JP2890771B2 - Manufacturing method of superconducting thin film element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a superconducting thin film element, and more particularly, to a method for manufacturing a superconducting thin film element having a weakly coupled Josephson junction having a small superconducting transition temperature width. .

[Prior Art] With the progress of thin film forming technology in recent years, attempts have been made to form various types of sensors by forming a thin film of superconducting ceramics on a substrate, and in particular to realize a highly sensitive magnetic sensor. It is necessary to build a weakly coupled Josephson junction in a superconducting thin film.

Conventionally, as a method of realizing the weakly coupled Josephson junction, a method of forming a superconducting thin film into a predetermined shape by chemical or physical etching, laser trimming, or the like has been attempted.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional method, it is difficult to perform ultra-fine processing, and it has a bad influence by heat or the like on a relatively wide area other than the processed part, and particularly, high quality without crystal grain boundaries. In the film body, it was difficult to suppress the superconducting transition temperature width and realize a weakly coupled Josephson junction having a sufficiently small critical current value.

An object of the present invention is to provide a method of manufacturing a superconducting thin-film element which realizes a weakly coupled Josephson junction having a small critical current value in a state where the superconducting transition temperature width is sufficiently small, in order to solve such a problem. I do.

[Means for Solving the Problems] According to the manufacturing method of the present invention, a ceramic superconducting thin film 2 is formed on a substrate 1 to a thickness of 500 to 1000 mm,
Is cut to form a narrow bridge portion 21 having a width of 10 μm to 30 μm, and the surface thereof is irradiated with an electron beam at a width of 0.1 μm to 0.4 μm across the bridge portion 21. Things.

[Operation] The superconducting thin film element manufactured by such a method has a small superconducting transition temperature width of 10 K or less in absolute temperature and a sufficiently small critical current value. Such a method is extremely effective especially for a high-quality film having no crystal grain boundaries.

Example An example of the manufacturing method of the present invention will be described below with reference to FIGS. 1 to 4.

First, as shown in FIG. 1, (001) of the single crystal MgO substrate 1
On the surface, a superconducting thin film 2 of a ceramic oxide Y1Ba2C5Ox (referred to as YBCO) is formed with a predetermined thickness a. This thin film formation is RF-
The YBCO thin film 2 is deposited on the substrate 1 by a magnetron sputtering method. The conditions are as follows.

Target; Y1Ba2Cu4.5Ox sintered body Substrate temperature; 700 ° C Ar flow rate; 30 sccm O2 flow rate; 10 sccm Sputter pressure; 10 mTorr Sputter power; 150 W Distance between target substrates; 40 mm Deposition rate; 5 nm / min The portion is cut into a rectangular shape from both sides as shown in FIG. 2 to form a small bridge portion 21 having a predetermined width b. The formation of the bridge portion 21 is performed by chemical etching.
400-25, hydrochloric acid aqueous solution as etchant (0.15vol%)
It was used.

Thereafter, an electron beam is irradiated across the bridge portion 21 (arrow in FIG. 3). This electron beam irradiation is made by JEOL
Set the sample in the JEM-4000EX electron microscope and set the accelerating voltage to 4
The measurement was performed at 00 KV, a filament current of 132.5 μA, and an electron beam spot size of about 4 nm. Thus, a strip-shaped layer 22 having a predetermined width c, which is made non-superconductor, is formed on the YBCO thin film of the bridge portion 21 by electron beam exposure (FIG. 4).

In the above manufacturing method, the results of experiments obtained by changing the thickness a of the superconducting thin film, the width b of the bridge portion, and the width c of the electron beam processing layer are shown in a separate table. In the table, Tc · on is the superconducting onset temperature, ΔT is the temperature width required for a change in resistance at the superconducting transition point of 10 to 90% (superconducting transition temperature width), and Ic is the absolute temperature 10
It is the critical current value at K. The critical current value Ic is reduced by 1/10 from the state where the bridge portion is formed by electron beam processing.
The goal was to:

As can be seen from the table, in Examples 1, 2, and 4,
Absolute temperature is kept at 10K or less without a large increase in temperature width ΔT. Critical current value Ic is reduced to 1/10 or less in any state just after processing the bridge part, and weak coupling Josephson This indicates that a bond has been formed. In the third embodiment, the residual resistance is not zero and is not a strictly weak Josephson junction, but the temperature width ΔT is suppressed to an absolute temperature of 10 K or less, and various sensors are realized. Can be used.

According to these Examples 1 to 4, the thickness a (FIG. 1) of the YBCO thin film is 500 ° to 1000 °, and the width b of the bridge portion (FIG. 2).
Is 10 μm to 30 μm, the width c of the electron beam processing layer (FIG. 4)
Is preferably 0.1 μm to 0.4 μm.

On the other hand, if the film thickness is smaller than 500 °, the temperature width ΔT before processing is extremely large, which is not suitable (Reference Example 1).
On the other hand, when the film thickness exceeds 1000 °, the critical current value Ic is not sufficiently reduced (Reference Example 4) or the temperature width ΔT increases (Reference Example 5).

When the width of the bridge portion exceeds 30 μm, the temperature width ΔT increases (Reference Example 6). When the width of the electron beam processing layer is smaller than 0.1 μm, the critical current value Ic does not decrease (Reference Example 2),
If it exceeds 0.4 μm, the temperature width ΔT increases (Reference Example 3).

[Effects of the Invention] As described above, according to the manufacturing method of the present invention, a superconducting thin-film element having a weakly-coupled Josephson junction with a sufficiently small critical current value is realized with the superconducting transition temperature range kept small. This greatly contributes to the realization of a high-sensitivity magnetic sensor and the like.

[Brief description of the drawings]

1 to 4 are conceptual perspective views for explaining a manufacturing process of a superconducting thin film element. DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Superconducting thin film 21 ... Bridge part 22 ... Electron beam processing layer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroki Hoshizaki 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside of Denso Co., Ltd. In-company (72) Inventor Toru Imura 2-58 Higashiyama Motomachi, Chikusa-ku, Nagoya-shi, Aichi (56) References JP-A-1-239977 (JP, A) JP-A-1-202876 (JP, A) (58) Surveyed fields (Int. Cl. ⁶ , DB name) H01L 39/00 H01L 39/22 H01L 39/24

Claims (1)

(57) [Claims] 1. A ceramic superconducting thin film having a thickness of 500 to 1000 mm is formed on a substrate, and a part of the superconducting thin film is cut to form a narrow bridge portion having a width of 10 to 30 μm. 0.1μm ~
A method for manufacturing a superconducting thin film element, comprising irradiating an electron beam with a width of 0.4 μm.