JPH01260868A - Dc type superconducting quantum interference element using oxide superconductor - Google Patents

Abstract

PURPOSE:To increase the product of a superconducting critical current and a normal conductive resistance without changing the inductance of a loop by forming weak links in meander shapes, in a DC type superconducting quantum interference element having the weak links using oxide superconductive films at two places. CONSTITUTION:This element is composed of weak links at two places and a superconducting loop including the links. As a thin film 1, e.g., a YBa2Cu3O7-delta film formed by RF magnetron sputtering is used. The thin film is formed on a single crystal. Then, the superconductor thin film 1 is obtained by heat treatment. Photoresist is used in patterning, and etching is performed. In this SQUID, the weak links 2 are formed in meander shapes. The area of a hole 3 of the SQUID is made to be, e.g., 9,000 (mum<2>). The width of a line is made to be 20mum. The Iength is made to be about 800mum in terms of a straight line.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a DC-type superconducting quantum interference device (hereinafter referred to as DC-3QUID) using an oxide superconductor.

[Prior art] In general, a 5QUID is a device in which one or two Josephson junctions are connected to a loop circuit made of a superconductor.
(Superconducting Quantum
InterferenQQ oev+cc (abbreviation for superconducting quantum device) is a basic device used in Josephson digital devices and 5QUID magnetometers.

Also, is SQU ID with one junction l? P-3QI
The SQUID with two junctions, which is used as a JID magnetometer and a memory element, is called DC-9QUID.
It is used in the DC-8QUID magnetometer for storage and switching purposes.

As a device of this kind, the European Journal of the Japan Society of Applied Physics
anese Journal of Apphed P
hyslcs Vol, 2B, No, 11 Nov,
1987. pp. L1925-192[+ entitled "DC-8QUID of high critical temperature of oxide superconductor film".

For this, DC-3QU using YBa Cu O film
It is stated that the relationship between magnetic flux and voltage of ID237-δ was studied.

Also, DC-3QU using Ba2Cu30 film
The ID is made by a 7-δ graphical pattern and its DC
-8QLI ID is disclosed to be operated at a critical temperature of 72 or above.

Conventionally, this type of device is known as Y
A thin film of BaCuO was exposed to an RF magnetron 237-
It is formed by δ sputtering, and a superconducting loop including two weak links is formed by photonotching.

This weak link is caused by the fact that the grain boundary part in the YBa2Cu307-δ thin film forms a Josephson junction.
Unlike conventional Nb-based and PB-based superconductors, the Josephson effect is produced without forming tunnel junctions or processing weak links to submicron order.

In conventional superconductors, weak links are very small on the order of submicrons, which poses problems in terms of processing accuracy, but as shown in the above literature, oxide superconductors have weak links that are several hundred microns wide. DC-9QU
Since it is now possible to form an ID, processing has become easier.

[Problems to be Solved by the Invention] However, as described in the above-mentioned literature, the amount of change in the output voltage with respect to the magnetic flux is only about 1 μV;
This small output voltage has been a problem when constructing a magnetometer or the like using SQUID.

The main reason for this is that the product I R of the superconducting critical current 1 of the weak link and the normal conduction resistance R is
n on
One example is that it is small.

For this reason, it is possible to lengthen the weak link to increase the resistance, but if you do this, the SQU I D
This was impossible because the area of the hole would become larger, the inductance of the loop would become larger, and the 5QUID operation would be hindered, such as being more easily affected by external magnetic fields and increasing thermal noise.

The present invention is applicable to the conventional DC-9QU! described above. The purpose of this invention is to eliminate the drawback of low output voltage in DC-8QUID and provide a DC-8QUID with high output voltage.

[Means for Solving the Problems] The present invention provides a DC-type superconducting quantum interference device having two weak links using an oxide superconducting film, characterized in that the weak links have a meander shape. This is a DC-type superconducting quantum interference device using a superconductor.

[Function] In the DC type superconducting quantum interference device having two weak links using the oxide superconductor of the present invention, the weak link as a magnetoresistive element has a meander shape (m
Since the resistance value is increased by making the loop (eander meandering type), it is possible to increase the product I R of the superconducting critical current 1 of the weak link and the normal conductive resistance Rn without increasing the loop inductance. It is thing n.

Next, examples of the present invention will be described.

[Example] Figure 1(a) shows DC-8QU using an oxide superconducting film.
FIG. 1(b) is an explanatory diagram of a general pattern, and FIG. 1(e) is an explanatory diagram of an equivalent circuit of an ID.
- It is an explanatory diagram of a pattern of 3QUID.

In the figure, 1 is a superconducting film, 2 is a weak link, and 3 is a hole.

FIG. 1(a) and FIG. 1(b) are composed of two weak links 2 and a superconducting loop including the weak links 2.

Moreover, the hole in FIG. 1(C) has the same area as the hole in FIG. 1(b), and can increase the normal conduction resistance.

The thin film was made of YBa by RF magnetron sputtering.
A CuO film is used, and its formation conditions are as follows 237-
There are δ ways.

Gas pressure 5 x 1O-3Torr.

Gas used: A “Gas.

A thin film of 1.5 μ-thickness was formed on single crystal Mg0 (100) with a power of 2.5 v/cd.

Subsequently, a superconductor thin film was formed by heat treatment at 920° C. for 0.5 hours.

The critical temperature Tc of this superconductor thin film was 83, and the critical current density Jc was 900 A/cd (at 77 K).

In addition, patterning is done using positive resist (OK manufactured by Tokyo Ohka Co., Ltd.)
l? Etching was performed using phosphoric acid (2vt%) using R800').

As shown in Fig. 1(c), this 5QUID has a meandering weak ring 2, a hole area of 90000 (lJa+2), a line +l] of 20-1, and a length of approximately 80011+m in straight line terms. And so.

A 5QUID of the type shown in FIG. 1(b) was also formed using the same membrane, with a hole size of 300 x 300 IIm, and a weak link 2 having a length of 200 μm and a width of 20−.

FIG. 2 shows a relationship between the magnetic flux (Φ.) and the output voltage (μV) of the SQUID in FIGS. 1(b) and 1(e). These are each optimized for bias current.

From FIG. 2, it can be seen that in both DC-8QUIDs, the output voltage (μ■) is equal to the flux quantum Φ. It can be seen that the output characteristics change with a cycle that is an integral multiple of .

Due to this property, it is expected that it can be applied to various magnetic sensors.

Also, from FIG. 2, it is seen that the amplitude of the output voltage is 1.
2μV to 4μ during meander type weak link ■
It is clear that the output voltage increases to , and the output voltage is larger when the meander type is used than when the output voltage is not meandered.

[Effects of the Invention] As explained above, according to l) the C-type superconducting quantum interference device using the oxide superconductor of the present invention, the weak link of the DC-type superconducting quantum interference device DC is made into a meander shape,
Superconducting critical current without changing loop inductance! The product n 11 n of the normal conducting resistance R and the normal conducting resistance R can be increased.

Furthermore, the present invention has advantages such as that the amplitude of the output voltage increases from 1.2 μV in the conventional method to 4 μV in the present invention, making it easier to apply to magnetometers, etc. It is effective.

[Brief explanation of the drawing]

Figure 1(a) shows DC-3QU using an oxide superconducting film.
An explanatory diagram of the equivalent circuit of ID, FIG. 1(b) is an explanatory diagram of a general pattern, and FIG. 1(c) is an explanatory diagram of the DC-3Q of the present invention.
An explanatory diagram of the UID pattern, Figure 2, is similar to Figure 1 (b
) and the relationship between the magnetic flux and output voltage of 5QUID in FIG. 1(C). In the figure, 1 is a superconducting film, 2 is a weak link, and 3 is a hole. (0) (b') DC-5oUID pattern 3 of Fumozuki (C
) Figure 1 Narito (φ0) 5 bolts with λte ai-i Jifco Denmanni r? Figure 2 procedural amendment (voluntary) tjj, 11.21 Showa year, month, day

Claims (1)

[Scope of Claims] A DC type superconducting quantum interference device having two weak links using an oxide superconducting film, characterized in that the weak links have a meander shape. Superconducting quantum interference device.