JPH03155682A - Manufacture of superconducting thin film squid - Google Patents

Abstract

PURPOSE:To manufacture SQUID elements with better reproducibility and safety in short time, using a Tl superconducting film by performing etching before diffusing Tl into a Ba-Ca-Cu film. CONSTITUTION:A thin film 11 is deposited on the surface of a substrate 10 by sputtering using a target material of Ba2Ca2Cu3OX. Then, photoresist 13 is applied to the film 11, then patterning is carried out in required shape including a Josephson junction. A thin film exposed by the patterning operation is etched by an ion milling device so that the substrate 10 may be exposed. Then, the photoresist 13 is removed. The substrate is placed into an annealing device where the substrate is annealed in an O2 ambient atmosphere including Tl. After that process is over, Cr and Au are sputtered on a thin film of TlBa2Ca2 Cu3OX so as to bond Au wire.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a SQUID element using a Tl-based high temperature superconducting thin film.

<Prior art> Tl-based compounds composed of Tl-Ba-Ca-Cu-0 have the highest superconducting critical temperature at an absolute temperature of 125 among the currently confirmed stable oxide superconductors. Are known. This Tl-based high-temperature superconductor is then attached as a thin film to a substrate.

Attempts have been made to create SQUID devices by dry etching.

For example, I described in 15EC-1989-DEI-1
In the paper by W, J, Gallagher et al. of BM, a SQUID element was fabricated by patterning T1-Ba-Ca-Cu-0M formed on a substrate by dry etching.

<Problems to be Solved by the Invention> However, the manufacturing method described in the above paper has the following problems.

(2) Since the Tl-Ba-Ca-Cu-0 thin film is patterned by dry etching, the dry etching equipment is contaminated with toxic Tl.

■ The thickness of the Tl-Ba-Ca-Cu-0N film is approximately 4 μm, but when dry etching is performed, it becomes approximately 3 μm thick.
．． It takes 5 hours and work efficiency is extremely low.

(2) Since the film thickness is relatively thick at 4 μm, the etching pattern accuracy in both the length and width of the bridge deteriorates.

The present invention has been made in view of the problems of the prior art described above.
The purpose of this study is to manufacture SQUID devices with good reproducibility, safely, and in a short time using Tl-based superconducting thin films.

Means for Solving the Problems> The configuration of the present invention for solving the above problems is as follows:
In a method for manufacturing a SQUID device using an a-Ca-Cu-0 based superconducting thin film.

(i) A step of attaching a thin film containing B a -Ca -Cu -0 mixed at a predetermined ratio to a substrate.

(i1) A step of applying a photoresist film on the thin film and patterning the photoresist 1 to film into a desired shape.

(ii) etching the thin film not exposed by the patterning by ion milling to expose the substrate;

(IV) Step of removing the photoresist I/film; and M annealing the substrate in an O2 atmosphere containing Tl;
a step of diffusing the Tl into the thin film;

It is characterized by being manufactured by containing.

Effect> Since etching is performed before TI is diffused into the Ba-Ca-Cu-0 film, there is no risk of contamination of the equipment. Also,
The film thickness is thin before TZ is diffused (5rTi as a substrate).
When MgO is used as the substrate, the etching accuracy is approximately 0.8 μm, and when MgO is used as the substrate, the etching accuracy is approximately 1.2 μm).

<Example> Hereinafter, a manufacturing method of the present invention will be described with reference to the drawings. FIGS. 1(a) to 1(f) are schematic manufacturing process diagrams showing the configuration of an embodiment of the present invention.

Process description (i) A thin layer of I'll is deposited on the surface of the substrate 10 by sputtering using a target material of Ba2Ca2Cu30X.

(See Figure a) The sputtering conditions are as follows, for example.

Ar/O gas partial pressure ratio in container = 2/1 Sputtering gas pressure: 30 m'rorr target material
・Ba2 Ca2 Cu30x Substrate material: Single crystal 5rTi03; Single crystal Mg
0 RFt power, 200W substrate heating; 200-300℃ sputtering time
30 minute process description (i1) After coating the photoresist 13 on the Ba2Ca2Cu30X film 11, patterning is performed into a desired shape including a Josephson junction (see diagram) Step (2)) The photoresist WA13 Ba2C as a mask
The a2Cu30X film 11 is etched using an Ar ion milling device to expose the substrate 10 (this etching is performed so that the film thickness is 0.8 μm when the substrate is S r Ti O3).
Since it is about 30 to 40 minutes, the film thickness is 1.2 in the case of MgO.
(Since it is about .mu.m, it takes 45 to 60 minutes to complete) (see Figure C) Step (2) Remove the photoresist 13. (See Figure d) The process substrate is placed in an annealing device and annealed in an 02 atmosphere containing Tl. (See Figure e) Figure 2 shows a heat treatment apparatus for performing annealing. In the figure, l is a quartz tube, and 72 is a heating device formed by winding the quartz tube.

3a and 3b are bow I made of alumina, which are divided into upper and lower parts and stacked 9 times, and are formed so that gas can circulate with the inside through grooves formed at the edges (the flow grooves are (omitted in the figure). 4 is a substrate on which a thin film is formed (Sr
TLO, or Mg0).

5 is metal Tl or oxidized Tl; 1 these are arranged in an alumina boat. 6 is a cap made of alumina placed inside the quartz tube.

It is formed to allow gas flow. The arrow is 02
It shows the direction of distribution.

Annealing was performed under the conditions shown in FIG. After raising the temperature to 905℃ in 120 minutes and holding it for 5 minutes,
The temperature is lowered to 300°C in 0 minutes and slowly cooled.

The above annealing evaporates Tl in the alumina boat,
The evaporated T1 is patterned on the substrate surface.
2 Ca2 diffuses into the Cu30X thin film. Annealing was performed in an atmosphere with an oxygen flow rate of 0.2 mA'/min. In addition, cap 6 is evaporated 1゛! stays in the quartz tube 1 for a longer period of time, contributing to enhancing the atmosphere of T1.

The annealing equipment described above does not need to be installed in a clean room unlike a sputtering equipment, and it is relatively easy to treat toxic T1 vapor.

Step (7) Cr and A on TlBa2 Ca2 Cu30x thin metal
Sputter u and bond Au wire.
(Refer to the diagram) Figure 4 shows the magnetic flux-voltage characteristics when the SQUID element created by the above process is assembled into da misquid, and Figure 5 shows the measurement circuit for measuring the magnetic flux-voltage characteristics. It shows. Fifth
In the figure, 20 is a SQUID element, 21 is a direct current Ib
A bias current source 722 that supplies magnetic flux Φ to the SQUID element
23 is an alternating current source that sends an alternating current to the coil 22, 24 is a resistor inserted between the coil and the alternating current source, 25 is an amplifier that amplifies the electric signal flowing to the SQUID element, 26 is an amplifier 25 This is an oscilloscope in which the output of the resistor is input to the Y axis, and the output to one end of the resistor is input to the X axis. With the above configuration, the magnetic flux peak is 0 while the bias current is flowing.
Obtain the magnetic flux-voltage characteristics shown in Fig. 4 by changing . According to Fig. 4, when the bias current is fixed at a certain value (in the figure, there are 5 types including the case of bias current O) and the external magnetic flux is changed, the output voltage also changes. ) is accepted.

Figures 6(a) and (b) show MgO and 5rTio as substrates.
, shows the relationship between output and magnetic flux when using . That is, in FIG. 5(a), the magnetic flux Φ is changed by changing the voltage of the AC power supply 23 shown in FIG. The change in output was recorded with an X-Y recorder while changing the value, and the figure (b) shows the measurement results showing the magnetic flux-voltage conversion coefficient dv/d (μV/cloud).

According to the figure, the maximum amplitude of the output (p-p) for the MgO substrate
is about 30 uV, and about 10 μV for a 5rTiO) substrate.
■It is. Also, dv/di is 100 for MgO
μV/! +o, SrTiO3 is 40μV/ZO. Therefore, as a 5QUID element, Mg
It can be seen that the O substrate is superior.

Currently, an example of SQUID fabricated using an oxide superconducting thin film is 1, for example, Confucian Technical Report published by the Institute of Electronics, Information and Communication Engineers, Vo 1.88 No., p. 24531, using Y (yttrium) based SQUID An example in which the magnetic flux voltage conversion coefficient was 10 μV/mo, and the above-mentioned 477-48 of 15EC-1989-DEI-1.
An example has been described in which a 1X4:Tff-based 5QUID was used with an I'C magnetic flux-voltage conversion coefficient of 60 μV/L.1 However, when MgO is used as a substrate using the manufacturing method of the present invention, data exceeding these reports can be obtained. Obtainable.

FIGS. 7 and 8 show X-ray diffraction data of a superconducting thin film in which Tl is diffused into a MgO and 5rTt03 substrate. In the figure, 1223 phases (i16K), 12
12 phase (v1K) means T1. These are the composition ratio of Ba, Ca, and Cu and the critical temperature of the superconducting crystal <Tc). As the figure clearly shows, the MgO substrate exhibits a high Tc122
It is a mixed phase in which a certain proportion of the 1212 phase exhibiting a low Tc is included in the three phases, and in the Sr'r'i0) substrate, only the 1223 phase does not exhibit a high Tc. From this, it is presumed that a superconducting crystal that exists in a mixed phase is better as a 5QUID element than one that exists in a single phase.

9 In the manufacturing method of the present invention, BaCa, Cu, etc. are added to the substrate in advance.
, T1 is diffused after forming a thin film of O, but when producing the above-mentioned mixed phase, it is possible to obtain a stable mixed phase by adjusting the amount of oxidized Tl to be evaporated relative to the volume of the boat. (The X-ray diffraction measurement results shown in Figure 7 assume that the volume of the boat is approximately 10 cc1, and approximately 8 m
(It was made by putting an m square MgO substrate and 17 mg of thallium oxide and evaporating it.)

In this example, Ba2Ca2C was used as the thin film.
Although u30X is used, the component ratio is not limited to this, and can be arbitrarily changed as long as it exhibits superconductivity and a high flux-voltage conversion coefficient. Further, the sputtering conditions such as gas partial pressure ratio, substrate heating temperature, and sputtering time are not limited to those of this embodiment.

<Effects of the Invention> As described above in detail along with the examples, according to the present invention, etching is performed before Tl is diffused into Ba-Ca-Cu-0WA, so there is no risk of contamination of the etching equipment. Moreover, since the film is thin before Tf is diffused, highly accurate etching is possible and the etching time can be shortened.

[Brief explanation of the drawing]

Fig. 1 shows the schematic steps of the method for manufacturing a superconducting thin film SQUID of the present invention. Fig. 2 shows the heat treatment equipment for annealing, Fig. 3 shows the annealing conditions, and Fig. 4. is a diagram showing the relationship between bias current/external magnetic flux and output voltage, Figure 5 is a diagram showing a measurement circuit for measuring magnetic flux-voltage characteristics, and Figure 6 is a diagram using MgO and S r Ti Os as substrates. A diagram showing the relationship between output and magnetic flux in case of
The figure shows X11 diffraction data of a superconducting thin film in which Tl is diffused into a MgO and 5rTi03 substrate. io...Substrate, 11...B a-Ca-
Cu-OX pA. 13... Photoresist Il[, 14...1'l(
thallium) Figure 1 Figure 1 Cause ((L)

Claims (1)

[Claims] A method for manufacturing a SQUID element using a Tl-Ba-Ca-Cu-O based superconducting thin film, characterized in that the manufacturing method includes the following steps: . (i) A step of attaching a thin film containing Ba--Ca--Cu--O mixed at a predetermined ratio to a substrate. (ii) A step of applying a photoresist film on the thin film and patterning the photoresist film into a desired shape. (iii) Etching the thin film exposed by the patterning by ion milling to expose the substrate. (iv) removing the photoresist film; (v) Annealing the substrate in an O_2 atmosphere containing Tl to diffuse the Tl into the thin film.