JPS631085A - Superconducting three-terminal element - Google Patents

Abstract

PURPOSE:To form a superconducting circuit having large current gains by connecting a predetermined superconductor by another superconductor having an energy gap larger than the energy gap of the predetermined superconductor. CONSTITUTION:The title element consists of an injector composed of a superconductor 30, a tunnel barrier 31 and a superconductor 32, an acceptor made up of the superconductor 32, a tunnel barrier 33 and a superconductor 34 and an input terminal 35, an output terminal 36, a grounding 37, a superconductor 38 and connections 39, 40. Electrons injected to the conductor 32 through tunneling from the conductor 30 cannot diffuse and escape to the conductor 38 having a large energy gap connected to the grounding, and all of normal electrons injected effectively work in order to shrink the energy gap of the conductor 32, a lower section of which has the barrier 33. The energy gap of the conductor can be contracted efficiently by the injection of a small amount of input currents, thus tunnel currents flows between the conductors 32 and 34, then extracting output currents is extracted from the terminal 36.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a superconducting element, and more particularly to a single direct extraction portion of a superconducting three-terminal element consisting of two tunnel junctions.

(Prior Art) A superconducting three-terminal device consisting of a superconducting ball and two tunnel junctions is described, for example, in Uploaded Physics Letters, Vol. 32, No. 6, pp. 392-395. Fourth
The figure is a diagram for explaining a conventional superconducting three-terminal device, and shows an injector consisting of a superconductor 1, a tunnel barrier 2, and a superconductor 3, and a superconductor 3, a tunnel barrier 4, and a superconductor 5.
The superconductor t is connected to the input terminal 7 through the connection 6, the superconductor 3 is connected to the ground 9 through the connection 8, and the superconductor 5 is connected to the output terminal 1L through the connection toVC. Normal connections 6, 8° and 10 are each made of superconductor, the same material as 3.5.

For example, devices made of superconductors such as lead or niobium, and devices integrated in a planar manner on a substrate, are constructed of the same layer.

FIG. 5 shows an energy diagram for explaining the operation of a conventional superconducting three-terminal device.

3. In the figure (1), the superconductor in a state before the superconducting three-terminal element switches; 3. 5 energy bands are shown. The dotted line in the figure indicates the Fermi surface,
A DC voltage vb is applied between superconductors 3 and 5.

In addition, the energy gap of each superconductor 3.5 is Δ1°Δ5.Δ, as shown in the figure.The energy states shown in the shaded areas in the figure are each occupied by electrons.This state Then, normal electrons in superconductor 3 cannot tunnel because they cannot find an energy state that is not occupied in superconductor 5, and 1!
No tunnel current flows between and 5.

FIG. 5(b) shows an energy diagram when the 1-conductor three-terminal element is switched.

An input voltage Vin is applied between the superconductors 1 and 3, and normal electrons are injected from the superconductor 1 into the superconductor 3 as shown by the arrow, the normal electron density in the superconductor 3 increases, and the superconductor 3 The gap voltage V in

disappears, and the energy Iatit shown by the dotted line in the figure
A state of normal electron occupancy appears until . As a result of this, a tunnel current due to normal electrons flows from the superconductor 3 to the superconductor 5, and an output current appears at the output terminal 11. As can be seen from the above description, in order for the superconducting element b to operate efficiently, it is necessary to increase the normal electron density in the superconductor 3 as much as possible by injecting electrons from the superconductor 1 into the superconductor 3 by tunneling. To achieve this, the tunneling current of electrons from superconductor 1 to 3 can be increased, or the diffusion of normal electrons from superconductor 3 to connection 8 can be prevented, or the tunneling of normal electrons from superconductor 3 to 5 can be prevented. Possible options include making it smaller. Among the above methods, the method of increasing the tunneling current of electrons from superconductor 1 to superconductor 3 leads to an increase in the input current required for the superconducting three-terminal element to cause switching.
Ru. In addition, methods to reduce the tunneling current of normal electrons from the superconductor 3 to the superconductor 5 include increasing the potential of the tunnel barrier 4 or increasing the physical thickness of the barrier 4. rear,
This leads to a decrease in the output current flowing between the superconductors 3 and 5 due to tunneling. Both of these two improvements lead to a reduction in the input/output current ratio, that is, the current gain of the superconducting three-terminal element, which is unfavorable in terms of element operation. Therefore, a possible means is to prevent normal electrons from diffusing from the superconductor 3 to the connection 8. In other words, it is only the superconductor 3 with the tunnel barrier 40 that requires the gap voltage of the superconductor to disappear due to an increase in normal electron density, and even if the gap voltage of the superconductor forming the connection 8 disappears, the output current The point is that the mechanical knowledge that causes this does not contribute in any way.

(Problems to be Solved by the Invention) In the conventional superconducting three-terminal device, the superconductor 3 and the connection 8 to ground are made of the same superconducting material, and the wire 8 from the superconductor 3 to the tunnel barrier 4 is made of the same superconducting material. Diffusion of normal electrons occurred, the density of normal single electrons in the superconductor 3 decreased, and the gap voltage of the superconductor 3 could not be efficiently extinguished.

An object of the present invention is to eliminate the drawbacks of the conventional superconducting three-terminal elements described above and to provide a superconducting three-terminal element with a large current gain.

(Means for Solving the Problems) According to the present invention, a first superconductor or normal conductor, a second superconductor, the first superconductor or normal conductor, and the second superconductor In a superconducting three-terminal element comprising a first tunnel barrier sandwiched between a first tunnel barrier, a third superconductor, and a second tunnel barrier sandwiched between the second and third superconductors, the second tunnel barrier Superconductor energy
A superconducting three-terminal element is obtained, characterized in that the second superconductor is connected to a fourth superconductor having an energy gap larger than the gap.

(Example) Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a block diagram for explaining the present invention in detail.

This embodiment includes an injector consisting of a first superconductor 30, a first tunnel barrier 31, and a second superconductor 32, and a superconductor 32, a second tunnel barrier 33, and a third superconductor.
an acceptor consisting of a superconductor 34, an input terminal 35, an output terminal 36, a production area 37, a ground 37 and a superconductor 3
2, and the superconductor 38 that serves as a connection between
9.40 The superconductor 38 is made of a conductive material with a larger energy gap than the superconductor 32. The direct reading of the superconductors 32 and 38 is a superconducting contact, and superconducting current flows freely. Therefore, no voltage is generated between the superconductors 32 and 38, and the potential of the superconductor 32 is fixed at zero.

FIG. 2 is an energy diagram showing the energy bands at the superconducting contact portion of the superconductors 32, 38.

The energy of the normal electrons injected from the superconductor 30 through the tunnel barrier 31 has a large distribution near the band edge 41, which has a large dog-like density, and the normal electrons injected with energy higher than the band edge 41 have a large distribution of energy. is scattered by impurities in the superconductor or by phonons, and immediately settles into an electronic state with energy around the band edge 41, as indicated by the arrow in the figure. Normal electrons with energy around the band edge 41 do not have an energy state of electrons with corresponding energy in the superconductor 38, and therefore normal electrons cannot diffuse into the superconductor 38. Therefore, the injected normal electrons remain in the superconductor 32 and serve to eliminate the energy band drop of the superconductor 32.

FIG. 3 is a sectional view showing a layer structure when the embodiment of FIG. 1 is realized as an integrated circuit on a substrate 50.

51 indicates the third superconductor constituting the element and its connection part,
52 indicates a second superconductor, 53 indicates a layer constituting the first superconductor constituting the element and its connection part, 5
4 constitutes a connection of the superconductor 52. A superconductor layer is shown, and the superconductor 54 has a higher energy level than the superconductor 52.
have a gap.

55 and 56 are insulating layers, and the insulating layer 55 and superconductor layer 51 are flattened. 57.58 indicates the tunnel barrier.

In order to obtain sufficient effects of the present invention, the superconducting contact portion 59 between the superconducting layers 52 and 54 must be designed to have an area as small as possible.

As can be seen from the above description, in the embodiment shown in FIG. 1, electrons injected from the superconductor 30 into the superconductor 32 by the tunnel barrier diffuse into the superconductor 38 with a large energy gap, which is connected to ground. Therefore, all the injected normal electrons serve effectively to narrow the energy gap of the superconductor 32 with the tunnel barrier 33 underneath. Therefore, the energy gap of the superconductor 32 can be efficiently reduced by injecting a small input current, and as a result, a tunnel current flows between the superconductors 32 and 34, and an output current appears at the output terminal 36. Therefore, in the superconducting three-terminal element of this embodiment, a large value of the ratio of the output current to the input current, that is, the current gain, can be obtained.

Note that in this example, the superconductor 3 is used as an injector.
b'-1 using 0 As described in the above-mentioned document Ackbride Physics Letters, the same operation can be expected even if this is replaced with a normal conductor.

(Effects of the Invention) As explained in detail above, according to the present invention, a superconducting three-terminal element with a large current gain can be provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the superconducting three-terminal element according to the present invention, and FIG. 2 is an energy diagram showing the energy band of the superconducting contact portion between the second superconductor and its connection in the embodiment of FIG. 1. , FIG. 3 is a cross-sectional view of the circuit when this embodiment is realized as an integrated circuit, FIG. 4 is a schematic diagram showing a conventional example of a superconducting three-terminal element, and FIG. 5 explains the operation of the superconducting three-terminal element. FIG. 5A is a diagram showing the state when the input voltage Vin is not input, and FIG. 2B is a diagram showing the state when the input voltage Vin is applied. 1.30...First superconductor, 2,31...First tunnel barrier, 3,32...Second superconductor, 4゜3
3... Second tunnel barrier, 5, 34... Third superconductor, 6, 8, 10, 38, 39.40... Connection,
7.35...Input terminal, 11.36...Output terminal,
41...Band Edge. Agent Patent Attorney Shinsuke Honjo 7t〉Figure 2 Figure 5 (a)

Claims (1)

[Claims] a first superconductor or normal conductor, a second superconductor, a first tunnel barrier sandwiched between the first superconductor or normal conductor and the second superconductor, a third superconductor , and a fourth superconductor having an energy gap larger than that of the second superconductor in a superconducting three-terminal element comprising a second tunnel barrier sandwiched between the second and third superconductors. A superconducting three-terminal element, characterized in that a connection of the second superconductor is formed by the body.