JPH05136470A - Tunnel type josephson element - Google Patents

Abstract

PURPOSE:To offer a tunnel type Josephson element exhibiting an excellent characteristic of an oxide high-temperature superconductor and having junction characteristic of a reduced junction noise and 1/f noise. CONSTITUTION:A lower superconductor layer 1a, an insulator layer 2 and an upper superconductor layer 1b are laminated on a substrate while the superconductor layers 1a, 1b consist of an oxide high-temperature superconductor of a Bi group or a Ti group. The interfaces between the superconductive layers 1a, 1b and an insulator layer 2 are constituted of superlattice structure of (a) a Ca atomic layer/Cu-O atomic layer/Sr (or Ba) -O atomic layer/Bi (or Tl) -O atomic layer/Bi (or Tl) -O atomic layer/insulator layer, or (c) Ca atomic layer/Cu-O atomic layer/Sr (or Ba) -O atomic layer/insulator layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tunnel type Josephson device. More specifically, the present invention relates to SQUIDs.
(Superconductive Quantum
The present invention relates to a superlattice structure of a tunnel type Josephson device composed of an oxide high temperature superconductor, which can be applied to an interference device (superconducting quantum interference device) and the like.

[0002]

2. Description of the Related Art Josephson devices have an S element due to their ultra-high speed, low power consumption, low noise, and high sensitivity.
There are great expectations for application to devices such as logic elements and memory elements of QUIDs and super-large computers. In order to realize these devices, the characteristics of the Josephson junction used must be kept good. In particular, S
In QUID, the ability to fabricate a low noise Josephson junction is an essential condition for providing a highly sensitive magnetometer. As a concrete configuration of this joining,
Several structures have been proposed.

A tunnel type Josephson element is known as one having the most typical structure among them. This tunnel type Josephson element has a structure in which an extremely thin insulator layer is inserted between a pair of superconductor layers, and is characterized by good reproducibility and integration. The tunnel-type Josephson device actually manufactured has Nb and Nb as superconductors.
N, Pb or the like is used, and as the insulator, an oxide in which the surface of Nb or Pb is oxidized or a vapor deposition film of MgO, α-Si or the like is formed is used. However, these metal-based superconductors generally have a very low superconducting critical temperature (Tc), and in reality, they have not exhibited effective properties unless cooled by extremely expensive liquid helium.

On the other hand, in 1986, [La, Sr] ₂ C
It has been found that an oxide sintered body such as uO ₄ is a superconducting material having a high Tc, followed by Y ₁ Ba ₂ Cu.
It was confirmed that the oxide superconductor represented by ₃ O _7-x exhibits effective superconducting properties in the temperature range above the temperature of liquid nitrogen. Since a material exhibiting superconducting properties at such a high temperature can use inexpensive liquid nitrogen as a cooling medium, practical application of superconducting technology has been studied, and high-temperature oxide superconducting materials have been used. Various attempts have been made to realize the Josephson device. As an example of a tunnel type Josephson device using an oxide high temperature superconductor having such good characteristics, Y ₁ Ba ₂ Cu _{3 having a} c-axis grown as a superconductor layer in a direction perpendicular to the substrate is used.
It is known that an oxide superconductor thin film represented by O _7-x is used and an insulating thin film such as MgO or SrTiO ₃ is used as an insulating layer.

[0005]

However, the conventional tunnel type Josephson element using the high temperature oxide superconductor exhibits good characteristics although it shows the current-voltage characteristics as a Josephson junction. It was not a joint.
That is, as a result of measuring the noise of the obtained device,
As shown in FIG. 6, it was found that a large amount of noise was generated, and there was a problem that it could not be applied to electronic devices such as SQUIDs. In particular, in SQUID applications of Josephson devices intended for high-sensitivity magnetometers, etc., to reduce not only the magnitude of noise but also the 1 / f noise seen on the low frequency side that is not caused by the tunnel effect of superconductors. Was desired.

By the way, the growth of the above-mentioned oxide high-temperature superconductor thin film has been carried out by various methods such as vapor deposition, sputtering and laser ablation. In each method, the constituent elements of the crystal are simultaneously supplied onto the substrate. I am taking it. Recently, in oxide high-temperature superconductor thin films, low-temperature growth, precise control of crystal structure such as orientation, and high Tc of Bi-based materials
A method for controlling the crystal growth of high temperature oxide superconductors on the atomic layer order was developed for the purpose of making the phases single. That is, it is a method of semi-artificially producing a layered structure of a superconductor layer by sequentially laminating each atomic layer. However, so far, when applying this method for producing a superconductor layer to a tunnel type Josephson device having a SIS (superconductor layer / insulator layer / superconductor layer) laminated structure, SQUI
It was unclear what kind of layered structure should be adopted in order to obtain low noise characteristics applicable to electronic devices such as D.

The present invention has been made in view of the above points, and an object thereof is to effectively exhibit the excellent superconducting characteristics of an oxide high temperature superconductor, and to obtain good joining characteristics with reduced joining noise and 1 / f noise. The purpose is to provide a tunnel type Josephson device.

[0008]

A tunnel type Josephson element according to the invention of claim 1 comprises a pair of superconductor layers made of a Bi-based or Tl-based oxide superconductor thin film, which is provided on a substrate; In order to achieve the above-mentioned object, the crystals constituting the pair of superconductor layers have a direction c perpendicular to the substrate.
As the axis, is grown epitaxially with the insulator layer, and the interface between the pair of superconductor layers and the insulator layer is (a) or (b) or (c) It is formed by a lattice structure. (a) Ca atomic layer / Cu-O atomic layer / Sr (or Ba)-
O atomic layer / Bi (or Tl) -O atomic layer / Bi (or T
l) -O atomic layer / insulator layer (b) Ca atomic layer / Cu-O atomic layer / Sr (or Ba)-
O atomic layer / Bi (or Tl) -O atomic layer / insulator layer (c) Ca atomic layer / Cu-O atomic layer / Sr (or Ba)-
O atomic layer / insulator layer

According to a second aspect of the present invention, in a tunnel type Josephson element, a pair of superconductor layers made of a Y-based oxide superconductor thin film provided on a substrate and an insulator formed between the superconductor layers. In order to achieve the above-mentioned object,
The crystals forming the pair of superconductor layers are epitaxially grown with the insulator layer with the c-axis in the direction perpendicular to the substrate, and the pair of superconductor layers and the insulator layer are formed. The interface with and is formed by the superlattice structure of any of (a) or (b) or (c) below. (a) Y atomic layer / Cu-O atomic layer / Ba-O atomic layer / Cu
-O atomic layer / Ba-O atomic layer / insulator layer (b) Y atomic layer / Cu-O atomic layer / Ba-O atomic layer / Cu
-O atomic layer / insulator layer (c) Y atomic layer / Cu-O atomic layer / Ba-O atomic layer / insulator layer

[0010]

In the conventional tunnel type Josephson element made of a metal-based superconductor, since the superconductor has a long coherence length, a superconductor / insulator / superconductor is simply laminated to obtain a good characteristic. I was able to get it. However, in the tunnel type Josephson device made of the high temperature oxide superconductor, it was not possible to obtain a device having good characteristics simply by laminating. Therefore, the present inventors examined the noise characteristics of the conventional tunnel-type Josephson element using the oxide high temperature superconductor and investigated the reason why good characteristics could not be obtained. As a result, it was found that the cause of the junction noise and 1 / f noise is fluctuation of the critical current of the Josephson junction, which is caused by the trapping of tunnel electrons in the subgap formed in the insulating layer. It was also found that this subgap was caused by deterioration of superconducting properties of the superconductor layer at the interface between the superconductor layer and the insulator layer.

This point will be described with reference to FIG. FIG. 15 (a) shows superconducting layers 1a and 1b in the conventional example.
2 shows the energy gap at the interface between the insulating layer 2 and the insulating layer 2. As shown in the figure, in the conventional example, the superconducting gap energy on the surfaces (interfaces) of the superconductor layers 1a and 1b becomes smaller over a distance longer than the coherence length ξ, and the characteristics of the superconductor layers deteriorate. is doing. That is, tunnel electrons are trapped in the shaded portion in the figure, causing fluctuations in the critical current of the tunnel junction. In order to obtain an element with low junction noise and 1 / f noise, superconducting layers 1a and 1b having no deterioration in superconducting properties (no reduction in energy gap) up to the surface are prepared as shown in FIG. 15 (b). This is very important. That is, as shown in FIG. 14B, if the energy gap can be reduced stepwise at the portion corresponding to the coherence length ξ, the trapping of tunnel electrons can be prevented and the fluctuation of the critical current can be eliminated.

By the way, the high-temperature oxide superconductors are 1. Oxygen, which is a constituent element, is relatively unstable and easily escapes from the surface of the thin film. 2. Low carrier density. 3. The coherence length is short. It has the property of Further, since the conduction electron system is an ideal two-dimensional system, it is very sensitive to alteration on the surface, and an electric barrier is easily formed. Therefore, the inventors of the present application adopt the superlattice structure in which the interface is formed by a specific atomic layer so that the superconducting property does not deteriorate to the surface, and the problem of the interface as shown in FIG. Therefore, the present invention has been accomplished on the basis that the tunnel type Josephson device having excellent characteristics can be obtained.

The basic structure and operation of the present invention will be described below. First, as the Bi-based (Tl-based) oxide superconductor used in the tunnel type Josephson device according to the invention of claim 1, Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _x , Tl ₂ B is used.
a ₂ Ca ₁ Cu ₂ O _x (hereinafter referred to as a 2-2-1-2 structure), Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10-y , Tl ₂ Ba ₂
Examples thereof include Ca ₂ Cu ₃ O _10-y (hereinafter referred to as a 2-2-2-3 structure), and a composite oxide obtained by adding Pb.

FIG. 1 shows a crystal structure diagram of a Bi-based (Tl-based) oxide superconductor. FIG. 1 (a) has a 2-2-1-2 structure, and FIG. 1 (b) has a 2-2-2-3 structure. 1 in the figure
The crystal structures of (a) are Bi (or Tl) in order from the bottom of the paper.
-O atomic layer / Bi (or Tl) -O atomic layer / Sr (or Ba) -O atomic layer / Cu-O atomic layer / Ca atomic layer / Cu
It has a laminated structure in which units of —O atomic layer / Sr (or Ba) —O atomic layer are repeated. In each of the Cu-O atomic layers in the 2-2-1-2 structure, oxygen is located only on one side of the Cu site to form a Cu-O pyramid.
It is a u-O atomic layer.

Further, the crystal structure of FIG. 1 (b) has a Bi (or Tl) -O atomic layer / Bi (or Tl) sequence from the bottom of the paper.
-O atomic layer / Sr (or Ba) -O atomic layer / Cu-O atomic layer / Ca atomic layer / Cu-O atomic layer / Ca atomic layer / Cu
It has a laminated structure in which units of —O atomic layer / Sr (or Ba) —O atomic layer are repeated. In the case of the 2-2-2-3 structure, the Cu-O atomic layer is the Ca atomic layer and the Sr (or B
a) A Cu-O atomic layer in which oxygen is located only on one side of the Cu site to form a Cu-O pyramid between the -O atomic layer, and a peak oxygen is present between the Ca atomic layer and the Ca atomic layer. CuO ₂ without having a square CuO ₄ forms a plane
It is a sheet.

In the invention of claim 1, Bi in the arrow A in the figure
Bi (or Tl) -O atomic layer between (or Tl) -O atomic layer and Sr (or Ba) -O atomic layer, or Sr of arrow B
Bi (or Tl) -O atomic layer between (or Ba) -O atomic layer and Bi (or Tl) -O atomic layer, or C of arrow C
Cu-O between a atomic layer and Sr (or Ba) -O atomic layer
An interface with the insulator layer is formed by one of the atomic layers.

Next, as the Y-based oxide superconductor used in the tunnel type Josephson device according to the second aspect of the present invention, a composite oxide represented by Y ₁ Ba ₂ Cu ₃ O _7-x , Examples thereof include a composite oxide having a composition in which Y of the composite oxide is replaced by a lanthanoid element such as Ho or Er.

FIG. 8 shows a crystal structure diagram of the Y-based oxide superconductor. This crystal structure is Cu-
It has a laminated structure in which units of O atomic layer / Ba—O atomic layer / Cu—O atomic layer / Y atomic layer / Cu—O atomic layer / Ba—O atomic layer are repeated. The Cu-O atomic layer in FIG. 8 is a Cu-O atomic layer (sheet) in which oxygen is located only on the opposite side of the Y site to form a Cu-O pyramid, and two Cu-O atomic layers containing apex oxygen are included. Cu-O atomic layer between the Ba-O atomic layers of Cu-
O atomic layers are regularly arranged in one direction to have a Cu-O chain structure.

In the invention of claim 2, a Ba—O atomic layer between a Cu—O atomic layer (chain) and a Cu—O atomic layer (sheet) indicated by an arrow D in the figure, or a Ba—O atom indicated by an arrow E. Layer and Ba
The Cu-O atomic layer (chain) between the -O atomic layers or the Ba-O atomic layer between the Cu-O atomic layer (sheet) and the Cu-O atomic layer (chain) indicated by the arrow F is an insulator layer. The interface with is constructed.

Examples of the insulator used in the inventions of claims 1 and 2 include oxides having a lattice constant close to that of superconductors such as MgO, SrTiO ₃ , LaAlO ₃ , and the like. Now, regarding how the superlattice structure described above ensures excellent superconducting properties, the mechanism of superconducting properties and development of oxide high-temperature superconductors has not been clarified at present. However, although the action on the superconducting properties of the superlattice structure of the present invention cannot be clearly stated, the clue to solving the action of the superlattice structure of the present invention is as follows in the crystal structure of the oxide high temperature superconductor. It can be said that this is the role of the atomic layer.

(1) A CuO ₂ sheet in which oxygen is located only on one side of the Cu site to form a Cu—O pyramid, or a square CuO ₄ has no apical oxygen to form a flat surface, It is an atomic layer that contributes to the development of superconducting properties. (2) The CuO ₂ sheet is originally an insulator, and in the layer next to it, the Y atomic layer and the Ba—O atomic layer in the Y system are formed of Bi.
In the system (Tl system), when the Ca atomic layer and the Sr (Ba) -O atomic layer are arranged, the CuO ₂ sheet is doped with carriers to become a conductive layer. At this time, the surface of the superconducting layer is simply C which is a superconducting atomic layer.
Even if it is formed by using the u-O atomic layer, the Cu-O atomic layer on the surface is not sufficiently doped with carriers, so that the superconducting property of the superconducting layer at the interface is deteriorated and the tunnel type Josephson having good properties is obtained. It turned out that the element could not be obtained.
Therefore, not only the Cu—O layer but also the superlattice structure including a layer to be carrier-doped in this layer constitutes the superconducting surface so that there is no influence of the interface and the superconducting property does not deteriorate to the surface. A tunnel type Josephson element having good characteristics can be obtained.

[0022]

EXAMPLES Examples of the present invention will be described below. First,
The structure of the oxide high temperature superconductor thin film growth apparatus used in the examples of the present invention is shown in FIG. In the figure, K cell (K
Nudsen Cell) 101a to 101d are filled with metal, oxide, or organic complex, which are the respective constituent elements of the oxide high-temperature superconductor, and are heated to a temperature to obtain a desired vapor pressure by the heaters 102a to 102d, respectively. It The evaporation rate of these four elements is measured by a crystal vibration type film thickness monitor 103a.
-10d to feed back to the output of the heater so that the desired speed is obtained during film formation. Board 4
Is heated to a desired temperature by the heater 105. The shutters 106a to 106d are the film thickness monitor 1
It is interlocked with 03a to 103d, and has a mechanism to automatically intermittently open and close when a desired film thickness is reached, enabling sequential stacking. Further, the cylinder 107 is filled with a gas such as O ₂ , O ₃ , N ₂ O or NO ₂ which supplies oxygen to the thin film, and the valve 108 and the mass flow meter 10 are provided.
It is introduced into the chamber through the nozzle 9 and is sprayed to the vicinity of the substrate 4 through the nozzle 110. Further, 111 is an exhaust pump, and 112 is a chamber pressure control valve.
The reaction gas, which is an oxygen supply source, effectively performs an oxidizing action in the vicinity of the substrate 4, promotes the incorporation of oxygen into the oxide superconductor thin film, and plays a role of improving superconducting properties. However, if the evaporating raw material portion is not kept in a high vacuum, inconveniences such as the oxidation of the raw material will occur. Therefore, the differential exhaust plate 113 is installed. During the growth of the thin film, the lower material portion is kept at a high vacuum of 10 ⁻⁶ Torr or less, and the vicinity of the substrate 4 where the nozzle 110 has a high oxygen pressure locally causes about 10 ⁻⁴ Tor.
It is rr.

In order to realize the tunnel type Josephson element of the present invention, the sequential stacking method is applied using the above-described oxide high temperature superconductor thin film growth apparatus. In forming the thin film, since it is necessary that the electric charge be neutral in the entire thin film, the growth of the oxide high-temperature superconductor thin film is sequentially laminated so as to be an integral multiple of the unit lattice.

The first to fifth embodiments of the invention of claim 1 are shown. FIG. 2 is a conceptual diagram showing the structure of the device according to Example 1,
3 is a conceptual diagram showing the structure of an element according to Example 3, FIG. 4 is a conceptual diagram showing the structure of an element according to Example 4, and FIGS. 5 to 7 are conceptual diagrams showing the structure of an element according to yet another example. ..

Example 1 In FIG. 11, K ₂ cell 101a was supplemented with Bi ₂ O ₃
01b is Sr metal, 101c is Ca metal, 101d
Cu metal is filled in each of the heaters 102a-1
02d at 820 ° C, 800 ° C, 850 ° C, 11
Each raw material was evaporated by heating to 00 ° C. The evaporation rate of each raw material is independently controlled by the crystal vibration type film thickness monitors 103a to 103d, and the desired evaporation rate (about 0.05 to 1Å /
Seconds). The substrate 4 is SrTiO ₃ (10
0) A single crystal substrate is used, and the heater 5 is used beforehand for 450 to
It is heated to 600 ° C. The cylinder 107 is filled with NO ₂ , the valve 108 is opened, the mass flow meter 109 adjusts to 20 sccm, and the gas is introduced into the chamber. NO ₂ is passed through the nozzle 110 to the substrate 4
Reaches the vicinity of, and plays the role of effectively oxidizing each metal element. During film formation, the inside of the chamber was 5 × 10 ⁻⁵ To on average by the valve 112 and the exhaust pump 111.
It is kept at rr.

First, film growth of the lower superconducting layer 1a in the tunnel type Josephson element was performed as follows. Set the shutter 106 to (b → d → c → d → c → d
→ b → a → a → b → d → c → d → c → d → b → a → a)
As a repeating unit, the metal is sequentially opened and closed to deposit each metal on the substrate 4 in an atomic layer thickness. That is, SrCuC
aCuCaCuSrBiBiSrCuCaCuCaCu
It is the repetition of SrBiBi. By this operation,
Although a Bi-based oxide superconductor having a 2-2-2-3 structure as shown in (b) is obtained, in the present embodiment, as the lower superconductor layer 1a, a Bi—O atomic layer on the crystal structure is used. Sr-O
Thickness with Bi-O atomic layer sandwiched between atomic layers as the surface 70
A superconducting thin film of 0Å was formed.

The Bi-based oxide conductor thin film formed by the above-mentioned operation was subjected to a structural analysis by X-ray diffraction measurement (XRD). As a result, the c-axis grew in the direction perpendicular to the surface of the substrate 4. It was found to be a Bi-based oxide superconductor thin film having a -2-2-3 structure. In addition, as a result of observing the cross section of the grown superconductor thin film by observation with a high resolution transmission electron microscope, in the Bi-based oxide superconductor thin film of 2-2-2-3 structure, the Bi—O atomic layer and Sr on the crystal structure
It was confirmed that the Bi-O atomic layer sandwiched between the -O atomic layers formed the surface of the superconductor layer.

Next, another K cell not shown in FIG. 11 was filled with Mg metal as an evaporation raw material, and the corresponding heater was heated to 650 ° C. to evaporate Mg metal. At this time,
The other film forming conditions were the same as those for the lower superconductor layer 1a. Since the oxidizing gas is introduced, the evaporated Mg metal is oxidized in the vapor phase or on the substrate 4, and MgO grows. The MgO insulator layer 2 was formed on the lower superconducting layer 1a formed earlier by 20Å. After the growth, the structure of the film surface was observed by RHEED, and it was found that the MgO layer was epitaxially grown. Finally, the upper superconductor layer 1b is formed. The atomic layer is grown in the reverse order of that of the lower superconductor layer 1a, that is, the shutter 106 is moved to (a → a → b → d → c → d → c → d → b → a →).
a → b → d → c → d → c → d → b) are sequentially opened and closed to deposit each metal on the previously formed MgO insulator layer 2 in an atomic layer thickness. To go. That is, BiB
iSrCuCaCuCaCuSrBiBiSrCuCa
A Bi-based oxide superconductor thin film was grown by the same method as that for the lower superconductor layer 1a except that CuCaCuSr was repeated. By this operation, it was composed of a Bi-based oxide superconductor having a 2-2-2-3 structure (Fig. 1 (b)) and was sandwiched between the Sr-O atomic layer and the Bi-O atomic layer on the crystal structure. An upper superconducting layer 1b having a thickness of 700Å, in which the Bi-O atomic layer forms the interface with the insulator layer 2 as the lowermost layer, was formed.

The Bi-based oxide superconductor thin film formed by the above operation was subjected to structural diffraction by X-ray diffraction measurement (XRD), and as a result, the c-axis direction grew in a direction perpendicular to the substrate surface. It was found to be a Bi-based oxide superconductor thin film having a 2-2-2-3 structure. Further, as a result of observing the cross section of the formed superconductor thin film by observation with a high resolution transmission electron microscope, in the Bi-based oxide superconductor thin film of 2-2-2-3 structure, an Sr-O atomic layer on the crystal structure It was confirmed that the Bi-O atomic layer sandwiched between the Bi-O atomic layers formed the interface with the MgO insulator layer 2 at the lowermost layer of the upper superconductor layer 1a. After the growth was completed, the structure of the film surface was observed by RHEED, and it was found that the upper superconductor layer (BSCCO layer) 1b was epitaxially grown.

The above-mentioned lamination operation was performed in the same apparatus (so-called In-Situ). In the SIS type laminated structure thus obtained, RIB with SF ₆ gas is applied to a part of the region until the lower superconducting layer 1b is exposed.
E is dry-etched using the (R eactive I on B eam E tching) method, the superconducting layer 1a, the electrode 3a by the respective gold deposited on the upper surface 1b, the was formed 3b (FIG. 12). Figure 1
As shown in 2, the tunnel type Josephson device
A lower superconducting layer 1a, an insulating layer 2, and an upper superconducting layer 1b are sequentially laminated on a substrate 4. Further, a part of the insulator layer 2 and the upper superconducting layer 1b is removed, and a part of the lower superconducting layer 1a is exposed on the surface. The exposed region and the surface of the upper superconducting layer 1b are respectively provided with electrodes. 3a and 3b are formed. In the first embodiment, the single crystal substrate 4 is made of SrT.
iO ₃ (000), lower superconducting layer 1a and upper superconducting layer 1b are c-axis oriented, 2-2-2-3 structure Bi-based oxide superconductor, insulator layer 2 is (100) MgO having a thickness of 20Å, voltage Electrodes 3a- (a), 3b- (a) and current electrodes 3a- (b),
3b- (b) was composed of Au.

FIG. 13 shows the results of measuring the voltage-current characteristics of the tunnel type Josephson element according to this example at 77K. As shown in the figure, in this tunnel type Josephson element, the current drastically decreased in the vicinity of 10 mV corresponding to the energy gap, and it was confirmed that a good-quality tunnel junction was formed. Also, 10.8 at the joint
When irradiated with a microwave of GHz, a Shapiro step of about 20 μV was observed on the voltage-current curve, and it was confirmed that this junction has a Josephson junction effect. Fig. 14 shows the tunnel-type Josephson device manufactured at 77K.
The power spectrum of the low frequency side noise in is shown (a comparative example is mentioned later).

Example 2 Example 1 except that the material of the insulator layer 2 was SrTiO _3.
BSCCO upper superconductor layer / S
SI of rTiO ₃ insulator layer / BSCCO lower superconductor layer
An S stacking type junction was formed to produce a tunnel type Josephson device. The evaluation results were the same as in Example 1.

Example 3 Lower superconductor layer 1 in tunnel type Josephson device
In order to form a, the shutter 106 is moved to (a → a → b
→ d → c → d → c → d → b → a → a → b → d → c → d →
c → d → b) is used as a repeating unit to open and close in sequence,
Each metal is deposited on the substrate 4 in an atomic layer thickness. That is, BiBiSrCuCaCuCaCuSrBiBiS
A Bi-based oxide superconductor thin film was formed by the same method as in Example 1 except that rCuCaCuCaCuSr was repeated. By this operation, as shown in Fig. 1 (b),
Although a Bi-based oxide superconductor thin film having a -2-2-3 structure is obtained, the Sr-O atomic layer sandwiched between the Cu-O atomic layer and the Bi-O atomic layer on the crystal structure becomes the surface of the thin film. It is different from the first embodiment that the interface with the insulator layer 2 is formed after the growth of the insulator layer 2.

Next, in order to form the upper superconducting layer 1b of the tunnel type Josephson element, the growth order of atomic layers is opposite to that of the lower superconducting layer (BSCCO layer) 1a, that is, Press the shutter 106 (b → d → c
→ d → c → d → b → a → a → b → d → c → d → c → d →
b → a → a) is used as a repeating unit to open and close in sequence,
Each metal is deposited on the insulator layer 2 in the atomic layer thickness.
That is, SrCuCaCuCaCuSrBiBiSrCu
A Bi-based oxide superconductor thin film was formed by the same method as in Example 1 except that CaCuCaCuSrBiBi was repeated. By this operation, a Bi-based oxide superconductor having a 2-2-2-3 structure is obtained, but the Sr-O atomic layer sandwiched between the Cu-O atomic layer and the Bi-O atomic layer on the crystal structure is It differs from the first embodiment in that the lowermost layer of the upper superconductor layer 1b forms an interface with the insulator layer 2.

Except for the above, the SIS laminated structure formed by the same operation as in Example 1 was subjected to X-ray diffraction measurement (XR
D) and high resolution transmission electron microscope observation,
The superconductor layers 1a and 1b are epitaxially grown with the insulator layer 2 with the c-axis perpendicular to the substrate 4, and the interface with the insulator layer 2 is a Cu—O atomic layer having a crystalline structure. Bi having a 2-2-2-3 structure having a superlattice structure formed by an Sr-O atomic layer sandwiched between a Bi-O atomic layer and a Bi-O atomic layer
It was found to be a system oxide superconductor thin film. By the above operation, the BSCCO upper superconductor layer (700Å) / MgO insulator layer (20Å) / B as shown in FIG.
An SCCO lower superconductor layer (700 Å SIS laminated junction was formed to fabricate a tunnel-type Josephson device. The evaluation result was the same as that of Example 1.

Example 4 In order to form the lower superconducting layer 1a of the tunnel type Josephson device, the shutter 106 was set to (a → b → d → c →).
d → c → d → b → a → a → b → d → c → d → c → d → b
→ Open and close in sequence with a) as a repeating unit, and
Each metal is deposited on top of this in atomic layer thicknesses. That is, Bi
SrCuCaCuCaCuSrBiBiSrCuCaC
A Bi-based oxide superconductor thin film was formed by the same method as in Example 1 except that uCaCuSrBi was repeated. By this operation, a Bi-based oxide superconductor thin film having a 2-2-2-3 structure can be obtained.
It differs from Example 1 in that the Bi—O atomic layer sandwiched between the atomic layer and the Bi—O atomic layer forms the surface of the thin film, and forms an interface with the insulating layer 2 after the growth of the insulating layer 2. There is.

Next, in order to form the upper superconductor layer 1b of the tunnel type Josephson device, the growth order of the atomic layers is opposite to that of the lower superconductor layer (BSCCO layer) 1a, that is, Shutter 106 (a → b → d
→ c → d → c → d → b → a → a → b → d → c → d → c →
Repeatedly open and close with d → b → a) as a repeating unit,
Each metal is deposited on the insulator layer 2 in the atomic layer thickness.
That is, BiSrCuCaCuCaCuSrBiBiSr
A Bi-based oxide superconductor thin film was formed by the same method as in Example 1 except that CuCaCuCaCuSrBi was repeated. By this operation, a Bi-based oxide superconductor thin film having a 2-2-2-3 structure can be obtained, but the Bi- sandwiched between the Sr-O atomic layer and the Bi-O atomic layer on the crystal structure.
The O atomic layer is the lowermost layer of the upper superconductor layer 1b and is the insulator layer 2.
It is different from Example 1 in that an interface with and is formed. S formed by the same operation as in Example 1 except for the above
X-ray diffraction measurement (XRD) and high-resolution transmission electron microscope observation of the IS laminated structure revealed that the superconducting layers 1a and 1b were grown epitaxially with the insulator layer 2 with the c-axis perpendicular to the substrate 4. And the interface with the insulator layer 2 has a Sr-O atomic layer and a Bi-O on the crystal structure.
It was found to be a Bi-based oxide superconductor thin film having a 2-2-2-3 structure having a superlattice structure formed by Bi—O atomic layers sandwiched between atomic layers. By the above operation,
As shown in FIG. 4, the BSCCO upper superconductor layer (700
Å) / MgO insulator layer (20Å) / BSCCO lower superconducting layer (700Å) SIS laminated type junction was formed to produce a tunnel type Josephson device. The evaluation result is
It was the same as in Example 1.

In the above embodiment, the surfaces of the lower and upper superconductor layers 1a and 1b (interfaces with the insulator layer 2) are made of the same crystal structure layer. As long as the conditions (a), (b), and (c) of the lattice structure are satisfied, both surfaces need not be the same layer. An example of this is shown in FIG. In the example of FIG. 5, the lower and upper superconductor layers 1a and 1b are Bi-based oxide superconductor thin films having a 2-2-2-3 structure, and the surface of the lower superconductor layer 1a is Cu—O.
The upper superconductor layer 1b is formed of a Sr-O atomic layer sandwiched between the atomic layer and the Bi-O atomic layer, and the surface of the upper superconductor layer 1b is a Bi-O atomic layer sandwiched between the Sr-O atomic layer and the Bi-O atomic layer. Has been formed.

Further, in Examples 1 to 4, an example of the 2-2-2-3 structure (FIG. 1 (b)) was shown.
An example in which the lower and upper superconductor layers 1a and 1b are composed of a Bi-based oxide superconductor thin film having a 1-2 structure (FIG. 1 (a)) is shown. In the example of FIG. 6, the lower and upper superconductor layers 1a and 1b
The surface of B is sandwiched between Sr-O atomic layer and Bi-O atomic layer.
It is formed of an i-O atomic layer. In the example of FIG. 7, the surfaces of the lower and upper superconductor layers 1a and 1b are formed of Sr—O atomic layers sandwiched by Cu—O atomic layers and Bi—O atomic layers.

Comparative Example 1 In order to form the lower superconducting layer of the tunnel type Josephson device, the shutter 106 was set to (b → a → a → b → d →).
c → d → c → d → b → a → a → b → d → c → d → c →
Using d) as a repeating unit, the metals are sequentially opened and closed to deposit each metal on the substrate 4 in an atomic layer thickness. That is, SrB
iBiSrCuCaCuCaCuSrBiBiSrCu
B was prepared in the same manner as in Example 1 except that CaCuSrBiBiSrCuCaCuCaCu was repeated.
An i-based oxide superconductor thin film was formed. 2 by this operation
Although a Bi-based oxide superconductor thin film having a -2-2-3 structure is obtained, the Cu-O atomic layer sandwiched between the Sr-O atomic layer and the Ca atomic layer on the crystal structure serves as the surface of the thin film, and thus the insulator. It differs from Example 1 in that an interface with the insulator is formed after the layer growth.

Next, in order to form the upper superconductor layer of the tunnel type Josephson device, the growth order of the atomic layers is opposite to that of the lower superconductor layer (BSCCO layer), that is, the shutter 106. (D → c → d → c → d
→ b → a → a → b → d → c → d → c → d → b → a → a →
Using b) as a repeating unit, opening and closing are sequentially performed to deposit each metal on the insulator layer in the thickness of the atomic layer. That is, Cu
CaCuCaCuSrBiBiSrCuCaCuCaC
A Bi-based oxide superconductor thin film was formed by the same method as in Example 1 except that uSrBiBiSr was repeated. By this operation, a Bi-based oxide superconductor thin film having a 2-2-2-3 structure can be obtained.
It differs from Example 1 in that the Cu—O atomic layer sandwiched between the O atomic layer and the Ca atomic layer forms an interface with the insulator layer at the lowermost layer of the upper superconductor layer.

Except for the above, the SIS laminated structure formed by the same operation as in Example 1 was subjected to X-ray diffraction measurement (XR
D) and high resolution transmission electron microscope observation,
The lower and upper superconductor layers are epitaxially grown with the insulator layer with the c-axis perpendicular to the substrate, and
The interface with the insulator layer is C and the Sr-O atomic layer on the crystal structure.
a formed by Cu-O atomic layers sandwiched between a atomic layers,
It was found to be a Bi-based oxide superconductor thin film having a 2-2-2-3 structure having a superlattice structure. By the operation described above, the BSCCO upper superconductor layer (700Å) / MgO insulator layer (20Å) / BSCCO lower superconductor layer (700
A tunnel type Josephson device was produced by forming the SIS laminated junction of Å). FIG. 14 shows the power spectrum of low-frequency noise at 77K in the manufactured tunnel-type Josephson device.

As is clear from a comparison between Examples 1, 2, 3, 4 and Comparative Example 1, the tunnel type formed by the superlattice structure of the Bi-based oxide superconductor thin film according to the invention of claim 1 It can be said that the Josephson element is an element having good junction characteristics with reduced junction noise and 1 / f noise. In Comparative Example 1, as the atomic layer forming the interface between the superconductor layer and the insulator layer, the above-mentioned Cu—O was used.
Other than the atomic layer, the atomic layers other than Examples 1, 2, 3 and 4 were used, but the results were the same as those of Comparative Example 1.

Example 5 K cell 101a was filled with Tl ₂ O ₃ and 101b with Ba, the heater 102a was heated to 720 ° C., and 102b to 740.
By the same method as in Example 1 except that the heating was performed at 2 ° C, 2
A Tl-based oxide superconductor thin film having a -2-2-3 structure was grown to form lower and upper superconductor layers. Other than the above,
X-ray diffraction measurement (XRD) and high-resolution transmission electron microscope observation of the SIS laminated structure formed by the same operation as in Example 1 revealed that the lower and upper superconductor layers had the c-axis perpendicular to the substrate. T which is grown epitaxially with the insulator layer and whose interface with the insulator layer is sandwiched between the T1-O atomic layer and the Ba-O atomic layer on the crystal structure.
2- with a superlattice structure formed by an I-O atomic layer
It was found to be a Tl-based oxide superconductor thin film having a 2-2-3 structure. As described above, the TBCCO upper superconductor layer (700Å) / MgO insulator layer (20Å) / TBC
A tunnel type Josephson device was prepared by forming a SIS laminated junction of the CO lower superconductor layer (700 Å). The evaluation results were the same as in Example 1.

Comparative Example 2 In order to form a lower superconductor layer of a tunnel type Josephson device, a Tl-based oxide superconductor thin film was formed under the same growth conditions as in Example 5 and the same shutter operation as in Comparative Example 1. Filmed That is, BaTlTlBaCuCaCuCaC
It is the repetition of uBaTlTlBaCuCaCuCaCuCu. By this operation, a Tl-based oxide superconductor thin film having a 2-2-2-3 structure can be obtained.
It differs from Example 5 in that the Cu—O atomic layer sandwiched between the atomic layer and the Ca atomic layer becomes the surface of the thin film, and forms an interface with the insulator after the insulator layer has grown.

Next, in order to form the upper superconducting layer of the tunnel type Josephson element, under the same growth conditions as in Example 5, the atomic layers were grown in the lower superconducting layer (TBCC).
The Tl-based oxide superconductor thin film was grown so as to be opposite to the case of the O layer), that is, by the same shutter operation as in Comparative Example 1. By this operation, a Tl-based oxide superconductor thin film having a 2-2-2-3 structure can be obtained.
It differs from Example 5 in that the Cu—O atomic layer sandwiched between the O atomic layer and the Ca atomic layer forms an interface with the insulating layer at the lowermost layer of the upper superconductor layer.

X-ray diffraction measurement (XR) was performed on the SIS laminated structure grown by the same operation as in Example 5 except for the above.
D) and high-resolution transmission electron microscope observation revealed that the lower and upper superconductor layers were epitaxially grown with the insulator layer with the C-axis perpendicular to the substrate, and the interface with the insulator layer was , A 2-2-2-3 structure Tl-based oxide superconductor thin film having a superlattice structure formed by a Cu-O atomic layer sandwiched between a Ba-O atomic layer and a Ca atomic layer on a crystal structure I knew that. As described above, the TBCCO upper superconducting layer (700Å) / MgO insulator layer (20Å) / TBCCO lower superconducting layer (700
A tunnel type Josephson device was produced by forming the SIS laminated junction of Å). The evaluation result was the same as that of Comparative Example 1.

As can be seen from Example 5 and Comparative Example 2, the tunnel type Josephson element formed by the superlattice structure of the Tl-based oxide superconductor thin film according to the invention of claim 1 has a junction noise and 1 / f. It has been improved to a device having good junction characteristics with reduced noise. Comparative Example 2
In Example 1, the atomic layer forming the interface between the superconductor layer and the insulator layer was a layer other than the above-mentioned Cu—O atomic layer.
The results were the same as those of Comparative Example 2, although the atomic layers other than 2, 3, 4, and 5 were implemented.

Next, Examples 6 to 8 according to the invention of claim 2 will be described. FIG. 9 is a conceptual diagram showing the structure of the element according to Example 6, and FIG. 10 is a conceptual diagram showing the structure of the element according to Example 7. Example 6 Y has a high evaporation temperature and is difficult to evaporate in the K cell. Therefore, Y is filled in a crucible made of carbon and heated by an electron gun. On the other hand, K cell 101a is filled with Ba and 101b is filled with Cu,
Heaters 102a to 102b at 740 ° C. and 1
Heat to 100 ° C. and evaporate. The shutter immediately above the crucible filled with Y is 106e (not shown). In order to form the lower superconducting layer 1a of the tunnel type Josephson device, the shutter 106 is (b → e → b → a → b →).
Using a) as a repeating unit, each metal is deposited on the substrate 4 in atomic layer thickness by sequentially opening and closing. That is, CuY
Example 1 except that CuBaCuBa is repeated
A Y-based oxide superconductor thin film was formed by the same method as described above. By this operation, Y of 1-2-3 structure as shown in FIG. 8 is obtained.
Although a system-based oxide superconductor thin film is obtained, in the present embodiment, the Cu—O atomic layer on the crystal structure and the B sandwiched between the Cu—O atomic layers are formed.
After the a-O atomic layer becomes the surface of the thin film and the insulator layer is grown,
Form an interface with the insulator.

In order to form the upper superconducting layer 1b of the tunnel type Josephson element, the growth order of atomic layers is reversed from that of the lower superconducting layer (YBCCO layer) 1a, that is, the shutter 106 is formed. (A → b → a → b → e
→ Using b) as a repeating unit, opening and closing are sequentially performed to deposit each metal on the insulating layer 2 in the thickness of the atomic layer. That is,
A Y-based oxide superconductor thin film was formed by the same method as in Example 1 except that BaCuBaCuYCu was repeated. By this operation, a Y-based oxide superconductor thin film having a 1-2-3 structure as shown in FIG. 8 is obtained, but in this example, it is sandwiched between the Cu—O atomic layer and the Cu—O atomic layer on the crystal structure. The Ba—O atomic layer forms the interface with the insulator layer 2 at the lowermost layer of the upper superconductor layer 1b.

X-ray diffraction measurement (XR) was performed on the SIS laminated structure formed by the same operation as in Example 1 except for the above.
D) and high resolution transmission electron microscope observation,
The lower and upper superconductor layers are epitaxially grown with the insulator layer with the c-axis perpendicular to the substrate, and the interface with the insulator layer has a Cu--O atomic layer and Cu on the crystal structure.
It was found to be a Y-based oxide superconductor thin film having a 1-2-3 structure having a superlattice structure, which was formed by Ba-O atomic layers sandwiched between -O atomic layers. As described above, the YBCO upper superconductor layer (700
Å) / MgO insulator layer (20Å) / YBCO lower superconducting layer (700Å) SIS laminated junction was formed to produce a tunnel type Josephson device. The evaluation results were the same as in Example 1.

Example 7 In order to form the lower superconducting layer of the tunnel type Josephson element, the shutter 106 was set to (a → b → e → b → a →).
Using b) as a repeating unit, the metals are sequentially opened and closed to deposit each metal on the substrate 4 in an atomic layer thickness. That is, BaC
Example 6 except that uYCuBaCu is repeated
A Y-based oxide superconductor thin film was grown by the same method as described above. By this operation, Y of 1-2-3 structure as shown in FIG. 8 is obtained.
-Based oxide superconductor thin film is obtained, but Ba on the crystal structure
The Cu-O atomic layer sandwiched between the -O atomic layer and the Ba-O atomic layer becomes the surface of the thin film, and after the growth of the insulating layer 2, the insulating layer 2 is formed.
It is different from Example 6 in that the interface with is formed.

Then, in order to form the upper superconducting layer 1b of the tunnel type Josephson device, the growth order of the atomic layers is opposite to that of the lower superconducting layer (YBCO layer) 1a, that is, Set the shutter 106 to (b → a → b →
e → b → a) as a repeating unit, open and close in sequence,
Each metal is deposited on the insulator layer 2 in the atomic layer thickness.
That is, a Y-based oxide superconductor thin film was formed by the same method as in Example 6 except that CuBaCuYCuBa was repeated. By this operation, 1-2 as shown in FIG.
Although a Y-based oxide superconductor thin film having a -3 structure is obtained, a Ba-O atomic layer on the crystal structure and a C sandwiched between the Ba-O atomic layers are obtained.
It differs from Example 6 in that the u-O atomic layer forms an interface with the insulator layer at the lowermost layer of the upper superconductor layer.

X-ray diffraction measurement (XR) was performed on the SIS laminated structure formed by the same operation as in Example 6 except for the above.
D) and high resolution transmission electron microscope observation,
The lower and upper superconductor layers 1a and 1b are epitaxially grown with the insulator layer with the c-axis being the direction perpendicular to the substrate, and the interface with the insulator layer 2 has a crystal structure of Ba-
1-2-3 structure Y having a superlattice structure formed by a Cu-O atomic layer sandwiched between an O atomic layer and a Ba-O atomic layer
It was found to be a system oxide superconductor thin film. As described above, the YBCO upper superconductor layer (700Å) / MgO insulator layer (20Å) / YBC as shown in FIG.
A tunnel type Josephson device was produced by growing a sis laminated junction of the O lower superconductor layer (700 Å). The evaluation result was the same as in Example 6.

Example 8 In order to form the lower superconducting layer of the tunnel type Josephson device, the shutter 106 was set to (b → a → b → e → b →).
Using a) as a repeating unit, each metal is deposited on the substrate 4 in atomic layer thickness by sequentially opening and closing. That is, CuB
Example 6 except that aCuYCuBa is repeated
A Y-based oxide superconductor thin film was formed by the same method as described above. By this operation, Y of 1-2-3 structure as shown in FIG. 8 is obtained.
-Based oxide superconductor thin film is obtained, but Cu on the crystal structure
It differs from Example 6 in that the Ba-O atomic layer sandwiched between the -O atomic layer and the Cu-O atomic layer becomes the surface of the thin film, and forms an interface with the insulator after the growth of the insulating layer. ..

Then, in order to form the upper superconductor layer of the tunnel type Josephson device, the growth order of the atomic layers is reversed from that of the lower superconductor layer (YBCO layer), that is, the shutter 106. (A → b → a → b → e →
Using b) as a repeating unit, opening and closing are sequentially performed to deposit each metal on the insulator layer in the thickness of the atomic layer. That is, Ba
A Y-based oxide superconductor thin film was formed by the same method as in Example 6 except that CuBaCuYCu was repeated. By this operation, a Y-based oxide superconductor thin film having a 1-2-3 structure as shown in FIG. 8 can be obtained.
It differs from Example 6 in that the Ba-O atomic layer sandwiched between the u-O atomic layer and the Cu-O atomic layer forms an interface with the insulator layer at the lowermost layer of the upper superconductor layer. ..

Except for the above, the SIS laminated structure formed by the same operation as in Example 6 was subjected to X-ray diffraction measurement (XR
D) and high resolution transmission electron microscope observation,
The lower and upper superconductor layers are epitaxially grown with the insulator layer with the c-axis perpendicular to the substrate, and
The interface with the insulator layer is a Cu-O atomic layer having a crystalline structure and Cu.
It was found to be a Y-based oxide superconductor thin film having a 1-2-3 structure having a superlattice structure, which was formed by Ba-O atomic layers sandwiched between -O atomic layers. As above, Y
S of BCO upper superconductor layer (700Å) / MgO insulator layer (20Å) / YBCO lower superconductor layer (700Å)
An IS stacked junction was grown to produce a tunnel type Josephson device. The evaluation result was the same as in Example 6.

Comparative Example 3 In order to form the lower superconducting layer of the tunnel type Josephson element, the shutter 106 was (a → b → a → b → e →).
Using b) as a repeating unit, the metals are sequentially opened and closed to deposit each metal on the substrate 4 in an atomic layer thickness. That is, BaC
Example 6 except that uBaCuYCu is repeated
A Y-based oxide superconductor thin film was formed by the same method as described above. By this operation, Y of 1-2-3 structure as shown in FIG. 8 is obtained.
A system oxide superconductor thin film is obtained, but the Cu—O atomic layer sandwiched between the Y atomic layer and the Ba—O atomic layer on the crystal structure becomes the surface of the thin film, and after the insulating layer is grown, it becomes The difference from Example 6 is that an interface is formed.

Then, in order to form the upper superconductor layer of the tunnel type Josephson device, the growth order of the atomic layers is reversed from that of the lower superconductor layer (YBCO layer), that is, the shutter 106. (B → e → b → a → b →
Using a) as a repeating unit, opening and closing are sequentially performed to deposit each metal on the insulator layer in the thickness of the atomic layer. That is, Cu
A Y-based oxide superconductor thin film was formed by the same method as in Example 6 except that YCuBaCuBa was repeated. By this operation, a Y-based oxide superconductor thin film having a 1-2-3 structure as shown in FIG. 8 can be obtained.
The Ba-O atomic layer sandwiched between the atomic layer and the Ba-O atomic layer is
It differs from Example 6 in that the interface with the insulator layer is formed in the lowermost layer of the upper superconductor layer.

X-ray diffraction measurement (XR) was performed on the SIS laminated structure formed by the same operation as in Example 6 except for the above.
D) and high resolution transmission electron microscope observation,
The lower and upper superconductor layers are epitaxially grown with the insulator layer with the c-axis perpendicular to the substrate, and
The interface with the insulator layer has a Y-atom layer and Ba—O on the crystal structure.
It was found to be a Y-based oxide superconductor thin film having a 1-2-3 structure having a superlattice structure formed by Cu—O atomic layers sandwiched between atomic layers. As above, YBCO
Upper superconductor layer (700 Å) / MgO insulator layer (20
Å) / YBCO lower superconducting layer (700Å) SIS laminated type junction was grown to produce a tunnel type Josephson device. The evaluation result was the same as that of Comparative Example 1.

Comparative Example 4 In the oxide high temperature superconductor thin film growth apparatus of FIG. 11, the shutters 106a, 106b and 106e are simultaneously opened instead of sequentially laminating the atomic layers by intermittently opening and closing the shutters, thereby forming a crystal structure. The elements were simultaneously supplied onto the substrate 4 to grow a Y-based oxide superconductor thin film having a 1-2-3 structure. At this time, the crystal vibration type film thickness monitor 1
The evaporation rate of each element is controlled by 03 to form a Y-based oxide superconductor thin film having a predetermined composition on the substrate 4.
In addition, the substrate temperature is set to 600 to 700 ° C. by the heater 105.
Heated to. By stacking the superconductor layer by the above operation and the insulator layer described in Example 1 in the same device (In-Situ), the YBCO upper superconductor layer (700 Å)
/ MgO insulator layer 20Å) / YBCO lower superconductor layer (700Å) was formed into a SIS laminated type junction to produce a tunnel type Josephson device.

The superconducting layer of the obtained device was c-shaped as a result of X-ray diffraction measurement (XRD) and high-resolution transmission electron microscope observation.
It was grown epitaxially with the insulator layer with the axis perpendicular to the substrate, but the atomic layer forming the interface with the insulator layer was found to be different for each crystal grain. .. FIG. 14 shows the power spectrum of the low-frequency noise at 77K of the manufactured tunnel-type Josephson device. As can be seen from Examples 6, 7 and 8 and Comparative Examples 3 and 4, the tunneling type Josephson element formed by the superlattice structure of the Y-based oxide superconductor thin film according to the invention of claim 2 has a junction noise. And 1 / f noise has been reduced,
It has been improved to an element having good junction characteristics. In Comparative Example 3, as the atomic layer forming the interface between the superconductor layer and the insulating layer, a Y atomic layer other than the Cu—O atomic layer described above was used, but the result is the same as that of Comparative Example 3. there were.

[0063]

As described above, according to the present invention, the SI
Since the interface between the superconductor layer and the insulator layer in the S laminated structure is formed by a specific superlattice structure of the oxide high-temperature superconductor, the junction noise of the tunnel-type Josephson element and 1 /
f noise can be reduced. The tunnel-type Josephson device of the present invention effectively exhibits the excellent superconducting properties of the oxide high-temperature superconductor and exhibits good junction properties.
It can be preferably used for ID and the like.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a crystal structure of a superconductor layer according to claim 1.

FIG. 2 is a conceptual diagram showing a structure of a tunnel type Josephson element according to Example 1.

FIG. 3 is a conceptual diagram showing a structure of a tunnel type Josephson element according to a third embodiment.

FIG. 4 is a conceptual diagram showing the structure of a tunnel type Josephson element according to Example 4.

FIG. 5 is a conceptual diagram showing the structure of a tunnel type Josephson device according to another embodiment.

FIG. 6 is a conceptual diagram showing the structure of a tunnel type Josephson device according to another embodiment.

FIG. 7 is a conceptual diagram showing a structure of a tunnel type Josephson device according to another embodiment.

FIG. 8 is a conceptual diagram showing a crystal structure of a superconductor layer according to claim 2.

FIG. 9 is a conceptual diagram showing the structure of a tunnel-type Josephson device according to Example 6.

FIG. 10 is a conceptual diagram showing the structure of a tunnel type Josephson element according to Example 7.

FIG. 11 is a configuration diagram of an oxide high temperature superconductor thin film growth apparatus used in Examples and Comparative Examples.

FIG. 12 is a perspective view of a tunnel type Josephson device manufactured in an example.

FIG. 13 is a diagram showing the voltage-current characteristics of the tunnel type Josephson device manufactured in the example.

FIG. 14 is a diagram showing a power spectrum of low frequency side noise of the tunnel type Josephson element manufactured in the example.

15 (a) and 15 (b) are conceptual diagrams showing a state of an energy gap at an interface between a superconductor layer and an insulator layer.

FIG. 16 is a diagram showing a power spectrum of low-frequency noise of a conventional tunnel type Josephson element.

[Explanation of symbols]

 1a Lower superconductor layer 1b Upper superconductor layer 2 Insulator layer 3a Voltage electrode 3b Current electrode 4 Substrate

Front page continuation (72) Inventor Shoji Yoshihara 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (2)

[Claims] 1. A tunnel comprising a pair of superconductor layers made of a Bi-based or Tl-based oxide superconductor thin film provided on a substrate, and an insulator layer formed between the pair of superconductor layers. Type Josephson device, the crystals forming the pair of superconductor layers are epitaxially grown with the insulator layer with the c-axis in the direction perpendicular to the substrate, and the pair of superconductor layers are formed. A tunnel-type Josephson device characterized in that an interface between the insulating layer and the insulating layer is formed by a superlattice structure of any one of (a), (b) and (c) below. (a) Ca atomic layer / Cu-O atomic layer / Sr (or Ba)-
O atomic layer / Bi (or Tl) -O atomic layer / Bi (or T
l) -O atomic layer / insulator layer (b) Ca atomic layer / Cu-O atomic layer / Sr (or Ba)-
O atomic layer / Bi (or Tl) -O atomic layer / insulator layer (c) Ca atomic layer / Cu-O atomic layer / Sr (or Ba)-
O atomic layer / insulator layer 2. A tunnel-type Josephson device comprising a pair of superconductor layers made of a Y-based oxide superconductor thin film provided on a substrate, and an insulator layer formed between the superconductor layers, Crystals constituting the pair of superconductor layers are epitaxially grown with the insulator layer with the c axis perpendicular to the substrate, and the pair of superconductor layers and the insulator layer are formed. The interface of (a) or
A tunnel-type Josephson device characterized by being formed by the superlattice structure of either (b) or (c). (a) Y atomic layer / Cu-O atomic layer / Ba-O atomic layer / Cu
-O atomic layer / Ba-O atomic layer / insulator layer (b) Y atomic layer / Cu-O atomic layer / Ba-O atomic layer / Cu
-O atomic layer / insulator layer (c) Y atomic layer / Cu-O atomic layer / Ba-O atomic layer / insulator layer