JPH04345075A - Superconducting element and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a multilayered superconducting element having a stable junction structure using oxide superconductor. CONSTITUTION:A superconducting element of a planar type structure is formed as follows; a junction is formed by bringing a non-superconducting layer 12 into contact with a superconducting layer 13 formed of a lead based superconducting oxide thin film in which at least lead, copper and oxygen are contained as main components, the superconducting layer 13 is isolated into at least two parts and turned into superconducting poles, the non- sperconducting layer 12 is formed of a lead based oxide thin film containing oxygen more than the superconducting layer 13, and a superconducting junction part is formed by using the above layers 12, 13.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting element formed from an oxide superconductor thin film having a high critical temperature, and a method for manufacturing the same.

0002

[Prior Art] Muller (Muller) is a high-temperature superconductor.
An oxide superconductor with a perovskite-type structure was discovered by E.L.R. Since then, superconductivity has been confirmed in various oxide systems. It has been discovered that superconductors have a superconducting critical temperature of about 70K, for example, as reported in Nature, Vol. 336, pp. 211-214 [R. J. Cava, B.
．． Batlogg, J. J. Krajewski, L.
．． W. Rupp, L. F. Schneemeyer,
T. Siegrist, R. B. van Dove
r, P. Marsh, W. F. Peck, Jr.
P. K. Gallagher, S. H. Glarum
, J. H. Marshall, R. C. Farro
w, J. V. Waszczak, R. Hull an
dP. Trevor, Nature, Vol. 3
36, 211-214 (1988)].

[0003] As a result of detailed analysis, this material has a layered structure similar to other high-temperature oxide superconductors, with two layers of perovskite structural units (A, Ln) and CuO3 adjacent to each other.
It has a structure sandwiched between bO-Cu-PbO block layers. The ideal chemical composition is (Pb2Cu)(A,Ln)3C
u2Ox, and (Pb2Cu)S is a typical substance.
r2(Y,Ca)Cu2Ox is known.

On the other hand, a superconducting junction element is a typical element using a superconductor material. This device features a structure in which a non-superconducting layer is sandwiched between two superconductors, and is expected to be used as an ultra-high-speed switch, ultra-high frequency signal processing, etc. At present, this type of device using high-temperature superconducting materials includes a point-contact superconducting junction device in which an oxide superconductor such as YBa2Cu3Oy is split in half and brought into slight contact again; Prototype bridge-type superconducting junction devices have been produced in which the thin film is processed into a constricted shape.

[0005]

[Problems to be Solved by the Invention] Among the superconducting bonding devices that have been prototyped so far, the point contact type in which oxide superconductors are brought into contact with each other has not been able to achieve reproducibility and has unstable characteristics. Another disadvantage of the bridge type, in which the oxide superconductor is constricted, is that it can be damaged by even the slightest electrostatic shock.

[0006] Therefore, a planar superconducting element having a stable junction structure using an oxide superconductor is desired. This is characterized by a structure in which a superconducting thin film and a non-superconducting thin film are laminated, and this superconducting thin film is separated into at least two parts to form a superconducting electrode. Since the lamination is carried out at a relatively high temperature, the elements constituting the superconducting layer and non-superconducting layer may diffuse, or the materials used for the superconducting layer and the material for the non-superconducting layer may have different coefficients of thermal expansion, resulting in heat loss. There were problems such as the stress impairing the superconductivity of the superconducting layer and the formation of pinholes in the non-superconducting layer.

[0007] Furthermore, problems have been pointed out, such as poor crystallinity of the superconducting layer due to lattice mismatch due to differences in crystal structures between the materials used for the superconducting layer and the materials for the non-superconducting layer. Ta.

The present invention provides a superconductor that has a chemically stable crystal structure, has little deterioration in the superconducting properties of a superconducting layer, and can maintain the superconducting properties of a superconducting electrode laminated on a non-superconducting layer. The purpose of the present invention is to provide an element and a method for manufacturing the same.

[0009]

[Means for Solving the Problems] The present invention uses a superconducting layer and a non-superconducting layer formed by stacking lead-based oxide thin films containing at least lead, copper and oxygen as main components, Separate into two parts in the plane direction, and
A superconducting junction is formed by separating the two superconducting layers into a superconducting junction where current flows through a non-superconducting layer containing a larger amount of oxygen than the superconducting layers. This aims to solve the previous problem by using a superconducting element with a unique structure.

0010

[Operation] In the superconducting element of the present invention, a lead-based thin film oxide is laminated on a substrate, and the lead-based oxide directly above the substrate is a non-superconducting layer.
The lead-based oxide on this non-superconducting layer is a superconducting layer, and this superconducting layer is divided into at least two in the plane direction, and when forming the non-superconducting layer, the oxygen partial pressure is controlled high, Conversely, this can be achieved by lowering the oxygen partial pressure when forming a superconducting layer. The reason why a thin film structure is better when the oxygen partial pressure is lower is not clear, but it may be because the valence of the metal element in the PbO-Cu-PbO block layer is low, so excessive oxidation will destroy the structure of the block layer. It is thought that there is.

[0011] Furthermore, since the non-superconducting layer contains the same lead as the superconducting layer, it is thermally stable and has little diffusion even with the lead element, which has a high vapor pressure, making it possible to reproduce an almost perfectly uniform non-superconducting layer. It is possible to form a superconducting element with good properties and exhibit good current-voltage characteristics. At the same time, since the non-superconducting layer of this superconducting element has the same crystal structure as the superconducting layer, the crystallinity of the non-superconducting layer itself and the superconducting layer material formed thereon is improved.

0012

[Example] The present invention has the advantage that the oxide superconducting properties can be controlled by adjusting the oxygen partial pressure, and by using this to change the oxygen partial pressure when stacking oxide thin films, any layer becomes non-superconducting. lead-based oxide superconductors, unlike other oxide superconductors, can obtain a better thin film structure and superconducting properties by lowering the oxygen partial pressure; The fact that oxide thin film superconductors can be formed at relatively lower substrate temperatures than other oxide superconductors, and by taking advantage of these factors, they can be formed on non-superconducting layers of planar thin film superconducting elements. This was achieved based on five factors: the superconducting layers can be stacked without changing their atomic structures.

In the conventional production of oxide superconducting thin films,
It is important to promote oxidation to obtain good superconducting properties.
They were produced by increasing the oxygen partial pressure in the production atmosphere as much as possible, or by using active oxygen, atomic oxygen, ozone, etc., which have higher oxidizing ability, in place of ordinary oxygen molecules.

However, this technology was applied to Pb-based superconductor Pb-A-Ln-Cu-O, which is the same high-temperature oxide superconductor.
When applied to , it was not possible to obtain the crystal structure of a superconductor in a thin film. As mentioned above, this is Pb
The valence of the metal element in the O-Cu-PbO block layer is low,
Assuming that excessive oxidation would destroy the structure of the block layer, the inventors conducted an experiment in which the oxygen partial pressure in the creation atmosphere was extremely lowered, and found that although it was an oxide material, First, it was surprisingly discovered that a thin film having a crystalline structure of a Pb-based superconductor can be obtained satisfactorily below a certain oxygen partial pressure. It is better for the oxygen partial pressure to be moderately low, but the upper limit is 0.1 Pa.
It was about.

As a result, when creating a Pb-based thin film by sputtering deposition, for example, instead of the usual sputtering gas that uses a mixed gas of oxygen and inert gas for oxide thin films, only an inert gas that does not contain oxygen is used. If this is done, a good Pb-based superconducting thin film can be obtained. In addition, when creating this Pb-based thin film using a high vacuum evaporation apparatus such as MBE, electron beam evaporation, ion beam sputtering, or laser evaporation, active oxygen, which has strong oxidizing power,
There is no need to use special gases such as atomic oxygen or ozone, and the vacuum level near the substrate can be created at a high vacuum of, for example, 10-3 Pa or less, making it particularly effective for atomic layer controlled deposition. emits.

[0016] Furthermore, with this Pb-based material, the temperature of the substrate during thin film formation is relatively low compared to other oxide superconducting materials.
It can be produced at 400-600°C. If the substrate temperature is higher than this, the Pb element in the film will re-evaporate, so P
It was confirmed that a good crystal structure of the b-based superconductor could not be obtained.

When such a Pb-based layered oxide is used as a material for a superconducting layer and a non-superconducting layer of a superconducting junction in a superconducting element, the Pb-based superconducting thin film of the superconducting layer can be formed at a relatively low temperature. There is no need to pay special attention to the oxidation conditions that are a problem when thinning oxide superconducting materials other than Pb to achieve superconductivity, and the non-superconducting thin film is Since the Pb-based superconducting thin film can be formed simply by controlling the oxygen conditions, a stable process can be realized in manufacturing the device.

[0018] Furthermore, since the non-superconducting layer also contains the same Pb, it is thermally stable and has little diffusion even with the Pb element, which has a high vapor pressure, and it is possible to reproduce a non-superconducting layer that has an almost perfectly uniform layer structure. It is possible to form a superconducting element with good properties and exhibit good current-voltage characteristics. At the same time, since the non-superconducting layer of this superconducting element has the same crystal structure as the superconducting layer, the crystallinity of the non-superconducting layer itself and the superconducting layer material facing it are improved. In particular, by using thin films of Pb-based layered oxides, which serve as superconducting and non-superconducting layers, in which the c-axis of the crystal is oriented perpendicular to the substrate surface, it has good crystallinity. A superconducting thin film with superconducting properties can be realized, which makes it possible to realize a more stable superconducting junction device.

The form of the superconducting element of the present invention is a planar type, and its manufacturing method includes the above-mentioned sputtering vapor deposition,
This can be done by conventional techniques such as MBE, electron beam evaporation, ion beam sputtering, or laser evaporation. As mentioned above, the superconducting element of the present invention uses a Pb-based oxide thin film, that is, a thin film containing at least lead (Pb) and copper (Cu) as main metal components is deposited on a heated substrate, and then the thin film is first deposited on the substrate. is Pb
During the Pb-based oxide thin film formation step or the Pb-based oxide thin film formation step is interrupted, and non-superconductivity is achieved by either introducing an oxidizing gas or irradiating oxidizing ions. Next, when a Pb-based oxide thin film whose main metal is the same as that of the non-superconducting layer is deposited on this non-superconducting layer, this Pb-based oxide thin film becomes a superconducting layer. As mentioned above, the superconducting layer of the superconducting element of the present invention has the same constituent metal elements as the non-superconducting layer. Problems such as deterioration of crystallinity of the superconducting layer due to lattice mismatch due to differences in materials between the superconducting layer and the superconducting layer can be solved. In addition, since the superconducting element of the present invention uses a lead-based oxide thin film for both the non-superconducting layer and the superconducting layer, it is thermally stable even with lead element having a high vapor pressure, has little diffusion, and has a good current flow. A superconducting element having voltage characteristics can be provided.

As the oxidizing gas used in the above-mentioned non-superconducting process, for example, ozone gas or nitrogen oxide gas is used, but ozone gas, N2O gas or NO
2 gases are preferred because they have strong oxidizing power. In addition, as the oxidizing ions scattered in the above-mentioned non-superconducting process, for example, oxygen ions, sulfur ions, chlorine ions, fluorine ions, etc. are provided, but oxygen ions are preferable because they exist easily as individual ions and are easy to handle. preferable.

Furthermore, when fabricating the superconducting element of the present invention, in order to protect the superconducting layer from treatment processes such as etching, a stable protective layer such as platinum is formed on the superconducting layer using a conventional method. Of course, it may also be provided by

In order to further understand the content of the invention made by the present inventors, a Josephson device will be taken up as an example of the superconducting device of the present invention and will be explained using specific examples.

Embodiment 1 FIGS. 1 to 5 are process diagrams showing an embodiment of the present invention.

Pb-based oxide superconductor Pb-Sr-Y-C
The a-Cu-O thin film was created using a high-frequency magnetron sputtering device. The sputtering target is Pb5Sr2Y1.25Ca0.7Cu3.3O5
It was made into a disk with a diameter of 80 mm. Mg heated to 550℃
A thin film was formed on an O single crystal (100) plane substrate by performing sputtering discharge at 100 W. 2000 in about 30 minutes
A Pb2Sr2Y0.5Ca0.5Cu3Ox thin film of about .ANG. was formed. When a sputtering gas containing only pure argon was used, a Pb-based superconducting thin film with good c-axis orientation was obtained. The lattice constant of this film is c=15.75 Å, and P
This value coincided with the value obtained for b-based superconducting sintered bodies. Moreover, the superconducting transition temperature was 70K.

[0025] To create the element, first, as shown in FIG.
Using an MgO substrate as the base 11, argon gas and 0.2P
Oxygen gas at a partial pressure of a (that is, a partial pressure of 0.1 Pa or more) is introduced to form a P layer with a thickness of about 200 nm as the non-superconducting layer 12.
b-Sr-Y-Ca-Cu-O thin film was deposited. This non-superconducting layer 12 is made of a material with the same constituent elements as the lead-based superconducting oxide, but has a higher oxygen content and slightly weaker crystallinity than the superconducting material. After forming this non-superconducting layer 12, the oxygen gas in the same vacuum chamber was subsequently evacuated, and as shown in FIG. 2, pure argon of 0.4 Pa was introduced to form a Pb-Sr- A Y--Ca--Cu--O thin film was formed as the superconducting electrode 13. Furthermore, in this example, in order to protect the superconducting layer 13 from the process described later, the substrate temperature was lowered and a platinum layer 14 was deposited in the same manner. Thereafter, as shown in FIG. 3, the superconducting layer 13 and the platinum layer 14 are separated into two parts by approximately 0.1 μm apart by electron beam lithography using an electron beam resist 15 and ion milling, and the superconducting layer 1
3 was patterned as a superconducting electrode. At this time, the ion milling is performed on the superconducting layer 13 on the surface of the non-superconducting layer 12.
and the platinum layer 14, and the non-superconducting layer 12
A portion of the material is milled, but this is done in such a way that it is not electrically separated. Thereafter, the electron beam resist 15 was removed, and the non-superconducting layer 12, superconducting electrode 13 and platinum layer 14 were patterned into a Josephson junction shape by photolithography and ion milling using a negative resist 16, as shown in FIG. As described above, 250 nm of CaF was used as the interelectrode separation layer 17 without removing the negative resist 16.
2 was deposited by vacuum evaporation, the surface of the platinum layer 14 was exposed by ultrasonic cleaning using trichloroethane and a lift-off method using O2 gas plasma treatment.

Finally, a metal mask is used to contact parts of the two platinum electrodes of the separated platinum layer 14, and
As shown in FIG. 5, the contact electrode 18 is 200nm.
A superconducting device was completed by depositing m of platinum by high-frequency magnetron sputtering.

[0027] A superconducting element manufactured by this manufacturing method can be manufactured at 70K.
showed good superconducting properties and Josephson effect. FIG. 6 shows an example of the characteristics of a superconducting junction called SNS obtained when the non-superconducting layer has a conductivity of several ohms.cm. A superconducting current of 100 μA flowed in this device.

Example 2 Another example is shown in which a Pb-Sr-Y-Ca-Cu-O thin film was formed using an MBE apparatus. Raw materials include PbO compound, Sr metal, Y metal, Ca metal, Cu
Using metal, each element is individually evaporated by filling five heated crucibles. After the vapor deposition chamber was evacuated to 10 −5 Pa or less, vapor deposition was performed on a substrate heated to 550° C. The chemical composition of the thin film is Pb2Sr2Y0.5Ca0.5Cu
The amount of vapor deposition of each element was set so that the amount was 3Ox. Oxygen gas was introduced into the deposition chamber during film formation, and a thin film with the crystal structure of a Pb-based superconductor was obtained when the degree of vacuum near the substrate was 10 −3 Pa or less. In reality, the degree of vacuum near the substrate is 1
The vacuum is quite high (0-4 Pa), and precise structural control such as atomic layer control is possible. It was confirmed by backscattered electron diffraction that the obtained thin film was an epitaxial thin film in which the c-axis was oriented perpendicularly and the crystal orientation was aligned with the MgO substrate. This film showed a steep superconducting transition at 85K.

The basic form of the element itself is the same as in Example 1, and the method for manufacturing it is as follows: First, the vapor deposition chamber is evacuated, oxygen gas is introduced, and the amount of evaporation from each crucible is controlled.
As shown in Fig. 1, a 0 nm Pb-Sr-Y-Ca-Cu-O thin film was heated to 500°C on a NdGaO3 substrate 1.
It was formed on the surface of 1. After forming this thin film, the substrate temperature remained the same and the oxygen gas introduced into the same vacuum chamber was adjusted to 0.
The atmosphere was evacuated to 1 Pa or less, and then a superconducting layer of about 100 nm, Pb-Sr-Y-Ca-Cu-O, was deposited. Thereafter, a superconducting element as shown in FIG. 5 was completed by photolithography, ion milling, etc. in the same manner as in Example 1.

Example 3 Another example using the MBE vapor deposition method will be described. First, by evacuating the vapor deposition chamber and controlling the amount of evaporation from each crucible, a 200 nm thick superconducting Pb-Sr-
The Y-Ca-Cu-O thin film was deposited at 500 nm as shown in Figure 1.
It was formed on the surface of the NdGaO3 substrate 11 heated to .degree. After forming this thin film, ozone gas at 10 Pa was introduced into the same vacuum chamber while the substrate temperature remained unchanged to oxidize the superconducting thin film, thereby forming a uniform non-superconducting layer 12. Gases such as ozone, N2O or NO2 instead of oxygen gas were also effective. After that, the oxygen gas introduced into the same vacuum chamber was evacuated to 0.1 Pa or less, and the oxygen gas was continuously
Superconducting layer Pb-Sr-Y-Ca-Cu-O of about 0 nm
was deposited. Thereafter, a superconducting element as shown in FIG. 5 was completed by photolithography, ion milling, etc. in the same manner as in Example 1.

This non-superconducting layer 12 is made of the same constituent elements as the superconducting electrode formed on its surface, but has a higher oxygen content and slightly weaker crystallinity than the superconducting electrode. There is.

Regarding the formation of a non-superconducting layer in the formation of a superconducting junction by this MBE method, a method of depositing a superconducting layer on a substrate and then irradiating the surface with oxygen ions was also highly effective. In this case, oxygen ions generated by, for example, a Kauffman type ion source may be accelerated at a voltage of several hundred volts or less and irradiated onto the surface of the first superconducting electrode. Various ion sources can be used, such as an ECR ion source.

[0033]Although the above embodiments have all been described using Josephson elements as an example, the superconducting element of the present invention is not limited to Josephson elements, and may be any superconducting element using superconducting junction. Of course, the principle is the same in both cases.

[0034]

[Effects of the Invention] As explained above, the superconducting element of the present invention has a structure in which a non-superconducting layer and a superconducting layer are laminated, both of which are composed of a Pb-based layered oxide.
Since the material composition and crystal structure are the same, they are chemically stable, and there is little deterioration in the superconductivity of the superconducting layer, making it possible to manufacture excellent superconducting elements.

Furthermore, the manufacturing method uses Pb-S, which is an oxide superconducting material that does not require an oxygen atmosphere during thin film formation.
By selecting r-Y-Ca-Cu-O, it is possible to use precise thin film formation methods such as high vacuum evaporation, making it possible to form a highly uniform non-superconducting layer. Ta. Furthermore, by simply oxidizing the superconducting electrode, it is possible to form a uniform non-superconducting layer with good controllability, which is extremely simple and highly controllable, resulting in excellent uniformity and stability in device fabrication. , has the advantage of providing highly reliable bonding characteristics.

[0036] This means that although a superconducting quantum interferometer that uses a superconducting junction element as a component is currently in practical use as one of the superconducting applications, the superconducting element of the present invention does not operate as a superconducting junction element. Therefore, using this element has the effect of making it possible to construct a high-performance superconducting quantum interferometer.

Furthermore, the superconducting element of the present invention can be used as a switching element with low power consumption, or as a high-sensitivity high-frequency mixer that utilizes nonlinearity or quantum effects specific to superconductors.

From these points alone, it is clear that the superconducting element of the present invention has great practical effects in computer applications, electronic equipment applications, and the like.

[Brief explanation of drawings]

FIG. 1: Process diagram of a method for manufacturing a superconducting element according to an embodiment of the present invention

[Fig. 2] Process diagram of a method for manufacturing a superconducting element according to an embodiment of the present invention

[Fig. 3] Process diagram of a method for manufacturing a superconducting element according to an embodiment of the present invention

[Fig. 4] Process diagram of a method for manufacturing a superconducting element according to an embodiment of the present invention

[Fig. 5] Process diagram of a method for manufacturing a superconducting element according to an embodiment of the present invention

[Figure 6] Diagram of electrical characteristics of a thin film obtained in an example of the present invention

[Explanation of symbols]

11 Base 12 Non-superconducting layer 13 Superconducting layer 14 Platinum layer 15　Electron beam resist 16 Negative resist 17 Interelectrode separation layer 18 Contact electrode

Claims (7)

[Claims] 1. A non-superconducting layer and a superconducting layer formed in contact with a surface of the non-superconducting layer are formed on a substrate, and the superconducting layer is separated into at least two parts.
In a planar superconducting element having two superconducting electrodes, the main component of the non-superconducting layer and the superconducting layer is at least lead,
A lead-based oxide thin film containing copper and oxygen, characterized in that the oxygen content of the thin film forming the non-superconducting layer is greater than the oxygen content of the thin film forming the superconducting layer. superconducting element. 2. A non-superconducting layer forming step of vapor depositing a lead-based oxide non-superconducting thin film containing at least lead, copper and oxygen as main components on a heating substrate; It includes a superconducting layer forming step of vapor depositing a lead-based oxide superconducting layer thin film having at least the same main metal component as the non-superconducting oxide thin film, and the oxidizing atmosphere during the non-superconducting layer forming step is A method for producing a superconducting element characterized by being stronger than the oxidizing atmosphere during the layer formation process. 3. A lead-based non-superconducting layer in which the non-superconducting layer forming step includes vapor deposition of a lead-based oxide in an atmosphere containing an oxidizing gas, introduction of an oxidizing gas after vapor-depositing the lead-based superconducting layer, and irradiation with oxidizing ions. 3. The method of manufacturing a superconducting element according to claim 2, wherein either oxide deposition or oxidizing ion irradiation is performed after the lead-based superconducting layer is deposited. Claim 4: The oxidizing gas is ozone, N2O or N
4. The method for manufacturing a superconducting element according to claim 3, wherein the material is O2. 5. The method of manufacturing a superconducting device according to claim 3, wherein the oxidizing ions are generated by an ECR plasma source. 6. The method according to claim 2 or 3, wherein the superconducting layer forming step is performed by vapor deposition after exhausting either the oxidizing gas or the oxidizing ions in the non-superconducting layer forming step. Method for manufacturing superconducting elements. [Claim 7] The exhaust gas in the superconducting layer forming step is 0.1P.
7. The method for manufacturing a superconducting element according to claim 6, wherein the superconducting element is made less than or equal to a.