JPH09266331A - Tunnel type josephson device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tunnel type Josephson device which uses a inherent Josephson device of an oxide high temperature superconductor and its manufacturing method. SOLUTION: Heating treatment is conducted at a temperature higher than the crystallinity temperature of an oxide high temperature superconductor comprising Bl2 , Sr2 , Ca1 , Cu2 and O8 on a board 11 made of single crystal of MgO and a plurality of single crystalline particles 12A, 12B and 12C comprising Bl2 , Sr2 , C1 , Cu2 and O8 enveloped with the crystalline field 13 are formed. A projected area 12a, whose cross section is 400μm<2> and whose height is below ten times the spacing of block layers of Bl2 , Sr2 , Ca1 , Cu2 and O8 , is formed on the top of the single crystalline particle 12A. A first electrode 14A comprising Au is formed on the top of the projected area 12a of the single crystalline particle 12A. A second electrode 14B is formed in the area other than the projected area 12a in the single crystalline particle 12A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film element and a method of manufacturing the same, and more particularly, to a tunnel type Josephson thin film element which utilizes an intrinsic Josephson junction of an oxide high temperature superconductor and is applicable to high frequency communication and logic circuits. And a manufacturing method thereof.

[0002]

2. Description of the Related Art With the recent progress of thin film forming technology, thin film elements having various functions have been put into practical use. For example, in a thin film element using an oxide thin film, an infrared sensor utilizing the pyroelectricity of a lead titanate-based thin film and a surface acoustic wave filter utilizing the piezoelectricity of a zinc oxide thin film have been put to practical use. There is. These thin film elements have such factors that the degree of crystallization of the thin film required for device formation is not strict, and that the thin film element has a simple crystal structure and thus can be easily formed into a thin film having the required crystallinity. Therefore, it was put into practical use without much difficulty.

However, in an element utilizing the strong anisotropy of crystals, a slight disorder of crystallinity (crystal orientation) has a great influence on the characteristics of the element, and therefore a thin film having high crystallinity is required. It For example, when an extremely thin insulating layer is sandwiched by two superconductors, a tunneling phenomenon of electron pairs occurs between these two superconductors, and the superconducting current flows through the thin insulating layer even if there is no applied voltage from the outside. The tunnel type Josephson device is obtained because of the flow of the magnetic field. However, in reality, the tunnel type Josephson device in which the high-temperature oxide superconductor sandwiches the thin oxide insulating layer is manufactured with the coherence length of the superconducting pair. It was very short and difficult to achieve.

Recently, it was revealed that the two-dimensional crystal structure of the oxide high-temperature superconductor essentially forms a Josephson junction, that is, an intrinsic Josephson junction.
As disclosed in Japanese Patent Laid-Open No. 58366, there has been proposed a method of manufacturing a tunnel type Josephson element as a thin film element made of an oxide high temperature superconductor.

A conventional method of manufacturing a tunnel type Josephson device will be described below with reference to the drawings.

FIG. 13 is a sectional view in order of the steps, showing a conventional method for manufacturing a tunnel type Josephson element. Briefly explaining each manufacturing method of the tunnel type Josephson element,
First, as shown in FIG. 13A, after forming a first superconductor thin film 102 having a thickness of about 100 nm on a substrate 101, a photo is selectively formed on the upper surface of the first superconductor thin film 102. A resist pattern 103 is formed.

Next, as shown in FIG. 13B, the first superconductor thin film 102 is etched to a thickness of, for example, 10 nm using the photoresist pattern 103 as a mask.

Next, as shown in FIG. 13C, the substrate 1
On the entire surface of No. 01, the interlayer insulating film 104 is deposited to the same extent as the above etching amount.

Next, as shown in FIG. 13D, the photoresist pattern 103 is lifted off to remove the interlayer insulating film 104 on the photoresist pattern 103, and then the photoresist in the first superconductor thin film 102 is removed. The surface covered with the pattern 103 is cleaned with an oxygen ion beam, and then a second superconductor thin film 105 having a thickness of about 150 nm is deposited over the entire surface of the substrate 101 without breaking the vacuum. Then, as shown in FIG. 13E, the width is 100 μm with respect to the second superconductor thin film 105.
Etching is performed so that

[0010]

However, the conventional method of manufacturing a tunnel type Josephson device is not shown in FIG.
The crystallinity of the junction region 102a, which is the interface between the first superconducting thin film 102 and the second superconducting thin film 105 shown in (e), becomes poor. Specifically, FIG. 14B is a plan view of FIG. 14B, which is an enlarged view of the bonding region 102a in FIG. 13E, and FIG. 14A is a cross-sectional structure taken along line XIV-XIV of FIG. 14B. As described above, the layered structure of the crystal is not retained in the entire bonding region 102a and is partially discontinuous at the atomic level. Therefore, the high resistance layer (block layer) in the crystal layered structure may not be sufficiently electrically insulated, so that the upper and lower (c-axis direction) low resistance layers are electrically separated in the crystal layered structure. There is a problem that the tunnel junction characteristics cannot be obtained due to the connection.

Further, the joining region 102 shown in FIG.
Since a is finely formed by the fine processing technique, at least a size (about 1 μm or more) that can be processed by the present fine processing technique when forming the first superconductor thin film 102.
It is necessary to obtain the single crystal region of (3) in a state where it can be easily distinguished from other regions, but it is difficult to obtain the single crystal region that satisfies such a condition with the current thinning technology.

Further, since the steps of forming the first thin film, microfabrication, and forming the second thin film are required when forming the bonding region 102a, impurities such as water molecules adhere to the bonding region 102a. It will be easier. Therefore, when the impurities adhere to the c-axis oriented film in the oxide high-temperature superconductor having the intrinsic Josephson junction in which the superconducting layers and the insulating layers are alternately oriented, two or more new insulating layers are formed in the insulating layer. Since the layers are stacked, the tunnel junction characteristic cannot be obtained. As described above, when the superconductor thin film is formed in a plurality of times, it is difficult to obtain a good quality joint.

As described above, the tunnel type Josephson thin film device having substantially good device characteristics cannot be manufactured by the method proposed in Japanese Patent Laid-Open No. 7-58366.

The present invention solves the above-mentioned conventional problems and provides a tunnel type Josephson device using an intrinsic Josephson junction of an oxide high temperature superconductor and a method for manufacturing the same.

[0015]

In order to achieve the above-mentioned object, the present invention forms a thin film of an oxide high temperature superconductor on a main surface of a substrate, and forms a crystal of the oxide high temperature superconductor on the thin film. After forming a single crystal grain having c-axis orientation in the thin film by performing a heat treatment at a temperature equal to or higher than the crystallization temperature, a first electrode is formed on the upper surface of the single crystal grain, and the first electrode is formed on the main surface of the substrate. , In a region different from the region where the single crystal grain is formed,
To form the electrode.

[0016] Specifically, the solution of the invention of claim 1 is to provide a tunnel type Josephson element with a conductive region formed on a substrate and an oxide high temperature superconducting device provided on the conductive region. A single crystal grain formed by heat-treating the body at a temperature equal to or higher than the crystallization temperature of the oxide high-temperature superconductor, and electrically connected to a surface of the single crystal grain opposite to the conductive region. And a second electrode electrically connected to a region on the conductive region different from the region where the single crystal grain is formed, the single crystal grain being a tunnel type. The configuration is such that it has the Josephson effect.

According to the structure of claim 1, single crystal grains made of an oxide high temperature superconductor formed in the crystal axis direction showing the tunnel type Josephson effect on the conductive region on the substrate,
Since the oxide high-temperature superconductor is formed by heat treatment at a temperature equal to or higher than the crystallization temperature, the first electrode electrically connected to the surface opposite to the conductive region and the conductive region are interposed. By providing the second electrode that is electrically connected to the thin film element having the tunnel-type Josephson effect.

Here, the crystallization temperature is the temperature at which the compound starts to crystallize. Conventionally, a thin film formed on a substrate is
When heat-treated at a temperature equal to or higher than the crystallization temperature of the compound forming the thin film, the crystallinity of each crystal grain of the compound forming the thin film is improved, but a large number of grain boundaries occur in the thin film. Was considered unavailable. However, the present inventors have found that when a thin film of a compound whose crystal has anisotropy is heat-treated at a temperature equal to or higher than the crystallization temperature of the compound, the compound having a crystal axis anisotropy in the thin film can be processed by a fine processing technique. Machinable size single crystal grain (particle size:
It has been found that the single crystal grains are oriented in a certain direction with respect to the main surface of the substrate, and the crystal plane having the single crystal grains obtained by the heat treatment is determined based on this finding. A thin film element is realized by adopting an element configuration in which the crossing direction is the current direction.

According to a second aspect of the present invention, in the structure of the first aspect, the cross-sectional area in the direction perpendicular to the c-axis direction of the region showing the tunnel type Josephson effect in the single crystal grain is 4
A structure having a size of 00 μm ² or less is added.

According to the second aspect of the invention, the voltage value when the device jumps to the voltage state due to the generation of the current exceeding the Josephson critical current is approximately the same as the tunnel voltage determined by the number of intrinsic Josephson junctions or Since it can be limited to less than that, heat generated when the element jumps to the voltage state when the element is operated can be suppressed.

According to a third aspect of the present invention, in the structure of the first or second aspect, the length in the c-axis direction of the region showing the tunnel type Josephson effect in the single crystal grain is the same as that of the high temperature oxide superconductor. A configuration in which the interval between the block layers is 10 times or less is added.

According to the structure of claim 3, the length of the region showing the tunnel type Josephson effect in the c-axis direction is 10 times or less than the distance between the block layers of the high temperature oxide superconductor.
Since the thickness of the single crystal grain is 10 times or less than the distance between the block layers of the high temperature oxide superconductor, the number of junctions operating as intrinsic Josephson junctions can be limited to 10 or less.

According to a fourth aspect of the present invention, in the structure of the first to third aspects, the oxide high temperature superconductor is Bi (bismuth), S.
r (strontium), Ca (calcium), Cu
The composition is a compound containing (copper) and O (oxygen).

According to the structure of claim 4, since the Bi-based superconductor having a strong crystal axis anisotropy is used as the oxide high-temperature superconductor, a single crystal grain having excellent crystallinity can be obtained. Can be reliably formed.

According to a fifth aspect of the present invention, there is provided a method for manufacturing a tunnel-type Josephson element, comprising: a superconductor thin film forming step of forming a thin film of an oxide high temperature superconductor on a main surface of a substrate; A single crystal grain forming step of forming a single crystal grain of the oxide high temperature superconductor having c-axis orientation by performing heat treatment on the thin film at a temperature equal to or higher than the crystallization temperature of the oxide high temperature superconductor; A first electrode forming step of forming a first electrode electrically connected to the single crystal grain in one region on the upper surface of the thin film, and an electrical connection between the single crystal grain and the first electrode in another region on the upper surface of the thin film. And a second electrode forming step of forming second electrodes that are electrically connected to each other.

According to the structure of claim 5, a thin film made of an oxide high temperature superconductor formed on the main surface of the substrate is heat-treated at a temperature not lower than the crystallization temperature of the oxide high temperature superconductor, Single crystal grains made of an oxide high temperature superconductor and having c-axis orientation are formed in the thin film. Therefore, it is possible to form the first electrode electrically connected to the upper surface portion of the single crystal grain in a certain area on the upper surface of the thin film, and at the other area different from the area where the first electrode is formed. By forming the second electrode, the second electrode is electrically connected to the lower portion of the single crystal grain of the thin film.

According to a sixth aspect of the present invention, there is provided a method for manufacturing a tunnel-type Josephson element, comprising: a superconductor thin film forming step of forming a thin film of an oxide high temperature superconductor on a main surface of a substrate; First in a region on the top surface of the thin film
First electrode forming step of forming the second electrode, a second electrode forming step of forming a second electrode in another region on the upper surface of the thin film, and a crystal of the oxide high temperature superconductor for the thin film. By performing heat treatment at a temperature above the oxidization temperature,
And a single crystal grain forming step of forming a single crystal grain having the c-axis orientation made of the oxide high temperature superconductor.

According to the structure of claim 6, a thin film made of an oxide high-temperature superconductor formed on the main surface of the substrate is heat-treated at a temperature higher than the crystallization temperature of the oxide high-temperature superconductor, Single crystal grains made of an oxide high temperature superconductor and having c-axis orientation are formed in the thin film. Therefore, it is possible to form the first electrode electrically connected to the upper surface portion of the single crystal grain in a certain area on the upper surface of the thin film, and at the other area different from the area where the first electrode is formed. The formed second electrode is electrically connected to the lower portion of the single crystal grain of the thin film.

According to a seventh aspect of the present invention, in the structure of the fifth aspect, a region other than a predetermined region in the upper surface portion of the single crystal grain is provided between the single crystal grain forming step and the first electrode forming step. A step of forming a convex portion formed of the predetermined region on the upper surface portion of the single crystal grain by removing to a predetermined depth with respect to the main surface of the substrate, wherein the first electrode forming step includes The method includes the step of forming the first electrode on the upper surface of the convex portion of the single crystal grain, and the second electrode forming step forms the second electrode in a region of the single crystal grain excluding the convex portion. The configuration including the step of performing is added.

According to the structure of claim 7, the first electrode is formed on the upper surface of the convex portion which is a substantial element forming region, and
Since the second electrode is formed in the region excluding the convex portion of the single crystal grain, the region excluding the convex portion may be used as a conductive region for operating the convex portion of the single crystal grain which is an element forming region. it can. Therefore, by forming the second electrode in the region excluding the convex portion, the second electrode is electrically connected to the lower portion of the convex portion of the single crystal grain. Can be taken out as an element.

Here, the oxide high-temperature superconductor generally becomes a c-axis oriented film in a wide temperature range, and the critical current density in the c-axis direction is extremely smaller than that in the direction parallel to the c-plane. . Therefore, by connecting the electrodes to the upper surface of the convex portion and the surface exposed and removed so that the direction perpendicular to the substrate (c-axis direction) in the convex portion becomes the current direction, the convex portion is substantially formed. It operates as a simple element part. Also,
The region other than the convex portion of the single crystal grain can be considered as a channel which is simply a conductive region.

The invention of claim 8 is the addition of the structure of claim 7, wherein the area of the upper surface of the convex portion of the single crystal grain is 400 μm ² or less.

According to the structure of claim 8, the voltage value when the device jumps to the voltage state due to the current exceeding the Josephson critical current is set to be equal to or less than the tunnel voltage determined by the number of intrinsic Josephson junctions. Since it can be limited, heat generated when the element jumps to the voltage state when the element is operated can be suppressed.

According to a ninth aspect of the present invention, in the structure of the seventh or eighth aspect, the height of the convex portion of the single crystal grain is the block of the oxide high temperature superconductor formed in the superconductor thin film forming step. A structure having a layer spacing of 10 times or less is added.

According to the structure of claim 9, the height of the convex portion on the upper surface of the single crystal grain is not more than 10 times the interval between the block layers of the high temperature oxide superconductor, so that the thickness of the single crystal grain is high. Since the distance between the block layers of the superconductor is 10 times or less, the number of junctions that operate as intrinsic Josephson junctions can be limited to 10 or less.

According to a tenth aspect of the present invention, there is provided the structure of the fifth aspect.
Between the single crystal grain forming step and the first electrode forming step, a frame-shaped recessed groove having a predetermined depth is formed in the upper surface portion of the single crystal grain to form an upper surface of the single crystal grain. The step of dividing into a first region surrounded by the recessed groove and a second region outside the recessed groove, wherein the first electrode formation step is performed on the first region of the single crystal grain. The method includes the step of forming the first electrode, and the second electrode forming step adds a configuration including a step of forming the second electrode in the second region of the single crystal grain. .

According to the structure of claim 10, a frame-shaped concave groove having a predetermined depth is formed in the upper surface portion of the single crystal grain, and the upper surface of the single crystal grain is surrounded by the first groove. And a second region outside the concave groove, and by making the area of the second region larger than the first region by one digit or more, the first region, which is an element formation region, can be formed. The critical current value of the c-axis junction is smaller than the critical current value of the c-axis junction in the second region by one digit or more. Therefore,
The second region can be used as a conductive region for operating the first region which is an element formation region. As a result, by forming the second electrode in the second region, the second electrode is electrically connected to the lower portion of the first region, so that the c-axis direction of the first region is increased. Electrical characteristics can be taken out as an element.

According to the invention of claim 11, in the structure of claim 10, the area of the first region in the single crystal grain is 40.
A structure having a size of 0 μm ² or less is added.

According to the structure of claim 11, the voltage value when the element jumps to the voltage state due to the current exceeding the Josephson critical current is set to be equal to or less than the tunnel voltage determined by the number of intrinsic Josephson junctions. Since it can be limited, heat generated when the element jumps to the voltage state when the element is operated can be suppressed.

According to a twelfth aspect of the present invention, the predetermined depth of the concave groove of the single crystal grain is 10 times or less than the interval between the block layers of the oxide high temperature superconductor formed in the superconductor thin film forming step. Is added.

According to the twelfth aspect, since the predetermined depth of the concave groove in the upper surface portion of the single crystal grain is 10 times or less than the interval between the block layers of the high temperature oxide superconductor, the thickness of the single crystal grain is also. Oxide high-temperature superconductor block layer spacing 10
Since it is twice or less, the number of junctions that operate as intrinsic Josephson junctions can be limited to 10 or less.

According to a thirteenth aspect of the present invention, in the structure of the fifth or sixth aspect, a frame-shaped concave groove having a predetermined depth is formed in the main surface portion of the substrate before the superconductor thin film forming step. And a step of dividing the main surface portion of the substrate into a first region surrounded by the concave groove and a second region outside the concave groove, wherein the superconducting thin film forming step includes the main surface of the substrate. The step of forming a thin film of an oxide high temperature superconductor having a film thickness larger than a predetermined depth of the recessed groove on the entire surface, wherein the first electrode forming step includes A step of forming the first electrode on the upper portion of the first region, and the second electrode forming step forms the second electrode on the upper portion of the second region of the substrate in the thin film. A configuration including steps is added.

According to the structure of the thirteenth aspect, since the thin film made of the high temperature oxide superconductor is formed on the main surface of the substrate in which the element forming region is defined by the frame-shaped concave groove, the element forming region in the thin film is also thin film. Since it is defined by the frame-shaped concave groove formed in the above step, the process of etching the thin film becomes unnecessary.

Further, the thin film is subjected to a heat treatment so that the element forming region defined by the concave groove in the thin film is c-axis oriented to be a single crystal grain, that is, the area of the region of the thin film to be c-axis oriented is limited. Therefore, it is possible to obtain single crystal grains of an oxide high temperature superconductor having excellent crystallinity in the element formation region.

Further, since the formation position of the single crystal grain can be controlled by the concave groove formed on the main surface of the substrate, the work of specifying the position of the single crystal grain by the actual microscope becomes unnecessary.

Further, since the thickness of the thin film made of the high temperature oxide superconductor is larger than the depth of the concave groove formed in the substrate, the second crystal is formed below the single crystal grains formed in the first region.
There is a thin film formed integrally with the thin film in the region. Therefore, when the second electrode connected to the second region of the thin film is formed, the second electrode is electrically connected to the second region of the thin film and the lower portion of the single crystal grain of the thin film.

According to a fourteenth aspect of the present invention, in addition to the configuration of the thirteenth aspect, the area of the upper portion of the first region of the substrate in the thin film is 400 μm ² or less.

According to the structure of claim 14, the voltage value when the device jumps to the voltage state due to the current exceeding the Josephson critical current is made equal to or less than the tunnel voltage determined by the number of intrinsic Josephson junctions. Since it can be limited, heat generated when the element jumps to the voltage state when the element is operated can be suppressed.

The invention of claim 15 is the invention of claim 13 or 14.
In addition to the above structure, the predetermined depth of the concave groove in the thin film is 10 times or less than the interval between the block layers of the oxide high temperature superconductor formed in the superconductor thin film forming step. is there.

According to the structure of the fifteenth aspect, since the predetermined depth of the concave groove is 10 times or less than the distance between the block layers of the oxide high-temperature superconductor, the thickness of the single crystal grain is also the block layer of the oxide high-temperature superconductor. Since it is 10 times or less than the interval of, the number of junctions operating as intrinsic Josephson junctions can be limited to 10 or less.

According to a sixteenth aspect of the invention, in the structure of the fifth or sixth aspect, the main surface portion of the substrate is divided into a first flat surface portion and a second flat surface portion before the superconductor thin film forming step. In addition, an angle of 15 degrees or more and 75 degrees or less with respect to the main surface of the substrate is formed between the first plane portion and the second plane portion, and the first plane portion and the The superconducting thin film forming step includes a slope forming step of forming a slope connecting to the second flat surface, wherein the superconducting thin film forming step has an oxide high temperature having a film thickness smaller than a height of the slope on the main surface of the substrate. The step of forming a thin film of a superconductor over the entire surface, wherein the single crystal grain forming step includes forming the single crystal grain in a region of the thin film including an upper portion of the inclined surface portion of the substrate, and thereafter forming the single crystal grain. A band portion made of the single crystal grain is provided on the slope portion of the crystal grain in the direction of inclination of the slope portion. The first electrode forming step includes a step of forming the first electrode electrically connected to the first flat surface portion of the single crystal grain on the first flat surface portion. Including the second electrode forming step,
A configuration including a step of forming the second electrode electrically connected to the second flat surface portion of the single crystal grain is added to the second flat surface portion.

According to the sixteenth aspect, the main surface portion of the substrate is divided into the first flat surface portion and the second flat surface portion, and the first flat surface portion is formed.
Between the first plane portion and the second plane portion of
After forming the slope part connecting the flat part of the substrate, a thin film of oxide high temperature superconductor having a film thickness smaller than the height of the slope part is formed on the entire main surface of the substrate, and then the slope part is formed. In order to form single crystal grains in the region including the second surface portion, for example, when the upper side of the slope portion is the first flat surface portion and the lower side of the slope portion is the second flat surface portion, the second flat surface portion is formed. The electrodes of
Since it is formed in the region including the inclined surface portion and is electrically connected to the lower part of the single crystal grain which is a substantial element formation region, c
The electrical characteristics in the axial direction can be taken out as an element.

Further, a band-shaped portion made of a single crystal grain is formed in a region connecting the upper portion of the first flat surface portion and the upper portion of the second flat surface portion in the single crystal grain to substantially cut the element formation region. In order to reduce the area, the voltage value when the device jumps to the voltage state due to the current exceeding the Josephson critical current can be limited to the same level as or lower than the tunnel voltage determined by the number of intrinsic Josephson junctions. It is possible to suppress heat generated when the element jumps to a voltage state when operating the element.

Further, in the single crystal grain forming step, since the growth of the single crystal grains is promoted in the vicinity of the sloped surface, it is not necessary to perform the heat treatment so that grain boundaries are clearly formed in the thin film.

According to a seventeenth aspect of the invention, in the structure of the fifth or sixth aspect, the main surface portion of the substrate is divided into a first flat surface portion and a second flat surface portion before the superconductor thin film forming step. In addition, the method includes a step of forming a protrusion between the first flat surface portion and the second flat surface portion, the projection portion defining the first flat surface portion and the second flat surface portion, The step of forming a thin film of a superconductor includes the step of entirely forming a thin film of an oxide high temperature superconductor having a film thickness smaller than the height of the protrusion on the main surface of the substrate, and forming the single crystal grain. The process is
After forming the single crystal grain in a region including the protrusion on the main surface of the substrate, including a step of forming a band-shaped portion made of the single crystal grains in a region straddling the protrusion in the single crystal grain, The first electrode forming step includes a step of forming the first electrode on the first flat surface portion, the first electrode being electrically connected to the first flat surface portion of the single crystal grain, and the second electrode forming step. The electrode forming step adds a configuration including a step of forming, on the second flat surface portion, the second electrode electrically connected to the second flat surface portion of the single crystal grain.

According to the structure of claim 17, the main surface portion of the substrate is divided into the first flat surface portion and the second flat surface portion, and the first flat surface portion is formed.
Between the first plane portion and the second plane portion of
After forming a protrusion that separates from the plane part of the substrate, a thin film of an oxide high temperature superconductor having a film thickness smaller than the height of the protrusion is formed on the entire main surface of the substrate, and then the protrusion is formed. In order to form a single crystal grain in a region including, the first electrode formed in the first plane portion and the second electrode formed in the second plane portion are formed in the region including the protrusion, Since it is electrically connected to the lower part of the single crystal grain, which is a substantial element formation region, the electrical characteristics in the c-axis direction can be taken out as an element.

Further, in order to reduce the substantial cross-sectional area of the element formation region by forming a band portion made of single crystal grains in a region of the single crystal grain that straddles the protrusion, the device is driven by a current exceeding the Josephson critical current. Since the voltage value when jumping to the voltage state can be limited to the same level as or lower than the tunnel voltage determined by the number of intrinsic Josephson junctions, it occurs when the element jumps to the voltage state when operating the element. The heat generated can be suppressed.

Further, in the single crystal grain forming step, since the growth of the single crystal grains is promoted in the vicinity of the slope portion, it is not necessary to perform the heat treatment so that grain boundaries are clearly formed in the thin film.

According to an eighteenth aspect of the present invention, in the structure of the fifth to seventeenth aspects, the oxide high-temperature superconductor in the superconductor thin film forming step is made of Bi (bismuth), Sr (strontium), Ca (calcium), Cu. (Copper) and O (oxygen)
A structure which is a compound containing is added.

According to the eighteenth aspect, since the Bi type superconductor having a strong crystal axis anisotropy is used as the oxide high temperature superconductor, a single crystal grain having excellent crystallinity can be obtained. Can be reliably formed.

[0061]

Embodiments of the present invention will be described with reference to the drawings. In each of the embodiments, a tunnel type Josephson device using a Bi (bismuth) -based high temperature superconductor for a compound having c-axis anisotropy will be described. The present invention is made of a compound having crystal axis anisotropy. It can be widely applied to the case where a thin film is formed into an element.

(First Embodiment) FIG. 1 is a sectional view of a tunnel type Josephson element according to the first embodiment of the present invention. In FIG. 1, a substrate 11 made of MgO single crystal is heat-treated at a temperature equal to or higher than the crystallization temperature of an oxide high temperature superconductor made of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ and surrounded by crystal grain boundaries 13. A plurality of single crystal grains 12A, 12B, 12C, ... Made of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ are formed. The cross-sectional area is 4 on the upper surface of the single crystal grain 12A.
Bi ₂ Sr ₂ Ca ₁ Cu ₂ O with a height of 00 μm ² or less
_The convex portion 12a is formed that is 10 times or less the interval (15 nm) between the _eight block layers. Convex portion 1 of single crystal grain 12A
A first electrode 14A made of Au (gold) is formed on the upper surface of 2a, and a second electrode 14B serving as a conductive channel is formed in the conductive region of the single crystal grain 12A other than the convex portion 12a. . 15 is formed on the single crystal grains 12A and 12B, and is formed on the first electrode 14A and the single crystal grains 12A and 1B.
It is an insulator film made of CaF ₂ (calcium fluoride) that insulates the first electrode 14A from the second electrode 14B and insulates the first electrode 14A from the second electrode 14B.

As described above, the cross-sectional area is 400 μm ^{2 on} the upper surface of the single crystal 12A formed on the substrate 11 and heat-treated at a temperature equal to or higher than the crystallization temperature of the high temperature oxide superconductor.
The convex portions 12a having a height not more than 10 times the distance between the block layers of the oxide high temperature superconductor are formed below.
A first electrode 14A electrically connected to the opposite surface of the conductive channel, and a single crystal 1 that is a conductive channel.
By providing the second electrode 14B formed in the region excluding the protrusion 12a in 2A, the second electrode 14B is electrically connected to the lower portion of the protrusion 12a of the single crystal grain 12A. Therefore, the electrical characteristics of the convex portion 12a in the c-axis direction can be taken out as an element. Therefore, a thin film element having a tunnel type Josephson effect can be realized.

In addition, the single crystal grain 12 which is the substantial element portion
Since the cross-sectional area of the convex portion 12a of A is 400 μm ² or less, the voltage value when the element jumps to the voltage state due to the current exceeding the Josephson critical current is the tunnel voltage determined by the number of intrinsic Josephson junctions. Since it can be limited to the same level or less than that, it is possible to suppress the Joule heat generated when the element jumps to the voltage state when operating the element. As a result, an element that operates stably can be realized.

Further, since the height of the convex portion 12a of the single crystal grain 12A is 10 times or less than the interval between the block layers of the oxide high temperature superconductor, the number of joint portions operating as intrinsic Josephson junction is 10 It can be limited to: As a result, the voltage required for the operation of the element can be set to several hundred mV or less, so that the unstable operation of the Josephson element due to Joule heat can be suppressed and the power consumption can be reduced.

2 is a partial plan view of the tunnel type Josephson element according to the present embodiment, and FIG. 1 is a sectional structure taken along line II-II in FIG. In FIG. 2, FIG.
The same reference numerals denote the same or corresponding parts. Further, although the crystal grain boundary 13 is represented by a square for convenience, it is actually a polygon having an uneven shape. In addition, as shown in FIG. 2, the first electrode 14
A third electrode 14C having the same shape as A and a fourth electrode 14D having the same shape as the second electrode 14B are formed. For example, a current can be passed between the first electrode 14A and the second electrode 14B to measure the voltage between the third electrode 14C and the fourth electrode 14D, but it is not necessary to use four terminals as an element. Is not what you need.

Hereinafter, a method of manufacturing a tunnel type Josephson device according to the first embodiment of the present invention will be described with reference to the drawings.

FIGS. 3A to 3D are sectional views in order of the steps of the method for manufacturing the tunnel type Josephson element according to the first embodiment of the present invention. First, as shown in FIG. 3A, for example, by using a high frequency magnetron sputtering method, 600
(10 of the substrate 11 made of MgO single crystal heated to ℃
On the (0) plane, the composition is Bi: Sr: Ca: Cu = 2.1:
2: 1: thickness of about 200nm the Bi-Sr-Ca-Cu- O is 2 as the target Bi ₂ Sr ₂ Ca ₁ C
A thin film 12 made of u ₂ O ₈ is formed. The atmosphere gas in this case is a mixed gas of argon and oxygen, and the mixing ratio is Ar.
/ O ₂ = 90/10. The gas pressure during film formation was 1.0 Pa. Generally, Bi ₂ Sr ₂ with good crystallinity
To obtain the thin film 12 made of Ca ₁ Cu ₂ O ₈ , 8
Since the substrate temperature close to 00 ° C. is required, the crystallinity of the thin film 12 formed at the substrate temperature of 600 ° C. is not so good. However, due to the substrate temperature of 600 ° C.
It was found that a large single crystal grain can be obtained by performing a heat treatment described later after forming, so that 600 ° C. is used as the substrate temperature when forming the thin film 12. Since it is difficult to determine the amount of oxygen in the oxide high temperature superconducting thin film, the amount of oxygen in the thin film 12 has not been actually confirmed.

Further, the film forming method and the film forming conditions such as the substrate temperature, the gas ratio of the mixed gas, and the gas pressure are set so that the composition of the formed thin film 12 is close to that of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _8. Can be changed appropriately.

Next, as shown in FIG. 3B, Bi ₂ S
Single crystal grains 1 in a thin film 12 made of r ₂ Ca ₁ Cu ₂ O ₈
In order to grow 2A, 12B, 12C, ...
The thin film 12 is heat-treated in an oxygen atmosphere at a temperature of 870 ° C. for 24 hours. Heat-treated thin film 1
2 was measured by X-ray diffraction. As a result, the thin film 12 was Bi ₂ S.
r ₂ Ca ₁ Cu ₂ O ₈ as a main component, and Bi ₂ S as a secondary component
It was found to be a very highly crystallized c-axis (axis perpendicular to the surface of the substrate 11) oriented film containing r ₂ Cu ₁ O ₆ . Also, by observation using a scanning electron microscope,
Many single crystal grains 12A, 1 having a grain size of 10 μm or more
It was found that 2B, 12C, ... And grain boundaries 13 exist. Furthermore, from the results of energy dispersive X-ray spectroscopy, the composition in the crystal grains was Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈
And these crystal grains are single crystal grains oriented in the c-axis, and Bi ₂ Sr ₂ Cu ₁ O is present at the grain boundary portion of the crystal grain boundary 13.
It was confirmed that ₆ phases were present.

When the electric resistance temperature dependence of the single crystal grains 12A and the like was measured, the onset of the superconducting transition was about 80K and the zero resistance temperature was 40K. The transition is broad because the measurement shows the characteristics including the grain boundary part, and the onset is lower than 90K because the single crystal grain 12A
It can be presumed that these are in the overdoped region due to the heat treatment of the above in an oxygen atmosphere.

Next, as shown in FIG. 3C, for example,
2 μm × 5 μm on the upper surface of one single crystal grain 12A
Of the single crystal grains 12 other than the convex portions 12a.
The upper surface of A is removed to a depth of about 10 nm. At this time,
Since the crystal grain boundaries 13 have grown so large that they can be easily viewed with a stereoscopic microscope by the heat treatment for a long time in the above process, it is easy to identify the single crystal grains 12A.

Next, as shown in FIG.
A first electrode 14A made of Au is formed on the upper surface of a, and a second electrode 14B made of Au is formed in a region of the single crystal grain 12A excluding the protrusion 12a, and the electrodes are connected to each other or the first electrode is formed. Ca that insulates 14A and single crystal grain 12A
An insulating film 15 made of F ₂ is formed. In addition,
As shown in FIG. 2, the third
The electrode 14C and the fourth electrode 14D are simultaneously formed.

With the above configuration, the ab of the single crystal grain 12A is
Since the electric resistance is small in the plane direction (plane parallel to the surface of the substrate 11), the second electrode 14B is electrically connected to the lower portion of the convex portion of the single crystal grain 12A. 12
The electrical characteristics of A in the c-axis direction can be used as an element.

FIG. 4 shows current-voltage characteristics of the tunnel type Josephson element manufactured according to this embodiment.
The measurement temperature is 50K. An energy gap about 4 times as large as 2Δ = 40 meV (Δ is a superconducting energy gap) is measured, and it can be understood that this is a characteristic that four intrinsic Josephson junctions are connected in series.

According to this embodiment, Bi ₂ Sr ₂ Ca ₁
After the Cu ₂ O ₈ thin film 12 is formed, the thin film 12 is heat-treated to form a single crystal of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ having strong c-axis anisotropy. Grains 12A, 12B, 12C, ... Are formed. By setting the c-axis direction of one of these single crystal grains as the current direction, it is possible to obtain a thin film element having excellent element characteristics in which the intrinsic Josephson junction characteristic of the thin film 12 is stably maintained.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

FIGS. 5A to 5D are sectional views in order of the steps, showing the method of manufacturing the tunnel type Josephson element according to the second embodiment of the present invention. First, as shown in FIG. 5A, the same method as in the first embodiment is used, and 600
The substrate 11 (10
0) on the surface of Bi ₂ Sr ₂ Ca ₁ with a thickness of about 200 nm
A thin film 12 made of Cu ₂ O ₈ is formed.

Next, as shown in FIG. 5B, the thin film 12
For 24 at a temperature of 870 ° C. in an oxygen atmosphere.
Bi ₂ Sr ₂ Ca ₁ C
Single crystal grains 12A, 12B, 12C, ... Surrounded by grain boundaries 13 are grown in a thin film 12 made of u ₂ O ₈ .

Next, as shown in FIG. 5C, a frame-shaped concave groove 12c having a width of 2 μm and a depth of 10 nm is formed on the upper surface of one single crystal grain 12A to form the single crystal grain 12A.
Is surrounded by the concave groove 12c and has an area of 2 μm × 5 μm
The first region 12b and the second region 12d located outside the concave groove 12c are divided.

Next, as shown in FIG. 5D, the concave groove 1
After forming an insulator film 15 made of CaF _{2 on} 2c and a predetermined region of the single crystal grain 12A, a first electrode 14A made of Au and a second electrode 14A made of Au are formed on the upper surface of the first region 12b of the single crystal grain 12A. The second electrode 1 made of Au is formed on a predetermined portion of the region 12d.
4B are formed respectively.

Further, as shown in the partial plan view of FIG. 6, a third electrode 14C equivalent to the first electrode 14A and a fourth electrode 14D equivalent to the second electrode 14B are formed respectively. Every 4 terminals can be measured. In FIG.
5 (d) shows the same or corresponding portions as in FIG. 5 (d), and FIG. 5 (d) is a sectional view taken along line VI-VI in FIG.

As described above, the junction structure by the second electrode 14B in the c-axis direction having a sufficiently large area with the ab plane of the second region 12d in the single crystal grain 12A has the first structure.
Since the electric resistance is sufficiently smaller than that of the first region 12b of the single crystal grain 12A, the second electrode 14B is electrically connected to the lower portion of the first region 12b of the single crystal grain 12A.
The electrical characteristics in the c-axis direction can be used as an element.

The current-voltage characteristics measured at a temperature of 50 K showed the same characteristics as those of the first embodiment shown in FIG.

A feature of this embodiment is that the single crystal grains 12A are
Single crystal grain 1
Since the damage due to the etching of 2A is reduced, stable operation becomes possible.

(Third Embodiment) Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

FIGS. 7A to 7D are sectional views in order of the steps, showing the method of manufacturing the tunnel type Josephson element according to the third embodiment of the present invention. First, as shown in FIG. 7A, the plane orientation of the substrate 11 made of MgO single crystal is (10
For example, an argon ion milling method is applied to the main surface (0) to form a first square groove 11a having a planar square shape with a width of 2 μm and a depth of 10 nm. It is divided into a first region 16 surrounded by the concave groove 11a and a second region 17 located outside the first concave groove 11a. In the present embodiment, the size of the first region 16 is set to 5 μm × 10 μm.

Next, as shown in FIG. 7B, under the condition that the substrate temperature is 600 ° C., the composition is Bi: Sr: Ca: Cu.
= 2.1: 2: 1: 2 of Bi-Sr-Ca-Cu- O high-frequency magnetron sputtering method using a target made of, Bi ₂ Sr ₂ Ca ₁ Cu having a thickness of about 100nm on the substrate 11 _A thin film 12 of ₂ O ₈ is formed. The atmosphere gas in this case is a mixed gas of argon and oxygen, and the mixing ratio is, for example, Ar / O ₂ = 90/10. The gas pressure during film formation was 1.0 Pa. Substrate 1
Since the first concave groove 11a is formed in the first thin film 12, a second concave groove 12e having a depth of 10 nm corresponding to the first concave groove 11a is also formed in the thin film 12, and
The region 16 has a shape surrounded by the second concave groove 12e.

As in the above-described embodiment, the film forming method and the film forming conditions such as the substrate temperature, the gas ratio, the gas pressure and the like are such that the composition of the thin film 12 produced is Bi ₂ Sr ₂ Ca ₁ Cu ₂ O. _It can be changed appropriately within a range close to ₈ .

Next, as shown in FIG. 6C, the thin film 12
For 24 at a temperature of 860 ° C. in an oxygen atmosphere.
Heat treatment for a time. As a result of measuring the heat-treated thin film 12 by X-ray diffraction, the thin film 12 was found to be Bi ₂ Sr ₂ C.
a ₁ Cu ₂ O ₈ as a main component and Bi ₂ Sr ₂ C as a secondary component
It was found to be a very highly crystallized c-axis oriented film containing u ₁ O ₆ . Moreover, it was found from the observation using the atomic force microscope that the first region 16 in the thin film 12 had a flat surface having only irregularities at the unit lattice level. Further, from the result of the energy dispersive X-ray spectroscopy measurement, the first region 16 in the thin film 12 is Bi ₂ S
It was concluded that it was a single crystal grain 12A of r ₂ Ca ₁ Cu ₂ O ₈ .

Next, as shown in FIG. 7 (d) showing the sectional structure taken along line VIII-VIII in FIGS. 8 and 8, single crystal grains 1
2A and the first, second, third and fourth insulating films 15 made of CaF ₂ and Au on the respective predetermined regions on the thin film 12.
The electrodes 14A, 14B, 14C and 14D are formed respectively to obtain a tunnel type Josephson device.

In FIG. 8, the same reference numerals as those in FIG. 7D indicate the same or corresponding portions, and the first and third electrodes 14 are shown.
A and 14C are connected to the single crystal grain 12A,
The second and fourth electrodes 14B and 14D are connected to the second region 17 of the thin film 12. The electrode connected to the single crystal grain 12A is separated into the first electrode 14A and the third electrode 14C, and the electrode connected to the second region 17 of the thin film 12 is separated from the second electrode 14B and the second electrode 14B. The four electrodes 14D are separated to enable four-terminal measurement.

As described above, a tunnel type Josephson element can be manufactured in which the electrical characteristics of the single crystal grains 12 in the c-axis direction are utilized as the Josephson effect.

A feature of this embodiment is that Bi ₂ Sr ₂ C is used.
The thin film 12 made of a ₁ Cu ₂ O ₈ is heat-treated at a temperature equal to or higher than the crystallization temperature, and the second concave groove 12e in the thin film 12
In order to make the first region 16 which is the element formation region partitioned into the single crystal grains of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ c-axis oriented, that is, the area of the region of the thin film 12 to be c-axis oriented is Since it is limited, single crystal grains 12A having excellent crystallinity can be obtained in the first region 16.

Further, the formation position of the single crystal grain 12A is set on the substrate 1
Since it can be controlled by the concave groove 11a formed on the main surface of No. 1, the work of specifying the position of the single crystal grain 12A by a physical microscope becomes unnecessary.

Further, since the film thickness of the thin film 12 is larger than the depth of the concave groove 11a formed in the substrate, the first region 16 is formed.
Below the single crystal grains 12A formed in the second region 1
There is a thin film formed integrally with the thin film 12 of 7. Therefore, the second region connected to the second region 17 of the thin film 12
When the second electrode 14B is formed, the second electrode 14B is electrically connected to the lower surface of the single crystal grain 12A through the second region 17 of the thin film 12 and the lower portion of the single crystal grain 12A of the thin film 12. .

Further, since an etching process such as argon ion milling for the single crystal grains 12A is not necessary, the tunnel type Josephson device can be manufactured with high yield.

The current-voltage characteristics of the tunnel type Josephson element manufactured according to this embodiment at a measurement temperature of 50 K were similar to the characteristics of the thin film element obtained according to each of the above embodiments.

The thin film elements obtained by the first to third embodiments described above are the first electrode 1 which is a substantial element portion.
Four tunnel-type Josephson junctions are connected in series at the junction between 4A and single crystal grain 12A. That is, Bi ₂ Sr ₂ Ca ₁ which is an oxide high temperature superconductor thin film.
The etching amount of the Cu ₂ O ₈ thin film 12 is obtained at 4 times or more and 5 times or less of the distance between the block layers (BiO layers) in the thin film. In the present invention, it suffices to include at least one block layer in the joint portion with the first electrode 14A, which is a substantial element portion, and is not limited to the element configurations shown in the first to third embodiments. . In particular, when the number of block layers included in the junction is manufactured to be 10 or less as in the device of each of the above-described embodiments, the operating voltage can be limited to about 400 mV or less, resulting in low consumption of the Josephson device. Electricity can be saved.

In the element of each of the above embodiments, the area (cross-sectional area) of the joint is 2 μm × 5 μm or 5 μm ×.
It is set to 10 μm. In the present invention, the area of the bonding portion between the first electrode 14A and the single crystal grain 12A is controlled so as to suppress the Joule heat generated at the bonding portion due to the voltage value when the bonding portion jumps to the voltage state. It is preferable that the area is such that the voltage value can be suppressed to the same level as or lower than the tunnel voltage determined by the number of intrinsic Josephson junctions of the portion. In reality, considering the Joule heat generated at the joint, it is preferable to set the joint to 400 μm ² or less.

(Fourth Embodiment) A fourth embodiment of the present invention will be described below with reference to the drawings.

FIGS. 9A to 9D are sectional views in order of the steps, showing the method of manufacturing the tunnel type Josephson element according to the fourth embodiment of the present invention. First, as shown in FIG. 9A, a substrate 11 made of a MgO single crystal has a tilt angle of 60 degrees with respect to the (100) main surface and has a thickness of 200 n.
A slope portion 18 having a step of m is provided, and the main surface of the substrate 11 is divided into a first plane portion 19 and a second plane portion 20 with the slope portion 18 as a boundary.

Next, as shown in FIG. 9B, the substrate 11
Bi ₂ Sr ₂ Ca of 150 nm over the entire surface of
After forming the thin film 12 of ₁ Cu ₂ O ₈ ,
As shown in (c), the thin film 12 is heat-treated in an oxygen atmosphere at a temperature of 850 ° C. for 6 hours, so that the single crystal grains are formed on the sloped portion 18 and the peripheral portion of the sloped portion 18 in the thin film 12. 12A is formed. Here, the heat treatment temperature and the time for performing the heat treatment are lower and shorter than those in each of the above-described embodiments. This is because when the sloped portion 18 is provided on the substrate 11, the heat treatment temperature and the time for performing the heat treatment are close to each other. Crystal grain 1
This is because the growth of 2A is promoted, and the single crystal grains 12A are formed without performing heat treatment such that crystal grain boundaries are clearly formed in the thin film. In the thin film 12, the single crystal grains 12A are formed of a superconductor so that the first flat surface portion 19
Is connected to the flat portion 20. In addition, the first flat portion 1
Although the 9 and the second flat portion 20 are not single-crystallized, the crystallization is promoted to become a superconductor.

Next, as shown in FIG. 9D showing the sectional structure taken along line XX in FIG. 10 and FIG.
The width is 1 in parallel with the inclination direction of the slope portion 18 in 2A.
Single crystal grains 12A so as to form a band-like pattern of 0 μm or more
Etching is performed on. In addition, the first and second
Etching processing is performed on the flat surface portions 19 and 20 so that the widths thereof are both 1 mm in the extending direction of the inclined surface portion 18. Note that, in FIG. 10, the same reference numerals as those in FIG. 9D denote the same or corresponding portions.

Next, the first flat surface portion 19 of the thin film 12 is formed.
First electrode 14A and third electrode 14C made of Au
And the second flat surface portion 20 of the thin film 12 is formed.
Second electrode 14B and fourth electrode 14D made of Au
To form The first flat surface portion 19 and the second flat surface portion 20 are electrically connected to the upper surface or the lower surface of the inclined surface portion 18 of the single crystal grain 12A, respectively. In the present embodiment as well, four electrodes are formed so that four-terminal measurement can be performed, but the number of electrodes is not limited to this.

If the member forming the electrode is a member that can withstand the heat treatment, the electrode can be formed before the heat treatment.

The current-voltage characteristics of the tunnel type Josephson element manufactured according to this embodiment at a measurement temperature of 50 K were similar to the characteristics of the thin film element obtained according to each of the above embodiments.

A feature of this embodiment is that Bi ₂ Sr ₂ C is used.
When forming single crystal grains in the thin film 12 made of a ₁ Cu ₂ O ₈ , it is not necessary to perform heat treatment enough to form crystal grain boundaries in the thin film, and therefore, compared with each of the above embodiments. The device can be easily manufactured.

The height of the inclined surface portion 18 of the substrate 11, that is, the step between the first flat surface portion 19 and the second flat surface portion 20 is set to 200 nm, and the thickness of the thin film 12 is set to 150 nm.
However, the present invention is not limited to this. Make sure that the band-shaped pattern on the inclined surface portion 18 of the single crystal grain 12A does not have an ab plane penetrating the first flat surface portion 19 and the second flat surface portion 20, that is, the current flowing through the strip-shaped pattern is always the c-axis. In order to allow flow in the direction
By satisfying the condition that the height is larger than the film thickness of the thin film 12, an element having the same effect as that of the present embodiment can be obtained.

Further, in the present embodiment, the inclination angle of the inclined surface portion 18 of the substrate 11 with respect to the substrate surface is formed to be 60 degrees, but the present invention is not limited to this. That is, according to the present invention, an element having the same effect as that of the present embodiment can be obtained if the inclination angle of the slope portion 18 is in the range of 15 degrees to 75 degrees.

Further, in this embodiment, the single crystal grain 12 is used.
The width of the strip-shaped pattern on the slope portion 18 in A is 10 μm
However, the present invention is not limited to this. That is, according to the present invention, the width of the strip pattern is 1 μm to 100 μm.
Within the range of m, the same effect as this embodiment can be obtained.

(Fifth Embodiment) Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings.

11A to 11D are sectional views in order of the steps, showing the method of manufacturing the tunnel type Josephson element according to the fifth embodiment of the present invention. First, as shown in FIG. 11A, a strip-shaped protrusion 21 having a height of 200 nm and a width of 2 μm is provided on the main surface of the substrate 11 made of MgO single crystal, and the substrate 21 is separated by the protrusion 21. The main surface is the first flat surface portion 22.
And the second plane portion 23.

Next, as shown in FIG. 11B, the substrate 1
150 nm of Bi ₂ Sr ₂ C on the entire surface of No. 1
After forming the thin film 12 made of a ₁ Cu ₂ O ₈ , as shown in FIG.
As shown in (c), the thin film 12 is heat-treated in an oxygen atmosphere at a temperature of 850 ° C. for 6 hours, whereby the projections 21 in the thin film 12 and the stepped portions of the projections 21 are c-axis oriented. The formed single crystal grains 12A are formed. Here, the heat treatment temperature and the time for performing the heat treatment may be a low temperature and a short time as in the case of the fourth embodiment, and if the protrusion 21 is provided on the substrate 11, the heat treatment may be performed near the protrusion 21. The growth of the crystal grains 12A is promoted. After that, the width of the single crystal grain 12A is 10 μm in the direction orthogonal to the protrusion 21.
Etching is performed on the single crystal grains 12A so as to form the strip-shaped pattern. In the thin film 12, the single crystal grains 12A are connected to the first flat surface portion 22 and the second flat surface portion 23 by a superconductor. Although the first plane portion 22 and the second plane portion 23 are not single-crystallized, their crystallization is promoted to become a superconductor.

Next, XII-XI in FIG. 12 and FIG.
As shown in FIG. 11D showing the cross-sectional structure of the I line, the first electrode 14A and the third electrode 14C made of Au are formed on the first plane portion 22 of the thin film 12, and at the same time, The second electrode 14B and the fourth electrode 14D made of Au are formed on the second flat portion 23. The first plane portion 22 and the second plane portion 23 are electrically connected to both sides of the protrusion 21 of the single crystal grain 12A, respectively. In the present embodiment as well, four electrodes are formed so that four-terminal measurement can be performed, but the number of electrodes is not limited to this. Note that, in FIG. 12, the same reference numerals as those in FIG. 11D indicate the same or corresponding portions.

If the member forming the electrode is a member that can withstand the heat treatment, the electrode can be formed before the heat treatment.

The current-voltage characteristics of the tunnel-type Josephson element manufactured according to this embodiment at a measurement temperature of 50 K were similar to the characteristics of the thin-film element obtained according to each of the above-mentioned embodiments.

As a feature of this embodiment, as in the fourth embodiment, the strip-shaped protruding portion 21 has Bi ₂ Sr ₂ Ca ₁
In order to promote the single crystallization of the thin film 12 made of Cu ₂ O ₈ , it is necessary to perform a heat treatment at the time of forming the single crystal grain 12A in the thin film 12 so that a crystal grain boundary is clearly formed in the thin film 12. Therefore, the element can be easily manufactured.

In the present embodiment, the width of the strip-shaped protrusion 21 is set to 2 μm, but the present invention is not limited to this. That is, the width of the protrusion 21 may be adjusted according to the size of the single crystal grain 12A, that is, the processing condition of the heat treatment step.

Further, in the present embodiment, the height of the strip-shaped protruding portion 21 is set to 200 nm, and Bi ₂ Sr ₂ Ca is formed.
_{Although the} thin film 12 made of ₁ Cu ₂ O ₈ is formed to have a thickness of 150 nm, the present invention is not limited to this. Single crystal grain 12
The ab plane penetrating the first flat surface portion 22 and the second flat surface portion 23 does not exist in the strip-shaped pattern on the protrusion 21 in A, that is, the current flowing through the strip-shaped pattern always flows in the c-axis direction. In order to do so, if the condition that the height of the protrusion 21 is larger than the film thickness of the thin film 12 is satisfied, the present invention can obtain an element having the same effect as that of the present embodiment.

In this embodiment, the single crystal grain 1
The width of the portion orthogonal to the protruding portion 21 in 2A is 10 μm
However, the present invention is not limited to this. That is, according to the present invention, if the width of the portion of the single crystal grain 12A orthogonal to the protrusion 21 is in the range of 1 μm to 100 μm, an element having the same effect as that of the present embodiment can be obtained.

Further, in the devices obtained according to the fourth and fifth embodiments, it is difficult to specify the area of the band-shaped junction and the number of Josephson junctions in the junction. However, since these elements show the same element characteristics as the elements obtained in the first to third embodiments, the elements according to the fourth and fifth embodiments are the same as those in the first embodiment.
It is considered that the tunnel type Josephson device similar to the devices of the first to third embodiments is configured.

In each of the above-mentioned embodiments, a thin film of Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ is used as the oxide high temperature superconductor film, but the present invention is not limited to this, and other than that. Similar effects can be obtained by using an oxide high-temperature superconductor film having another composition. Especially,
Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ and Pb were included (B
i, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ is Bi ₂ Sr ₂
Since it is an oxide high temperature superconductor having a higher superconducting critical temperature than Ca ₁ Cu ₂ O _8, it is possible to operate the device at a high temperature of liquid nitrogen temperature of 77 K or higher when using this thin film. Also, as in the Bi-based high-temperature oxide superconductor, Tl having a double block layer in its crystal structure is used.
The system oxide high-temperature superconductor has a higher superconducting critical temperature than the Bi-system oxide high-temperature superconductor having the same crystal structure, and is therefore useful for operating the device at high temperatures.

In each of the above embodiments, the single crystal grains are c-axis oriented with respect to the substrate, but the present invention is not limited to this. That is, the same effect can be obtained as long as the orientation direction of the single crystal grains is clear.

Further, in each of the above-mentioned embodiments, the M
Although the gO single crystal was used and the Bi ₂ Sr ₂ Ca ₁ Cu ₂ O ₈ film was formed on the (100) plane of the MgO single crystal, the present invention is not limited to this. That is, according to the present invention, the substrate has, for example, a (100) plane of SrTiO ₃ single crystal or LaAlO ₃ single crystal, or a (001) plane of NdGaO ₃ single crystal.
Similar effects can be obtained by using a plane and forming an oxide high temperature superconductor film on these crystal planes.
In this case, the lattice constant mismatch is reduced as compared with the case of using the (100) plane of the MgO single crystal, so that the grain size of the single crystal grain formed in the thin film is expected to be large, It is also possible to fabricate a plurality of elements in one single crystal grain.

[0126]

According to the tunnel type Josephson element of the first aspect of the present invention, the single crystal grains of the oxide high temperature superconductor formed on the conductive region on the substrate are made of oxide high temperature superconductor. Since it is formed by heat treatment at a temperature equal to or higher than the crystallization temperature, the anisotropic electrical characteristics of the crystal exhibiting the crystal axis anisotropy are stably maintained, and the element exhibits good element characteristics.

According to the tunnel type Josephson element according to the invention of claim 2, the effect of the tunnel type Josephson element according to the invention of claim 2 is obtained, and the element jumps to a voltage state when the element is operated. Since the heat generated at the time is suppressed, the operation of the element is stabilized.

According to the tunnel type Josephson element according to the invention of claim 3, the effect of the tunnel type Josephson element according to the invention of claim 1 or 2 is obtained, and in addition, the thickness of the single crystal grain is high in the oxide high temperature. The spacing of the superconductor block layer is 10
Since the number of junctions operating as intrinsic Josephson junctions can be limited to 10 or less, the voltage required for the operation of the element can be set to several hundred mV or less, and thus the low power consumption of the Josephson element And stable operation can be realized.

According to the tunnel type Josephson element according to the invention of claim 4, the effect of the tunnel type Josephson element according to the inventions of claims 1 to 3 is obtained, and in addition, the crystal axis is anisotropic as an oxide high temperature superconductor. Since a Bi-based superconductor having a strong property is used, a single crystal grain having excellent crystallinity can be obtained, so that an intrinsic Josephson junction can be reliably formed. Thereby, a more stable operation can be realized.

According to the method of manufacturing a tunnel-type Josephson device according to the invention of claim 5 or 6, heat treatment is performed at a temperature equal to or higher than the crystallization temperature of the oxide high temperature superconductor, so that a thin film of the oxide high temperature superconductor is formed. Since a single crystal grain having a c-axis orientation is formed in the film, the anisotropic electrical characteristics of the crystal exhibiting the crystal axis anisotropy can be stably maintained. Therefore, a Josephson device having good device characteristics should be manufactured. You can

According to the method of manufacturing a tunnel-type Josephson device according to the invention of claim 7, the effect of the method of manufacturing a tunnel-type Josephson device according to the invention of claim 5 can be obtained, and in addition to the high temperature oxide superconductor, By forming the second electrode in a region excluding the convex portion formed on the upper surface of the single crystal grain, the second electrode is electrically connected to the lower portion of the convex portion of the single crystal grain. Therefore, the electrical characteristics in the c-axis direction can be taken out as an element. As a result, it is possible to reliably utilize the intrinsic Josephson junction of the single crystal grain made of the oxide high temperature superconductor.

According to the method of manufacturing a tunnel type Josephson element according to the invention of claim 8, 11 or 14, heat generated when the element jumps to a voltage state when the element is operated can be suppressed, so that it is stable. It is possible to manufacture a Josephson device that operates as described above.

According to the method of manufacturing a tunnel type Josephson element according to the invention of claim 9, 12 or 15, the thickness of the single crystal grain is 10 times the interval between the block layers of the oxide high temperature superconductor.
Since the number of junctions operating as intrinsic Josephson junctions can be limited to 10 or less, the voltage required for the operation of the element can be set to several hundred mV or less, and thus the low power consumption of the Josephson element And stable operation can be realized.

According to the method of manufacturing a tunnel-type Josephson device according to the invention of claim 10, the effect of the method of manufacturing a tunnel-type Josephson device according to the invention of claim 5 can be obtained and, in addition, a high temperature oxide superconductor can be used. By forming the second electrode in the second region, which is an outer portion of the first region that is the element forming region, in the single crystal grain, the second electrode causes the lower portion of the first region to be formed. Since it is electrically connected to the first electrode via the device, the electrical characteristics in the c-axis direction can be taken out as an element. As a result, it is possible to reliably utilize the intrinsic Josephson junction of the single crystal grain made of the oxide high temperature superconductor.

According to the method of manufacturing a tunnel-type Josephson element according to the invention of claim 13, the effect of the method of manufacturing a tunnel-type Josephson element according to the invention of claim 5 or 6 is obtained, and the tunnel-type Josephson element is formed on a substrate. Since the element formation region in the thin film can be controlled by the frame-shaped concave groove, the process of etching the thin film is not necessary, and the thin film is not damaged by the etching, so that the yield of the Josephson device is improved and the c-axis of the thin film is improved. Since the area of the oriented region is limited, it is possible to obtain a single crystal grain composed of an oxide high temperature superconductor having excellent crystallinity in the device forming region, so that a Josephson device that operates stably can be manufactured. be able to.

Further, since the position of the single crystal grain can be controlled by the concave groove formed in the main surface portion of the substrate, the work of specifying the position of the single crystal grain by a stereoscopic microscope becomes unnecessary, and therefore, a manufacturing method suitable for industrialization can be provided. realizable.

Further, since the thickness of the thin film made of the high temperature oxide superconductor is larger than the depth of the concave groove formed in the substrate, the thin film is formed on the upper portion of the first region of the substrate, that is, on the upper surface of the single crystal grain. High temperature oxide formed in the first region of the thin film by passing a current between the first electrode connected to the second electrode connected to the upper part of the second region of the substrate in the thin film The intrinsic Josephson junction of a single crystal grain made of a superconductor can be surely utilized.

According to the method of manufacturing a tunnel-type Josephson element according to the invention of claim 16, the effect of the method of manufacturing a tunnel-type Josephson element according to the invention of claim 5 or 6 can be obtained, and in addition to the high temperature oxide. In order to form a single crystal grain in a region including a slant surface of a thin film made of a conductor, the upper surface of the slant surface is defined as a first flat surface portion and the lower surface of the slant surface portion is defined as a second flat surface portion. Since the second electrode formed in the portion is electrically connected to the lower portion of the single crystal grain formed in the region including the inclined surface portion, the electric characteristics in the c-axis direction can be taken out as an element. As a result, it is possible to reliably utilize the intrinsic Josephson junction of the single crystal grain made of the oxide high temperature superconductor.

Since the heat generated when the element jumps to the voltage state when operating the element can be suppressed,
A Josephson device that operates stably can be manufactured.

Further, in the single crystal grain forming step, since the growth of the single crystal grains is promoted in the vicinity of the slope portion, it is not necessary to perform the heat treatment so that grain boundaries are clearly formed in the thin film.
Manufacturing becomes easier.

According to the method of manufacturing a tunnel-type Josephson element according to the invention of claim 17, the effect of the method of manufacturing a tunnel-type Josephson element according to the invention of claim 5 or 6 is obtained, and in addition to the high temperature oxide. Since the single crystal grains are formed in the region including the protrusion of the thin film made of a conductor, the first electrode formed on the first plane and the second electrode formed on the second plane are Since they are electrically connected to the lower portions of the single crystal grains formed in the regions including the parts, the electrical characteristics in the c-axis direction can be taken out as an element. As a result, it is possible to reliably utilize the intrinsic Josephson junction of the single crystal grain made of the oxide high temperature superconductor.

Further, in the single crystal grain forming step, since the growth of the single crystal grains is promoted in the vicinity of the slope portion, it is not necessary to perform the heat treatment so that grain boundaries are clearly formed in the thin film.
Manufacturing becomes easier.

According to the method of manufacturing a tunnel-type Josephson element according to the invention of claim 18, the effects of the method of manufacturing a tunnel-type Josephson element according to the invention of claims 5 to 17 can be obtained, and in addition, high temperature oxide superconductivity can be obtained. Since a Bi-based superconductor having a strong crystal axis anisotropy is used as the body, a single crystal grain having excellent crystallinity can be obtained, so that an intrinsic Josephson junction can be surely formed, and thus more stable. A working Josephson device can be manufactured.

As described above, according to the present invention, the oxide high temperature widely used in the superconducting computer, the superconducting digital circuit, the superconducting quantum interference device or the mixer for detecting the electromagnetic wave in the millimeter wave or far infrared region. The tunnel-type Josephson device using the intrinsic Josephson junction of the superconductor can be manufactured easily and reliably, so that the industrial value of the present invention is extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view of a tunnel type Josephson element according to a first embodiment of the present invention.

FIG. 2 is a partial plan view of a tunnel type Josephson element according to the first embodiment of the present invention.

3A to 3D are cross-sectional views in order of the steps of a method of manufacturing a tunnel-type Josephson device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a current-voltage characteristic of the tunnel type Josephson element according to the first embodiment of the present invention.

5A to 5D are cross-sectional views in order of the steps of a method of manufacturing a tunnel-type Josephson device according to the second embodiment of the present invention.

FIG. 6 is a partial plan view of a tunnel type Josephson device according to a second embodiment of the present invention.

7A to 7D are cross-sectional views in order of the steps of a method of manufacturing a tunnel-type Josephson device according to the third embodiment of the present invention.

FIG. 8 is a partial plan view of a tunnel type Josephson element according to a third embodiment of the present invention.

9A to 9D are cross-sectional views in order of the steps of a method for manufacturing a tunnel-type Josephson device according to the fourth embodiment of the present invention.

FIG. 10 is a partial plan view of a tunnel type Josephson element according to a fourth embodiment of the present invention.

11A to 11D are cross-sectional views in order of the steps in a method for manufacturing a tunnel-type Josephson device according to the fifth embodiment of the present invention.

FIG. 12 is a partial plan view of a tunnel type Josephson device according to a fifth embodiment of the present invention.

FIG. 13 is a cross-sectional view in order of the steps of a method for manufacturing a conventional tunnel Josephson device.

FIG. 14A is an enlarged sectional view of a junction region of a conventional tunnel type Josephson element. (B) is an enlarged plan view of a junction region of a conventional tunnel type Josephson element.

[Explanation of symbols]

 Reference Signs List 11 substrate 11a first concave groove 12 thin film 12a convex portion 12b first region 12c concave groove 12d second region 12e second concave groove 12A single crystal grain 12B single crystal grain 12C single crystal grain 13 crystal grain boundary 14A first 1st electrode 14B 2nd electrode 14C 3rd electrode 14D 4th electrode 15 Insulator film 16 1st area | region 17 2nd area | region 18 Slope part 19 1st plane part 20 2nd plane part 21 Projection part 22 1st plane part 23 2nd plane part

Front page continuation (72) Inventor Kentaro Seitsune 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (18)

[Claims] 1. A conductive region formed on a substrate, and a high temperature oxide superconductor provided on the conductive region and heat-treated at a temperature equal to or higher than a crystallization temperature of the high temperature oxide superconductor. A first electrode electrically connected to a surface of the single crystal grain opposite to the conductive region, and the single crystal grain formed on the conductive region. And a second electrode electrically connected to a different region, wherein the single crystal grain is formed so as to have a tunnel type Josephson effect. element. 2. The cross-sectional area of the single crystal grain in the region showing the tunnel type Josephson effect in a direction perpendicular to the c-axis direction is 400 μm ² or less. Tunnel type Josephson device. 3. The length in the c-axis direction of the tunnel type Josephson effect region in the single crystal grain is 10 times or less than the distance between the block layers of the oxide high temperature superconductor. The tunnel type Josephson device according to claim 1 or 2. 4. The oxide high temperature superconductor is a compound containing Bi (bismuth), Sr (strontium), Ca (calcium), Cu (copper) and O (oxygen). 4. The tunnel type Josephson device according to any one of 3 to 3. 5. A superconductor thin film forming step of forming a thin film of an oxide high temperature superconductor on a main surface of a substrate, and a heat treatment for the thin film at a temperature equal to or higher than a crystallization temperature of the oxide high temperature superconductor. By carrying out, a single crystal grain forming step of forming a single crystal grain made of the oxide high temperature superconductor and having c-axis orientation, and electrically connected to the single crystal grain in one region on the upper surface of the thin film. A first electrode forming step of forming a first electrode, and a second electrode forming step of forming a second electrode electrically connected to the single crystal grain in another region on the upper surface of the thin film. A method of manufacturing a tunnel-type Josephson device, characterized by being provided. 6. A superconducting thin film forming step of forming a thin film of an oxide high temperature superconductor on a main surface of a substrate, and a first electrode forming forming a first electrode in one region on an upper surface of the thin film. And a second electrode forming step of forming a second electrode in another region on the upper surface of the thin film, and heat treating the thin film at a temperature equal to or higher than the crystallization temperature of the high temperature oxide superconductor. And a single crystal grain forming step of forming single crystal grains made of the oxide high-temperature superconductor and having c-axis orientation, according to the method of manufacturing a tunnel type Josephson device. 7. A region other than a predetermined region in the upper surface of the single crystal grain is formed between the single crystal grain forming process and the first electrode forming process,
The step of forming a convex portion formed of the predetermined region on the upper surface portion of the single crystal grain by removing to a predetermined depth with respect to the main surface of the substrate, wherein the first electrode forming step includes The method further includes the step of forming the first electrode on the upper surface of the convex portion of the crystal grain, and the second electrode forming step forms the second electrode in a region of the single crystal grain excluding the convex portion. The method of manufacturing a tunnel type Josephson device according to claim 5, further comprising steps. 8. The method of manufacturing a tunnel-type Josephson device according to claim 7, wherein an area of an upper surface of the convex portion of the single crystal grain is 400 μm ² or less. 9. The height of the convex portion of the single crystal grain is 10 times or less than the distance between the block layers of the high temperature oxide superconductor formed in the superconductor thin film forming step. A method of manufacturing a tunnel type Josephson device according to claim 7. 10. Between the single crystal grain forming step and the first electrode forming step, a frame-shaped concave groove having a predetermined depth is formed in the upper surface portion of the single crystal grain to form the single crystal grain. The step of dividing the upper surface of the crystal grain into a first region surrounded by the concave groove and a second region outside the concave groove, wherein the first electrode forming step includes A step of forming the first electrode in a first region, and a step of forming the second electrode includes a step of forming the second electrode in the second region of the single crystal grain. The method of manufacturing a tunnel-type Josephson device according to claim 5. 11. The method of manufacturing a tunnel type Josephson device according to claim 10, wherein the area of the first region in the single crystal grain is 400 μm ² or less. 12. The predetermined depth of the concave groove of the single crystal grain is 10 times or less than the interval between the block layers of the high temperature oxide superconductor formed in the superconductor thin film forming step. The method for manufacturing a tunnel-type Josephson device according to claim 10 or 11. 13. A frame-shaped concave groove having a predetermined depth is formed in the main surface portion of the substrate before the step of forming the superconductor thin film, and the main surface portion of the substrate is surrounded by the concave groove. A step of dividing into a first region and a second region outside the concave groove, wherein the superconducting thin film forming step has a film thickness larger than a predetermined depth of the concave groove on the main surface of the substrate. And forming a thin film of an oxide high-temperature superconductor having: on the entire surface, the first electrode forming step forms the first electrode on the upper portion of the first region of the substrate in the thin film. 7. The method according to claim 5 or 6, wherein the second electrode forming step includes a step of forming the second electrode in an upper portion of the thin film on the second region of the substrate. A method for manufacturing a tunnel-type Josephson device as described. 14. The method of manufacturing a tunnel type Josephson device according to claim 13, wherein an area of an upper portion of the first region of the substrate in the thin film is 400 μm ² or less. 15. The predetermined depth of the concave groove in the thin film is 10 times or less than the distance between the block layers of the high temperature oxide superconductor formed in the superconductor thin film forming step. A method of manufacturing a tunnel type Josephson device according to claim 13. 16. The main surface portion of the substrate is divided into a first flat surface portion and a second flat surface portion, and the first flat surface portion and the second flat surface portion are formed before the step of forming the superconductor thin film. Between the plane part and the main surface of the substrate, 15 degrees or more and 75
A slope portion forming step of forming a slope portion connecting the first flat surface portion and the second flat surface portion with an angle of less than or equal to 5 degrees, wherein the superconductor thin film forming step is performed on the main surface of the substrate. Including a step of forming a thin film of an oxide high-temperature superconductor having a film thickness smaller than the height of the inclined surface on the whole surface, wherein the single crystal grain forming step is above the inclined surface of the substrate in the thin film. After forming the single crystal grain in a region including a portion, including a step of forming a band-shaped portion made of the single crystal grain in the slope portion of the single crystal grain in the inclination direction of the slope portion, the first electrode The forming step includes a step of forming, on the first flat surface portion, the first electrode electrically connected to the first flat surface portion of the single crystal grain, and the second electrode forming step, The second flat portion of the single crystal grain is provided on the second flat portion. 7. The method of manufacturing a tunnel type Josephson device according to claim 5, further comprising the step of forming the second electrode electrically connected to the surface portion. 17. The main surface portion of the substrate is divided into a first flat surface portion and a second flat surface portion, and the first flat surface portion and the second flat surface portion are formed before the step of forming the superconductor thin film. A step of forming a protrusion that separates the first flat portion and the second flat portion between the flat portion and the flat portion, wherein the superconductor thin film forming step is performed on the main surface of the substrate. A step of forming a thin film of an oxide high-temperature superconductor having a film thickness smaller than the height of the protrusion on the whole surface, wherein the single crystal grain forming step includes forming the protrusion on the main surface of the substrate. After forming the single crystal grains in the region containing, including a step of forming a band-shaped portion made of the single crystal grains in a region straddling the protrusion in the single crystal grains, the first electrode forming step, Electrically connected to the first plane portion of the single crystal grain on the first plane portion. The step of forming the first electrode that continues, the second electrode forming step includes the step of electrically connecting the second plane portion to the second plane portion of the single crystal grain. 7. The method for manufacturing a tunnel type Josephson device according to claim 5, further comprising the step of forming two electrodes. 18. The high temperature oxide superconductor in the step of forming a superconductor thin film is a compound containing Bi (bismuth), Sr (strontium), Ca (calcium), Cu (copper) and O (oxygen). 18. The method for manufacturing a tunnel type Josephson device according to claim 5, further comprising: