern complementary to that used in step A is formed. Was used to expose the resist, and the resist was developed using an alkaline developer. As a result, the groove 62 under the YBCO thin film 63 is formed.
The resist layer was removed, leaving a portion corresponding to. Next, the 0.4 μm-thick YBCO thin film exposed at this removed portion was removed by ion beam etching with argon. The etching time at this time was about 40 minutes. afterwards,
When the residual resist was removed using a stripping solution, the groove 62
The surface of the YBCO thin film 63 filling the inside and the substrate 6 around it
The surface of No. 1 was at the same position level, and a flush surface was formed (FIGS. 6C and 7C).

(Step D) In step C, the inside of the groove 62 is filled with the YBCO thin film 6
A photoresist is applied to the surface of the substrate 61 filled with 3 with a spin coater, and the surface of the substrate 61 has a thickness of 0.5 μm.
After the entire surface was covered with the photoresist layer, the resist was exposed by using a photomask having a mask pattern corresponding to a predetermined planar shape of the interlayer insulating film, and the resist was developed by using an alkali developing solution. As a result, an opening having the same shape as the planar shape of the interlayer insulating film is formed in the YBCO thin film 6 in the groove 62.
3 was formed on the resist layer. Next, the surface of the YBCO thin film 63 exposed from this opening was subjected to ion beam etching with argon for about 20 minutes. After that, the residual resist was removed using a stripping solution, and a depth of 0.2 μm having the same opening shape as the planar shape of the interlayer insulating film was formed at a predetermined position on the surface of the YBCO thin film 63 in the groove 62.
Another groove 64 of m is formed, and a superconducting thin film cross wiring portion 75 having connection portions 75a and 75b at the same position level as the substrate surface is formed at both ends of the groove 64 (FIGS. 6D and 7).
D).

(Step E) In step D, the substrate 61 on which the superconducting thin film cross wiring portion 75 is formed is set in a high frequency magnetron sputtering apparatus, and an insulating film 65 made of MgO is formed on the entire surface as a second layer. It was grown to a thickness of 2 μm.
The film forming conditions at this time are as follows: the substrate 61 is heated to 500 ° C.
Argon gas was introduced as the sputtering gas, and the total gas pressure was 1 mTorr. A MgO sintered body was used as the target, and the film formation time was 2 hours. As a result, the groove 64 on the surface of the cross wiring portion 75 is filled with the MgO insulating film just up to the opening edge, and a 0.2 μm thick M
A gO insulating film was laminated (FIGS. 6E and 7E).

(Step F) A photoresist is applied to the insulating film 65 of the substrate 61 obtained in the step E by a spin coater, and the surface of the insulating film 65 is entirely covered with a photoresist layer having a thickness of 0.5 μm. The resist was exposed using a photomask having a mask pattern complementary to that used in step D, and the resist was developed using an alkali developing solution. As a result, the resist layer was removed, leaving a portion corresponding to the groove 64 under the insulating film 65. Next, the insulating film 65 having a thickness of 0.2 μm exposed at the removed portion was removed by ion beam etching with argon. The etching time at this time was about 60 minutes. Then, when the residual resist is removed by using a stripping solution, an interlayer insulating film 74 is formed by the insulating film 65 filling the inside of the groove 64, and the surface of the interlayer insulating film 74 and the surrounding substrate 61 and each connection. The surfaces of the parts 75a and 75b were at the same position level, and a flat surface was formed (FIGS. 6F and 7F).

(Step G) The substrate 61 having a flat surface obtained in the step F is set in a high frequency magnetron sputtering apparatus, and a YBCO thin film 66 having a thickness of 0.4 μm is formed on the entire flat surface as a third layer. Grow in thickness. The film forming conditions at this time were the same as those in the step B. As a result, the YBCO thin film 66 having a thickness of 0.4 μm is laminated on the entire surface of the substrate 61, and the cross connection wiring part 75 is located under the YBCO thin film 66 via the interlayer insulating film 74. 7
The connection parts 75a and 75b of No. 5 and the YBCO thin film 66 were joined (FIGS. 6G and 7G).

(Step H) A photoresist is applied by a spin coater to the surface of the substrate 61 on which the YBCO thin film 66 is laminated in step G, and the YBCO thin film 66 on the surface of the substrate 61 is entirely covered with a photoresist layer having a thickness of 0.5 μm. After coating, the superconducting thin film coil turn portion and the first and second predetermined
The resist was exposed to light using a photomask having a mask pattern corresponding to each planar shape of the superconducting thin film wiring part, and the resist was developed using an alkali developing solution. As a result, the surface of the YBCO thin film 66 was exposed, leaving a resist pattern having the same shape as the planar shapes of the superconducting thin film coil turn portion and the first and second superconducting thin film wiring portions.

Then, the exposed YBCO thin film 66 was subjected to ion beam etching with argon for about 40 minutes, and then the residual resist was removed by using a stripping solution. As a result, the superconducting thin-film coil 72 (turn portion) was obtained. Also, the first and second superconducting thin film wiring portions 73b and 73a are formed at a predetermined position on the substrate 61 with a thickness of 0.4 μm, and the superconducting thin film cross connection wiring portion 75 which is previously embedded in the substrate 61 is formed.
At the same time, an input coil 70 for a superconducting quantum interference device was obtained (FIGS. 6H and 7H).

The first and second superconducting thin film wiring portions 73 of the input coil 70 of the fifth embodiment produced as described above.
When a gold electrode was formed in b and 73a and the critical temperature Tc and the critical current Ic were measured by the DC four-terminal method, the critical temperature Tc was 85K and the critical current Ic was 55mA at 77K.

= Sixth Embodiment = An input coil for a superconducting quantum interference device was prepared in the same process as in the fifth embodiment by using a substrate made of SrTiO ₃ (100) single crystal instead of MgO (100) single crystal. , A gold electrode is similarly formed, and its critical temperature Tc and critical current I are measured by the DC four-terminal method.
When c was measured, the critical temperature Tc was 86K and the critical current Ic was 62 mA at 77K.

= Seventh Example = An input coil for a superconducting quantum interference device was prepared in the same manner as in the sixth example except that the interlayer insulating film was changed from MgO to SrTiO ₃ . In this case, the conditions for forming SrTiO ₃ as the interlayer insulating film are as follows: the substrate is set in a high-frequency magnetron sputtering device and heated to 300 ° C., argon gas is introduced into the chamber of the device as a sputtering gas, and the total gas pressure is set to It was set to 2 mTorr. A SrTiO ₃ sintered body was used as the target, and the film formation time was 1 hour.

Gold electrodes are similarly formed in the first and second superconducting thin film wiring portions of the input coil of the seventh embodiment thus produced, and their critical temperature Tc is obtained by the DC four-terminal method.
When the critical current Ic is measured, the critical temperature Tc is 8
6K, and the critical current Ic was 68mA at 77K.

= Eighth Embodiment = An input coil for a superconducting quantum interference device was prepared in the same manner as in the fifth embodiment except that the material of each superconducting thin film was changed from YBCO to Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _X. . In this case, the film forming conditions of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _X as each superconducting thin film are as follows: the substrate is set in a high frequency magnetron sputtering device and heated to 800 ° C. The mixed gas of 2 was introduced and the total gas pressure was set to 100 mTorr. Further, a Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _X sintered body was used as a target, and the film formation time was 5
It was time.

Gold electrodes are similarly formed in the first and second superconducting thin film wiring portions of the input coil of the eighth embodiment thus produced, and their critical temperature Tc is obtained by the DC four-terminal method.
When the critical current Ic is measured, the critical temperature Tc is 8
It was 2K and the critical current Ic was 41mA at 77K.

From the measurement results of the first to eighth examples, the critical current in the input coil having the laminated thin film structure according to the present invention is incomparable to that of the conventional examples of FIGS. 3 and 4 described above. It was confirmed to be the size of.

[0073]

As described above, the input coil for a superconducting quantum interference device of the present invention has a thin film laminated structure capable of forming a superconducting thin film on a substantially flat surface. Therefore, not only can it be formed by a high-temperature superconductor known as an oxide superconductor having a perovskite structure by a film-forming technique by a normal thin-film process such as sputtering, but also on a surface having unevenness or steps when forming a high-temperature superconducting thin film. Since it is possible to eliminate the step of forming a film at all, there is no formation of a local high-angle grain boundary part in the superconducting thin film during the process. Therefore, it is possible to prevent a decrease in the critical current due to the interposition of a high-angle tilt grain boundary part in the closed circuit formed by the superconducting thin film, and to realize an input coil in which the critical current is dramatically improved compared to the conventional one. It can contribute to the improvement of the detection sensitivity of SQUID.

Therefore, a sufficiently large critical current can be passed through the closed circuit of the magnetic flux transformer constituted by the input coil according to the present invention, and the sensitivity of the SQUID can be remarkably increased as compared with the conventional case.

[Brief description of drawings]

1A to 1H are schematic plan views showing a thin film stack structure of an input coil for a superconducting quantum interference device according to a first embodiment of the present invention in the order of steps A to H of a film forming process. .

2A to 2H are schematic cross-sectional views showing the thin film laminated structure of the input coil for the superconducting quantum interference device according to the first embodiment in the order of steps A to H corresponding to FIG.

FIG. 3A is an enlarged plan view showing an example of an input coil in a conventional magnetic flux transformer, and FIG. 3B is a schematic sectional view taken along the line BB of FIG. 3A.

FIG. 4A is an enlarged plan view showing another example of the conventional input coil, and FIGS. 4B and 4C are B- of FIG. 4A, respectively.
FIG. 3 is a schematic cross-sectional view taken along arrows B and C-C.

FIG. 5 is a schematic cross-sectional view for explaining a local high-angle grain boundary portion formed in a high temperature superconducting thin film during a film forming process.

6A to 6H are schematic plan views showing the thin film laminated structure of an input coil for a superconducting quantum interference device according to a fifth embodiment of the present invention in the order of steps A to H of the film forming process. .

7A to 7H are schematic cross-sectional views showing the thin film laminated structure of the input coil for the superconducting quantum interference device according to the fifth embodiment in the order of steps A to H corresponding to FIG.

[Explanation of symbols]

11: Substrate 12: Groove (groove formed under the surface of substrate) 13: YBCO thin film 14: Groove (groove formed under surface of superconducting thin film coil) 15: MgO insulating film 16: YBCO thin film 20: Superconducting quantum Input coil for interference device 22: Superconducting thin film coil (turn part) 23: Superconducting thin film wiring part 23a: Connection part between outer coil end and superconducting thin film wiring part 24: Interlayer insulating film 25: Superconducting thin film cross connecting wiring part 25a: Inside Connection part between coil end and superconducting thin film cross connecting wiring part 61: Substrate 62: Groove (groove formed under the substrate surface) 63: YBCO thin film 64: Groove (formed under superconducting thin film cross connecting wiring part surface Groove) 65: MgO insulating film 66: YBCO thin film 70: Input coil for superconducting quantum interference device 72: Superconducting thin film coil (turn part) 73a: Second superconducting thin film wiring part 73b: First Superconducting thin film wiring portion 74: Interlayer insulating film 75: Superconducting thin film cross connecting wiring portion 75a: Connection portion between inner coil end and superconducting thin film cross connecting wiring portion 75b: First superconducting thin film wiring portion and superconducting thin film cross connecting wiring portion Connection

Claims (4)

[Claims] 1. A pickup coil for magnetic field detection and a superconducting closed circuit formed as a thin film laminated structure on a substrate so as to be magnetically coupled to a superconducting ring including a Josephson junction for constituting a superconducting quantum interference device. An input coil connected so as to form a magnetic flux transformer, which is for connecting the spiral superconducting thin film coil (22) with multiple turns and the outer coil end of the superconducting thin film coil (22) to one end of the pickup coil. A superconducting thin film cross connection for connecting the superconducting thin film wiring part (23) and the other end of the pickup coil across the turn part of the superconducting thin film coil (22) from the inner coil end of the superconducting thin film coil (22) in the radial direction. Wiring part (25), superconducting thin film cross connection Wiring part (25) and superconducting thin film coil (2
The inter-layer insulating film (24) for insulating between the turn portion of (2) and the turn portion of the superconducting thin film coil (22), the first groove formed under the surface of the substrate (11). The interlayer insulating film (24) embedded in (12) is embedded in the second groove (14) formed below the surface of the superconducting thin film coil (22), and the surface of the superconducting thin film coil (22) is Characterized in that the superconducting thin film wiring portion (23) and the superconducting thin film cross connection wiring portion (25) are formed on the substantially flat substrate surface in the region including the surface of the interlayer insulating film (24) Input coil for superconducting quantum interference device. 2. A surface of a connecting portion (23a) between an outer coil end of the superconducting thin film coil (22) and the superconducting thin film wiring portion (23), an inner coil end of the superconducting thin film coil (22) and a superconducting thin film cross connecting wiring portion. The surface of the connection part (25a) with (25) is the interlayer insulation film (24).
Superconducting thin film wiring part (23) and superconducting thin film cross connection from a single flat superconducting thin film layer (16) which is on the same level as the surface of the substrate (11) together with the surface of The input coil for a superconducting quantum interference device according to claim 1, wherein a wiring portion (25) is formed. 3. A thin film laminated structure formed on a substrate so as to be magnetically coupled to a superconducting ring including a Josephson junction for constituting a superconducting quantum interference device,
An input coil connected so as to form a magnetic field detection pickup coil and a magnetic flux transformer of a superconducting closed circuit, which is a spiral superconducting thin film coil (72) with multiple turns and an outer coil of the superconducting thin film coil (72). The first superconducting thin film wiring section (7) for connecting the end to one end of the pickup coil.
3b) and a second superconducting thin film wiring part (7) for connecting the inner coil end of the superconducting thin film coil (72) and the other end of the pickup coil.
3a) and a superconducting thin film cross-connect wiring part (7a) that crosses the turn part of the superconducting thin film coil (72) radially from the inner coil end of the superconducting thin film coil (72) to reach the second superconducting thin film wiring part (73a).
5), the superconducting thin film cross connection wiring part (75) and the superconducting thin film coil (7
2) which has an interlayer insulating film (74) for insulating between the turn part and the turn part, the superconducting thin film cross connecting wiring part (75) is a superconducting thin film coil.
The inter-layer insulation film (74) is embedded in the first groove (62) formed below the surface of the substrate (61) at a position crossing the turn part of the (72), and the inner coil of the superconducting thin film coil (72). Formed below the surface of the superconducting thin film cross connecting wiring part (25) except the respective end portions (75a, 75b) of the superconducting thin film cross connecting wiring part (75) to the end and the second superconducting thin film wiring part (73a). Embedded in the formed second groove (64), and the superconducting thin film is formed on the substantially flat substrate surface in the region including the surfaces of the connection portions (75a, 75b) and the surface of the interlayer insulating film (74). An input coil for a superconducting quantum interference device, comprising a coil (72), a first superconducting thin film wiring portion (73b) and a second superconducting thin film wiring portion (73a). 4. The surface of each connecting portion (75a, 75b) of the superconducting thin film cross connecting wiring portion (75) with respect to the inner coil end of the superconducting thin film coil (72) and the second superconducting thin film wiring portion (73a) is an interlayer. The surface of the insulating film (74) and the surface of the substrate (61) are on the same level level plane, and a single flat superconducting thin film layer (66) formed on this plane is replaced with the superconducting thin film coil (72). The first superconducting thin film wiring section (73b) and the second superconducting thin film wiring section (7b)
The input coil for a superconducting quantum interference device according to claim 1, wherein 3a) is formed.