JPS6218776A - Superconductive device - Google Patents

Abstract

PURPOSE:To obtain the Josephson element having variable I-V characteristic by depositing an insulating layer, an injection electrode layer, an insulating layer, and an upper electrode layer on a lower electrode layer spread on a substrate and cutting one end of those layers with inclination and spreading a thin weak combining body on that inclined plane, thereby combining the upper and lower electrode layers. CONSTITUTION:A lower electrode layer 22 consisting of Nb or Pb is spread on a substrate 21 and further on that, an SiO2 layer 23, an injection electrode layer 24 consisting of a normally-conductive metal or a superconductive metal such as Nb, an SiO2 layer 25, and an upper electrode layer 25 of superconductive metal are formed by lamination. One end of this lamination is cut obliquely in expansion toward the lower layers while keeping those layers placed on the electrode layer 22. Then, a weak combining body 27 consisting of Bi, Te, or Al several hundred Angstrom thick is spread from the end surface of the electrode layer 26 to the electrode layer 27. Thus, tunnel barriers are produced between the weak combining body 27 and the electrodes 22, 24, and 26, respectively and the wide-range control of I-V characteristic becomes possible. And, the quasi-plane type Josephson element of high speed and low electric consumption can be obtained.

Description

[Detailed Description of the Invention] [Summary] The present invention is a superconducting device, and a conventional quasi-planar Josephson device has a two-terminal structure, making it impossible to control voltage-current characteristics. In the present invention, an injection electrode is provided in the insulating film to connect to the weak coupling part, and a quasi-planar Josephson element with a three-terminal structure is formed. - To provide a superconducting device using a quasi-planar Josephson element whose current characteristics can be controlled and varied.

[Industrial Field of Application] The present invention relates to superconducting devices, and particularly to a quasi-planar Josephson device with a three-terminal structure.

Josephson devices with superconducting properties have the characteristics of high speed and low power consumption, and are attracting attention as devices for ultra-high speed electronic computers.

There is a quasi-planar Josephson device as a superconducting device.
It has a two-terminal structure in which a lower electrode and an upper electrode are formed via an insulating film, and the lower electrode and upper electrode are connected by a weak bond, but because it is a two-terminal element, the voltage-current characteristics change. That is impossible.

On the other hand, a quasi-particle injection superconducting three-terminal device represented by QUI TERON has been proposed, in which an injection electrode is formed on top of an upper electrode with a structure in which an upper electrode and a lower electrode are tunnel-coupled. The voltage-current characteristics can be varied by adjusting the amount of quasiparticles injected from the injection electrode, but this structure requires an appropriate coupling area between the upper electrode and the injection electrode. If the area is large, the gain decreases, and if it is small, the implantation amount is small, which limits control and makes it difficult to fabricate the device.

For these reasons, there is a demand for a structure in which the voltage-current characteristics can be varied over a wide range using a quasi-planar Josephson element.

[Prior Art] FIG. 3 is a schematic cross-sectional view of a main part of a conventional quasi-planar Josephson element.

The lower electrode 2 and upper electrode 3 formed on the substrate 1 are made of superconducting material, such as niobium (Nb) or lead (Pb).
) etc. are used.

An insulating material such as silicon dioxide is used as an insulator 4 in the gap between the lower electrode 2 and the upper electrode 3, and the lower electrode 2 and the upper electrode 3 are connected by a weak bonding body 5. The material is, for example, bismuth (Bi) or tellurium (T).
e) etc. are used.

When a voltage is applied to the terminals TI and T2 between the lower electrode and the upper electrode of the quasi-planar Josephson element with this structure, the lower electrode and the lower electrode, which are superconducting materials, tunnel at the junction with the weak coupler 5. The effect provides superconducting voltage-current characteristics.

Since this quasi-planar Josephson element is a two-terminal element, the voltage-current characteristics of the element are uniquely determined by the constituent materials and structure, and it is impossible to change these characteristics.

In order to provide controllability to the voltage-current characteristics of such a quasi-planar Josephson device, a quasiparticle-injected superconducting three-terminal device, represented by a quasitron, has recently been proposed.

FIG. 4 is a schematic cross-sectional view of the main part of a normal Quitron.

A lower electrode 12 of a superconductor is provided on the surface of a substrate 11, an opening 14 is provided in an insulating film 13 formed on the surface, an upper electrode 15 of a superconductor is formed on the surface, and an upper electrode 15 of a superconductor is formed on the surface of the insulating film 13. An insulating film 16 is formed on the insulating film 16, a frontage part 17 is formed in a part, and an injection electrode 18 is formed to be connected to the opening part.

Quitrons with such a structure can be used to change the gap parameter Δ (representing the density of superconducting electrons in the superconductor) by injecting excess quasiparticles from the injection electrode into the upper electrode of the superconductor, thereby increasing the voltage - Current characteristics can be changed.

In general, the gear knob parameter Δ is calculated as follows: Δ/ΔT=1-2n (1) (1), where ΔT is the gap parameter in the equilibrium state, n = (Ngp - NgpT) / 4 N(0)
Δ11'Jgp: Quasiparticle density NgpT: Quasiparticle density in equilibrium N(0): Single spin state density at Fermi level Δ1: Can be expressed as a gap parameter at absolute zero.

It can be seen from this that the higher the quasi-particle density, the greater the change in the gear and pull parameters, and to achieve this, the area into which the quasi-particles are injected should be made smaller.

However, the Quitron is just a double tunnel junction, and the area of the implanted region is large, several micrometers by several micrometers, and as a result, a current of several hundred micrometers is required, which has the disadvantage of reducing the gain of the device.

[Problems to be solved by the invention] Since the conventional quasi-planar Josephson device is a two-terminal device, it is impossible to control the voltage-current characteristics. , the injection current is several hundred μ
The problem is that the gain of the device decreases because current is required to flow into the device.

[Means for Solving the Problems] The present invention provides a superconducting device for solving the above-mentioned problems. In order to inject quasiparticles into the coupling part of the dicocefson element, which has a structure in which an upper electrode formed through an insulating film is placed and the upper capillary electrode and the lower electrode are coupled by a weak coupling part, an insulating film is placed. An injection electrode is provided in the membrane, one end of the injection electrode is connected to a weak coupling part, and a current is injected from the injection electrode to create variable voltage-current characteristics (removable three-terminal The solution is to use a quasi-planar Josephson element.

[Function 1] The present invention has the following advantages: the conventional quasi-planar Josephson element is a two-terminal element, so there is no controllability of the voltage-current characteristics, and the Quitron is three-terminal, so it is possible to control the voltage-current characteristics. In view of the fact that the injection current is large and the gain is low, a new quasi-planar Josephson device is developed with an injection electrode in the insulating film to connect to the weak coupling part between the upper and lower electrodes. A quasi-planar Josephson element with a structure is formed, and quasiparticles are injected from this injection element to increase the voltage -
The present invention provides a quasi-planar Josephson element that controls the current characteristics, thereby allowing the voltage-current characteristics most suitable for the device used to be freely varied.

Embodiment FIG. 1 is a schematic cross-sectional view of the essential parts of a quasi-planar Josephson device with a three-terminal structure according to the present invention.

The lower electrode 22 has a thickness of 1000 mm on the surface of the substrate 21.
For example, a material such as Nb or (Pb) is used, and an insulating material such as silicon dioxide is formed on the surface as an insulating layer 23 to a thickness of 1000 mm.

Further, on the surface thereof, an injection electrode 24 with a thickness of about 100 mm is added.
The material may be either a superconducting metal or a normal conducting metal, and for example, niobium (Nb) can be used.

On the injection electrode, an insulating layer 25 having a thickness of 1000 mm and made of a material such as silicon dioxide, and an upper electrode 26 having a thickness of 1000 mm and made of a superconducting material are successively formed.

The bond between the lower electrode 22 and the upper electrode 26 is a weak bond 27
The weak bond has a width of 1 μm and a thickness of diagonal reentrant, and the material used is a weak superconductor, normal metal, semimetal, or semiconductor, such as bismuth (Bi), tellurium, etc. is used.

In such a quasi-planar Josephson element with a three-terminal structure of terminals T3, T4, and T5, the weak coupler 27 is connected to the lower electrode 22.
, a tunnel barrier is formed at the junction with the injection electrode 24 and the upper electrode 26, and the width of the weak coupling part is 1 μm, so it is possible to inject extremely high density quasiparticles, and the material of the weak coupling part is Since the selection range is wide, it is possible to select a suitable material, for example, a material with a small gear parameter in an equilibrium state, a material with a small non-equilibrium relaxation time, etc.

FIG. 2 shows the voltage-current characteristics of the quasi-planar Josephson device having a three-terminal structure according to the present invention.

There are characteristics a, b, c, and d as voltage-current characteristics.
In a conventional quasi-planar Josephson element with a two-terminal structure, in a single element, only the -characteristic voltage-current characteristic, for example, only the a-characteristic, can be obtained, but the three-terminal quasi-planar Josephson element of the present invention In the voltage-current characteristics of the Son element, a,
All characteristics b, c, and d can be obtained continuously.

[Effects of the Invention] As explained above in detail, the quasi-planar Josephson element with the three-terminal structure according to the present invention has the characteristic that the voltage-current characteristics can be appropriately controlled over a wide range, and can be used at high speed. This has the great effect of providing a quasi-planar Josephson element with low power consumption.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of essential parts of a quasi-planar Josephson element of the present invention, and FIG. 2 is a voltage-voltage diagram of a quasi-planar Josephson element of the present invention.
In the current characteristic diagram, FIG. 3 is a schematic cross-sectional view of the main part of a conventional quasi-planar Josephson element, and FIG. Insulating layer, 24 is an injection electrode, 25 is an insulating layer, 2
6 is an upper electrode, and 27 is a weak bond, respectively. +The 11th floor of the 11th floor of the 1st floor of the 1st floor of the 1st floor. l 乎面tk7So〉于J-电脣】υ
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Claims (1)

[Claims] A lower electrode (22) is formed on the substrate (21), and an insulating film (23), an injection electrode (24), and an insulating film (25) are formed on the surface of the lower electrode (22).
) and an upper electrode (26) are laminated, and the ends of the laminated insulating film (23), injection electrode (24), insulating film (25), and upper electrode (26) on the same side form a weak coupling part. (27), and its weak coupling portion (27) is connected to a lower electrode (22).