JPH04774A - Squid and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to manufacture SQUID without requiring a high temperatures process, such as heat treatment, by forming a thin film on an insulation substrate by vacuum-depositing an organic superconducting complex and providing a constriction by removing a part thereof. CONSTITUTION:First, an organic superconducting complex is put into a deposition boat 2 inside a chamber 1 of a vacuum deposition apparatus. After the pressure inside the chamber is decreased to a vacuum degree of 10Pa or smaller, the deposition boat 2 is heated to the vicinity of a sublimation point of the organic superconducting complex, usually in the range of 150 deg. to 260 deg.C, and the complex is deposited on the substrate held in a substrate holder 4. The thickness of the deposited film is adjusted by opening/closing a shutter 5 while the thickness is being monitored by a quartz oscillator film thickness gauge 6. The size of the film is controlled by the type of the deposition boat. A SQUID is produced by forming a constriction 13 by removing a part of the organic superconducting thin film 12 provided on an insulation substrate 11 in the above way by using a mechanical cutting member or a method of decomposing superconducting complexes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel SQUID element and a method for manufacturing the same. More specifically, the present invention relates to a SQUID device using an organic superconducting complex that can be manufactured without requiring high-temperature processes such as heat treatment, and a method for efficiently manufacturing this device using only low-temperature processes. It is.

[Prior art] Squid element (Superconductor)
antuminterference device)
The superconducting material has a weak coupling part (Josephson junction), that is, a constricted part, etc. inside the superconducting material, and is used, for example, in SQUID magnetometers and Josephson voltage standard devices.

Conventionally, Pb has been used as a superconducting material in SQUID devices.
Although Pb-based alloys and Nb-based alloys have been used, Nb-based materials are now the mainstream because Pb-based materials are easily oxidized.

However, when a SQUID element is manufactured by forming a homogeneous thin film using this Nb-based alloy, there is a drawback that a high temperature of 700° C. or more is required in the thinning process.

In addition, for example, YBa2Ctz is used for manufacturing SQUID devices.
A method using oxide superconductors such as Oy-, etc. has been proposed (Japanese Unexamined Patent Publication No. 1-120879), but this method also has the drawback of requiring a high temperature (heat treatment) process of 900°C or higher. have.

On the other hand, in recent years, charge transfer complexes, in which two types of molecules are bound by the charge transfer force between an electron donor and an electron acceptor, have been developed with properties such as conductivity, paramagnetism, sensitivity to electron beams, and electrical sensitivity to humidity. It has attracted attention and is being actively researched because it can be applied as, for example, electronic materials, resist materials, electrode active materials, moisture-sensitive elements, electromic display elements, etc.

Among such charge transfer complexes, organic superconductors, which exhibit superconductivity below a critical temperature, have recently attracted attention because they can be used, for example, in Josephson junction devices and high-sensitivity magnetic sensing.

[Problems to be Solved by the Invention] The present invention has been made for the purpose of providing a novel SQUID element that can be manufactured without requiring high-temperature processes such as heat treatment.

[Means for Solving the Problems] In order to achieve the above object, the present inventors have conducted extensive research; as a result, a SQUID element consisting of an organic superconductor thin film provided on an insulating substrate has been developed. The inventors have found a way to achieve this objective, and have completed the present invention based on this knowledge.

That is, the present invention provides a SQUID element comprising an organic superconductor thin film provided on an insulating substrate.

According to the present invention, the SQUID element comprises vacuum-depositing an organic superconducting complex on an insulating substrate to form a thin film;
It can then be manufactured by removing a portion of it to provide a constricted portion.

The present invention will be explained in detail below.

As the organic superconducting complex used in the present invention, for example, bis(ethylenedithio)tetrathiafulvalene (B
EDT-TTF) as an electron donor, specifically, those shown in Table 1 can be mentioned. Among these, considering the high superconducting transition temperature (B E
D T T T F ) zCu(SCN)2 and (
BEDT-TTF) 213 is preferred.

1) σ-(BEDT 1st Table TTF)21. These organic superconducting complexes are prepared by heating bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) and the corresponding electron acceptor using known methods such as electrolytic crystal growth, diffusion, slow cooling, etc. Growth method or BEDT-TT
It can be produced by a method of reacting F with a halogen element in a gas phase, liquid phase, or solid phase.

Examples of insulating substrates used in the present invention include single crystals of sodium chloride and potassium chloride, glass,
Examples include quartz glass and organic materials such as polyvinyl chloride and polyethylene.

As a method for forming the organic superconductor thin film on these insulating substrates, for example, a thin film forming method such as a vacuum evaporation method, a sputtering method, an ion cluster beam method, or a CVD method can be used. As a method, a vacuum evaporation method is used, which is a low energy thin film forming method in which the organic superconducting complex is difficult to decompose.

In this vacuum evaporation method, the distance between the substrate and the organic superconducting complex is preferably kept within 10 cm, preferably within 5 cm. If this distance exceeds locm, the superconducting complex tends to decompose, and the formed thin film tends to have insufficient orientation.

Further, the degree of vacuum is usually selected within the range of 10 Pa (Pascal) or less, preferably 10-2 Pa or less. If the degree of vacuum exceeds 10 Pa, the superconducting complex may be oxidized or decomposed, which is not preferable. The superconducting complex is usually heated so that its temperature reaches near the sublimation point, but the heating temperature is appropriately selected depending on the type of the complex. The temperature of the substrate is usually selected in the range of 30 to 150°C. This temperature is 15
Above 0°C, the complex tends to decompose.

Next, one example of a suitable method for forming an organic superconductor thin film will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of an example of a vacuum evaporation apparatus for forming a superconductor thin film, and there is a evaporation port 2 in a chamber 1 and a sublimation port 3 with a diameter of 10 cm.
A substrate holder 4 is installed at a distance within the range of 1 to 3, and a shutter 5 is further provided between the vapor deposition port 2 and the substrate holder 4.

First, the required organic superconducting complex is put into the vapor deposition port 2, and the pressure inside the chamber is reduced to a degree of vacuum of 10 Pa or less, preferably 10-2 Pa or less via the exhaust valve 7, and then the vapor deposition port 2 is filled with the organic superconducting complex. Up to near the sublimation point, usually 15
The complex is deposited on the substrate held by the substrate holder 4 by heating to a temperature in the range of 0 to 260°C. At this time, the inside of the chamber 1 may be replaced with an inert gas such as argon in advance, and then the pressure may be reduced. The thickness of the deposited film is adjusted by opening and closing the shutter 5 while monitoring with a crystal resonator film thickness meter 6. According to this method, the film thickness is several 1
The film size can be controlled by the type of vapor deposition port. The organic superconductor thin film thus obtained is oriented such that the direction of high electrical conductivity is parallel to the substrate surface, and consists of a single phase.

In addition, (B E D T - T T F ) 21 s
According to this method, the σ type (B E D
T - T T F ) 21 s (which does not exhibit superconductivity) may also be mixed in, but in this case, by heat treatment in air at a temperature of 30-150°C, the structure of the film can be changed to β-type, etc. It can be made into a phase that exhibits superconductivity. β
The .theta., .gamma. and .gamma. types occur at temperatures of approximately 60.degree. C., 140.degree. C. and 130.degree. C., respectively.

The thickness of the organic superconductor thin film thus formed is 1
The thickness is preferably about 0 nm to 1 μm; if it is too thin, the conductivity will be poor, and if it is too thick, it will tend to become brittle.

The SQUID element of the present invention is obtained by removing a portion of the organic superconductor thin film thus provided on the insulating substrate to form a constricted portion. To remove this part, for example, mechanical cutting using a wire saw or tire cutter, or decomposition of the superconducting complex by electron beam or laser irradiation can be used. In this case, the former method is suitable, and on the other hand, when miniaturization and integration are desired, the latter method is suitable.

The SQUID device of the present invention produced in this way is
If desired, the entire structure may be encapsulated in an organic insulating polymer such as polycarbonate to improve mechanical strength and adverse effects from the environment (such as water vapor).

The SQUID element of the present invention is shown in FIGS. 2(a) and 2(a).
By molding as shown in b), it is also possible to use it as an RF Squid or a DCC Squid. In this figure, 11 is an insulating substrate, 12 is an organic superconductor thin film, and 13 is a constricted portion.

[Examples] Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way.

Example I Using BEDT-TTF [manufactured by Nippon Carlit Co., Ltd.] and tetrabutylammonium triodide [manufactured by Wako Tsumugi Co., Ltd.] as raw materials, BEDT-TTF was produced by an electrolytic crystal growth method.
-TTF)2I3 complex was prepared.

Next, using the vacuum evaporation apparatus shown in FIG. 1, the complex lo
mg into a crucible (evaporation port) 2, and hold a 3 x 3 x 0.3 cm3 sodium chloride single crystal substrate in a substrate holder 4 at a position 2 cm away from the crucible mouth (elevating port) 3.
Vacuum evaporation was performed under the conditions of a substrate temperature of 70°C, a crucible temperature of 200°C, and a chamber vacuum of 10-'Pa to form a thin film with a thickness of 500 nm on the substrate. This was then annealed in air at 70°C for 5 hours to transform it into a phase exhibiting a high superconducting transition temperature.

From the thin film obtained in this way, the remaining film was removed with a knife, leaving the 0.5Xlc film part, and then a constriction was formed in the center of the remaining film with a wire saw. Insulator substrate 1 as shown in Figure 3
A SQUID element having a structure in which an organic superconductor thin film 12 having a constricted portion 13 with an area of 1 mm 2 was provided on top of the organic superconductor thin film 12 was fabricated.

Current and voltage terminals were attached to this element using gold paste, and the voltage-current characteristics of the constricted portion were examined.

Figure 4 shows a conceptual diagram of this measurement system. That is, the SQUID element 14 is provided with terminals 15 a, using gold paste.
Install 15 b, 15 c, 15 d, and power supply 16
, a signal processing device 17 and a 10Ω resistor 18 are installed.

The measurement is carried out by first cooling the element 14 to liquid helium temperature to make it superconducting, then applying a voltage to the constriction part 13 and the resistor 18 from the power supply 16, and converting the current flowing through the constriction part 13 into the voltage generated across the resistor 18. At the same time, the voltage generated at the constricted portion 13 is measured from the voltage terminals 15c and 15d attached to the element 14. From these two voltages, the voltage-current characteristics of the constricted portion 13 are determined by the signal processing device 1.
Investigated in 7.

Figure 5 shows the voltage-current characteristic curve when the constriction is irradiated with microwaves, showing a step-like change (Shapiro step) indicating that the constriction is a Josephson junction, which is necessary for the constriction to function as a SQUID element. It was observed. Also,
It was confirmed that the voltage of this stepped step is proportional to the microwave frequency.

[Effects of the Invention] According to the present invention, an organic superconducting complex is used as a superconducting material, and after an organic superconducting thin film is formed on an insulating substrate by a vacuum evaporation method, a part of the organic superconducting thin film is removed to form a constricted portion. As a result, a SQUID element can be manufactured using only a low-temperature process without requiring a high-temperature process such as heat treatment.

By appropriately molding the SQUID element of the present invention thus obtained, it can be used as an RF SQUID or DCC SQUID, and is suitably used, for example, in a SQUID magnetometer, a Josephson voltage standard device, and the like.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of a vacuum evaporation apparatus used in manufacturing the SQUID device of the present invention, and FIGS. 2(a) and (b)
) and FIG. 3 are schematic diagrams showing the structures of different examples of the SQUID element of the present invention, FIG. The figure is a graph showing an example of voltage-current characteristics when the constricted portion of the SQUID element of the present invention is irradiated with microwaves. In Figure 1, numeral 1 is a chamber, 2 is a deposition port, 3 is a sublimation port, 4 is a substrate holder, 5 is a shutter, and 6
is a membrane pressure needle, 7 is an exhaust valve, and Figures 2, 3, and 4
In the figure, 11 is an insulator substrate, 12 is an organic superconductor thin film, 13 is a constriction part, 14 is a SQUID element, and 15 a
, 15 b, 15 c, and 15 d are terminals attached with gold paste, 16 is a power supply, 17 is a signal processing device, and 18 is a resistor.

Claims (1)

[Claims] 1. A SQUID device comprising an organic superconductor thin film provided on an insulating substrate. 2. The method for manufacturing a SQUID device according to claim 1, characterized in that the organic superconducting complex is vacuum-deposited on the insulating substrate to form a thin film, and then a portion of the thin film is removed to provide a constricted portion.