JPH07106646A - Superconducting device - Google Patents

Abstract

PURPOSE:To obtain a novel structure allowing fabrication of a superconducting device using an oxide superconducting material and a fabrication step of superconducting junction, and to obtain a superconducting junction and a superconducting device exhibiting specified superconducting characteristics while reducing the area of superconducting junction as compared with a junction of conventional structure. CONSTITUTION:The superconducting device comprises, as a unit, a pair of superconducting electrodes 2, 4, and a normal conducting layer 3 interposed between and connecting them electrically, i.e., a planar structure of superconducting-normal conducting-super conducting junctions 2, 3, 4. A plurality of superconducting junctions are connected in series geometrically and electrically wherein each superconducting electrode being shared as a junction electrode between two adjacent junctions and the normal conducting layer is shared by a plurality of junctions connected in series.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to superconducting electronics that exhibit unique performance by using superconductivity such as voltage standard, microwave or millimeter wave detection circuit, high-speed digital circuit, and analog data processing circuit. The present invention relates to a superconducting device having a structure suitable for high performance such as miniaturization and high voltage or high current of output signals.

[0002]

2. Description of the Related Art In a conventional superconducting device such as a voltage standard, a microwave detecting element, and a mixer, a superconducting-insulating layer having a laminated structure in which an ultrathin insulating film is inserted between two superposed conductive electrodes. -Superconducting junctions have been used. This superconducting-insulating layer-superconducting junction utilizes the fact that a superconducting current and a normal conducting current flow between the superconducting electrodes due to the so-called tunnel effect. Among these, the superconducting current component reacts to microwave irradiation by the Josephson effect, and a current step is generated with a direct current voltage proportional to the frequency as a cycle.

Such a response phenomenon to microwaves is used in microwave detection elements, mixers and the like. In particular, the ratio between the microwave frequency and the generated voltage is a constant amount given as the ratio between the Planck constant, which is a physical constant, and the elementary charge. Based on this principle, superconducting devices are used as voltage standards. When microwaves are applied to one superconducting-insulating layer-superconducting junction, the generated voltage is at a level of several tens of microvolts and does not reach the level required for practical use. In a superconducting device intended for a voltage standard, a practically required voltage is obtained by connecting a large number of superconducting-insulating layers-superconducting junctions in series.

[0004]

In order to obtain a superconducting device such as the voltage standard, the microwave detecting element, and the mixing ratio described in the section of the prior art, and to use it for practical use, the following is required. It is necessary to solve the two issues mentioned below. The first issue is as follows. That is, in a conventional superconducting device such as a voltage standard, a microwave detecting element, and a mixing ratio, a metallic superconducting material intended to operate at a liquid helium temperature has been used. In order to operate a superconducting device using liquid nitrogen, which is cheaper and easier to handle than liquid helium, it is natural to obtain a superconducting junction using an oxide superconducting material having a superconducting critical temperature of around 100K. There is a need. However, it is extremely difficult to produce a superconducting-insulating layer-superconducting junction having a laminated structure using an oxide superconducting material as an electrode, and it is not expected to obtain a superconducting device by such superconducting junction. The reason for this is that a high substrate temperature of about 700 ° C. is required to form an oxide superconducting thin film, so when an oxide superconducting thin film to be an upper electrode is deposited on an ultrathin insulating film having a thickness of several nm, This is because a diffusion reaction occurs between the insulating layer and superconductivity, and both the superconductivity of the superconducting thin film and the insulating property of the insulating layer deteriorate. Therefore, the first problem is to obtain a new structure of a superconducting device that enables the production of a superconducting device by using an oxide superconducting material and passing through the superconducting junction manufacturing process.

The second problem is as follows. That is, since the superconducting-insulating layer-superconducting junction of the laminated structure occupies a relatively large area on the substrate, it is not possible to arrange the junctions of the laminated structure in units of thousands or tens of thousands on one substrate. If possible, or even possible, it would occupy a significant portion of the substrate area. It is desirable that the occupied area per superconducting junction constituting the superconducting device is as small as possible. Therefore, the second problem is to make the joint occupying area smaller than that of the laminated structure type joint,
In addition, it is to obtain a structure of a superconducting junction and a superconducting device exhibiting predetermined superconducting characteristics.

An object of the present invention is to solve the problems of the above-mentioned prior art and enable the production of a superconducting device by using an oxide superconducting material and passing through a superconducting junction manufacturing process. It is to obtain a new structure of such a superconducting device, and to obtain a structure of a superconducting junction and a superconducting device having a superconducting junction occupying area smaller than that of the conventional structure and exhibiting predetermined superconducting characteristics.

[0007]

The above object is to provide a superconducting material having a planar structure composed of a pair of superconducting electrodes and a normal conductive layer between the electrodes and electrically connecting the electrodes.
In a superconducting device including a normal-superconducting junction as a unit, a plurality of the above-mentioned superconducting junctions are geometrically and electrically connected in series, and each superconducting is shared as two adjacent junction electrodes. The superconducting device is characterized in that the conductive layer is shared by a plurality of junctions connected in series, and further, an insulating film is disposed in contact with the superconducting conductive electrode of the above-mentioned junction, and is in contact with the insulating film. A conductive film or a superconducting film, and the superconducting electrode of the junction,
A capacitor is composed of an insulating film and a conductive film or a superconducting film, and the capacitor is electrically connected in parallel to the junction,
The insulating film and the conductive film or the superconducting film are shared by a plurality of junctions connected in series, and a superconducting device can be achieved.

Regarding the material constitution of the superconducting device, the superconducting electrode is an oxide type superconducting film containing Cu, and the normal conducting layer is Au, Ag, Pt, Rh, Re,
It is made of Pd or an alloy thereof.

Further, the superconducting electrode is an oxide superconducting film containing Cu, and the normal conducting layer is also composed of an oxide normal conducting film containing Cu.

Further, the conductive film or the superconducting film forming the above-mentioned capacitance is made of an oxide thin film containing Cu.

With regard to the structure of the superconducting device, the superconducting device is provided with means for irradiating microwaves or millimeter waves, and an output voltage signal corresponding to the frequency of microwaves or millimeter waves, or irradiation of microwaves or millimeter waves is used. A configuration is provided in which a means for detecting a change in current generated at both ends of the plurality of junction rows is provided.

Further, regarding the structure of the superconducting device, there is provided a means for detecting an output voltage signal corresponding to a frequency of a microwave or a millimeter wave, and a means for comparing the detected signal with another voltage signal.

[0013]

The reason why the above problems of the prior art can be solved by using the superconducting device having the structure of the present invention will be described below. First, the first problem will be described. When a superconducting junction is composed of an oxide-based superconducting thin film and a superconducting device including such superconducting junction and capacitance, resistance, etc. is to be obtained, the oxide superconducting thin film must be formed at a high temperature of 600 ° C. or higher Prevents the formation of any device structure. When an oxide superconducting film is used, it is extremely difficult to insert an insulating layer having a thickness of several nm between two superconducting thin films, unlike the case of a conventional metal-based superconducting junction. For example, when an oxide superconducting thin film is deposited on an insulating layer having a thickness of several nm at a substrate temperature of 600 ° C. or higher, a diffusion reaction occurs between the insulating layer and the oxide superconducting thin film to obtain an intended superconducting junction. Absent. Further, even if the diffusion reaction does not occur, when the insulating film having a different crystal structure is in contact with the oxide superconducting electrode, the electronic structure in the atomic layer adjacent to the insulating layer in the oxide superconducting electrode is distorted, This results in deterioration of the superconducting property at the interface.

On the other hand, in the superconducting device of the present invention, the superconducting junction has a planar structure, and the current does not flow in the direction perpendicular to the substrate surface, but in the parallel direction, the superconducting electrode film, Ag. , Au, Pt, Ph, Re, Pd or an alloy thereof or an oxide-based thin film containing Cu, and a superconducting electrode film. In the case of an element having such a structure, it is not necessary to have an extremely thin film layer, and it is not necessary to stack electrodes for superconducting junction. Therefore, the junction characteristics including the superconducting characteristics do not deteriorate during the process of manufacturing the superconducting junction. In addition, there is no problem that Ag, Au, Pt, Ph, Re, Pd or alloys thereof contact the superconducting electrode and impair the superconducting property of the superconducting electrode interface. Alternatively, when the normal conducting oxide thin film having a crystal structure similar to that of the superconducting electrode and the superconducting thin film are in contact with each other, distortion of the electronic structure at the interface is suppressed, so that the superconducting property adjacent to the normal conducting layer is deteriorated. No problems arise. For the above reasons
In the superconducting device constituted by the superconducting junction according to the present invention, there is provided a superconducting device structure capable of obtaining the superconducting junction without deteriorating the characteristics during the manufacturing process.

Next, the second problem will be described. In the conventional superconducting junction, each coupling layer, the electrode film and the interlayer insulating film that compose the capacitor, etc. are individually arranged for these component parts attached to or in parallel with each superconducting junction. The structure of such a superconducting device hinders the reduction of the occupied area per superconducting junction.

On the other hand, in the configuration of the present invention, A
A coupling layer using g, Au, Pt, Ph, Re, Pd, or an alloy thereof, or a normal conductive layer made of a Cu oxide having a crystal structure similar to that of the superconducting conductive electrode is arranged in parallel or in series. The area occupied by the superconducting junction is reduced by arranging it as a continuous layer without being isolated between the junctions. Further, by using the above-mentioned coupling layer material and superconducting electroconductive electrode material, the material constitution and structure that enables such arrangement are provided.
Furthermore, by arranging the capacitors arranged in parallel with the superconducting junctions arranged in parallel or in series, and arranging them as a continuous layer without being isolated between the junctions, the inter-layer insulating film and the electrode film forming the capacitors can be formed. Occupies less space. Moreover, by using an oxide superconducting thin film or the like for the capacitor electrode as well, the material constitution and structure that enables such arrangement are provided.

The reason for reducing the size of the superconducting device by applying such a structure is clear as compared with the conventional superconducting device structure. That is, in the case of the conventional structure in which the coupling material and the capacity of these superconducting junctions are connected to each superconducting junction by itself, the positioning of each coupling material or capacity to the superconducting junction, etc. The space for the gap is unnecessary, and by eliminating them, the required area per superconducting junction is significantly reduced. The reason for this is that in the planar junction structure as in the case of the present invention, the size of the main part of the superconducting junction is 1 μm or less in length, which is extremely small. Therefore, even in a superconducting device that requires thousands or tens of thousands of superconducting junctions, such as a superconducting device used as a voltage standard comparator, the superconducting junction can be constructed without particularly considering the occupied area.

[0018]

EXAMPLES The superconducting device having the constitution of the present invention will be described in more detail below with reference to examples. (Embodiment 1) The construction of one embodiment of the superconducting device of the present invention will be described with reference to FIG. In the figure, 1 is (11
0) Oriented strontium titanate substrate, 2 is Y-Ba-
Cu oxide thin film, 3 is strontium titanate thin film, 4
Is a Y-Ba-Cu oxide thin film, 5 is a coupling layer (A
g) is shown. First, a Y-Ba-Cu oxide thin film 2 having a film thickness of 100 nm was formed on a (110) oriented strontium titanate substrate 1 by a laser deposition method. Here, the laser evaporation source was a KrF excimer laser, the substrate temperature during film formation was 650 ° C., and the oxygen partial pressure was 1 Pa. Next, a pattern as a capacitor electrode film was formed on this Y-Ba-Cu oxide thin film. The capacitive electrode film was not separated between the junctions, and the entire junctions connected in series had a continuous pattern. The pattern was formed by forming a resist film pattern by an electron beam drawing method and transferring the resist film pattern to the Y-Ba-Cu oxide thin film 2 by an ion beam etching method using Ar.

Next, a strontium titanate thin film 3 was formed by a laser vapor deposition method using a KrF excimer laser as in the case of forming the Y-Ba-Cu oxide thin film.
Here, the film forming conditions such as oxygen pressure and substrate temperature are the same as those in Y-B above.
It was the same as in the case of the a-Cu oxide thin film. The film thickness is 150
nm. Further, similarly to the above, an electron beam drawing method and an ion beam etching method were used to form a pattern as a capacitive insulating layer on the strontium titanate thin film. The capacitive insulating film pattern was not separated between the junctions, and was a continuous pattern in the entire junction connected in series.

Further, a Y-Ba-Cu oxide thin film 4 having a film thickness of 100 nm, which also serves as a capacitor electrode and an electrode layer for superconducting junction, was formed by a laser deposition method. The pattern as the electrode of the capacitor and the electrode layer of the superconducting junction was formed by using the electron beam drawing method and the ion beam etching method. In this pattern forming process, the electrode interval of the joint is 0.1 μm.
The dimensions are such that the superconducting current can flow through the normal conductive layer. The electrode width was 10 μm. The distance between adjacent joints is 1 μm, and the total length is 100 μm.
The dimensions were such that 100 joints could fit in a region with a width of 10 μm. Furthermore, current is applied at both ends of the superconducting junction array,
A terminal for detecting the voltage is provided.

Next, a pattern for the coupling layer 5 of the superconducting junction was formed. The pattern is continuous over the entire superconductivity, and the width of the joint is 10 μm.
A so-called lift-off pattern was used in which no resist was present in the region where the coupling layer was to be formed. After the pattern formation, Y-
Coupling is performed by cleaning the surface of the Ba-Cu oxide electrode film, subsequently forming an Ag film 5 by a vacuum deposition method, and removing the resist film and the Ag film deposited on the resist film by a lift-off method. Layers were obtained. By the above method, 100 superconducting junctions are connected in series,
Moreover, a superconducting device was obtained in which the capacitors were connected in parallel across the entire junction. Furthermore, this superconducting device was mounted on a ceramic holder, voltage and current lines were connected to terminals, and a single coaxial cable portion for irradiating microwaves was arranged near the substrate superconducting joint.

The superconducting device manufactured by the above manufacturing process showed voltage-current characteristics as shown in FIG. That is, when the superconducting device is mounted in a container filled with liquid nitrogen, the superconducting current is detected at zero voltage without irradiation of microwaves, and when the voltage is applied, the voltage can be increased or decreased. The superconducting levels have slightly different characteristics. This superconducting device has a frequency of 9G
The applied voltage is 1.8 when irradiated with microwaves of Hz.
The characteristic that a current step occurs at mV and a voltage that is an integral multiple of this is obtained. This step voltage is a voltage value that exactly corresponds to the microwave frequency. Therefore, this characteristic can be used as a reference voltage for a voltage standard.

The material of the coupling layer is Ag.
Besides, similar superconducting device characteristics can be obtained by using Au, Pt, Rh, Re, Pd or alloys thereof. Furthermore, as a superconducting electrode or a capacitance electrode, Y-
In addition to the Ba-Cu oxide thin film, Bi-Sr-Ca-Cu
Similar superconducting device characteristics can be obtained by using other oxide superconducting thin films such as oxide thin films.

(Embodiment 2) The construction of another embodiment of the superconducting device of the present invention will be described with reference to FIG. In addition,
In the figure, the same reference numerals as those in the first embodiment indicate the same contents. First, a Y-Ba-Cu oxide thin film 2 having a film thickness of 100 nm was formed on a (110) oriented strontium titanate substrate 1 by a laser deposition method. Here, the laser evaporation source was a KrF excimer laser, the substrate temperature during film formation was 650 ° C., and the oxygen partial pressure was 1 Pa. This Y-
A pattern as a capacitor electrode film was formed on the Ba-Cu oxide thin film. The capacitive electrode film does not separate between junctions,
A continuous pattern was formed over the entire joints connected in series.
The pattern was formed by forming a resist film pattern by an electron beam drawing method and transferring the resist film pattern to the Y-Ba-Cu oxide thin film by an ion beam etching method using Ar.

Next, a strontium titanate thin film 3 was formed by a laser vapor deposition method using a KrF excimer laser as in the case of the Y-Ba-Cu oxide thin film. The film forming conditions such as oxygen pressure and substrate temperature are Y-Ba-Cu.
It was the same as the case of forming the oxide thin film. The film thickness is 150 nm
And Further, similarly to the above, a pattern as a capacitive insulating layer was formed on the strontium titanate film by using the electron beam drawing method and the ion beam etching method. In addition, the capacitive insulating film pattern was not separated between the junctions, and was a continuous pattern in the entire junction connected in series.

Further, a Y-Ba-Cu oxide thin film 4 having a film thickness of 100 nm, which also serves as a capacitor electrode and a superconducting junction electrode, was formed by a laser deposition method. The pattern as the electrode of the capacitor and the electrode layer of the superconducting junction was formed by using the electron drawing method and the ion beam etching method. In this pattern formation step, the electrode interval at the joint was 0.1 μm and the electrode width was 10 μm. That is, the dimensions were such that superconducting current could be obtained through the normal conductive layer. The distance between adjacent joints is 1
As a result, 100 junctions are accommodated in a region of about 100 μm in both length and width, 10 of these junction rows are arranged in the lateral direction, and each of the junction rows is connected in series to each other, As a result, 1000 junctions are connected in series. Further, terminals for applying a current and detecting a voltage were provided at both ends of the superconducting junction array.

Next, Pr-Ba- which becomes a coupling layer.
The Cu oxide thin film 15 was formed by the laser deposition method. In this case, the film forming conditions such as oxygen pressure and basic temperature are Y-Ba-
It was the same as the case of forming the Cu oxide thin film. Next, a pattern as a coupling layer was formed by an electron beam drawing method and an ion beam etching method using Ar gas.
By the method described above, a superconducting device was obtained in which 1000 superconducting junctions were connected in series and the capacitors were connected in parallel across the entire junction. This superconducting device is further mounted on a ceramic holder, voltage and current wires are connected to the terminals,
The end of the coaxial cable for irradiating the microwave was placed near the substrate superconducting joint.

The superconducting device manufactured by the above manufacturing process showed the voltage-current characteristics as shown in FIG. That is, when the superconducting device is mounted in a container filled with liquid nitrogen, the superconducting current is detected at zero voltage under the condition without microwave irradiation, and the current is increased when the voltage is applied and decreased when the voltage is applied. A characteristic having a so-called hysteresis, which is slightly different in level, was exhibited. Further, when this superconducting device was irradiated with a microwave having a frequency of 9 GHz, a characteristic that a current step was generated at an applied voltage of 18 mV was obtained. This step voltage is a voltage value that exactly corresponds to the microwave frequency. Therefore, this characteristic can be used as a reference voltage for a voltage standard.

[0029]

As described above, by using a superconducting device as a device having the constitution of the present invention, the problems of the prior art can be solved, and an oxide superconducting material can be used to realize a superconducting junction. Obtaining a new structure of a superconducting device that allows manufacturing of a superconducting device through the manufacturing process, and occupying a smaller area of the superconducting junction than that of a conventional structure and exhibiting predetermined superconducting properties. The structure of the superconducting junction and the superconducting device could be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of an embodiment of a superconducting device of the present invention.

FIG. 2 is a voltage-current characteristic of the superconducting device having the configuration shown in FIG.

FIG. 3 is a plan view showing the configuration of another embodiment of the superconducting device of the present invention.

4 is a voltage-current characteristic of the superconducting device of FIG.

[Explanation of symbols]

1 ... (110) oriented strontium titanate substrate, 2 ...
Y-Ba-Cu oxide thin film, 3 ... Strontium titanate thin film, 4 ... Y-Ba-Cu oxide thin film, 5 ... Coupling layer (Ag), 15 ... Coupling layer (Pr-Ba-)
Cu oxide thin film).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shoichi Akamatsu 1-280 Higashi Koikeku, Kokubunji City, Tokyo Metropolitan Research Laboratory, Hitachi, Ltd. (72) Iekawa Imagawa 1-280 Higashi Koikeku Ku, Kokubunji, Tokyo Hitachi Ltd. (72) Inventor Tokuumi Fukasawa 1-280 Higashi Koikeku, Kokubunji City, Tokyo Metropolitan Hitachi, Ltd. Central Research Institute (72) Inventor Uki 1-280 Higashi Koikeku, Kokubunji, Tokyo Hitachi Central Research Co., Ltd. In-house

Claims (7)

[Claims] 1. A superconducting device comprising a unit of a superconducting-normal conducting-superconducting junction having a planar structure composed of a pair of superconducting electrodes and a normal conducting layer interposed between the electrodes and electrically connecting the electrodes. , A plurality of junctions in which the above-mentioned superconducting junctions are geometrically and electrically connected in series, each superconducting element is shared as two adjacent junction electrodes, and a normal conductive layer is connected in series. A superconducting device characterized by being shared by. 2. A superconducting electrode, an insulating film, and a conductive film or a superconducting film of the junction, wherein an insulating film is arranged in contact with the superconducting electrode of the joint, and a conductive film or a superconducting film is arranged in contact with the insulating film. Is formed by a capacitor, the capacitor is electrically connected in parallel to the junction, and the insulating film and the conductive film or the superconducting film are shared by a plurality of junctions connected in series. Claim 1
The superconducting device described. 3. The superconducting electrode is an oxide-based superconducting film containing Cu, and the normal conducting layer is Au, Ag, Pt, R.
The superconducting device according to claim 1, which is made of h, Re, Pd, or an alloy thereof. 4. The superconducting electrode is an oxide-based superconducting film containing Cu, and the normal conductive layer is also composed of an oxide-based normal conducting film containing Cu. Superconducting device. 5. The superconducting device according to claim 1 or 2, wherein the conductive film or the superconducting film forming the capacitance is formed of an oxide thin film containing Cu. 6. The superconducting device according to claim 1 or 2 is provided with means for irradiating microwaves or millimeter waves,
A superconducting device is further provided with means for detecting an output voltage signal corresponding to a frequency of microwave or millimeter wave, or a change in current generated at both ends of a plurality of junction rows by irradiation of microwave or millimeter wave. 7. A superconducting device according to claim 1, 2 or 6, wherein means for detecting an output voltage signal corresponding to a microwave or millimeter wave frequency and means for comparing the detected signal with another voltage signal. A superconducting device characterized by being provided with.