JPH04102380A - Manufacture of josephson element - Google Patents

Abstract

PURPOSE:To acquire a Josephson element by selectively forming a Bi2Sr2Ca2Cu3 Ox layer having a strip part on a substrate and by selectively laminating an RBa2Cu3Ox layer at a specified substrate temperature. CONSTITUTION:A BSCCO layer 6 is formed on a single-crystal MgO substrate (with (100)-plane) 1 to a thickness of 200A with the substrate heated to 650 deg.C. A resist pattern 10A is applied and a strip 6A (width of 0.3mum) of the BSCCO layer is formed by etching. A YBCO layer 7 is formed to a thickness of 100Angstrom by sputtering. A substrate temperature is 550 deg.C. A Bi diffusion region 11 is produced. A resist 10B is applied to form a YBCO layer 7A. The Bi diffusion region 11 becomes normal-conductive, and a BSCCO layer with a decreased bismuth content an insulator. A planar type Josephson element of S/N/S structure can be acquired in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a Josephson device, and more particularly to a method for manufacturing a Brehner-type Josephson device with an S/N/S structure using an oxide superconductor. .

[Conventional technology]

The manufacturing process of a conventional planar Josephson device using an oxide superconductor is shown in FIG. This is silicon S
S/N/ using chemical reaction between i and oxide superconductor
This is to create an S structure.

FIG. 6 (fat) is a cross-sectional view of a step in which silicon 62 is formed on an MgO substrate 61. 6th opening) is a cross-sectional view related to a process in which silicon is patterned into a strip-shaped silicon 66 by a photolithography method. FIG. 6 tc+ shows 30 oxide superconductors YBa and Cu (hereinafter referred to as YB
63 is a cross-sectional view related to a step in which layers (abbreviated as CO) 63 are laminated at a predetermined temperature. At this time, YBC063 and silicon Si
A reaction region 65 is formed by the reaction. This reaction region 65 is an insulator. FIG. 6 (dl is a cross-sectional view relating to the step of forming silver Ag as a normal conductor 64 on the reaction end region 65. The strip-shaped silicon 66 has a higher electrical resistance than YBCO and can be approximated to an insulator. In this way, a Josephson element with a superconductor (S)/normal conductor (N)/superconductor (S) structure is obtained.

A method of manufacturing a Josephson element having an S/I (insulator)/S structure by plasma treatment is also known.

This method utilizes the fact that the superconductivity of RBazCusO* (R refers to a rare earth element) depends on the amount of oxygen. After forming a YBCO layer on the substrate, argon gas at a temperature of 800°C is flowed in an electric furnace.
Oxygen is desorbed from the CO layer and it becomes an insulator.

When the required parts are masked with a metal mask and oxygen plasma is applied to the exposed parts, oxygen is absorbed into the exposed parts again.
Become a superconductor. In this way, a Josephson element with an S/I/S structure is obtained.

Furthermore, using a focused ion beam (FIB), S/N/
A method of manufacturing a Josephson element made of Sl is also known. This method uses oxide superconductors such as BizSr and Ca on a substrate.
After depositing zCu30 (hereinafter abbreviated as B5CC0), approximately 3000 grooves are formed using FIB, and then gold Au is deposited in the grooves to obtain an S/N/S structure.

[Problem to be solved by the invention]

However, the conventional method for manufacturing the Brehner type Josephson element as described above has the following problems. ! However, in the manufacturing method of diffusing silicon into YBCO, the YBCO used and the silicon material have different coefficients of thermal expansion, which causes cracks in the device.

Ri enters. In addition, in the method of controlling the amount of oxygen by plasma treatment, the diffusion constant of oxygen is large, so the reproducibility of device fabrication is poor.Furthermore, in the method of manufacturing using FIB, superconductivity occurs at the S/N interface. Since it deteriorates, it is necessary to perform heat treatment to recover from the deterioration.

This invention was made in view of the above points, and its purpose is to use a material with good thermal compatibility with RBCO in place of silicon, thereby eliminating cracks, providing excellent reproducibility, and preventing deterioration of superconducting properties. An object of the present invention is to provide a method for manufacturing a Josephson element.

[Means to solve the problem]

According to the present invention, the above-mentioned object has 1) a first step and a second step, and the first step is to prepare a B+xSr having a strip portion on a substrate.
An xCazCus Ox layer is selectively formed, and the second step is a step of selectively laminating an RBa1Cu30
, ti refers to earth elements.

2) It has a first step and a second step, the first step is to selectively form an RBazCus○8 layer on the substrate, where R refers to a rare earth element, and the second step is to selectively form the RBazCus○8 layer on the substrate. and RBazCus A process of selectively laminating a Bi*Sr□CaYCLI3Ox layer having a strip portion on the OX layer at a predetermined substrate temperature.
BizSrzCazCu3Ox on top of the 2Cu3Ox layer
This is achieved by laminating strips of layers, or 3) in the manufacturing method according to claim 1 or 2, laminating at a substrate temperature of 550°C.

The B5CC0 layer having strips is formed into a predetermined pattern by photolithography.

The RBCO layer can also be formed into a predetermined pattern using photolithography.

In claim 2, the manufacturing process is opposite to that in claim 1.

[Effect]

When the B5CC0 layer and the RBCO layer are reacted at a predetermined temperature,
Bismuth Bi in the B5CC0 layer diffuses into the RBCO layer, and Y
The BCO layer loses its superconductivity and becomes normal conductivity. Bi diffusion has excellent reproducibility and does not deteriorate the S/N interface, BS
CC○ and YB Co have similar coefficients of thermal expansion and do not cause cranking.

〔Example〕

Next, an embodiment of this invention will be explained based on the drawings.
As a result of scanning Augier microprobe analysis, it was found that when 0 and RBCO were reacted, Bi diffused into YBCO.

FIG. 3 is a diagram showing the temperature dependence of electrical resistance for a Y2O2 layer formed on a B5CC0 layer at a substrate temperature of 550°C. Due to the diffusion of bismuth, superconductivity is not observed even at 4.2K, and the material exhibits a residual resistance of about 10-SΩ and becomes a normal conductor. The measurement sample is a substrate 51 shown in FIG. 5, which is an Mgo (100) single crystal wafer, on which a strip-shaped B5CC0 layer 56 of 1 m width and 100 angstroms is deposited using a metal mask, and then a YBCo layer 56 is deposited using a metal mask. 57 layers were laminated to a thickness of 7200 angstroms.

The B5CC0 layer 56 is formed at a substrate temperature of 650°C, and the YB
The CO layer 57 was deposited at 550° C. as described above.

FIG. 4 is a diagram showing the temperature dependence of electrical resistance for a Y2O2 layer formed on a B5CC0 layer at a substrate temperature of 670°C. Due to excessive bismuth diffusion, the RBCO layer becomes an insulator. 6 Whether the Y2O2 layer becomes a normal conductor or an insulator due to the diffusion of bismuth is determined by the substrate temperature.
When the substrate temperature is below 650°C, the RBCo layer becomes a normal conductor, and when it exceeds 650°C, it becomes an insulator.

FIG. 1 is a process diagram of a method for manufacturing a Josephson device according to an embodiment of the present invention. Figure 1 (Ml? 1gO single crystal substrate ((100) crystal plane) 1 on top of B5CC0
FIG. 3 is a cross-sectional view showing a step of forming a layer to a thickness of 200 angstroms using a sputtering method. The substrate temperature was 650°C. FIG. 1 To) is a cross-sectional view of a process of applying and patterning a photoresist to form a resist pattern IOA. Fig. 1 fc) shows a strip 6A (width 0.3Q) of B5CC0 layer by etching.
) and removing the resist pattern IOA.

FIG. 1 (dl is a cross-sectional view of the step of forming a YBCO layer 7 with a thickness of 100 angstroms by sputtering method. The substrate temperature is 550° C.) Bi diffusion region 1
1 is generated. FIG. 1(8) is a cross-sectional view of the process of applying resist 10B. FIG. 1 (fl is a plan view related to the step of forming a batting-sample YBCO layer 7^. Bi-diffused slanted castle 1 of the YBCO layer 7A becomes normal conductive and exhibits metallic behavior, while B5CC with reduced bismuth
The 0 layer becomes an insulator. A Brehner-type Josephson device with an S/N/S structure is obtained.

FIG. 2 is a diagram showing the characteristics of the obtained S/N/S structure Brehner type Josephson device. A characteristic line 21 is a weakly coupled characteristic when microwave irradiation is not performed. Characteristic!
I22 is a sharp step when irradiated with microwaves.

〔Effect of the invention〕

According to the present invention, the invention includes l) a first step and a second step;
The second step is to selectively form an RBazCu30 layer on the substrate and the strip portion of the Bix5rxCalCu30 x layer at a predetermined substrate temperature. refers to a rare earth element, 2) has a first step and a second step, the first step selectively forms an RBaxCus OX layer on the substrate, where R refers to a rare earth element; The second step is a step of selectively laminating a BizSrzCatCu308 layer having a strip portion on the substrate and the RBaxCui Ox layer at a predetermined substrate temperature.
B i zsr tca z on top of zCutO11 layer
The strip portions of the Cu ff Ow layer are laminated;
or 3) In the manufacturing method according to claim 1 or 2, since the layers are laminated at a substrate temperature of 550°C, Bi in the B5CC0 layer diffuses into the RBCO layer, making the RBCO layer a normal conductor, and S/N/S A Brehner-type Josephson device with this structure is obtained. At this time, at a substrate temperature of 550°C, the B5CC0 layer and the RB
When reacted with the CO layer, an appropriate amount of Bi diffuses and forms RBCO.
The layer becomes a normal conductor.

Bi diffusion has excellent reproducibility and does not deteriorate the S/N interface.B5CC0 and RBC○ have similar coefficients of thermal expansion and do not generate cracks.In this way, it is easy to create a Brehner-type Josephson element with excellent reliability. Moreover, it becomes possible to manufacture with good reproducibility.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing a method of manufacturing a Josephson device according to an embodiment of the present invention, FIG. 2 is a diagram showing the characteristics of the obtained S/N/S structure planar Josephson device, and FIG. is YB formed on the B5CC0 layer at a substrate temperature of 550°C.
A diagram showing the temperature dependence of electrical resistance for the CO layer, Figure 4 shows the YB formed on the B5CC0 layer at a substrate temperature of 670°C.
A diagram showing the temperature dependence of electrical resistance for the CO layer, Fig. 5 is a plan view showing a measurement sample related to a preliminary experiment, and Fig. 6 is a cross-sectional view showing the manufacturing process of a conventional planar Josephson element. be. 1: Mg○ substrate, 6: B5CC0 layer, 6A: B5CC0
Strip of layers, 7.7A: YBCO layer, 10A pattern on resist, 10B resist, 11: Bi diffusion region, -

Claims (1)

[Claims] 1) It has a first step and a second step, and the first step is Bi_2S having a strip portion on the substrate.
The r_2Ca_2Cu_3O_x layer is selectively formed, and the second step is to form the r_2Ca_2Cu_3O_x layer on the substrate and Bi_2Sr_2Ca_2C.
RBa_2Cu_ on the strip part of u_3O_x layer
1. A method for manufacturing a Josephson device, characterized in that it is a step of selectively laminating 3O_x layers at a predetermined substrate temperature, where R represents a rare earth element. 2) comprising a first step and a second step, the first step selectively forming an RBa_2Cu_3O_x layer on the substrate, where R refers to a rare earth element;
The second step is Bi_2Sr_2Ca_2Cu_ having a strip part on the substrate and the RBa_2Cu_3O_x layer.
In this step, the 3O_x layer is selectively laminated at a predetermined substrate temperature.
A method for manufacturing a Josephson device, characterized in that strip portions of _2Sr_2Ca_2Cu_3O_x layers are laminated. 3) A method for manufacturing a Josephson element according to claim 1 or 2, characterized in that the layers are laminated at a substrate temperature of 550°C.