JP3016566B2 - Superconducting switch element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting switch element that can be applied as a switch element in the field of superconducting electronics and a switch element in an integrated circuit such as a computer.

[Conventional technology]

2. Description of the Related Art Conventionally, research and development of superconducting materials has been actively carried out everywhere, but most of them have been metallic ones such as Nb-based superconducting alloys. However, in recent years, oxide-based superconductors have been discovered, and have attracted attention as new materials applicable to the electronics field. However, its application is limited to Josephson devices, SQUIDs, and infrared sensors. However, an example using an oxide high-temperature superconductor as a switching element is known (T.
NISHINO, H.NAKANE and U.KAWABE: Jpn.J.Appl.Phys., 26
(1987) L1320, etc.).

Switching device using the oxide superconductor, MgO _{substrate, Y 1 Ba 2 Cu 3 O} x superconducting thin film, CdS photoconductive thin film, current electrodes, and a optical fiber.

The superconducting thin film here is formed by forming a film using a high frequency sputtering method and then performing a heat treatment. The superconducting thin film has a thickness of 2 μm and a critical temperature of 85K. At the center of the superconducting thin film, a groove having a width of 8 mm and a depth of 5 μm is provided in advance, and the thickness of the superconducting thin film at the bottom edge of the groove is 0.5 μm or less. Part, a CdS thin film was further added on this by 0.2 μm by vacuum evaporation.
m thickness.

When a current is applied to the superconducting thin film formed as described above, the current initially flows at a voltage of 0, but the voltage increases as the current value increases. Next, 0.35
When light having a wavelength of μm to 0.8 μm is irradiated, the current value decreases as compared to before irradiation. Therefore, the switching operation is performed using this effect.

[Problems to be solved by the invention]

However, in the above conventional superconducting switch element,
A means for irradiating light from the outside, such as an optical fiber, is required, and it has been difficult to incorporate the light into an integrated circuit. In addition, since light irradiation means using an optical fiber or the like is required, there is a problem that the cost is increased.

The present invention has been made in view of the above circumstances, utilizing low power consumption, high-speed response characteristics of the superconductor,
Moreover, an object of the present invention is to provide a superconducting switch element that does not irradiate light from the outside or apply a magnetic field.

[Means for solving the problem]

In order to achieve the above object, a superconducting switch element of the present invention comprises a first superconducting thin film and an insulating film formed on an insulating substrate, and a superconducting thin film and an insulating film formed on the first superconducting thin film and the insulating film. An oxide antiferromagnetic thin film, a second superconducting thin film formed on the antiferromagnetic thin film and the insulating film, and a current application electrode provided on the first and second superconducting thin films. A signal reading electrode, and an electric field applying electrode provided above and below a laminated portion of the first and second superconducting thin films and the antiferromagnetic thin film for applying an electric field perpendicular to the antiferromagnetic thin film. Wherein a switching operation is performed by applying a voltage to the electric field applying electrode and applying an electric field perpendicularly to the antiferromagnetic thin film of the laminated portion.

[Action]

Here, the antiferromagnetic thin film is, in particular, chromium oxide: Cr
_{A 2} O ₃ thin film is used. This material plays an important role in the operation of this device. When an electric field is applied perpendicularly to or parallel to the c-axis, a magnetic moment is induced in the direction of the electric field. The magnetic effect (E.KITA, A.TASAKI and K.SHIRATORI: Jpn.J.App
l.Phys., 18 (1979) 1361). Hereinafter, the Cr ₂ O ₃ thin film is referred to as an electro-magnetic effect film, and is abbreviated as an ME film.

In the present invention, when a voltage is applied to the electric field application electrodes provided above and below the laminated portion of the first and second superconducting thin films and the ME film, and an electric field is applied perpendicularly to the ME film in the laminated portion, The electric moment is induced by the magnetic moment to generate an electric resistance to perform a switching operation. That is, the switching operation is performed by turning on and off the electric field.

〔Example〕

Hereinafter, the present invention will be described in detail based on illustrated embodiments.

FIG. 1 is a schematic perspective view of a superconducting switch element showing one embodiment of the present invention. This superconducting switch element has an insulating ceramic (MgO) substrate 1 and a first conductive member formed on the substrate 1. 1 superconducting thin film 2A and insulating film 7 and the first
Film 3 formed on superconducting thin film 2A and insulating film 7
A second superconducting thin film 2B formed on the ME film 3 and the insulating film 7; a current application electrode 5 provided on the first and second superconducting thin films 2A and 2B; Signal reading electrodes 6 and the upper and lower layers of the first and second superconducting thin films 2A and 2B and the ME film 3 for applying an electric field to the ME film 3 vertically. The basic configuration is a configuration including the electrode 4 for applying an electric field.

As the constituent material of the first and second superconducting thin films 2A and 2B, Y ₁ Ba ₂ Cu ₃ O _x , Bi ₂ Sr ₂ Ca ₂ Cu exceeding a critical temperature of 77K are used.
Oxide high-temperature superconductors such as ₃ O _x and Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _x are desirable. Platinum and gold are used as electrode materials.

As a method for producing the first and second superconducting thin films 2A and 2B, known methods such as a sputtering method, a vacuum deposition method, an MBE method, an ICB method, and a CVD method are used. Further, the ME film 3, the electrodes 4, 5, 6 and the insulating film 7 are formed by using a vacuum deposition method (electron beam type, low resistance heating type).

The first and second superconducting thin films 2A and 2B have a thickness of 0.2 μm to 0.5 μm.
The thickness of the ME film 3 is preferably 0.1 μm to 0.15 μm, the thickness of each of the electrodes 4, 5, 6 is 1 μm or less, and the insulating film 7 is
Of the superconducting thin film 2A.

 Next, the operation principle of the present element will be described.

In FIG. 1, a power supply is connected to the current applying electrodes 5 of the first and second superconducting thin films 2A and 2B, and a current is applied between the two superconducting thin films while the element is cooled below a critical temperature. Then, a superconducting current flowing in one superconducting thin film flows in the ME film 3 and reaches the other superconducting thin film side, so that a current flows by a so-called “proximity effect”.

Next, a voltage is applied between the electric field applying electrodes 4 to apply an electric field perpendicular to the substrate 1 (that is, an electric field perpendicular to the ME film 3). When applied to the ME film 3, a magnetic moment is induced in a direction parallel to the direction of the electric field, and the ME film 3 enters a ferromagnetic state. At this time, the direction perpendicular to the substrate 1 of the ME film is the c-axis. Due to the induced magnetic moment, the superconducting current becomes a normal conducting current, and a resistance is generated to generate a voltage. Therefore,
If a voltage signal change between the signal reading electrodes 6 that generates a finite voltage from zero voltage before and after the application of the electric field is read, and this is made to correspond to the ON-OFF operation, it functions effectively as a switch element.
In order to read the voltage change remarkably, it is desirable that the value of the flowing current be equal to or less than the maximum zero voltage current (critical current).

Next, more specific embodiments of the superconducting switch element according to the present invention will be described.

First, an Au film serving as the lower electric field applying electrode 4 is vapor-deposited to a thickness of 0.5 μm on a MgO (100) single crystal substrate 1 by vapor deposition, and a first film having a width of 5 mm, a length of 10 mm, and a film thickness of 0.5 μm is formed thereon. Y ₁ Ba ₂ CU ₃ O _x
The superconducting thin film 2A is formed by a sputtering method or the like.

The target composition at the time of sputtering was a composition close to Y: Ba: Cu = 1: 2: 3, and a pressure of 2 × in a mixed gas atmosphere of Ar: O ₂ = 9: 1.
The substrate was fabricated at a temperature of about 550 ° C. at 10 ⁻² torr. Thereafter, the mixture was heated to 900 ° C. in an electric furnace and subjected to a heat treatment for several hours in an oxygen stream at about 1 atm. The critical temperature of the resulting superconducting thin film was 90K.

Next, the ME film 3 is formed by an electron beam evaporation method.
Cr ₂ O ₃ powder sintered body is used as the evaporation source, width 5mm, length 10m
An ME film 3 having a thickness of 0.1 μm and a thickness of 0.1 μm was deposited. The fabrication conditions at this time are as follows: oxygen atmosphere, pressure 1 × 10 ^-4 torr, substrate temperature 400 ° C.
I went in. Further, at this time, when the oxygen gas was converted into a plasma state by a high-frequency electric field, a better film was formed. still,
In each case, the obtained ME film 3 was c-axis oriented.

Next, as shown in FIG.
The Y ₁ Ba ₂ Cu ₃ O _x thin film 2B is formed in the same size as the first superconducting thin film 2A. And finally, the upper electric field applying electrode 4,
The current applying electrode 5 and the signal reading electrode 6 are formed. This electrode was formed by evaporating an Au electrode to a width of 2 mm to 3 mm, a length of 3 mm to 5 mm, and a thickness of 0.5 μm by a vacuum evaporation method.

When the above-mentioned thin films were formed, they were prepared by placing a mask on a substrate so as to have a predetermined shape.

Now, the superconducting switch element manufactured as described above is cooled at a temperature of 70 K, and when the first and second superconducting thin films 2A and 2B are in a superconducting state, a current of 0 to 40 mA is applied to the electrode 5. Flows, the relationship between the current flowing through the element and the voltage detected between the signal reading electrodes 6 is as shown in FIG. 2 (before application). Next, a voltage is applied to the electrode 4 to form the ME film 3.
When an electric field of 50 V / cm was applied, the relationship between the current and the voltage was as shown in FIG. 2 (after application), and a switching operation was possible.

〔The invention's effect〕

As described above, according to the present invention, a superconductor has low power consumption and high-speed response, and can perform a switching operation without using external light or a magnetic field. A new, low-cost superconducting switch element can be provided.

Further, since the superconducting switch element according to the present invention does not require external light irradiation or application of a magnetic field, it can be easily incorporated into an integrated circuit or the like.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a superconducting switch element showing one embodiment of the present invention, and FIG. 2 is an explanatory diagram of a switching operation of the superconducting switch element having the constitution shown in FIG. DESCRIPTION OF SYMBOLS 1 ... Insulating substrate, 2A ... 1st superconducting thin film, 2B ... 2nd superconducting thin film, 3 ... Oxide antiferromagnetic thin film (ME film), 4 ... Electrode for applying an electric field, 5 ... Electrode for current, 6 ... Signal for reading signal, 7
... insulating film.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 39/00 H01L 39/22 H01L 39/24

Claims (1)

(57) [Claims] A first superconducting thin film and an insulating film formed on an insulating substrate; an oxide antiferromagnetic thin film formed on the first superconducting thin film and the insulating film; A second superconducting thin film formed on the ferromagnetic thin film and the insulating film; a current application electrode and a signal reading electrode provided on the first and second superconducting thin films; A superconducting thin film and a superconducting thin film and an anti-ferromagnetic thin film, and an electric field applying electrode for applying an electric field perpendicular to the antiferromagnetic thin film, and a voltage applied to the electric field applying electrode. And a switching operation is performed by applying an electric field perpendicularly to the antiferromagnetic thin film of the laminated portion.