JP3059806B2 - Superconducting element and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave sensor,
The present invention relates to a superconducting element used for a Josephson element such as an ID, a bolometer, and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art As an electromagnetic wave sensor, in particular, a sensor using a superconductor as a sensor for detecting an electromagnetic wave in an ultra-high frequency band on the order of several tens of GHz has attracted attention because of its extremely high sensitivity. In particular, YBa ₂ Cu ₃ O discovered several years ago
Oxide superconductors represented by _7-x (hereinafter abbreviated as YBaCuO) enter a superconducting state at a relatively high temperature of about 77 K, which is indicated by liquid nitrogen, and are therefore expected to have a wide range of applications.

A Josephson device using this superconductor is disclosed in, for example, Japanese Patent Application Laid-Open No. 3-79091. As an electromagnetic wave sensor for detecting an electromagnetic wave in an ultrahigh frequency band on the order of several tens of GHz to several THz, it is generally considered that the higher the normal conduction resistance between element terminals is, the better the detection sensitivity is. In a Josephson device as disclosed in JP-A-79091, the resistance value of the device was low, and it was not possible to expect high sensitivity as an electromagnetic wave sensor. In addition, other superconducting elements such as SQUIDs and bolometers have the same problem.

In a bridge type Josephson thin film element, a Josephson junction (SEJJ) using a step edge of a substrate or a Josephson junction of a bicrystal in which crystal planes having different crystal orientations are bonded are used. JJ: Bicrystal Joseph
son Junction) or a grain boundary Josephson junction (GBJJ; Grain Boudary Josephson Junc
element degradation due to oxygen deficiency in a bridge portion, a crystal surface junction, and a grain boundary portion.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a high-impedance high-resistance material in which a high-resistance material is interposed at the particle interface of a thin-film or thick-film formed or bulk-processed rare-earth oxide superconductor. An object of the present invention is to provide a superconducting element and a method for manufacturing the same, and a superconducting element capable of preventing element deterioration due to oxygen deficiency in a bridge portion such as a bridge type Josephson thin film element and a method for manufacturing the same.

[0006]

The superconducting element according to the present invention is characterized in that a high-resistance film made of a raw material satisfying the following conditions is laminated on a desired region on a substrate made of an oxide superconductor. A superconducting element, 1) supplying oxygen to the rare earth element-based oxide superconductor particles, or not depriving the superconducting particles of oxygen, 2) having an electric conductivity lower than that of the rare earth element-based oxide superconductor. , Wherein the raw material is Bi ₂ O ₃ .

[0007]

[0008]

According to the present invention, only the high-resistance material is melted or evaporated by simultaneously heat-treating the rare-earth-element-based oxide superconductor and the high-resistance material at a temperature at which the rare-earth-element-based oxide superconductor does not melt, A grain boundary layer made of a high-resistance material can be interposed at a grain boundary between the rare-earth-element-based oxide superconductor particles, and a superconducting element having a high resistance value of the element can be obtained, and several tens of GH can be obtained.
A superconducting element exhibiting a high inter-terminal resistance suitable as a sensor for detecting an electromagnetic wave in an ultrahigh frequency band from z to several THz is provided.

In addition, a protective film made of a high-resistance material which does not supply oxygen to the superconductor particles or takes oxygen from the superconductor particles is bridged to a desired region on the substrate made of the rare earth element oxide superconductor. By laminating the bridge part of the Josephson thin film element without heat treatment,
In particular, it is possible to prevent element deterioration due to oxygen deficiency in the grain boundary region of the bridge portion which occurs during the heat treatment.

[0010]

[First Embodiment] First, the structure of a superconducting element of the present invention will be described.

FIG. 1 is a perspective view showing an example of an electromagnetic wave sensor using a Josephson element comprising the superconducting element of the present invention, wherein 1 is a crystalline insulating substrate such as MgO, SrTiO ₃ , crystallized glass, and 2 The superconducting film provided on the surface of the substrate 1 is mainly composed of, for example, a YBaCuO-based rare earth oxide superconducting material. A width of 10 to 50 μm, a length of 200 to 300 μm, which functions as an electromagnetic wave sensor by reducing the width of the central portion of the superconducting film 2;
The sensor section 3 having a thickness of about 50 μm is widened, and both ends thereof are output electrodes (inside) 4 a and 4 a made of gold or the like having a thickness of about 0.1 to 1 μm, and a bias current electrode (outside). 4b and 4b are respectively constituted.

Here, a specific configuration of the superconducting film 2 will be described. As shown in an enlarged scale in FIG. 2, the film 2 is made of a YBaCuO-based rare-earth oxide superconducting material and has superconductor particles 5, 5.
The grain boundary layer 6 having a thickness of about 1000 Å or less is formed on the grain boundaries of the particles 5, 5...
Intervening. The grain boundary layer 6 is mainly made of a Bi—Ba—O-based oxide (high-resistance material) in which Ba and Bi ₂ O ₃ of YBaCuO are bonded, followed by YBaCuO from which a part of Ba is removed.
And Bi ₂ O ₃ (high resistance material). The grain boundary layer 6 made of such a high-resistance material is for increasing the resistance of the interface between the superconductor particles 5, 5,... Of the superconducting film 2 to improve the device characteristics.

Next, the superconducting element of the first embodiment and a method of manufacturing the same will be described in detail.

First, a method of manufacturing the rare-earth-element-based oxide superconducting material used in this embodiment will be described.

A sintered body of superconductor particles made of YBaCuO is formed by a conventionally well-known coprecipitation method and firing of the product. That is, yttrium nitrate Y (NO ₃ ) ₃ .3.5H
₂ O, barium nitrate Ba (NO ₃ ) ₂ , copper nitrate Cu (N
O _{3) 2} · 2H ₂ O were each dissolved in water, Y, Ba, C
Mix so that u becomes 1: 2: 3 in molar ratio. Then, 7 mol of an aqueous solution of oxalic acid H ₂ C ₂ O ₄ .2H ₂ O is added to 2 mol of Ba element to cause a reaction. At this time, the pH was adjusted by adding ammonia water NH ₄ OH dropwise to adjust pH = 4 to 7, specifically pH = 4.6, and the composition ratio of Y, Ba, and Cu became 1: 2: 3. To do. The precipitate generated by this reaction is filtered and then sufficiently dried to obtain a superconductor powder.

The powder thus obtained is fired in the atmosphere at 830 to 880 ° C. for 9 hours as primary firing. In this example, baking was performed at 870 ° C. for 9 hours. By this firing, powder particles having a particle size of 1 μm or less are obtained. The powder particles are formed at a pressure of about 2 ton / cm ² into a compact having a desired size.

This molded body is subjected to secondary firing to obtain YBaC
A sintered body made of YBaCuO superconductor particles having a particle diameter of 1 μm or less (superconducting phase ratio: 98%) is fired at 900 to 1000 ° C. in which uO crystal grains grow, in this example, at 925 ° C. for 8 hours in an oxygen atmosphere. ) Is formed.

The superconducting film 2 in the Josephson element shown in FIG. 1 is made of a bismuth oxide solution (melting point 81) in a molten state.
7 ° C.), immersed the superconductor particles of YBaCuO prepared by the above method, annealed at 900 ° C. for 48 hours in an O ₂ atmosphere, and gradually cooled to room temperature to obtain a bulk having a predetermined shape. It is formed by cutting and polishing. At this time,
Since the superconductor YBaCuO has a melting point of 1000 ° C. or higher, it does not melt, and the bismuth oxide solution in a molten state permeates the grain boundary layer of the superconductor particles, and the superconducting film 2 forms the structure shown in FIG.

Here, the conditions required for the raw material forming the grain boundary layer 6 are as follows: 1) supply oxygen to the superconductor particles 5, 5,... Made of YBaCuO, or Do not take oxygen from 5 ...
2) the melting point is lower than that of the superconducting particles 5, 5,... Made of YBaCuO; 3) the superconductivity particles 5, 5,.
Lower than that of the three.

In particular, 1) does not deprive oxygen except at least when the melt produced by melting the raw materials reacts at the superconductor interface, that is, the oxide superconductor does not deprive oxygen, and thus has a superconducting property. Will be retained.

Further, 2) is necessary for forming a grain boundary layer without destroying superconducting characteristics.

Further, 3) is indispensable because this raw material becomes a material constituting the grain boundary layer.

As a raw material for forming the grain boundary layer 6, the above-mentioned Bi ₂ O ₃ has an oxygen content that decreases as the temperature decreases, that is, supplies oxygen to the outside, as shown in Table 1 below. It has properties and satisfies the condition of 1). Further, the melting point is 817 ° C. as described above, and the electrical conductivity under the condition of 3) is that YBaCuO is 100 to 1000 S / cm (specific resistance: 10
1.6 × 10 ⁻⁴ S / c compared to ⁻³ to 10 ⁻² Ω · cm)
m (specific resistance: 6250 Ω · cm), which satisfies all the required conditions.

[0024]

[Table 1]

The superconducting film 2 thus formed is
As shown in FIG. 2, the thickness of the superconductor particles 5, 5...
In the following grain boundary layer 6, in addition to Bi ₂ O ₃ which is a high resistance material,
Further, Bi-Ba of a high resistance material made of BiBaO _2.77 or the like is used.
The superconducting film 2 having such a configuration is mainly in the form of an intervening -O-based oxide, and the superconducting film 2 has a state in which electrons flow through the grain boundary layer like a tunnel phenomenon due to the proximity effect of superconductivity.
It shows the characteristics as a Josephson element having a Josephson junction, and satisfies all the characteristics required for the sensor unit 3 of the electromagnetic wave sensor.

[Second Embodiment] Next, a superconducting element of a second embodiment and a method of manufacturing the same will be described in detail.

The oxide superconductor sintered body produced by the same method as in the first embodiment was ground in a mortar and weighed 1 to 5 μm.
After the powdery sintered body has a particle size of 1 μm
The following powdered Bi ₂ O ₃ (mixing ratio of 15 wt% or less based on the total amount) was added, and further ground in a mortar to uniformly mix to prepare a mixed powder (mixture) having a particle size of about 1 to 2 μm. . Thereafter, the mixed powder is mixed with a superconductor particle made of YBaCuO superconductor and Bi at a pressure of about 2 ton / cm ^2.
Approximately 10 mm x 5 mm x 1 mm with ₂ O ₃ particles uniformly mixed
To form a molded product (mixture). FIG. 3 is an enlarged sectional view showing an outline of a main part of the molded body. Reference numeral 5 denotes superconductor particles made of a YBaCuO superconductor, and 7 denotes particles of a high-resistance material made of Bi ₂ O ₃ .

The YBaCuO superconductor particles 5, 5,...
May be formed by a conventionally well-known method other than the coprecipitation method, and can be appropriately changed.

Subsequently, in an electric furnace, the compact is placed on a bed of particles made of zirconia having a diameter of 1 mm.
After raising the temperature to about 940 ° C. in about 3 hours, maintaining the temperature at 900 to 940 ° C. for about 3 to 48 hours, and gradually cooling to room temperature at about 100 ° C./hr, a heat treatment is performed to obtain a heat-treated molded body.
That is, by this heat treatment, the Bi ₂ O ₃ particles in the compact are melted to form a bismuth oxide melt, and as a result,
Superconductor particles made of a YBaCuO superconductor are immersed in this bismuth oxide solution, and the structure shown in FIG. 2 is obtained.

FIG. 4 shows the differential thermal analysis at a mixing ratio of 15 wt% and the measurement results of the weight change at that time. The measurement conditions at this time are as follows: the temperature change rate is 10 ° C./min, and the sample weight is 7
2.336mg, oxygen gas atmosphere (80ml / min)
It is.

From this figure, it can be seen that the calorie change (a) and the weight change (b) occur at 930 ° C., and that the chemical change is remarkable. In this measurement, the temperature of the sample is lowered by more than ten degrees Celsius due to the setting of the thermocouple, so that the chemical reaction actually occurs at a temperature slightly higher than 940 degrees Celsius. As a result, when the compact is heat-treated at 950 ° C. (holding for 3 hours), no superconducting properties appear in the compact. Further, when the molded body is subjected to a heat treatment at 900 ° C. or lower (held for 48 hours), the molded body becomes brittle, which is inconvenient as an element.

Therefore, the heat treatment holding temperature for immersing the superconductor particles composed of the YBaCuO superconductor in the bismuth oxide solution is desirably higher than 900 ° C.
It can be seen that it is necessary to carry out in a temperature range of 0 ° C. or less.

[0033] 5-9 (weight percentage of Bi ₂ O ₃ / powder mixture) the mixing ratio of Bi ₂ O ₃ in the mixed powder is the mixed powder is 0,5,10,15,20Wt% respectively 5 shows resistance-temperature characteristics of a heat-treated molded body (held at 940 ° C. for 3 hours) prepared from the above.

From these figures, it can be seen that the heat-treated molded body with a mixing ratio of 0 to 10 wt% has good superconducting properties, and even at a mixing ratio of 15 wt%, although it has a slight tail near the critical temperature, the superconducting properties are not practical. It turns out that there is no problem. On the other hand, in the heat-treated molded body with a mixing ratio of 20 wt%, a clear critical temperature is not seen, and it can be seen that good superconducting properties cannot be obtained. Therefore, the mixing ratio of Bi ₂ O ₃ in the mixed powder is 15
wt% or less.

FIG. 10 shows the relationship between the superconducting films formed from different mixing ratios and the specific resistance ρ at the time of onset.

From this figure, it can be seen that as the mixing ratio increases, the specific resistance ρ, that is, the element resistance Rn when the element is formed, increases. Therefore, the characteristics of the Josephson element manufactured from a mixture having a large mixture ratio out of the mixture ratio showing the practicable superconducting characteristics of 15 wt% or less are improved.

Next, the same electromagnetic wave sensor as that of the first embodiment was prepared by using the heat-treated molded body obtained as described above (heat-treatment holding temperature: higher than 900 ° C. and lower than 940 ° C.). That is, after the heat-treated molded body is melt-solidified with, for example, a Pb-based low-melting glass having a melting point of about 400 ° C. on an insulating substrate 1 such as MgO or crystallized glass, or joined with a resin or the like,
The heat-treated molded body is polished and processed into a desired shape to obtain the electromagnetic wave sensor shown in FIG.

FIGS. 11A and 11B are sectional views showing the results of SEM analysis of the superconducting film 2 (mixing ratio: 15 wt%) and the comparative example (mixing ratio: 0 wt%), respectively.

The superconducting film thus formed has a shape in which a grain boundary layer having a thickness of about 1000 mm or less is interposed between the gaps of the superconducting particles made of YBaCuO having a particle size of several μm as shown in FIG. It has become.

The grain boundary layer 6 includes superconductor particles YBaC
Ba and Bi from uO_TwoO_ThreeIs a high-resistance material combined with
BiBaO_2.77Bi-Ba-O-based oxides such as
Rare, followed by a part inside the presence of its superconductor particles
Such as YBaCuO (Y_TwoBa₁Cu₁O_X, C
uO and Y_TwoO_Three), But on the outside Bi, which is a high resistance material _Two
O_ThreeX-ray analysis reveals that there are many components in order
did.

The superconducting film 2 having such a structure has a state in which electrons flow as if by a tunneling phenomenon through the grain boundary layer due to the proximity effect of superconductivity, and exhibited characteristics as a Josephson element having a Josephson junction. It satisfies all the characteristics required for the sensor unit 3 of the sensor.
For example, the element resistance Rn (50K) of the conventional electromagnetic wave sensor having no interface layer made of a high-resistance material is about 0.1Ω, whereas the element resistance Rn of the electromagnetic wave sensor of the present embodiment is about 0.1Ω.
(50K) is improved to 0.2 to 0.3Ω at a mixing ratio of 5 wt%. Further, at a mixing ratio of 10 wt%, Rn (50K) becomes 3
Ω, the element sensitivity Rv increases to 100 V / W due to a reduction in impedance loss between the element and the space-propagating electromagnetic wave or an improvement in the electromagnetic wave detection sensitivity of the element itself, and a semiconductor sensor (3) made of GaAs Schottky.
00K), the characteristics are better. Further, at a high mixing ratio of 15 wt%, Rn is 5 to 13Ω and the mixing ratio is 1
Rv becomes larger than 0 wt%.

Since the superconducting film of this embodiment is heat-treated at a heat treatment holding temperature higher than 900 ° C. and not higher than 940 ° C., it is more preferable because it is not brittle as compared with the superconducting film of the first embodiment.

In the above description, the superconducting film is made of YBa
A type in which a bulk obtained through a immersion step and a slow cooling step of a molten bismuth oxide solution of superconducting particles of CuO is cut and polished into a predetermined shape, or YBaCuO
Description of the so-called bulk type, such as a type in which a superconductor particle is mixed with Bi ₂ O ₃ powder, and a bulk obtained through a molding step, a heat treatment step, and a slow cooling step is cut and polished into a predetermined shape to form the bulk. However, it can also be realized with a thin film configuration.

More specifically, a YBaCuO thin film is formed on an MgO substrate to a thickness of 20 μm by a method such as magnetron sputtering, ion beam sputtering, or laser beam sputtering, and then a thin film of Bi ₂ O ₃ is formed on the YBaCuO thin film. By applying a heat treatment at about 900 ° C. by applying a thickness of 10 to 20 μm using a sputtering method, as shown in FIG. 2, the superconductor particles 5, 5. About 100
Obtaining a structure in which a grain boundary layer 6 made of a high-resistance material mainly composed of a Bi-Ba-O-based oxide having a thickness of 0 ° or less, YBaCuO and Bi ₂ O ₃ from which Ba has been removed, is obtained. Can be.

[Third Embodiment] Next, a superconducting element of a third embodiment and a method of manufacturing the same will be described in detail.

In the second embodiment, a superconducting thin film made of a rare-earth oxide superconductor and a high-resistance film made of a high-resistance material are sequentially formed on a substrate, and then heat-treated to form a high-resistance film on the interface of the superconductor particles. When a superconducting element such as a Josephson element is formed with a material interposed, the high-resistance material evaporates during the heat treatment, so that a desired amount of the high-resistance material is interposed at the interface between the superconductor particles. It is difficult to set various conditions such as film thickness and heat treatment temperature control.

Therefore, in the third embodiment, a superconducting material capable of easily interposing a high resistance material at the particle interface of a rare earth oxide superconductor formed as a thin film while preventing evaporation of the high resistance material during heat treatment. A method for manufacturing the device will be described. FIG. 12 shows a manufacturing process of the superconducting element according to the third embodiment.

First, the M having the (100) crystal plane on the upper surface
gO substrate or SrTiO whose upper surface is a (110) crystal plane
Insulating substrate 31 of about 6 mm x 6 mm x 1 mm such as ₃ substrates
Prepare

Next, as shown in FIG. 12A, a width of 1 mm, a length of 5 mm, and a thickness of 300 to 10 mm is formed on the upper surface of the insulating substrate 21 by ion beam sputtering through a metal mask.
B, which is a high resistance material having a thickness of about 500
A high resistance film 23 made of i ₂ O ₃ is formed. This film is
The target is made of a desired bismuth oxide target, for example, under the conditions of Ar gas pressure: 2 × 10 ⁻⁴ Torr, substrate temperature: room temperature, and film formation rate: 2000 ° / hr.

Subsequently, as shown in FIG. 12B, a resist is applied on the high resistance film 23 by a spin coating method, and has a dot-like pattern having a diameter of about 1 μm and a mutual interval of about 1 μm. After exposing and developing through a metal mask, a dot-like resist pattern having a diameter of about 1 μm and an interval of about 1 μm is formed on the high-resistance film 23, for example,
Etching by ion beam etching method,
The high-resistance film 23s is formed of a high-resistance film 23s having a shape in which high-resistance materials are distributed about 1 μm in diameter and about 1 μm apart from each other. FIG. 13 shows the high-resistance film 2 having the distributed shape.
It is an enlarged view of 3s.

Thereafter, as shown in FIG. 12 (c), about 0.3 to 1 μm thick, for example, 0 to 1 μm of YBaCuO is formed on the high resistance film 23s by ion beam sputtering through a mask corresponding to the shape of the electromagnetic wave sensor. An element wafer 24 is formed by forming a superconducting thin film 22 having a thickness of 0.5 μm.
For this film formation, a target made of YBa ₂ Cu _4.5 O _7-x is used, for example, a total gas pressure ratio: 2 × 10 ⁻⁴ Torr (flow rate ratio, Ar gas: O ₂ gas = 2: 1), and a substrate temperature: 670.
It is formed under the conditions of -700 ° C. and a film forming rate of 2000 ° / hr. The values of the thicknesses of the high-resistance film and the superconducting thin film are determined based on YBaCuO and Bi having good superconducting characteristics and element resistance.
It may be appropriately selected so as to be in the range of the mixing ratio with ₂ O ₃ .

The element wafer 24 formed as described above
Is heated in an electric furnace in an oxygen atmosphere, for example, from room temperature to a predetermined temperature in about 3 hours.
After holding for a time, it is gradually cooled to room temperature at about 100 ° C./hr.
In this case, the predetermined temperature is the melting point of Bi ₂ O ₃ (817
° C) and lower than the temperature at which the reaction takes place and the superconductivity is lost (940 ° C). By this heat treatment, Bi ₂ O ₃ constituting the high-resistance film 23 is melted into a bismuth oxide solution, so that the YBaCuO superconductor particles are immersed in the bismuth oxide solution, and the superconducting thin film 22 is obtained.

When the superconducting film is formed by the thin film forming method as described above, heat treatment may be performed in the range from the melting point of Bi ₂ O ₃ to 940 ° C., but the superconducting thin film may be peeled off. It is preferable to perform the heat treatment at an upper limit in a range from 940 ° C. to a temperature lower by about 20 ° C., particularly at a temperature of 900 ° C. or less, at which there is no fear that the superconducting particles grow and reduce the resistance.

Subsequently, the heat-treated element wafer 24
Is cut into a predetermined shape to produce the electromagnetic wave sensor shown in FIG.

Here, Bi ₂ O ₃ forming the high resistance film is used.
Has the property that the oxygen content of the melt decreases as the temperature decreases, that is, oxygen is supplied to the outside. The melting point of YBaCuO is higher than 1000 ° C.
17 ° C., and the electric conductivity was 10% for YBaCuO.
0 to 1000 S / cm (specific resistance: 10 ^-3 to 10 ^-2 Ω · c
1.6 × 10 ⁻⁴ S / cm (specific resistance: 62)
(50 Ω · cm). Therefore, since the molten liquid created by melting the high-resistance material does not take at least oxygen except at least when reacting at the superconductor interface, the composition of the oxide superconductor does not change, and the high-resistance material is melted. The superconductor is not melted when
Since the structure of the oxide superconductor does not change, the superconductivity is not impaired. Furthermore, high resistance materials have low electrical conductivity,
It is suitable as a material constituting a grain boundary layer of a superconducting element.

The superconducting film 22 thus formed
As shown in FIG. 2, Bi ₂ O ₃ as a grain boundary layer 6 of a high-resistance material and B of superconductor YBaCuO are interposed between gaps of superconductor particles 5 made of YBaCuO having a particle size of several μm.
Bi-Ba such as BiBaO _2.77 in which a is bonded to Bi ₂ O ₃
-O-based oxide and YBaC from which Ba of YBaCuO is removed
In this configuration, uO is mainly interposed. The superconducting film 2 having such a configuration exhibits characteristics as a Josephson element having a grain boundary coupling type Josephson junction in which a large number of superconductors and normal conductors are joined, and the element resistance Rn is used as the sensor unit 3 of the electromagnetic wave sensor. About 10Ω, element sensitivity Rv is 1000V
/ W.

The high-resistance film 23s in which the high-resistance material is dispersed is effective even if the high-resistance material is non-uniformly dispersed. However, it is preferable that the high-resistance material is uniformly dispersed as in the above embodiment. This is desirable because the melt of the high-resistance material is uniformly diffused by the superconducting thin film during the heat treatment. Further, the dispersed high-resistance material does not have to have a circular dot shape, but can be changed as appropriate. For example, a mesh shape may be used.

Further, a superconducting thin film may be directly formed on the high-resistance film 23. However, if the high-resistance film has a shape in which the high-resistance material is dispersed as described above, the bismuth oxide melt during heat treatment is formed. Desirably, the superconducting particles are diffused radially into the superconducting thin film so that the superconducting particles are uniformly immersed. Also, since the superconducting thin film can be formed mainly on the surface of the substrate, deterioration of the superconducting characteristics can be suppressed, and furthermore, the superconducting material and In order to make the resistance material a desired mixing ratio, the high resistance film 23s in the form of being dispersed and arranged can be made thicker than the high resistance film 23, so that the film thickness can be easily controlled.

In the above embodiment, the insulating substrate is used as the substrate. However, an insulating film formed on a substrate made of a superconductor may be used and can be appropriately changed.

The method for forming the high-resistance film and the superconducting thin film is not limited to the sputtering method, but may be MOCVD, C
Various thin film forming techniques such as a VD method or a vapor deposition method can be used as appropriate, and a paste in which a high-resistance material and a superconductor powder are dispersed may be formed by screen printing and firing, or may be changed as appropriate. It is possible.

In the method for manufacturing a superconducting element according to the present invention, a superconducting thin film is formed on a high-resistance film made of a high-resistance material. To prevent evaporation of the high-resistance material from the superconducting film. As a result, a high-resistance interface layer can be easily formed. In particular, it is desirable to form the high-resistance film into a shape in which the high-resistance material is dispersed, since the high-resistance material is uniformly diffused into the superconducting thin film.

[Fourth Embodiment] Next, a superconducting element of a fourth embodiment and a method of manufacturing the same will be described in detail.

In the fourth embodiment, as another specific structural example having a thin film structure, as shown in FIG. 14, (1) SEJJ using a step edge of a substrate (FIG. 14A),
(2) Bicrystal JJ in which crystals having different crystal orientations are joined (FIG. 14B), and (3) Multi-grain boundary GBJJ (FIG. 14)
(C)) A superconducting element having a structure using a Bi ₂ O ₃ thin film which can provide an effect as a protective film for a bridge portion as described above, and a method of manufacturing the same will be described.

As a cause of deterioration of the bridge type Josephson thin film element composed of an oxide superconductor applied to an electromagnetic wave sensor or an element for SQUID, oxygen deficiency, impurity adsorption, or crack generation due to a heat cycle in an artificial grain boundary region or the like. Can be considered.

Here, Bi ₂ O ₃ used as a protective film is
1) Supplying oxygen to the superconductor particles or not taking oxygen from the superconductor particles; 2) Electric conductivity is lower than that of the rare earth element-based oxide superconductor. Therefore, if this Bi ₂ O ₃ thin film is formed by the above-described method so as to cover a bridge portion where cracks are likely to occur, it is possible to prevent, for example, the out-of-film release of oxygen at the bridge portion, and Ic (Critical current), Tc
(Critical temperature) and deterioration of element characteristics of the bridge type Josephson thin film element, which are caused by a decrease in Rn (element resistance).

FIG. 14 shows a specific example in which an effect as a protective film in a bridge portion of a bridge type Josephson thin film element can be obtained.

First, in the same manner as in the first embodiment, Y
Using an oxide superconductor made of BaCuO, 1500
Bridge-type Josephson thin-film devices 32, 42, and 52 having a thickness of about 2000 mm are formed on the substrates 31, 41, and 51. Subsequently, a protective film composed of Bi ₂ O ₃ films 33, 43 and 53 is formed on a bridge portion serving as a sensor portion of this element. The Bi ₂ O ₃ film is formed by RF magnetron or ion beam sputtering or the like at a room temperature of a film forming substrate at a desired area such as a bridge portion where oxygen vacancies and cracks are easily generated on the superconductor YBaCuO film. By forming the film at room temperature, oxygen vacancies from the surface of the underlying YBaCuO film can be minimized, and evaporation of Bi ₂ O ₃ during film formation can be prevented. At this time, the thickness of the Bi ₂ O ₃ film is 500
制 御 Laminate by controlling to about. This film thickness is such that the stress due to the difference in thermal expansion coefficient can be ignored.

FIG. 14A shows the M direction in the crystal direction (100).
The crystallographic direction (00) is applied to the step-shaped substrate 31 made of gO or the like.
1) The case where the Josephson element 32 made of YBaCuO is formed (SEJJ), and its perspective view (a1).
And its II-II 'sectional view (a2) are shown. A junction having a different crystal orientation is formed at the edge portion e of this step.
Conventionally, many defects such as oxygen deficiency have occurred in the grain boundary portion f of this joint. When the Bi ₂ O ₃ film 33 is provided in this portion,
Since this film is made of a material that does not supply oxygen to the superconductor particles or does not deprive the superconductor particles of oxygen, oxygen deficiency of the oxide superconductor is suppressed, and as a result, the element of the Josephson element Deterioration of characteristics can be prevented.

FIG. 14B is a cross-sectional view of a case where the YBaCuO film 42 having different crystal orientations h and l on a flat substrate 41 is applied to an artificial grain boundary (bicrystal JJ). . Also in this case, defects such as oxygen vacancies are likely to occur in the grain boundary portion b. However, by providing the Bi ₂ O ₃ film 43 in this portion, similarly, the deterioration of the superconducting element can be prevented.

FIG. 14C shows the YBaCu on the substrate 51.
This is a plan view in which a Bi ₂ O ₃ film 53 is formed as a protective film on a superconducting element 52 formed by a granular superconductor made of O (multi-grain boundary GBJJ). Also in this case, oxygen deficiency at the grain boundary of the granular superconductor can be prevented, and similarly, deterioration of the superconducting element can be prevented.

As described above, in the fourth embodiment, Bi ₂ O ₃
When a high-resistance film such as a film is used as a protective film for preventing deterioration of a superconducting element due to oxygen deficiency, the oxide superconductor is made of YB
aCuO and other rare-earth oxide superconductors
i based _{(Bi 2 Sr 2 Ca 1 Cu} 2 O X , etc.), or even in the case of Tl system _{(Tl 2 Ba 2 Ca 2 Cu} 3 O X , etc.), the effect of preventing the deterioration of the same superconductive element is obtained.

As described above, in the first to fourth embodiments, YBaCuO is used as the superconductor particles. However, the present invention is not limited to YBaCuO, but EuBaCuO, in which Y is replaced with another rare earth element,
Various rare earth element-based oxide superconductors such as HoBaCuO and ErBaCuO can be used as appropriate.

As a high resistance material, MoO ₃ is used in addition to Bi ₂ O ₃ used in the first to fourth embodiments. This M
oO _{3 is} also a metal oxide, does not take oxygen from YBaCuO, has a melting point of 795 ° C., and an electric conductivity of about 1.0 × 10 ⁻⁴ S / cm, and is suitable for high-resistance materials. I have. Further, in addition to Bi ₂ O ₃ and MoO ₃ , SbO, Pb
O, B ₂ O ₃ , PtO _2, etc. could also be used as high resistance materials as well.

The method for manufacturing a superconducting element of the present invention is not limited to the above-mentioned electromagnetic wave sensor, but can be used for other Josephson elements such as SQUIDs and also for other superconducting elements such as bolometers.

[0075]

According to the superconducting element and the method of manufacturing the same of the present invention, a high-resistance film made of a raw material satisfying the following conditions is laminated on a desired region on a substrate made of an oxide superconductor. 1) Supplying oxygen to the rare earth element-based oxide superconductor particles or not taking oxygen from the superconductor particles; 2) Electric conductivity lower than that of the rare earth element-based oxide superconductor Since the raw material is Bi ₂ O ₃ , a Josephson element exhibiting a high interparticle resistance is provided, and a high-sensitivity electromagnetic wave sensor for detecting an electromagnetic wave in an ultrahigh frequency band of several tens of GHz to several THz is provided. Can be realized.

According to the method for manufacturing a superconducting element of the present invention, a superconducting thin film is formed on a high-resistance film made of a high-resistance material, so that the high-resistance material that melts or evaporates during heat treatment constitutes the superconducting thin film. A high-resistance interface layer that is adhered to the interface of the superconductor particles can be easily formed.

Further, according to the method for manufacturing a superconducting element of the present invention, deterioration of the element can be prevented by using the Bi ₂ O ₃ thin film as a protective film for the bridge portion of the bridge type Josephson thin film element.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structure of a superconducting element according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing an outline of a main part of a superconducting element of the present invention.

FIG. 3 is an enlarged sectional view showing an outline of a main part of a manufacturing process of a superconducting element according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a differential thermal analysis of a superconducting film according to the present invention and a change in mass thereof.

FIG. 5 is a diagram showing a relationship between resistance and temperature characteristics of a superconducting film of a comparative example of the present invention.

FIG. 6 is a diagram showing a relationship between resistance and temperature characteristics of a superconducting film according to the present invention.

FIG. 7 is a diagram showing a resistance-temperature characteristic relationship of a superconducting film according to the present invention.

FIG. 8 is a diagram showing a relationship between resistance-temperature characteristics of a superconducting film according to the present invention.

FIG. 9 is a diagram showing a resistance-temperature characteristic relationship of a superconducting film according to the present invention.

FIG. 10 shows the specific resistance and Bi ₂ O _{3 of the} superconducting film according to the present invention.
It is a figure which shows the relationship of the addition amount of.

FIG. 11 is a diagram showing a cross section of a superconducting film according to the present invention and a comparative example.

FIG. 12 is a process chart showing a manufacturing process of a superconducting element according to a third embodiment of the present invention.

FIG. 13 is an enlarged view showing a distributed arrangement of high-resistance films according to a third embodiment of the present invention.

FIG. 14 is a view showing a structure of a superconducting element according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Superconducting film 3 Sensor part 5 Superconducting particle 6 Grain boundary layer

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C23C 14/08 H01B 12/06 ZAA H01B 12/06 ZAA H01L 39/22 ZAAD H01L 39/22 ZAA C04B 35/00 ZAA (56) References Features JP-A-1-215007 (JP, A) JP-A-2-192402 (JP, A) JP-A-64-10676 (JP, A) JP-A-1-138770 (JP, A) (58) Int.Cl. ⁷ , DB name) H01L 39/24 C01G 1/00 C01G 3/00 C04B 35/00 C23C 14/06 C23C 14/08 H01B 12/06 H01L 39/22 H01L 39/02 H01L 39/00

Claims (7)

(57) [Claims] 1. A superconducting element characterized in that a high resistance film made of a raw material satisfying the following conditions is laminated on a desired region on a substrate made of an oxide superconductor. 1) A rare earth element-based oxide superconductor Supplying oxygen to the particles or not depriving the superconducting particles of oxygen; 2) electric conductivity is lower than that of the rare earth oxide superconductor; and the raw material is Bi ₂ O ₃ . A superconducting element, comprising: 2. A method for manufacturing a superconducting element in which a grain boundary layer made of a high-resistance material is interposed at a grain boundary between rare earth element-based oxide superconductor particles, the method comprising the steps of: A method of manufacturing a superconducting element, comprising: a step of immersing in a melt of a raw material satisfying the following conditions at a temperature at which the superconducting particles do not melt; 2) the melting point is lower than that of the rare earth oxide superconductor, and 3) the electric conductivity of the rare earth oxide superconductor. Lower. 3. A method of manufacturing a superconducting element in which a grain boundary layer made of a high-resistance material is interposed at a grain boundary between rare-earth-element-based oxide superconductor particles, comprising a substrate made of a raw material satisfying the following conditions. A step of sequentially laminating a resistive film and a superconducting thin film made of the rare-earth element-based oxide superconductor, a step of performing a heat treatment at a temperature at which the rare-earth-based oxide superconductor particles do not melt, and a step of gradually cooling; A) a method for manufacturing a superconducting element, which comprises: 1) supplying oxygen to the rare earth element-based oxide superconductor particles or not removing oxygen from the superconductor particles; and 2) melting point of the rare earth element. 3) The electric conductivity is lower than that of the rare earth oxide superconductor. 4. The method according to claim 3, wherein the high resistance film has a shape in which the raw materials are dispersed. 5. The method according to claim _{2, wherein} said raw material is Bi ₂ O ₃ . 6. A temperature at which the rare-earth-element-based oxide superconductor particles are immersed in a melt of the raw material, and a temperature at which the raw material is in a molten state in the heat treatment step is 9.
The method for producing a superconducting element according to claim 2, wherein the temperature is higher than 00 ° C and equal to or lower than 940 ° C. 7. A mixing ratio of the raw material to the total amount of the raw material and the rare earth oxide superconductor is 0 wt%.
7. The method for manufacturing a superconducting element according to claim 2, wherein the content is not more than 15 wt%.