JP2908346B2 - Superconducting structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting structure having a laminated film of a plurality of oxide superconducting layers and a non-superconducting oxide layer.

[0002]

2. Description of the Related Art Oxide superconductors are expected to be applied to Josephson junction devices, superconducting transistors, LSI wiring and the like. In order to realize these, it is indispensable to laminate the oxide superconductor thin films in multiple layers. For example, in a Josephson junction device, at least two oxide superconductor layers are laminated with a non-superconductor layer interposed therebetween, and a junction between the oxide superconductor layer and the non-superconductor layer is formed. When fabricating a superconducting element having a multilayer laminated structure of such an oxide superconductor layer, various processing processes are performed after or during the multilayer lamination, but the conventional thin film forming technology and the processing process technology are as follows. There was a problem as shown.

[0003] That is, as the oxide superconductor, RE
-Βa-Cu-O (RE indicates Y and lanthanide elements (except when RE is all Pr))
, I-Sr-Ca-Cu-O, Tl-Ba-Ca
-Cu-O system, (Βa, K) ΒiO ₃ system and the like are used. Examples of the film forming method include a sputtering method, a laser ablation method, a ΔE method, and a ΔOCVD method.
In each case, the substrate was SrTiO ₃ , ΔgO, N
It is common to use dGaO ₃ , LaAlO ₃ , YSΖ or the like.

[0004] In the case of forming a junction between an oxide superconductor layer and a non-superconducting layer by the above-described method, first, a lower superconducting electrode and, if necessary, an interlayer insulating film and the like are formed. In many cases, it is necessary to cool the electrode to room temperature and take it out to the atmosphere, and then to subject the electrode portion to a working process. As a processing process, using normal photolithography, dry etching of the electrode portion by ion milling etc.,
Generally, wet etching is performed using a liquid etchant, or surface treatment using plasma is performed. Then, after passing through these processes, in order to further form a non-superconducting layer, an upper superconducting electrode, and the like, they are again introduced into a film forming chamber and undergo a heating and film forming process.

At this time, for example, the surface portion of the lower superconducting electrode which has undergone the dry etching process has been damaged by irradiation with Ar ions or the like, and has been deteriorated before forming the non-superconducting layer. Therefore, the surface layer portion of the lower superconducting electrode becomes unstable and accelerates its deterioration by the subsequent heating and film forming process, so that the flatness of the interface between the oxide superconducting layer and the non-superconducting layer, lattice matching, There is a problem that physical properties such as steepness and electrical characteristics are deteriorated.

Further, a state in which an organic solvent or an etchant liquid used in the processing process is adsorbed on the surface of the oxide superconductor layer, and furthermore, foreign substances such as water molecules are removed as oxides are taken out into the atmosphere. When a subsequent heating process is performed while being adsorbed on the surface of the superconductor layer, a reaction between the oxide superconductor and those molecules occurs, thereby promoting the deterioration of the oxide superconductor surface. The deterioration of the oxide superconductor surface due to the surface contamination has also adversely affected physical properties such as flatness, lattice matching, steepness, and electrical characteristics of the interface between the oxide superconductor layer and the non-superconducting layer.

[0007]

As described above, in a conventional superconducting element having a multi-layer structure of an oxide superconducting layer and a non-superconducting layer, a multi-step film forming process and a processing process are performed at a joint portion. In this case, the physical properties such as the interface structure between the oxide superconductor layer and the non-superconducting layer and the electrical characteristics, which are particularly important, are adversely affected, and as a result, the device characteristics are reduced and the reproducibility of the characteristics is reduced. Such a problem is not limited to a superconducting element, but also applies to a superconducting wiring formed on a superconducting ground plane via a non-superconducting layer.

In order to solve the above-mentioned problem of the interface,
In particular, it is considered effective to suppress a reaction with a foreign substance or a decomposition reaction of the superconducting phase itself on the surface of the lower oxide superconducting layer immediately before forming the non-superconducting layer. In particular, in a superconducting structure using an oxide superconductor that requires a film formation process at a high temperature, it is necessary to ensure the high-temperature structural stability of the surface of the oxide superconductor layer immediately before forming an interface. Basically important.

SUMMARY OF THE INVENTION The present invention has been made to address such a problem, and it is an object of the present invention to improve the structural stability of an interface by a lower oxide superconductor layer and, consequently, the stability of physical properties such as electric characteristics. Accordingly, it is an object of the present invention to provide a superconducting structure capable of improving characteristics and reproducibility thereof.

[0010]

Superconductor structure of the present invention, in order to solve the problems] comprises a laminated film of a non-superconducting oxide layer interposed the plurality of oxide superconductor layers and the oxide superconductor layer of multiple In the superconducting structure, the plurality of oxide superconductor layers disposed via the non-superconducting oxide layer are generally
Formula: REAE ₂ M ₃ O _y (where RE is Y and lanthanum)
At least one element selected from the group consisting of AE
Is at least one kind selected from Ca, Ba and Sr
Element, M is a transition element containing Cu at a ratio of 70% or more.
Where y is a number that satisfies 6.2 ≦ y ≦ 7.5)
Having the composition represented, and the plurality of oxide superconductor layers
Among them, the material constituting the lower oxide superconductor layer has a higher decomposition reaction initiation temperature than the material constituting the upper oxide superconductor layer.

[0011]

In a superconducting structure such as a superconducting element using an oxide superconductor represented by YΒCO, a c-axis oriented film is frequently used, and the formation temperature of a good quality c-axis oriented film depends on the material-specific temperature. In general, the temperature is several hundred K lower than the melting point or the decomposition temperature (hereinafter, referred to as decomposition reaction start temperature). Further, the minimum temperature for forming a good quality film tends to increase as the decomposition reaction start temperature increases.

The present invention takes advantage of this property to make use of the oxide superconductor layer whose surface is exposed immediately before forming the non-superconducting oxide layer, that is, a plurality of oxides disposed via the non-superconducting oxide layer. In the oxide superconductor layer located on the lower side of the superconductor layer, the decomposition reaction initiation temperature is higher than that of the oxide superconductor layer formed after the non-superconducting oxide layer, that is, the oxide superconductor layer located on the upper side. By using the substance, the decomposition reaction start temperature of the lower oxide superconductor layer is set to have a sufficient difference from the formation temperature of the upper oxide superconductor layer formed later. . By utilizing the fact that the instability of the surface of the lower oxide superconductor layer is suppressed by this, the surface of the lower oxide superconductor layer It is possible to ensure stability.

[0014] Particularly, in the oxide superconductor having the so-called 123 structure, by changing the type of metal ions, it is possible to change the decomposition reaction starting temperature. By actively utilizing this property, the instability of the interface between the oxide superconductor layer and the non-superconducting oxide layer can be specifically suppressed.

[0015]

Embodiments of the present invention will be described below.

FIG. 1 is a diagram schematically showing a configuration of an embodiment in which the superconducting structure of the present invention is applied to an edge type junction element which is an example of a Josephson junction element. In FIG. 1, reference numeral 1 denotes a substrate, on which an oxide superconductor layer is formed as a lower superconducting electrode 2.

The lower superconducting electrode 2 made of an oxide superconducting layer has an end surface (inclined end surface) 2a inclined at an angle α with respect to the substrate surface 1a. Such an inclined end surface 2a
Is to selectively etch the oxide superconductor layer by means of ion milling or the like so that the etching end surface is exposed at an angle α with the substrate surface 1a using an appropriate mask such as a resist, for example. Thereby, it can be easily formed. Specifically, an interlayer insulating film 3 is provided on lower superconducting electrode 2, and by etching including the end surfaces of interlayer insulating film 3, inclined end surfaces 2 a are formed on these end surfaces.

A non-superconducting layer 4 made of a non-superconducting oxide is formed on the lower superconducting electrode 2 made of the above-described oxide superconducting layer so as to cover at least the inclined end face 2a. This non-superconducting layer 4 is, specifically, the bevel end face 2
It is formed from the surface 1a of the substrate 1 exposed by the etching to the surface of the interlayer insulating film 3 via the surface a.
This non-superconducting layer 4 may be made of either an insulator or a normal conductor. An upper superconducting electrode 5 composed of an oxide superconducting layer is formed on the non-superconducting layer 4 similarly to the lower superconducting electrode 2, and these form an edge-type junction element 6.

Here, it is important to epitaxially grow up to the upper superconducting electrode 5 formed on the non-superconducting layer 4 in order to obtain a Josephson junction having good characteristics. For this reason, as a material for forming the non-superconducting layer 4, the superconducting property is weakened by doping an impurity element such as PrBa ₂ Cu ₃ O _7-δ which is a layered perovskite oxide having no superconducting property or Co. REBa ₂
Insulating oxide such as Cu ₃ O _7-δ , SrTiΟ ₃ or the like which is lattice-matched with the lower superconducting electrode 2 in a pseudo manner, or CaRuO.
It is preferable to use a non-superconducting oxide such as a conductive oxide such as ₃ .

The lower superconducting electrode 2 / non-superconducting layer 4
/ When viewed as a joint consisting of the upper superconducting electrode 5,
The oxide superconductor layer located on the lower side, in other words, the oxide superconductor layer formed before the non-superconducting layer 4, that is, the oxide superconductor forming the lower superconducting electrode 2, has a temperature at which the decomposition reaction starts ( Decomposition reaction start temperature), the upper superconducting electrode 5 formed on the upper side and formed after the non-superconducting layer 4.
Is set higher than the decomposition reaction start temperature of the oxide superconductor constituting the above.

[0021] Here, although the lower superconducting electrodes 2 and upper superconductive electrode oxide superconductor as 5 is not particularly limited, considering the critical current density J _c and film forming property and the like, the general formula: REAE ₂ Μ ₃ O _y (1) (wherein RE is Y and a lanthanide element (RE
Are all Pr))
AE is at least one element selected from Ca, Ba and Sr, and Μ is Cu at a ratio of 70% or more.
Wherein y is a number that satisfies 6.2 ≦ y ≦ 7.5), such as an RE-Ba-Cu-O-based oxide superconductor having a composition substantially represented by: It is preferred to use Here, the reason for excluding the case where all the RE elements are Pr is that a substance in which all of the RE is occupied by Pr does not exhibit superconductivity.

Since many oxide superconductors can define the melting and decomposition temperature as a eutectic temperature and a peritectic temperature, the decomposition reaction will be discussed below using the eutectic or peritectic temperature. For example, if the eutectic temperature is defined as the decomposition temperature,
(The decomposition reaction initiation temperature of (La, Sr) ₂ CuO ₄ system is about 1423 K, that of YBa ₂ Cu ₃ O ₇ system is about 1173 K, N
dBa ₂ Cu ₃ O ₇ system is about 1273 K, Bi ₂ Sr ₂ C
a _l Cu ₂ O _z system is about 1123 K. Above these temperatures, each system begins to melt and decompose into a different material.

FIG. 2 shows an equilibrium diagram of the Y @ a ₂ Cu ₃ O ₇ system. As shown in FIG. 2, YΒa ₂ Cu ₃
When O ₇ about compositionally decomposition starts in the Ba and Cu rich melt and YΒa ₂ Cu ₃ O ₇ solid 1173K, further heated to about 1273K which is peritectic temperature, Y ₂ BaCu
O ₅ system decomposes and to mixtures melt. At this time, the temperature at which the decomposition reaction starts is defined as about 1173 K at which YΒa ₂ Cu ₃ O ₇ starts to decompose for the first time. As shown in FIG. 3, taking the REBa ₂ Cu ₃ O ₇ system as an example, the decomposition reaction start temperature increases as the ionic radius of the RE element from Yb to Nd increases, and NdBa ₂ Cu ₃ O ₇
Is about 100K higher than YBa ₂ Cu ₃ O ₇ .

The present invention utilizes the above-described difference in the decomposition temperature of the two oxide superconductors, which become the lower superconducting electrode 2 and the upper superconducting electrode 5, to utilize the lower superconducting electrode 2 just before the production of the non-superconducting layer 4. In this case, the structural stability of the oxide superconductor layer is improved. For example, the non-superconducting layer 4
An rBa ₂ Cu ₃ O ₇ layer is used as the lower superconducting conductive electrode 2 formed temporally earlier than the non-superconducting layer 4.
By using the YBa ₂ Cu ₃ O ₇ layer for the upper superconducting electrode 5 formed later in time while using the dBa ₂ Cu ₃ O ₇ layer, the lower superconducting electrode 2 just before the non-superconducting layer 4 is formed This is for preventing structural deterioration of the NdBa ₂ Cu ₃ O ₇ layer.

The prevention of the structural deterioration of the lower superconducting electrode 2 will be described with reference to the manufacturing process of the edge type junction element 6 shown in FIG. First, in a film forming chamber of, for example, a vacuum film forming apparatus, a lower superconducting electrode 2 made of, for example, an Nd @ a ₂ Cu ₃ O ₇ layer and an interlayer insulating film 3 made of, for example, an SrTiO ₃ layer are sequentially formed on a substrate 1 (FIG. 4). -A). Next, a resist 7 is formed at the edge formation portion on the interlayer insulating film 3 by ordinary photolithography through a step of taking out the film from the film formation chamber to the atmosphere (FIG. 4B). In this state, it is introduced into an ion milling device, and as shown in FIG. 4C, ion milling is performed with Ar ions or the like to form an inclined end face 2a.

Thereafter, the film is taken out again to the atmosphere, the resist 7 is removed (FIG. 4D), and the film is introduced again into the film forming chamber of the vacuum film forming apparatus to form a barrier layer such as ΡrBa ₂ Cu _3.
A non-superconducting layer 4 consisting of O ₇ layer, sequentially formed an upper superconductive electrode 5 made of YΒa ₂ Cu ₃ O _7-layer (FIG. 4
e). At the time of this film formation, the substrate 1 and the lower superconducting conductive electrode 2 composed of a pre-formed Nd @ a ₂ Cu ₃ O ₇ layer consisted of a ΡrBa ₂ Cu ₃ O ₇ layer and a YΒa ₂ Cu ₃ O ₇ layer.
It is heated to the film forming temperature of _seven layers.

As described above, N as the lower superconducting electrode 2
The dBa ₂ Cu ₃ O ₇ layer is taken out into the atmosphere before the formation of the non-superconducting layer 4, and then undergoes a processing process of forming the inclined end face 2 a by ion milling or the like. Immediately before the formation of the layer 4, a large amount of foreign molecules have been adsorbed. The processing process is to cut the NdBa ₂ Cu ₃ O ₇ layer by ion milling.
The inclined end face 2a of the NdBa ₂ Cu ₃ O ₇ layer is structurally degraded due to damage during milling, and may become amorphous if the acceleration voltage during ion milling is high.

Although the inclined end face 2a is the most important part constituting the interface, the non-superconducting layer 4
In addition, during the process of raising the temperature when the upper superconducting electrode 5 is manufactured, the upper superconducting electrode 5 becomes unstable for the above-mentioned reason, and the reaction is remarkably accelerated, and the interface may be structurally deteriorated. On the other hand, the decomposition reaction initiation temperature of the lower superconducting electrode 2 is higher than that of the YBa ₂ Cu ₃ O ₇ layer as the upper superconducting electrode 5.
When a Ba ₂ Cu ₃ O ₇ layer is used, ΔdBa ₂ Cu ₃
The O ₇ layer has a decomposition reaction initiation temperature about 100 K higher than the YBa ₂ Cu ₃ O ₇ layer. Therefore, the substrate temperature when forming a good quality film on the substrate 1 by, for example, the sputtering method is about 100 K higher. .

That is, the NdBa ₂ Cu ₃ O ₇ layer is
After forming a 3K, taking out into the atmosphere and forming a slanted end face 2a, a process of forming a high-quality thin film of the YBa ₂ Cu ₃ O ₇ layer as the upper superconducting electrode 5 is performed.
Heated again to 3K. At this time, NdBa ₂ Cu ₃ O ₇
The decomposition temperature of the layer is about 100K higher, and the decomposition reaction does not proceed even at the time of reheating at 1023K, and a good surface is maintained. On the other hand, when the YBa ₂ Cu ₃ O ₇ layer is applied to the lower superconducting conductive electrode 2, the interface is in a molten state by the high-temperature process at the time of reheating, and the YBa ₂ Cu ₃ O ₇ layer is decomposed. It is not possible to obtain a superconducting element having excellent interface characteristics and excellent element characteristics.

On the lower superconducting electrode 2 composed of the above-mentioned NdBa ₂ Cu ₃ O ₇ layer, as a non-superconducting layer 4, ＢrBa ₂
When the Cu ₃ O ₇ layer was formed, the interface was NdBa ₂ Cu ₃
It is ideal because the O ₇ layer surface is stable,
In addition, since the temperature at the time of forming the YBa ₂ Cu ₃ O ₇ layer as the upper superconducting electrode 5 on the PrBa ₂ Cu ₃ O ₇ layer can be made sufficiently high as 1023 K, the non-superconducting layer 4 and the upper superconducting electrode 5 Can also be ideally formed.

As described above, by applying the oxide superconductor having a high decomposition reaction initiation temperature to the lower superconducting electrode 2, the reaction with foreign molecules at the interface, the decomposition reaction of the oxide superconductor itself, and the formation of a molten state are achieved. I can prevent going out,
It is possible to avoid a decrease in device characteristics and a decrease in reproducibility due to structural nonuniformity of the interface. Therefore, the flatness, lattice matching, steepness, electrical characteristics, and the like of the interface can be improved, and a superconducting device with improved device characteristics and its reproducibility can be obtained.

[0032] In the embodiment described above, the lower superconducting electrodes 2 with use of NdBa ₂ Cu ₃ O ₇ layer, has been described using the YBa ₂ Cu ₃ O ₇ layer on top superconducting electrode 5, the present invention is However, the same effect can be obtained by using an oxide superconductor layer having a decomposition reaction start temperature higher than that of the oxide superconductor layer constituting the upper superconducting electrode 5 for the lower superconducting electrode 2.

However, when a combination having almost no difference in the decomposition reaction initiation temperature is used as the two superconducting electrodes 2 and 5, the above-described effect of suppressing the decomposition reaction is not obtained as significant, and the non-superconducting layer 4 Since the decomposition reaction of the lower superconducting electrode 2 may occur during the film formation of the upper superconducting electrode 5 and the upper superconducting electrode 5, a combination in which at least the difference in the decomposition reaction initiation temperature between the two superconducting electrodes 2 and 5 is 30K or more is applied. Is preferred. As such a combination, in addition to the above-mentioned NdBa ₂ Cu ₃ O ₇ and YBa ₂ Cu ₃ O ₇ ,
Preferred examples include a combination of EuBa ₂ Cu ₃ O ₇ and YBa ₂ Cu ₃ O ₇ .

As described above, the oxide superconductor layer is made of RE in consideration of the critical current density _Jc and the film forming property.
-Ba-Cu-O foregoing such system (1) that uses an oxide superconductor substantially represented by formula.

Next, an embodiment in which the superconducting structure of the present invention is applied to a stacked junction device as an example of a Josephson junction device will be described with reference to FIGS.

The laminated junction element 11 shown in FIG.
2, a lower superconducting electrode 13, a non-superconducting layer 14, and an upper superconducting electrode 15 are sequentially laminated and formed.
In this stacked junction element 11 as well, the lower superconducting electrode 13 is connected to the upper superconducting electrode 15 similarly to the above-described embodiment.
The oxide superconductor layer whose decomposition reaction initiation temperature is higher than that of the oxide superconductor layer constituting the above is used. The specific constituent materials of the superconducting electrodes 13 and 15 and the constituent material of the non-superconducting layer 14 are the same as those in the above-described embodiment.

In such a stacked junction element 11 as well, by using the oxide superconductor layer having a higher decomposition initiation temperature than the oxide superconductor layer constituting the upper superconducting electrode 15 for the lower superconducting electrode 13, the non-superconducting layer is used. Lower superconducting electrode 1 when forming layer 14 and upper superconducting electrode 15
3 can be prevented from being decomposed and produced in a molten state.

In particular, as shown in FIG. 6, after the lower superconducting electrode 13 is formed on the substrate 12 (FIG. 6-a), it is once taken out into the atmosphere and introduced into an ion milling device, and the lower superconducting electrode 13 is formed by Ar ions. After the surface is cleaned and flattened (FIG. 6-b), it is introduced again into a film forming chamber of a vacuum film forming apparatus or the like, and the non-superconducting layer 14 and the upper superconducting electrode 15 are formed.
7 or as shown in FIG. 7, after forming the non-superconducting layer 14 (FIG. 7-a), once take it out to the atmosphere, introduce it into the ion milling device, and use Ar ions to form the surface of the non-superconducting layer 14 After cleaning and flattening (FIG. 7B), when the upper superconducting electrode 15 is formed by being introduced again into a film forming chamber of a vacuum film forming apparatus or the like, the lower superconducting electrode 13 can be more effectively used. Decomposition reaction and creation of a molten state can be prevented.

With these, it is possible to avoid a decrease in device characteristics and a decrease in reproducibility due to the structural nonuniformity of the interface, and it is possible to improve the flatness, lattice matching, steepness, and electrical characteristics of the interface. It becomes possible. Therefore, the element characteristics of the superconducting element and the reproducibility thereof can be improved.

In the above-described embodiment, the embodiment in which the superconducting structure of the present invention is applied to a Josephson junction element has been described. However, the present invention is not limited to this. It can be applied to various superconducting structures as long as it has a laminated film having a plurality of oxide superconductor layers arranged in a row.

For example, in the case of various superconducting elements such as superconducting transistors, superconducting wires, etc., a superconducting ground plane may be formed below. In such a case, a laminated film of superconducting ground plane / non-superconducting oxide layer / oxide superconducting layer is formed. In such a structure, the upper oxide superconducting layer is added to the lower oxide superconducting layer. By using a substance having a decomposition reaction initiation temperature higher than that of the material constituting the superconductor layer, the decomposition reaction of the lower oxide superconductor layer when forming the non-superconducting oxide layer and the upper oxide superconductor layer can be performed. The production in a molten state can be prevented, and a good interface can be formed.
In some cases, a superconducting ground plane is also formed in a Josephson junction element.
The present invention may be applied to each of the two joining portions, or may be applied to only one of the joining portions.

[0042]

Next, specific examples of the present invention will be described.

Example 1 First, NdBa ₂ Cu whose structure was shown in FIG.
An example in which an edge-type junction element having a ₃ O ₇ / PrBa ₂ Cu ₃ O ₇ / YBa ₂ Cu ₃ O ₇ laminated film is manufactured will be described.

First, an SrTiO ₃ (100) substrate was used as the substrate 1, and an Nd @ a ₂ Cu ₃ O ₇ layer was formed as the lower superconducting electrode 2 on the substrate 1 under the conditions shown in Table 1.
SrTi at 900K as interlayer insulating film 3 by in-situ process
An O ₃ film was formed. The thickness of each layer was 300 nm.

Then, through a process of taking out the film from the film forming chamber to the atmosphere, a resist 7 was formed on the edge forming portion by ordinary photolithography. In this state, it was introduced into an ion milling apparatus, and an inclined end face 2a (angle α = 30 °) was formed by ion milling using Ar ions.

Thereafter, the resist is taken out again to the atmosphere to remove the resist 7, and is again introduced into the film forming chamber, where ΔrBa ₂ Cu ₃ O as the non-superconducting layer 4 serving as a barrier layer is formed.
YBa ₂ Cu ₃ O as ₇ layers and upper superconducting electrode 5
_The temperature was raised to 1023K, which is the formation temperature of the _seven layers. The temperature was raised while flowing a mixed gas of argon and oxygen. ΡrBa ₂ Cu ₃ O ₇ as the non-superconducting layer 4 under the conditions shown in Table 1.
Layer (film thickness: 1 to 20 nm) and YBa as upper superconducting electrode 5
_{A 2} Cu ₃ O ₇ layer (thickness: 200 nm) was formed, and then oxygen gas was introduced to 1 atm. After about 1 hour, the layer was taken out to the atmosphere.

[0047]

[Table 1] FIG. 8 shows an enlarged photograph (SEM image) of the fine structure of the inclined end face portion of the edge-type junction element according to the first embodiment. FIG.
FIG. 8A is an enlarged photograph of an inclined end face of a laminated film of a Nd @ a ₂ Cu ₃ O ₇ layer and an SrTiO ₃ film before a barrier layer is formed, and FIG. 8B is an enlarged photograph after the heat treatment. It is a photograph. FIG. 9 is an enlarged photograph (SEM image) of the fine structure of the inclined end face portion of the edge type junction element using the YBa ₂ Cu ₃ O ₇ layer also for the lower superconducting electrode manufactured as a comparative example with the present invention. FIG. 9A shows YBa ₂ Cu ₃ O _7.
FIG. 9B is an enlarged photograph of the inclined end surface of the laminated film of the layer and the SrTiO ₃ film before the heat treatment, and FIG. 9B is an enlarged photograph after the heat treatment.

As is apparent from FIGS. 8 and 9, when the Nd @ a ₂ Cu ₃ O ₇ layer having a decomposition reaction starting temperature higher by about 100 K is used as the lower superconducting electrode, the edge portion as seen in the Y system is not affected. No structural degradation that could be attributed to the melt decomposition reaction on the slope was observed, indicating that the morphology before heating was maintained. As a result, the oxide superconductor having a high decomposition reaction start temperature has a remarkably low melt decomposition reaction in the reheating process and reactivity with water, etc., and retains the same surface properties and electrical properties as non-heated up to high temperatures. It has proven to be extremely effective.

FIG. 10 shows the current-voltage characteristics of the edge-type junction element (when the barrier layer has a thickness of 5 nm) according to Example 1, and FIG. 11 shows the magnetic field dependence of the critical current value. The characteristics were a typical RSJ type with an I _c · R _n product of 2.0 mV, and an ideal Josephson junction showing a clear Fraunhofer pattern when a magnetic field was applied. The characteristics of the edge-type junction element manufactured according to Example 1 were such that when the thickness of the barrier layer was less than 10 nm, it had tunneling and resonance tunneling conduction properties, and when the thickness of the barrier layer was 10 nm or more, only the insulating properties were exhibited. As described above, according to the present invention, it has been found that not only the element characteristics are improved, but also the structural reliability and reproducibility in forming the barrier layer at the unit cell level are remarkably increased.

Example 2 REBa ₂ Cu ₃ O ₇ whose structure is shown in FIG. 1 by a sputtering method
An edge type junction device having a / PrBa ₂ Cu ₃ O ₇ / RE′Ba ₂ Cu ₃ O ₇ laminated film was produced by applying the same processing method as in the first embodiment. The specific film configuration and the film formation temperature (substrate temperature) of each film are as shown in Table 2. As a result, RSJ-like characteristics were obtained in all the junctions. It has been found that when an oxide superconductor having a decomposition temperature difference is used as both electrodes, the quality of the interface is significantly improved.

[0051]

[Table 2] Example 3 SmB whose structure is shown in FIG. 1 by a laser ablation method
a ₂ Cu ₃ O ₇ / PrBa ₂ Cu ₃ O ₇ / HoBa ₂ C
An example in which an edge-type junction element having a u ₃ O ₇ laminated film is manufactured will be described.

Using SrTiO ₃ (100) as a substrate,
First, as shown in Table 3, an Sm ₂ Cu ₃ O ₇ film was formed at 1100 K by a laser ablation method, and the temperature was lowered to 900 K, and then an SrTiO ₃ film as an interlayer insulating film was formed. The film thicknesses are both 300 nm. Next, it was taken out into the atmosphere and the inclined end face was formed on the lower superconducting electrode by the same process as in Example 1.

Thereafter, the film is introduced again into the film forming chamber,
The substrate temperature was raised to 1023 K in an oxygen gas flow of 65 Pa, and PrBa ₂ Cu ₃ having a thickness of 10 nm was used as a barrier layer.
An O ₇ film was formed. At the end of the barrier layer formation, the substrate temperature was raised to 1063K in the deposition chamber,
A 200 nm HoBa ₂ Cu ₃ O ₇ film was formed.

The edge type junction device according to the third embodiment is
It was a typical RSJ-type Josephson junction having 2.0 mV as the I _c · R _n product. Further, iota _c by the magnetic field applied to indicate the Fraunhofer properties, it was found that an ideal Josephson junction.

[0055]

[Table 3] Example 4 NdBa ₂ Cu ₃ O ₇ / PrBa ₂ whose structure is shown in FIG.
An example in which a stacked junction device having a Cu ₃ O ₇ / HoBa ₂ Cu ₃ O ₇ stacked film is manufactured will be described.

First, for the first sample, NdBa ₂ Cu ₃ O was used as the lower superconducting electrode under the same conditions as in Example 1.
After forming the _seven layers, the layers were taken out to the atmosphere and introduced into an ion milling chamber, and N ions were introduced with Ar ions as shown in FIG.
The surface of the dBa ₂ Cu ₃ O ₇ layer was cleaned and flattened, and then introduced again into the film forming chamber. The PrBa ₂ Cu ₃ O ₇ layer and the upper superconducting electrode were used as barrier layers under the same conditions as in Example 1. YΒa ₂ Cu ₃ O ₇ was formed.

For the second sample, the lower super
NdBa as conductive electrode_TwoCu_ThreeO₇Layers and barrier layers
PrBa_TwoCu_ThreeO₇After forming the layer,
Take out and PrBa by ion milling_TwoCu_ThreeO₇Layer table
After cleaning and flattening the surface,
YΒa as the upper superconducting electrode at 1023K _Two
Cu_ThreeO₇Was formed.

[0058] multilayer junction devices of two different types were carried out the surface treatment shown in the fourth embodiment, as I _c · R _n product respectively
Typical RSJ type IV with 1.0mV, 1.2mV
It was an ideal Josephson device exhibiting characteristics.

[0059]

As described above, according to the superconducting structure of the present invention, the structure of the interface between the oxide superconducting layer and the non-superconducting oxide layer can be kept extremely stable. And the physical property value is improved. Therefore, it is possible to improve the element characteristics and the like, and to improve the reproducibility. As a result, the reliability of the superconducting element or the like at a practical level is significantly increased, and the contribution of the oxide superconductor to electronics is accelerated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a configuration of an embodiment in which a superconducting structure according to the present invention is applied to an edge-type junction element which is an example of a Josephson junction element.

FIG. 2 is an equilibrium diagram of a Y—Ba—Cu—O-based oxide superconductor.

FIG. 3 is a diagram showing the relationship between the decomposition reaction initiation temperature of RE-Ba-Cu-O-based oxide superconductor and the ionic radius of RE element.

FIG. 4 is a diagram showing a main part of a manufacturing process of the edge-type junction device shown in FIG. 1;

FIG. 5 is a cross-sectional view schematically showing a configuration of another embodiment in which the superconducting structure of the present invention is applied to a stacked junction element as an example of a Josephson junction element.

FIG. 6 is a view showing a main part of one manufacturing process of the stacked junction element shown in FIG. 5;

FIG. 7 is a diagram showing a main part of another manufacturing process of the stacked junction element shown in FIG. 5;

FIG. 8 is an enlarged photograph (SEM photograph) of the fine structure of the inclined end face portion of the edge type junction device manufactured in Example 1 of the present invention.
(A) is an enlarged photograph before the heat treatment, and (b) is an enlarged photograph after the heat treatment.

FIG. 9 is an enlarged photograph (SEM photograph) of a fine structure of an inclined end face portion of an edge type junction element manufactured as a comparative example with the present invention, (a) is an enlarged photograph before a heat treatment, and (b) is a heated photograph. It is an enlarged photograph after processing.

FIG. 10 is a diagram showing an example of a current-voltage characteristic of the edge type junction device manufactured in Example 1 of the present invention.

FIG. 11 is a diagram showing an example of magnetic field dependence of a critical current value of the edge junction device manufactured in Example 1 of the present invention.

[Explanation of symbols]

 2, 13 ... lower superconducting electrode composed of oxide superconductor layer 3 ... interlayer insulating film 4, 14 ... non-superconducting layer composed of non-superconducting oxide 5, 15 ... upper superconducting electrode composed of oxide superconducting layer

Continued on the front page (51) Int.Cl. ⁶ identification code FI H01L 39/24 ZAA H01L 39/24 ZAAJ (58) Fields investigated (Int.Cl. ⁶ , DB name) H01L 39/02 ZAA C30B 29/22 501 H01L 39/22 ZAA H01L 39/24 ZAA

Claims (1)

(57) [Claims] 1. A superconducting structure comprising a stacked film of a plurality of oxide superconductor layers and a non-superconducting oxide layer interposed between the plurality of oxide superconductor layers, wherein the non-superconducting oxide layer is The plurality of oxide superconductor layers interposed therebetween have a general formula: REAE ₂ M ₃ O _y (where RE is selected from Y and a lanthanide element)
At least one element, AE is Ca, Ba and Sr
At least one element selected from the group consisting of:
Represents a transition element containing Cu at a ratio of y = 6.2 ≦ y ≦
Which satisfies 7.5) .
The material constituting the lower oxide superconductor layer among the plurality of oxide superconductor layers has a higher decomposition reaction initiation temperature than the material constituting the upper oxide superconductor layer. A superconducting structure characterized by the following.